# 55. International Winter Meeting on Nuclear Physics

Europe/Berlin
Bormio, Italy

#### Bormio, Italy

, ,
Description
Long-standing conference bringing together researchers and students from various fields of subatomic physics. The conference location is Bormio, a beautiful mountain resort in the Italian Alps.
• Monday, 23 January
• 06:00 07:00
Pre-Conference School
• 06:00
Selected Topic in Hadron Physics 10m
Speaker: Dr Diego Bettoni (Istituto Nazione di Fisica Nucleare)
• 06:10
Selected Topics in Heavy Ion Physics 10m
Speaker: Torsten Dahms (Excellence Cluster Universe - Technische Universität München)
• 06:20
Selected Topic in Nuclear Structure and Nuclear Astrophysics 10m
Speaker: Dr Pierre Capel (Université Libre de Bruxelles (ULB))
• 06:30
Selected Topics in Flavour Physics 10m
Speaker: Prof. Marcel Merk (Nikhef)
• 09:00 13:40
Monday Morning
• 09:00
Welcome 10m
• 09:10
Classical Novae and the Physics of Exploding Stars 45m
At the turn of the 21st Century, new tools and developments, at the crossroads of theoretical and computational astrophysics, observational astronomy, cosmochemistry, and nuclear physics, have revolutionized our understanding of the physics of stellar explosions. The use of space-borne observatories has opened new windows to study the cosmos through multifrequency observations. In parallel to the elemental stellar abundances inferred spectroscopically, cosmochemists are now providing isotopic abundance ratios from micron-sized presolar grains extracted from meteorites. Encapsulated in those grains is pristine information about the suite of nuclear processes that took place in their stellar progenitors. The dawn of supercomputing has also provided astrophysicists withe appropriate tools to study complex physical phenomena that require a multidimensional approach. Last but not least, nuclear physicists have developed new techniques to determine nuclear interactions close to stellar energies. In this talk, a number of breakthroughs from all these different disciplines will be presented, with emphasis on the physical mechanisms that operate during nova explosions.
Speaker: Prof. Jordi Jose (Univ. Politcnica de Catalunya)
• 09:55
Higgs and New Physics at ATLAS and CMS 45m
..
Speaker: Prof. Stefano Giagu (CERN)
• 10:40
Coffee Break 30m
• 11:10
News from BESIII 40m
BESIII is an experiment located at the Institute of High Energy Physics in Beijing, China. It consists of a state-of-the-art 4π magnetic spectrometer that surrounds the beam-beam intersection region of the BEPCII e+e- collider that is operated by an international collaboration of nearl 400 researchers from 13 countries. BEPCII provides BESIII with record-high luminosity e+e- data over a center-of-mass energy range that includes the thresholds for pair production of all of the stable strange baryons, charmed mesons, -leptons and c charmed baryons, and direct access to charmonium and many of the XYZ charmoniumlike mesons that are strong candidates for non-standard, four-quark mesons. This talk will focus on a subset of recent BESIII results, including some unexpected phenomena seen at different baryon-antibaryon thresholds and high statistics measurements of properties of the Y(4260) that provide some insight into its underlying structure.
Speaker: Prof. Stephen Lars Olsen (Institute of Basic Science, Korea)
• 11:50
Detector at HL/LHC and Future Colliders 40m
Detector at HL/LHC and Future Colliders
Speaker: Dr Werner Riegler (CERN)
• 17:00 19:20
Monday Afternoon
• 17:03
Silicon Tracking System of the future CBM experiment at FAIR 3m
The physics aim of the Compressed Baryonic Matter (CBM) experiment is to explore the phase diagram of strongly interacting matter at highest net baryon densities and moderate temperatures in the range reachable with AA collisions between 2-45 AGeV, initially 2-14 AGeV (SIS 100). The Silicon Tracking System (STS) is the central detector for charge particle tracking and momentum determination. It is designed to be operated at high occupancies at collision rates up to 10 MHz. It is planned to reach the track reconstruction efficiency of 95%. The momentum resolution is expected to be around 1.5%. To achieve these goals, double sided double metal silicon sensors with a pitch of 58 μm are used. The sensors are mounted on light-weight carbon ladders, forming 8 stations. The read-out electronics is kept outside of the detector acceptance. The self-triggering read-out electronics is connected with the silicon microstrip sensors through the multi-line microcables. The resulting material budget is about 1%X0 per station. The entire system is going to be operated in a thermal enclosure to maintain constant temperature of -5◦C. Before the mass production of the silicon sensors, several studies are performed with prototypes. They include electrical and optical inspection, measurements with the radioactive sources and beam tests of the sensors and the read-out electronics. Particularly, we study possible impact of the severe radiation environment (10^14 neq cm^−2 ) to the sensor performance. The STS project is realized in cooperation of institutes from Germany, Poland, Russia and Ukraine. This presentation is given on behalf of the CBM Collaboration.
Speaker: Dr Maksym Teklishyn (FAIR)
• 17:06
Timing in a FLASH 3m
Very precise timing below the 100ps-mark is gaining importance in modern detector designs. Many technology demonstrators achieving this goal were based on the Cherenkov effect exploiting its prompt light emission. One common requirement is the necessity to compensate inherent walk effects to reach the sub-100ps timing precison. In traditional approaches either the amplitude is measured in addition to the timestamp, which requires the signal to be split, or a constant fraction discriminator is used. More recent developments include sampling the signal and extracting the relevant features which requires powerful frontend electronics and is not suited for all experimental circumstances. With the advent of high-precision TDCs another method becomes feasible: measuring the signal amplitude via Time-over-Threshold. In this case the frontend electronics can be kept simple by only using a discriminator circuit and, optionally, a wide-band amplifier. A prototype detector, called FLASH (Fast Light Acquiring Start Hodoscope), was built based on QUARTIC's design ideas. The fused silica radiator bars were coupled to a 10 micron-pore type PLANACON MCP-PMT with 64 channels and readout with custom electronics based on the NINO ASIC. The TRB3 system, a high-precision TDC implemented in an FPGA, was used as data acquisition system. The performance of the system was investigated at a dedicated test experiment at the Mainz Microtron (MAMI) accelerator. The validity of the Time-over-Threshold approach could be established and an overall timing resolution of approx 70ps could be achieved. The intrinsic resolution of the frontend electronics including the TDC was measured to be less than 25ps.
