two- and three-particle jet- like correlations in the …...30 summary 2- and 3-particle jet-like...
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Two- and Three-Particle Jet-Two- and Three-Particle Jet-like Correlations in the ALICE like Correlations in the ALICE
Experiment at the LHCExperiment at the LHCJason Glyndwr UleryJason Glyndwr Ulery
For the ALICE CollaborationFor the ALICE CollaborationUniversity of FrankfurtUniversity of Frankfurt
55thth High-pT Physics at the LHC, Mexico High-pT Physics at the LHC, Mexico28 September 201028 September 2010
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Outline
● Motivation● 2-Particle Correlations
● ∆φ● ∆φ−∆η● jT and kT
● 3-Particle Correlations● ∆φ−∆φ
● Summary
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ALICE Experiment
● A Large Ion Collider Experiment
● Dedicated heavy-ion experiment at the LHC.
● Analysis uses chaged tracks in:● Time Projection
Chamber● Inner Tracking System
– Silicon pixel, strips and drift.
TPC
ITS
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Motivation
● Heavy-ions:● Probe medium created using jets:
– Modification of medium by the jet.– Modification of jet by the medium.– At prior experiments interesting effects seen:
● Energy loss and away-side suppression● Near-side ridge● Conical emission
● pp Collsions:● Reference for heavy-ion data● Study jet properties.
7 TeV pp Collisionin ALICE
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Jet-Like Correlations
● Study angular correlations between intermediate and high pT trigger particles and lower pT associated particles.
● ∆φ=φTrigger-φAssociated
● ∆η=ηTrigger-ηAssociated
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Unsubtracted Correlations
● Single particle efficiency corrected.● Mixed event acceptance corrected.
|∆φ|<1.5
|∆φ|>1.5
7 TeV pp4<pT
Trigger<6 GeV/c0.25<pT
Assoc<4 GeV/c|ηAssociated|<0.8
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Background Subtraction
● Background from mixed events.
● Triggering biases background level.
● Jet signal positive definite● Maximum level of
background is Zero Yield At Minimum.
● Normalizing to● |∆φ±1.5|<0.2 radians.
|∆φ|<1.5
7 TeV pp4<pT
Trigger<6 GeV/c0.25<pT
Assoc<4 GeV/c|η|<0.8
Normalized Mixed Event
Mixed Event
Mixed Event
Normalized Mixed Event
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Prior ExperimentsAway-Side Suppression
● Away-side in central Au+Au was found to almost entirely disappear for intermediate (~2 GeV/c) pT associated.
● Returns (but suppressed relative to d+Au) for high pT associated.
PRL 90 082302PRL 91 072304 PRL97 162301
STAR 200 GeV
STAR 200 GeV
4<pTTrig<6 GeV/c
2<pTAssoc<pT
Trig GeV/c
8<pTTrig<15
pTAssoc>6 GeV/c
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Prior ExperimentsAway-side Modification
● Enhanced and broadened away-side in heavy-ions for low and intermediate pT.
● Even dipped for associated ~1 GeV/c
STAR 200 GeV PRL 95 152301Ulery QM05
PHENIX 200 GeVPRL 97 052301
●0-5% Au+AuCERES 17.3 GeVPL B678 259
4<pTTrig<6, 0.15<pT
Assoc<4 GeV/c 2.5<pTTrig<4, 1<pT
Assoc<2.5 GeV/c
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Prior ExperimentsRidge
200 GeV
STARPRC 80 649120-10% Au+Au, d+Au3<pT
Trigger<4 GeV/cpT
Assoc>2 GeV/c
PHOBOSPreliminaryWenger, QM080-30% Au+AupT
Trigger>2.5 GeV/cpT
Assoc>0.02 GeV/c
● Near-side ridge correlated in azimuth but not pesudorapidity seen in heavy-ions. ● Not present in minimum bias d+Au
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Pythia Comparison Unsubtracted
● Perugia-0 tune of Pythia has less particles in triggered events then the data.
4<pTTrigger<6 GeV/c
0.25<pTAssoc<4 GeV/c
|η|<0.8
7 TeV 900 GeV
Pythia tune Perugia-0
Performance21-09-2010
Performance21-09-2010
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Pythia Comparison
● Near-side peak increases with energy.● Pythia reproduces 900 GeV fairly well.
7 TeV 900 GeV
4<pTTrigger<6 GeV/c
0.25<pTAssoc<4 GeV/c
|η|<0.8
Performance21-09-2010
Performance21-09-2010
Pythia tune Perugia-0
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2-D Comparison7 TeV 900 GeV
3<pTTrigger<4 GeV/c
2<pTAssoc<3 GeV/c
Pythia Pythia
● No “ridge” structure present in minimum bias pp.
