Workshop on proton-nucleus collisions at the LHC ALICE results on identified particle spectra in p-pb collisions for the ALICE Collaboration Museo Storico della Fisica e Centro Studi e Ricerche Enrico Fermi, Roma INFN, Sezione di Bologna ECT* Trento, 6th 10th May 2013
Outline ALICE overview the ALICE detector definition of multiplicity classes in p-pb central-barrel particle identification Transverse momentum spectra in p-pb ± ± 0 π K K S p(p) Λ(Λ) over a wide pt range Hadron-production vs. multiplicity particle-production ratios and pt 0 K/π, p/π and Λ/K S ratios vs. pt comparison with Pb-Pb and pp results Spectral-shape analysis and hydro models global Blast-Wave fits and parameters comparison with Pb-Pb and PYHTIA comparison with viscous hydro predictions Summary and conclusions 2
The ALICE experiment at LHC a dedicated heavy-ion experiment at the LHC designed to cope with very high chargedparticle multiplicities dnch/dη 8000 3D tracking with TPC moderate B = 0.5 T thin materials for low-pt particles uses all known PID techniques de/dx time-of-flight transition radiation Cherenkov radiation calorimetry muon filters topological decay 3
The ALICE detector p Pb ycms = 0.465 ITS TOF TPC VZERO, T0 ALICE sub-detectors relevant for this analysis: VZERO ITS TPC TOF (+T0) trigger, beam-bkg rejection, multiplicity classes tracking + vertexing tracking + vertexing + PID (de/dx) PID (time-of-flight) p-pb multiplicity 0-5% (high) 60-80% (low) 4
p-pb analysis and multiplicity selection Analysis performed with p-pb collision data collected in 2013 at the LHC snn = 5.02 TeV asymmetric energy/nucleon in the beams cms moves with rapidity ylab = -0.468 measurement performed in 0.0 < ycms < 0.5 p Pb VZERO-A The correlation between protonnucleus collision geometry and particle multiplicity is not trivial We define seven p-pb multiplicity event classes based on the amplitude of the signal of VZERO-A (V0A) detector (A is the direction of Pb beam) V0A signal proportional to chargedparticle multiplicity in 2.8 < ηlab < 5.1 from high- to low-multiplicity: 0-5% 5-10% 10-20% 20-40%... 5
± ± Particle-identification: π K p(p) TPC: main tracking detector PID via de/dx in gas up to 159 samples, σ ~5% TOF: PID at intermediate momenta PID via time-of-flight technique σ < 100 ps 3σ K/π separation up to 2.5 GeV/c 3σ p/π separation up to 4.0 GeV/c 6
0 S Topological reconstruction: K Λ(Λ) p V0-decays: topological reconstruction identification over a large pt range reconstruction of candidate weak-decays TPC de/dx selection of daughters invariant mass extraction of signal 0 K + S π π - Λ IP Λ p πλ p π+ π 7
Transverse momentum spectra pt spectra in several V0A multiplicity classes π± K± p(p) K0 S Λ(Λ) 0.2 3.0 GeV/c 0.25 2.5 GeV/c 0.45 4.0 GeV/c 0 6.0 GeV/c 0.6 6.0 GeV/c 8
Transverse momentum spectra dotted lines: individual Blast-Wave fits for low/high-pt extrapolation π± K± p(p) K0 S Λ(Λ) 0.2 3.0 GeV/c 0.25 2.5 GeV/c 0.45 4.0 GeV/c 0 6.0 GeV/c 0.6 6.0 GeV/c 9
Particle ratios vs. charged-multiplicity systematic errors are largely correlated across multiplicity K/π integrated ratio vs. dnch/dη: p/π integrated ratio vs. dnch/dη: in line with the trend of Pb-Pb and lower-energy RHIC results hints at a small increase with multiplicity also in p-pb collisions in line with the values of pp, Pb-Pb and lower-energy RHIC results no significant evolution with multiplicity in p-pb collisions ALICE, arxiv:1303.0737 [hep-ex] STAR, PRC 79, 034909 (2009) PHENIX, PRC 69, 03409 (2004) BRAHMS, PRC 72, 014908 (2005) 10