Speaker: Dr Matthias Hoek (JGU Mainz)
• 17:12
The upgrade of the ALICE Inner Tracking System 3m
ALICE (A Large Ion Collider Experiment) aims at studying the nuclear matter at high densities and temperatures characterizing a particular state of matter called Quark-Gluon Plasma (QGP), using proton-proton, proton-nucleus and nucleus-nucleus collisions at the CERN Large Hadron Collider (LHC). The third run of LHC will start in 2021 after a shutdown of two years to allow the upgrade of both the accelerator and the experiments. In Run 3 Pb-Pb collisions will be performed at a centre of mass energy per nucleon of 5.5 TeV, with a luminosity L_int=6×10^27 cm^(-2) s^(-1). The interaction rate will be up to 50 kHz and 400 kHz for Pb-Pb and pp collisions, respectively. To fulfil the requirements of the ALICE physics program for Run 3 of the LHC, a major upgrade of the experimental apparatus is planned for installation in 2019-2020. A key element of the ALICE upgrade is the construction of a new, ultra-light, high-resolution Inner Tracking System (ITS). The new ITS will significantly enhance the determination of the distance of closest approach to the primary vertex, the tracking efficiency at low transverse momenta, and the read-out rate capabilities, with respect to what achieved with the current detector. It will consist of seven layers equipped with silicon Monolithic Active Pixel Sensors with a pixel size of the order of 28x28 µm^2. To transmit (receive) data to (from) the sensors, Flex Printed Circuits (FPC) will be wire-bonded to the sensors themselves. The goal is to improve the reconstruction capabilities of heavy flavour (c and b quarks) mesons and baryons. In addition, the new tracking detector will allow us to study low-mass dileptons and low-p_T charmonia at mid (e^+ e^-) rapidities. In the talk, the first part is dedicated to the description of the present ALICE apparatus focusing the attention on the ITS, it’s operational limits and the physics motivations of its upgrade. Then, the future ITS layout will be outlined entering in the details of the various hardware components. In the second part, an overview of the expected physics performance will be shown.
Speaker: Dr Ivan Ravasenga (DISAT, Politecnico di Torino)
• 17:15
Study of corrections to the eikonal approximation 3m
For the last decades, multiple international facilities have developed Radioactive-Ion Beams (RIB) to measure reaction processes including exotic nuclei. These measurements coupled with an accurate theoretical model of the reaction enable us to infer information about the structure of these nuclei. The partial-wave expansion and the Continuum-Discretised Coupled Channel method (CDCC) provide a precise description of two- and three-body collisions respectively. Unfortunately, these methods have one main drawback: their computational cost. To cope with this issue, the eikonal approximation is a powerful tool as it reduces the computational time and still describes the quantum effects observed in reaction observables. Nevertheless, its range of validity is restricted to high energy and to forward scattering angles. In this work, we analyze the extension of the eikonal approximation to lower energies and larger angles through the implementation of two kinds of corrections. These aim to improve the treatment of the nuclear and Coulomb interactions within the eikonal model. The first correction is based on an expansion of the T-matrix [1] while the second relies on a semi-classical approach [2,3]. They permit to better account for the deflection of the projectile by the target, which is neglected in the standard eikonal model. The gain in accuracy of each correction is evaluated through the analyses of angular cross sections computed with the standard eikonal model, its corrections and either the partial-wave expansion (two-body collisions) or CDCC (three-body collisions). These analyses have been performed for tightly bound projectiles ($^{10}\mathrm{Be}$) and halo nuclei ($^{11}\mathrm{Be}$) from intermediate energies ($70$ MeV/nucleon) down to energies of interest of future RIB facilities such as HIE-ISOLDE and ReA12 at MSU ($10$ MeV/nucleon). [1] S. J. Wallace, Ann. Phys. 78, 190 (1972). [2] T. Fukui, K. Ogata, and P. Capel. Phys. Rev. C 90, 034617 (2014). [3] C. E. Aguiar, F. Zardi and A. Vitturi, Phys. Rev. C 56, 1511 (1997).
Speaker: Ms Chloë Hebborn (Université libre de Bruxelles)
• 17:18
New strategies of the LHC experiments to meet the computing requirements of the HL-LHC era 3m
The performance of the Large Hadron Collider (LHC) during the ongoing Run 2 is above expectations both concerning the delivered luminosity and the LHC live time. This resulted in a volume of data much larger than originally anticipated. Based on the status of current data production levels and the structure of the LHC experiment computing models, the estimates of the data production rates and resource needs were re-evaluated for the era leading into the High Luminosity LHC (HL-LHC), the Run 3 and Run 4 phases of LHC operation. It turns out that the raw data volume will grow ~10 times by the HL-LHC era and the processing capacity needs will grow more than 60 times. While the growth of storage requirements might in principle be satisfied with a 20% budget increase and technology advancements, there is a gap of a factor 6 to 10 between the needed and the available computing resources. The threat of a lack of computing and storage resources was present already in the beginning of Run 2, but could still be mitigated e.g. by improvements in the experiment computing models and data processing software or utilization of various types of external computing resources. For the years to come, however, new strategies will be necessary to meet the huge increase in the resource requirements. In contrast with the early days of the LHC Computing Grid (WLCG), the field of High Energy Physics (HEP) is no longer among the biggest producers of data. Currently the HEP data and processing needs are ~1% the size of the largest industry problems. Also, HEP is no longer the only science with large computing requirements. In this contribution, we will present new strategies of the LHC experiments towards the era of the HL LHC, that aim to bring together the desired requirements of the experiments and the capacities available for delivering physics results.
Speaker: Dr Dagmar Adamova (NPI ASCR Prague/Rez)
• 17:21
K* resonance dynamics in heavy-ion collisions 3m
We study the dynamics of the strange vector meson resonance K* in heavy-ion collisions using the microscopic Parton-Hadron-String-Dynamics (PHSD) transport approach with hadronic and partonic degrees-of-freedom and dynamics hadronisation. We investigate the behaviour of the K* in the medium by using Breit-Wigner spectral functions with self-energies based on the G-Matrix approach. The results from PHSD are compared to data from STAR at RHIC and ALICE at the LHC for different collisions, energies and centralities. The analysis shows that the final K*s (which can be observed experimentally) are produced predominantly during the hadronic phase, dominated by inelastic kaon-pion collisions, whereas K*s from the QGP decay and rescatter and thus are lost during the reconstruction. Furthermore the in-medium effects are relatively small at high energies (RHIC and LHC) as compared to lower energies (FAIR). Therefore the influence of the in-medium effects on the K* is rather modest.
Speaker: Andrej Ilner (Frankfurt Institute for Advanced Studies)
• 17:27
Backbending in the pear shaped 223Th nucleus : First evidence of a high spin octupole to quadrupole shape transition in the actinides. 3m
An experiment as been realized using the EUROBALL IV array at Strasbourg to study the fission products produced in the reaction 208Pb(180; F ). Nevertheless, the experiment also lead to the production of 223Th produced in the fusion-evaporation channel of this reaction with three neutrons evaporated. The structure of thorium isotopes is known to present features of octupole collectivity. The aim of the present talk is to report new results about the structure of 223Th, with possible consequences on the characterization of its octupole properties. Indeed, the quality of the data allowed us to establish more than 25 new levels and extend the yrast band up to 49/2+ . This observation has brought to light a sharp backbending occuring at the highest spins promoting the 223Th as the heavier thorium isotope having an accident observed in its moment of inertia. The interpretation of this phenomenon in terms of band crossing will be discussed by comparing experimental evidences with various calculations. This backbending is the first expected evidence of a quadrupole-octupole shape transition in the actinides at high spin. Moreover, a new non-yrast structure was discovered showing very dierent features and further details will be presented.
