Transcript Probing the Color Gauge Link via Heavy Quark TSSA in p+p Collisions Ming X.

Probing the Color Gauge Link via
Heavy Quark TSSA in p+p Collisions
Ming X. Liu
Los Alamos National Lab
INT Spin Workshop 11/2010
A new Experimental Test of color dynamics in hard scattering
- TSSA for Open (anti)charm, J/Psi and DY
- Test color structures for quark and anti-quark
- Experimental opportunity: RHIC and other future Exp’s
An experimentalist’s point of approach
Drawing from D. Sivers @Santa Fe Polarized Drell-Yan Workshop Dinner 10/31-11/1, 2010
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Color Flow in DY and DIS
• The sign change – a new fundamental test of color gauge formalism
• Charm TSSA could provides a new independent experimental test of
the underlying physics
Collins ‘02
Twist-3: sign change from gluonic-pole in hard parts
In the overlapped region – consistent description
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Ji, Qiu, Vogelsang, Yuan ‘06
Bacchetta, Boer, Diehl, Mulders ‘08
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Nice things about heavy quarks
• Experimentally tag Fermion
and anti-Fermion
• Theoretically “clean” to use
pQCD
– MQ >> ΛQCD
– Hard fragmentation
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RHIC 20,000 GeV beam
Do we understand the physics?
The Challenge of “Too Large”
Large Transverse Single Spin Asymmetry (SSA)
in forward meson production persists up to
RHIC energy.
FNAL 200 GeV beam
AGS 22 GeV beam
ZGS 12 GeV beam
PRL (2004)
PRD65, 092008 (2002)
PLB261, 201 (1991)
PLB264, 462 (1991)
PRL36, 929 (1976)
Perturbative cross section
Non-Perturbative cross section
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Color Interaction and TSSA
• Do we understand the underlying physics?
– the Sivers asymmetry, for example
• What can we learn more from future data?
– DY, charm, direct-photon…
We are colliding hadrons, not partons!
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Gamberg, Kang 2010
Generalizing GPM… with modified hard
cross sections (gluonic-pole cross sections)
PRL 99 (2007) A. Bacchetta et al,
PRD 72 (2005) A. Bacchetta, C.J. Bomhof,
P.J.Mulders, F.Pijlman
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Charm and anti-Charm TSSA and Color Structure
• Quark and anti-Quark have different color structure in hard
scatterings
•
Experimentally Charm and anti-Charm can be cleanly identified,
AN (c) : c     X
AN (c ) : c     X
?
AN (c) AN (c )
• AN(charm) provide new insight to the underlying physics of TSSA

– Directly test the different color structure for quark and anti-quark
A new clean experimental test of the color coupling
to quark vs antiquark in hard scatterings!
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TSSA in Heavy Quark Production
Kang, Qiu, Vogelsang, Yuan, PRD 2008
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Open Charm TSSA in Twist-3 Approach
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TSSA in Charm Production at Low Energy (I)
q  q cc
• Low energy
F. Yuan and J. Zhou PLB 668 (2008) 216-220
• Initial state interactions

• Final state interactions
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Heavy Quark TSSA at Low Energy (cont.)
Twist-3 quark-gluon correlation fun.
• Different color factors for charm and anti-charm
q  q cc
F. Yuan and J. Zhou PLB 668 (2008) 216-220

1
2N C2
NC2  2
~
2NC2
Initial state
Charm
~

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~
2
2N C2
anti-Charm

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AN : q  q c(c )  X
JPARC p+p
GSI: p+pbar
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Heavy Flavor TSSA @RHIC
• Sensitive to gluon Sivers function
* probe gluon’s orbital angular momentum?
-- Minimize Collins’ effects
* heavy flavor production dominated by gluon
gluon fusion at RHIC energy
Pythia 6.1 simulation (LO)
cc : gg  cc 95%
bb : gg  bb
85%
cc : gg  cc 95%
bb : gg  bb
85%
* gluon has zero transversity
Open Charm
• Tri-gluon correlation functions
• Also sensitive to J/ψ production mechanisms
and QCD dynamics
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Johann Riedl, SPIN2008
Heavy Quark SSA at High Energy (II)
Twist-3 tri-gluon correlation
g  g c  c
• Consequence of different color factors for charm and anti-charm

