Performance of Prototype MRPC Detector for STAR Frank Geurts (Rice Univ.) for the STAR TOF...

Performance of Prototype MRPC

Detector for STAR

Frank Geurts (Rice Univ.)

for the

STAR TOF collaboration

RPC2003 -- Oct. 20, 2003 F.Geurts -- Performance of Prototype MRPC Detector for STAR

2

Outline

STAR Time of Flight MRPC Prototype: TOFr TOFr at AGS

test results TOFr at RHIC (STAR)

physics results Summary


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Solenoidal Tracker At RHIC

Great interest in large acceptance PID over an extended pT range full TOF replaces the existing Central

Trigger Barrel. covers the TPC tracking detector

based on Multi-gap Resistive Plate Chambers (MRPC) prototype detector: TOFr


4

STAR Time of Flight STOP detector:

future: barrel of MRPCs prototype single tray of MRPCs: TOFr

START detector dedicated detector, close to the beam line run II – IV: pseudo-Vertex Position

Detectors particle trajectories and momentum:

TPC tracker σ(p)/p ~ 1-2%, σ(s)/s~0.2%

Requirements: total time resolution σ(t)~100ps

MRPC resolution ~80ps detector segmentation to limit occupancy to

10-15% fit into integration envelope for present

CTB operate in 0.5T magnetic field operate at particle fluxes ~200Hz/cm2

inexpensive safe not impair performance of other

subsystems (interaction material, gas containment)


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STAR MRPC Tests at BNL

AGS testnear E949 exp.

STARdetector

Brookhaven National LabUpton, NY


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MRPC Moduledimensions: 21.8 x 8.4 cm2

sensitive area: 20.0 x 6.1 cm2

6 gas gaps spacing 220 micron outer glass thickness: 1.1 mm inner glass thickness: 0.54 mm

6 Copper pick-up pads 6.1 x 3.4 cm2

0.3 cm spacing


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Tray Layout form factor: Central Trigger

Barrel tray 241 x 21.6 x 8.9 cm3

TOFr single tray 28 modules installed

168 channels two HV busses

full TOF 120 trays in two barrels different tray design φ-coverage: 60 x 6˚ z-coverage: 2 x (Δη=1) 32 modules/tray

192 channels

η=1 sideη=0 side


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TOFr Tray Construction

FEEs installed

η~1 side

η~0 side

all MRPC modules installed

February 2002Rice Univ., Houston TX


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TOFr at the AGS close to E949 experiment

no test beam, but radiation area significant non-relativistic

momentum spread significant radiation during the spills

in-spill (2s) dark current: 60nA out-spill (3s): 30nA no AGS operation: 10nA

measurements Optimal FEE threshold voltages Optimal high voltage gas mixtures


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8 PMTs’ coincident signal as TDC start and ADC gate.

AGS Trigger Set-up

in-beam view

4 x 19 cm2 covered area by scintillators

along-beam viewtray

FE

E

beamdirection

tray


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AGS TOFr Analysis strict cuts on all PMT trigger pedals strict cuts on single MRPC pad signals

no neighboring hits ADC signal < (μped + 1.5*σped)

effectively select on central hits eliminate edge effects (5ps effect)

T-A (slewing) corrections reference PMTs MRPCs

(Shao Ming et al.)

CE

RN

T1

0 d

ata

AGS – MRPC slewing


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AGS TOFr Analysis (cont’d) Time resolution for one MRPC pad (t) ~70 ps after PMT T-A

correction no accurate position information:

remaining position smearing 45 ps/cm propagation time < 4 cm wide

raw MRPC timing(incl. start timing)

start timing(based on 8

PMTs)

0 -18˚ ~30˚ σ(t) distributions for different

incident angles 12 modules at η=0

0-18˚ 4 modules at η=1

~30˚


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AGS: HV & FEE Threshold

90% Freon + 5% iso-butane + 5% SF6 FEE threshold voltages:

