Multiplicity dependence of light flavor production in p-pb collisions measured with ALICE at the LHC

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1 Multiplicity dependence of light flavor production in p-pb collisions measured with ALICE at the LHC Gyula Bencedi Winger Research Centre for Physics, Budapest, Hungary Instituto de Ciencias Nucleares/UNAM, Mexico City for the ALICE Collaboration XV MEXICAN WORKSHOP ON PARICLES AND FIELDS - November 05, Playa Mazatlán Beach Hotel

2 Outline Introduction Particle identification in ALICE Light flavor production at 5.0 AeV in p-pb collisions Multiplicity dependence of pion, kaon and proton production Blast wave analysis of particle spectra Multiplicity dependence of kaon/pion and proton/pion particle ratios Nuclear modification factor of pions, kaons and protons Summary

3 Introduction p-a collisions: control measurement (beside pp collisions) in order to better understand heavy ion collisions, i.e. disentangle initial- and final state effects At high p (final state effects) study parton energy loss mechanisms in QGP At intermediate p (initial state effects) obtain higher precision in the existing measurements (IS, PC, OF) study Cold Nuclear Matter effects (e.g. Cronin enhancement) and modification of particle ratios (p/pi and K/pi) by flow-like effects 3

4 Cold Nuclear Matter effects v{pc, sub} ALICE p-pb snn =5.0 ev >0. (Near side only) (0-0%) - (0-0%) h K p <p,trig < GeV/c <p,assoc p-pb snn =5.0 ev < GeV/c (0-0%) - (0-0%) Double ridge structure, long-range angular correlations in p-pb collisions at high multiplicity (near- and away side) Flow-like patterns observed Mass ordering and crossing is qualitatively similar to observations in A-A collisions at low pcan be described by hydrodynamic models d Nassoc (rad-) Ntrig d d ALI PUB 5 ALICE, PLB 79 (03) 9- ALICE, PLB 7 (03) -77 ALICE, PLB 7 (0) 5-3 CMS,November PLB 7 (03) 795 3, p (GeV/ c) ALI PUB - -

5 he ALICE apparatus y>0 A-side C-side y<0 ALICE, IJMPA 9,300 (0) 5

6 he ALICE apparatus ylab -0.5 y>0 A-side C-side y<0 p-pb p Forward detector: V0A (trigger, multiplicity) Beam energy: ev per Z (resulting 5.0 AeV) V0A:.<ηlab<5., positioned in the Pb-going direction ALICE, IJMPA 9,300 (0)

7 Npart ALICE PRC 9 (05) Glauber-MC p-pb snn = 5.0 ev Npart Multiplicity estimation: V0A 00 - Glauber-MC Pb-Pb snn =.7 ev b (fm) b (fm) For small systems there is a weak correlation between the impact parameter (b) and the number of participants (Npart) For this reason particle production is studied in event multiplicity classes V0A estimator is used (as in the first ALICE publication on identified hadron production in p-pb collisions) V0A detector:.<ηlab<5., positioned in the Pb-going direction 7

8 he ALICE apparatus y>0 A-side C-side y<0 p-pb Decay opology p PC rde /dx HMPID Central barrel ( η <, B = 0.5 ) pi tracking and PID Forward detector: V0A (trigger, multiplicity) ALICE, IJMPA 9,300 (0) OF PC de /dx IS de /dx p (GeV/c )

9 Particle Identification rack-by-track ID (n-σ cut) in the /β region PID in the relativistic rise using statistical approaches PC OF Dedicated to charged hadron Identification in the intermediate momentum region racking + standalone reconstruction: PID via de/dx from SDD and SSD analog read-out Standalone tracking in the low-p region (down to 0MeV/c) IS 9

10 Light flavor production at 5.0 AeV in p-pb collisions

11 /Nev /( p ) dn /(dp dy) [(GeV/ c)] V0A multiplicity 0-5% (x) 5-% (3x) -0% (x) 0-0% (x) 0-0% (x) 0-0% (x) 0-0% (x) <ycms<0.5 for p < 3.0 GeV/ c ycms <0.3 for p > 3.0 GeV/ c - - p-pb, snn = 5.0 ev High multiplicity -7 p+p 3 0<ycms<0.5 for p <.0 GeV/ c ycms <0.3 for p >.0 GeV/ c - p-pb, snn = 5.0 ev /Nev /( p ) dn /(dp dy) [(GeV/ c)]- Multiplicity dependence of pi/k/p spectra 0 V0A multiplicity 0-5% (x) 5-% (3x) -0% (x) 0-0% (x) 0-0% (x) 0-0% (x) 0-0% (x) p (GeV/ c) ALI PREL 09 G.BencediALI PREL 0970 for the ALICE Collaboration High multiplicity p (GeV/ c)