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Kang et al 2008
Koike et al 2010
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The Physics Goals
Experimental Study of the Color Flow via Open Heavy Quark TSSA
• Current understanding of TSSA based on the color
gauge invariant QCD formalism
– Twist-3, modified GPM …
– Expect significant difference between AN(c) and AN(c-bar)
• The process dependence of TSSA can be tested
experimentally
– DY vs DIS
– Charm (quark) vs anti-charm (anti-quark)
– Other processes ..
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Experimental Prospects
• RHIC – @high energy
• Other facilities @low energy
– JPARC
– GSI/FAIR
– Fermilab
– EIC
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Open Charm Production in p+p
with PYTHIA (LO)
RHIC 62GeV
RHIC 200 GeV
E906
JAPRC
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Charm Production p+p @200GeV
• At low pT, g+g dominates
LO
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NLO
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More on Open Charm Production
• Fixed targets vs NLO
• Collider mode @RHIC
EPJ C 52, 987 (2007) J. Riedl, A. Schafer, M. Stratmann
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PRL 95, 122001 (2005) M. Cacciari, P. Nason, R. Vogt
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Forward Open (anti)Charm AN
 D meson production dominated by gluon-gluon
D (-)
fusion at RHIC energy
 Sensitive to gluon Sivers effect
 AN measured for muons from D decay
 Smear by decay kinematics
Gluon Sivers=Max
Measurement for Gluon Sivers=0
Calculations for D mesons
Anselmino et al, PRD 70, 074025 (2004)
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TSSA and J/Ψ Production
J/ψ TSSA is sensitive to the production mechanisms
Assuming a non-zero gulon sivers function, In pp scattering, TSSA vanishes if
the pair are produced in a color-octet model but survives in the colorsinglet model
Feng Yuan, Phys. Rev D78, 014024(2008)
One color-singlet diagram
— no cancellation,
asymmetry generated by the
initial state interaction
Two color-octet diagrams
— cancellation between initial and
final state interactions, no asymmetry
In Collinear higher twist approach, the relation is not quiet simple. There
are partial but not full cancellation of terms.
Z. Kang
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PHENIX Detector
•Central Arm
e
|| < 0.35
+
e-
 Drift Chamber (DC)
 PbGl and PbSc
 Ring Imaging Cherenkov Detector (RICH)
 Pad Chambers (PC)
 Time Expansion Chamber (TEC)
•Global Detectors (Luminosity,Trigger)
μ+
 BBC
 ZDC
•Muon Arms 1.2 < |η| < 2.4
μ-
 Muon tracker (MuTr)
 Muon Identifier (MuID)
Year
s [GeV]
Recorded L
Pol [%]
FOM (P2L)
2006 (Run 6)
200
2.7 pb-1
51
700 nb-1
2008 (Run 8)
200
5.2 pb-1
46
1100 nb-1
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J/ψ Measurements in the Muon and Central Arms
In Muon Arm
J /     
ANIncl:
oppositely-charged muon pairs in the
invariant mass range ±2σ around J/ψ mass.
ANBG:
oppositely-charged muon pairs in the
invariant mass range 1.8 (2.0run8) < m <2.5
along with charged pairs of the same sign in
invariant mass range 1.8 (2.0run8) < m < 3.6
J /
N
A
In Central Arm
J /  e e
ANIncl.  r  ANBG

1 r
arXiv: 1009.4864
BG subtraction: 2*sqrt{Ne+e+Ne-e-}
Remaining continuum background
Is small, not enough statistics
Assuming: ANBG=0
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J/ψ AN at Forward Rapidity
X. Wang, SPIN2010, arXiv: 1009.4864
Asymmetries were obtained as a function of J/Psi Feynman-x,
with a value of -0.086 ± 0.026 (stat.) ± 0.003 (sys.) in the forward
region.
- Suggests possible non-zero tri-gluon correlation functions in
transversely polarized protons.
- If well defined in this reaction, the results suggests non-zero
gluon Sivers distribution functions.
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NRQCD and J/ψ Production
PHENIX, PRL 92, 051802 (2004)
Theoretical predictions of J/Ψ production at RHIC are in good agreement with the
PHENIX data: COM process dominant
◦
◦
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PRD 68 (2003) 034003 G. Nayak, M. Liu, F. Cooper
PRL 93 (2004) 171801 F. Cooper, M. Liu, G. Nayak
NRQCD and J/ψ Polarization
NRQCD failed on J/ψ polarization.
J/ψ production mechanism is still an open question.
Very active field of theoretical study…
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Near Future Prospects
PHENIX Silicon VTX Upgrades: by 2011
• Precision Charm/Beauty Measurements
• BJ/, Drell-Yan, ’
Drell-Yan
prompt
p
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Charm SSA to Probe Gluon Sivers Distribution
D meson Single-Spin Asymmetry:
• Production dominated by gluon-gluon fusion
• Sensitive to gluon Sivers distribution
• PHENIX-2006 data ruled out the max. gluon Sivers
?
AN (c)  AN (c )
• Much improved results expected with VTX detectors
Kang, Qiu, Yuan, Vogelsang, Phys. Rev. D 78,114013(2008)

