Carl Gagliardi – DIS2008 – Jets in pp at RHIC 1
Jet Production in Polarized pp Collisions at RHIC
Carl A. GagliardiTexas A&M University
for the Collaboration
Outline• Introduction• 2005 results• 2006 results• Looking ahead
STARSTAR
Carl Gagliardi – DIS2008 – Jets in pp at RHIC 2
Origin of the proton spin?Polarized DIS: 0.2~0.3 Poorly Constrained
gz
qz
pz LLGS
2
1
2
1
• A primary goal of the RHIC Spin program is to determine the gluon polarization distribution
Three recent fits of equal quality:– ΔG = 0.13 ± 0.16– ΔG ~ 0.006– ΔG = -0.20 ± 0.41all at Q2 = 1 GeV2
Leader et al, PRD 75, 074027
Carl Gagliardi – DIS2008 – Jets in pp at RHIC 3
Polarized pp collisions at RHIC
LLba
baLL a
ff
ffA ˆ
f: polarized parton distribution functions
cos
For most RHIC kinematics, gg and qg dominate, making ALL for jets sensitive to gluon polarization. 10 20 30 pT(GeV)
Partonic fractions in jet production at 200 GeV
0
0.25
0.5
0.75
1
0 0.2 0.4 0.6 0.8 1
|cos (theta*)|
qg
->
qg
FO
M
0
Carl Gagliardi – DIS2008 – Jets in pp at RHIC 4
RHIC: the world’s first polarized hadron collider
“Thousands of millions”
• Spin varies from rf bucket to rf bucket (9.4 MHz)• Spin pattern changes from fill to fill• Spin rotators provide choice of spin orientation• “Billions” of spin reversals during a fill with little if any depolarization
BRAHMS
PHENIX
AGS
BOOSTER
Spin Rotators(longitudinal polarization)
Solenoid Partial Siberian Snake
Siberian Snakes
200 MeV PolarimeterAGS Internal Polarimeter
Rf Dipole
RHIC pC PolarimetersAbsolute Polarimeter (H jet)
AGS pC Polarimeters
Strong Helical AGS Snake
Helical Partial Siberian Snake
Spin Rotators(longitudinal polarization)
Spin flipper
Siberian Snakes
STAR
PHOBOS
Pol. H- SourceLINAC
Carl Gagliardi – DIS2008 – Jets in pp at RHIC 5
E-M Calorimeter
Time of Flight
Projection Chamber
STAR detector
Carl Gagliardi – DIS2008 – Jets in pp at RHIC 6
Midpoint cone algorithm(Adapted from Tevatron II - hep-ex/0005012)
• Seed energy = 0.5 GeV
• Cone radius in -• R=0.4 with 0.2 < < 0.8 (2005)• R=0.7 with -0.7 < < 0.9 (2006)
• Splitting/merging fraction f=0.5
Jet reconstruction in STARD
etec
tor
etcp
e
,,
,
gq,
GE
AN
TP
YT
HIA
Data jets MC jets
Par
ticl
e
Use PYTHIA + GEANT to quantify detector response
Carl Gagliardi – DIS2008 – Jets in pp at RHIC 7
Jet production at RHIC
STARSTAR PRL 97, 252001
• Jet structure at 200 GeV is well understood
• Mid-rapidity jet cross section is well described by pQCD over 7 orders of magnitude
Carl Gagliardi – DIS2008 – Jets in pp at RHIC 8
• Reconstruction bias: combination of steeply falling spectrum and ~25% jet ET resolution
• Trigger bias: non-uniform sampling of gg, qg, and qq processes
• Will illustrate impact on ALL with 2006 data
Neutral Energy Fraction
2005 inclusive jets ALL systematics
ALL systematics (x 10 -3)
Reconstruction + Trigger Bias
2-5 (pT dep)
Non-longitudinal Polarization
0.1-0.8 (pT dep)
Relative Luminosity 0.94
Backgrounds 0.70
pT systematic [-5.4%,+6.7%]
Carl Gagliardi – DIS2008 – Jets in pp at RHIC 9
2005 inclusive jets ALL
• Comparison to predictions within the GRSV framework with various input values of ΔG demonstrate sensitivity
STARSTAR hep-ex arXiv:0710.2048
Model calcs from:Jager et al, PRD 70, 034010
200 GeV0.2 < η < 0.8
Carl Gagliardi – DIS2008 – Jets in pp at RHIC 10
Limits on ΔG from 2005 jet results
• Significant new constraints on ΔG when compared to predictions derived from one global fit to DIS data
GRSV DIS
STARSTAR hep-ex arXiv:0710.2048
Carl Gagliardi – DIS2008 – Jets in pp at RHIC 11
Other global analyses
• There are many other global analyses of the polarized DIS data
xΔg(x) atQ2 = 10 GeV2
Carl Gagliardi – DIS2008 – Jets in pp at RHIC 12
Additional ALL predictions for 2005
• Many predictions for ALL vs. pT
• Is the sensitivity unique to GRSV?