Speaker: Mr Guillaume Maquart (IPNl)
• 17:30
Coherent pi0 photoproduction on spin-zero nuclei 3m
The method of coherent pi0 photo production (gamma + Ag.s.-> pi0 +Ag.s., where Ag.s. is a nucleus in its ground state) provides an ecient tool to study the neutron skin of various nuclei. We will investigate the case of nuclei with zero spin and isospin from theoretical point of view in the framework of a distorted wave impulse approximation in momentum space. For the pion-nucleus nal-state interaction we will employ phenomenological pion-nucleus optical potential, which involves analysis of pion-pion elastic scattering as the solution of a Lippmann-Schwinger integral equation. As a rst application, we will show results for 12C.
Speaker: Dr Slava Tsaran (Uni. Mainz)
• 17:40
Poster Discussion 1h 20m
• Tuesday, 24 January
• 09:00 13:30
Tuesday Morning
• 09:00
Electric Dipole Moment Searches 45m
Electric Dipole Moment Searches
Speaker: Prof. Peter Fierlinger (TUM)
• 09:45
Status and perspectives of nuclear chiral EFT" 45m
I will present the status of nuclear forces and electroweak exchange currents in chiral effective field theory and discuss selected applications to few-nucleon systems.
Speaker: Prof. Evgeny Eppelbaum (Uni. Bochum)
• 10:30
Coffee Break 30m
• 11:00
recent results from ALICE on heavy flavor probes of the quark gluon plasma 45m
recent results on open charm and beauty observables as well as quarkonia will be reported
Speaker: Prof. Johanna Stachel (Universitaet Heidelberg)
• 11:45
Subthreshold charm and strangeness production at FAIR energies 30m
We present results on the sub- and near threshold production of multi-strange hadrons and of charmed hadrons. These particle allow to explore multi-step processes in dense hadronic matter. We provide an alternative explanation for the observed transparency ratios and show how the observed enhanced Cascade production at HADES energies can be explained. For the near and subtrehsold production of charmed hadrons, we present the first estimates for the SIS-100 energies, indicating that charm studies might still be feasable, even without SIS-300.
Speaker: Prof. Marcus Bleicher (Univ. Frankfurt)
• 12:15
Blessings of a phantom: what remains from the 750 GeV diphoton resonance 30m
Blessings of a phantom: what remains from the 750 GeV diphoton resonance
Speaker: Prof. Matthias Neubert (JGU)
• 17:00 19:40
Tuesday Afternoon
• 17:00
The FOOT (FragmentatiOn Of Target) Experiment 20m
Particle therapy uses proton or 12-C beams for the treatment of deep-seated solid tumors. Due to the features of energy deposition of charged particles a small amount of dose is released to the healthy tissue in the beam entrance region, while the maximum of the dose is released to the tumor at the end of the beam range, in the Bragg peak region. Dose deposition is dominated by electromagnetic interactions but nuclear interactions between beam and patient tissues inducing fragmentation processes must be carefully taken into account. In proton treatment the target fragmentation produces low energy, short range fragments along all the beam range. In 12-C treatments the main concern are long range fragments due to projectile fragmentation that release dose in the healthy tissue after the tumor. The FOOT experiment (FragmentatiOn Of Target) of INFN (Istituto Nazionale di Fisica Nucleare) is a new project designed to study these processes. Target (16-O,12-C) fragmentation induced by 150-250 MeV proton beam will be studied via inverse kinematic approach, where 16-O and 12-C beams, in the 150-200 AMeV energy range, collide on graphite and hydrocarbons target to allow the extraction of the cross section on Hydrogen. This configuration explores also the projectile fragmentation of these beams. The detector includes a magnetic spectrometer based on silicon pixel detectors, a scintillating crystal calorimeter with TOF capabilities, able to stop the heavier fragments produced, and a ΔE detector to achieve the needed energy resolution and particle identification. The detector, the physical program and the timetable of the experiment will be presented
Speaker: Dr Giuseppe Battistoni (INFN)
• 17:20
First measurement of the charge form factor of the proton at very low Q2 with Initial State Radiation 20m
In this talk, a new experimental method based on initial-state radiation (ISR) in e-p scattering will be presented, in which the radiative tail of the elastic e-p peak is used to extract information on the proton charge form factor (G_E^p) at extremely small Q^2. The ISR technique was validated in a dedicated experiment using the spectrometers of the A1-Collaboration at the Mainz Microtron (MAMI). This provided first measurements of G_E^{p} for 0.001
Speaker: Dr Harald Merkel (Institut für Kernphysik, Johannes Gutenberg-Universität Mainz)
• 17:40
Open heavy-flavour measurements in Pb-Pb collisions with ALICE at the LHC 20m
Strongly interacting matter at high densities and temperatures can be created and carefully studied under laboratory conditions in high-energy collisions of heavy atomic nuclei. Heavy quarks (charm and beauty) provide particular good probes to study the so-called Quark-Gluon Plasma state and its evolution since they are predominantly produced in initial hard partonic scattering processes in the early stages of the collision. Since 2010 the Large Hadron Collider at CERN delivers lead-lead collisions at an unprecedented energy in the TeV range. The measurement of open heavy-flavour production in heavy-ion collisions allows studies of the dynamical properties of the plasma phase. The ALICE experiment has measured charm and beauty production in Pb-Pb collisions at $\sqrt{\rm s_{NN}}$ = 2.76 TeV and 5.02 TeV, via the exclusive reconstruction of hadronic D-meson decays and semi-leptonic D and B-meson decays. In this contribution, I will give an overview of current open heavy-flavour results from ALICE ranging from the nuclear modification factor to elliptic flow measurements and of the interpretation of the data by comparing with different model calculations of in-medium energy loss.
Speaker: Andre Mischke (Utrecht University)
• 18:00
Looking for new Physics with Pion Decays 20m
In the Standard Model, electrons, muons, and tau leptons have identical electroweak gauge interactions, a hypothesis known as lepton universality. PIENU is a high precision measurement of the ratio of the rate of the pion decay to electron plus neutrino compared to pion decay to muon plus neutrino, including radiative processes. The SM theoretical prediction of this ratio is one of the most accurately calculated weak interaction observables involving quarks with uncertainty of <0.01%. The experimental value is an order of magnitude less precise. Testing lepton universality can constrain many non-Standard Model scenarios. However, pseudoscalar or scalar interactions induced by leptoquarks, supersymmetric particles, extra dimensions etc. can cause measurable deviations from the theoretical prediction. Experimental observation of such a deviation would be clear evidence of new physics sensitive to mass scales up to 1000 TeV. In this talk we present the latest results from the PIENU experiment which provide the most stringent test of lepton universality as well as limits on the presence of massive neutrino states coupled to electrons.
