Talk

Simulation results of the feasibility studies of time-like proton electromagnetic form factors at PANDA (FAIR) are presented. The simulation was performed using the PandaRoot software framework in a wide $q^2$ range. The signal $\bar p p \to e^+ e^-$ and the background $\bar p p \to \pi^+ \pi^-$ channels have been studied using two different methods. Individual signal efficiency and background suppression techniques were applied to extract proton form factors. The statistical precision of the proton form factors extraction is determined. The results of two methods are consistent with each other. A number of systematic uncertainties have also been evaluated. The competitiveness of the PANDA experiment with existing data and planned experiments is presented.

This contribution presents the current status of the feasibility studies for the measurement of time-like proton electromagnetic form factors (FF's) using reactions of the type $\bar{p} p \rightarrow \mu^{+} \mu^{-}$ at the PANDA experiment at FAIR. Electromagnetic form factors are fundamental quantities which parameterize the electric and magnetic structure of hadrons. In the time-like region, the FF's can be accessed through reactions of the type $p\bar{p}\rightarrow l^{+} l^{-}$, where l = e, $\mu$, under the assumption of one photon exchange. It will be the first time that muon pairs in the final state will be used for the measurement of the TL em FF's of the proton. One advantage of using this channel is that radiative corrections due to final state radiation are suppressed by the heavy mass of the muon. Measuring $\bar{p} p \rightarrow \mu^{+} \mu^{-}$ will also serve as a consistency check of the TL em FF data from $\bar{p} p \rightarrow e^{+} e^{-}$. In frame of the PANDARoot software, which encompasses full detector simulation and event reconstruction, the statistical precision at which the proton FF's will be determined at PANDA is estimated for the signal reaction $p \bar{p} \rightarrow \mu^{+} \mu^{-}$ at different antiproton beam momenta. The signal identification and the suppression of the main background process ($p\bar{p} \rightarrow \pi^{+} \pi^{-}$) are studied. The preliminary results at different beam momenta are presented.

The PANDA experiment at the FAIR facility in Darmstadt, Germany, is aiming at precise measurement of hadron properties in the charmonium region and investigation of exotic-matter states. This will be possible because of employment of the annihilation of antiprotons with very low momentum spread of 2e-5 and high luminosity, up to 1e32 1/(cm s). At the highest luminosity the annihilation rate will rise up to 20MHz. Moreover, the decay topology of events of interest is very similar to the one of background events. This excludes any reasonable performance of a classical triggered readout system. Therefore, a new readout has been developed where self-triggered front-end electronics is able to autonomously detect hits and extract all relevant physics information, a dedicated custom network builds events based on hit time-stamps, and an FPGA/GPU/CPU-based computing system, which selects events of interest on-line using the complete reconstruction, in order to achieve a data-reduction factor of about up to 1000. Such a readout system is called “trigger-less”. Since there is no trigger signal which forces simultaneous readout of acquired data from all front-ends, the electronics should use the same clock signal and should be synchronized. Therefore, a precise clock-distribution and -synchronization platform SODANET has been developed. The SODANET is a bi-directional data-transfer protocol for optical links which foresees transfer of detector- and slow-control data and synchronization messages with fixed latency. The synchronization messages have the highest priority and can be transmitted even if transmission of another packet is not yet finished. The synchronous operation is implemented only in the downstream direction and requires defined latency configuration of serializers/deserializers. A complete prototype of the readout system which employs the SODANET protocol has been constructed. During the presentation the SODANET platform and its performance will be discussed.

Three algorithms, designed to search for clusters in the electromagnetic calorimeter (EMC) of the future PANDA experiment, are described and evaluated. The high rate of 2E7 interactions/s between the antiproton beam and the proton target leads to a high probability for pile-up and event mixing, complicating the search for clusters. To reduce the amount of data produced by the experiment, the detector will preprocess as much data as possible online, and select events of interest based on online reconstruction. To perform these reconstructions, input from the cluster finding algorithm, which is part of the online preprocessing, is essential. The algorithms are tested using simulated data for both their efficiency and processing time using two 5000 event data samples in the high rate
case, a lower rate case (factor 100 lower rate), and the case with completely disjoint events. The first sample is a low photon-multiplicity sample of direct two-photon production events. The efficiency, i.e. the number of successful reconstructions, is similar for all methods, around 90%. The algorithm that is most eligible for online usage runs the fastest, as expected. The second sample tests the high photon-multiplicity channel of the hc meson to 7 photons, and will also be expanded with background events. More detailed results on the performance evaluation will be presented.

The electromagnetic calorimeter (EMC) of the PANDA detector at the future FAIR facility comprises more than 15,000 lead tungstate (PWO) crystals. The barrel part will consist of 11 crystal geometries with different degree of tapering, which causes a non-uniformity in light collection as an interplay between the focusing and the internal absorption of the light. For the most tapered crystals the detected light is enhanced by 40%, if the scintillation light is created in the front part of the crystal. Due to the shower development and its fluctuations the non-uniformity leads to a reduction of the energy resolution. To reduce this effect, one lateral crystal side face has been depolished to a roughness of 0.3 µm. Measurements confirm an increase of the light yield in the rear part of the crystal. In contrast, only a slight decrease can be observed in the front part. The overall non-uniformity is significantly reduced below 5%. This paper will discuss the experimental studies based on GEANT4 and optical simulations to understand the impact of a de-polished side face on the light collection. For consequences on the future performance, a 3x3 sub-array of de-polished crystals was directly studied using a tagged photon beam in the energy range from 50 MeV up to 800 MeV, respectively, performed at the tagged photon facility at MAMI, Mainz. The comparison to an array composed of polished crystals confirms a significant improvement of the energy resolution in the region above 200 MeV, resulting in a reduction of the constant term of the energy resolution from more than 2 % down to 0.5 % and only a small increase of the statistical term. The results can be reproduced in GEANT4 simulations.

The project is supported by BMBF, GSI and HIC for FAIR.

The presentation shows the usage of message queues based on FairMQ for the reconstruction of MVD test beam data.

PANDA is a key experiment of the future FAIR facility and the Micro Vertex Detector (MVD) is the innermost part of its tracking system. It will be composed of four barrels and six disks, instrumented with silicon hybrid pixel detectors and double-sided microstrip detectors.
PASTA (PAnda STrip ASIC) is the readout chip for strip sensors.
An overview of the chip, of its readout system and of the first results of its characterization will be presented.
Supported by BMBF, HIC4FAIR and JCHP.