the time of flight detector of the alice experiment

Nov 15, 2006 The TOF detector of the ALICE experiment E. Scapparone

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The Time Of Flight detector of the ALICE experiment

- The role of the TOF in ALICE;

- The optimal detector choice: the MRPC;

- FRONT-END and Readout Electronics;

- Supermodule construction and test;

- The installation of the first two supermodules

- Conclusions

E. Scapparone (INFN – Bologna)on behalf of the TOF(*) GroupQM2006, Nov 15, 2006

(*) INFN and University, Bologna (Italy) – INFN and University, Salerno (Italy) – ITEP Moskow (Russia) - Kangnung University (South Korea)


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TPC + ITS (dE/dx)

/KK/p

e /

0 1 p(GeV/c)

Particle Identification in ALICE

0 1 2 3 4 5 p(GeV/c)

TOF (100 ps)

/KK/p

e /TOF ( 50 ps)

/KK/p

e /

TOF (3.7 m from the beam pipe)TOF (3.7 m from the beam pipe)

ITSITS

HMPIDHMPID

/KK/p

TPCTPC

0 1 2 3 4 5 p(GeV/c)

HMPID


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TOF requirements:

Large array to cover the ALICE barrel (~150 m2)Time resolution σ < 100 ps High efficiency, ε > 95%High segmentation: few thousands of particles per unit of rapidity expected in Pb-Pb collision at s = 5.5 TeV/nucleon pair

ALICE choice: a detector based on MRPC, segmented in ~157,000 channels, (3.5 x 2.5) cm2 area

√


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M = p ((t2 c2 /L2 )-1)1/2

σTOF = 80 ps ; B = 0.5 T


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Combined PID Performance Efficiency/Contamination

Kaon PID (the most difficult case...)

ITSTPC

TOF(*)(120 ps)

p (GeV/c) p (GeV/c) p (GeV/c)

(C : CK : Cp = 0.75 : 0.15 : 0.1)

Higher efficiency & Lower contamination wrt individual detectors

p (GeV/c)

Combined PID ITS & TPC & TOF

(*) very conservative


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A TOF SuperModule in the Space Frame

2 crates /side157248 pads, total sensitive area: ~150 m2

18 Supermodules, each made of 5 modules: 2 external (19 strips), 2 intermediate (19 strips), 1 central (15 strips)

7.4 m

Readout performed bytwo VME Crates/Side


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Central module0º

3.2º

4.3º

5.3º

0.5º 1.6º 2.7º 4.8º3.7º

1º

2.1º

15.30 cm8.5 cm

70138209276349415492

6.3º

7.4º

5.9º 6.9º 7.9º

99 cm114 cm

27.8º28.7º 29.6º 30.5º 31.5º 32.3º 33.3º 34.2º 34.9º 35.8º 36.6º 37.4º 38.3º 39.2º 40.1º 40.8º 41.6º 42.4º 43.1º 43.9º

173 cm

178.2 cm

Outer module

44.3º

27.3º 28.2º 30.1º 31.0º 32.8º 33.7º 34.6º35.4º 36.3º37.1º 38.8º 39.6º 40.4º 41.2º 42.0º 42.8º

43.5º

37.9º31.9º29.2º

8.2º 9.3º 13.4º12.4º11.4º10.3º

8.7º

9.8º

10.8º

11.9º

12.9º

13.9º

14.9º

16º

17º

18º

19.1º

20.1º

21.1º 23º

22.1º

23.9º 24.9º 25.9º 26.8º

147 cm

134.30 cm

27.3º

14.5º 15.5º 16.5º 17.5º 18.5º 19.5º 20.5º 21.5º 22.5º 23.4º 24.4º 25.4º 26.3º

Intermediate module


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Cross section of a double-stack MRPC strip

2 rows of 48 readout pads (3.5 x 2.5 cm2)

Active strip length = 120 cm

Differential signal to FEA card


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-

Produced up to now ~1550 strips ~ 95 % of the total MPRC production

MRPC CONSTRUCTION AND TEST IN BOLOGNAMRPC CONSTRUCTION AND TEST IN BOLOGNA

- Signal connector soldering test; - Gap size test ;