AN


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A few Observations and Comments
•
Twist-3 and Generalized TMD Parton Model
– Color gauge approach
•
Quark sector: some knowledge
– Quark Sivers and Collins functions
– Twist-3 quark-gluon correlation functions
•
Gluon sector: largely unknown
– Gluon Sivers function(s)??
– Twist-3 tri-gluon correlation functions
•
Next experimental step for p+p
–
–
–
–
•
Heavy quark probe!
Directly access the color charge coupling to quark and anti-quark
Multi probes in a wide kinematic range
High luminosity polarized fixed target Drell-Yan and Charm experiment?
It is all about the color flow in hard scattering
– TSSA @RHIC-SPIN
– p/d+A @RHIC
– Jlab-12, EIC…
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Charm TSSA @EIC
• Open charm
• J/Psi
• Need model
calculations
Kang and Qiu PRD (2008)
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EIC: J/Psi TSSA (I)
• TSSA could be closely connected to J/Psi production
mechanisms
F. Yuan PRD 70, 074025
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EIC: J/Psi SSA (II)
• Color octet channel
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New Idea: High Luminosity Polarized Fixed Target p+p?
• Drell-Yan
• Open charm@ low √s
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Example (I): E906 Drell-YanXTarget
XBeam
Polarized DY possibility:
• Polarized targets
• Polarize the Main
Injector
• Or both
• 120 GeV proton beam
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D. Crabb MENU10
UVA/J-Lab/SLAC Polarized
proton/deuteron target
•
•
•
•
Polarized NH3/ND3 targets
Dynamical Nuclear Polarization
Operate at 5 T and 1 K. Pol ~ B/T
Used with high beam intensities –
up to ~100 nA
• Large capacity pumps
• Polarizations:
– p > 90%,
– d ~ 50%
• Able to handle high luminosity
– up to ~ 1035 (Hall C)
~ 1034 (Hall B)
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Expected DY AN Sensitivity @120 GeV.
Target
- 6 cm NH3
- 1019 proton
Also open charm and J/psi
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Summary and Outlook
• Experimental confirmation (or disproval) of color
flow dynamics in hard scattering is a critical step
toward understanding the mechanisms of SSA
• Drell-Yan
• Charm vs anti-Charm
• Future experimental prospects – exciting
opportunity!
– RHIC, high energy
– EIC
– Polarized fixed targets, low energy
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Backup
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Critical Role of VTX/FVTX for Drell-Yan and Open Charm
• Tracking muons with MuTr+FVTX
– Prompt muons from DY
– Displaced tracks from π/K and heavy
quark decays
Drell Yan
ϒ-states
DCA < 1 σ cut:
Increase DY/bb ~ 5
Drell Yan
J/Ψ
beauty
DY: 4 GeV < M < 9 GeV;
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B-background: use FVTX
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charm
combinatorial background
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Example (II): Polarized DY w/ Fixed Target
@RHIC ?
BRAHMS
PHENI
X
Polarized fixed target DY
exp. with extracted
polarized proton beams:
Fixed Target DY
Exp.
@Beam Dump
STAR
1. High density
LH2/LD2 target
2. High density
polarized targets
3 Map out x-dep.
- 250 GeV proton beams
- Pol up to 70%
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Fixed Target @RHIC ?
• Beam dump experiment: dimuon channel
– Parasitic mode
• Significant beams still left at the end of a store (~50%)
• Cycle time ~8hr
– Dedicated fixed target
• Cycle time ~ 1hr
– Dimu x-section @ 250 GeV (M>4) ~20pb
• Targets
– E906-like unpolarized LH2 target
• 51cm LH2 (2.1x1024/cm2)
• Can handle L ~ 1x1036cm-2s-1
– Polarized solid target
• UVA/J-Lab/SLAC: L ~1035cm-2s-1
• Advantages
–
–
–
–
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Polarized beams
(polarized) targets
Higher Energy and large x-coverage
High luminosity
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DY AN Sensitivity @250 GeV Fixed Target
4.5<M<8 GeV
qT < 1 GeV
10 fb-1
50 fb-1
xF
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Open charm at fixed target (cross section)
scc in pN,pN
•
•
s1/2(GeV)
Charm cross section by fixed
target experiments are
reasonably reproduced by LO
pQCD event generator (PYTHIA)
with large K-factor, or by NLO
pQCD calculation (HVQMNR).
Note that pQCD may or may not
be applicable to charm
production because charm mass
is small (~1.5GeV)
In the left figure, world pi+N data
and p+N data are compared with
PYTHIA calculation. The s1/2
dependence of the calculation
mainly reflects the underlying
PDF.
Charm production
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Proton Efficiency: Collider vs Fixed Target Mode
• Design value: 2x1011x100 = 2 x 1013 proton per store per ring
• Collision rate ~ 10 MHz
– Num. of collisions per store
– 10M x 3600sec x 8 hr = 2.9 x 1010
– Fract. of p’s used = 3 x1011 / 2 x 1013 = 1.5 x 10-2
• In the fixed target mode, for a ~20% interaction length, we can use ~20%
of the protons from the beam
– 0.2/ 1.5 x 10-2 = 13x gain in luminosity
• Center of Mass Energies for p+p
– Collider mode: sqrt(s) = 500 GeV
– Fixted T mode: sqrt(s) = 22 GeV
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Color Flow in Twist-3
Kang @RBRC workshop 2010
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Generalized Parton Model
• Assume TMD factorization
Anselmino et al.
TMD factorization breakdown… a failure or an opportunity?
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Mulders, Xiao..
@RBRC workshop 2010
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