12 /Nev /( p ) dn /(dp dy) [(GeV/ c)] p+p High multiplicity p-pb, snn = 5.0 ev 0<ycms<0.5 for p <.0 GeV/ c ycms <0.3 for p >.0 GeV/ c - 0<ycms<0.5 for p < 3.0 GeV/ c ycms <0.3 for p > 3.0 GeV/ c - - Similarities to Pb-Pb results are observed: -3-3 p-pb, snn = 5.0 ev /Nev /( p ) dn /(dp dy) [(GeV/ c)]- Multiplicity dependence of pi/k/p spectra of the p spectra at low p (< GeV/c) -A multiplicity- and mass-dependent flattening V0A multiplicity 0-5% (x) 5-% (3x) -0% (x) 0-0% (x) 0-0% (x) 0-0% (x) 0-0% (x) V0A multiplicity 0-5% (x) 5-% (3x) -0% (x) 0-0% (x) 0-0% (x) 0-0% (x) 0-0% (x) p (GeV/ c) ALI PREL 09 G.BencediALI PREL 0970 for the ALICE Collaboration High multiplicity p (GeV/ c)

13 Blast wave fits to the spectra he flattening and mass ordering of the p spectra can be studied by applying simultaneous Blast-Wave fits to pi, K, p, K0s and Λ p spectra in V0A multiplicity classes kin (GeV) multiplicity increases % ALICE, p-pb, snn = 5.0 ev Qualitatively similar V0A Multiplicity Classes (Pb-side) 0.0 behavior observed for p-pb ALICE, Pb-Pb, snn =.7 ev and Pb-Pb collisions 0.0 Larger radial flow parameter obtained in p-pb than in Pb-Pb collisions ALI DER 59 at similar multiplicity consequence of selection bias of harder events? consequence of stronger radial gradients? (Phys.Rev. C (03), 095) In p-pb data there is a presence of flow-like effects In Pb-Pb strong radial flow is observed Phys. Rev. Lett. 9 (0) 530 3

14 Blast wave fits to the spectra he flattening and mass ordering of the p spectra can be studied by applying simultaneous Blast-Wave fits to pi, K, p, K0s and Λ p spectra in V0A multiplicity classes Simulated pp events (PYHIA, CR) without hydrodynamical expansion of the system show similar trend to those observed in p-pb and Pb-Pb collisions kin (GeV) multiplicity increases ALICE, p-pb, snn = 5.0 ev V0A Multiplicity Classes (Pb-side) ALICE, Pb-Pb, snn =.7 ev PYHIA, s = 7 ev (with Color Reconnection) PYHIA, s = 7 ev (without Color Reconnection) ALI PUB 55 A. Ortiz et al. PRL (03), 000

15 Blast wave fits to the spectra he flattening and mass ordering of the p spectra can be studied by applying simultaneous Blast-Wave fits to pi, K, p, K0s and Λ p spectra in V0A multiplicity classes Simulated pp events (PYHIA, CR) without hydrodynamical expansion of the system show similar trend to those observed in p-pb and Pb-Pb collisions kin (GeV) multiplicity increases ALICE, p-pb, snn = 5.0 ev V0A Multiplicity Classes (Pb-side) ALICE, Pb-Pb, snn =.7 ev ALICE, pp, s = 7 ev PYHIA, s = 7 ev (with Color Reconnection) PYHIA, s = 7 ev (without Color Reconnection) ALI DER 533 A. Ortiz et al. PRL (03), 000 pp collisions exhibit flowlike behavior 5

