GGGG 05/27/2008 5/27/08 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 STAR Longitudinal Spin Program Jason C. Webb, Valparaiso University Outline: 1) The Spin Puzzle 2) The STAR Experiment 3) Inclusive Jet Results 4) Inclusive Hadron Results 5) Coming Attractions 6) Summary

GGGG 05/27/2008 5/27/08 The STAR Longitudinal Spin Program The Spin Puzzle The STAR Experiment Inclusive Jets Inclusive Hadrons Coming Attractions Summary Polarized DIS Measurements Measurements of the g 1 p structure function provides information on quark and antiquark distributions. D. de Florian et al. Phys. Rev. D (2005)‏ Q 2 =10 GeV 2 Only  30% the proton's spin can be attributed to spin of the quarks. The rest must be due to the spin of the gluons and orbital motion of the partons. The main goal of the STAR Longitudinal Spin Program is to determine the gluon's contribution to the proton's spin, by studying inclusive jet, inclusive hadron, dijet and gamma+jet production. At leading order:

GGGG 05/27/2008 5/27/08 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 p T 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 Inclusive hadrons: Inclusive jets and dijets: Gamma+jet: Abundant  Low “x” resolution  Comparatively rare High “x” resolution Inclusive channels integrate over large x-range. Dijet and g+jet channels can reconstruct (at leading-order) initial state kinematics.

GGGG 05/27/2008 5/27/08 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 Gamma+jet: quark-gluon Compton scattering dominates Inclusive hadrons: mix of partonic subprocesses Inclusive jets and dijets: 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.

GGGG 05/27/2008 5/27/08 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

GGGG 05/27/2008 5/27/08 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

GGGG 05/27/2008 5/27/08 The STAR Longitudinal Spin Program 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)‏ < h < 2.0 Forward Meson Spectrometer (Pb Glass)‏ ~2.5 < h < 4.0 Upgrade program increases physics reach: FMS (2008), DAQ1k (2009), FGT (2010),...  E xtend measurements to lower x Bjorken  Increase livetime to ~90-95%  Improved forward tracking Level-0 triggers: single calorimeter towers to  x  = 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

GGGG 05/27/2008 5/27/08 The STAR Longitudinal Spin Program The Spin Puzzle The STAR Experiment Inclusive Jets Inclusive Hadrons Coming Attractions Summary ` Hardware trigger patches Software (L2) trigger patches Hardware high tower Hardware jet patches 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

GGGG 05/27/2008 5/27/08 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: P Y ≈ P B ≈ 50%  Inclusive jets, hadrons 0 <  < 1 pp 2006 longitudinal  Sampled luminosity: ≈ 4.7 pb -1  Achieved polarizations: P Y ≈ P B ≈ 55%  Inclusive jets -1 <  < 1  First dijets  Inclusive  +/- -1 <  < 1  Inclusive  0 -1 <  < 2 First constraints on  g from inclusive jets Dijet cross section measurement underway Midrapidity  0 cross sections A LL Inclusive hadron (  0,  ± ) A LL Significantly enhanced FOM for all channels Greatly enhanced statistical precision for inclusive jet A LL Sufficient statistics for first ALL(dijet)‏ Inclusive hadron (  0,  ± ) A LL Statistical precision sufficient to begin to discriminate between models First measurement of (p0) for < 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

GGGG 05/27/2008 5/27/08 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

GGGG 05/27/2008 5/27/08 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/ )‏ 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. Experimental cross section agrees with NLO pQCD over 7 orders of magnitude The Spin Puzzle The STAR Experiment Inclusive Jets Inclusive Hadrons Coming Attractions Summary Add Reference to Publication

GGGG 05/27/2008 5/27/08 The STAR Longitudinal Spin Program The Spin Puzzle The STAR Experiment Inclusive Jets Inclusive Hadrons Coming Attractions Summary Inclusive Jet Asymmetries (2005)‏ ARXIV: , accepted for publication in PRL 200 GeV 0.2 < η < Backgrounds 0.94Relative Luminosity (p T dep)‏Non-longitudinal Polarization 2-5 (p T dep)‏Reconstruction + Trigger Bias (x )‏A LL systematics [-5.4%,+6.7%]p T systematic GRSV DIS Results from the 2005 run yielded significant new constraints on  g, compared with fits based only on DIS measurements. The Spin Puzzle The STAR Experiment Inclusive Jets Inclusive Hadrons Coming Attractions Summary

GGGG 05/27/2008 5/27/08 The STAR Longitudinal Spin Program The 2006 jet asymmetries provide significant new constraints on  g. GRSV DIS The Spin Puzzle The STAR Experiment Inclusive Jets Inclusive Hadrons Coming Attractions Summary Inclusive Jet Asymmetries 1 st bin ~ 0.5 all others ~ 0.1 Backgrounds 0.94Relative Luminosity ~ 0.03 (p T dep)‏ Non-longitudinal Polarization [-1,+3] (p T dep)‏ Reconstruction + Trigger Bias (x )‏A LL systematics  6.7% p T systematic 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)‏

