CLAS12 Particle Identification
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Transcript of CLAS12 Particle Identification
CLAS12 Particle Identification
S. Stepanyan (JLAB)
Probing Strangeness in Hard Processes
INFN Frascati, October 18 – 21, 2010
Outline2
S. Stepanyan PSHP, INFN Frascati, October 18-21, 2010
– CLAS12: physics and instrumentation
– PID in forward detector (baseline design)• e/ separation
• neutral particle identification
• charge hadron identification
– Charge hadron identification in central detector (baseline design)
– Improvements to the baseline design• K/ separation in forward detector
• neutron detection in central detector
• low energy recoil detector
– CLAS12 trigger
– Summary
CLAS12 physics program
3D Structure of the Nucleon - the new Frontier in Hadron Physics
Nucleon GPDs and TMDs – exclusive and semi-inclusive processes with high precision
Precision measurements of structure functions and forward parton distributions at high xB
Elastic & Transition Form Factors at high momentum transfer
Hadronization and Color Transparency
Hadron Spectroscopy – heavy baryons, hybrid mesons, …
Already approved experiments correspond to about 5 years of running
2/25/09
S. Stepanyan PSHP, INFN Frascati, October 18-21, 2010
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Forward Central Detector Detector
Angular rangeTracks 50 – 400 350 – 1250
Photons 20 – 400 ---Resolutionp/p (%) < 1 @ 5 GeV/c < 5 @ 1.5 GeV/c(mr) < 1 < 10 - 20(mr) < 3 < 5 Photon detectionEnergy (MeV) >150 --- (mr) 4 @ 1 GeV ---Neutron detection
Neff < 0.7 (EC+PCAL) n.a.Particle ID
e/Full range ---p< 5 GeV/c < 1.25 GeV/c/K < 2.6 GeV/c < 0.65 GeV/c
K/pGeV/c < 1.0 GeV/cFull range ---
CLAS12 – Design ParametersForward Detector
Central Detector
S. Stepanyan PSHP, INFN Frascati, October 18-21, 2010
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L =1035cm−2s−1
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S. Stepanyan PSHP, INFN Frascati, October 18-21, 2010
Detectors used for PID
High Threshold Cherenkov Counter (HTCC) for e/ separation, cGeVPth /7.4
Low Threshold Cherenkov Counter (LTCC) for e/ separation, cGeVPth /7.2
Scintillator counters (fTOF) @ ~650cm from the target, time resolution of 80ps
Electromagnetic calorimeters (PCAL&EC), 54 layers of lead and scintillators, 22 r.l.
CLAS12, Sector mid-plane
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Scintillator counters (cTOF) @ 50 cm from the target, time resolution of 60ps
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LTCC & HTCC
S. Stepanyan PSHP, INFN Frascati, October 18-21, 2010
Working gas CO2 at 1 atm. Pion threshold P=4.9 GeV/c
Ellipsoidal mirror system
48 5’’ quartz window PMTs
Working gas C4F10 at 1 atm. Pion threshold P=2.7 GeV/c
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ECal (EC&PCAL)
Lead-scintillator sandwich with three stereo readout planes (UVW). Total of 22 r.l. thick, 54 layers (EC+PCAL) with longitudinal segmented 15+15+24
Transverse segmentation 4.5 cm in the first 15 layers and ~10cm in the last 39 layers. Light collection form one end of 5 to 420 cm long scintillator strips
U - plane
V - plane
W - plane
Inner PMTOuter PMT
Outer bundle
Inner bundle
LG
S. Stepanyan PSHP, INFN Frascati, October 18-21, 2010
PCAL light readout with wavelength shifting fibers embedded in the scintillaotr strips
EC light readout with clear optical fibers connected to one end of scintillaotr strips
S. Stepanyan PSHP, INFN Frascati, October 18-21, 2010
e/ separation LTCCxHTCCxEC for P < 2.7 GeV/c HTCCxEC (will be used in the trigger) for P < 4.9 GeV/c EC for P > 4.9 GeV/c (/e rejection better than few %)
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HTCC 3p.e.
