Renee Fatemi Wayne State University Nuclear Seminar 1 Extracting the Gluon Piece of the Spin Puzzle New Results From STAR Renee Fatemi University of Kentucky November 9, 2007

Renee Fatemi Wayne State University Nuclear Seminar 2 Quick Historical Review of the Spin Puzzle Proton Quarks Gluons Contributions to the Spin Puzzle STAR

Renee Fatemi Wayne State University Nuclear Seminar 3  QED The Spin Puzzle  Key Question in Standard Model QCD spin 1/2spin 1 g QCD 99.9% of mass of the visible universe composed of quarks and gluons - the building blocks of the nucleon No access to free partons due to confinement! The proton is a stable and abundant source of partons How do partonic degrees of freedom - mass, charge, color, SPIN - manifest as the nucleon degrees of freedom?

Renee Fatemi Wayne State University Nuclear Seminar 4 Color Confinement forbids the isolation of free quarks and gluons. The stable and abundant Proton is an excellent “partonic laboratory” Proton Quarks Gluons Question: How do the quarks and gluons combine to form the quantum numbers of the hadrons which form 99% of the visible universe? The Proton is “bag” of 3 spin 1/2 quarks which are constantly interacting via spin 1 gluons. Gluons also interact with each other and produce quark + anti-quark pairs which make up the “sea”.

Renee Fatemi Wayne State University Nuclear Seminar 5 Deep Inelastic Scattering  = Resolution Increased E   means increased resolution  t = lifetime Increased E   means shorter interaction time  (fm) Q 2 (GeV 2 )

Renee Fatemi Wayne State University Nuclear Seminar 6 Momentum Parton Distribution Functions Strong violation of scaling at low x and high Q 2 Contrary to: Low Q 2 high x! Note: g(x) scaled by 0.05!

Renee Fatemi Wayne State University Nuclear Seminar 7 Initial Predictions for Polarized PDF’s: Constituent Quark Model Quark Parton Model ~60 % from quarks i.No gluon d.o.f ii.M quark = 1/3 M proton iii.Assume S-state iv.Relativistic Effect ~ 75% 100 % from quarks i.Allows massless gluons ii.M quark ~ 10’s MeV iii.Assume no strange sea constribution

Renee Fatemi Wayne State University Nuclear Seminar 8 Recipe for Measuring Quark Spins in Polarized DIS 1.Take one lepton beam with it’s spin aligned with it’s momentum 2.Scatter from proton target whose spin is (anti)aligned with the lepton spin 3.Count # scattered leptons with spin (anti) aligned with target

Renee Fatemi Wayne State University Nuclear Seminar 9 30 Years of Polarized DIS Experiments Yield… Quark Spin ~20-30% of proton! xx Unlike unpolarized case, reduced CM Energy, allows limited constraint on  g de Florian et al., Phys. Rev. D (2005) Q 2 =10 GeV 2

Renee Fatemi Wayne State University Nuclear Seminar 10 Using GRSV2000 Polarized Q 2 =5 GeV 2 DIS Contraints on Parton Spin Contributions

Renee Fatemi Wayne State University Nuclear Seminar 11 Dedicated DIS  G Measurements …from SPIN 2006 Disfavors maximal scenario but cannot determine sign PGF is access to  G in DIS Jet Proxy - high pT pairs Golden channel is Open Charm

Renee Fatemi Wayne State University Nuclear Seminar 12 Accessing  G at STAR  Reconstruction of partonic kinematics  Statistically limited - requires high luminosity  challenging pion background subtraction + + No FF! Average over partonic kinematics No FF! Reconstruct partonic kinematics. Statistically limited until Requires for partonic kinematics

Renee Fatemi Wayne State University Nuclear Seminar 13 Observable Sensitivity to  G Max Sensitivity in Inclusive  but Xsec suppressed Inclusive Jets provide sensitivity in high pT region where curves diverge Pions are less sensitive due to limited pT reach For qg processess, ALL(  ALL   tracks sign of  G range = over measured pT range for jets and hadrons

Renee Fatemi Wayne State University Nuclear Seminar 14 STAR Analysis Plan I. Cross-sections Establish validity of Next to Leading Order perturbative QCD for RHIC kinematics. Test understanding of detector, measured observable and quality of simulations N: Spin Yields P: Beam Pol. R: Relative Lumi. II. Asymmetries Provide access to polarized parton distributions

