Production of light flavor hadrons at intermediate and high p T - - PowerPoint PPT Presentation

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Production of light flavor hadrons at intermediate and high p T - - PowerPoint PPT Presentation

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Production of light flavor hadrons at intermediate and high p T measured with ALICE Michael Linus Knichel for the ALICE Collaboration Universitt Heidelberg May 19, 2014 Particle production at intermediate and high p T pp p-Pb Pb-Pb Pb p p

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SLIDE 1

Production of light flavor hadrons at intermediate and high pT measured with ALICE

Michael Linus Knichel for the ALICE Collaboration

Universität Heidelberg

May 19, 2014

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SLIDE 2

Particle production at intermediate and high pT

Michael L. Knichel Quark Matter 2014, 19.05.2014 2 .

Pb p p p

  • test of pQCD
  • fragmentation

functions

  • tuning of MC

generators

  • reference for

p-Pb and Pb-Pb

  • initial and final state cold

nuclear matter effects

  • collective effects?
  • reference for Pb-Pb
  • collective effects
  • parton energy loss
  • modified

fragmentation?

Eskola et al., JHEP 0904:065,2009

pp p-Pb Pb-Pb

Pb Pb

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SLIDE 3

The ALICE detector

Michael L. Knichel Quark Matter 2014, 19.05.2014 3 .

ITS: SPD-SDD-SSD

  • trigger (SPD)
  • tracking
  • vertex
  • PID

TPC

  • tracking
  • PID

TRD:

  • electron ID
  • tracking

magnet B = 0.5 T TOF

  • PID

EMCAL

  • electrons
  • γ, π0

ZDC

  • multiplicity
  • control trigger

Muon spectrometer TPC: full length tracks for |ηlab| < 0.8 VZERO

  • trigger
  • multiplicity
  • centrality

2.8 < ηlab < 5.1

  • 3.7 < ηlab < -1.7

HMPID

  • PID
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SLIDE 4

pT resolution with ALICE detector

Michael L. Knichel Quark Matter 2014, 19.05.2014 4 .

  • best pT resolution with combined TPC+ITS tracking
  • currently: σ(pT)/pT ~ 10% at pT = 50 GeV/c (pp, Pb-Pb)
  • p-Pb: improved reconstruction, expected also for pp and Pb-Pb

ALICE Collaboration, arXiv:1402.4476 [nucl-ex]

σ(pT)/pT ~ 1% at pT = 1 GeV/c σ(pT)/pT ~ 3% at pT = 50 GeV/c

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SLIDE 5

Charged particles in pp

  • pp is not simple pQCD
  • uncertainties of NLO only from scale

variations μ = 2pT, μ = pT/2

  • PDF and FF uncertainties not included

Michael L. Knichel Quark Matter 2014, 19.05.2014 5 . ALICE Collaboration, Eur.Phys.J.C (2013) 73:2662 NLO: Sassot, Zurita, Stratmann, Phys.Rev D 82, 074011 (2010)

μr = μf = μf‘ = μ = pT PDF: CTEQ6.6M FF: DSS

  • NLO overpredicts the cross

section by up to a factor 2

  • jet spectra are well described

e.g. ALICE, Phys. Lett. B 722(2013) 262-272

FF too hard at LHC energy

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SLIDE 6

pp reference for p-Pb

Michael L. Knichel Quark Matter 2014, 19.05.2014 6 .

power law interpolation in √s:

  • charged particles pT < 5 GeV/c
  • π, K, p

for RpPb a pp reference spectrum is needed (√s = 5.02 TeV)

  • ratio of pp cross sections

at different energies well described by NLO

ALICE Collaboration, Eur. Phys. J. C (2013) 73:2662

NLO scaling:

  • charged particles pT > 5 GeV/c
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SLIDE 7

Charged particles in p-Pb

Michael L. Knichel Quark Matter 2014, 19.05.2014 7 .