GGGG 05/27/2008 5/27/08 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  g The fit to  g 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  g. The Spin Puzzle The STAR Experiment Inclusive Jets Inclusive Hadrons Coming Attractions Summary  2 distribution as  g is varied w/in x-range constrained by the RHIC data. The STAR inclusive jet results provide significant constraints on  g. RHIC constraints It is interesting to note that the best fit has a zero-crossing at x ≈ 0.1. Over the next few years, STAR's emphasis will shift to dijet and gamma+jet measurements, which will map out the x-dependence of  g. RHIC pp data have recently been included, along with polarized DIS and semi-inclusive DIS data, in a global fit to the polarized pdfs. D. de Florian, et al., ARXIV:

GGGG 05/27/2008 5/27/08 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

GGGG 05/27/2008 5/27/08 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  p 0 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 p 0 ->gg candidates BEMC invariant mass spectrum: Well described by Monte Carlo simulations. Background in the  0 signal region is understood in terms of three components: combinatoric,  decays and cluster splitting. Data Simulation 10.5 < P T < 16.0 GeV/c BEMC -1 <  < 1 EEMC 1<h<2 EEMC invariant mass spectrum: Phenomenological fits to signal+background, with good chi2/ndf, parameterization which varies smoothly as a function of pT. Work underway to improve SMD response. EEMC SMD The Spin Puzzle The STAR Experiment Inclusive Jets Inclusive Hadrons Coming Attractions Summary

GGGG 05/27/2008 5/27/08 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 <  < 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

GGGG 05/27/2008 5/27/08 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 π 0 result sees a significant increase in statistical precision as well as a greater reach in P T compared to run 5. Similar statement applies for run 6 π ±. STAR is planning for a long pp run in 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

GGGG 05/27/2008 5/27/08 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/ A LL (  0 )=0. Statistical precision comparable to midrapidity results Result is an important step towards measuring A LL in the gamma+jet channel. The Spin Puzzle The STAR Experiment Inclusive Jets Inclusive Hadrons Coming Attractions Summary

GGGG 05/27/2008 5/27/08 The STAR Longitudinal Spin Program The Spin Puzzle The STAR Experiment Inclusive Jets Inclusive Hadrons Coming Attractions Summary 1.0 GeV/c pion band Charged Pions pp 2005 data analysis: - Trigger selection: Minbias || JP1 || JP <  < 1 - |z vertex | < 60cm (BBC timing)‏  Particle ID performed using dE/dx of charged particle tracks w/in the TPC tracking volume.  Events w/in -1 < N  < +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

GGGG 05/27/2008 5/27/08 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  + vs   fragmentation allow for the determination of the sign of  g.  Trigger-bias on A LL estimated using Pythia+ GEANT simulation, and GRSV pdfs  Preliminary results disfavor large gluon polarization (GRSV max). Analysis of 2006 data underway. The Spin Puzzle The STAR Experiment Inclusive Jets Inclusive Hadrons Coming Attractions Summary

GGGG 05/27/2008 5/27/08 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

GGGG 05/27/2008 5/27/08 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

GGGG 05/27/2008 5/27/08 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 = 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 Constraints from dijets The Spin Puzzle The STAR Experiment Inclusive Jets Inclusive Hadrons Coming Attractions Summary DSSV

GGGG 05/27/2008 5/27/08 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  and  0 → 2  decays. Prompt photon signal has been seen, demonstrated with   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 k T. W. Vogelsang 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

GGGG 05/27/2008 5/27/08 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 E T  / E T cone > 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.

GGGG 05/27/2008 5/27/08 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  decays. The Spin Puzzle The STAR Experiment Inclusive Jets Inclusive Hadrons Coming Attractions Summary

GGGG 05/27/2008 5/27/08 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

GGGG 05/27/2008 5/27/08 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  g. Inclusive hadron measurements can provide complementary information - fragmentation functions connect p T to x - additional sensitivity to sign of  g in  +/- channel Over the next few years we will begin to map out the x-dependence of  g using two complementary methods: - High statistics: dijets - High resolution:  +jet coincidences The STAR inclusive jet measurements from 2005/6 have already provided significant constraints on  g. Inclusive hadron measurements can provide complementary information - fragmentation functions connect p T to x - additional sensitivity to sign of  g in  +/- channel Over the next few years we will begin to map out the x-dependence of  g using two complementary methods: - High statistics: dijets - High resolution:  +jet coincidences

GGGG 05/27/2008 5/27/08 The STAR Longitudinal Spin Program

GGGG 05/27/2008 5/27/08 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