The relevance of pp results to the The relevance of pp results to the understanding of soft physics in AA understanding of soft physics in AA
collisions at RHIC and LHCcollisions at RHIC and LHC
R. Bellwied (Wayne State University)
Is hadron production in medium different than production in vacuum ?
1st Workshop of soft physics in ultrarelativistic heavy ion collisions, Catania, Italy, Sept.27-29,2006
The Physics Questions 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
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
dParton Distribution FunctionsHard-scattering cross-sectionFragmentation Function
c
chbbaa
abcdba
T
hpp
z
Dcdab
td
dQxfQxfdxdxK
pdyd
d
0
/222
)(ˆ
),(),(
High pT (> 2.0 GeV/c) hadron production in pp collisions:
~
Hadronization in QCD (the factorization theorem)
“Collinear factorization”
Do we understand hadron productionin elementary collisions ? (Ingredient I: PDF)
RHIC
Ingredient II: Fragmentation functionsKKP (universality), Bourrely & Soffer (hep-ph/0305070)
Non-valence quark contribution to parton fragmentation into octet baryons at low fractional momentum in pp !!
Quark separation infragmentation models is important. FFs are not universal.
Depend on Q, Einc,and flavorzz
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 functionof multiplicity
Deviation from a two component fit:Levy function (soft) + Gaussian (hard)
Conclusions:a.) hard component yield increases with nch
b.) not more energetic partons but high frequencyof events with single hard scattering (mean andwidth stays the same)c.) Levy function (soft component) = thermal radiation from moving sourcesd.) low Q2 parton scattering dominated by mini-jets
Transverse parton fragmentation = hardLongitudinal string fragmentation = soft (LUND ?)nucl-ex/0606028
Is there anything interesting in the non-identified two particle correlations ?
see T.Trainor’s talk on Friday
The Probe 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/0305013 S.S. Adler et al.
“Well Calibrated”
pp at RHICStrangeness 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 todescribe 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/0607033
How strong are the NLO corrections ?
• K.Eskola et al.(NPA 713 (2003)):Large NLO corrections notunreasonable atRHIC energies.
Should be negligibleat LHC.
STAR
New NLO calculation based on STAR data (AKK, hep-ph/0502188, Nucl.Phys.B734 (2006))
K0s
apparent Einc 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 GeVBump is intrinsic in pp, enhancement is unique to AA
Baryon/Meson ratio @ 630 and 1800 GeV(Boris Hippolyte, Hot Quarks 2006)
Extracting mixed ratio from UA1 spectra (1996) and from CDF spectra (2005)
Ratio vs pT seems very energy dependent (RHIC < SPS > FNAL ?)
Mt scaling in pp
Breakdown of mT scaling in pp ?
mT slopes from PYTHIA 6.3
Gluon dominance at RHICPYTHIA: Di-quark structures in baryon production cause mt-shiftRecombination: 2 vs 3 quark structure causes mt 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 productionJETSET is clearly favored by the data.
Correlated bar pairs are produced predominantly in the same jet, i.e. short range compensation of quantum numbers.
jetsqqZee 0
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 differencebetween RAA and RCP
(Helen Caines talk)‘Canonical suppression’ in ppis 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 (Nbin) scaling
Measurements direct D0
(event mixing)
c→+X
(dE/dx, ToF)
c→e+X
(ToF)
c→e+X
(EMC)
pT (GeV/c) 0.13.0 0.170.25 0.94.0 1.5
constraint , d/dpT , d/dpT d/dpT
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 pT >> mc where mass is not relevant– Calculations depend on quark mass mc, factorization scale F (typically F = mc or
2 mc), renormalization scale R (typically R = F), parton density functions (PDF)
– Hard to obtain large with R = F (which is used in PDF fits)
b
bb
FONLLbb
NLOcc
FONLLcc
99.067.0
381134
400146
87.1
244 ;256
from hep-ph/0502203
FONLL RHIC:LO:
NLO:
Charm - Experiment vs. Theory
• The non-perturbative charm fragmentation needed to be tweaked in FONLL to describe charm. FFFONLL is much harder than used before in ‘plain’ NLO FFFONLL ≠ FFNLO
RHIC: FONLL versus Data
• Matteo Cacciari (FONLL):
• factor 2 is not a problem• factor 5 is !!!
)FONLL(
) from STAR( 0
cc
TOFcc eD
– 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) spectrabetween STAR and PHENIX for the non-photonic electrons
hep-ex/0609010
nucl-ex/0607012
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/dpT, etc.) – after LHC start-up, with few tens of thousand events we will do: Claus Jorgensen
Mean pT vs multiplicity
Multiplicity distribution
pT spectrumof chargedparticles
Pseudorapidity density dN/dη
CDF:Phys. Rev. D41, 2330 (1990)30000 events at √s=1.8TeV9400 events at √s=640TeV
UA5:Z. Phys43, 357 (1989)6839 events at √s=900GeV4256 events at √s=200GeV
CDF:Phys. Rev. Lett.61, 1819 (1988)55700 events at √s=1.8TeV
CDF:Phys. Rev. D65,72005(2002)3.3M events at 1.8TeV2.6M 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/0607074)
NOT Year-1 physics. For later…
