The relevance of pp results to the understanding of soft physics in AA collisions at RHIC and LHC R. Bellwied (Wayne State University) Is hadron production in medium different than production in vacuum ? 1 st Workshop of soft physics in ultrarelativistic heavy ion collisions, Catania, Italy, Sept.27-29,2006

The Physics Questions What do we know about fragmentation ? Hadronization process studies Baryon vs. meson production in pp Flavor production in pp Alternatives to string fragmentation ? Is there collectivity in pp ?

hadrons leading particle Jet: A localized collection of hadrons which come from a fragmenting parton Parton Distribution Functions Hard-scattering cross-section Fragmentation Function a b c d Parton Distribution Functions Hard-scattering cross-section Fragmentation Function High p T (> 2.0 GeV/c) hadron production in pp collisions: ~ Hadronization in QCD (the factorization theorem) “Collinear factorization”

Do we understand hadron production in elementary collisions ? (Ingredient I: PDF) RHIC

Ingredient II: Fragmentation functions KKP (universality), Bourrely & Soffer (hep-ph/ ) Non-valence quark contribution to parton fragmentation into octet baryons at low fractional momentum in pp !! Quark separation in fragmentation models is important. FFs are not universal. Depend on Q, E inc, and flavor zz

The Lessons from RHIC (I) unidentified particles

Is there anything interesting in the non-identified charged particle spectra ? Deviations from a power-law as a function of multiplicity Deviation from a two component fit: Levy function (soft) + Gaussian (hard) Conclusions: a.) hard component yield increases with n ch b.) not more energetic partons but high frequency of events with single hard scattering (mean and width stays the same) c.) Levy function (soft component) = thermal radiation from moving sources d.) low Q 2 parton scattering dominated by mini-jets Transverse parton fragmentation = hard Longitudinal string fragmentation = soft (LUND ?) nucl-ex/

Is there anything interesting in the non-identified two particle correlations ? see T.Trainor’s talk on Friday

The Probe Identified particle spectra: - Meson / baryon spectra -Strangeness / heavy flavor spectra - Resonance spectra - Correlations (HBT etc.)

The Lessons from RHIC (II) identified particles

How to measure PID ? Initial PID: charged hadrons vs. neutral pions Detailed PID: –V0 topology –dE/dx –rdE/dx –TOF / RICH / TRD

Why measure these effects with K and  instead of  and p ? Particle identification benefits from fact that the topological reconstruction method has no intrinsic momentum cut-off compared to dE/dx.

…but the use of rdE/dx might change that at least for inclusive measurements

 0 in pp: well described by NLO (& LO) Ingredients (via KKP or Kretzer) –pQCD –Parton distribution functions –Fragmentation functions..or simply PYTHIA… p+p->  0 + X Hard Scattering Thermally- shaped Soft Production hep-ex/ S.S. Adler et al. “Well Calibrated”

pp at RHIC  Strangeness formation in QCD Strangeness production not described by leading order calculation (contrary to pion production). It needs multiple parton scattering (e.g. EPOS) or NLO corrections to describe strangeness production. Part of it is a mass effect (plus a baryon-meson effect) but in addition there is a strangeness ‘penalty’ factor (e.g. the proton fragmentation function does not describe  production). s is not just another light quark nucl-ex/

How strong are the NLO corrections ? K.Eskola et al. (NPA 713 (2003)): Large NLO corrections not unreasonable at RHIC energies. Should be negligible at LHC. STAR

New NLO calculation based on STAR data (AKK, hep-ph/ , Nucl.Phys.B734 (2006)) K0s apparent E inc dependence of separated quark contributions.

Non-strange baryon spectra in p+p Pions agree with LO (PYTHIA) Protons require NLO with AKK-FF parametrization (quark separated FF contributions) PLB 637 (2006) 161

The Lessons from RHIC (III) baryon / meson physics

Non-strange particle ratios – p+p collisions PLB 637 (2006) 161

Collision energy dependence of baryon vs. meson production 630 GeV Peak amplitude doubles in pp from 200 to 630 GeV Bump is intrinsic in pp, enhancement is unique to AA

Baryon/Meson 630 and 1800 GeV (Boris Hippolyte, Hot Quarks 2006) Extracting mixed ratio from UA1 spectra (1996) and from CDF spectra (2005) Ratio vs p T seems very energy dependent (RHIC FNAL ?)

Mt scaling in pp

Breakdown of m T scaling in pp ?

m T slopes from PYTHIA 6.3 Gluon dominance at RHIC PYTHIA: Di-quark structures in baryon production cause m t -shift Recombination: 2 vs 3 quark structure causes m t shift

Baryon production mechanism through strange particle correlations …  Test phenomenological fragmentation models OPAL ALEPH and DELPHI measurements: Yields and cos  distribution between correlated pairs distinguishes between isotropic cluster (HERWIG) and non-isotropic string decay (JETSET) for production mechanism. Clustering favors baryon production JETSET is clearly favored by the data. Correlated  bar pairs are produced predominantly in the same jet, i.e. short range compensation of quantum numbers.

The Lessons from RHIC (III) flavor physics

Strange enhancement vs. charm suppression ? But is it a flavor effect ? Kaon behaves like D-meson, we need to measure  c A remarkable difference between R AA and R CP (Helen Caines talk) ‘Canonical suppression’ in pp is unique to strange hadrons.

Charm cross-section measurements in pp collisions in STAR –Charm quarks are believed to be produced at early stage by initial gluon fusions –Charm cross-section should follow number of binary collisions (N bin ) scaling Measurementsdirect D 0 (event mixing) c→  +X (dE/dx, ToF) c→e+X (ToF) c→e+X (EMC) p T (GeV/c) 0.1    4.0  1.5 constraint , d  /dp T  d  /dp T

LO / NLO / FONLL? A LO calculation gives you a rough estimate of the cross section A NLO calculation gives you a better estimate of the cross section and a rough estimate of the uncertainty Fixed-Order plus Next-to-Leading-Log (FONLL) –Designed to cure large logs in NLO for p T >> m c where mass is not relevant –Calculations depend on quark mass m c, factorization scale  F (typically  F = m c or 2 m c ), renormalization scale  R (typically  R =  F ), parton density functions (PDF) –Hard to obtain large  with  R =  F (which is used in PDF fits) from hep-ph/ FONLL RHIC: LO: NLO:

Charm - Experiment vs. Theory The non-perturbative charm fragmentation needed to be tweaked in FONLL to describe charm. FF FONLL is much harder than used before in ‘plain’ NLO  FF FONLL ≠ FF NLO

RHIC: FONLL versus Data Matteo Cacciari (FONLL): factor 2 is not a problem factor 5 is !!! –Spectra in pp seem to require a bottom contribution –Does the factor 5 excess in the charm cross-section between FONLL and STAR also apply to bottom cross-section? This difference between STAR and PHENIX in the pp data (f=2.5), will lead to a significant difference in the R(AA) spectra between STAR and PHENIX for the non-photonic electrons hep-ex/ nucl-ex/

Conclusions We need to establish the energy dependence of the hadronization process in vacuum and the factorization theorem as a function of flavor. This is an interesting overlap topic with high energy physicists. Not everybody is involved in the Higgs search. Fragmentation studies are a link between pp and AA, between nuclear physics and high energy physics. Is there recombination in pp ? Novel ideas of nuclear physics need to be applied to pp (HBT, blastwave, v2). How collective is pp ?

Is there a radial flow component ? (blastwave fits to STAR data)

There is an elliptic flow component There is an interesting HBT component, see Mike Lisa’s talk

First publications It only takes a handful of events to measure a few important global event properties (dN/d , d  /dp T, etc.) – after LHC start-up, with few tens of thousand events we will do: Claus Jorgensen Mean p T vs multiplicity Multiplicity distribution p T spectrum of charged particles Pseudorapidity density dN/dη CDF: Phys. Rev. D41, 2330 (1990) events at √s=1.8TeV 9400 events at √s=640TeV UA5: Z. Phys 43, 357 (1989) 6839 events at √s=900GeV 4256 events at √s=200GeV CDF: Phys. Rev. Lett. 61, 1819 (1988) events at √s=1.8TeV CDF: Phys. Rev. D65,72005(2002) 3.3M events at 1.8TeV 2.6M events at 630GeV

Outlook There are significant questions regarding the fragmentation process at LHC energies Topological V0 and rdE/dx analysis will allow us to measure many properties particle identified. There is no ‘statistics’ problem out to 20 GeV/c. There is a viable physics program besides being a reference for AA: –Hadronization (baryons vs. mesons ?) –Fragmentation (universality ?, applicability ?) The collision energy dependence is crucial.

The Black Hole search….. (Humanic, Koch, Stoecker, hep-ph/ ) NOT Year-1 physics. For later…