# 56. International Winter Meeting on Nuclear Physics

22-26 January 2018
Bormio, Italy
Europe/Berlin timezone

## The Crystal Zero Degree Detector at BESIII

22 Jan 2018, 17:36
3m
Bormio, Italy

#### Bormio, Italy

Poster Applications and Instrumentations

### Speaker

Mr Leonard Koch (JLU Giessen)

### Description

The BESIII experiment at the BEPCII electron positron collider at IHEP (Beijing) is collecting data in the charm-$\tau$ mass region. In electron positron collisions one of the initial leptons may emit a real photon before the annihilation (initial state radiation, ISR). As a result, the remaining system is boosted and has an effective center-of-mass energy lower than the nominal one ($2m_e\leq\sqrt{s'}<\sqrt{s}$). While the accelerator is tuned to a fixed $\sqrt{s}$, the analysis of ISR events provides simultanious access to processes at different $\sqrt{s'}$ making it a great tool for measurements of e.g. timelike hadron formfactors or the $R$-value. However, the photons from ISR are strongly peaked towards small polar angles and are currently detected with limited efficiency. In order to increase the detection efficiency of these photons, we are developing small-size calorimeters to be placed in the very forward and backward regions. Each detector will consist of two arrays of LYSO crystals separated by a small gap. The scintillation light will be collected by silicon photomultipliers (SiPMs). The expected event rate in the MHz range requires flash ADCs recording the preamplified SiPM outputs. The digitized waveforms will be analyzed in realtime on FPGA-based hardware performing sub-event building, buffering, and event correlation with the BESIII trigger. A single crystal equipped with four SiPMs was instrumented as a prototype detector. Tests with an electron beam at the MAMI facility in Mainz were performed successfully.

### Primary author

Mr Leonard Koch (JLU Giessen)

 Slides