HTCC 3p.e. and EC+PCAL > 0.4 GeV
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EEE 1.0
Electron detection with EC/PCAL
Added pre-shower calorimeter with 15 lead-scintillator layers will allow to retain good energy resolution for up to 11 GeV/c
ECAL for e/ separation for P > 4.9 GeV/c: cuts on the energy detected in PCAL and Inner part of EC, a cut on the total energy in ECAL
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Cut on total energy in ECAL (GeV)
EC only
EC+PCAL
S. Stepanyan PSHP, INFN Frascati, October 18-21, 2010
S. Stepanyan PSHP, INFN Frascati, October 18-21, 2010
Neutron, , and 0 detection in PCAL+EC
Two cluster reconstruction from high energy 0 decays
Neutron detection efficiency
Neutron momentum (GeV/c)
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For neutron identification and momentum measurements, time-of-flight from the target to EC planes will be used. With time resolution of ~0.3 – 0.4 ns neutrons with P<3 GeV/c can be identified
4.5 cm transverse segmentation
10 cm transverse segmentation
S. Stepanyan PSHP, INFN Frascati, October 18-21, 2010
Forward TOF systemExisting TOF, Panel 1a and 2a, time resolution t=150ps-180ps
New TOF plane, Panel 1b, time resolution t=80ps
CLAS/e2 – 12C run
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58 counters in each sector, 6x6 cm2 scintillator bars with lengths from 32 to 375 cm
S. Stepanyan PSHP, INFN Frascati, October 18-21, 2010
Charged hadron ID with fTOF
In some limited cases, where exclusivity of the reaction can be used to aid kaon ID, LTCC can be used to veto charged pions with P>2.7 GeV/c.
t – time-of-flight difference
between different particles
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There is a gap in /K separation in forward detector for momenta above ~2.5 GeV/c.
Forward TOF at L~650 cm with t~80ps will allow clean (4-5) separation for /K with P< 2.6 GeV/c K/p with P<4 GeV /p with P<5 GeV/c
S. Stepanyan PSHP, INFN Frascati, October 18-21, 2010
Charged hadron ID in central detector
Silicon TrackerScintillator Counters, t=60ps
5T SC Solenoid Magnet
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K-
p-K
, =0.06 ns
Momentum measurements in the solenoid field using silicon tracker and time-of-flight measurements with 60 ps time resolution in central TOF counters will provide /K and K/p separation for momenta up to 0.7 GeV/c and 1.2 GeV/c, respectively. Should be sufficient for the main physics program.
CLAS12
cGeVPth /9.4
cGeVPth /7.2
Low Threshold Cherenkov Counters (LTCC)
High Threshold Cherenkov Counter (HTCC)
Electromagnetic calorimeters
CLAS12 Torus
Drift Chambers
Forward TOF Counters
CLAS12 Solenoid
S. Stepanyan PSHP, INFN Frascati, October 18-21, 2010
Large acceptance detector with excellent vertex reconstruction and good PID, capable of running with high energy electron beams on variety of targets - cryogenic, gausses, solid, polarized - at luminosity of ~1035 cm-2 s-1
Suitable for exclusive reactions with multi-particle final states
Forward TOF Counters
Si-tracker
There is always room for improvement!
/p
/KK/p
P, GeV/c3 4 5
detection in LTCCdetection in LTCC
fTOF
Charge kaons in FD
S. Stepanyan PSHP, INFN Frascati, October 18-21, 2010
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at Pp = 4.5GeV /c, − t ≈ 8(GeV /c)2
K/p separation > 4 - 5 GeV/c should not be a problem, production of energetic nucleons is highly suppressed -
The biggest problem is charged kaon identification above ~2.5 GeV/c.
Cherenkov counters will not help, small inefficiencies for pions will cause big problems with kaon spectrum contamination.
RICH with a radiator of n≈1.03 will be the ideal choice to carry over charged hadron PID above limits of CLAS12 fTOF.