16 Blast wave fits to the spectra V0A Multiplicity Class: 5-% he p spectra in high multiplicity pp and p-pb collisions show a clear evolution with multiplicity this effect is well known from heavy ion collisions models, e.g. the Kraków hydrodynamic model, reproduce the kaon and pion spectra fairly well below GeV/c A deviation for higher p might show the limit of hydrodynamical models. he data could indicate the onset of a non-thermal (hard) component, which is not dominated by the flow-boosted thermal component in more peripheral collisions Models incorporating final state effects, such as EPOS, give good description of the data Common kinetic freeze-out describes the spectra in high multiplicity p-pb collisions his feature is also observed in pp events simulated with PYHIA

17 Multiplicity dependence of kaon/pion and proton/pion particle ratios At intermediate p (<p< GeV/c), the proton-to-pion ratio increases with event multiplicity (and a corresponding depletion at low p) he behavior of this increase is qualitatively similar to that observed in Pb-Pb collisions its multiplicity dependence for p GeV/c is a feature of radial flow At high p (> GeV/c) the particle ratios in p-pb and Pb-Pb are consistent ( p + p )/( ) ALICE Preliminary 0. Pb-Pb, snn =.7 ev p-pb, snn = 5.0 ev 0-5% 0-0% 0-5% 0-0% p < 3.0 GeV/ c PLB 7, 5-3 (0) PLB 73, 9-07 (0) 0. V0A Multiplicity Classes (Pb-side) ALI DER 739 p (GeV/c ) 7

18 R ppb Nuclear modification factor of pi/k/p ALICE preliminary... Measured for NSD events Nuclear overlap < > is not ppb measured yet in mult. classes No pp measurement at 5.0 ev: it has to be interpolated between existing measurements. At intermediate p the proton RpPb shows a Cronin-like enhancement, while pions and kaons show little or no nuclear modification At higher p the pion, kaon and proton RpPb are consistent with unity NSD, p-pb snn = 5.0 ev , -0.5 < y < 0 for p <.0 GeV/ c CMS -0.3 < y < 0.3 for p >.0 GeV/ c CMS + K +K, -0.5 < y < 0 for p <. GeV/ c CMS -0.3 < y < 0.3 for p >. GeV/ c CMS p+p, -0.5 < y < 0 for p < 3.0 GeV/ c CMS -0.3 < y < 0.3 for p > 3.0 GeV/ c 0. CMS 0 ALI PREL p (GeV/ c)

19 Summary p-pb and Pb-Pb collisions have very similar behavior in many ways p-pb: p spectra show flow-like behavior p-pb: multiplicity dependence of the proton-to-pion ratio vs. p is qualitatively similar to the centrality evolution of this ratio in Pb-Pb collisions Cronin-like enhancement observed for protons at intermediate p (initial state effects); no nuclear modification at high p 9

20 Backup 0

21 he behavior of this increase is qualitatively similar to that observed in Pb-Pb collisions. ( p + p )/( ) At intermediate p (<p< GeV/c), the proton-topion ratio increases with the event multiplicity. ALICE Preliminary 0. p-pb, snn = 5.0 ev Pb-Pb, snn =.7 ev 0-5% 0-0% 0-5% 0-0% p < 3.0 GeV/ c PLB 7, 5-3 (0) PLB 73, 9-07 (0) 0. V0A Multiplicity Classes (Pb-side) At high p (> GeV/c) the particle ratios in p-pb and Pb-Pb are consistent. ALI DER 739 p (GeV/ c )

22 ( p + p )/( ) (p + p) / ( + + -) At intermediate p Also in INEL s =.7 ev pp 0.5 GeV/c), (<p< collisions the Pb-Pb, bump s at=.7 ev p-pb, snn = 5.0 ev the proton-topp s =.7 ev, PLB 7, 5-3 (0) NN ALICE 0.5 intermediate p is observed. Preliminary pion ratio 0-5% 0-5% 0. with the Pythia, Perugia0 increases 0-0% 0-0% NLO, PRD, (0) p < 3.0 GeV/ c event multiplicity. PLB 73, 9-07 (0) 0.35 he behavior of 0.3 this increase is 0.5 qualitatively similar0. to that observed in Pb-Pb 0.5 collisions. 0. At high p (> 0.05 GeV/c) the particle ratios in p-pb and 0 Pb-Pb areali DER 95 consistent. PLB 7, 5-3 (0) 0. V0A Multiplicity Classes (Pb-side) ALI DER p (GeV/ c ) p (GeV/ c )