Carl Gagliardi – DIS2008 – Jets in pp at RHIC 1 Jet Production in Polarized pp Collisions at RHIC Carl A. Gagliardi Texas A&M University for the Collaboration Outline Introduction 2005 results 2006 results Looking ahead STAR

Carl Gagliardi – DIS2008 – Jets in pp at RHIC 2 Origin of the proton spin? Polarized DIS: 0.2~0.3 Poorly Constrained 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 ~ –ΔG = ± 0.41 all at Q 2 = 1 GeV 2 Leader et al, PRD 75,

Carl Gagliardi – DIS2008 – Jets in pp at RHIC 3 Polarized pp collisions at RHIC  f: polarized parton distribution functions For most RHIC kinematics, gg and qg dominate, making A LL for jets sensitive to gluon polarization pT(GeV) Partonic fractions in jet production at 200 GeV 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

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/ ) 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 STAR Detector GEANT PYTHIA Data jets MC jets Particle Use PYTHIA + GEANT to quantify detector response

Carl Gagliardi – DIS2008 – Jets in pp at RHIC 7 Jet production at RHIC STAR PRL 97, 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 E T resolution Trigger bias: non-uniform sampling of gg, qg, and qq processes Will illustrate impact on A LL with 2006 data Neutral Energy Fraction 2005 inclusive jets A LL systematics A LL systematics(x ) Reconstruction + Trigger Bias 2-5 (p T dep) Non-longitudinal Polarization (p T dep) Relative Luminosity0.94 Backgrounds0.70 p T systematic[-5.4%,+6.7%]

Carl Gagliardi – DIS2008 – Jets in pp at RHIC inclusive jets A LL Comparison to predictions within the GRSV framework with various input values of Δ G demonstrate sensitivity STAR hep-ex arXiv: Model calcs from: Jager et al, PRD 70, GeV 0.2 < η < 0.8

Carl Gagliardi – DIS2008 – Jets in pp at RHIC 10 Limits on Δ G from 2005 jet results Significant new constraints on Δ G when compared to predictions derived from one global fit to DIS data GRSV DIS STAR hep-ex arXiv:

Carl Gagliardi – DIS2008 – Jets in pp at RHIC 11 Other global analyses There are many other global analyses of the polarized DIS data x Δ g(x) at Q 2 = 10 GeV 2

Carl Gagliardi – DIS2008 – Jets in pp at RHIC 12 Additional A LL predictions for 2005 Many predictions for A LL vs. p T 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 Δ G 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 STAR

Carl Gagliardi – DIS2008 – Jets in pp at RHIC 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 p T shift from detector jets to particle jets Step 2: Simulate the difference in A LL between particle and detector jets for various gluon polarization scenarios Particle jets Shifted detector jets Detector jets Maximum deviation determines A LL systematic Confidence level calculations take account of any residual

Carl Gagliardi – DIS2008 – Jets in pp at RHIC inclusive jets A LL Statistical uncertainties are 3-4 times smaller than in ’05 data for p T > 13 GeV/c A LL systematics(x ) Reconstruction + Trigger Bias [-1,+3] (p T dep) Non-longitudinal Polarization ~ 0.03 (p T dep) Relative Luminosity 0.94 Backgrounds1 st bin ~ 0.5 else ~ 0.1 p T systematic  6.7% Model curves calculated with cone radius 0.7 and -0.7 <  < GeV -0.7 <  < 0.9 STAR

Carl Gagliardi – DIS2008 – Jets in pp at RHIC 17 Limits on Δ G from 2006 jet results Within the GRSV framework: –GRSV-std excluded with 99% CL –Δ G < -0.7 excluded with 90% CL GRSV DIS STAR

Carl Gagliardi – DIS2008 – Jets in pp at RHIC 18 Looking beyond inclusive A LL measurements Inclusive A LL measurements at fixed p T 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: [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 MassRapidity |cos(  * )| Ratio 2005 preliminary di-jet distributions STAR

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 x 1 ~ 0.45 x 2 ~ 0.16 x 1 ~ 0.27 x 2 ~ 0.27 Rel FOM ~ 70% x 1 ~ 0.33 x 2 ~ 0.044

Carl Gagliardi – DIS2008 – Jets in pp at RHIC 22 Conclusions STAR inclusive jet A LL 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 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, A LL

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 Calorimeter 1.09<  <2 triggering & calorimetry  Beam-Beam Counters 3.4<|  |<5 triggering, luminosity, local polarimetry

Carl Gagliardi – DIS2008 – Jets in pp at RHIC 26 Other global analyses x Δ g(x) at Q 2 = 10 GeV 2

Carl Gagliardi – DIS2008 – Jets in pp at RHIC 27 Additional A LL predictions for 2005 A LL

Carl Gagliardi – DIS2008 – Jets in pp at RHIC 28 Charged Energy Fraction Estimating the non-jet background DataMonte 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

Carl Gagliardi – DIS2008 – Jets in pp at RHIC 29 A LL vs. run index for 2006 data STAR Preliminary

Carl Gagliardi – DIS2008 – Jets in pp at RHIC 30 False asymmetries in 2006 data STAR 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 A LL for fixed values of Δ G Calculations by Stratmann and Vogelsang within the GRSV framework