● Data is similar to Pythia.● Near-side peak
larger in Pythia at 7 TeV.
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2-D Comparison 7 TeV 900 GeV
2.5<pTTrig<20 GeV/c
0.25<pTAssoc<2.5 GeV/c
Pythia
● No “ridge” structure for low-pT associated in minimum bias pp.
Pythia
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Jet Fragmentation Transverse Momentum
● pT of jet particles perpendicular to the jet-axis.
● No significant pT dependence.
● No significant energy dependence.
● Only statistical errors shown.
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kT
● kT is initial transverse momentum of the partons in the hard-scattering
● Statistical errors only.
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3-Particle Correlations
● Select an intermediate or high-pT trigger particle.
● Look at relative angles between trigger and 2 other particles.
● ∆φ1=φTrigger-φAssociated,1
● ∆φ2=φTrigger-φAssociated,2
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3-Particle Correlations
● Select an intermediate or high-pT trigger particle.
● Look at relative angles between trigger and 2 other particles.
● ∆φ1=φTrigger-φAssociated,1
● ∆φ2=φTrigger-φAssociated,2
● Both particles from jet.● Our signal.
∆φ1
∆φ2
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3-Particle Correlations
● Select an intermediate or high-pT trigger particle.
● Look at relative angles between trigger and 2 other particles.
● ∆φ1=φTrigger-φAssociated,1
● ∆φ2=φTrigger-φAssociated,2
● 1 from jet and 1 from background.● Hard-soft background
∆φ1
∆φ2
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3-Particle Correlations
● Select an intermediate or high-pT trigger particle.
● Look at relative angles between trigger and 2 other particles.
● ∆φ1=φTrigger-φAssociated,1
● ∆φ2=φTrigger-φAssociated,2
● Both from background.● Soft-soft background
∆φ1
∆φ2
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∆φ−∆φ 3-Particle Correlations
Medium
away
near
di-jets
Mediumaway
near
deflected jets, kT
away
near
Medium
Conical Emission
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Prior Experiments
● Conical emission seen in heavy-ion collisions at RHIC.● Not seen in pp or d+Au.
200 GeVSTAR PRL 102:052302Au+Au 0-12% d+Au pp
3<pTTrig<4 GeV/c
1<pTTrig<2 GeV/c
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Prior Experiments
● Conical emission seen in heavy-ion collsions at RHIC.● Not seen in pp or d+Au.
200 GeVSTAR PRL 102:052302Au+Au 0-12% d+Au
3<pTTrig<4 GeV/c
1<pTTrig<2 GeV/c
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Unsubtracted Signal
● Contains:● 3-particle correlations● 2-particle correlations● Uncorrelated particles
7 TeV pp3<pT
Trig<4 GeV/c1<pT
Trig<2 GeV/c
∆φ1=φTrigger-φAssociated,1
∆φ2=
φ Trig
ger-φ
Ass
ocia
ted,
2 Performance21-09-2010
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Hard-Soft Background
● 1 particle jet-like correlated with trigger and 1 from background.
● Constructed from 2-particle correlation and its background.
● J2(∆φ1)⊗aB2(∆φ2)+J2(∆φ2)⊗aB2(∆φ1)
● a from 3-particle ZYAM
7 TeV pp3<pT
Trig<4 GeV/c1<pT
Trig<2 GeV/c
J2
aB2
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Soft-Soft Background
● Uncorrelated background and correlations independent of trigger.
● Constructed by mixing trigger with pairs of associated.
● Normalized by a2b.● a from 3-particle ZYAM● b= ⟨N N−1⟩/ ⟨N ⟩2 Triggered Events
⟨N N−1⟩ / ⟨N ⟩2 Mixed Events
7 TeV pp3<pT
Trig<4 GeV/c1<pT
Trig<2 GeV/c
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Terms
Raw Signal – Hard Soft – Soft Soft
3<pTTrig<4 GeV/c
1<pTTrig<2 GeV/c
7 TeVpp
900 GeVpp
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7 TeV 900 GeV3<pT
Trigger<4 Gev/c1<pT
Assoc<2 GeV/c
Pythia Pythia
● Background Subtracted● No evidence
of conical emission in minimum bias pp.
● Broadening along ∆φ1=∆φ2 diagonal.
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Projections7 TeV pp 900 GeV pp
● Similar away-side projections for both energies● Broadening consistent with kT broadening seen.
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Summary
● 2- and 3-particle jet-like correlations studied in ALICE in pp collisions at √s=900 GeV and 7 TeV.
● These analyses will be performed on heavy-ion data when available and pp provides a base line.
● No indication of medium modification in minimum bias pp collisions.
● Jet properties extracted from pp collisions:● Jet fragmentation transverse momentum measured.● Initial parton transverse momentum measured.● Away-side peak broadening from kT like effect.