Itzhak Tserruya IEEE 2007, October 29, 2007, Hawaii Itzhak Tserruya Weizmann Institute of Science, Rehovot, Israel for the HBD group: for the HBD group:

Itzhak TserruyaItzhak Tserruya

IEEE 2007, October 29, 2007, Hawaii

Itzhak TserruyaItzhak TserruyaWeizmann Institute of Science, Rehovot, Israel Weizmann Institute of Science, Rehovot, Israel

for the HBD group: for the HBD group:

BNL (Physics):BNL (Physics): B.Azmoun, A.Milov, R.Pisani, T.Sakaguchi, A.Sickles, S.Stoll, C.Woody B.Azmoun, A.Milov, R.Pisani, T.Sakaguchi, A.Sickles, S.Stoll, C.WoodyBNL (Instrumentation): J.Harder, P.O’Connor, V.Radeka, B.Yu J.Harder, P.O’Connor, V.Radeka, B.Yu Columbia Univ :Columbia Univ : C-Y. ChiC-Y. ChiSUNY: W.Anderson, A.Drees, Z. Citron, M.Durham, T.Hemmick, R.Hutter, B.Jacak, J.Kamin Weizmann:Weizmann: A.Dubey, Z.Fraenkel, A. Kozlov, M.Naglis, I.Ravinovich, D.Sharma, I.Tserruya A.Dubey, Z.Fraenkel, A. Kozlov, M.Naglis, I.Ravinovich, D.Sharma, I.Tserruya

Construction, Commissioning and Performance of a Hadron Blind Detector for

the PHENIX Experiment at RHIC

Itzhak TserruyaItzhak Tserruya IEEE-NSS, Hawaii, October 29, 2007IEEE-NSS, Hawaii, October 29, 2007 22

OutlineOutline

MotivationMotivation

ConceptConcept

ConstructionConstruction

Performance Performance

MotivationElectron pairs (or dileptons in general) are unique probes to study the matter formed in relativistic heavy ion collisions at RHIC:– best probe for chiral symmetry restoration and in-medium modifications of

light vector mesons , ω and – sensitive probe for thermal radiation:

QGP qqbar * e+e-

HG +- * e+e-

Experimental challenge:

huge combinatorial background arising from e+e- pairs from copiously produced from 0 Dalitz decay and conversions.

e+ e -

e+ e -

• Both members of the pair are needed to reconstruct a Dalitz decay or a conversion.

•Pair reconstruction limited by:– Low pT acceptance of outer PHENIX detector: ( p > 200MeV)– Limited geometrical acceptance of present PHENIX configuration

44

Upgrade Concept

Hardware* HBD in inner region* Inner coil (foreseen in original design) B0 for r 60cm Software * Identify electrons with p>200 MeV in PHENIX central arm detectors

* Match to HBD

* Reject if another electron is found in the HBD within opening angle < 200 mrad.

Strategy• Create a field free region close to the vertex to preserve opening angle of close pairs.

• Identify electrons in the field free region

• reject close pairs.

HBD ConceptHBD ConceptHBD concept:

♣♣ windowless Cherenkov detector (L=50cm) windowless Cherenkov detector (L=50cm)

♣♣ CFCF44 as radiator and detector gas as radiator and detector gas

♣♣ Proximity focus: Proximity focus:

detect circular blob not ringdetect circular blob not ring

50 cm

~1 cm

CF4 radiator

detector element

5 cmbeam axis

Why is it Hadron Blind? reverse bias between mesh and top GEM repels ionization charge away from multiplication area

Sensitive to UV and blind to traversing ionizing particles

E

hadronUV-photon

Detector element:Detector element:

♣♣ CsI reflective photocathodeCsI reflective photocathode

♣♣ Triple GEM with pad readoutTriple GEM with pad readout

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All panels made of honeycomb & FR4 structure

Mylar window

Readout plane

Service panel

Triple GEM module with mesh grid

The Detector The Detector The detector fits under 3%X0 (vessel 0.92%, gas 0.54%, electronics ~1.5%) and it is leak tight to keep water out 0.12cc/min (~1 volume per year)!

