Transcript Document
CsI/GEM-based RICH for SoLID
A RICH Technology Alternative.
Thomas K Hemmick
Stony Brook University, RHIG
1 SoLID Collaboration Meeting 2/3/2012
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Physics Drivers
statistical error bar σ A /A (%) shown at center of bins in Q 2 , x
standard model test charge symmetry violation
4 months at 11 GeV
higher twist sea quarks
C s
2 months at 6.6 GeV p /e is few hundred or less eID assisted by calorimeter, typical req. on RICH.
Total error ~0.5% in each x,Q 2
Physics
PVDIS SIDIS
Contami nation
1-2% <1% bin via 0.3% stats:
Precision
0.1% 1% Require high efficiency or “bright” RICH.
SoLID Collaboration Meeting 6/14/2012
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SoLID RICHes:
PVDIS SoLID Solenoidal Large Intensity Two varaints: Device.
SIDIS PVDIS– e threshold device (light RICH) SIDIS– e/ p threshold device (heavy RICH).
Concern principally centers on several issues: Strength & orientation of B at photo-sensor.
Backgrounds producing false hits (c.p. in window) CsI photocathode GEM (ala PHENIX HBD) Windowless promises less (or different) background.
Inexpensive.
Aggressively being developed for other contexts: EIC Ring-Imaging Development ( p ,K,p @ 80 GeV/c) Medical Imaging (Breskin et. al.) SoLID Collaboration Meeting 2/3/2012
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EIC R&D
BNL Administers the program for generic research into detector technologies for EIC.
Multiple applications consider CsI photo cathode readout: Central barrel proximity-focus using C 6 F 14 liquid.
End cap ring-imaging for p ,K,p @ 80 GeV/c TPC/HBD for tracking, dE/dx, eID.
SoLID bootstraps from these developments:
UVa funded for GEM planar tracking R&D. SBU funded for End Cap RICH & Mirror development.
Other opportunities available for collaboration (e.g. heavy gas forward RICH).
SoLID Collaboration Meeting 6/14/2012
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Reverse Bias (HBD)
HV g
photo electron e primary ionization
HBD Principle
Forward Bias
HV
primary ionization charged particle or photon Readout Pads Readout Pads • BRIGHT! ~20 photo-electrons in 50 cm of gas: • Principle source of photons at LOW WAVELENGTH!
• dN/d l ~ 1/ l 2 • QE falls linearly as l increases.
• Single electron gain ~10 4 (a bit limited by the CsI).
• You can see a blob…single p.e. difficult.
• More GEMs = higher gain…BUT there is a cost in hadron blindness.
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Hadron Blindness:
Hadron “Near-Sighted” • At slightly negative E d , photoelectron detection efficiency is preserved whereas charge collection is largely suppressed.
• Background #1: Charge collected from ~150μ layer above GEM.
• Background #2: Charge deposit in lower layers.
• With n GEMs, hadron gain reduced from G n to G n-1 • Background #3: Scintillation (CF 4 • Necessary program scintillates at 160 nm).
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Applications
Au+Au PHENIX HBD (2 yrs): Windowless, 50 cm, unfocussed.
22 p.e. per blob, N 0 =322 (!) EIC & sPHENIX: Develop CsI technology to measure rings.
Mirror technology (reflectivity at low l ).
Precision position measurement via charge division.
REQUIRES MUCH HIGHER GAIN!
SoLID (light cherenkov only) Threshold detector using mirror (background issues) Less sensitive to neutron and low-E gammas.
SoLID Collaboration Meeting 2/3/2012
SiPM PMT 10
Caveats!
HBD Single photon response varies w/ technology.
Affects efficiency & background rejection.
Gas Avalanche requires more light!
Pulse height Distribution PMT
.
PMT HBD photoelectrons
SiPM PMT 11
Caveats 2
HBD Background rates also as
HBD better rejection with background above cut.
Pulse height Distribution
PMT HBD Efficiency vs
.
