Fabbietti, L.

Lalik, R.

Maier, L.

Scordo, A.

Wirth, J.

GSI Repository

Tracking pions with CERBEROS∗ at the HADES spectrometer†J. Wirth1,2, L. Fabbietti1,2, R. Lalik1,2, L. Maier1, Alessandro Scordo3, and the HADES collaboration1Physik Department E12, Technische Universita¨t Mu¨nchen, 85746 Garching, Germany; 2Excellence Cluster ”Originand Structure of the Universe”, 85746 Garching, Germany; 3INFN LNF, Frascati, ItalyIn 2014 the HADES collaboration performed twosuccessful experimental campaigns with secondary pionbeams. Since the momentum distribution of the producedpion beam is very broad, two fast tracking stations wereinstalled along the pion chicane following the pion produc-tion target to reconstruct the momentum of each individualpion (Fig.1). Both stations consist of a double sided siliconstrip sensor with a large active area (10 × 10 cm2). Thesensors are read out with a n-XYTER ASIC chip [1].Due to its self-triggering architecture and local storagecapability, the chip enables tracking and online beammonitoring at high rates. The TRB3 board [2] on whichthe trigger logic is implemented completes the readoutchain and integrates the system into the Hades DAQ. Allhits registered by the n-XYTER are buffered inside thisboard and only events correlated in time with the CTS(Central Trigger System) are send to the Event Builder.Figure 1: Schematic of the pion beam chicane. The po-sitions of the two tracking stations are indicated in green.The first station is located at the dispersive plane.The pion momentum is reconstructed relying on thebeam optics transport calculation using the four spatialcoordinate informations provided by the tracking system.A large momentum spread translates into a large x-positiondeviation at the dispersive plane where the first detector islocated. The requested resolution of < 0.5% is two ordersof magnitude better than the spread in momentum due tothe beam line acceptance of about 8% and therefore allowsfor the exclusive analysis of reaction channels.Prior to the actual physics production run with the sec-ondary pion beam, the calibration of the reconstructed mo-mentum was performed. The calibration was carried outwith a proton beam with six different known momenta withrespect to the central beam momentum of 2.68 GeV/c setby the accelerator. Figure 2 presents the seven momenta∗Central Beam Tracker for Pions† Supported by VH-Ng-330, TMFABI1012 and BmBf 05P12WOGHHreconstructed on the basis of the beam optics calculationand the four spatial coordinates. All seven different val-ues can be clearly distinguished and are in good agreementwith the reference values. Since not all the momenta focusin the first detector plane the resolution of the various re-constructed momenta differ. But all resolutions are belowthe envisaged value of 0.5%.Figure 2: Reconstructed momentum calibration performedwith six known momenta with respect to the central beammomentum of 2.68 GeV/c, set by the accelerator.The momentum distribution of the pion beam is muchbroader due to its secondary nature and only limited by thebeam line acceptance. The reconstructed spectrum of thepion momentum is shown in Fig.3. The maximal transmis-sion occurs at the central beam momentum of 1.7 GeV/cwith an asymmetric transmission for different momenta.Figure 3: Reconstructed momentum distribution of thesecondary pion beam at a central beam momentum of1.7 GeV/c.References[1] A.Brogna et al., Nucl. Instr. and Meth., A 568 (2006) 301.[2] M. Traxler et al., J. Instrum., 6(12) (2011) C12004.GSI SCIENTIFIC REPORT 2014 MU-NQM-HADES-17DOI:10.15120/GR-2015-1-MU-NQM-HADES-17 19

Tracking pions with CERBEROS at the HADES spectrometer

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Tracking pions with CERBEROS at the HADES spectrometer

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