Particle ratios vs. charged-multiplicity systematic errors are largely correlated across multiplicity Λ/K0S integrated ratio vs. dnch/dη: Λ/π integrated ratio vs. dnch/dη: in line with the values of pp, Pb-Pb and lower-energy RHIC results no significant evolution from low to high multiplicity in line with the values of pp, Pb-Pb and lower-energy RHIC results hints at a small increase at low multiplicity in p-pb STAR, PRC 79, 034909 (2009) STAR, PRL 108, 072301 (2012) 11
pt vs. charged-multiplicity systematic errors are largely correlated across multiplicity identified-hadron pt vs. dnch/dη: pt increases with multiplicity in p-pb for all particles mass ordering: larger mass larger pt 12
pt vs. charged-multiplicity systematic errors are largely correlated across multiplicity pion and kaon pt vs. dnch/dη: p-pb results show similar behavior as in Pb-Pb pt increases with multiplicity p-pb values higher than Pb-Pb for similar multiplicity harder spectra pp minimum bias value in line with p-pb trend relative increase (low/high multiplicity) similar to Pb-Pb 13
pt vs. charged-multiplicity systematic errors are largely correlated across multiplicity proton pt vs. dnch/dη: protons show similar behavior as pions and kaons pt increases with multiplicity pt higher than Pb-Pb for similar multiplicity pp minimum bias value in line with p-pb trend relative increase (low/high multiplicity) softer than Pb-Pb different behavior wrt. pions and kaons 14
p-pb K/π production ratio vs. pt systematic errors are largely correlated across multiplicity Pb-Pb ALICE, arxiv:1303.0737 [hep-ex] K/π ratio vs. pt: weak evolution with multiplicity in p-pb small increase at intermediate pt with increasing V0A multiplicity corresponding small depletion in the low-pt region hints at similar behavior as observed in Pb-Pb collisions 15
p-pb p/π production ratio vs. pt systematic errors are largely correlated across multiplicity Pb-Pb ALICE, arxiv:1303.0737 [hep-ex] p/π ratio vs. pt: shows similar behavior as observed in Pb-Pb collisions significant increase at intermediate pt with increasing V0A multiplicity corresponding significant depletion in the low-pt region stronger enhancement than K/π Pb-Pb generally understood in terms of collective flow and/or recombination 16
0 p-pb Λ/K S production ratio vs. pt systematic errors are largely correlated across multiplicity Pb-Pb Λ/K0S ratio vs. pt: clear evolution with multiplicity in p-pb significant increase at intermediate pt with increasing V0A multiplicity corresponding significant depletion in the low-pt region also this is reminiscent of nucleus-nucleus phenomenology......generally understood in terms of collective flow and/or recombination 17
p-pb spectral-shape analysis π/k/p spectral-shape analysis: performed with hydromotivated Blast-Wave model Schnedermann, PRC 48, 2462 (1993) aims at characterizing spectral shapes in V0A multiplicity classes with a small set of parameters simultaneous fit of all particles with 3 parameters βt radial flow Tfo freeze-out temperature n velocity profile global fit performed in the following pt ranges: π K p 0.5 1.0 GeV/c 0.3 1.5 GeV/c 0.5 2.0 GeV/c p-pb Blast-Wave fits reasonable, though not very good worse than central Pb-Pb better than pp minimum bias 18
p-pb spectral-shape analysis π/k/p spectral-shape analysis: performed with hydromotivated Blast-Wave model Schnedermann, PRC 48, 2462 (1993) Blast-Wave fits reasonable, though not very good better than pp minimum bias: not successful at very low pt pp p-pb 19
p-pb spectral-shape analysis π/k/p spectral-shape analysis: performed with hydromotivated Blast-Wave model ALICE, arxiv:1303.0737 [hep-ex] Schnedermann, PRC 48, 2462 (1993) Blast-Wave fits reasonable, though not very good worse than central Pb-Pb: successful up to higher pt p-pb Pb-Pb 20
