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Status of P rojectile S pectator D etector A.Ivashkin INR , Moscow

I. Introduction to PSD. II. Motivations for PSD use in CBM III. Design and readout. IV. Results of beam test of PSD prototype. V. Summary. Status of P rojectile S pectator D etector A.Ivashkin INR , Moscow. PSD in CBM setup.

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Status of P rojectile S pectator D etector A.Ivashkin INR , Moscow

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  1. I.Introduction to PSD. II. Motivations for PSD use in CBM III. Design and readout. IV. Results of beam test of PSD prototype. V. Summary. Status of Projectile Spectator DetectorA.IvashkinINR , Moscow

  2. PSD in CBM setup. Very Forward Hadron Calorimeter for detection of projectile spectators PSD Projectile Spectators are non-interacting nucleon in beam ions. Experimental tasks: 1. Measurement of centrality: b~ A - Nspect ; 2. Measurement of event-by-event fluctuations; 3. Reconstruction of the reaction plane; 4. Monitor of beam intensity by detecting the neutrons from electromagnetic dissociation .

  3. Beam hole X PSD geometry. spectator spots at Z=15m Eau=15 AGeV Z Transverse sizes ~1x1 m2; Distance from target - 15 m; Number of modules – 107; Module dimensions – 10x10x1600 cm2

  4. 1. Measurement of centrality Impact parameter: b~Np, Npis number of interacting (participant) nucleons. Np=A - Nspect=A - Es/EA, Esis sum of spectator energies, measured by Zero Degree Calorimeter (ZDC) or by PSD; EAis beam energy. This technique is used in most heavy ion experiments at CERN (WA80, NA49, NA50, ALICE…) and RHIC.

  5. Afew methods of centrality measurement must be used to get the proper event selection Correlation between Ezdc and ET in NA50 experiment at CERN. (Pb+Pb at 158 AGeV)

  6. 2. Event-by-event fluctuations Total multiplicity :Ns- number of sources, mi- multiplicity from a single source. Geometry of collision physics! QGP? Second component is not interesting and must be removed Number of interacting nucleons must be known

  7. Reconstruction from centers of modules MC simulation Reconstructed angle of reaction plane, deg. 3. Reconstruction of Reaction Plane → →M rk rk – position vector Q = ∑ ----- , of the particle k k=1 → in perpendicular │rk│ to the beam axis plane M – particles in the event used for reconstruction Input UrQMD:reaction plane at 00 Good accuracy is due to fine transverse PSD granulation. To be improved by taking deposited energy weights.

  8. Design and readout Modular Lead/Scintillator sandwich compensating calorimeter. Sampling ratio Pb:Scint=4:1. Expectation:For thickness δPb=16 mm and δScint=4 mm σE/E ~ 50%/√E . Conception Light readout withWLS-fibersfor reliable and uniform light collection. Signal readout with Micropixel APD (MAPD) to avoid nuclear counter effect, detection of a few photons signal, compactness, low cost. Longitudinal segmentation – for permanent calibration of scintillators in radiation hard conditions, rejection of secondary particles. Modular design – transverse uniformity of resolution, good reconstruction of reaction plane, flexible geometry, simplicity.

  9. Structure of PSD module. MAPDs and amplifiers. • 60 lead/scintillator sandwiches. • 10 longitudinal sections. • 6 WLS-fiber/MAPD. • 10 MAPDs/module. • 10 Amplifiers with gain~40.

  10. Photodetectors in PSD are MAPDs, Micropixel Avalanche Photodiodes working in Geiger mode • deep micro-well type; • avalanche cells done by ion implantation; • number of pixels might achieve ~105/mm2. Initially developed by Z. Sadygov at Dubna. Now produced by Zecotek.com at Singapore. Active area: - 3x3 mm2. Number of pixels: - 15000/mm2. Photon detection efficiency: ~ 20%. Gain: ~ 5x104. Single electron noise: ~ 1 MHz/mm2. Working voltage: ~ 66.5 V.Dark current: ~ 50 nA Properties of MAPD3-A type used in PSD prototype

  11. pixels Pixel density is crucial for the calorimetry! Linearity of MAPD response. analytical formula (σ2 ~ Nph.el. in linear case ) Dependence of signal width (σ2) on signal amplitude Nph.el. (both in photoelectrons). 1.5 month long-term stability test. Irradiation with LED pulses: 1 MHz, 104 ph.e./pulse 10 MAPDs in test

  12. Perspectives of MAPDs (general comments) • MAPD is promising photodetector for large highly segmented • detectors with number of readout channels > 103. • The cost of one piece < $100. • Current Photon Detection Efficiency (PDE) of 20% might be • improved a few times. • Larger size – 5x5 mm2 are expected soon. • Fast MAPDs with ~1-2 ns rise time are expected soon. • MAPD application for very granular TOF systems is promising. • At present sTOF~100 ps is achievable for 20x20x20 mm3 plastic • scintillator. Might be significantly improved for fast samples.

  13. UrQMD+CBMRoot: ~5 MRad/(12 months of CBM run) Magnet ON. Proton and neutron spots are separated. Radiation doses for PSD. ~2 times scintillator light yield drop. No changes in uniformity and resolution. beam Neutron flux affects MAPDs. Recent tests at PSI: at flux ~1013 n/cm2 MAPD gain dropped ~2 times, dark current ~10 mA. But it works. Must be compared with Fluka simulation.

  14. In 2007 first nine PSD modules were assembled at INR for the beam test at CERN. assembling transportation readout part at beam

  15. Calibration of modules by 75 GeV muon beam (response of each section in module) l.y~2ph.e/MeV. Nice MAPD sensitivity to a few photons signal. Deposited spectra of pion energies in PSD prototype:simulationand experiment

  16. muons hadrons positrons Performance of calorimeter. Energy spectrum in first section of module for mixed 30 GeV beam of pions, positrons and muons. PID and rejection of secondary particles are possible. • The constant term in energy resolution is essential only for energy measurement of single particle. • It is not very important in case of measurement of total energy from many particles with the same energy. • The reason is dependence of energy resolution for N spectators as:

  17. Summary. • R&D on PSD calorimeter is going on. • The structure of PSD modules is well established now. • The readout of the modules is done by novel photodetectors, MAPDs. • These photodetectors are intensively developed as a good alternative of traditional PMTs. • Test of first PSD prototype confirmed the expected performance. • The energy resolution for hadrons ~54%/sqrt(E) was obtained. Depending on energy deposition in longitudinal sections the electrons, muons and hadron identification is possible. • The test of larger size prototype of 5x5 modules is planed. • Further R&D on PSD readout will be continued.

  18. Thank you!

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