  • minimum bias trigger
  • NSD collisions
  • 2013 data, Lint = 50.7 µb-1
  • 0.15 < pT < 50 GeV/c
  • reduced systematic

uncertainties

  • softer spectrum at

backward rapidity (Pb side)

  • in the ratio of η intervals

many systematic uncertainties cancel

ALICE Collaboration, arXiv:1405.2737 [nucl-ex]

sign convention: proton goes to y > 0, ηcms > 0

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SLIDE 8

RpPb of charged particles

Michael L. Knichel Quark Matter 2014, 19.05.2014 8 .

nuclear modification factor:

(pp reference: η < 0.8)

Npart scaling Npart scaling

  • Ncoll scaling at high pT
  • Npart scaling at low pT
  • small Cronin-like

enhancement at intermediate pT

ALICE Collaboration, arXiv:1405.2737 [nucl-ex]

pT (GeV/c) ·RpPbÒ |ηcms|<0.3 ± stat. ± syst. ± norm. 10-20 0.995 0.007 0.084 0.06 20-28 0.990 0.031 0.090 0.06 28-50 0.969 0.056 0.090 0.06 ‚TpPbÒ = ‚NcollÒ / σNN; σNN = 70 ± 5 mb (interpolation) ⇒ σtot = 2.1 b; ‚bÒ = 5.56 fm; ‚NcollÒ = 6.9 ± 0.6; ‚TpPbÒ = 0.0983 ± 0.0035 mb-1

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SLIDE 9

Comparison of RpPb to other measurements

Michael L. Knichel Quark Matter 2014, 19.05.2014 9 .

  • CMS:

strong anti-shadowing at large pT – not seen in ALICE data

  • also pp references are different
  • ALICE charged jets RpPb

consistent with unity up to pT,jet = 100 GeV/c

  • ATLAS (0-90%, pT < 22 GeV/c) RpPb in agreement with ALICE

jet RpPb: M. Connors (poster E-06)

  • R. Haake (poster E-09)
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SLIDE 10

RpPb compared to models

Michael L. Knichel Quark Matter 2014, 19.05.2014 10 .

not included in the Figure:

  • CGC predictions are for low pT and agree with the data

(rcBK-MC, Albacete et al. Nucl. Phys. A 897, 2013)

  • EPOS3 with hydro describes RpPb and the spectra (within ~20%)

(K. Werner et al., arXiv:1312.1233)

  • PHSD transport model does not describe the spectra for pT > 2 GeV/c

(V. P. Konchakovski et al., arXiv:1401.4409)

  • NLO with EPS09s nPDF:

agrees for pT > ~6 GeV/c

  • LO with cold nuclear matter

effects: not supported by data

  • HIJING 2.1: stronger decrease
  • f RpPb with pT not seen in data
  • none of the models reproduces

the Cronin enhancement

NLO+EPS09s: Helenius et al., JHEP 1207 (2012) 073 LO+CNM: Kang et al., Phys.Lett. B718 (2012) 482-487 HIJING: Xu et al., Phys.Rev. C86 (2012) 051901 ALICE Collaboration, arXiv:1405.2737 [nucl-ex]

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SLIDE 11

Particle Identification in ALICE

Michael L. Knichel Quark Matter 2014, 19.05.2014 11 .

  • remark

ALICE Collaboration, arXiv:1402.4476 [nucl-ex] ALICE Collaboration, arXiv:1402.4476 [nucl-ex]

Time-of-flight ITS dE/dx TPC dE/dx HMPID Cherenkov

ALICE Collaboration, arXiv:1402.4476 [nucl-ex] ALICE Collaboration, arXiv:1402.4476 [nucl-ex]

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SLIDE 12

TPC relativistic rise dE/dx

Michael L. Knichel Quark Matter 2014, 19.05.2014 12 .

  • fit of 4 Gaussians (π, K, p, e) in intervals of η and pT
  • peak positions and width fixed from identified particles
  • π, K, p spectra on statistical basis for 3 < pT < 20 GeV/c

ch ch T ch T

N N dp d N d p E dydp N d

π π π

ε ε η × × =

2 2

from TPC dE/dx

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SLIDE 13

Identified hadron spectra in p-Pb collisions

Michael L. Knichel Quark Matter 2014, 19.05.2014 13 .

