1 Alexander Milov QM2006, Shanghai Nov 15, 2006 Construction and expected performance of the Hadron...

1Alexander Milov QM2006, Shanghai Nov 15, 2006

Construction and expected Construction and expected performance of the Hadron Blind performance of the Hadron Blind Detector for PHENIX experiment Detector for PHENIX experiment

at RHICat RHICAlexander Milov

(for the PHENIX HBD group)

XIX International conference on Ulterarelativistic Nucleus-Nucleus Collisions, Shanghai, China


Weizmann Institute of Science (Israel)A.Dubey, Z.Fraenkel, A. Kozlov, M.Naglis, I.Ravinovich, D.Sharma, L.Shekhtman (on leave from BINP), I.Tserruya (project leader)

Stony Brook University (USA)W.Anderson, A.Drees, M.Durham, T.Hemmick, R.Hutter, B.Jacak, J.Kamin

Brookhaven National Lab (USA)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 (USA)C-Y. Chi

University of Tokyo (Japan)T. Gunji, H.Hamagaki, M.Inuzuka, T.Isobe, Y.Morino, S.X.Oda, K.Ozawa, S.Saito

RIKEN (Japan)S. Yokkaichi

Waseda University (Japan)Y. Yamaguchi

KEK (Japan)S. Sawada

People in this projectPeople in this project


Why di-electrons?Why di-electrons?

Part of the p+p run no bkg. subtraction

Entire AuAu run

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)

Lepton pairs are unique probes because they provide direct information undistorted by further interactions.

• ρ (m = 770MeV τ ~ 1.3fm/c) e+e-

• ω (m = 782MeV τ ~ 20fm/c) e+e-

• φ (m =1020MeV τ ~ 40fm/c) e+e-


e+ e -

e+ e -

S/B ~ 1/500

“combinatorial pairs”

total background

Irreducible charm background

signal

charm signal

Background sourcesBackground sources Main source of the background due to external and internal conversions of the photons coming from π0.

π0 e+ e-

π0 e+ e-

The goal is to reduce the background by a factor of 100

Distinct pattern of the background producing decays: small inv. mass small opening angle

A rejection factor of >90% on a close pair will reduce the background to an acceptable level.


The detector conceptThe detector concept Proximity Focused Windowless Cherenkov Detector

Radiator gas = Working gasPrimary choice pure CF4n = 1.00062 (=28 ) L = 50cmBlind to π0 with pT<4GeV/c

Radiating particles produce blobs on an image plane

(θmax = cos-1(1/n)~36 mradBlob diameter ~ 3.6 cm)

To preserve the pair opening angle θpair the magnetic field is turned off (compensated) in the detector

Background processes produce 2 close blobs and single electrons only 1

Image plane:CsI photocathode on top of tiple GEM stack used for electron amplification separated by 90% transparent mesh from the main volume

~ 1 m

signal electron

Cherenkov blobs

partner positronneeded for rejection

e+

e-

pair

opening angle

B≈0


Challenges & SolutionsChallenges & Solutions The space where B can be compensated is limited to ~50cm but the number of p.e. must be high enough to allow for effective amplitude analysis of overlapping and distorted blobs.

Match the CsI Q.E.~70% @ 10eV and pure CF4 bandwidth (6-11.5 eV) to get unprecedented N0 ≈840 cm-1 (x6 larger than any e/π RICH ever built!)

The detector has to let all ionizing particles through without seeing them, but pick up single photoelectrons.

Make CsI + GEMs into a new type of semitransparent photocathode such that it a) is sensitive to the ionization reaching its surface from Cherenkov light

b) electric field drives MIP ionization back into the gas volume

The detector must be thin to produce little own background but leak tight to keep water away from absorbing UV light.

Windowless design (CF4 without quencher = gaseous radiator = detector gas). Combine functions of the detector structural elements (pad plane = gas seal)


The Image plane The Image plane Start with a GEM

Put a photocathode on top

Electron from Cherenkov light goes into the hole and multiplies

Use more GEMs for larger signal

Pick up the signal on pads

And why is it Hadron Blind?

Mesh with a reverse bias drifts ionization away from multiplication area

HV

Sensitive to UV and blind to traversing ionizing particles


Honeycomb panels

Mylar window

Readout plane

Service panel

Triple GEM module with mesh grid

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

Side panel

Sealing frame

HV terminals

Detector is designed and built at the Weizmann Institute

FEEs

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

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


Detector elements 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


“Clean Tent” a.k.a. “The Battle Field of Stony Brook”

CsI Evaporator and quantum efficiency

measurement(on loan from INFN)

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 assemblyDetector assembly


CsI evaporation station was given on loan to Stony Brook from INFN/ISS Rome

Thank you Franco Garibaldi & Italian team!

Produces 4 photocathodes per shot240 – 450nm of CsI @ 2 nm/secVacuum drops to 10-5 Torr and then to 10-7 Torr (water out of the structure).Contaminants measured with RGA

Photocathode Q.E. is measured “in situ” from in 165-200 nm wavelength range over entire area

Photocathodes transported to glove box without exposure to air

4 small “chicklets” evaporated at same time for full QE control (120-200 nm)

Photocathode productionPhotocathode production


First module installed in HBD West

Some of the production stepsSome of the production stepsGEMs pre-installed for evaporation

Photocathode installation chain:removal from transfer box, gain test, installation into the HBD.


