Hadron Physics at RHIC

1
Hadron Physics at RHIC

• M. Grosse Perdekamp
• UIUC and RBRC

• RHIC Physics
• Low x ? Saturation?
• Access to Nucleon Structure?
• pQCD vs Experiment
• Proton Spin Structure
• RHIC and Experiments
• Gluon Spin
• Transverse Spin

pp2pp
Observables in Antiproton-Proton Interactions and
their Relevance to QCD
2
Physics at the Relativistic Heavy Ion Collider

• Quark Matter at high Temperatures and Densities
• ion-ion collisions (Cu-Cu, Au-Au vsNN22.5,
  62, 130, 200 GeV)
• Proton Spin Structure
• polarized proton-proton collisions (p-p
  vs200 to 500 GeV)
• Low-x and high parton densities
• ion-deuteron collisions (d-Au vsNN200 GeV)

very active field eg. 76 Physical Review Letters
in the first 5 years
with more than 6800 citations in SPIRES
3
Proton Spin Structure in Polarized
p-p Collisions at RHIC
available channels jets, hadrons, photons,
photon-jet, heavy flavor Single spin lepton
asym- metries in W-production, Lambda
production (1) AN (2) ATT in Collins- and
Interference-Fragmentation (3) ATT and AT In
Drell Yan
goals determine first moment of the
spin dependent gluon distribution. flavor
separation of quark and anti-quark spin
distributions measurement of trans- versity
and Sivers distributions
4
Heavy Ion Physics

• Structure of Neutron Stars
• physics goal
• to find quark matter
• and survey its properties
• experimental method
• heavy ion collisions at
• high energies

5
Heavy Ion Physics

• A brief history of
• Heavy Ion Experiment
• Bevalac
• AGS
• GSI
• SPS
• RHIC
• LHC

Find quark matter and survey its properties
6
RHIC 2001 2005 the sQGP !

• Key Observations
• Jets are suppressed in central Au Au collisions
• Suppression is flat up to pt 10 GeV/c
• Absence of suppression in dAu
• Strong elliptic flow
• Scaling of v2 with eccentricity shows that a high
  degree of collectivity builds up at a very early
  stage of collision evidence for early
  thermalization
• Data described by ideal hydrodynamic models?
  fluid description of matter applies.
• Energy density allows for a non-hadronic state of
  matter
• Energy density estimates from measurements of
  dN/dy are well in excess of the 1 GeV/fm3
  lattice QCD prediction for the energy density
  needed to form a deconfined phase.

Strongly interacting Quark Gluon Plasma !
7
Is the Initial State in Heavy IonCollisions
Determined by Saturation Effects in the Gluon
Field ?
8
BRAHMS dAu Results as Function of Rapidity and
Centrality
BRAHMS, PRL 93, 242303 and R. Debbe
YdAu
RdAu
NcollYpp
Hadron production is suppressed at large
rapidity consistent with saturation effects at
low x in the Au gluon densities ? CGC
9
Similar Effects Seen by PHENIX and PHOBOS
PRL 94, 082302
Suppression in the d direction and enhancement in
the Au frag. region








10
Saturation Picture (CGC) Consistent with Data
A. Dumitriu et al. Nucl. Phys. A770 57-70,2006
Not bad! However, Large K factors, ?-dependent.
We hope for NLO calculations soon
11
Access to Nucleon Structure inHadron
Collisions?
12
Access to Nucleon Structure at RHIC
Measure (spin dependent) cross sections
QCD analysis (spin dependent) distribution
functions
13
Example DG(x) from global NLO pQCD analysis
using projected future direct photon data from
RHIC
QCD analysis of inclusive DIS data
QCD analysis DIS data future direct photons
M. Hirai, H.Kobayashi, M. Miyama et al.
(Asymmetry Analysis Collaboration)
14
Example ?G(x) from global NLO pQCD analysis
using projected future direct photon data from
RHIC

• Does NLO pQCD provide a reliable framework
  for the interpretation of polarized proton data
  in terms of polarized parton distribution
  functions?

QCD analysis of inclusive DIS data
QCD analysis DIS data future direct photons
M. Hirai, H.Kobayashi, M. Miyama et al.
(Asymmetry Analysis Collaboration)
15
Is pQCD applicable in p-p Collisions ?

• Tevatron data as input to CTEQ
• QCD analysis of hard scattering
• data, specifically G(x,Q2)
• Comparison
• NLO pQCD vs RHIC data
• ? inclusive hadrons
• ? inclusive jets
• ? direct photons

16
CTEQ Global QCD Analysis for G(x,Q2) and q(x,Q2)
J. Pumplin et.al JEHP 0207012 (2002)
CTEQ6 use DGLAP Q2-evolution of quark and
gluon distributions to extract q(x,Q2) and
G(x,Q2) from global fit to data sets at different
scales Q2.
error on G(x,Q2)
/- 10
Quark and Gluon Distributions
H1 Zeus F2
CTEQ6M
up-quarks
CDF D0 Jets
gluon
CTEQ5M1
10-410-3 10-2 10-1
0.5 x
error for d(x,Q2)
error for u(x,Q2)
down
anti-down
/- 5
/- 5
10-410-3 10-2 10-1
0.5 x

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G(x,Q2) and q(x,Q2) pQCD beautifully agree
Tevatron HERA!
J. Pumplin et.al JEHP 0207012 (2002)
ZEUS F2
D0 Jet Cross Section
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Data vs NLO pQCD at RHIC Inclusive p0
PHENIX p0 cross section a ?lt0.35
Phys.Rev.Lett.91241803,2003
STAR p0 cross section a 3.4lt?lt4.0
Phys.Rev.Lett.92171801,2004
NLO QCD from W. Vogelsang
19
Direct Photons and Inclusive Jets vs NLO pQCD
Inclusive Jet Cross section
Direct Photon Cross section
NLO QCD from W. Vogelsang
PHENIX Preliminary
Theory calculation show good agreement with the
experimental cross section.
STAR Preliminary
NLO QCD from W. Vogelsang
20
Direct Photons in Heavy Ion Collisions
Use hard probes (hadrons vs direct photons) to
study medium formed in heavy ion collisions at
RHIC
quark ? jet
g
q
direct photon
21
Collision Geometry Impact Parameter vs
Collisions and Participants
Spectators
Participants
Npart (No. participants) Nbinary
(No. binary collisions)
15 fm b
0 fm
0 Npart
394
0 Nbinary
1200
22
pQCD vs Direct Photons in AuAu
PRL 94, 232301
pQCD x number of binary nucleon-nucleon
collisions, Nbinary , in heavy in collisions
(Werner Vogelsang)
pQCD calculations permit calibration of hard
probes in heavy ion collisions at RHIC in a
model indepen- dent way
23
pQCD vs Inclusive Hadrons Jet Suppresion
pp comparison data (and pQCD!)

• Suppression is strong (factor 5) up to 20 GeV/c
• Medium is extremely opaque
• The data provide a lower bound on the initial
  gluon density

24
RHIC
25
RHIC ion-ion and polarized p-p Collider
26
RHIC ? five complementary experiments
pp2pp
27
A novel experimental method Probing Proton
Spin Structure Through High Energy Polarized
p-p Collisions
RHIC pC Polarimeters
Absolute Polarimeter (H jet)
Siberian Snakes
BRAHMS PP2PP
PHOBOS
2005 Complete!
high current polarized source
high energy proton polarimetry
helical dipoles magnets
Siberian Snakes
Spin Flipper
PHENIX
STAR
Spin Rotators
Partial Snake
Strong Snake
Helical Partial Snake
Polarized Source
LINAC
AGS
BOOSTER
200 MeV Polarimeter
Rf Dipole
AGS Polarimeter
28
2006 Figure of Merit Goals and Actual
goals
0.88
1.11
7 times Run-5
P2L Transverse
P4L Longitudinal
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BRAHMS AN for charged p,K, p, low x
100 transverse spin! Two spectrometer arms with
good particle ID at high momenta
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PHENIX ?G, ?q/?q, Sivers, dq, low x
EM Calorimeter
Beam-Beam Counter
Time Expansion Chamber
Muon Tracking Chambers
Central Arms
Muon ID Panels
Pad Chambers
North Muon Arm
Multiplicity/Vertex Detector
Drift Chambers
South Muon Arm
Time of Flight Panels
Four spectrometer arms with excellent trigger
and DAQ capabilities.
Ring Imaging Cerenkov
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STAR ?G, ?q/?q, Sivers, dq, low x
Large acceptance TPC and EMC -1lt?lt2
32
RHIC Detector Status and Upgrades
o All instrumentation is in place for the
planned measurements on spin dependent gluon
distributions and transverse spin. o
W-physics (flavor separation of quark and
anti-quark polarizations) requires upgrades in
PHENIX (muon trigger, funded by NSF and JSPS)
and STAR (forward tracking, grant proposal to
DOE in preparation). o In PHENIX a central
silicon tracking upgrade and a forward
tungsten silicon calorimeter upgrade will
significantly enhance capabilities for jet and
photon-jet physics. o A RHIC luminosity upgrade
(RHIC II) for heavy ions with electron cooling
will gain a factor 3-5 (beyond design) in
luminosity from 2012.
33
Gluon Spin Distribution
ALL in inclusive Jets (STAR)
ALL for inclusive p0 (PHENIX)

34
ALL from Inclusive Jets in pp Collisions at
vs200GeV
jet cone0.4
STAR Preliminary
STAR Projections for 2006
) Predictions B.Jager et.al,
Phys.Rev.D70(2004) 034010

• Results limited by statistical precision
• Total systematic uncertainty 0.01 (STAR)
  beam pol. (RHIC)
• GRSV-max gluon polarization scenario disfavored

35
Run 5 ALL(p0) First constraints for ?G(x)
Comparison with ?G from QCD analysis of DIS data
M. Glück, E. Reya, M. Stratmann, and W.
Vogelsang, Phys. Rev. D 53 (1996) 4775.
max ?G from DIS
Excludes large gluon spin contributions! Needs
to be quantified with NLO pQCD analysis!
standard ?G from DIS
min ?G possible
?G 0
40 scale error (missing abso- lute polarization
measurement).

36
NLO QCD Analysis of DIS A1 ALL(p0)
M. Hirai, S. Kumano, N. Saito, hep-ph/0603212 (Asy
mmetry Analysis Collaboration)
DIS A1 ALL(p0)
ACC03
x
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?G Measurements by 2012
see Spin report to DOE http//spin.riken.bnl.gov/
rsc/
?s200 GeV incl. ?0 prodn
?s500 GeV incl. jet prodn

• Final results on ?G will come from combined NLO
  analysis of all channels at
  RHIC and in DIS
• RHIC measurements will span broad range in x
  with good precision. multiple channels with
  independent theo. and exp. uncertainties.
• Uncertainty through extrapolation to small x

38
Transverse Spin AN for
inclusive hadrons
(BRAHMS, PHENIX, STAR)

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QCD Cross Sections for Transverse Spin
QCD Asymmetries for transverse spin are small
at high energies (Kane, Pumplin, Repko,
PRL 41, 16891692 (1978) )

QCD Test !
40
QCD Cross Sections for Transverse Spin
QCD Asymmetries for transverse spin are small
at high energies (Kane, Pumplin, Repko,
PRL 41, 16891692 (1978) )

Experiment (E704, Fermi National Laboratory)
p
p0
p-
Suggestions Sivers-, Collins-, Qui-Sterman,
Koike mechanisms !?
Can QCD be re-conciled with large transverse
asymmetries?
41
AN Results from PHENIX and STAR
PHENIX AN(p0) and AN(p0) at ?lt0.35 Phys.Rev.Lett
.95202001,2005
STAR AN(p0) at 3.4lt?lt4.0 Phys.Rev.Lett.92171801,2
004 and (hep-ex/0502040)

• Sizable asymmetries for xF gt 0.4
• Back angle data consistent
• with AN 0

42
BRAHMS AN
Pions
p
p
Protons
p-
p
K
Kaons

• DIS 2006, prel. stat. errors only
• First AN for kaons and protons
• AN(K-) and AN(p) dont agree
• with naive expectation from
• valence quark fragmentation

K-
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AN Maximum Asymmetries Possible
M. Anselmino, M. Boglione, U. DAlesio, E.
Leader, S. Melis and F. Murgia hep-ph/0601205
(I) Sivers quark and gluon distributions
Correlation between proton-spin and
transverse quark momentum
(II) Transversity quark-distributions and
Collins fragmentation Correlation
between proton- und quark-spin and spin
dependent fragmentation
quark-Sivers
Transversity x Collins
gluon-Sivers
RHIC 2006 precision measurements of AN with
20 x ?Ldt and 2-3 x Pbeam on tape ? QCD
analysis to separate effects !?
44
Measurement of Transversity- and
Sivers-Distributions in Polarized p-p Collisions
at RHIC
RHIC Luminosity?
AN
excellent! AN(jet/hadron-correlations)
good
(Sivers signature!) AT
(Collins FF) just enough AT
(Interference FF) just enough AT (Drell
Yan) no ATT( Drell Yan)
no

requires Collins and Interference FFs ? ee- at
Belle
RHIC II Luminosities
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RHIC II Luminosity UpgradeTransversity Sivers
Boer-Mulders in Drell Yan
Transversity correlation between transverse
proton spin and
quark spin Sivers correlation
between transverse proton
spin and quark
transverse momentum Boer/Mulders
correlation between transverse quark spin
and quark
transverse momentum
46
Sivers-Asymmetries, AT in Drell Yan (J. Collins
et al.)
Q4GeV
Q20GeV
Q4GeV
Q20GeV
AT
AT
STAR for 125pb-1
Dedicated DY Experiment 1250 pb-1
o 10 oclock ? 100 transverse polarization o
mini-quads o acceptance -3 lt ? lt 3
47
Transversity in Drell Yan with a Dedicated Drell
Yan Experiment for Transverse Spin
ATT for Drell Yan with dedicated DY detector
projections for 1250pb-1 of running, 5-10 higher
polarization, with RHIC II luminosities and
large acceptance
Drell Yan 1.25fb-1, large acceptance detector
for Drell Yan
This measurement appears to be also possible at
500 GeV
48

Summary
RHIC and its experiments are the worlds first
facility capable of colliding high energy
polarized protons and heavy ions. Collider and
Experiments are complete and first
high statistics polarized proton runs took place
in 2005 and 2006. Hadron Collisions at RHIC
provide a powerful experimental tool to study
the structure of the nucleon. We are at the
beginning of a broad new program on spin
dependent nucleon substructure and phenomena in
nucleon structure at low x.
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NLO QCD Analysis vs High
pT Hadron Production in DIS
High pT hadron production provides
additional constraints to fit for 0.07 lt x lt 0.3,
high pT data consistent with the three fit
results for ?G/G
DIS A1 ALL(p0)
DIS A1
DIS A1 ALL(p0) neg ?Ginitial
50
Back-to-back di-Jets Access to Gluon Sivers
Function
Measurements near mid-rapidity with STAR search
for spin-dependent deviation from back-to-back
alignment
gt 7 GeV trigger jet gt 4 GeV away side jet
Current measurements should be sensitive at the
level of predictions
D. Boer and W. Vogelsang, Phys.Rev. D 69 (2004)
094025
PHENIX measurement of back-to-back di-hadrons.
51
Best Approach to Transversity at RHIC ?!
Interference Fragmentation
Jian Tang , Thesis MIT, June 1999
R. Jaffe, X.Jin, J. Tang Phys. Rev. D57 (1999)5920
Jet
X. Ji, Phys. Rev. D49 (1994)114
IFF
J. Collins, S. Heppelmann, G. Ladinsky,
Nucl.Phys. B420 (1994)565
Proton Structure
Hard Scattering Process
Jet
ee- spin dep. FF
PDFs
pQCD
extract
52
Transverse Single Spin Asymmetry
(Tang, Thesis, MIT)
Maximum Asymmetry
200 GeV
500 GeV
53
Rates for Asymmetries in Interference
Fragmentation in PHENIX for 32 pb-1
Example
32
1
2
IFF from Belle AT from STARPHENIX
54
Collins (and Interference) Fragmentation Function
Measurement in ee- at Belle
ee- CMS frame
R. Seidl, spin Th 1730
j2-p
e-
Q
j1
j2
j1
e
2-hadron inclusive transverse momentum dependent
cross section
55
Collins Asymmetries for pp- Pairs

• Experimental method to remove acceptance effects
  and asymmetries from QCD radiative processes.
• First direct measurement of the Collins function.
• First QCD analysis (Anselmino et al.) for Hermes
  and Belle data show good agreement between Belle
  FF and Hermes
• See this weeks PRL for details..

z1
z2
56
LO-QCD Analysis of HERMES and Belle
Results (Efremov, Goeke, Schweitzer,
hep-ph/0603054)
HERMES PRELIMINARY
BELLE PRELIMINARY
Combined fit to Hermes asymmetries (Transversity
x Collins-FF) and Belle asymmetries (Collins-FF2)
? Excellent agreement!