alice: towards the first pb-pb run

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ALICE: towards the first Pb-Pb run Federico Antinori (INFN Padova, Italy) on behalf of the ALICE Collaboration

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ALICE: towards the first Pb-Pb run. Federico Antinori (INFN Padova, Italy) on behalf of the ALICE Collaboration. Contents. Running configuration Expected conditions and triggering Readiness for high data rates Physics outlook for the first run (examples) Conclusions. The detector. - PowerPoint PPT Presentation

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Page 1: ALICE: towards the first Pb-Pb run

ALICE: towards the first Pb-Pb run

Federico Antinori

(INFN Padova, Italy)

on behalf of the ALICE Collaboration

Page 2: ALICE: towards the first Pb-Pb run

Contents

• Running configuration

• Expected conditions and triggering

• Readiness for high data rates

• Physics outlook for the first run (examples)

• Conclusions

FA - ALICE - LHCC - 22 September 2010 2

Page 3: ALICE: towards the first Pb-Pb run

• designed for dNch/dy > 6000

– excellent tracking, particle id, vertexing capabilities

(e.g.: see this morning’s presentation by J.P. Revol)

• configuration: same as for pp– ITS, TPC, TOF, HMPID, MUON, V0, T0, FMD, PMD, ZDC (100%)– TRD (7/18)– EMCAL (4/12) – PHOS (3/5)– HLT (60%)

The detector

FA - ALICE - LHCC - 22 September 2010 3

some changes for Pb-Pb:• V0 HV settings• ITS-SDD sampling rate (2040 MHz)• event size! 100’s kB 10’s MB

Page 4: ALICE: towards the first Pb-Pb run

Pb-Pb running scenario

• expected luminosity ~ 2 orders of magnitude below nominal– 1027 cm-2 s-1 ~ 1025 cm-2 s-1

– ~ /10 from number of bunches

– ~ /10 from increased beam size (lower energy, less focussing)

(see presentation by J Jowett) 50 – 100 Hz min bias

strategy: low bias trigger

• expected data sample?– estimate from J Jowett : ~ 1 – 3 µb-1 (@ TH workshop, 3/IX/2010)

• e.g.: 2 µb-1 = 1.6 107 min bias events

– for comparison: ALICE targets:

• 0.5 nb-1 for rare triggers

• a few 107 central events for central physics

FA - ALICE - LHCC - 22 September 2010 4

Page 5: ALICE: towards the first Pb-Pb run

Triggering

• low bias – basically as low as

backgrounds allow

• little information on expected backgrounds important to measure

early-on with circulating beams

• three triggers running in parallel: from SPD, TOF, V0

+ TOF ultra-peripheral J/Ψ (depending on backgrounds)

FA - ALICE - LHCC - 22 September 2010 5

SPD

TOF

V0AV0C

Page 6: ALICE: towards the first Pb-Pb run

6

Inefficiency vs threshold:

3.5% (nFO > 20) 10.4% (nFO > 50) 16.5% (nFO > 100)

SPD trigger

• Using chip-by-chip FASTOR– 1200 chips in complete SPD barrel

FA - ALICE - LHCC - 22 September 2010

Page 7: ALICE: towards the first Pb-Pb run

V0 trigger

• e.g.: varying gain on Pb-Pb simulation– using same thresholds as in pp

FA - ALICE - LHCC - 22 September 2010 7

Page 8: ALICE: towards the first Pb-Pb run

FA - ALICE - LHCC - 22 September 20108

2 MRPC = 2 x 96 ch

2 x ½-MRPC.OR. of 96 chMaxiPad (MP)

TOF pad (~ 10 cm2)Digit (in simulation)

91 MRPC

MaxiPad

TOF trigger MaxiPads

barrel divided into 46 (z) × 36 (φ) MaxiPads

2 x ½-MRPC.OR. of 96 chMaxiPad (MP)