Speaker: Dr Luca Doria (TRIUMF)
• 18:20
Lifetime of the eta-prime meson at low temperature 20m
This work constitutes one part of an investigation of the low-temperature changes of the properties of the eta-prime meson. In turn these properties are strongly tied to the U(1) axial anomaly of Quantum Chromodynamics. The final aim is to explore the interplay of the chiral anomaly and in-medium effects. We determine the lifetime of an eta-prime meson being at rest in a strongly interacting medium as a function of the temperature. To have a formally well-defined low-energy limit we use in a first step Chiral Perturbation Theory for a large number of colors. We determine the pertinent scattering amplitudes in leading and next-to-leading order. In a second step we include resonances that appear in the same mass range as the eta-prime meson. The resonances are introduced such that the low-energy limit remains unchanged and that they saturate the corresponding low-energy constants. This requirement fixes all coupling constants. We find that the width of the eta-prime meson is significantly increased from about 200 keV in vacuum to about 10 MeV at a temperature of 120 MeV.
Speaker: Mrs Elisabetta Perotti (Uppsala University)
• 18:40
Nuclear medium modifications of properties of kaons measured around threshold with FOPI 20m
Modifications of basic properties of kaons, like mass and decay constants, in hot and dense nuclear medium, often parameterized by the in-medium potentials, are an intensely studied topic in the last two decades. However, until recently the experimental samples obtained from the heavy-ion collisions at 1-2A GeV, used to draw conclusions on the scale of these potentials were limited to narrow windows of the momentum space [1-4]. An installation of the new RPC-based ToF detector within the FOPI setup at GSI allowed for a considerable enhancement of the acceptance range of charged kaons. Recent measurement of the directed and elliptic flow of charged kaons [5], has been followed by the extraction of the K-/K+ ratio across phase space, and was supplemented by the determination of contribution of Phi meson decays to the K- meson yield at freeze-out. This new experimental data set may help to sharpen information on the scale of in-medium modifications of properties of charged kaons via comparisons to the predictions of the transport models. __________ [1] K.Wiśniewski et al., Eur. Phys. J. A 9, 515 (2000). [2] F.Laue et al., Eur. Phys. J. A 9, 397 (2000). [3] W.Scheinast et al., Phys. Rev. Lett. 96, 072301 (2006). [4] P.Gasik et al., Eur. Phys. J. A 52, 177 (2016). [5] V.Zinyuk et al., Phys. Rev. C 90, 025210 (2014).
Speaker: Dr Krzysztof Piasecki (University of Warsaw - Faculty of Physics)
• 19:00
Advances on micro-RWELL gaseous detector 20m
The R&D project on the micro-Resistive-WELL (μ-RWELL) detector technology aims in developing a new scalable, compact, spark-protected, single amplification stage Micro-Pattern Gas Detectors (MPGD) for large area HEP applications as tracking and calorimeter device as well as for industrial and medical applications as X-ray and neutron imaging gas pixel detector. The novel micro-structure, exploiting several solutions and improvements achieved in the last years for MPGDs, in particular for GEMs and Micromegas, is an extremely simple detector allowing an easy engineering with consequent technological transfer toward the photolithography industry. Large area detectors (up 1x2 m$^2$) can be realized splicing μ-RWELL_PCB tiles of smaller size (about 0.5x1 mm$^2$ – typical PCB industrial size). The detector, composed by few basic elements such as the readout-PCB embedded with the amplification stage (through the resistive layer) and the cathode defining the gas drift-conversion gap has been largely characterized on test bench with X-ray and with beam test.
Speaker: Dr Gianfranco Morello (LNF-INFN)
• Wednesday, 25 January
• 09:00 14:00
Wednesday Morning
• 09:00
Beam Energy Scan results from STAR 40m
..
Speaker: Dr Lijuan Ruan (BNL)
• 09:40
Standard Model and Heavy Ion Physics with CMS 40m
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Speaker: Dr Elisabetta Gallo (DESY)
• 10:20
Coffee Break 30m
• 10:50
News about Experiments at JPARC 35m
..
Speaker: Prof. Masa Iwasaki (Riken)
• 11:25
Nuclear Astrophysics at the Low-Energy Frontiers: Updates from the Laboratory 35m
Unlike powerful explosive scenarios such as supernovae and novae, quiescent stellar evolution is characterised by nuclear reactions at the lowest thermal energies, well below the Coulomb barrier of interacting nuclei. When trying to reproduce these processes in terrestrial laboratories, we are faced with tremendous experimental challenges that require the use of dedicated setups ideally in an underground environment to maximise the possibility for rare event detection. In this talk I will present some updates from recent investigations of key nuclear reactions that take place in various astrophysical sites and during different stages of stellar evolution. I will underline the challenges faced in each and review upcoming opportunities for future scientific advances.
