# 54. International Winter Meeting on Nuclear Physics

Jan 25 – 29, 2016
Bormio, Italy
Europe/Berlin timezone

## Measurement of neutral mesons in pp and Pb-Pb collisions at midrapidity with the ALICE experiment at the LHC

Jan 29, 2016, 5:20 PM
20m
Bormio, Italy

#### Bormio, Italy

Short Contribution Relativistic Heavy Ion Physics

### Speaker

Ms Lucia Leardini (Physikalisches Institut (PI) Heidelberg)

### Description

Neutral mesons, such as $\pi^{0}$ and $\eta$, are probes for the study of the energy loss of partons traversing the hot and dense medium, the Quark-Gluon Plasma, that is formed in heavy-ions collisions. Moreover, they represent the largest background for the direct photon measurement and an accurate estimate is therefore necessary to determine the decay photon contribution. The ALICE experiment measures $\pi^{0}$ and $\eta$ mesons via the two-gamma decay channel. The photon detection can either be direct, using the electromagnetic calorimeters EMCal and PHOS, or by reconstructing the electron-positron pairs from photon conversions in the detector material (photon conversion method, PCM). With the PCM, photons are reconstructed using the ALICE Inner Tracking System (ITS) and the Time Projection Chamber (TPC). This method has full azimuthal coverage, which compensates for the small conversion probability. It provides a precise measurement at low transverse momentum. The calorimeters have reduced acceptance but trigger capabilities and provide the high $p_{\mbox{\tiny{T}}}$ measurement, where they also have good energy resolution. The errors from these measurements are independent thus their comparison is a good cross check and their combination gives a more precise result. In this presentation, we will show the $\pi^{0}$ and $\eta$ spectra in Pb--Pb collisions at $\sqrt{s_{\mbox{\tiny NN}}}$ = 2.76~TeV and pp collisions at different center of mass energy obtained over a wide transverse momentum range.

### Primary author

Ms Lucia Leardini (Physikalisches Institut (PI) Heidelberg)

 Slides