jwebb-RHIC-AGS-Users-Meeting-2008_0

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Published on December 4, 2008

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Slide 1: 5/26/08 The STAR Longitudinal Spin Program Outline: 1) The Spin Puzzle 2) The STAR Experiment 3) Inclusive Jet Results 4) Inclusive Hadron Results 5) Coming Attractions 6) Summary Outline: 1) The Spin Puzzle 2) The STAR Experiment 3) Inclusive Jet Results 4) Inclusive Hadron Results 5) Coming Attractions 6) Summary Slide 2: 5/26/08 The STAR Longitudinal Spin Program The Spin Puzzle The STAR Experiment Inclusive Jets Inclusive Hadrons Coming Attractions Summary Polarized DIS Measurements Measurements of the g1p structure function provides information on quark and antiquark distributions. At leading order: Slide 3: 5/26/08 The STAR Longitudinal Spin Program The Spin Puzzle The STAR Experiment Inclusive Jets Inclusive Hadrons Coming Attractions Summary Polarized Proton-Proton Interactions at RHIC RHIC is the world's first polarized proton-proton collider. Several complementary probes of the gluon's helicity preference are available. The STAR experiment is pursuing several, each with their own experimental advantages and challenges. High statistics Require fragmentation functions to connect measured pT to x. p+/- sensitive to sign of Dg High statistics Integrates over ff's Resolution limited by jet energy scale Dijets allow the reconstruction of the initial state (leading-order)‏ kinematics Rare process (luminosity hungry!)‏ Determine initial state (leading order)‏ kinematics with good resolution using EM calorimeters Challenging backgrounds The Spin Puzzle The STAR Experiment Inclusive Jets Inclusive Hadrons Coming Attractions Summary The Spin Puzzle The STAR Experiment Inclusive Jets Inclusive Hadrons Coming Attractions Summary Slide 4: 5/26/08 The STAR Longitudinal Spin Program The Spin Puzzle The STAR Experiment Inclusive Jets Inclusive Hadrons Coming Attractions Summary Polarized Proton-Proton Interactions at RHIC The Spin Puzzle The STAR Experiment Inclusive Jets Inclusive Hadrons Coming Attractions Summary The Spin Puzzle The STAR Experiment Inclusive Jets Inclusive Hadrons Coming Attractions Summary Inclusive Measurements: Abundant probe Poor x-resolution (integrates over wide x-range, jet energy scale, frag. functions)‏ Gamma+jet: Able to reconstruct initial state (LO) kinematics (x1,x2)‏ Good resolution, limited by energy- resolution of EM calorimeters. Rare probe (needs luminosity!)‏ Challenging backgrounds Dijets: Abundant probe Able to reconstruct initial state (LO)‏ kinematics (x1,x2)‏ Limited x-resolution, depends on jet → parton energy resolution Several pieces which should “fit together nicely”... RHIC is the world's first polarized proton-proton collider. Several complementary probes of the gluon's helicity preference are available. The STAR experiment is pursuing several, each with their own experimental advantages and challenges. Slide 5: 5/26/08 The STAR Longitudinal Spin Program The Spin Puzzle The STAR Experiment Inclusive Jets Inclusive Hadrons Coming Attractions Summary Partonic analyzing powers depend on the particular process and scattering angle. Theory: Experimental observables are connected to the parton helicity distributions using pQCD. Experiment: Longitudinal spin asymmetries access information on the polarized cross sections pQCD Fragmentation Extract via global fits Putting the Puzzle Together (assumes universality of pdfs and ff's.)