Speaker: Prof. Maria Luisa Aliotta (Univ. Edinburgh)
• 12:00
New results on the Be-8 anomaly 25m
Recently, we measured the e+e− angular correlation in internal pair creation for the M1 transition depopulating the 18.15 MeV 1+ state in 8Be, and observed a peak-like deviation from the predicted IPC [1]. To the best of our knowledge no nuclear physics related description of such deviation can be made. The deviation between the experimental and theoretical angular correlations is significant and can be described by assuming the creation and subsequent decay of a boson with mass: m0c2= 16.70 ± 0. 35(stat) ± 0. 5(sys) MeV. The branching ratio of the e+e− decay of such a boson to the γ decay of the 18.15 MeV level of 8Be is found to be 5. 8x10-6 for the best fit [1]. The data can be explained by a 17 MeV vector gauge boson X that is produced in the decay of the excited state to the ground state, and then decays to e+e− pairs [2]. The X boson would mediate a fifth force with a characteristic range of 12 fm and would have millicharged couplings to up and down quarks and electrons, and a proton coupling that is suppressed relative to neutrons [2]. Recently we reinvestigated the anomaly observed previously by using a new Tandetron accelerator of our Institute. The multi-wire proportional counters were replaced with silicon DSSD detectors, as well as the complete electronics and data acquisition system was changed from CAMAC to VME. We have measured the e+e− angular correlation in internal pair creation for the M1 transition depopulating the 17.64 MeV 1+ state in 8Be, and observed a peak-like deviation from the predicted IPC as well. It is a smaller deviation than we observed from the decay of the 18.15 MeV 1+ state, and appeared at larger angles corresponding to the mass of: m0c2 = 17.0± 0. 3(stat) ± 0. 5(sys) MeV. The branching ratio of the e+e− decay of such a boson to the γ-decay agrees well with the prediction of Feng et al. [2]. [1] A.J. Krasznahorkay et al., Phys. Rev. Lett. 1 16 042501 (2016) [2] J. Feng et al., Phys. Rev. Lett. 1 17, 071803 (2016)
Speaker: Dr Attila Krasznahorkay (MTA Atomki, Hungary)
• 17:00 19:00
Wednesday Afternoon
• 17:00
Ab-initio calculation of neutrino-carbon scattering in the quasi-elastic region 20m
Several upcoming experiments have the ambitious goal to understand neutrino mixing, including the mass hierarchy and CP violation, to search for physics beyond the standard model. These experiments aim to reach a precision at the per-cent level, and, in order to accurately interpret these measurements, the knowledge of the neutrino-nucleus interaction is critical. In this talk we will present recent Green's Function Monte Carlo calculations of the euclidean correlation functions that are relevant for the neutrino-12C scattering in the quasi-elastic region. These non-perturbative calculations fully include long- and short-range correlations in the nuclear wave function, and give an excellent description of properties of light nuclei. We will show that the inclusion of two-body operators consistent with the nuclear Hamiltonian is crucial and their contribution is quite sizable, as already predicted by similar calculations and experimental measurements of electron-scattering. These contributions are necessary to understand electron scattering and are also very important in neutrino-nucleus scattering.
Speaker: Dr Stefano Gandolfi (Los Alamos National Laboratory)
• 17:20
First observation of $\Sigma^{0}$ production in proton induced reactions on a nuclear target* 20m
We have studied the production of neutral $\Sigma^{0}$ baryons in the nuclear reaction p + Nb at an incident proton energy $E_{kin}$ = 3.5 GeV. The measurement has been performed with the HADES experiment setup at GSI, Darmstadt. $\Sigma^{0} \rightarrow \Lambda^{0} \gamma$ decays were identified via the charged decay $\Lambda^{0} \rightarrow p \pi^{-}$ coincident to $e^{+}e^{-}$ pairs from external gamma conversion. Experimental details, analysis procedures and background determination are presented. An observed total of about 250 candidate events is used to determine the $\frac{\Lambda + \Sigma}{\Sigma}$ production ratio. The obtained numbers and spectra are compared to predictions from transport model calculations and are discussed in the context of thermal particle production in nuclear fireballs. *Supported by the Excellence Cluster Universe
Speaker: Mr Tobias Kunz (Technische Universität München)
• 17:40
Baryon Form Factors at BESIII 20m
The BESIII detector at the BEPCII $e^+e^-$ collider has been taken data since 2008. With a small amount of data, we have measured the cross section of $e^+e^-\to p\bar{p}$ at 12 center-of-mass energies from 2.2324 to 3.6710 GeV. Much larger data samples have been collected, for examples, energy scan in 2-3.1 GeV for 650/pb and in 3.85-4.6 GeV for 500/pb, in addition to other data samples. The prospect of baryon form factors measurements will be discussed, including $p\bar{p}$, $n\bar{n}$, $\Lambda\bar\Lambda$, etc. The preliminary but unexpected result of form factors of $\Lambda\bar\Lambda$ measurement is shown, as well as the expectation from the data collected at the threshold of $\Lambda_c\bar\Lambda_c$. Initial State Radiation (ISR) technique is also used, in both tagged and untagged methods, for $p\bar{p}$ study.
Speaker: Dr Cristina Morales
• 18:00
Recent results on soft QCD topics from ATLAS 20m
The ATLAS collaboration has performed several measurements in special data sets with low LHC beam currents, recorded at a center-of-mass energy of 13 TeV: Measurements of the inclusive charged-particle multiplicity and its dependence on transverse momentum and pseudorapidity are presented and compared with predictions of various MC generators. The collaboration has also performed measurements of the number and transverse-momentum sum of charged particles as a function of properties of the leading high pT track in the event at a center-of-mass energy of 13 TeV. The results are compared to predictions of several MC generators. In addition, the total inelastic proton-proton cross section and the diffractive part of the inelastic cross section was measured, using special forward scintillators or the calorimeters. The latter result completes the measurement of the elastic pp cross section in a dedicated run with high beta* optics at 8 TeV centre-of-mass energy with the ALFA Roman Pot detector. From the extrapolation of the differential elastic cross section to t=0, using the optical theorem, the total cross section is extracted with the luminosity-dependent method with high precision. Furthermore, the nuclear slope of the elastic t-spectrum and the total elastic and inelastic cross sections are determined. Finally, the collaboration has studied the hard double parton interactions (DPI) in events with 4 hadronic jets and translated into a measurement of the effective DPI cross section. Several DPI-sensitive variables are unfolded to particle level and compared to predictions of different MC models.
Speaker: Dr Andrey Minaenko (Protvino IHEP)
• 18:20
Open heavy-flavour measurements in pp and p-Pb collisions with ALICE at the LHC 20m
Heavy quarks (charm and beauty), produced in ultra-relativistic heavy-ion collisions, are formed in hard partonic scattering processes in the early stage of the collision, and therefore offer a unique opportunity to probe the properties of the strongly-interacting medium created. An interpretation of measurements in heavy-ion collisions requires measurements in pp and p-Pb collisions, which can themselves offer important information about heavy-flavour production. The study of heavy-flavour production in pp collisions offers a baseline measurement to understand in-medium modification in Pb-Pb collisions as well as a test of pQCD predictions, and p-Pb measurements can give crucial information on cold nuclear matter effects, such as nuclear modification of parton distribution functions, $k_T$ broadening or energy loss in cold nuclear matter, as well as address the possibility of collective behaviour in smaller systems. More differential measurements can give further insight into heavy-flavour production. The measurement of D-meson yields as a function of multiplicity in pp and p-Pb collisions can offer unique insight into particle production mechanisms, including the interplay between hard and soft mechanisms, and the role of multi-parton interactions in heavy-flavour production. In addition the study of angular correlations between D-mesons and charged particles can give interesting insight into particle production mechanisms and jet properties. The ALICE detector is well suited to measure charmed meson decays via hadronic channels and semi-leptonic heavy-flavour decays. This talk will give an overview of heavy-flavour measurements made with the ALICE detector during Run 1 in pp and p-Pb collisions, as well as outline current and future measurements for Run 2.