  • multiplicity classes from V0A detector
  • spectra combined from low-pT and high-pT analysis
  • harder spectra for higher multiplicities
  • mass ordering of π, K, p: harder spectra larger mass

π K p

p-Pb

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SLIDE 14

Identified hadron spectra in Pb-Pb collisions

Michael L. Knichel Quark Matter 2014, 19.05.2014 14 .

  • shape of the spectrum in Pb-Pb differs from pp reference
  • difference most pronounced in central collisions

ALICE Collaboration, arXiv:1401.1250 [nucl-ex]

π K p

Pb-Pb

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SLIDE 15

Identified hadron ratios p-Pb

Michael L. Knichel Quark Matter 2014, 19.05.2014 15 .

  • no multiplicity dependence in K/π
  • K/π ratio reaches ~0.55 at high pT

K/π p/π

  • enhancement of protons at intermediate pT (2-6 GeV/c)
  • p/π ratio ~0.1 at high pT
  • results from low-pT (< 3 GeV/c) and high-pT (> 3 GeV/c) analysis

p-Pb

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SLIDE 16

Identified hadron ratios in Pb-Pb collisions

Michael L. Knichel Quark Matter 2014, 19.05.2014 16 .

  • p/π up to ~0.8 around pT = 3 GeV/c (central 0-5%)
  • K/π and p/π diferent from pp at intermediate pT (radial flow)
  • at large pT particle fractions do not differ from those in pp

ALICE Collaboration, arXiv:1401.1250 [nucl-ex]

K/π p/π

Pb-Pb

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SLIDE 17

Identified hadron RpPb

Michael L. Knichel Quark Matter 2014, 19.05.2014 17 .

  • pp reference from interpolation
  • π, K not different charged particle RpPb

π K p

  • mass ordering in the Cronin-region: π, K, p, Ξ
  • notable enhancement for p, Ξ
  • Cronin peak in charged RpPb from protons
  • RpPb of π, K, p consistent with unity at large pT

Ξ

p-Pb

strange baryons: D. Alexandre, Wed 9:00

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SLIDE 18

Identified hadron RAA

Michael L. Knichel Quark Matter 2014, 19.05.2014 18 .

  • mass ordering at intermediate pT
  • less suppression of protons

at intermediate pT

  • at large pT (> 8 GeV/c) no difference

between particle species

ALICE Collaboration, arXiv:1401.1250 [nucl-ex]

Pb-Pb

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SLIDE 19
  • no deviation from Ncoll scaling in high pT p-Pb
  • at large pT RpPb and RAA universal for hadron species

particle ratios not different from pp vacuum fragmentation

  • mass ordering at intermediate pT similar in p-Pb and Pb-Pb (flow?)
  • Cronin enhancement in p-Pb caused by protons
  • description of RpPb over full pT range remains a challenge for models

Summary/Conclusion

Michael L. Knichel Quark Matter 2014, 19.05.2014 19 . ALICE, Phys. Lett. B 720 (2013) 52–62 CMS, Eur. Phys. J. C 72 (2012) 1945 ALICE, arXiv:1405.2737 [nucl-ex] CMS, Phys. Lett. B 710 (2012) 256 CMS, Phys. Lett. B 715 (2012) 66 CMS, Phys.Rev.Lett.106:212301,2011

collective effects: C. Andrei, Mon 12:00

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SLIDE 20

Additional Slides

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SLIDE 21

EPS09 nPDF for Pb nuclei

Michael L. Knichel Quark Matter 2014, 19.05.2014 21 . Eskola et al., JHEP 0904:065,2009

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SLIDE 22

RCP of jets and charged particles

Michael L. Knichel Quark Matter 2014, 19.05.2014 22 .