‏ The Spin Puzzle The STAR Experiment Inclusive Jets Inclusive Hadrons Coming Attractions Summary Slide 6: 5/26/08 The STAR Longitudinal Spin Program The Spin Puzzle The STAR Experiment Inclusive Jets Inclusive Hadrons Coming Attractions Summary The Spin Puzzle The STAR Experiment Inclusive Jets Inclusive Hadrons Coming Attractions Summary Outline: 1) The Spin Puzzle 2) The STAR Experiment 3) Inclusive Jet Results 4) Inclusive Hadron Results 5) Coming Attractions 6) Summary Slide 7: 5/26/08 The STAR Longitudinal Spin Program The Spin Puzzle The STAR Experiment Inclusive Jets Inclusive Hadrons Coming Attractions Summary The Spin Puzzle The STAR Experiment Inclusive Jets Inclusive Hadrons Coming Attractions Summary Detector Overview Magnet 0.5 T Solenoid Minbias Trigger + Luminosity Beam-Beam Counters 3.4 < |h| < 5.0 Central Tracking Large-volume TPC |h| < ~1.5 Electromagnetic Calorimetry Barrel EMC (Pb/Scintilator)‏ -1 < h < 1 Endcap EMC (Pb/Scintilator)‏ 1.086 < h < 2.0 Forward Meson Spectrometer (Pb Glass)‏ ~2.5 < h < 4.0 Upgrade program increases physics reach: FMS (2008), DAQ1k (2009), FGT (2010), ... Extend measurements to lower xBjorken Increase livetime to ~90-95% Improved forward tracking Level-0 triggers: single calorimeter towers to DhxDf = 1x1 jet patches Level-2 triggers: tower clusters and dijet coincidence trigger (2006). The Spin Puzzle The STAR Experiment Inclusive Jets Inclusive Hadrons Coming Attractions Summary Slide 8: 5/26/08 The STAR Longitudinal Spin Program The Spin Puzzle The STAR Experiment Inclusive Jets Inclusive Hadrons Coming Attractions Summary ` STAR Jet and Photon Trigger Capabilities ... plan to draw example hardware and software triggers in the BEMC... The Spin Puzzle The STAR Experiment Inclusive Jets Inclusive Hadrons Coming Attractions Summary Slide 9: 5/26/08 The STAR Longitudinal Spin Program The Spin Puzzle The STAR Experiment Inclusive Jets Inclusive Hadrons Coming Attractions Summary The 2005 and 2006 Longitudinal Data Samples pp 2005 longitudinal Sampled luminosity: ≈ 1.6 pb-1 Achieved polarizations: PY ≈ PB ≈ 50% Inclusive jets, hadrons 0 < h < 1 pp 2006 longitudinal Sampled luminosity: ≈ 4.7 pb-1 Achieved polarizations: PY ≈ PB ≈ 55% Inclusive jets -1 < h < 1 First dijets Inclusive p+/- -1 < h < 1 Inclusive p0 -1 < h < 2 First constraints on Dg from inclusive jets Dijet cross section measurement underway Midrapidity p0 cross sections ALL Inclusive hadron (p0, p±) ALL Significantly enhanced FOM for all channels Greatly enhanced statistical precision for inclusive jet ALL Sufficient statistics for first ALL(dijet)‏ Inclusive hadron (p0, p±) ALL Statistical precision sufficient to begin to discriminate between models First measurement of (p0) for 1.086 < h < 2.0. Sufficient statistics to begin looking for gamma+jet coincidences ` 2005 Dijet Event RHIC runs in 2005 and 2006 have provided a rich data sample for solving the spin puzzle. The Spin Puzzle The STAR Experiment Inclusive Jets Inclusive Hadrons Coming Attractions Summary Slide 10: 5/26/08 The STAR Longitudinal Spin Program Outline: 1) The Spin Puzzle 2) The STAR Experiment 3) Inclusive Jet Results 4) Inclusive Hadron Results 5) Coming Attractions 6) Summary The Spin Puzzle The STAR Experiment Inclusive Jets Inclusive Hadrons Coming Attractions Summary Slide 11: 5/26/08 The STAR Longitudinal Spin Program The Spin Puzzle The STAR Experiment Inclusive Jets Inclusive Hadrons Coming Attractions Summary Inclusive Jet Production Detector GEANT PYTHIA Particle 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 Simulation reproduces the distribution of energy versus distance from jet thrust axis. The Spin Puzzle The STAR Experiment Inclusive Jets Inclusive Hadrons Coming Attractions Summary Add Reference to Publication Slide 12: 5/26/08 The STAR Longitudinal Spin Program The Spin Puzzle The STAR Experiment Inclusive Jets Inclusive Hadrons Coming Attractions Summary Inclusive Jet Asymmetries (2005)‏ ARXIV:0710.2048, accepted for publication in PRL 200 GeV 0.2 < η < 0.8 The Spin Puzzle The STAR Experiment Inclusive Jets Inclusive Hadrons Coming Attractions Summary Slide 13: 5/26/08 The STAR Longitudinal Spin Program The Spin Puzzle The STAR Experiment Inclusive Jets Inclusive Hadrons Coming Attractions Summary Inclusive Jet Asymmetries The 2006 results are a significant improvement over the 2005 measurement: Full BEMC Jet finder extends into EEMC Cone radius enlarged to 0.7 Increases in luminosity and polarization Statistical uncertainties are 3x-4x smaller for high pT (pT > 13 GeV). The Spin Puzzle The STAR Experiment Inclusive Jets Inclusive Hadrons Coming Attractions Summary Inclusive Jet Asymmetries (2006)‏ Slide 14: 5/26/08 The STAR Longitudinal Spin Program The Spin Puzzle The STAR Experiment Inclusive Jets Inclusive Hadrons Coming Attractions Summary Global Analysis -- DSSV Recently, RHIC pp data has been included in a global analysis, on equal footing with polarized DIS and semi- inclusive DIS results. STAR is providing significant constraints on Dg. The fit to Dg crosses zero at x ≈ 0.1. STAR's emphasis is beginning to shift towards dijet and gamma+jet measurements, which will allow us to map out the x-dependence of Dg. The Spin Puzzle The STAR Experiment Inclusive Jets Inclusive Hadrons Coming Attractions Summary Slide 15: 5/26/08 The STAR Longitudinal Spin Program The Spin Puzzle The STAR Experiment Inclusive Jets Inclusive Hadrons Coming Attractions Summary Outline: 1) The Spin Puzzle 2) The STAR Experiment 3) Inclusive Jet Results 4) Inclusive Hadron Results 5) Coming Attractions 6) Summary Slide 16: 5/26/08 The STAR Longitudinal Spin Program The Spin Puzzle The STAR Experiment Inclusive Jets Inclusive Hadrons Coming Attractions Summary Neutral Pions In 2005 full EEMC w/ SMD readout In 2006 full BEMC w/ SMD readout, level-2 p0 and g trigger, improved shielding, ... Event Reconstruction: 1) Clusters are formed around seed strips in shower-maximum detectors. 2) Clusters in orthogonal views associated to form points, and calorimeter energy divided 3) Pairs of points reconstructed into p0->gg candidates BEMC invariant mass spectrum: Well described by Monte Carlo simulations. Background in the p0 signal region is understood in terms of three components: combinatoric, h decays and cluster splitting. The Spin Puzzle The STAR Experiment Inclusive Jets Inclusive Hadrons Coming Attractions Summary Slide 17: 5/26/08 The STAR Longitudinal Spin Program The Spin Puzzle The STAR Experiment Inclusive Jets Inclusive Hadrons Coming Attractions Summary Lsampled: 0.4 pb-1 (HT triggers), 44 mb-1 (MB)‏ Point-to-point systematics from yield extraction Total systematics dominated by 5% uncertainty in BEMC energy scale, significant contribution from correction factor uncertainty Compared to NLO pQCD (CTEQ6M pdfs) using KKP and Kretzer fragmentation func. better agreement with KKP large scale uncertainties in pQCD calculations, indicated by choosing different scales for KKP calculations BEMC Coverage: 0 < h < 1 Luminosity: 0.4 pb-1 (HT) and 44 mb-1 (Minbias) Good agreement with NLO QCD over seven orders of magnitude. CTEQ6M pdfs Kretzer and KKP fragmentation functions Better agreement w/ KKP Large scale uncertainties in pQCD 2005 Neutral Pion Cross Section Point-to-point systematic uncertainties due to uncertainties in yield extraction. The Spin Puzzle The STAR Experiment Inclusive Jets Inclusive Hadrons Coming Attractions Summary Slide 18: 5/26/08 The STAR Longitudinal Spin Program The Spin Puzzle The STAR Experiment Inclusive Jets Inclusive Hadrons Coming Attractions Summary Neutral Pion Asymmetries in the BEMC  compared to NLO calculations (ignoring systematic errors): GRSV Std: ~ 3 GRSV Max: ~ 10 GRSV Min: ~ 3 GRSV Zero: ~ 2 GRSV Max scenario strongly disfavored 2006 data a significant improvement over 2005: 1) BEMC fully installed 2) Increased luminosity 3) Increased polarization 4) Improved trigger 5) Better shielding Results consistent with PHENIX 2006 preliminary The run 6 π0 result sees a significant increase in statistical precision as well as a greater reach in PT compared to run 5. Similar statement applies for run 6 π±. STAR is planning for a long pp run in 2009. Expecting large increase in FOM with 60% polarization and 50 pb-1 The Spin Puzzle The STAR Experiment Inclusive Jets Inclusive Hadrons Coming Attractions Summary Slide 19: 5/26/08 The STAR Longitudinal Spin Program Neutral Pion Asymmetries in the EEMC The Spin Puzzle The STAR Experiment Inclusive Jets Inclusive Hadrons Coming Attractions Summary 2006 data a significant improvement over 2005: 1) Increased luminosity 2) Increased polarization 3) Improved trigger 4) Better shielding, reduces beam-like background trigger rate by more than an order of magnitude. Data are consistent w/ ALL(p0)=0. Statistical precision comparable to midrapidity results Result is an important step towards measuring ALL in the gamma+jet channel. The Spin Puzzle The STAR Experiment Inclusive Jets Inclusive Hadrons Coming Attractions Summary Slide 20: 5/26/08 The STAR Longitudinal Spin Program The Spin Puzzle The STAR Experiment Inclusive Jets Inclusive Hadrons Coming Attractions Summary Charged Pions pp 2005 data analysis: - Trigger selection: Minbias || JP1 || JP2 - -1 < h < 1 - |zvertex| < 60cm (BBC timing)‏ Particle ID performed using dE/dx of charged particle tracks w/in the TPC tracking volume. Events w/in -1 < Ns < +2 from the mean of the pion energy loss band are selected for analysis. Deflection of the track in the magnetic field determines charge of the pion. The Spin Puzzle The STAR Experiment Inclusive Jets Inclusive Hadrons Coming Attractions Summary Slide 21: 5/26/08 The STAR Longitudinal Spin Program The Spin Puzzle The STAR Experiment Inclusive Jets Inclusive Hadrons Coming Attractions Summary Charged Pions Preliminary Results 2005 Differences in p+ vs p- fragmentation allow for the determination of the sign of Dg. Trigger-bias on ALL estimated using Pythia+ GEANT simulation, and GRSV pdfs Preliminary results disfavor large gluon polarization (GRSV max). The Spin Puzzle The STAR Experiment Inclusive Jets Inclusive Hadrons Coming Attractions Summary Slide 22: 5/26/08 The STAR Longitudinal Spin Program The Spin Puzzle The STAR Experiment Inclusive Jets Inclusive Hadrons Coming Attractions Summary Outline: 1) The Spin Puzzle 2) The STAR Experiment 3) Inclusive Jet Results 4) Inclusive Hadron Results 5) Coming Attractions 6) Summary Slide 23: 5/26/08 The STAR Longitudinal Spin Program The Spin Puzzle The STAR Experiment Inclusive Jets Inclusive Hadrons Coming Attractions Summary Dijet Measurements For dijets (and any 2 → 2 process), the initial state kinematics can be determined from final state observables (assumes LO). Data is well described by simulations. Cross section and asymmetry analysis in progress. The Spin Puzzle The STAR Experiment Inclusive Jets Inclusive Hadrons Coming Attractions Summary Slide 24: 5/26/08 The STAR Longitudinal Spin Program The Spin Puzzle The STAR Experiment Inclusive Jets Inclusive Hadrons Coming Attractions Summary Dijet Projections for 50 pb-1 with <P> = 60% Significant new constraints from dijets expected in upcoming run(s). Plot compares anticipated statistical precision to several fits for four different kinematic regions. Inclusives 2005/6 The Spin Puzzle The STAR Experiment Inclusive Jets Inclusive Hadrons Coming Attractions Summary DSSV Slide 25: 5/26/08 The STAR Longitudinal Spin Program The Spin Puzzle The STAR Experiment Inclusive Jets Inclusive Hadrons Coming Attractions Summary Gamma+Jet Measurements ` Analysis of 2006 data underway In situ measurements of transverse shower profile and conversion prob. in the EEMC preshower system using reconstructed h and p0 → 2g decays. Prompt photon signal has been seen, demonstrated with c2 analysis and conversion rates Worst-side residual from fit to transverse shower profile in agreement with expectations from pythia+ GEANT+ data driven lineshapes. Conversion method: Utilizes different probability for signal and background to convert w/in the first radiator. Simulated x-gluon resolution As with dijets, the gamma+jet channel allows us to reconstruct the initial state kinematics. The x- resolution is only limited by the calibration of the calorimeters and intrinsic kT. Backgrounds present a significant experimental challenge. At pT = 10 GeV s/b is 1/10, and gets worse as one goes to lower pT. Isolation cuts and pT matching with the awayside jet can reduce the background significantly, but further discrimination power is required. The Spin Puzzle The STAR Experiment Inclusive Jets Inclusive Hadrons Coming Attractions Summary Slide 26: 5/26/08 The STAR Longitudinal Spin Program The Spin Puzzle The STAR Experiment Inclusive Jets Inclusive Hadrons Coming Attractions Summary Gamma+Jet Measurements Gamma+jet channel is still a work in progress. Isolation cuts - require ETg / ETcone > 0.99 Plot compares data (3.1 pb-1) to MC simulations of g+jet signal and dijet backgrounds (scaled to 3.1 pb-1) after same set of cuts applied. S/B ratio after isolation is smaller than the 1/3 expected from original simulations. Work underway to improve isolation cuts. Planned upgrade (FGT) will also improve the isolation cuts. Slide 27: 5/26/08 The STAR Longitudinal Spin Program Gamma+Jet Measurements The Spin Puzzle The STAR Experiment Inclusive Jets Inclusive Hadrons Coming Attractions Summary Analysis of the transverse shower shapes will provide additional discrimination. Real events are compared with a “library” of photon shapes, obtained from in situ measurements of h decays. The Spin Puzzle The STAR Experiment Inclusive Jets Inclusive Hadrons Coming Attractions Summary Slide 28: 5/26/08 The STAR Longitudinal Spin Program Outline: 1) The Spin Puzzle 2) The STAR Experiment 3) Inclusive Jet Results 4) Inclusive Hadron Results 5) Coming Attractions 6) Other measurements (time permitting)‏ 7) Summary The Spin Puzzle The STAR Experiment Inclusive Jets Inclusive Hadrons Coming Attractions Summary Slide 29: 5/26/08 The STAR Longitudinal Spin Program The Spin Puzzle The STAR Experiment Inclusive Jets Inclusive Hadrons Coming Attractions Summary Summary The STAR inclusive jet measurements from 2005/6 have already provided significant constraints on Dg. Inclusive hadron measurements can provide complementary information - fragmentation functions connect pT to x - additional sensitivity to sign of Dg in p+/- channel Over the next few years we will begin to map out the x-dependence of Dg using two complementary methods: - High statistics: dijets - High resolution: g+jet coincidences Slide 30: 5/26/08 The STAR Longitudinal Spin Program Slide 31: 5/26/08 The STAR Longitudinal Spin Program The Spin Puzzle The STAR Experiment Inclusive Jets Inclusive Hadrons Coming Attractions Summary The 2005 and 2006 Longitudinal Data Samples Backup slides to be added

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