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					     Construction, Commissioning and
Performance of a Hadron Blind Detector for
     the PHENIX Experiment at RHIC
                                    Itzhak Tserruya
                      Weizmann Institute of Science, Rehovot, Israel
                                  for the HBD group:

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




          IEEE 2007, October 29, 2007, Hawaii

    Itzhak Tserruya
                           Outline
           Ø Motivation

           Ø Concept

           Ø Construction

           Ø Performance



Itzhak Tserruya        IEEE-NSS, Hawaii, October 29, 2007   2
                                    Motivation
    Electron 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 r, ω and f
      – sensitive probe for thermal radiation:
            QGP qqbar à g* à e+e-
            HG p+p- à r à g* à e+e-
   Experimental challenge:                              g ® e+ e -
                                                     p o ® g e+ e -
   huge combinatorial background
   arising from e+e- pairs from
   copiously produced from p0 Dalitz
   decay and g conversions.

• Both members of the pair are needed to
reconstruct a Dalitz decay or a g conversion.
•Pair reconstruction limited by:
      – Low pT acceptance of outer PHENIX
      detector: ( p > 200MeV)
      – Limited geometrical acceptance of
      present PHENIX configuration
  Strategy
• Create a field free region close
to the vertex to preserve            Upgrade Concept
opening angle of close pairs.
• Identify electrons in the field
free region
• reject close pairs.

   Hardware
* HBD in inner region
* Inner coil (foreseen in original
   design) à B~0 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.                            4
       HBD Concept
HBD concept:
 ♣ windowless Cherenkov detector (L=50cm)
                                                       UV-photon               hadron
 ♣ CF4 as radiator and detector gas
 ♣ Proximity focus:
                                     ~1 cm                         detector element
   detect circular blob not ring
                                                   E
Detector element:
 ♣ CsI reflective photocathode
 ♣ Triple GEM with pad readout             50 cm
                                                                           CF4 radiator



 v Why is it Hadron Blind?
  reverse bias between mesh and top
 GEM repels ionization charge away from
 multiplication area
                                           5 cm
                                                                   beam axis
 Sensitive to UV and blind to traversing
 ionizing particles
                              The Detector
      Detector designed and built at the Weizmann Institute
                              v The detector fits under 3%X0 (vessel 0.92%, gas 0.54%,
 Two identical arms
                              electronics ~1.5%) and it is leak tight to keep water out
                              0.12cc/min (~1 volume per year)!
All panels made of honeycomb & FR4
              structure                          v Readout plane with 1152 hexagonal
                                     FEEs
                                                 pads is made of Kapton in a single sheet
                                                 to serve as gas seal
                                                            v Each side has 12 (23x27cm2)
                  Side                                      triple GEM detectors stacks:
                  panel                     Readout         Mesh electrode àTop gold
                                             plane
                                                            plated GEM for CsI à Two
                                                            standard GEMs à pads
 Mylar
window                                             HV
                                                terminals



                                 Service    Triple GEM module
                    Sealing       panel       with mesh grid
                                                                                       6
                     frame
          Detector elements
Jig for box assembly     v Detector construction involves
                         ~350 gluing operations per box
                         v Dead areas are minimized by
                         stretching GEM foils on a 5mm
                         frames and a support in the middle.




                       v GEM positioning elements are
                       produced with 0.5mm mechanical
                       tolerance.
                      Detector assembly
  CsI evaporation and detector assembly in clean tent at Stony Brook”

Laminar Flow                                                        CsI Evaporator and
Table for GEM                                                       quantum efficiency
  assembly                                                             measurement
                                                                    (on loan from INFN)
                                                                     Can make up to 4
                                                                     photocathodes in
                                                                          one shot


High Vacuum
GEM storage
                                                                  6 men-post glove box,
                                                                      continuous gas
                                                                  recirculation & heating

                                                                       O2 < 5 ppm
                                                                      H2O < 10 ppm



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

    Itzhak Tserruya          IEEE-NSS, Hawaii, October 29, 2007                    8
                    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.

                                                    Typical noise performance
§ 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
                                                                                9
presently being analyzed.
         Tracking & position resolution
         Run 226502 ES4 at 3600V FB
                                                                 Hadrons selected in central arm:
                                                                     Vertex +/- 20 cm
                                                                     < 50 tracks
                                                                     3s matching to PC3 and EMCal
                                                                     n0 < 0
                                                                     EMC energy < 0.5


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




                                                                    Position resolution:
                                                                      sz ≈ sf ≈ 1 cm
                                                                    Dictated by pad size:
                                                                    hexagon a = 1.55 cm
                                                                    (2a/√12 = 0.9 cm)


Itzhak Tserruya             IEEE-NSS, Hawaii, October 29, 2007                                  10
      Hadron Blindness & e-h separation
      Hadron suppression illustrated by
    comparing hadron spectra in FB and RB
       (same number of central tracks)

                                                             Electron - hadron separation (RB)


             Hadron rejection factor


                                                 Strong suppression of
                                                  hadron signal while
                         Pulse height          keeping efficient detection
                                                   of photoelectrons
                                                   at reverse drift field


                          Pulse height




Itzhak Tserruya                  IEEE-NSS, Hawaii, October 29, 2007                        11
                      Electron detection efficiency
        §   Identify e in central arm using RICH and EMCal
        §   Project central arm track to HBD
        §   Relative e-detection efficiency in HBD obtained by varying
            the charge threshold of the closest (matched) pad
              EN3 G ≈ 3300                              All modules <G> ≈ 6600
    (several runs at “nominal” voltage)          (Run 237092 “nominal” voltage + 100V)




            ~4 p.e.                                       ~4 p.e.
§   Efficiency drop at pad threshold larger than about 4p.e. probably due to
    electrons converted in the gas near the GEMs. Needs further study.
                                                                                    12
                          Summary

   Low-mass e+e- pairs is a significant observable to diagnose the
   matter formed at RHIC.
Ø A novel HBD detector has been constructed and installed in the
  PHENIX set-up
Ø A commissioning run took place in spring 2007
Ø Preliminary analysis of data show:
     Ø Clear separation between e and h
     Ø Hadron rejection factor
     Ø Good electron detection efficiency




 Itzhak Tserruya          IEEE-NSS, Hawaii, October 29, 2007         13

				
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posted:7/18/2013
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