Speaker: Mr Jaime Norman (University of Liverpool)
• 18:40
From the deuteron to Pc(4450) 20m
Heavy hadrons interacting via pion exchange can form bound states (hadronic molecules), analogous to conventional nuclei. The potential between charmed hyperons and charmed mesons, with parameters constrained by the deuteron, leads naturally to a bound state, whose mass and quantum numbers are consistent with the LHCb "pentaquark" $P_c(4450)$. An appealing feature of the model is that it does not imply a proliferation of unobserved partner states. Within a significant (and constrained) parameter range, and independently of the poorly-known short-distance potential, only one additional partner with the same flavour is expected, and its experimental absence (so far) has a possible explanation. A further partner with different flavour is also predicted, and could be discovered in $\Lambda_b$ decays. A characteristic feature of the molecular interpretation is isospin mixing, resulting in striking signatures in production and decay.
Speaker: Dr Timothy Burns (Swansea University)
• Thursday, 26 January
• 09:00 13:20
Thursday Morning
• 09:00
Inferences on the specific heat and neutrino emissivity of dense matter from accreting neutron stars 45m
Many neutron stars are in binaries and accrete matter transferred from their companion. Often, this accretion is intermittent: the neutron star accretes rapidly for a time, and then is quiescent for a long time. In this talk, I will discuss recent efforts to constrain the core heat capacity and neutrino emissivity of matter at densities above saturation from observations of the surface temperatures of quiescent neutron star transients immediately following an accretion outburst.
Speaker: Prof. Edward Brown (MSU)
• 09:45
Optical Lattice Clocks: Reading the 18th decimal place of frequency 45m
Optical lattice clocks [1] benefit from a low quantum-projection noise by simultaneously interrogating a large number of atoms trapped in the standing wave of light (optical lattice) tuned to the “magic frequency” that mostly cancels out the light shift perturbation in the clock transition [2]. About a thousand atoms enable such clocks to achieve 10-18 instability in a few hours of operation [3-5], allowing intensive investigation and control of systematic uncertainties, such as multipolar and higher order light shifts [6] and the blackbody radiation shift [5]. It is now the uncertainty of the SI (International System of Units) second (~10-16) itself that restricts the absolute frequency measurements of such optical clocks [7, 8]. Direct comparisons of optical clocks are, therefore, the only way to demonstrate and utilize their superb performance beyond the SI second. In this presentation, we report on frequency comparisons of optical lattice clocks with neutral strontium (87Sr), ytterbium (171Yb) and mercury (199Hg) atoms. By referencing cryogenic Sr clocks [5], we have determined the frequency ratios, R = νYb/νSr and νHg/νSr of a Yb clock and a Hg clock with uncertainty at the mid 10-17 [9]. Such ratios provide an access to search for temporal variation of the fundamental constants [10]. We also present remote comparisons of cryogenic Sr clocks located at RIKEN and the University of Tokyo over a 30-km-long phase-stabilized fiber link. The gravitational red shift Δν/ν0 ≈ 1.1×10-18 Δh cm-1 reads out the height difference of Δh~15 m between the two clocks with uncertainty of 5 cm [11], which demonstrates a step towards relativistic geodesy [12]. Finally, we mention our ongoing experiments that reduce clock uncertainty to 10-19 by applying “operational magic frequency” [13] that effectively cancels out higher-order light shifts arising from the dipole, multipolar, and hyper-polarizability effects for a certain range of lattice intensity. References: [1] H. Katori, Optical lattice clocks and quantum metrology, Nature Photon. 5, 203 (2011). [2] H. Katori et al., Ultrastable optical clock with neutral atoms in an engineered light shift trap, Phys. Rev. Lett. 91, 173005 (2003). [3] N. Hinkley et al., An atomic clock with 10-18 instability, Science 341, 1215 (2013). [4] T. L. Nicholson et al., Systematic evaluation of an atomic clock at 2×10-18 total uncertainty, Nature Commun. 6, 6896 (2015). [5] I. Ushijima et al., Cryogenic optical lattice clocks, Nature Photon. 9, 185 (2015). [6] P. G. Westergaard et al., Lattice-Induced Frequency Shifts in Sr Optical Lattice Clocks at the 10-17 Level, Phys. Rev. Lett. 106, 210801 (2011). [7] R. Le Targat et al., Experimental realization of an optical second with strontium lattice clocks, Nature Commun. 4, 2109 (2013). [8] C. Grebing et al., Realization of a timescale with an accurate optical lattice clock, Optica 3, 563 (2016). [9] N. Nemitz et al., Frequency ratio of Yb and Sr clocks with 5 × 10−17 uncertainty at 150 seconds averaging time, Nature Photon. 10, 258 (2016). [10] J.-P. Uzan, The fundamental constants and their variation: observational and theoretical status, Rev. Mod. Phys. 75, 403 (2003). [11] T. Takano et al., Geopotential measurements with synchronously linked optical lattice clocks, Nature Photon. 10, 662 (2016). [12] C. Lisdat et al., A clock network for geodesy and fundamental science, Nature Commun. 7, 12443 (2016). [13] H. Katori et al., Strategies for reducing the light shift in atomic clocks, Phys. Rev. A 91, 052503 (2015).
Speaker: Prof. Hidetoshi Katori (Uni TOkyo)
• 10:30
Coffee Break 30m
• 11:00
Recent developments in nuclear structure theory 30m
Atomic nuclei constitute the heart of matter. They drive the synthesis of chemical elements, serve as star fuel and as laboratories to test fundamental interactions and the Standard Model. Predictions of nuclear properties that start from forces among nucleons and their interactions with external probes as described by chiral effective field theory are arguably the doorway to a solid connection between observations and the underlying fundamental theory of quantum chromo-dynamics. Today, thanks to advances in many-body theory and high performance computing, we can calculate nuclear structure and reactions in a unified way for increasingly large systems and estimate theoretical uncertainties. Recent highlights will be presented, that portrait the role of ab-initio calculations to tackle contemporary issues, such as the investigation of neutron-rich nuclei and the proton-radius puzzle.