Side panel

Sealing frame

HV terminals

Detector designed and built at the Weizmann Institute

FEEs Readout plane with 1152 hexagonal pads is made of Kapton in a single sheet to serve as gas seal

Each side has 12 (23x27cm2) triple GEM detectors stacks: Mesh electrode Top gold plated GEM for CsI Two standard GEMs pads

Two identical arms

Detector elements

GEM positioning elements are produced with 0.5mm mechanical tolerance.

Dead areas are minimized by stretching GEM foils on a 5mm frames and a support in the middle.

Detector construction involves ~350 gluing operations per box

Jig for box assembly


CsI evaporation and detector assembly in clean tent at Stony Brook”

CsI Evaporator and quantum efficiency

measurement(on loan from INFN)Can make up to 4 photocathodes in

one shot

6 men-post glove box, continuous gas

recirculation & heating

O2 < 5 ppmH2O < 10 ppm

Laminar Flow Table for GEM

assembly

High Vacuum GEM storage

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

Detector assembly

99

HBD Engineering Run

The HBD was commissioned during the 2007 RHIC run.

After overcoming an initial HV problem, the detector operated smoothly at a gas gain of 3000-6000 for several months.

The CF4 recirculation gas system worked very smoothly. The oxygen and water content of the gas were monitored at the input as well as at the output of each vessel. In addition the gas transparency was monitored with a monochromator system. A reasonable transmittance of ~80% was achieved at a gas flow of 4 lpm.

The entire readout chain (both analog and digital) worked smoothly.

The excellent noise performance of the device (pedestal rms corresponding to 0.15 fC or 0.2 p.e. at a gain of 5000) allowed online implementation of a simple zero suppression algorithm to reduce the data volume.

A few billion minimum bias Au+Au collisions at √sNN = 200 GeV were collected and are presently being analyzed.

Typical noise performance


Tracking & position resolution

Run 226502 ES4 at 3600V FB

Position resolution:

z ≈ ≈ 1 cm

Dictated by pad size: hexagon a = 1.55 cm(2a/√12 = 0.9 cm)

Hadrons selected in central arm:

Vertex +/- 20 cm< 50 tracks3 matching to PC3 and EMCaln0 < 0EMC energy < 0.5

Projected onto HBD:Z in HBD +/- 2 cm in HBD +/- 25 mrad


Hadron Blindness & e-h separationHadron suppression illustrated by

comparing hadron spectra in FB and RB(same number of central tracks)

Pulse height

Hadron rejection factor

Pulse height

Electron - hadron separation (RB)

Strong suppression of hadron signal while

keeping efficient detection of photoelectrons

at reverse drift field

1212

Electron detection efficiency Identify e in central arm using RICH and EMCalIdentify e in central arm using RICH and EMCal Project central arm track to HBD Project central arm track to HBD Relative e-detection efficiency in HBD obtained by varying Relative e-detection efficiency in HBD obtained by varying

the charge threshold of the closest (matched) pad the charge threshold of the closest (matched) pad

EN3 G ≈ 3300 EN3 G ≈ 3300

(several runs at “nominal” voltage) (several runs at “nominal” voltage)

All modules <G> ≈ 6600 All modules <G> ≈ 6600

(Run 237092 “nominal” voltage + 100V)(Run 237092 “nominal” voltage + 100V)

~4 p.e. ~4 p.e.

Efficiency drop at pad threshold larger than about 4p.e. probably due to Efficiency drop at pad threshold larger than about 4p.e. probably due to electrons converted in the gas near the GEMs. Needs further study. electrons converted in the gas near the GEMs. Needs further study.


SummarySummary

Low-mass eLow-mass e++ee-- pairs is a significant observable to diagnose the pairs is a significant observable to diagnose the matter formed at RHIC.matter formed at RHIC.

A novel HBD detector has been constructed and installed in the PHENIX set-up

A commissioning run took place in spring 2007

Preliminary analysis of data show:

Clear separation between e and h

Hadron rejection factor

Good electron detection efficiency

Documents

Itzhak Tserruya IEEE 2007, October 29, 2007, Hawaii Itzhak Tserruya Weizmann Institute of Science, Rehovot, Israel for the HBD group: for the HBD group: