strange particle measurements at the cern sps na49 and...

Grzegorz Stefanek HYP2012, Barcelona, Spain, 1 – 5 October 2012

Grzegorz StefanekJan Kochanowski University in Kielcefor the NA49 and NA61 Collaborations

Strange Particle Measurements Strange Particle Measurements at the CERN SPS at the CERN SPS

NA49 and NA61/SHINE Experiments NA49 and NA61/SHINE Experiments Outline:

• Experiments • Motivation• Evidence for the onset of deconfinement• Strange particle production measurements • Fluctuations in particle composition• Summary


S.Afanasiev et al., NiM A430, 210 (1999)

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NA61/SHINE and NA49 experiments

http://na61.web.cern.ch/na61/xc/index.html


Phase diagram of strongly interacting matter

• QCD considerations suggest a 1st order phase boundary ending in a Critical End Point (CEP)

• lattice calculations locate CEP in the SPS energy range Z.Fodor, S.D.Katz,JHEP 0404,050 (04), R.V.Gavai, S.Gupta,PRD 71,114014 (05)

• maximum of Critical End Point signal is expected for freeze-out close to CEP → SPS energy range

SPSRHIC

AGS

CEP

SIS

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Phase diagram scan – NA49, NA61 experimentshttp://na61.web.cern.ch/na61/xc/index.html

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completed

approved

future program

High statistics scan with a new vertex det.

Detailed scan with existing detector

• NA49 – scan with energy Pb+Pb at 20A, 30A, 40A, 80A, 158A GeV and with system size p+p, C+C, Si+Si, Pb+Pb at 158A GeV

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• NA61 - 2D scan (T, μB ) with six SPS beam energies 13A, 20A, 30A, 40A, 80A, 158A GeV and five different systems p+p, p+Pb, Be+Be, Ar+Ca, Xe+La - higher statistics – at least 106 events per energy and per reaction - better centrality selection (PSD detector) and reduction of interactions

in the gas inside VTPCs (Helium beam pipe) - similar analysis like in NA49 with better precision


Evidence for the onset of deconfinement

horn

• rapid changes in energy dependence of hadron production properties provide evidence for the phase transition

• the LHC and RHIC BES points confirm NA49 measurements and trendsData:NA49: C.Alt et al., PRC 77, 024903 (2008)STAR: L.Kumar, arXiv:1106:6071 (2011), B.Mohanty,QM2011ALICE: J.Schukraft QM2011, M.Floris QM2011, A.Toia QM2011

Theoretical predictions: M.Gazdzicki, M.Gorenstein, APP B30, 2705 (99)

and A.Rustamov, arXiv:1201.4520

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step dale

Evidence for the onset of deconfinement in Pb+Pb collisions at √s

NN ≈ 8 GeV

Pb+PbPb+Pb Pb+Pb


K*(892), K*(892) production measured by NA49

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• yield of K* exceeds that of K* by factors of two similar like for K+ and K- yields (same valence quark composition)

• yield of K* and K* per wounded nucleon appears to increase from p+p to C+C, Si+Si and then decrease for Pb+Pb collisions at 158A GeV

• <K*>/<K+>, <K*>/<K-> ratios decrease with increasing size of colliding nuclei.

T. Anticic et al., PRC 84, 064909 (2011)

Substantial duration of the hadronic stage of the fireball ?

p+p, C+C, Si+Si, Pb+Pb 158A GeV


K*(892), K*(892) production measured by NA49

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• yields of K* mesons in central Pb+Pb collisions are about 2.5 lower than the predictions of HGM with parameters fitted to the yields of stable hadrons

• for the yields of several resonance states (K*, K*, Λ, φ) measured by NA49 the suppression respect to HGM predictions seems to get stronger with decreasing lifetime of the resonance

T. Anticic et al., PRC 84, 064909 (2011)

Reduction of K* yield by rescattering of decay products during hadronic stage ?

Pb+Pb 158A GeV

p+p, C+C, Si+Si, Pb+Pb 158A GeV


First K- production measurements by NA61/SHINE

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• NA61/SHINE and NA49 spectra agree

• EPOS model reproduces data trends; significant quantitative differences for K-

NA49 points obtained from xF – p

T spectra

Eur.Phys. J. C68, 1 (2010)EPOS: PRC 74, 044902 (2011)


Fluctuations in particle composition – motivation and measures

• In the vicinity of phase transition distinct fluctuations patterns are expected • Event-by-event maximum likelihood fits were used to extract relative species abundances

• Studied fluctuation measures :

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i , j – particle species (π,K,p)

ν dyn≈sgn (σ dyn)σ dyn2

Method: C.Alt et al., PRC 79, 044910 (2009)

Var (N i/ N j)

⟨N i/N j ⟩2

- scaled variance (multiplicity fluctuations)


Identity method • The identity method allows to obtain second and third moments of identified particle multiplicity distribution corrected for misidentification effect.

