V0, jyg, ALICE week, March 2003 1

Preparing for the V0 TDR(Lyon-Mexico project)

The V0 detector in 3 chapters 1 - Tests and simulations of detection elements• V0L and V0R design after tests in next August 2 - Photodetectors and Front End Electronics• first plans and prototypes 3 - Simulations of the V0 responses (PPR

contribution)• efficiencies for minimum bias triggers: p-p et Pb-

Pb• multiplicity indicator• luminosity control• background filter for central detector and

dimuon Conclusion

V0, jyg, ALICE week, March 2003 2

Chapter 1 - The V0 detector

V0 in both sides of the vertex

V0L at –3.5 meters• -5.1 < η < -2.75 • 4.3 < R < 44.5 cm V0R at 0.9 meter • on the front absorber • 1.7 < η < 3.8 • 4.0 < R < 33.6 cm

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RingV0L V0R

ηmax/ηmin max/min ηmax/ηmin max/min

1 -5.1/-4.6 -0.7/-1.2 3.8/3.4 2.6/3.8

2 -4.6/4.2 -1.2/-1.7 3.4/2.9 3.8/6.3

3 -4.2/-3.7 -1.7/-2.8 2.9/2.5 6.3/9.4

4 -3.7/-3.2 -2.8/-4.7 2.5/2.1 9.4/14.0

5 -3.2/-2.8 -4.7/-7.0 2.1/1.7 14.0/20.7

V0 segmentation

Arrays with 72 detectors according to 5 rings/12 sectors

• in the FMD acceptance, in the dimuon arm acceptance

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V0 scintillator element

Elementary channel (ring i element)• plastic scintillator (SC)• wave length shifting fibers in grooves

(WLS)• clear optical fibers for light transport (CL)• photomultiplier (PMT)• electronics (FE) for:…. triggering (V0, V1, V2)…. charge and time numerizations (Q, T)

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Setup A

Coupling of WLS fibers on one of the front flat edges of scintillating elements

• 1 cm thick scintillator• from 8 to 2 WLS fibers• 40 cm long

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Setup B

Coupling of WLS fibers on the latteral flat edges of scintillating elements

• 1 cm thick scintillator• 8 WLS fibers on each side• 40 cm long

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Tests in T10 and with cosmics

From the MIP through several V0 elements Fast scintillator from BICRON (BC408)• 425 nm maximum emission, 2.1 ns decay constant Shifting fibers (Y11 from Kuraray) directly on PM XP2020• 430 nm maximum absorption, 476 nm maximum emission Light yield as a function of:• glue or no glue for fixing the fibers (BC600) (-35% difference)• Al/Teflon envelope on scintillator (factor 2 gain compared to

TiO2 paint)• no reflector on fiber ends (-30% loss compared to Al or Teflon) Time resolution with threshold discriminator:• as a function of elements• as a function of the collected light

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Light yield from setup Adirect proportion

No fix ratio between the collected light and the number of fibers

• saturation when increasing fibers Light yield dependence on element and number of WLS

fibers• more results from very close setup by Gerardo next talk

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Light / time from setup A

p1/N + p2

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Light / time from setups A and B

Much more light with setup B better time resolution

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Simulations

Simulation based on the LITRANI code (C++/ROOT program)

• generation and propagation of the optical photons from their emission point to detecting devices

Geometry and optical parameters of the V0 elements • absorption, diffusion, scattering lengths• reflection, diffusion coefficients Light yield • within the fiber acceptance • in the direction of the PMT

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Light yield from setup A

Data normalized on ring 4 element with 4 fibers Good relative agreement between measures and

calculations

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Light map from setup A

Large inhomogeneity in the light production• depends on the WLS fiber positions • zones of inefficiency in the corners

fiber positions

inefficiency zones

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Light map from setup B

Better uniformity with setup B• extreme MIP light dispersion of a factor 2.5

minimum contribution

maximum contribution

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Light yield from setups A and B

Ring

Setup A (10 mm)

Setup B(10 mm)

Setup B(15 mm)

1 26 49 65

2 23 49 65

3 18 48 65

4 14 49 65

5 16 52 69

Setup A (8 fibers): light depends on the geometry (~factor 2)