Page 9: ALICE: towards the first Pb-Pb run

TOF Triggers

• Interaction– condition on MaxiPad

multiplicity

• Ultra-Peripheral J/Ψ– 2 MaxiPads– correlation in φ

FA - ALICE - LHCC - 22 September 2010 9

degrees

Angle between leptons

150o < < 170o

distribution for J/Ψ decays

Page 10: ALICE: towards the first Pb-Pb run

• extensive tests at Point 2 with artificially created Pb-Pb-like event sizes– verify correct operation of DAQ/Trigger– test data transfer bandwidths

at expected luminosity for this year HLT filtering is not needed

High data rate tests

Detectors DAQ

DAQ CASTOR

FA - ALICE - LHCC - 22 September 2010 10

Rate to DAQ vs L0 trigger rate

~ 20 MB/event

expected range for this year

Page 11: ALICE: towards the first Pb-Pb run

Physics reach?• global event properties

– multiplicity – azimuthal asymmetry (v2)– Bose-Einstein correlations (HBT)– bulk strangeness

• with a pT reach dependent on statistics…– particle correlations– nuclear modification factors– strange, identified particle spectra

• a first glimpse of hard probes?– jets– J/ψ– heavy flavour

• surprises?(always there so far at each new AA energy) FA - ALICE - LHCC - 22 September 2010 11

Page 12: ALICE: towards the first Pb-Pb run

Charged particle multiplicity

• connected to temperature, energy density, parton density,…– day 1 measurement primary input to models

• considerable spread of predictions…

FA - ALICE - LHCC - 22 September 2010 12

from Néstor Armesto @ CERN TH Institute3 September 2010

Page 13: ALICE: towards the first Pb-Pb run

Azimuthal asymmetry (v2)

• azimuthal asymmetry in geometry of non-central collisions

• transfer of asymmetry to momentum space measures strength of collective phenomena

• asymmetry of momentum distribution measured by second coefficient of Fourier expansion (v2)

• v2 close to hydrodynamic limit at low pT at RHIC

FA - ALICE - LHCC - 22 September 2010 13

Reactionplane

In-planeOut

-of-

plan

e

Y

XFlow

Flo

w

Reactionplane

In-planeOut

-of-

plan

e

Y

XFlow

Flo

w

Reactionplane

In-planeOut

-of-

plan

e

Y

XFlow

Flo

w ...)2cos(2)cos(212

121

vv

dydpp

dN

dyddpp

dN

TTTT

v1 = 0 at central y

Page 14: ALICE: towards the first Pb-Pb run

v2 measurement studiesStandard event-plane method Lee-Yang Zero method

FA - ALICE - LHCC - 22 September 2010 14

500 HIJING events centrality b = 8fm multiplicity <M> = 1900 integrated v2 = 3.3%

1100 HIJING events centrality b = 9 fm multiplicity <M> = 1200 integrated v2 = 6%red – modified LYZ method (J-Y Ollitrault)

107 events approach 20 GeV (asymmetry still there?)

generatedreconstructed

Page 15: ALICE: towards the first Pb-Pb run

Nuclear modification factor

• in Au-Au @ RHIC particle production suppressed by factor ~ 5 at high pT w.r.t. binary-scaled p-p

• e.g.: expected reach in ALICE for 106 central (with no suppression):

FA - ALICE - LHCC - 22 September 2010 15

Tp

TT

T pdpd

dNp )(NN

>(p

T)

pT (GeV/c)

Page 16: ALICE: towards the first Pb-Pb run

,K* ,K0s, …

300 central events

13 /evt

107 events:

pt reach ,K,~ 13-15 GeV

pt reach ~ 9-12 GeV

central Pb-Pb K+K-

Mass resolution ~ 1.2 MeV

hadrochemical analysis

chemical/kinetic freeze-out

medium modifications of mass, widths

FA - ALICE - LHCC - 22 September 2010 16

Page 17: ALICE: towards the first Pb-Pb run

Identified particles v2

• sensitive to hydrodynamics and recombination effects– e.g. @ RHIC: ~ scales with # of valence quarks

