Prototype Tests and Construction of the Hadron Blind Detector for the PHENIX Experiment at RHIC Craig Woody Brookhaven National Lab For the PHENIX Collaboration

Prototype Tests and Construction of the Hadron Blind

Detector for the PHENIX Experiment at RHIC

Prototype Tests and Construction of the Hadron Blind

Detector for the PHENIX Experiment at RHIC

Craig WoodyBrookhaven National Lab

For the PHENIX Collaboration

N41-5

2006 IEEE Nuclear Science Symposium and Medical Imaging ConferenceSan Diego, CA

November 2, 2006

C.Woody, NSS-N41-5, November 2, 2006 2

HBD TeamHBD Team

Weizmann Institute of Science• A.Dubey, Z. Fraenkel, A. Kozlov, M. Naglis, I. Ravinovich, D.Sharma, L.Shekhtman, I.Tserruya*

Stony Brook University• W.Anderson, A. Drees, M. Durham, T.Hemmick,

R.Hutter, B.Jacak, J.Kamin

Brookhaven National Lab• B.Azmoun, A.Milov, R.Pisani, T.Sakaguchi, A.Sickles, S.Stoll, C.Woody (Physics)• J.Harder, P.O’Connor, V.Radeka, B.Yu

(Instrumentation Division)

Columbia University (Nevis Labs)• C-Y. Chi

* Project Leader


Motivation - Measurement of Low Mass Electron Pairs in Relativistic Heavy Ion Collisions

Motivation - Measurement of Low Mass Electron Pairs in Relativistic Heavy Ion Collisions

Low mass dilepton pairs are unique probes for studying chiral symmetry restoration in dense nuclear matter

Chiral symmetry is the symmetry between light quark flavors, which is normally broken due to the finite value of the constituent quark masses. At high temperatures and/or high baryon densities,

this symmetry may be at least partially restored

Effects of chiral symmetry restoration manifest themselves in terms of in-medium modifications of the line shapes of low mass vector mesons (e.g., mass shifts, spectral broadening)

• ρ (m = 770MeV t ~ 1.3 fm/c) e+e-

• ω (m = 782MeV t ~ 20fm/c) e+e-

• φ (m =1020MeV t ~ 40fm/c) e+e-

R. Rapp nucl-th/0204003

e-e+


Experimental Challenges at RHIC Experimental Challenges at RHIC

Large combinatorial pair background due to copiously produced photon conversions and Dalitz decays

Need rejection factor > 90% of e+ e - and e+ e -

e+ e -

e+ e -

S/B ~ 1/500

“combinatorial pairs”

total background

Irreducible charm background

all signal

charm signal

Would like to improve S/B by ~ 100-200

e+e- Pair Spectrum in PHENIIX


The Hadron Blind DetectorThe Hadron Blind Detector

Cherenkov blobs

e+

e-

pair opening angle

~ 1 m

Radiator gas = Working gasGas volume filled with pure CF4 radiator

(nCF4=1.000620, LRADIATOR = 50 cm)

Proximity Focused Windowless Cherenkov Detector

Electrons produce Cherenkov light, but hadrons with P < 4

GeV/c do not

Radiating tracks form “blobs” on an image plane

(max = cos-1(1/n)~36 mrad Blob diameter ~ 3.6 cm)

Tracks pass through the HBD in an essentially zero field region in PHENIX

Electron pairs do not open up

Dalitz pairs & conversions maketwo blobs, single electrons make one


The Hardon Blind ConceptThe Hardon Blind Concept

• Primary ionization is drifted away from GEM and collected by a mesh

• UV photons produce photoelectrons on a CsI photocathode and are collected in the holes of the top GEM

• Triple GEM stack provides gain ~ 104

• Amplified signal is collected on pads and read out

Mesh

CsI layer

Triple GEM

Readout Pads

e-Primary ionizationg

HVPrimary ionization signal is

greatly suppressed at slightly negative drift field while photoelectron collection

efficiency is mostly preserved

Test with UV photons and a particles

Z.Frankel et.el., NIM A546 (2005) 466-480.A.Kozolov et.al. NIM A523 (2004) 345-354.


Detector ConstructionDetector Construction

24 Triple GEM Detectors (12 modules per side)

Area = 23 x 27 cm2

• Mesh electrode• Top gold plated GEM for CsI• Two standard GEMS• Kapton foil readout plane One continuous sheet per side Hexagonal pads (a = 15.6 mm)

Honeycomb panels

Mylar entrance window

HV panel

Pad readout plane

HV panel Triple GEM module with mesh grid

Very low mass (< 3% X0 including gas)

Detector designed and built at the Weizmann Institute


GEM PerformanceGEM Performance

• All GEMs produced at CERN• 133 produced (85 standard, 48 Au plated)• 65 standard, 37 Au plated passed all tests• 48 standard, 24 Au plated installed • The three GEMs in each stack are matched to minimize gain variation over the entire detector

• All GEMs pumped for many hours under high vacuum (~ 10-6 Torr) prior to installation

• Gain of each module was mapped for all sectors

• Resulting gain variation is between 5-20 %

20%

5%


Gain Stability of GEMsGain Stability of GEMs• During gain mapping, a single pad is irradiated with a 8 KHz 55Fe source for ~ 20 min. Then all other pads are measured, and the source is returned to the starting pad.

• Gain is observed to initially rise and then reach a plateau. Rise can be ~ few % to almost a factor of 2.