- Glass test;

- HV test;

- Cosmic test (sample);

Several quality assurance testsSeveral quality assurance tests::

9191 MRPC strips /SM to be produced = MRPC strips /SM to be produced = 16381638


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TOF front end electronics: 6552 FEA TOF front end electronics: 6552 FEA cardscards

LV

To LTM

- Input stage (and following) fully differential;

- Adjustable input resistance ( 30 Ohm – 100 Ohm);

- Power: 40 mW/channels (to be compared with 400 mW/channels of the COTS amplifier);

- Nice matching with detector capacitance ( 30 pf );

- LVDS Output signal, compatible with HPTDC input

3 NINO ASICs (8 ch) /card

The benefit of the ASIC:


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TOF Electronics: 2 VME CRATES @ each SM TOF Electronics: 2 VME CRATES @ each SM sideside

TRMTRM

TRMTRMTRM

TRMTRMTRMLTM DRM

TRMTRM

TRMTRM

TRMTRMTRM

TRMTRM

CPDMLTMDRM

TRMTRM

- Pulser to MRPC

- Clock distribution

TRMDRM

30 High Performance

TDC Chips

- FEA LV monitor- FEA thresh. set & monitor- FEAC temperature monitor- FEA OR signals for trigger- Wake up to TRD

LTMLTM

CPDMCPDM - VME master - TRM readout

- DAQ (DDL) - L0,L1,L2 (TTC)

- Slow control

Crate left Crate right

The chips contained in these boards were carefully tested in radiation (PSI, Louvain, Legnaro) and magnetic (CERN) enviroments.

Taking advantage of the very fast time response, TOF partecipates to the ALICE L0 trigger ( T < 800 ns sfter the collision)


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An example: TRM (TDC Readout Module): 240 channels

Leading and trailing edge measurements signal width (TOT) for time slewing correction

Each TRM is equipped with 10 piggy-backs. Each piggy-back contains 3 HPTDC ASIC chip ( 8 channels, 25 ps intrinsic resolution)


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Time slewing correction is mandatory to get extremely goodtime resolutions.TOT is a good charge substitute.


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Test beam of single strips E

ffic

ien

cy

Tim

e re

solu

tio

n(

ps)ε > 99.9 %

average ~ 50 ps

Gas mixture: C2F4H2(90%) – SF6 (5%) – C4H10(5%)

Similar results obtained when strips are inserted inside the modules


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Ageing study:

Total charge = 14 mC/cm2

Charge/event = 2 pC

7 *109 events /cm2 @ 50 Hz/cm2

T=1.4 108 sec = 1620 days Pb-Pb run

Time(min)

two MRPC strips irradiated at GIF


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GIF results: No current increase

Source on

Source off

Source on

Source off

I (A)Flow = 1.4 cm3/s

The gas going to the chamber 2 was bubbled through water for some

time of the exposure


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GIF results

No ageing effect measured at PS

Working voltage = 13 kV


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TOF Modules moved to CERN Cosmic Facility

MODULE 5

MODULE 1

MODULE 2

MODULE 3

MODULE 4

Scintillator Trigger

Modules are tested with the same electronics, service (HV+LV) and cables used in the experiment

Scintillator Trigger


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-

SUPERMODULE CABLINGSUPERMODULE CABLING

~750 cables/Supermodule

Read out Crate Read out Crate

Signal cablesLV

FEAs

SM 1 during the cabling

HV


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AFTER CABLING: START A NEW SET OF TESTSAFTER CABLING: START A NEW SET OF TESTS- Gas system. - Cooling system test - pipe tightness, cooling test, temp monitor;

- HV test up to 4000 V;

- Power on the LV for crates ( 3.3 V ) + FEAs ( 2.5 V) + Vth measurement;

- New Pulser test (a first pulser test on each module done when modules arrive at CERN );

- Readout checks;

- Slow control test, Data on Dim server, PVSS control.


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Installing the first TOF Supermodule


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Oct. 5, 20062 TOF SMs inserted


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CONCLUSIONS

All productions (MRPCs, mechanics, electronics) well in progress.