Speaker: Dr Sonia Bacca (TRIUMF)
• 11:30
LHCb Results on Flavour Physics 30m
LHCb Results on Flavour Physics
Speaker: Dr Stefania Ricciardi (STFC)
• 12:00
Theoretical Prediction of the Be8 anomaly 25m
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Speaker: Dr Tim Tait (UCI)
• 17:00 19:05
Thursday Afternoon
• 17:00
Nuclear Reactions for Neutrinoless Double Beta Decay 25m
Nuclear Reactions for Neutrinoless Double Beta Decay
Speaker: Dr Manuela Cavallaro (LNS)
• 17:25
Calculations of kaonic nuclei based on chiral meson-baryon coupled channel interaction models 20m
We review our latest calculations of $K^-$-nuclear quasi-bound states. We apply a self-consistent scheme for constructing $K^-$-nuclear potentials from subthreshold chirally inspired $K^-$$N$ scattering amplitudes, which are derived within several chirally motivated meson-baryon coupled-channel interaction models: Prague [1], Kyoto- Munich [2], Murcia [3], and Bonn [4]. They capture the physics of the Λ(1405) and reproduce low energy $K^-N$ observables, including the 1s level shift and width in the $K^-$ hydrogen atom from the SIDDHARTA experiment [5]. We consider the in-medium versions of the scattering amplitudes taking into account Pauli blocking in the intermediate states. We calculate $K^-$ binding energies and widths in various nuclei and study the effects of 2N absorption, core polarization and the P-wave interaction on the considered observables. The chirally inspired $K^-N$ potentials supplemented with phenomenological terms representing $K^-$ multinucleon processes were recently confronted [6] with kaonic atom and $K^-$ absorption data to provide another test of considered interaction models. [1] A. Cieply, J. Smejkal, Nucl. Phys. A 881 (2012) 115 [2] Y. Ikeda, T. Hyodo and W. Weise, Nucl. Phys. A 881 (2012) 98 [3] Z. H. Guo and J. A. Oller, Phys. Rev. C 87, no. 3,(2013) 035202 [4] M. Mai and U.-G. Meißner, Nucl. Phys. A 900, (2013) 51 [5] M. Bazzi et al (SIDDHARTA Collaboration), Phys. Lett. B 704 (2011) 113 [6] E. Friedman, A. Gal, to be published, arXiv:1610.04004 [nucl-th]
Speaker: Mrs Jaroslava Hrtankova (Nuclear Physics Institute, 25068 Rez, Czech Republic)
• 17:45
Recent results from the ATLAS heavy ion program 20m
The heavy ion program in the ATLAS experiment at the Large Hadron Collider aims to probe and characterize the hot, dense matter created in relativistic lead-lead collisions, in the context of smaller collision systems involving nuclei and hadrons. This talk presents recent results based on LHC Run 1 and Run 2 data, including measurements of bulk collectivity, electroweak bosons, jet modifications, and quarkonium suppression. Results will also be presented on electromagnetic processes in ultra-peripheral collisions, including forward dilepton production and light-by-light scattering.
Speaker: Dr Radim Slovak (Prague CU)
• 18:05
Constraining the symmetry energy at high density with the first SπRIT experiments 20m
The nuclear Equation of State (EoS) is a fundamental property of nuclear matter that describes relationships between energy, pressure, temperature, density, and isospin asymmetry in a nuclear system. The asymmetric part of EoS, which is originated by the isospin asymmetry, has not been well constrained yet above the saturation density, contrary to the symmetric part of EoS. Transport model calculations predict that pions emitted from the heavy-ion collisions are sensitive probe to constrain the symmetry energy above the saturation density. The SπRIT Time Projection Chamber (TPC) and ancillary trigger detectors were specifically designed and constructed to constraint the symmetry energy above the saturation density using the radioactive isotope beams produced by the Radioactive Isotope Beam Factory (RIBF) at RIKEN by measuring pions as well as light ions. In this talk, the SπRIT TPC and the first experimental campaign, completed in 2016, are described and preliminary results are presented. Data was collected for the four collision systems: 132Sn+124Sn, 112Sn+124Sn, 124Sn+112Sn, and 108Sn+112Sn with beam energy of 270 AMeV.
Speaker: Dr Giordano Cerizza (Michigan State University/NSCL)
• 18:25
Two-neutron removal from $^{11}$Li in a (p,t) reaction at low incident energy 20m
The structure of halo nuclei, such as $^{11}$Li is of considerable interest [1]. The two-neutron transfer reaction $^{11}$Li(*p,t*) $^{9}$Li promises to provide valuable information on the halo-neutron correlation of this exotic Borromean nuclear species. Unfortunately a relatively sophisticated theoretical prediction does not reproduce the first experimental cross section angular distribution of this reaction at an incident energy of 3 MeV [2] particularly well. The hope that a more refined calculation would be successful seems to be somewhat elusive, because a fairly sophisticated theoretical attempt fails spectacularly [3] to reproduce the angular distribution for the same reaction at a slightly higher incident energy of 4.4 MeV. On the other hand, as will be shown in this work, a very simplistic simultaneous transfer, zero-range distorted-wave Born Approximation gives an excellent reproduction of the angular-distribution shape. The implications of this surprising result will be discussed. [1] I. Tanihata, H. Savajols, and R. Kanungo, Progress in Particle and Nuclear Physics **68** (2013) 215. [2] I. Tanihata et al., Phys. Rev. Lett. **100** (2008) 192502. [3] Ian Thompson, 2011 Theory and Calculation of Two-Nucleon Transfer Reactions Lawrence Livermore National Laboratory, Report LLNL-PRES-492069 (unpublished).
Speaker: Prof. Anthony Cowley (Stellenbosch University)
• 18:45
Selected CMS Results in Higgs Physics 20m
In this talk a selection of the most recent results on the measurement of Higgs boson production and properties from the CMS experiment is presented
Speaker: Dr Milos Dordevic (Uni Belgrade)
• Friday, 27 January
• 09:00 13:10
Friday Morning
• 09:00
Sterile Neutrinos 45m
Sterile neutrinos
Speaker: Prof. Susanne Mertens (TUM, MPA)
• 09:45
Hadron Spectroscopy and Heavy Ion Results at LHCb 45m
Hadron Spectroscopy and Heavy Ion Results at LHCb
Speaker: Dr Giovanni Passaleva (INFN FI)
• 10:30
Coffee Break 30m
• 11:00
Challenging the Standard Model: SuperKEKB and the Belle II Experiment 40m
With SuperKEKB and the Belle II experiment a new era of high statistics flavor physics at the Upsilon (4S) resonance is at the horizon, providing almost two orders of magnitude more luminosity compared to the eminently successful B factories PEP II and KEKB. In this presentation we first give a short introduction into the B-meson system and CP violation within the Standard Model, summarize the present experimental tensions, and then present SuperKEKB’s potential searching for physics beyond the Standard Model. Concurrently with the construction of SuperKEKB, a massive detector upgrade of the Belle detector (“Belle II”) is ongoing. Most importantly, the tracking and particle ID systems are in the focus. Due to the largely increased background close to the beam pipe traditional Silicon strip detector will no longer work. We report on the design and construction of a unique pixel vertex detector for Belle II, coined “PXD”. The PXD sensors are based on the DEPFET-technology, with which an extremely small material budget and a high signal to noise ratio can be reached. The principles of the DEPFET technology will be explained as well as the construction of large self-supporting pixel matrices, making up the PXD. Finally, we show the various steps, tests and commissioning phases for the accelerator and the Belle II detector which are scheduled for first nano-beam collisions by early 2018.
