crystal detector r&d proposal for soft photon measurement in star university of california at...
Post on 19-Dec-2015
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Crystal Detector R&D proposalfor Soft Photon Measurement in STAR
University of California at Los Angeles Joint Institute for Nuclear Research
Institute of Modern Physics at Lanzhou
Presented by Gang Wang (UCLA)
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Soft photons: 20 - 1000 MeV
• Physics motivations : New physics domain exploration Radiative decays of particles EM radiation from bulk medium
• Experimental opportunities : TPC +TOF +HFT +Crystal Detector
= unique combination, new particle measurement capability
Larger photon cross-section allows smaller acceptance
See next page for details…
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Physics motivations• Pre-equilibrium and thermal photons
Pre-equilibrium stage of the heavy ion collision and its evolution decidedly unexplored.
Thermal photon radiation from the QGP and HRG phases
• Radioactive decays of particles 0+ cJ/ +
J/ from feed-down decays
• EM radiation from bulk medium quark jets traversing the QCD color medium
high pT charged hadron – soft photon back-to-back correlation -> properties of the dense partonic matter
high angular momentum of bulk quark matter dipole radiation
Synchrontron radiation from possible formation of longitudeinal E/B fields
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Experiment: direct photons at WA98Direct Photon Production in 158 A GeV 208Pb+208Pb Collisions
Range:
0.5 < pT < 3.5 GeV/c
Yield of the direct photons at low pT extracted from the strength of the two-photon correlation.(See efforts by the Yale Group)
Low-Low-ppTT range [0.02, 1.0] GeV/ range [0.02, 1.0] GeV/cc is not accessible is not accessible
WA98, Phys. Rev. Lett. 93 (022301), 2004
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Experiment: direct photons at PHENIX
Probing the QCD equation of state with thermal photons in nucleus-nucleus collisions at RHICDavid d’Enterria and Dimitri Peressounko, nucl-th/0503054
Range: 1.0 < pT < 10.0 GeV/cDirect photon spectra obtained with the statistical subtraction method
Low-Low-ppTT range [0.02, 1.0] GeV/ range [0.02, 1.0] GeV/cc is not accessible is not accessible
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Soft photon measurement
Can not be measured by PHENIX, ALICE and STAR with present detectors
Predicted yield is large and even with a small crystal patch measurements seem to be possible at STAR in near future
How well (for how much) we can do that ? Needed R&D in FY07 to find out
ppTT coverage : from 20 to 1000 MeVcoverage : from 20 to 1000 MeV
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Crystals
Inorganic crystals is the only practical option for STAR,CsI(Tl) from IMP is the one we propose to investigate.
Crystal NaI(Tl)
CsI(Tl) BGO PbWO4
Density (g/㎝ 3) 3.67 4.51 7.13 8.28
Radiation length (㎝ ) 2.59 1.85 1.12 0.89
Molière radius (cm) 4.8 3.8 2.3 2.0
DE/dx (Mev/cm)(per mip) 4.8 5.6 9.2 13.0
Nucl. Int. length (㎝ ) 41.4 37 21.8 18
Refractive index (480 nm) 1.85 1.79 2.15 2.16
Peak emission λ (nm) 410 560 480 420-560
Relative light output 100 45(PMT)/140(PD)
15 0.01
Light yield temp.coef. (%/0C)
~0 0.3 -1.6 -1.9
Decay time (ns) 230 1000 300 10-50
Hygroscopic strong slight no no
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Monte-Carlo simulations
Crystal calorimeter:
Three projective “super-cubes” 9x20
Total 540 crystals in x 0.66x6o
Crystals: 2.54 cm x 2.54 cm x 25 cm
Crystal Detector is implemented within STARSIM framework. It is located in place of BEMC module 88 and TOF tray 88.
Crystal PatchCrystal Patch
Super-cube : 9x20 crystalsSuper-cube : 9x20 crystals
Crystal PatchCrystal Patch
STAR EAST VIEWSTAR EAST VIEW
Interaction pointInteraction point
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Crystal Detector: sample MC events
Hijing central Au +Au event: clean, two photons
Hijing central Au +Au event: hadronic background example
photonsphotons
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Occupancy and Energy Deposition
Occupancy data indicates that even in central Au +Au events it is possible to identify soft photons cleanly!
Background sources which contribute to detector occupancy : charged tracks and albedo from BEMC modules.
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Photon rates for low-pT region
Preliminary estimations show that we will need ~1M central events for ~3% error in yield measurements (low-pT region for all centrality bins)
Preliminary photon count rates for 0.02 < pT < 0.20 GeV are calculated using fully reconstructed Hijing events (starsim + BFC). Cluster finder algorithm efficiency is not included yet, charged hadron background removal is considered to be 100% efficient at this moment.
Small acceptance is compensated by large photon yield!
Expected energy resolution 5-10%, depends on cluster size: 3x3, 4x4 crystals and photo detector cutoffs.
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FY07, R&D Goals: MC simulationsComplete understanding of the efficiency and purity of
reconstructed soft photons in the Crystal Detector :• Various cluster finder algorithms investigation• Robust procedure for removal of non-photonic backgrounds
• Possible hardware veto layer for charged tracks?• Shower shape analysis possibilities and isolation cuts• Extended BEMC albedo studies
• Shielding, isolation cuts?Required dataset for detailed analysis :
• 50k fully reconstructed AuAu200 central events (Hijing) with most probable geometry settings (help from S&C group)
• Disk space is the most important issue here• Disk space required for studies is ~0.5 Tb
Various performance issues :• Pileup, leakages, optimizations etc…
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FY07, R&D Goals: Hardware Define crystal detector element.
• crystal, wrapping, coupling with Photo Detector, Photo-detector, readout• lots of things known from literature – need first hand experience.
Optimize light yield/uniformity. Investigate possibility of using TPC DAQ1000
• PSA/Altro chips for readout of PD. (Counting on help from Tonko)
Make preliminary design of a mechanical support structure and investigate integration into the STAR detector. (help from STSG)
Understand radiation conditions, required rad. hardness tests and monitoring scheme for crystals.
By the end of FY07 we want to define cost/schedule.
Requests:1. Acquire crystals from IMP. (in progress)2. Acquire PD from Hamamatsu.3. Acquire/Borrow radioactive sources 4. Set up a testing lab at BNL
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SummaryVery first and preliminary results look optimistic. More detailed R&D work is needed in FY07 and
we hope to reach a firm decision on feasibility of the soft photon physics with crystals in STAR
We need more collaborators!
Thanks to STAR Software team for their help!
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Backup slides
• Energy resolution: require a lot of explanation
• graph 3x3 20-200 MeV band (10% to as low as 3%?)
• Shower shape in crystals
3x3 – central fraction, leak from sides
put here light yield per MeV, realistic cutoff
How crystal patch can be compared with conversion on gas of TPC?