Setup B: light yield independent of the geometry• goes like the SC thickness

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Plan

Test of quadrants in August 2003• in a real configuration (SC/WLS fibers/connector/CL fibers/PMT)…. in independent elements (setup B with 1 and 1.5 cm in

thickness)…. and from one unique SC plate (similar to setup A) next talk• with (x, y) measurement of tracks Last options chosen for a final design• included in the TDR in September 2003 Mechanical construction starting in 2004

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V0R with setup B

optical fibers

absorberV0R

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CERN Maquette 1:1

Si outerabsorber Si inner

T0R V0R

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Chapter2 - PMT and FEE PMT signal dynamics: 1 - 1000• for a dynamics of 1- 300 MIP’s (expected in Pb-Pb)• and a 1 MIP efficiency > 97% (required for pp) Signal picked up from anode and last dynode (A/D = 6)• fast rise and decay times (pulses within 20 ns))• good linearity (minimum signal distorsion)• low dark noise (minimum V0 auto-triggering) Good candidates exist Fast electronics providing 3 levels of trigger to the CTP • one MB in pp and Pb-Pb: V0 trigger and TRD wake-up • one central and one semi-central in Pb-Pb: V1 and V2

triggers Signal dynamics numerization• 1 to 1000 in charge (relatively to minimum threshold)• 0 to 256 ns in time (relatively to the bunch clock)

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PMT noise measurement

Threshold: 5 p.e.

• V0 self-triggering

• XP2020: 20 c/s• XP2972,

R7400P: … 0.003 c/s

5

1

from NA49

400

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Ele

ctro

nic

s dia

gra

m

CTP

digitization

MB trigger

scin

till a

tor

centrality triggers

CTP

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Integration in ALICE

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Chapter 3 - Simulations

PYTHIA for pp extrapolated to proton beams of 7 TeV• MB cross-section: tot = el + inel = 101 mb el = 22 mb and inel = 79 mb• each term will be measured by TOTEM at LHC energies Limited covering of V0 at small angles (max = -5.1 / 3.8)• no detection of charged particles from elastic process Luminosity: L = (Ninel/effinel)/inel

• if PYTHIA is correctly calibrated (inel ), we should be able to evaluate the term effinel from simulations (within few %)

• … and counting Ninel should allow to measure the luminosity Two components for inel = SD + NSD :• SD: p + p > p + X (14 mb)• NSD: p + p > X + Y (65 mb)

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Triggering efficiency

pp multiplicity distribution in 4• white: Pythia without transport Events with at least 1 MIP • light grey: Pythia in vacuum• light and dark grey: Pythia in

AliRoot Production of secondaries improves

the triggering efficiency effinel = 84% from V0L*V0R

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Efficiency function

Triggering efficiency as a function of the minimum number of left/right cells required for the coincidence V0L*V0R

If Ncell cut = 1 for L and R

• effinel from Pythia + AliRoot:

(0.53 x 14 + 0.93 x 65) / 79 = 0.86 Threshold could be necessary to

kill residual p-gas background in the trigger rate

Simulations to evaluate the p-gas contribution are in progress

SD

NSD

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Efficiency values

effinel

Ncut on Left cells

1 2 3 4 5 6

Ncut on Right cells

1 0.86 0.80 0.76 0.70 0.66 0.60

2 0.82 0.78 0.74 0.69 0.65 0.59

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Multiplicity in pp

Multiplicity from Pythia + AliRoot

• 1000 events• Signal in clear• Signal + background in dark Many secondaries due to the

setup• big effects in rings 1 left/right

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Multiplicity in Pb-Pb

Multiplicity from Hijing + AliRoot

• 30 events with b = 0-11.2 fm Line = pure signal Points = signal + background • circle: V0L• square: V0R Many secondaries due to the

setup• big effects in rings 1 left/right

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Background from AliRoot

S/B as a function of (ring)

• B > 2S

Background in V0R

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Vertex distribution

Reconstructed tracks• 1000 pp events Important in V0R• from ITS support, bellows

and flange

Background in V0R

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Conclusion

Three chapters for the V0 in the TDR:• detector (design and performances in September 2003)• front end electronics (design and first tests by August)• simulations (present and close future results)