Using Jet Asymmetries to Access  G at Renee Fatemi Massachusetts Institute of Technology for the STAR Collaboration March 23, 2006 Moriond QCD, La Thuile, Italy 1. Measurements aimed at extraction of  G at STAR 2. RHIC Facility and STAR Experiment 3. STAR Jet Algorithm and Jet Characteristics 4. Jet Cross-Section and NLO comparisons 5. Double Spin Jet Asymmetries and implications for  G 6 Future Improvements and Measurements STAR

A Short History of  G Indirectly accessed from DIS via Next-to- Leading order fits I. Hirai,Kumano and Saito hep-ph/ % proton spin. Data from Fixed Target DIS ep scattering Limited CM energy range results in large error on  G fit. For Q 2 =1 GeV 2 I. II. Need polarized electron-proton collider or direct access to the gluon in order to continue experimental study of  G II. SMC Collaboration Phys.Rev. D58 (1998)  G=

+ + No FF! Average over partonic kinematics No FF! Reconstruct partonic kinematics. Statistically limited until Requires for partonic kinematics Accessing  G at STAR  Reconstruction of partonic kinematics  Statistically limited - requires high luminosity  challenging pion background subtraction Inclusive measurements have contributions from several sub-processes Understanding of inclusive channels necessary for analysis of clean jet + photon channel

RHIC Complex + STAR Detector  Spin Rotators (transverse/ longitudinal) STAR IR RHIC polarimeters Siberian Snakes Siberian Snakes PHENIX IR  Colliding 100 GeV beams  Each bunch filled with distinct polarization state  Spin Rotators at STAR IR allow for transverse and longitudinal spin orientation  Bunch Xings every ns  CNI polarimeters + Hydrogen Jet target provide run by run & absolute polarization  TPC charged tracks -1.4<  <1.4  EMC neutral energy -1 <  < 1 ( only 0<  < 1)  Beam Beam Counters (BBC) provide MINBIAS trigger as well as spin dependent luminosity 3.4 <  < 5.0.  High Tower (HT) trigger : Requires 1 tower (0.05 x 0.05) with E T > GeV   = -ln[tan(  /2)]

What does a jet at STAR look like? What does it mean to identify a jet with E T =5 GeV at ? “One can usefully define jets down to E T  5 GeV” UA1 Collaboration Nuclear Physics B (1988) 2-particle azimuthal correlations seen at STAR show clear evidence of correlated clusters of particles separated by also known as DIJETS! Real test is collecting these clusters into a “jet” and comparing to NLO pQCD calculations Simple Jet Definition: A cluster of particles correlated in  and  that result from the fragmentation and hadronization of scattered partons. nucl-ex pT (GeV) A. Mischke tomorrow 10:30

STAR Jet Algorithm i.P  of TPC track, EMC tower OR particle used as seed for cluster formation ii.Cluster P  around seed inside Jet Cone Radius = 0.4 iii.Look for additional stable clusters at “midpoint” between two clusters iv.Merge jets if Energy overlap > 50% v.Sum of P  in each stable cluster forms jet vi.Require Jet pT > 5 GeV vii.Same algorithm used for DATA, GEANT and PYTHIA jets PARTON PARTICLE DETECTOR GEANT JETS DATA JETS PYTHIA JETS Midpoint Cone Algorithm (hep-ex/ ) - Collinear and infrared safe - DATA JETS GEANT JETS PYTHIA JETS Corrected Jet Yield = X Correction factor incorporates detector resolution, and energy losses due to fiducial cuts and undetected neutral energy

Jet Cross-Section Analysis 2004 DATA SAMPLE ~0.15 pb -1 sampled lum 0.8/1.4M MINB/HT events 2004 X-sec Cuts |vertex| < 60 cm 0.2 < jet  < 0.8 Trig E T > 3.5 GeV Neutral E T / Jet E T <0.9 RAW per-event Yield Good agreement between DATA and Simulation - PYTHIA (CDF Tune A) + GEANT (Geisha) EmcEt/JetEt (p T > 21.3 GeV/c) Enhanced neutral energy in jets motivates background cut

Jet Cross-Section Results B. Jager et.al, Phys.Rev.D  Two point overlap between HT and MINB show good agreement.  50% systematic shown in yellow band comes from uncertainty in jet energy scale. Need or gamma-jet to reduce this error.  Agreement -within systematics over 7 orders of magnitude!  Bin migration  Detector and Jet Reconstruction inefficiency  Trigger inefficiency  Undetected Neutral Energy Bin by Bin Correction Factors

Dominant Cross-Section Systematics * Under Study Normalization Pythia slope Statistics of c(pt) Background BBC Trigger Energy Scale Fractional Change in x-section Fragmentation Function Systematic: Comparison between PYTHIA and HERWIG results in no significant difference in correction factors.

Jet Asymmetry Analysis DATA Sample 0.3 pb -1 sampled luminosity = 0.3/0.4 for 03/04 125/162k Jets after cuts 03/ /2004 Cuts |vertex| < 75/60 cm 0.2 < jet  < 0.8 Neutral E T / Jet E T < 0.8/0.9 bunch crossing# B Y S = Scaler board counts from BBC (anti) aligned (+-) ++ helicity states Excellent Agreement between 2003/2004 A LL

Jet A LL First Double Spin Asymmetry from STAR!  A LL is consistent with zero.  Results tend to disfavor the GRSV  g=g scenario  Agrees well with previous DIS evaluations  Errors are statistical only  STAR systematic errors ~0.01  Polarization Systematic ~25% not included in figure Predictions: B.Jager et.al, Phys.Rev.D70(2004)

Asymmetry Systematics I A. Single spin Asymmetries consistent with zero as expected B. Relative Lum Systematic Error Estimated by comparing BBC scaler results from two different timing cuts. C.Random Fill Pattern Analysis1.Randomly assign spin patterns to 56 bunches. 2.Recalculate A LL - fit with line 3.Repeat 400x and histogram fit 4.RMS of histogram is on order of A LL statistical error indicating no systematic associated with a specific bunch A LL Run IDFit Mean p0= ± RMS=

Asymmetry Systematics II 2004  (det)<1 bg Jet E EMC /E Tot 4. Background Asymmetry - showers from beam scraping results in jets with an excess of neutral energy. Estimate systematic effect on A LL by calculating background fraction (f BG ) and asymmetry (A LL BG ). Jet E EMC /E Tot >0.9  (det)<1 A bg LL 2004  bg A LL < Trigger Bias - The HT trigger can alter the “natural” weight of contributions from gg,qg,qq. Use GRSV std + CTEQ5L to simulate A LL and estimate systematic due to A) subprocess changes B) detector bias C) bin migration  TRG A LL <  PYTHIA jets  High Tower jets A LL PYTHIA - HT Simulations

Future Results I.Use of new Jet Patch trigger in 2005 increased jet reconstruction efficiency, reduced trigger bias and reduced the size of trigger efficiency corrections for Jet cross-section measurements II.Longer dedicated runs will increase statistics Increased Statistics will allow STAR to distinguish between gluon senarios Projections from data on tape  2005 HT1  2005 JP1 C (p T ) PYTHIA Simulations

Summary  First Jet Results from STAR reflect several years of work on Detector Design, Trigger Algorithms, Jet Algorithms and Luminosity Monitoring tools.  Jet X-sec i.Understand Detector/Trigger enough to provide good agreement between Simulation/Data ii.Agreement within systematics for NLO pQCD calculations iii.Future possibilities - access to high x PDFs + jet shape analysis iv.Motivates application of Jet Algorithm in this energy regime to jet asymmetry measurements.  Jet Asymmetry i.First double spin asymmetry results are consistent with zero. ii.This measurement is in full agreement with previous DIS evaluations of the gluon polarization iii.Initial measurements are statistics limited.  results reflect statistics from limited preliminary runs. Inclusive predictions from statistics indicate the ability to discriminate between gluon scenarios.

BACKUP SLIDES

pp Run >2006 CM Energy 200 GeV 500 GeV and direction at STAR 0.15 T0.30 T/L0.40 L0.45 L/T0.7 L/T L max [ s -1 cm -2 ] L int [pb -1 ] at STAR / Stable polarization direction - transverse Longitudinal polarization at STAR/Phenix AGS Heclical Partial Snake Number of bunches: x10 11 protons/bunch (max) PHOBOS

Jet Cross-Section Results hep-ph/  Due to size of systematic errors connected with small c(p T ) at low pT bins only use HT data > 7 GeV  Two point overlap between HT and MINB show good agreement.  50% systematic shown in yellow band comes from uncertainty in jet energy scale. Need or gamma-jet to reduce this error.  Agreement (within systematics) over 7 orders of magnitude!

p+ 12 C CNI elastic scattering: Recoil Carbon Detection –Carbon filament target (5 m g/cm 2  10  m) in the RHIC beam. –Measure recoil carbon ions at  Lab  90 º having energies, 100 keV < E carbon < 1 MeV –Measure E and TOF to identify recoil carbon ions, determine 4-momentum (-t) and determine left-right/up-down asymmetries. –All data analysis performed on wave-form digitizer board to allow high counting rates (~0.5 MHz) via scaler measurement  ~ 3  in ~1 minute. Coulomb Nuclear Interference (CNI) Polarimeter at RHIC Beam ’ s View Si #1 Si #2Si #4 Si #3 left right down up ADC values Arrival time (ns) Carbon E950 PRL 89 (2002) O. Jinnouchi (RIKEN) and I. Akekseev (ITEP) SPIN 2002