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

Production of light flavor hadrons at intermediate and high p T measured with ALICE Michael Linus Knichel for the ALICE Collaboration Universität Heidelberg May 19, 2014

Particle production at intermediate and high p T pp p-Pb Pb-Pb Pb p p p Pb Pb • test of pQCD • fragmentation • initial and final state cold functions nuclear matter effects • collective effects • tuning of MC • collective effects? • parton energy loss generators • reference for Pb-Pb • modified • reference for fragmentation? p-Pb and Pb-Pb Eskola et al., JHEP 0904:065,2009 Michael L. Knichel Quark Matter 2014, 19.05.2014 2 .

The ALICE detector EMCAL ITS: - electrons SPD-SDD-SSD - γ , π 0 TPC - trigger (SPD) - tracking - tracking - PID - vertex - PID VZERO HMPID - trigger - PID - multiplicity - centrality TRD: 2.8 < η lab < 5.1 - electron ID -3.7 < η lab < -1.7 - tracking Muon spectrometer TOF ZDC - PID magnet - multiplicity B = 0.5 T - control trigger TPC: full length tracks for | η lab | < 0.8 Michael L. Knichel Quark Matter 2014, 19.05.2014 3 .

p T resolution with ALICE detector • best p T resolution with combined TPC+ITS tracking • currently: σ ( p T )/ p T ~ 10% at p T = 50 GeV/ c (pp, Pb-Pb) • p-Pb: improved reconstruction, expected also for pp and Pb-Pb σ ( p T )/ p T ~ 1% at p T = 1 GeV/ c σ ( p T )/ p T ~ 3% at p T = 50 GeV/ c ALICE Collaboration, arXiv:1402.4476 [nucl-ex] Michael L. Knichel Quark Matter 2014, 19.05.2014 4 .

Charged particles in pp • pp is not simple pQCD • uncertainties of NLO only from scale variations μ = 2 p T , μ = p T /2 • PDF and FF uncertainties not included μ r = μ f = μ f‘ = μ = p T NLO: Sassot, Zurita, Stratmann, Phys.Rev D 82, 074011 (2010) PDF: CTEQ6.6M FF: DSS ALICE Collaboration, Eur.Phys.J.C (2013) 73:2662 • 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 Michael L. Knichel Quark Matter 2014, 19.05.2014 5 .

pp reference for p-Pb for R pPb a pp reference spectrum is needed ( √ s = 5.02 TeV) • ratio of pp cross sections NLO scaling: at different energies well • charged particles p T > 5 GeV/ c described by NLO ALICE Collaboration, Eur. Phys. J. C (2013) 73:2662 power law interpolation in √ s: • charged particles p T < 5 GeV/ c • π , K, p Michael L. Knichel Quark Matter 2014, 19.05.2014 6 .

Charged particles in p-Pb • minimum bias trigger • NSD collisions • 2013 data, L int = 50.7 µb -1 • 0.15 < p T < 50 GeV/ c • reduced systematic uncertainties • softer spectrum at backward rapidity (Pb side) • in the ratio of η intervals many systematic uncertainties cancel sign convention: proton goes to y > 0, η cms > 0 ALICE Collaboration, arXiv:1405.2737 [nucl-ex] Michael L. Knichel Quark Matter 2014, 19.05.2014 7 .

R pPb of charged particles nuclear modification factor: (pp reference: η < 0.8) • N coll scaling at high p T • N part scaling at low p T N part scaling • small Cronin-like enhancement at ALICE Collaboration, arXiv:1405.2737 [nucl-ex] intermediate p T · R pPb Ò p T ± ± ± (GeV/ c ) | η cms |<0.3 stat. syst. norm. 10-20 0.995 0.007 0.084 0.06 N part scaling 20-28 0.990 0.031 0.090 0.06 28-50 0.969 0.056 0.090 0.06 ‚ T pPb Ò = ‚ N coll Ò / σ NN ; σ NN = 70 ± 5 mb (interpolation) ⇒ σ tot = 2.1 b; ‚ b Ò = 5.56 fm; ‚ N coll Ò = 6.9 ± 0.6; ‚ T pPb Ò = 0.0983 ± 0.0035 mb -1 Michael L. Knichel Quark Matter 2014, 19.05.2014 8 .

Comparison of R pPb to other measurements • ALICE charged jets R pPb • CMS: consistent with unity up to strong anti-shadowing at large p T p T,jet = 100 GeV/ c – not seen in ALICE data • also pp references are different jet R pPb : M. Connors (poster E-06) R. Haake (poster E-09) • ATLAS (0-90%, p T < 22 GeV/ c ) R pPb in agreement with ALICE Michael L. Knichel Quark Matter 2014, 19.05.2014 9 .