Installation of first 2 SM in July and August (20/7-2/8!!!??) will be “critical” test (as usual when you install “first” pieces.... + service ready?? + very short time window!)

We are confident to have 2 (already inserted) + 8/9 SM assembled in January.

Installation time @ the pit could be critical!

- MRPC is an optimal choice to achieve a time resolution below 100 ps with high efficiency on a highly segmented detector (> 157,000 ch);

-Test beam, radiation and cosmic tests gave very good results in terms of time resolution, efficiency and ageing;

- MRPC strips production and front end + read out electronics delivery being completed;

- First and second Supermodule of the ALICE TOF succesfully installed;

- The second TOF installing period is planned for May 2007.


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RISERVE


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DISMOUNTING MODULES FROM COSMIC SETUP


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MOUNTING MODULES ON THE ASSEMBLY BENCH


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Module construction

30% modules assembly February July 2006

100% modules construction December 2006 May 2007

SuperModules Installation (new ALICE installation schedule)

Start installation SM [Stage 1] March July 2006

End installation ( 2 SM) [Stage 1] July August 2006

TOF production milestones :

SM 50% (9 SM) ready for installation August December 2006

SM 100% (18 SM) ready for installation March August 2007

With the present ALICE installation schedule we foresee to install in

February 2007 ~ 10 SuperModules.

Electronics

TRM+Crates+LV 30% production Nov. 2005 December 2006

TRM+Crates+LV 100% production Oct. 2006 February 2007

DRM+Trigger Start production Nov. 2005 March 2006

DRM 30 % production Feb. 2006 December 2006

DRM 100 % production July 2006 February 2007

TOF construction (installation) schedule (Notice that, e.g., February = 28/02, April = 30/04, July = 31/07, ….)

Notes : i) One complete order for TRM +Crates+ LV system

ii) One complete order for DRM + Trigger system, to the

same company as for TRM+ Crates + LV system


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98.4 %


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- Module box + honeycomb production(first company, BERCELLA) Completed within this summer

-Interface card production Completed within this summer (second company, ELTOS )

- Interface card assembly on honeycomb (third company, RAV) Completed within Dec. 06

- 1st Supermodule modules tested, mechanic structure mounted, cabling completed. - 2nd Supermodule modules in the Cosmic test facility at CERN - 3rd Supermodule working on the assembly

Module production and assembly:

Supermodules status

Honeycomb

Module box


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LTM (Local Trigger Module) 4/Supermodule TOTAL = 72

Production 5 produced and tested OK for 1° SMschedule 4 expected within Jun 06 OK for 2° SM 32 expected within Sep 06 40 expected within Nov 06


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CPDM (Clock and Pulser Distributor Module): 1 per 2 SMs TOTAL = 36

Production 2 produced and tested schedule 7 expected within Jun 06 (OK for 4 SMs)

Da mettere foto piu’ recente....

CLKPulser

TOF Standalone PID (80 ps res. as in the PPR)


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GIF resultsNo current increase

Source on

Source off

Source on

Source off

I (A)

No current increase

E. Scapparone RPC2003


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Chemical analysis (Chromatography) of the outgoing gasfrom both MRPCs (CH1, CH2) by CERN EST/SM-CP : measured concentration of Fluorine under the limit of

detection (0.02 ppm), I.e. no trace of HF in the samplesppm

- No sign of degradation;

- No increase of dark current;

- No degradation in efficiency;

- No degradation in time resolution;

E. Scapparone RPC2003

- Active detector volume is 2% of the total volume of the gas box;- Diffusion for the gas exchange between strip and the surrounding gas.


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POSITION SCAN ACROSS BOUNDARIES

Sharing of charge between neighbouring pads causes :

Global efficiency loss due to boundaries < 2%

Global double hit probability ~15%

Deterioration in resolution at the bordersCould use algorithm like average, pulse height weighted average etc..

Sharpness of boundaries depends on :

Threshold/dynamic range of charge spectrum

Size of footprint of avalanche on pickup pads

the time of flight detector of the alice experiment

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