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Renee Fatemi Massachusetts Institute of Technology for the STAR Collaboration

STAR. Using Jet Asymmetries to Access  G at. 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

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Renee Fatemi Massachusetts Institute of Technology for the STAR Collaboration

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  1. STAR Using Jet Asymmetries to Access Gat 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 Renee Fatemi Massachusetts Institute of Technology for the STAR Collaboration March 23, 2006 Moriond QCD, La Thuile, Italy

  2. G= 20-30% proton spin. Data from Fixed Target DIS ep scattering A Short History ofG Indirectly accessed from DIS via Next-to-Leading order fits Limited CM energy range results in large error on G fit. For Q2=1 GeV2 I. II. I. Hirai,Kumano and Saito hep-ph/0601087 II. SMC Collaboration Phys.Rev. D58 (1998) 112002 Need polarized electron-proton collider or direct access to the gluon in order to continue experimental study of G

  3. No FF! Average over partonic kinematics • Reconstruction of partonic kinematics • Statistically limited - requires high luminosity • challenging pion background subtraction No FF! Reconstruct partonic kinematics. Statistically limited until 2006. Accessing G at STAR Inclusive measurements have contributions from several sub-processes + + Understanding of inclusive channels necessary for analysis of clean jet + photon channel Requires for partonic kinematics

  4. RHIC polarimeters Siberian Snakes Siberian Snakes STAR IR PHENIX IR Spin Rotators (transverse/ longitudinal) RHIC Complex + STAR Detector • 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 100-200ns • CNI polarimeters + Hydrogen Jet target provide run by run & absolute polarization • TPC charged tracks -1.4<<1.4 • EMC neutral energy -1 <  < 1 (2003-2005 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 ET > 2.2-3.4 GeV •  = -ln[tan(/2)]

  5. What does a jet at STAR look like? What does it mean to identify a jet with ET=5 GeV at ? “One can usefully define jets down to ET 5 GeV” UA1 Collaboration Nuclear Physics B309 405-425 (1988) Simple Jet Definition: A cluster of particles correlated in andthat result from the fragmentation and hadronization of scattered partons. nucl-ex0306024 pT (GeV) A. Mischke tomorrow 10:30 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

  6. DETECTOR GEANT JETS DATA JETS PARTICLE PYTHIA JETS PYTHIA JETS Corrected Jet Yield = X DATA JETS GEANT JETS PARTON STAR Jet Algorithm Midpoint Cone Algorithm(hep-ex/0005012) - Collinear and infrared safe - P of TPC track, EMC tower OR particle used as seed for cluster formation Cluster P around seed inside Jet Cone Radius = 0.4 Look for additional stable clusters at “midpoint” between two clusters Merge jets if Energy overlap > 50% Sum of P in each stable cluster forms jet Require Jet pT > 5 GeV Same algorithm used for DATA, GEANT and PYTHIA jets Correction factor incorporates detector resolution, and energy losses due to fiducial cuts and undetected neutral energy

  7. EmcEt/JetEt (pT > 21.3 GeV/c) 2004 DATA SAMPLE ~0.15 pb-1 sampled lum 0.8/1.4M MINB/HT events Jet Cross-Section Analysis 2004 X-sec Cuts |vertex| < 60 cm 0.2 < jet  < 0.8 Trig ET > 3.5 GeV Neutral ET / Jet ET<0.9 Good agreement between DATA and Simulation - PYTHIA 6.205 (CDF Tune A) + GEANT (Geisha) RAW per-event Yield Enhanced neutral energy in jets motivates background cut

  8. Jet Cross-Section Results Bin by Bin Correction Factors • Bin migration • Detector and Jet Reconstruction inefficiency • Trigger inefficiency • Undetected Neutral Energy • 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! B. Jager et.al, Phys.Rev.D70 034010

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

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

  11. 2003+2004 Jet ALL First Double Spin Asymmetry from STAR! • ALL 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) 034010

  12. 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 Analysis Randomly assign spin patterns to 56 bunches. Recalculate ALL - fit with line Repeat 400x and histogram fit RMS of histogram is on order of ALL statistical error indicating no systematic associated with a specific bunch p0=0.007613 ±0.0169 RMS= 0.0164 ALL Run ID Fit Mean

  13. bg 2004 0<h(det)<1 Jet EEMC/ETot 2004 AbgLL Jet EEMC/ETot>0.9 0<h(det)<1 Asymmetry Systematics II 4. Background Asymmetry - showers from beam scraping results in jets with an excess of neutral energy. Estimate systematic effect on ALL by calculating background fraction (fBG) and asymmetry (ALLBG). dbgALL< 0.003 Simulations dTRGALL< 0.006 ALL 5. Trigger Bias - The HT trigger can alter the “natural” weight of contributions from gg,qg,qq. Use GRSV std + CTEQ5L to simulate ALL and estimate systematic due to A) subprocess changes B) detector bias C) bin migration • PYTHIA jets • High Tower jets • PYTHIA - HT

  14. PYTHIA Simulations Future Results C (pT) 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 Longer dedicated runs will increase statistics • 2005 HT1 • 2005 JP1 2005 Projections from data on tape Increased Statistics will allow STAR to distinguish between gluon senarios.

  15. 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 • Understand Detector/Trigger enough to provide good agreement between Simulation/Data • Agreement within systematics for NLO pQCD calculations • Future possibilities - access to high x PDFs + jet shape analysis • Motivates application of Jet Algorithm in this energy regime to jet asymmetry measurements. • Jet Asymmetry • First double spin asymmetry results are consistent with zero. • This measurement is in full agreement with previous DIS evaluations of the gluon polarization • Initial measurements are statistics limited. • 2003+2004 results reflect statistics from limited preliminary runs. Inclusive predictions from 2005+2006 statistics indicate the ability to discriminate between gluon scenarios.

  16. BACKUP SLIDES

  17. PHOBOS Stable polarization direction - transverse Longitudinal polarization at STAR/Phenix Number of bunches: 55 - 112 2x1011 protons/bunch (max) AGS Heclical Partial Snake

  18. Jet Cross-Section Results hep-ph/0404057 • Due to size of systematic errors connected with small c(pT) 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!

  19. Coulomb Nuclear Interference (CNI) Polarimeter at RHIC Carbon Arrival time (ns) up Si #3 Si #1 right left ADC values Si #2 Si #4 down Beam’s View E950 PRL 89 (2002) 052302 • p+12C CNI elastic scattering: • Recoil Carbon Detection • Carbon filament target (5mg/cm2  10 mm)in the RHIC beam. • Measure recoil carbon ions at qLab~90º having energies, 100 keV < Ecarbon< 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  de ~ 310-4 in ~1 minute. O. Jinnouchi (RIKEN) and I. Akekseev (ITEP) SPIN 2002

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