Speaker: Dr Christian Kiesling (Max Planck Institute for Physics)
• 11:40
Mesons in the medium - experimental probes for chiral symmetry restoration 30m
The in-medium modications of hadron properties have been identied as one of the key problems in understanding the non-perturbative sector of QCD. Several theoretical papers discuss the possibility of a partial restora- tion of chiral symmetry in a strongly interacting environment. However, is it possible to nd experimental evidence for partial symmetry restoration by studying the in-medium behaviour of mesons, in particular the meson- nucleus interaction? Is this interaction suciently strong to allow even the formation of mesic states only bound by the strong interaction? The an- swers can be given by studying the meson-nucleus optical potential. What are the experimental approaches to deduce this potential? In this presen- tation experimental results from CBELSA/TAPS on the determination of the meson-nucleus optical potential will be presented and discussed in view of these questions. Data taken on a C and Nb target at CB/TAPS@ELSA have been analyzed to deduce the 0- and !-nucleus optical potential. The data for both mesons are consistent with a weakly attractive potential. The formation and population of !-nucleus and 0-nucleus bound states will be discussed. In case of the ! meson the in-medium width is found to be larger than the potential depth which hampers a successful identication of !-mesic states. The relatively small in-medium width of the 0 meson encourages ongoing experiments to search for 0-nucleus bound states. ?Funded by DFG(SFB/TR-16
Speaker: Dr Mariana Nanova (Uni. Giessen)
• 12:10
The proton radius puzzle 30m
proton radius puzzle
Speaker: Prof. Marco Vanderhaeghen (Univ. Mainz)
• 17:00 19:00
Friday Afternoon
• 17:00
Signals for dynamical process form IMF-IMF correlation function 20m
In Heavy Ion Collisions (HIC) at Fermi energies (10 MeV/nucleon ≤ E/A ≤ 100 MeV/nucleon) hot nuclear systems are produced and they may disassemble by a variety of dynamical and statistical mechanisms with vastly different time scales (neck emission, fission, multifragmentation, fusion-evaporation, ecc.). The space-time sensitivity of the fragment-fragment Correlation Function to the emission of Intermediate Mass Fragments (IMFs 3≤ Z ≤ 25) has been investigated in order to pin down size and time characteristics of their emission region. In particular, IMF-IMF correlation functions have been applied to 124Sn+64Ni at E/A= 35 MeV reverse kinematics reactions where strong competition between dynamical and statistical production mechanisms of heavy fragments has been clearly demonstrated [1]. Preliminary comparisons between data and theoretical simulations, will be also discussed. [1]P. Russotto et al. PHYSICAL REVIEW C 91, 014610 (2015)
Speaker: Dr Emanuele Vincenzo Pagano (LNS-INFN)
• 17:20
Kaon-Production in Pion-Induced Reactions at 1.7 GeV/c 20m
The production and properties of $K^0_S$, $K^+$, $\Phi$ and $K^-$ in cold nuclear matter generated in pion-nucleon reactions ($\pi^- + A$, $A = C, W$) at $p_{\pi^-}= 1.7$ GeV/c has been investigated with the HADES detector at GSI. Similar to the $K^0$ production at the surface of the nuclei ($\sigma \sim A^{b}, b=2/3$), as already verified by the FOPI collaboration, it was assumed to apply also for the $K^+$ and $K^-$ production allowing for the study of in-medium effects. In this context the $K^-$ absorption in nuclear matter which should be apparent through strangeness exchange processes ($K^- N\rightarrow Y\pi$) is investigated, contrary to the $K^+$ with no conventional absorption mechanism known. In this talk we are presenting the $K^-$ absorption on the basis of the $K^-/K^+$ ratios in both nuclear environments and obtained cross-sections. In addition the $K^-$ production is shown in terms of the $\phi$ feed-down. * supported by the DFG cluster of excellence "Origin and Structure of the Universe"
Speaker: Ms Joana Wirth (TU München)
• 18:00
The continuing story of two-photon exchange: results from the OLYMPUS experiment 20m
Over the past two decades, a discrepancy has emerged between two different techniques for measuring the proton's electromagnetic form factors. Unpolarized electron-proton cross section measurements paint a picture of the proton's internal structure that is incompatible with measurements from polarization transfer experiments. The leading hypothesis is that the discrepancy is caused by a typically neglected radiative correction, hard two-photon exchange (TPE), which would affect the two measurement techniques in different ways. There is no model independent way to calculate hard TPE, but it can be measured experimentally by looking for an asymmetry between the positron-proton and electron-proton elastic cross sections. Three recent experiments have attempted to quantify this asymmetry, and, just last month, the third of these, called OLYMPUS, released its results (arXiv:1611.04685). The OLYMPUS experiment collected data in 2012 at DESY, alternating between 2 GeV electron and positron beams, directed through a hydrogen gas target. The scattered lepton and recoiling proton were detected in coincidence with a large acceptance toroidal spectrometer. The relative luminosity between the two beam species was monitored with three independent systems, and the results comprise 3 inverse fb of integrated luminosity, exceeding by a factor of three the other two TPE experiments combined. In this talk, the case for the TPE hypothesis will be presented, the OLYMPUS experiment will be described, and the results of all three experiments will be compared.
Speaker: Dr Axel Schmidt (MIT)
• 18:20
Bottomia physics at RHIC and LHC energies 20m
The suppression of Y mesons in the hot quark-gluon medium (QGP) versus reduced feed-down is investigated in UU collisions at RHIC energies and PbPb collisions at LHC energies. Our centrality- and p_T-dependent model encompasses screening, collisional damping and gluodissociation in the QGP. For Y(1S) it is in agreement with both STAR and CMS data provided the relativistic Doppler effect and the reduced feed-down from the Y(nS) and chi_b(nP) states are properly considered. At both energies, most of the suppression for the Y(1S) state is found to be due to reduced feed-down, whereas most of the Y(2S) suppression is caused by the hot-medium effects. The role of the in-medium effects relative to reduced feed-down increases with energy. The p_T-dependence is flat due to the relativistic Doppler effect. We predict the Y(1S)-suppression in PbPb at sqrt(s_NN) = 5.02 TeV and consider the hot-medium vs. cold nuclear matter (CNM) contribution to the suppression in the asymmetric pPb system at the same energy. [1] J. Hoelck, F. Nendzig and G. Wolschin, arXiv:1602.00019
Speaker: Prof. Georg Wolschin (U Heidelberg)
• 18:40
Measurement of polarization transfer to a bound proton at large virtuality 20m
A measurement of the ratio $P_x/P_z$ of polarization transfer components in the $\mathrm{D}(\vec{e},e'\vec{p})n$ reaction at different missing momenta will be reported. The $P_x/P_z$ ratio observed for H, D, and $\mathrm{^{4}He}$, respectively, indicates a dependency on the proton's virtuality and the missing momentum direction, but not the average nuclear density.
Speaker: Dr Ulrich Müller (Inst. für Kernphysik, Univ. Mainz)