1.2, 2.2 and 2.7 V High voltages: 13.25 – 16 kV typical noise rates (mod.#2)

Vthres=1.2V, HV=14.5kV: 7 - 8Hz caveat:

no control over the beam quality possible time dependent spread


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AGS: Gas Mixtures

module #2 tested at various HVs all other modules at fixed HVs (table) Vthres = 1.2 V start time corrected σ(t) SF6: stronger quenching, higher HV larger primary ionization for iso-butane similar efficiencies for A and B mixtures

HV

[kV]

efficiency

[%]

σ(t)

[ps]

A. freon + iso-butane + SF6 15 96.4 72.4

B. freon + iso-butane 14 97.2 76.8

C. freon 14.5 96.1 87.0


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TOFr in STAR

run II (2001/2): Au+Au, p+p start: pVPD stop: TOFp (PMT+scintillators)

run III (2003): d+Au, p+p start: pVPD stop: TOFp + TOFr

TOFr tray

East-TPC

TOFp TOFr

x

y

54˚


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TOFr Operations in STAR High voltage at 14kV Vthres = 1.2V gas mixture: 95% freon + 5% iso-butane 72 digitized out of 168 available channels

2 dead channels noise rate for 70 channels: ~240 Hz

Δφ=6°, Δη~0.4 only ~0.3% TPC coverage

large data sets, dedicated TOFr trigger 25M STAR minimum bias events

6.6M pVPD events 0.7M TOFr hits 0.1 hits per pVPD physics event

2.5M STAR TOFr trigger events 2.0M pVPD events 2.4M TOFr hits 1.22 hits per pVPD physics event.


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start time: pVPD coincidence 3 detector elements per pVPD coverage

19% solid angle 4.43 < η < 4.94

start timing resolution is multiplicity dependent Au+Au (run II): σ(t) ~ 24ps d+Au (run III): σ(t) ~ 80ps p+p: σ(t) ~ 120ps

path length and momentum TPC track extrapolation to TOFr tray

primary tracks only, i.e. must originate from the primary collision vertex

at least 15 out of maximum 45 hits in the TPC tracker

match tracks to TOFr hits calibration

T0 correction T-A slewing correction local z-position correction MRPC stop timing resolution ~80ps

consistent for d+Au and p+p data

STAR: TOFr Analysis

TPC

pVPDeast

pVPDwest

Aud

TOFx

STAR TOFrp+pσ(total)~162ps

STAR TOFrp+pσ(start)~139ps

(Lijuan Ruan et al.)


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STAR: TOFr Analysis (cont’d)

• 1/β vs. momentum for π±, K± and p(pbar) from 200 GeV d+Au collisions.

• insert shows m2=p2(1/β2-1) for 1.2 < pT <1.4 GeV/c


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STAR: TPC tracking and TOFr matching efficiencies

TPC trackingefficiency for pbar

TPC-TOFr matchingefficiency for pbar


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STAR: TOFr Results other corrections:

particle feed-down and contamination trigger background and biases energy loss

invariant cross sections for π±, K± and p(pbar) in 200GeV/c d+Au and p+p collision

(p+pbar)/h ratios measured by TOFr compared with other measurements similar for d+Au at 200GeV/c, and p+pbar

at 1.8TeV/c and p+p at 23.8GeV/c ratio for Au+Au at 130GeV/c twice that of

d+Au Final state rescattering, Cronin effect can

not explain this.


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STAR: TOFr Physics!nucl/ex-0309012, submitted to PRL


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Summary prototype TOF detector build in Feb.2002 tested at the AGS for various Vthres, HVs and gas settings

optimal running conditions for STAR HV=14kV Vthres=1.2V gas mixture: 95% Freon + 5% Iso-butane

STAR d+Au and p+p run very successful large data set dedicated trigger very stable operations

fast and relevant physics results important push for full MRPC-based STAR TOF proposal

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Performance of Prototype MRPC Detector for STAR Frank Geurts (Rice Univ.) for the STAR TOF...

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