  • RCP of charged jets similar to RCP of charged hadrons at

comparable parton pT

ALICE Collaboration, arXiv:1405.1849 [nucl-ex] ALICE Collaboration, Phys.Lett. B720 (2013) 52-62 ATLAS Collaboration, Phys.Lett. B719 (2013) 220-241 CMS Collaboration, Eur.Phys.J. C72 (2012) 1945

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SLIDE 23

RAA double ratio

Michael L. Knichel Quark Matter 2014, 19.05.2014 23 . ALICE Collaboration, arXiv:1401.1250 [nucl-ex]

  • partial cancellation of systematic uncertainties
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SLIDE 24

RpPb compared to predictions

Michael L. Knichel Quark Matter 2014, 19.05.2014 24 .

  • gluon saturation models (CGC)

are in agreement with the data

  • NLO with EPS09s PDF and

DSS fragmentation functions are also in agreement

  • LO pQCD + cold nuclear

matter: too low at high pT

  • none of the HIJING 2.1

predictions are consistent with the data in the full pT range

  • DPMJET (not shown)

describing dN/dη very well, but fails to describe RpPb

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SLIDE 25

RpPb: comparison to ATLAS

Michael L. Knichel Quark Matter 2014, 19.05.2014 25 . ATLAS Collaboration, ATLAS-CONF-2013-107

  • pilot run data

ALICE: Phys.Rev.Lett. 110 (2013)

  • ATLAS 0-90% centrality
  • consistent within

uncertainties

  • no sign of Cronin-

enhancement in ATLAS data

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SLIDE 26

p/π ratio in p-Pb and Pb-Pb

Michael L. Knichel Quark Matter 2014, 19.05.2014 26 .

  • similar trend vs. centrality/multiplicity
  • much stronger „baryon enhancement“ in Pb-Pb
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SLIDE 27

RAA of charged π, K, p

Michael L. Knichel Quark Matter 2014, 19.05.2014 27 .

0-5% central 60-80% central

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SLIDE 28

p-Pb collision geometry

Michael L. Knichel Quark Matter 2014, 19.05.2014 28 .

|∆ycm|= 0.465 p ηlab < 0 y > 0 ηcms > 0 p 4 TeV Pb 1.58 ATeV Pb ηlab > 0 y < 0 ηcms < 0 √sNN = 5.02 TeV Pb 1.58 ATeV p 4 TeV p-Pb Pb-p √sNN = 5.02 TeV |∆ycm|= 0.465 Pb ηlab < 0 y < 0 ηcms < 0 p ηlab > 0 y > 0 ηcms > 0 the direction fo the proton is always at positive y ≡ ycms and positive ηcms

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SLIDE 29

Transverse momentum resolution in Pb-Pb

  • pT resolution almost

independent of multiplicity

  • same performance

in pp and Pb-Pb

  • resolution estimated from

covariance matrix of the Kalman Filter algorithm used for tracking

  • verified with invariant mass

analysis of K0 -> π+π- and cosmic ray measurements

  • syst. uncertainty on the

resolution ~20%

Michael L. Knichel Quark Matter 2014, 19.05.2014 29 .

resolution: σ(pT)/pT ~10% at 50 GeV/c

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SLIDE 30

Track selection & ALICE performance

  • tracking based on combined information from TPC and ITS
  • two hits in the ITS, one in the innermost two layers (SPD)
  • long tracks in the TPC selected (resolution at high pT)
  • tracks must point to the primary vertex

Michael L. Knichel Quark Matter 2014, 19.05.2014 30 .

  • verall acceptance × efficiency lower than TPC efficiency
  • contamination corresponds to strict DCA cuts

ALICE Collaboration, arXiv:1402.4476 [nucl-ex] ALICE Collaboration, arXiv:1402.4476 [nucl-ex]

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SLIDE 31

PID in ALICE

Michael L. Knichel Quark Matter 2014, 19.05.2014 31 . ALICE Collaboration, arXiv:1402.4476 [nucl-ex]