• Gain increase is somewhat rate dependent (10-30%)

Not a fundamental problem in PHENIX• GEMs will reach operating plateau in a few hours• Rates are low

1.5 Initial Rise

Effect seen in other GEMsSee talk by B.Azmoun, Workshop on Micropattern Gas Detectors, 10/29

Secondary rise


Photocathode Production and Detector AssemblyPhotocathode Production and Detector Assembly

“Clean Tent” at Stony Brook

CsI Evaporator and quantum

efficiency measurement

Large glove boxO2 < 5 ppm

H2O < 10 ppm

Laminar Flow Hood

High Vacuum

GEMStorage

Container

Class 10-100 ( N < 0.5 mm particles/m3)


Evaporator and QE MeasurementEvaporator and QE MeasurementComplete CsI evaporation station was given on

loan to Stony Brook from INFN/ISS Rome (Thank you Franco Garibaldi !)

Produces 4 photocathodes per evaporation• Deposit 2400 – 4500 Å CsI @ 2 nm /sec• Vacuum ~ 10-7 Torr• Contaminants measured with RGA

• Measures photocathode quantum efficiency in situ from 165-200 nm over entire area

• Photocathodes transported to glove box without exposure to air

Virtually no water !

Small “chicklets” evaporated at

same time for full QE measurement

(120-200 nm)


Photocathode QualityPhotocathode Quality

Large bandwidth of CF4 (6-11.5 eV), windowless construction and high QE of CsI in deep VUV gives very large

N0 (840 cm-1)

Expect ~ 36 p.e. per blob

Photocathodes are produced with consistently good quantum

efficiencies

Need to monitor photocathode performance over the lifetime of the experimentNumber of photoelectrons

36 72

Gives good separation between single and double

electrons

Flat position dependence

27 cm


Construction of the Actual DetectorConstruction of the Actual Detector

All twelve modules installed in HBD West


Gas Transmission MonitorGas Transmission Monitor

Oxygen and water must be kept at the few ppm level to avoid absorption in the gas

Heaters are installed on each detector to drive out water from GEMs and

sides of detector vessel

Lamp Monitor Gas Cell Monitor

Measure photocathode current of CsI PMTs

D2 lamp

Scanning Monochrometer (120-200 nm)

Movable mirror

Turbopump

Transmittance in 36cm of Ar Vs PPM's of H2O

0

10

20

30

40

50

60

70

80

90

100

110

1100 1200 1300 1400 1500 1600 1700 1800 1900 2000

Wavelength [Angstroms]

% T

rans

mitt

ance

[%] ~10ppm H2O

~40ppm H2O

~200ppm H2O


Test of a Full Scale Prototype Detector in PHENIXTest of a Full Scale Prototype Detector in PHENIX

electronshadrons

Cluster Size

Tested in PHENIX with p-p collisions at RHIC April-June ‘06

• Full scale detector with one GEM module • 68 readout channels• Full readout chain• Operated with full pure CF4 gas system

electronshadrons

Pulse height

Forward BiasReverse Bias

Landau fit

MIP

Reverse Bias, B=0

Hadron rejection ~ 85% at e ~ 90 %


Both Halves of the HBD Installed in PHENIXBoth Halves of the HBD Installed in PHENIX

HBD West (front side)Installed 9/4/06

HBD East (back side)Installed 10/19/06


SummarySummary

The HBD will provide a unique capability for PHENIX to measure low mass electron pairs in heavy ion collisions at RHIC This detector incorporates several new technologies (GEMs, CsI photocathodes, operation in pure CF4 with a windowless design) to achieve unprecedented performance in photon detection (N0 ~ 840 cm-1)

The operating requirements are very demanding in terms of leak tightness and gas purity, but we feel they can be achieved Tests with the full scale prototype were very encouraging and demonstrated the hadron blindness properties of the detector. The final detector is now installed in PHENIX and ready for commissioning and data taking during the upcoming run at RHIC


Backup SlidesBackup Slides


Present PHENIX Capabilities Present PHENIX Capabilities

~12 m

e+

e+

e-e-


HBD Detector ParametersHBD Detector Parameters

Acceptance nominal location (r=5cm) || ≤0.45, =135o

retracted location (r=22 cm) || ≤0.36, =110o

GEM size (,z) 23 x 27 cm2

Number of detector modules per arm 12Frame 5 mm wide, 0.3mm crossHexagonal pad size a = 15.6 mmNumber of pads per arm 1152Dead area within central arm acceptance 6%Radiation length within central arm acceptance box: 0.92%, gas: 0.54%Weight per arm (including accessories) <10 kg


Readout ElectronicsReadout Electronics

Preamp (BNL IO-1195)2304 channels total

19 mm

15 mmDifferential

output

Noise on the bench looks very goodGaussian w/o long tails

3s cut < 1% hit probability


Run Plan for the HBD at RHICRun Plan for the HBD at RHIC Run 7 (Dec ‘06 – June ’07)

• ~ 4 weeks commissioning with Au x Au beams at sNN = 200 GeV • 10 weeks data taking with Au x Au at sNN = 200 GeV • 10 weeks data taking with polarized p-p beams at s = 200 GeV

Run 8 (Fall ’07 – Summer ’08)• 15 weeks d-Au at sNN = 200 GeV• 10 weeks polarized p-p at s = 200 GeV

Run 9 (Fall ’08 – Summer ’09)• 10-15 weeks heavy ions (different energies and possibly species)• 15-10 weeks polarized p-p at s = 500 GeV (including commissioning)

Run 10 (Fall ’09 – Summer ’09)• HBD is removed in order to install new silicon vertex detector in PHENIX

Documents

Prototype Tests and Construction of the Hadron Blind Detector for the PHENIX Experiment at RHIC Craig Woody Brookhaven National Lab For the PHENIX Collaboration