10/26/06takao sakaguchi, bnl1 hadron blind detector for the phenix experiment at rhic takao...

10/26/06 Takao Sakaguchi, BNL 1

Hadron Blind Detector for the PHENIX experiment at RHIC

Takao SakaguchiBrookhaven National Laboratory

For the PHENIX Collaboration


Excellent QGP detector: Thermal dileptons

• Thermal dileptons are an excellent probe for investigating the property of the hot and dense medium produced at RHIC.

• Thermal dileptons are “brother” of “thermal photons”

• No additional strong interaction in the medium produced

• Provide information on temperature, dof, etc.

• Signal to (Combinatorial random) Background is very small

• Estimated to be ~1/200!• Mostly from Dalitz decay of neutral

pions and photon conversions• Proven by the recent data from

PHENIX (firstly shown at QM’05)

• Need to identify the origin of electrons to reduce combinatorial background

• We want to see S/B ratio of at least ~1/10

Recent data from CERES coll.

PHENIX preliminary data

Black: ForegroundRed: Random BackgroundBlue: Net signal


Solution: Hadron Blind Detector• Tag background electron pairs via op

ening angle • Veto electrons with partner in field fre

e region• PHENIX has two (inner and outer) coils

to make such a region• Electron pairs do not open up

• Hadron Blind Detector (HBD) : • Proximity Focus Windowless Cherenk

ov detector • 50cm radiator length, 2*135, |y|<0.45

• Radiator Gas=Working Gas• Pure CF4 radiator• nCF4=1.000620, th=28 (~4GeV/c for )

• CsI photocathode + Triple GEM with pad readout

• Radiating tracks form “blobs” on the pad plane max=cos-1(1/n)~36 mradRBLOB~3.6cm)• Dalitz pairs & conversions make two b

lobs, single electrons make one

signal electron

Cherenkov blobs

partner positronneeded for rejection

e+

e-

pair opening angle

~ 1 m

Reductionby ~100!


How to Blind Hadrons

Mesh

CsI layer

Triple GEM

Readout Pads

e-Primary ionizationgEd

Absolute Quantum efficiency measured as a function of WL

• 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

• Primary ionization signal is greatly suppressed at slightly negative Ed while photoelectron collection efficiency is mostly preserved

Hadron Blindness as a function of Ed

Wave length [nm]


Detector Construction

24 Triple GEM Detectors (12 modules per side)

Area = 23x27 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


Gas system• Photon transmittance of the Gas is monitored at the input and output of the

detector• Water and oxygen level is also monitored

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

ran

sm

itta

nc

e [

%]

~10ppm H2O

~40ppm H2O

~200ppm H2O

Transmittance as a function of H2O contamination


heating elements •2 on each side, 2 on bottom (seen in next slide). 6 total on one hbd

38 x 25 cm185cm2 35um thickTraces (assume Cu)

HBD before installation into PHENIX


HBD Installed in PHENIX

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

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


GEM Performance

20%

5%

• All GEMs produced at CERN• 133 produced (85 standard, 48 Au pl

ated)• 65 standard, 37 Au plated passed all

tests• Good GPA! (~75%)

• 48 standard, 24 Au plated installed • Three GEMs in each stack are match

ed 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 an entire sector

• Resulting gain variation is between 5-20 %


Gain Stability of GEMs

This appears to be a charging effect that has typically been seen in GEMs before, but

the magnitude is large !

• 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.

• Gain increase has two components• Charge up: ~30% increase• Rate dep. Change: ~10%

First Layer is coated by CsI

Our HBD is operated at a very low rate (~ a few Hz) Not a big problem


Hadron blindness of the detector

• Read 12 samples per trigger with 16 nsec interval for each channel (=200nsec, 2B.C.)

• MIP distribution nicely fitted with a Landau distribution for Forward Bias

• Derive detector gain from the mean of MIP distribution

• Reverse Bias rejects ionization electrons almost perfectly -> Blinding Hadrons!

• Hadron rejection power: ~15@90% elec. eff.

Full scale prototype result

Timing Sample (n-1, 16nsec step)

Raw FADC dist. (sample”0” is subtracted from all other samples)

electronshadrons

Pulse Height: B=0, Reverse BIAS 505 VForward BIASReverse BIAS Landau Fit

Detector gain: 2500

Pulse height

MIP!


Summary

• PHENIX installed a Hadron Blind Detector to reject the random combinatorial background by electrons and the hadrons

• Identify electrons (single electron and photon converted electron pairs) in field free region

• GEMs are used as readout modules of photo/dEdX electrons

• Good GPA

• On-Beam Test of Full scale Prototype demonstrated the basic hadron blindness properties of the detector, and also provided information helpful for constructing the final detector

• Rejects primary ionization signals (dE/dx) of electrons and hadrons while keeping high photoelectron detection efficiency

13

Principle PlayersPrinciple Players

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, B.Jaca

k, J.Kamin, R.Hutter

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 (Instrumentatio

n Division)

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

* Project Leader


Backup


The SB plant (I): CsI evaporation facility

• 4 photocathodes produced per shot together with chicklets for QE monitoring• Excellent reproducibility. • Excellent stability

Cathode Stable


Detector GainMPV, Mean and Gain derived from the mip distribution of the different runs

VGEM = 495 V up to run # 203145 505 V from run # 203146


heating elements •2 on each side•2 on bottom at the centers of each front panel•(6 total) on one hbd

38 x 25 cm185cm2 35um thickTraces (assume Cu)

3.5m of 25mm copper tape60um thick on one side and ½ length on the otherAdd ½ m for the facesAdd 22gauge Cu wire twice the length(0.64mm in diam Cu +1.5mm Teflon)

HBD before installation into PHENIX

18

Present PHENIX Capabilities Present PHENIX Capabilities

~12 m

e+

e+

e-e-

19

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

10/26/06takao sakaguchi, bnl1 hadron blind detector for the phenix experiment at rhic takao...

Documents

phenix experiment

phenix preliminary datablack

gold plated gem

windowless cherenkov

gemtriple gem stack

recent data

amplified signal

outprimary ionization