• Once detector response ( ρi ) and Wi distributions are known the method is used to

obtain moments of identified particle multiplicity distributions.

• No event-by-event fits and mixed events required in identity method10

ρi ,W

i ,... → <N

i2>, <N

i · N

j >

PRC 83,054907PRC 84,024902arXiv:nucl-th/1204.6632


Fluctuations of particle composition

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Trend of NA49 results at low energies confirmed. Differences between STAR and NA49 results remains.

• p/π: νdyn < 0 due to resonance decay (reproduced by multiplicity scaling model)

• K/π: νdyn > 0 anti-correlation (reproduced by multiplicity scaling model)

• K/p: νdyn shows a strong dependence on energy, going from positive values at low energies to νdyn < 0 at high energies (not reproduced by multiplicity scaling model)

Unchanged correlation strength (same physics) with energy ?

Underlying correlation physics (baryon-strangeness) changing with energy ?

Model: V.Koch, T. Schuster, PRC 81, 034910 (2010) ν dyn∝1

⟨N i⟩+ 1

⟨N j ⟩


Fluctuations of particle composition – dependence on acceptance

• clear difference of NA49 and STAR acceptance for 30A GeV

• identity method can work with low multiplicity and acceptance cuts can be applied

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• clear dependence on acceptance cut at low SPS energies for K,π and K,p • no energy dependence of particle composition for “STAR equivalent” acceptance

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Differences between NA49 and STAR results can be explained by different acceptance

Fluctuations of particle composition – dependence on acceptance


Multiplicity fluctuations of π , K , p

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• increase of ωπ in Pb+Pb collisions due to

NW

fluctuations ?

• ωK > 1 →

• ωp < 1 →

• decrease of ωp with energy in Pb+Pb collisions

but increase in p+p interactions

• EPOS model agrees with p+p data

strangeness conservationat least in p+p collisions ?

baryon number conservation at least in p+p collisions ?

NA61: p+p; NA49: Pb+Pb (3.5%)


Summary• Onset of deconfinement in central Pb+Pb, NA49 measurements are confirmed: - results from RHIC agree with relevant NA49 data - first LHC data confirm the interpretation

• K*(892), K*(892) productions in central C+C, Si+Si, Pb+Pb and inelastic p+p coll.:

- observed suppression of K* yields in central Pb+Pb collisions as well as the decrease of <K*>/<K+>, <K*>/<K-> with increasing size of the colliding nuclei may suggest a substantial duration of the hadronic stage of the fireball

• K- production was measured by NA61 in p+p collisions as a function of y, pT

• Fluctuations of particle composition : - differences between NA49 (Pb+Pb) and STAR (Au+Au) results can be explained by different acceptance

- K/π and p/π fluctuations as a function of energy can be described by a simple multiplicity scaling model whereas K/p fluctuations show a deviation from the model. It can be a hint of changing of underlying correlation physics

- multiplicity fluctuations in p+p collisions mainly reflect conservation laws; they are reproduced by EPOS model

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NIKHEF, Amsterdam, NetherlandsUniversity of Athens, Athens, GreeceComenius University, Bratislava, SloveniaEotvos Lorand University, Budapest, HungaryKFKI IPNP, Budapest, HungaryMIT, Cambridge, USAINP, Cracow, PolandJoint Institute for Nuclear Research, Dubna, RussiaGSI, Darmstadt, GermanyUniversity of Frankfurt, Frankfurt, GermanyCERN, Geneva, SwitzerlandJan Kochanowski Univeristy, Kielce, PolandUniversity of Marburg, Marburg, GermanyMPI, Munich, GermanyCharles University, Prag, Czech RepublicUniversity of Washington, Seattle, USA Faculty of Physics, University of Sofia, Sofia, BulgariaSofia University, Sofia, BulgariaINR&NE, BAS, Sofia, BulgariaState University of New York, Stony Brook, USASoltan Institute for Nuclear Studies, Warsaw, Poland Warsaw University of Technology, Warsaw, PolandUniversity of Warsaw, Warsaw, PolandRudjer Boskovic Institute, Zagreb, Croatia