PMT HBD photoelectrons
• • • • • • • Hall A Background Studies High purity recirculating gas • ~1 ppm H 2 O & O 2 CAMAC DAQ LeCroy High Voltage GEM detector o Divider box allows for 'on the fly' stack size changes • Neutron Counters BF 3 10 B + n 7 Li + 4 He o o Bare counter (slow) Wax counter (slow & fast) Scintillators SoLID Collaboration Meeting 2/3/2012
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Neutron Data
60 Hz • Bare Neutron Counter shows few, if any, counts while beam is on target. Some runs show rates of ~0.6 Hz.
• Average rate for Fast (plus Slow) neutrons ~35 Hz.
• Counter sensitivity: 1.9 cps per 1 thermal neutron/cm 2 • Typical background = 18 thermal neutron/cm 2 inside wax
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GEM Detector
EIC (rings) Solid (threshold) Not Blind Blind • • • Legend: Blue = +40 V Teal = +20 V Pink = 0 V Green = -20 V Red = -40 V As the stack has few GEMs, you are able to achieve a better hadron blindness.
This is because ionization can occur in the gap between the first and second GEM.
For fewer GEMs we were unable to get small signals above the hardware threshold. SoLID Collaboration Meeting 2/3/2012
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MIPs
Solid (threshold) Not Blind Not Blind – Blind = MIP Blind • • • • When the difference is taken between the forward • most and reverse-most bias, one should see MIPs.
Best for fewer GEMs via the G n-1 principle.
Normally we expect ~15 p.e. for 1.5mm of CF 4 .
Here tracks are inclined ~17 o above horizontal.
15/sin(17) ~ 50….SWEET!
SoLID Collaboration Meeting 2/3/2012
Threshold Rates
16 Single Pad Scale by photon/total Neighbor Coincidence Reverse Bias always better.
3-GEM stack always better.
Rate 0.07-0.08 Hz/nA with 2 p.e. threshold.
Requiring neighbor coincidence 10X better: 0.008 Hz/nA with 2 p.e. threshold.
SoLID Collaboration Meeting 2/3/2012
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EIC HBD
“Beam” consists of scattered electrons & pions.
Particles must be
collimated
.
Remote table position control.
eID via “TCAL” (PreShower & Shower).
SoLID Collaboration Meeting 2/3/2012
Pad Plane
10x10 cm 2 Pad Plane for Ring Imaging ala FGT SoLID would use 4 pads in this area (1/4 ring – quad coincidence).
5 GEMs for high gain SoLID would use 3 GEMs.
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Optics
Optics defined by GEM size (R ring < 5 cm).
Rad-length for SoLID perfect fit for optics!
Should see 20 p.e. or more.
Better than 0.1 ppm O 2 & H 2 O Mirror @ 80% by manufacturer spec.
Gain above 70000.
SoLID Collaboration Meeting 2/3/2012
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eID works
e p p Local beam dump and other obstacles forced detector to beyond 35 degrees.
During beam tuning, saw nicely separated electron band.
Band disappeared after beam stopped scraping.
Took only a few million triggers: Two PC deaths; One HV mainframe death; SoLID Collaboration Meeting 6/14/2012
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Rare Signals
Most triggers are false coincidence.
44/80000 events have a collimated track.
A few of those show an HBD hit in reverse bias.
No electrons yet spotted… SoLID Collaboration Meeting 6/14/2012
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Funded R&D
Interference Maximum Second Beam Test (FNAL likely).
Ordinary MgF 2 cutoff l <140nm.
Overcoat thickness = thin film reflection max!
Develop in house evaporation.
8’ diameter vessel SoLID Collaboration Meeting 2/3/2012
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Summary
SoLID benefits from EIC-funded R&D efforts where applicable with small changes: U.Va funded for planar GEM tracker work.
SBU funded for CsI-RICH && high quality mirrors.
Other opportunities… CsI photo-cathodes are an interesting alternative to PMT readouts and may offer: Reduced cost Reduced background sensitivity.