Carl Gagliardi – DIS2008 – Jets in pp at RHIC 13
Comparison to other global analyses
• The STAR data exclude a broad range of models that have ΔG larger than that in GRSV-std
• The counterexample is GS-C, which is negative at large x, has a node near x ~ 0.1, and has a large first moment at small x
STARSTAR
Carl Gagliardi – DIS2008 – Jets in pp at RHIC 14
2006 data
Improved figure of merit Luminosity : 2 4.7 pb-1
Polarization: 50% 60% (online polarization)
Barrel EMC coverage: [0,1] [-1,1]
In addition Jet cone radius: 0.4 0.7 -0.7 < jet axis < 0.9 Neutral energy fraction < 0.85
Increased trigger thresholds
Inclusion of Endcap EMC towers
Improved tracking at large ||
Shielding from backgrounds
Carl Gagliardi – DIS2008 – Jets in pp at RHIC 15
Jet reconstruction and trigger bias for 2006 data
Step 1: Use PYTHIA+GEANT to estimate the pT shift from detector jets to particle jets
Step 2: Simulate the difference in ALL between particle and detector jets for various gluon polarization scenarios
Particle jetsShifted detector jetsDetector jets
• Maximum deviation determines ALL systematic
• Confidence level calculations take account of any residual
Carl Gagliardi – DIS2008 – Jets in pp at RHIC 16
2006 inclusive jets ALL
• Statistical uncertainties are 3-4 times smaller than in ’05 data for pT > 13 GeV/c
ALL systematics (x 10 -3)
Reconstruction + Trigger Bias
[-1,+3]
(pT dep)
Non-longitudinal Polarization
~ 0.03
(pT dep)
Relative Luminosity
0.94
Backgrounds 1st bin ~ 0.5
else ~ 0.1
pT systematic 6.7%
Model curves calculated with cone radius 0.7 and -0.7 < < 0.9
200 GeV-0.7 < < 0.9
STARSTAR
Carl Gagliardi – DIS2008 – Jets in pp at RHIC 17
Limits on ΔG from 2006 jet results
• Within the GRSV framework:– GRSV-std excluded with 99% CL– ΔG < -0.7 excluded with 90% CL
GRSV DIS
STARSTAR
Carl Gagliardi – DIS2008 – Jets in pp at RHIC 18
Looking beyond inclusive ALL measurements
• Inclusive ALL measurements at fixed pT average over a broad x range.
• Need a global analysis to determine the implications• Can hide considerable structure if Δg(x) has a node
Carl Gagliardi – DIS2008 – Jets in pp at RHIC 19
DSSV – first global analysis with polarized jets
• The first global NLO analysis to include inclusive DIS, SIDIS, and RHIC pp data on an equal footing
• Finds a node in the gluon distribution near x ~ 0.1, but with the opposite phase from GS-C
de Florian et al., arXiv:0804.0422 [hep-ph]
Carl Gagliardi – DIS2008 – Jets in pp at RHIC 20
The next few years: di-jets and Δg(x)
• Di-jets provide direct access to parton kinematics at LO
Mass Rapidity |cos(*)|
Ratio
2005 preliminary di-jet distributions
2
|ηη|tanh|cosθ|
2
ηη
x
xln
2
1y
sxxM
epeps
1x
epeps
1x
43*
43
2
1
21
η4
η32
η4
η31
43
43
STARSTAR
Carl Gagliardi – DIS2008 – Jets in pp at RHIC 21
Projected di-jet sensitivity for the 2009 run
• Assumes 50 pb-1 of 200 GeV pp collisions with 60% polarization
GS-C
x1 ~ 0.45x2 ~ 0.16
x1 ~ 0.27x2 ~ 0.27
Rel FOM ~ 70%
x1 ~ 0.33x2 ~ 0.044
Carl Gagliardi – DIS2008 – Jets in pp at RHIC 22
Conclusions• STAR inclusive jet ALL measurements have excluded
extreme gluon polarization scenarios
• Over the next few years, STAR di-jet measurements will provide direct information about Δg(x)
• STAR will also obtain complementary information about Δg(x) from γ + jet
• Stay tuned!
Carl Gagliardi – DIS2008 – Jets in pp at RHIC 23
Carl Gagliardi – DIS2008 – Jets in pp at RHIC 24
ALL
1
P1P2
N RN
N RN
N : Spin dependent yields (# of reconstructed jets)
P : Beam polarization (measured by RHIC Polarimeter)
R : Relative luminosities between different spin states
Double longitudinal spin asymmetry, ALL
Carl Gagliardi – DIS2008 – Jets in pp at RHIC 25
STAR detectors for jet measurements
Time Projection Chamber ||<1.4 tracking
Barrel EM Calorimeter||<1 triggering & calorimetry
Endcap EM Calorimeter1.09<<2 triggering & calorimetry
Beam-Beam Counters3.4<||<5 triggering, luminosity, local polarimetry
Carl Gagliardi – DIS2008 – Jets in pp at RHIC 26
Other global analyses
xΔg(x) atQ2 = 10 GeV2
Carl Gagliardi – DIS2008 – Jets in pp at RHIC 27
Additional ALL predictions for 2005
ALL
Carl Gagliardi – DIS2008 – Jets in pp at RHIC 28
Charged Energy Fraction
Estimating the non-jet background
Data Monte Carlo
• Non-jet backgrounds stand out in the data as single-jet events that have a small charged energy fraction
• Isolate the background in the ratio of mono-jet to di-jet events vs. charged energy fraction
Data
Charged Energy Fraction
Charged Energy Fraction
Carl Gagliardi – DIS2008 – Jets in pp at RHIC 29
ALL vs. run index for 2006 data
STAR Preliminary
Carl Gagliardi – DIS2008 – Jets in pp at RHIC 30
False asymmetries in 2006 data
STAR PreliminarySTAR Preliminary
• Longitudinal single-spin (parity-violating) asymmetries are consistent with zero, as expected at this precision
Carl Gagliardi – DIS2008 – Jets in pp at RHIC 31
Inclusive jet ALL for fixed values of ΔG
• Calculations by Stratmann and Vogelsang within the GRSV framework