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APPROXIMATION OF JET AXIS IN RAPIDITY SEPARATED DIHADRON CORRELATIONSJosh PerryIowa State UniversityPHENIX Collaboration
MEASUREMENT AT PHENIX Collide transversely polarized protons
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Right
Left PA
RL
RLN
1
= particle yield to the left versus particle yield to the right
NA
Experiment
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ASYMMETRY SOURCES Sivers Effect
Initial state effect Proton spin and parton transverse momentum
are correlated
Right
Left
kT
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Sivers Effect Initial state effect Proton spin and parton transverse momentum are correlated
Final state quark momentum leaves asymmetrically Results in final state Left/Right asymmetry of fragmentation
hadrons
Right
Left
ASYMMETRY SOURCES
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ASYMMETRY SOURCES
Right
Left
Collins Effect (coupled with Transversity) Final state effect Final state quark leaves WITHOUT asymmetry but
inherits proton polarization (through transversity)
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ASYMMETRY SOURCES Collins Effect (coupled with Transversity)
Final state effect Final state quark leaves WITHOUT asymmetry but inherits proton
polarization (through transversity)
Quark spin and quark fragmentation shape are correlated Results in a final state Left/Right asymmetry of fragmentation hadrons
Right
Left
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MY RESEARCH Measure the Collins Effect independent of
Sivers Find a way to ignore initial state Sivers EffectCollins and Sivers (possibly
more)Collins alone, no Sivers
?
We’re going to need a place to collide protons and detect particle showers exiting the collision...
MPC Single Cluster Asymmetry
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RHIC Relativistic Heavy Ion Collider
200 GeV CMS ~60% Polarization Data I am analyzing is from Run12 (Spring of 2012)
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PHENIX (PIONEERING HIGH ENERGY NUCLEAR INTERACTIONS EXPERIMENT)
Central arms Forward arms
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PHENIX (PIONEERING HIGH ENERGY NUCLEAR INTERACTIONS EXPERIMENT)
Central arms Forward arms
MPC 3.1 < | η | < 3.9• Neutral Pions
Central Arms | η | < 0.35•Neutral Pions• Photons•Electrons•Etc.
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PHENIX CRAYON DRAWINGPHENIX Central Arm Detectors
PHENIX Forward EM Calorimeter (MPC)
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HARD SCATTERING 2 -> 2 scattering at leading order
Conservation of momentum Outgoing partons back-to-back in CM frame
G Gq q
G q
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HARD SCATTERING 2 -> 2 scattering at leading order
Conservation of momentum Outgoing partons back-to-back in CM frame
G Gq q
GHigher x
q
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HARD SCATTERING 2 -> 2 scattering at leading order
Conservation of momentum Outgoing partons back-to-back in CM frame
G Gq q
GHigher x
Lower xq
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KINEMATIC SELECTION
G
PHENIX Central Arm Detectors
PHENIX Forward EM Calorimeter (MPC)
Automatic bias of parton species from our detector positions (and kinematic selection)The goal is Collins: now we just need transversely polarized quarks so we can detect the fragmentation products.
q
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TRANSVERSITY DISTRIBUTION How often is a quark’s spin parallel to the
proton’s spin direction?
u-quark
d-quark
parallelantiparallel qqq
Spin 1/2
hep-ph/070100v3
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KINEMATIC SELECTION
G
PHENIX Central Arm Detectors
PHENIX Forward EM Calorimeter (MPC)
We now have set up a bias for mostly transversely polarized quarks to be headed toward our detector!
q
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KINEMATIC SELECTION
G
PHENIX Central Arm Detectors
PHENIX Forward EM Calorimeter (MPC)fragmention neutral pion
fragmention hadrons
After the collision, the forward-going quark and central-going gluon fragment into particle showers
q
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q
KINEMATIC SELECTION
G
PHENIX Central Arm Detectors
PHENIX Forward EM Calorimeter (MPC)fragmention neutral pion
Sum up central particle shower constituent momenta to reconstruct central gluon (jet) momentum.FastJet Anti-K_T algorithm applied
Reconstructed central jet direction
PHENIX does not have hadronic calorimetery, jet energy goes missing…
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P_RECO/P_JET CORRECTION Apply a momentum correction based on the
sampled longitudinal momentum fraction during fragmentation i.e.; momentum of the reconstructed jet divided by
the momentum of the jet in monte carlo
<z> = P_hadron/P_parton
p p
<z> P_reco/P_jetForward pion Central jet
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q
‘FLIP AND SWAP’
G
PHENIX Central Arm Detectors
PHENIX Forward EM Calorimeter (MPC)fragmention (neutral pion)/<z>
Reconstructed (central jet)/(P_reco/P_jet) direction
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q
‘FLIP AND SWAP’ Perform Lorentz boost to CM frame of central
jet and forward neutral pion
G
Reconstructed (central jet)/(P_reco/P_jet) direction
forward jet direction (unobserved)
fragmentation (neutral pion)/<z>
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q
‘FLIP AND SWAP’ Flip reconstructed central jet direction
around 180 degrees
G
forward jet proxy direction
fragmentation neutral pion
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q
‘FLIP AND SWAP’ Flip reconstructed central jet direction
around 180 degrees Measure the hadron’s direction relative
to the forward jet (proxy) direction (and projected spin axis)
Asymmetry seen in fragmentation? Too much smearing due to ‘Flip and
Swap’?G
forward jet proxy direction
forward quark proxy direction
hadronquark spin
f
Let’s check with simulation.
