Transcript Document

Jet Physics with identified particles
at RHIC and the LHC
R. Bellwied (Wayne State University)
Is hadron production in medium different than in vacuum ?
22nd Winter Workshop on Nuclear Dynamics
La Jolla, March 11-19, 2006
The main topics
Hadron production through fragmentation in pp
Flavor separated fragmentation functions
Baryon – meson effects in pp
Canonical strangeness suppression at high pT in pp/AA
Tests of recombination through particle identified
particle correlations in AA
two-
Parton distribution functions at RHIC energies are well established
through DESY measurements (hep-ex/0305109)
RHIC
RHIC & LHC is gluon jet dominated
Non-Abelian energy loss
XNW, nucl-th/0410049
DEg=DEq
DEg=2DEq
Is energy loss non-abelian ?
Effects due to softer g-PDF and color factor
— pQCD @ 130 GeV
— Soft+Quench @ 130 GeV
Quark jet tagging through direct g-jets
Alternative: Heavy Quark Tag,
but g is ‘standard candle’
Life is easier at the LHC
p0 in pp: well described by standard NLO
p+p->p0 + X
• Ingredients (via KKP or Kretzer)
– pQCD
– Parton distribution functions
– Fragmentation functions
Thermallyshaped Soft
Production
Hard
Scattering
hep-ex/0305013 S.S. Adler et al.
pp at RHIC: Hadron formation in QCD
NLO for heavy masses requires quark separation in fragmentation function
FF depend
on Q, Einc,
and flavor
z
z
Non-valence quark contribution to parton fragmentation into
octet baryons at low fractional momentum in pp
Success of quark separated fragmentation
functions at RHIC
..but, this effect might be collision energy
dependent.
K0 spectra
STAR
LHC
KKP better at 630 GeV
AKK better at 200 GeV
The higher the collision energy,
the more reliable LO pQCD
Why is understanding pp so important ?
Is the hadronization process modified from pp to AA ?
(Hadronization in medium (universe) vs. hadronization in vacuum)
Is baryon production special ?
Are recombination effects unique to AA ?
The 400 pound gorilla:
baryon/meson differences
A clue to constituent quark scaling ? Is chiral symmetry
restored ? Is the sQGP degree of freedom ‘massive’ ?
Breakdown of mT scaling in pp –
a signal of gluon jet dominance ?
A baryon – meson effect, due to baryon production requirement
in string models (di-quark mechanism, di-quarks have lower p).
Distinctly different from recombination.
Baryon production mechanism
through strange particles correlations
 0
e e  Z  qq  jets…
Test phenomenological fragmentation
models
OPAL ALEPH and DELPHI measurements:
Yields and cosQ 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 L-Lbar pairs are produced
predominantly in the same jet, i.e. short
range compensation of quantum numbers.
Collision energy dependence of baryon
vs. meson production in pp
630 GeV
Baryon / meson differences already in pp collisions
How does the ratio look at the LHC ?
Life is easier at the LHC !
LHC vs. RHIC – leading particle range
Cross sections for p+p
14 TeV
total : s = 55 mb
quark : s= 15 mb
gluon: s = 38 mb
ALICE pp:
Event Recording Rate: 100 Hz
Event Recording Bandwidth: 20 MB/s
Running Time Per Year: 107 s
Events Per Year: 109
Are extensions of string models applicable
in AA collisions @ RHIC and LHC ?
e.g. EPOS++ (K.Werner’s talk)
Alternative to recombination and fragmentation models
Soft-Intermediate particle production through parton cascade in corona
Identified Particle RCP
• intermediate pt not dominated by fragmentation ?
• no flavor dependence in fragmentation region ?
• need to establish good high ptPID @ LHC (V0, rdE/dx, RICH ?)
RAA of strange baryons
A remarkable difference
between RAA and RCP
that seems unique to
strange baryons.
Ordering with strangeness
content.
Is ‘Canonical suppression’
unique to strange hadrons ?
This effect must occur ‘between’ pp and peripheral AA collisions
Flavor independence of meson RAA ?
u,d dominated
c,b dominated
no flavor dependence in energy loss ??
Strange enhancement vs. charm suppression ?
Why is canonical suppression (CS)
a baryon effect ?
CS > energy loss effect @ high pt
Is c more suppressed than s ?
Is there still CS at LHC energies ?
But is it a flavor effect ?
Kaon behaves like D-meson,
we need to measure Lc at LHC
RAA - A mocked up
string picture does well
(see V.Topor-Pop talk)
HIJING/BBar + KT ~ 1 GeV
Strong Color Field qualitatively
describes RAA.
SCF - long range coherent fields
SCF behavior mimicked by doubling
the effective string tension
SCF only produced in nucleusnucleus collisions RAA≠ RCP
Apparently EPOS++ can describe
data as well
Topor Pop et al. hep-ph/0505210
Correlation functions for strange particle
triggers in Au+Au at 200 GeV
trigger: baryon/meson
STAR preliminary
particle/antiparticle
STAR preliminary
Selection criteria:
• 3.0 GeV/c<pTtrigger<3.5 GeV/c
• 1 GeV/c<pTassociated<2 GeV/c
• |h|<1
STAR preliminary
STAR preliminary
Corrections applied:
•reconstruction efficiency
of charged particles
•TPC sector boundaries
correlation functions
before
ellipticflow
flowsubtraction
subtraction
after elliptic
Near side yield dependence on system size
Large AA/pp ratio of near side
associated yield
Although within statistical
errors all trigger particle
species behave similarly,
yield for “meson” triggered
correlations appears to be
systematically lower than
for “baryon” triggers
STAR preliminary
statistical errors only
Why is yield increasing
with Npart ?
What does a parton recombination model predict?
R. Hwa, Z.Tan: nucl-th/0503060
Au+Au @ 200 GeV
3GeV/c<pTtrigger<6GeV/c
Au+Au
d+Au
STAR preliminary
• the ratio of near-side associated yield in central/peripheral Au+Au
collisions is ~ 3 at pTassociated = 1 GeV/c and decreases slowly with
increasing pTassociated
• data are in a good agreement with predictions from a parton
recombination model: In Au+Au the thermal-shower recombination
dominates for Kaon and Lambda triggered jets (no flavor sensitivity)
Recombination contribution is quark content
dependent (R.Hwa, nucl-th/0602024)
mesons
baryons
Shower contribution significantly suppressed for sss and s-sbar states
No W or f trigger two particle correlations in AA. Tests underway
Is the near-side associated yield
(ridge or jet) flavor dependent ?
- need higher stats
- rdE/dx for p and p
- easy at LHC
Summary
Baryon production in pp requires multiple scattering (EPOS or NLO pQCD)
No strong flavor effects in high pt two particle correlations. Surprising absence of
pQCD effects (gluon vs. quark contributions) in pp and AA. Does the energy loss
show the color factor (non-Abelian energy loss ?).
High pt strange baryon production in AA enhanced instead of suppressed
compared to pp . Is this due to simple canonical suppression in pp ? Any
predictions for charmed baryons ?
Large associated particle yield in AA compared to pp. Long range Dh correlations
might be due to recombination. There might be a baryon/meson trend in
agreement with recombination, but it is a small effect. Predictions for f and W
need to be tested.
The universe consists of baryonic matter.
We need to understand basic baryon production in pp (string fragmentation vs.
recombination, di-quark formation ? Then we need to determine whether the
baryon production mechanism in AA collisions in modified.
High pt identified baryon spectra at LHC are crucial (pT > 10 GeV/c).
Baryon production in medium might solve ‘universal’ issues.