FA - ALICE - LHCC - 22 September 2010 17

STAR Preliminary

107 events strange particles’ v2 out to ~ 10 GeV/c

Page 18: ALICE: towards the first Pb-Pb run

Identified particles pT

• @ RHIC : as many - (K-) as p () at pT ~ 1.5 2.5 GeV

FA - ALICE - LHCC - 22 September 2010 18

Page 19: ALICE: towards the first Pb-Pb run

e.g.: identified particles Rcp

• @ RHIC: suppression sets on at larger pT for baryons

FA - ALICE - LHCC - 22 September 2010 19

central AA,

periphAA,

periph AA,

central AA,cp Yield

Yield

Ncoll

NcollR

S.Bass @ SQM`04

• recombination?

e.g.: 106 central Λ, K0s out to ~ 10 GeV

Page 20: ALICE: towards the first Pb-Pb run

• e.g.: disappearance of away-side peak at RHIC

• STAR Au-Au sample ~ 1.5 106 central

trigger particle: 4 < pT < 6 GeV/cassociated particles: pT > 2 GeV/c

High pT correlations

FA - ALICE - LHCC - 22 September 2010 20

Adams et al., Phys. Rev. Let. 91 (2003) 072304

q

q

hadronsleadingparticle

is this what happens?

Page 21: ALICE: towards the first Pb-Pb run

Quarkonia• present status:

SPS RHIC LHC

very similar suppression at RHIC and SPS... only ’and c melt? J/ melting

compensated by cc recombination?

larger J/ finally melts?

more cc reco dominates?

F.Karsch et al.: PLB637 75 (2006)

• performance critically dependent on L eg: for 2 µb-1, no suppression, no enhancement a few 1000s J/ψ

say 5 centrality bins significance ~ 15-20out to 6-7 GeV pT?

ψ’ marginal…a few 10s of Y at significance ~ 5?

21FA - ALICE - LHCC - 22 September 2010

Page 22: ALICE: towards the first Pb-Pb run

What about charm?

• heavy flavour: study colour charge and parton mass dependence of parton energy loss

• for O(106) central, ~ multiply errors by 3 marginal…

needs as much statistics as possible!

FA - ALICE - LHCC - 22 September 2010 22

• expected performance for 107 central Pb-Pb events at 2.75 TeV

Page 23: ALICE: towards the first Pb-Pb run

-jet

Poster by R Diaz

Poster Y Mao

Jets?

Jets are copiously produced…

pt (GeV)2 20 100 200

100/event 1/event 103 in first 106 Pb-Pb events

Underlying event fluctuationsSingle particle spectraCorrelation studies

4 108 central PbPb collisions (month)

6 105 events

ALICE Acceptance

ET threshold

Njets

50 GeV 5 104

100 GeV 1.5 103

150 GeV 300

200 GeV 50

106 central PbPb events

1.5 103 events

106 central Pb-Pb events

FA - ALICE - LHCC - 22 September 2010 23

Page 24: ALICE: towards the first Pb-Pb run

pp reference at s = 2.76 TeV

• modifications of particle production in Pb-Pb v pp

– e.g.: “nuclear modification factor” RAA: ratio of (suitably normalised) pT

distributions in Pb-Pb and pp

needs pp reference

– at high pT rely on pQCD interpolation between 0.9 and 7 TeV

– at low pT constrain with reference sample

• ~ 5 107 events (2 – 3 fills) would do

• depending on how run is going, we may want to request such a short pp run (at the end) asked machine to evaluate time

needed for switch if not done this year, as soon as

possible next year

• e.g.: uncertainty from pQCD at low pT

FA - ALICE - LHCC - 22 September 2010 24

R Sassot et al.: arXiv: 1008.0540 [hep-ph]

Page 25: ALICE: towards the first Pb-Pb run

Conclusions

• ALICE in stable running, producing good quality data, ready for Pb-Pb operation

• we are eagerly waiting for the first heavy-ion run:

essential information on general features of Pb-Pb events at LHC

+ a glimpse of harder physics

• rich and versatile apparatus

looking forward to surprises!

FA - ALICE - LHCC - 22 September 2010 25