fragmentation neutral pion
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SIMULATION No simulation existed to do what we needed
proton-proton collisions Transversity to give final state quarks a polarization Collins fragmentation
ToyMC Monte Carlo (simulation) Created at Iowa State University
Now available publically as TPPMC (http://code.google.com/p/tppmc/)
PYTHIA simulation package Performs hard scattering
Using Anselmino et al. global fits from HERMES and COMPASS fixed target data Initial state transversity weighting
Gives final state quarks polarization Independent fragmentation model
Applies Collins Effect to fragmentation Sivers final state event weighting is also available
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TRANSVERSITY
x
ToyMC consistent with published distributions; transv. opposite for down quarks.
hep-
ph/0
7010
0v3
ToyM
C M
onte
Car
lo
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FRAGMENTATION
z
(DSS)
u-quark fragmentation
z
gluon fragmentation
p+ p- p0
K+K- p np nK0 K0
Particle yield
Pion+Kaon+Proton(DSS)
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• Check implementation by reproducing Anselmino et. al. results:
COLLINS FUNCTION
ToyM
C M
onte
Car
lo
Phys
.Rev
.D75
:054
032,
2007
Large asymmetry at high z
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• Check implementation by reproducing Anselmino et. al. results:
COLLINS FUNCTION
Phys
.Rev
.D75
:054
032,
2007
fz
Actual fragmentation function sampled is now a 2D function
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‘FLIP AND SWAP’ SIMULATION RESULTS Use the ToyMC Monte Carlo Perform the ‘Flip and Swap’ procedure Collins effect seen? Sin(phi) distribution of
fragmentation hadrons about quark direction?
Neutral pionsforward quark proxy direction
hadronquark spin
f
Using the Anselmino group’s global fit mean values
Phi
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‘FLIP AND SWAP’ SIMULATION RESULTS Use the ToyMC Monte Carlo Perform the ‘Flip and Swap’ procedure Collins effect seen? Sin(phi) distribution of
fragmentation hadrons about quark direction?
Neutral pions
Using the Anselmino group’s global fit mean values
Phi
Large smearing Jet axis reconstruction ‘Flip and Swap’
Large asymmetry at high z
The asymmtery is large enough to be seen through the smearing
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PROJECTED RESOLUTION Simulation parameters
Statistical yield based on Run8 ‘proof of principle’ data analysis
Error bars are statistical errors for 33 pb^-1 (Run12+13) Taking into account PHENIX uptime, z vertex cut, etc.
Solid and dashed lines: 100% and 25% Collins contributions
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FUTURE Run 12 data currently being analyzed Central arm + forward MPC triggered events
Sampled: 17.6 pb-1
Collected: 215 million 58% polarization More statistics than projected
Lower central arm trigger threshold between Run8 and Run12 The ‘Flip and Swap’ method is viable
Collins can be measured at PHENIX The MPC-EX detector is being built at PHENIX to
enhance the MPC Allows measurement of direct photons for direct access to
Sivers A ‘full picture’ of Collins and Sivers in pp collisions is in our
future
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BACKUP End
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MPC ASYMMETRY Run8 (2008) transverse spin MPC data Instead of a fancy A*sin(phi) this compares
left and right halves Effectively A*sin(phi) with only two phi bins
x_F is similar to x
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RHIC The tunnel
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COMPARISON TO DATA
SOLID: Collins onlyDASHED: Collins+Sivers
Simulation
Simulation
Plot courtesy of John Lajoie
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PARTILE YIELD
p+ p- p0
K0 K0 K+ K- p np n
Plot courtesy of John Lajoie
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COMPARISON OF PION ASYMMETRIESparton
pionspin
π+
π-
π0
E704: Left-right asymmetries AN for pions:
AN
xF
• pi0 FF is taken as all favored (based on quark content)• shown averaged over all quark flavors
f (radians)
Black – pi+Red – pi-Blue – pi0
Plot courtesy of John Lajoie
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IDEAL CASE, PROBING TRANSVERSITY*COLLINS Throw a polarized quark,
watch it fragment
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IDEAL CASE, PROBING TRANSVERSITY*COLLINS Throw a polarized quark,
watch it fragment Put a big particle detector in
front of it
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IDEAL CASE, PROBING TRANSVERSITY*COLLINS Throw a polarized quark,
watch it fragment Put a big particle detector in
front of it … but of course we need a
quark from a proton At high x Polarized quark No gluons
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