ETH, Zurich, SwitzerlandFachhochschule Frankfurt, Frankfurt, GermanyFaculty of Physics, University of Sofia, Sofia, BulgariaKarlsruhe Institute of Technology, Karlsruhe, GermanyInstitute for Nuclear Research, Moscow, RussiaInstitute for Particle and Nuclear Studies, KEK, JapanJagiellonian University, Cracow, PolandJoint Institute for Nuclear Research, Dubna, RussiaWigner Research Centre, Budapest, HungaryLPNHE, University of Paris VI and VII, Paris, FranceUniversity of Silesia, Katowice, PolandRudjer Boskovic Institute, Zagreb, CroatiaNational Center for Nuclear Research, Warsaw, PolandSt. Petersburg State University, St. Petersburg, RussiaState Uniwersityof New York, Stony Brook, USAJan Kochanowski University in Kielce, PolandUniversity of Athens, Athens, GreeceIniversity of Belgrade, Belgrade, SerbiaUniversity of Bergen, Bergen, NorwayUniversity of Bern, Bern, SwitzerlandUniversity of Frankfurt, Frankfurt, GermanyUniversity of Nova Gorica, Nova Gorica, SloveniaUniversity of Geneva, Geneva, SwitzerlandUniversity of Warsaw, Warsaw, PolandWarsaw University of Technology, Warsaw, PolandThe Universidad Tecnica, Valparaiso, Chile


Additional Slides

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Evidence for the onset of deconfinement

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Fluctuation measures studied by NA49

2 2( )Var n n nn n

ω < > − < >= =< > < >

- scaled variance ω of the multiplicity distribution P(n)

- Φx measure of fluctuations of observable x (<pT>, <Φ>, Q)

- σdyn measure of particle ratio fluctuations ( K/π, p/π, K/p )

M.Gazdzicki and St.Mrowczynski, Z.Phys. C54, 127(1992)

2 2 2 2 2 = sign( ) ; = dyn data mix data mix dyn dynσ σ σ σ σ σ ν− −

• intensive fluctuation measure• independent particle emission: ω = 1 • wounded nucleon model: ω(A+A)=ω(N+N)+<n>ωW • ω affected by NW fluctuations

• superposition model: Φx(A+A)= Φx(N+N) • independent particle emission: Φx= 0• Φx strongly intensive fluctuation measure independent of NW and its fluctuations

• E-by-E fit of particle multiplicities required• mixed events used as the reference• σ2

dyn~ 1/NW , sensitive to fluctuations

- F2 factorial moments of low mass π+π- pair number fluctuations in pT space• proper mass window and multiplicity are required• mixed events used as the reference• power-law behavior from σ mode expected

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Particle ratio fluctuations (standard method)• event-by-event PID based on energy loss dE/dx in MTPCs • inclusive probability density function + event-by-event maximum likelihood fit to extract relative species abundances Θm

→• acceptance different for different species and depends on beam energy; it has to be taken into account for model comparisons

• reference sample of mixed events which preserve multiplicity distribution quantify effect of finite-number statistics and dE/dx resolution • dynamical fluctuations:

Method: C.Alt et al., PRC 79, 044910 (2009)

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Grzegorz Stefanek HYP2012, Barcelona, Spain, 1 – 5 October 2012 22

Identity method


Identity method


Particle ratio fluctuations

• Increase of |σdyn| towards peripheral collsions for all three ratios

• Similar trend in RHIC STAR data for (K++K-)/(π++π-) at √sNN = 62 and 200 GeV B.I.Abelev et al., PRL 103, 092301 (2009)

• UrQMD predicts similar behaviour with Nw

• Scaling with multiplicities, works for all three ratios

Unchanged correlation strength (same physics) with system size ? V.Koch, T.Schuster PRC 81, 034910 (2010)

NA49 data: T.Schuster QM2011

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• p/π: σdyn < 0 correlation due to resonance decay S.Jeon,V.Koch PRL 83, 5435 (99)

• reproduced by hadronic transport models (UrQMD, HSD)

• K/π: σdyn > 0 anti-correlation

• UrQMD and HSD models are contradictory; neither describes data well

Scaling with multiplicities:

Unchanged correlation strength (same physics) with energy ?

Scaling:V.Koch, T.Schuster PRC 81, 034910 (2010)

NA49 data: T.Schuster QM2011

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Is the underlaying correlation physics (baryon-stangeness) changing with energy ?

• σdyn shows a strong dependence on √sNN, going from positive values at low energies to σdyn < 0 at high energies

• ratio for positive charges K+/p+, has no resonance contribution

• neither hadronic models (UrQMD, HSD) nor scaling with multiplicities ( V.Koch, T.Schuster PRC 81, 034910 (2010) ) describe data

NA49 data: T.Anticic et al., PRC 83 061902 (2011); T.Schuster QM2011

Theory:V.Koch, A.Majumder, J.Randrup PRL 95, 182301 (05)

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