Global Blast-Wave fit parameters π/k/p spectral-shape analysis with hydro-inspired (Blast-Wave) model: p-pb presents similar features as observed in Pb-Pb parameters evolve with increasing multiplicity: larger βt, smaller Tfo Tfo is similar to Pb-Pb for similar multiplicity, βt is larger in p-pb these observations meet theoretical p-pb predictions stronger collective radial flow (smaller system) than Pb-Pb Shuryak, arxiv:1301.4470 [hep-ph] 21
Global Blast-Wave fit parameters π/k/p spectral-shape analysis with hydro-inspired (Blast-Wave) model: p-pb presents similar features as observed in Pb-Pb parameters evolve with increasing multiplicity: larger βt, smaller Tfo Tfo is similar to Pb-Pb for similar multiplicity, βt is larger in p-pb 0 same results when including also Λ and K S in the p-pb global fit 22
Global Blast-Wave fit parameters π/k/p spectral-shape analysis with hydro-inspired (Blast-Wave) model: also PYTHIA shows similar features from this analysis but there is no collective radial flow in PYTHIA... Blast-Wave fit spectral analysis not yet conclusive to shed light on possible collective features (radial flow) predicted in high-multiplicity p-pb data do not exclude hydro-like collective behavior complementary information will come from ID-correlation analysis 23
Comparison with hydro-prediction Prediction from Bozek model Bozek, PRC 85, 014911 (2012) initial conditions form Glauber Monte Carlo E-by-E (3+1)-D viscous hydrodynamic expansion statistical hadronization at freeze-out (Cooper-Frye) Comparison done for similar dnch/dη ALICE (5-10% V0A) dnch/dη = 36.4 ± 0.8 η < 0.5 Bozek (11 Npart 17) dnch/dη = 38.9 η < 1.0 reasonable agreement between data and model data/model ratio rather flat at low pt (where hydro would dominate) arbitrary absolute normalization (approximate multiplicity match) 24
Summary and conclusions ALICE has measured the transverse momentum distribution of identified hadrons in p-pb in several multiplicity classes ± ± 0 π K K S p(p) Λ(Λ) spectra over a wide pt range clear dnch/dη evolution of spectra (dynamical bias? radial flow?) Hadron-production vs. multiplicity integrated particle ratios in line with pp and Pb-Pb pt increases with multiplicity (higher than Pb-Pb for same dnch/dη) 0 evolution of p/π and Λ/K S vs. pt with dnch/dη (hint for K/π) Spectral-shape analysis and hydro models Blast-Wave model fits (characterize shapes, few parameters) some similarities with Pb-Pb (also in PYTHIA, where there is no flow) reasonable agreement with viscous hydro predictions Analysis not yet conclusive on possible collective features in high-multiplicity proton-nucleus events though current results do not exclude radial flow 25
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p-pb spectral-shape analysis π/k/p spectral-shape analysis: performed with hydromotivated Blast-Wave model Schnedermann, PRC 48, 2462 (1993) 0 adding K S and Λ global fit performed in the following pt ranges: π K p K0S Λ 0-5% (V0A) 0.5 1.0 GeV/c 0.3 1.5 GeV/c 0.5 2.0 GeV/c 0.0 1.5 GeV/c 0.6 2.0 GeV/c Blast-Wave fits reasonable, though not very good worse than central Pb-Pb better than pp minimum bias p-pb 27
Blast-Wave model fit parameters Schnedermann, PRC 48, 2462 (1993) 28
Blast-Wave model fit parameters spectral-shape analysis: performed with hydromotivated Blast-Wave model Schnedermann, PRC 48, 2462 (1993) Blast-Wave fits in different momentum ranges 29
Subtraction of secondary protons 30
TOF raw yield extraction 31