R pPb compared to models ALICE Collaboration, arXiv:1405.2737 [nucl-ex] • NLO with EPS09s nPDF: agrees for p T > ~6 GeV/ c • LO with cold nuclear matter effects: not supported by data • HIJING 2.1: stronger decrease of R pPb with p T 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 not included in the Figure: CGC predictions are for low p T and agree with the data • (rcBK-MC, Albacete et al. Nucl. Phys. A 897, 2013) EPOS3 with hydro describes R pPb and the spectra (within ~20%) • (K. Werner et al., arXiv:1312.1233) PHSD transport model does not describe the spectra for p T > 2 GeV/ c • (V. P. Konchakovski et al., arXiv:1401.4409) Michael L. Knichel Quark Matter 2014, 19.05.2014 10 .

Particle Identification in ALICE ALICE Collaboration, arXiv:1402.4476 [nucl-ex] ALICE Collaboration, arXiv:1402.4476 [nucl-ex] • remark TPC d E /d x ITS d E /d x ALICE Collaboration, arXiv:1402.4476 [nucl-ex] ALICE Collaboration, arXiv:1402.4476 [nucl-ex] Time-of-flight HMPID Cherenkov Michael L. Knichel Quark Matter 2014, 19.05.2014 11 .

TPC relativistic rise d E /d x • fit of 4 Gaussians ( π , K, p, e) in intervals of η and p T • peak positions and width fixed from identified particles • π , K, p spectra on statistical basis for 3 < p T < 20 GeV/ c ε 2 2 d N E d N N = × × π π π ch from TPC d E /d x η ε dydp p d dp N T T ch ch Michael L. Knichel Quark Matter 2014, 19.05.2014 12 .

Identified hadron spectra in p-Pb collisions p-Pb • multiplicity classes from V0A detector • spectra combined from low- p T and high- p T analysis π K p • harder spectra for higher multiplicities • mass ordering of π , K, p: harder spectra � larger mass Michael L. Knichel Quark Matter 2014, 19.05.2014 13 .

Identified hadron spectra in Pb-Pb collisions Pb-Pb • shape of the spectrum in Pb-Pb differs from pp reference • difference most pronounced in central collisions π K p ALICE Collaboration, arXiv:1401.1250 [nucl-ex] Michael L. Knichel Quark Matter 2014, 19.05.2014 14 .

Identified hadron ratios p-Pb p-Pb • no multiplicity dependence in K/ π • K/ π ratio reaches ~0.55 at high p T K/ π p/ π • enhancement of protons at intermediate p T (2-6 GeV/ c ) • p/ π ratio ~0.1 at high p T • results from low- p T (< 3 GeV/ c ) and high- p T (> 3 GeV/ c ) analysis Michael L. Knichel Quark Matter 2014, 19.05.2014 15 .

Identified hadron ratios in Pb-Pb collisions • p/ π up to ~0.8 around p T = 3 GeV/ c (central 0-5%) Pb-Pb • K/ π and p/ π diferent from pp at intermediate p T (radial flow) • at large p T particle fractions do not differ from those in pp p/ π K/ π ALICE Collaboration, arXiv:1401.1250 [nucl-ex] Michael L. Knichel Quark Matter 2014, 19.05.2014 16 .

Identified hadron R pPb • pp reference from interpolation p-Pb • π , K not different charged particle R pPb π K p • mass ordering in the Cronin-region: π , K, p, Ξ Ξ • notable enhancement for p, Ξ • Cronin peak in charged R pPb from protons • R pPb of π , K, p consistent with unity at large p T strange baryons: D. Alexandre, Wed 9:00 Michael L. Knichel Quark Matter 2014, 19.05.2014 17 .

Identified hadron R AA • mass ordering at intermediate p T Pb-Pb • less suppression of protons at intermediate p T • at large p T (> 8 GeV/ c ) no difference between particle species ALICE Collaboration, arXiv:1401.1250 [nucl-ex] Michael L. Knichel Quark Matter 2014, 19.05.2014 18 .

Summary/Conclusion • no deviation from N coll scaling in high p T p-Pb • at large p T R pPb and R AA universal for hadron species particle ratios not different from pp � vacuum fragmentation • mass ordering at intermediate p T similar in p-Pb and Pb-Pb (flow?) • Cronin enhancement in p-Pb caused by protons • description of R pPb over full p T range remains a challenge for models ALICE, Phys. Lett. B 720 (2013) 52–62 CMS, Phys.Rev.Lett.106:212301,2011 CMS, Eur. Phys. J. C 72 (2012) 1945 CMS, Phys. Lett. B 710 (2012) 256 CMS, Phys. Lett. B 715 (2012) 66 ALICE, arXiv:1405.2737 [nucl-ex] collective effects: C. Andrei, Mon 12:00 Michael L. Knichel Quark Matter 2014, 19.05.2014 19 .

Additional Slides

EPS09 nPDF for Pb nuclei Eskola et al., JHEP 0904:065,2009 Michael L. Knichel Quark Matter 2014, 19.05.2014 21 .

R CP of jets and charged particles • R CP of charged jets similar to R CP of charged hadrons at comparable parton p T 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 Michael L. Knichel Quark Matter 2014, 19.05.2014 22 .

R AA double ratio • partial cancellation of systematic uncertainties ALICE Collaboration, arXiv:1401.1250 [nucl-ex] Michael L. Knichel Quark Matter 2014, 19.05.2014 23 .