S. Stepanyan PSHP, INFN Frascati, October 18-21, 2010
Neutron detection in CD Deeply exclusive reactions on neutron, e.g. DVCS on neutron - gives access to GPD E, the least known and least constrained GPD that appears in Ji’s sum rule
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80% of neutrons recoil at θlab > 40°, in momentum range 0.2 to 1.2 GeV/c
Spectator tagging method is luminosity limited (few x1033 to 1034 cm-2 sec-1)
Direct detection of neutrons in CD will fully utilize high luminosity of CLAS12
Central neutron detector – ~10 cm thick scintillator in the space between
CTOF and solenoid inner cryostat Neutron identification and momentum
measurement using TOF Expected momentum resolution dp/p~5%,
expected efficiency ~10-15%
S. Stepanyan PSHP, INFN Frascati, October 18-21, 2010
Low energy recoil detector
Physics motivation: Neutron structure function – spectator tagging Nuclear DVCS – recoil (light) nuclei tagging Meson spectroscopy in coherent production on light nuclei
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Thin wall, e.g 30m kapton, high pressure (6-7 atm) gas targets
Lightweight target-tracking detector system will substitute dense target and central silicon tracker in the solenoid
RTPC based on cylindrical GEMs work well for 3 experiments with CLAS
Tracking detector
S. Stepanyan PSHP, INFN Frascati, October 18-21, 2010
Very forward electron detection (LowQ) Electroproduction at very small values of Q2 is equivalent to photoproduction
using partially linearly polarized photons Forward angle electron detector together with CLAS12 will be excellent place
for baryon (e.g., and ) and meson spectroscopy. Part of the program can be run in parallel with electron running
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TorusHTCC
R1 DC
ECal
Target Moller absorber
Silicon tracker
Variable Range Resolution
E’ 0.5 GeV to 4 GeV
2
1.8o to 5.2o
Q2 0.01 to 0.2 GeV2
mrad8mrad1
3.0%5.1
EE
Detector system: tracker (can be combined with CLAS12 forward vertex tracker), calorimeter, fast scintilation detector
Trigger logic with fast clustering is necessary to reject high energy showers (>7 GeV) from elastic and Moller electrons
S. Stepanyan PSHP, INFN Frascati, October 18-21, 2010
CLAS12 trigger CLAS12 will have free running DAQ system. ADCs and TDCs will collect data in
pipeline mode. Readout of data will be performed after trigger decision is made. Expected event readout rate ~10kHz. Inclusive electron rate at 1035 cm-2 s-1 is ~3kHz.
Available fast FPGA with flash-ADCs will allow to employ a multi layer trigger system in order to find clusters in ECal, reconstruct tracks in drift chambers and identify segments in Cherenkov counters and TOF counters
Trigger decision will be made after matching clusters, hits and tracks. The goal is: a) Achieve good electron selectivity using cluster energy cuts in ECal, momentum from
fast tracking, and hits in HTCC (+LTCC). Singles rates will be high, it is important to suppress accidentals. [CLAS Level 1 trigger for electrons is based on the total energy cut in EC and sector based ECxLTCC coincidence and only 7% of triggered events have electron at high energy runs]
b) Alow additional (multi-prong) triggers from photoproduction process –n tagged quasi-real photoproduction with LowQ setup n Qusi-real photoproduction of events when electron scattered at ~0 degree
[Some photoproduction reactions were successfully analyzed from CLAS high energy electroproduction data]
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S. Stepanyan PSHP, INFN Frascati, October 18-21, 2010
Summary
In the baseline design, CLAS12 particle identification system includes gaseous threshold Cherenkov counters, scintillator counters for time-of-flight measurements, and electromagnetic calorimeters
Despite excellent design characteristics of each element, requirements of some class of experiments cannot be fulfilled with the baseline system
Important improvements to CLAS12 detector system for already proposed/approved physics program are: neutron detection in CD very forward electron detection low-energy spectator/recoil detection charged kaon identification in forward detector at momenta >2.7 GeV/c
Hopefully, this workshop will bring us one big step closer to build RICH detectors for CLAS12
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