GEMs produced at CERNTested for 500V in air @ CERNFramed & tested @ WIS for gain uniformityTested at SUNYSB prior to installationGain uniformity between 5% and 20%

GEM statistics133 produced (85 standard, 48 Au plated)65 standard, 37 Au plated passed all tests48 standard, 24 Au plated installed GEMs combined into stacks are matched to minimize gain variation over the entire detector

All GEMs pumped for many days under 10-6 Torr prior to installation into detector

20%

5%

The GEM stacks The GEM stacks


During gain mapping, a single pad is irradiated with a 8kHz 55Fe source for ~20 min. Then all other pads are measured (~1.5h) and the source is returned to the starting pad.

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

Further study show that the gain increase is rate dependent (10-30%)

This does not impose a problem for GEM operation at PHENIX

GEMs will reach operating plateau in a few hoursRates are lower then during mapping

1.5 Initial Rise

Secondary rise

GEM gain stability GEM gain stability


Flat position dependence

27 cm

Photocathode qualityPhotocathode quality

Number of photoelectrons

36 72

Q.E. needs to distinguish a single electron from a pair.

Absolute Q.E. must be continuously controlled and preserved.

At the production stage During transportation and installation During physics data taking

At the production stage the Q.E. is as high as measured in R&D stage and uniform


H2O & O2 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

Monochromator (120-200 nm) is a part of the HBD gas system

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

Gas transparencyGas transparency


electronshadrons

Cluster size, reverse bias

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

Full scale detector prototype:1 GEM + CsI stack module installed in the volume68 readout channelsfull readout chain

Pure CF4 gas system LVL2 triggers to enrich e-sample

electronshadrons

Pulse height, reverse bias

Forward Bias+LandauReverse Bias

MIP

e/π rejection ~85% at εe ~90 %

Full scale prototype testFull scale prototype test


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

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

NowNow


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, 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

SummarySummary


BACKUPSBACKUPS


Challenges & SolutionsChallenges & Solutions The space where B can be compensated is limited to ~50cm but the number of p.e. must be high enough to allow for effective amplitude analysis of overlapping and distorted blobs.

Match the CsI Q.E.~70% @ 10eV and pure CF4 bandwidth (6-11.5 eV) to get unprecedented N0 ≈840 cm-1 (x6 larger than any e/π RICH ever built!)

The detector has to let all ionizing particles through without seeing them, but pick up single photoelectrons.

Make CsI + GEMs into a new type of semitransparent photocathode, which a) does not have usual losses for such type of photocathode

b) allows multi-stage multiplication to follow it.

The detector must be thin to produce little own background but leak tight to keep water away from absorbing UV light.

Go to windowless design by using CF4 without quenching gas both as a radiator and working gas due to the fact that GEMs have no photon feedback


~12 m

e+

e+

e-e-

PHENIX nowPHENIX now


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 12

Frame W:5mm T:0.3mm

Hexagonal pad size a = 15.6 mm

Number of pads per arm 1152

Dead area within central arm acceptance 6%

Radiation length (central arm acceptance) box: 0.92%, gas: 0.54%

Weight per arm (including accessories) <10 kg

HBD parametersHBD parameters


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

Readout chainReadout chain


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

Run PlanRun Plan


Photocathode and gas. Photocathode and gas. Photocathode:

CsI is an obvious choice. We are using INFN built evaporator, currently at Stony Brook to do this project.

High area, High vacuum, In-situ Q.E. control, Zero exposure to open air.

Gas CF4 (was not really known): Has high electron extraction probability Has avalanche self quenching mechanism

Gas CF4 (well known): Transparent up to 11.5 eV, makes perfect match to CsI Is a good detector gas.

0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 1000

2000

4000

6000

8000

10000

120000 20 40 60 80 100 120 140 160

Gain with UV Gain with x-rays

Ga

in

Time, h

1 PHENIX year ~ 16 C/cm2

Corrected for P/T variations

Acc.charge, C/cm2


Made of 2 units with R~60cm, the volume is filled with CF4

magnetic field is turned offElectrons emit Cherenkov light

Cherenkov light is registered by 12 photo-detectors in each unit

Signal is read out by 94 pads in each unit, pad size ~ size of a circle

Accumulating ~36 photoelectrons from each primary electron, while most other operational RICHes have ~15 or less.

High statistics allows to separate 2 close electrons even if their signals overlay!

Number of photoelectrons

36 72

The design. The design.


Event display (simulation). Event display (simulation).


Background sources? Background sources?

~12 m

In the decays contributing to the background:

π0 e+ e- γ π0 γ γ e+ e- γ

Only one electron is detected in PHENIX and another is lost

To cut the background we need a new detector such that:

It sees only electrons Located at the origin It does not produce its own background (is thin) … … …


• All raw materials (FR4 sheets, honeycomb, HV resistors, HV connectors) ordered and most of them in house

•Detector box design fully completed

• Jig design underway

• Small parts (insert, pins, screws, HV holders..) in the shops

• Detector construction to start Nov. 1st

• PCB design almost complete

• Detailed construction schedule foresees shipment of boxes to SUNY in January 2006.

What does it look like What does it look like


Mechanical parts and PCB.Mechanical parts and PCB.PCB final design.Quick MC shows no difference with standard cells

Entrance window frames are ready, the window itself to be tight between them

1 Alexander Milov QM2006, Shanghai Nov 15, 2006 Construction and expected performance of the Hadron...

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