Renee Fatemi Wayne State University Nuclear Seminar 15 The Experiment

Renee Fatemi Wayne State University Nuclear Seminar 16 Relativistic Heavy Ion Collider  Spin Rotators (transverse/ longitudinal) STAR IR RHIC polarimeters Siberian Snakes Siberian Snakes PHENIX IR 100 GeV beam proton beams Each bunch filled with a 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 pp Run Year % L max [ s -1 cm -2 ] L int [pb -1 ] at STAR (L/T)0 / / / 03.1 / / 10.2 …worlds 1st Collider

Renee Fatemi Wayne State University Nuclear Seminar 17 Detector components used in jet reconstruction STAR  = -ln[tan(  /2)] TPC |  |<1.4 Charged particle momentum BEMC |  |<1.0 Neutral Energy High pT Trigger EEMC 1<  <2 Neutral Energy High pT Trigger BBC 3.4<  <5 MinBias Trigger Relative Lumi  EndCap EMC BBC West Barrel EMC BBC East TPC Yellow beamBlue beam

Renee Fatemi Wayne State University Nuclear Seminar 18 X Trigger Interaction Vertex Composition of Events STAR Mother Nature Elastic, single+doubly diffractive, hard scattering Minimum Bias Requires in-time hit in ExW Very little change in hard scattering process mix High Tower1 tower above threshold Requires hard neutral fragmentation Jet Patch (2005/6 only) 400 localized towers above threshold. Allows for cluster of softer fragmentation The study of how the calorimeter triggers change the sub-process fraction is major contribution to the systematic error

Renee Fatemi Wayne State University Nuclear Seminar 19 Inclusive Jet Analysis STAR

Renee Fatemi Wayne State University Nuclear Seminar 20 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 ( ) or 0.7 (2006) 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 STAR

Renee Fatemi Wayne State University Nuclear Seminar 21 Inclusive Jet Cross-Section Analysis Use Simulation (MC) to provide correction to RAW jet yield - trigger and jet inefficiencies - jet resolution & bin migration - undetected particles (n +  ) - PYTHIA CDF Tune A - GEANT (Geisha) Verification of DATA/MC agreement essential The shape of the Fraction of Neutral Energy in the Jet (EMF) is sensitive to the trigger bias as well as contributions from beam background. Minbias JP2 HT2 STAR Preliminary C(p T )=GEANT/PYTHIA

Renee Fatemi Wayne State University Nuclear Seminar /2004 Inclusive Jet Cross-Section Results 3 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. Application of hadronization correction removes systematic offset from NLO and data Agreement -within- systematics over 7 orders of magnitude! B. Jager et.al, Phys.Rev.D

Renee Fatemi Wayne State University Nuclear Seminar Inclusive Jet A LL B. Jager et.al, Phys.Rev.D70, Submitted to PRL arXiv: <  < 0.8 R = 0.4 Systematics(x ) Reconstruction + Trigger Bias 2-5 (p T dep) Non- longitudinal Polarization (p T dep) Relative Luminosity 0.94 Backgrounds0.70 p T systematic -5.4%+6.7%-5.4%+6.7%

Renee Fatemi Wayne State University Nuclear Seminar 24 GRSV DIS 2005 Confidence Levels Theory (GRSV) CL  g = -g 0.06  g =  g = g ~ Data covers ~50% of GRSV total integral

Renee Fatemi Wayne State University Nuclear Seminar 25 Jet A LL Systematics: Jet Reconstruction Bias On average PARTICLE Jets are reconstructed in the DETECTOR with 20% increase in pT! REASON: 25% Jet Resolution + Steeply falling jet pT distribution Systematic offsets in pT cause dilutions of the jet asymmetry which depend on the size of the asymmetry!  G  G0G0

Renee Fatemi Wayne State University Nuclear Seminar 26 Jet A LL Systematics: Trigger Bias The trigger biases jets toward higher neutral energy. This may change nature’s mix of qq+qg+gg and therefore change the asymmetries Trigger Bias: JP << HT  A LL /A LL  larger at low pT Total Systematic: 1.Shift pT from Particle to Detector pT(GeV) “Mother Nature’s” Mix

Renee Fatemi Wayne State University Nuclear Seminar <  < 0.9 Cone Radius = Inclusive Jet A LL NEW! A LL systematics(x ) Reconstruction + Trigger Bias [-1,+3] (p T dep) Non-longitudinal Polarization 0.03 (p T dep) Relative Luminosity 0.94 Backgrounds p T systematic 6.7%6.7%

Renee Fatemi Wayne State University Nuclear Seminar 28 *Theoretical uncertainties not included GRSV DIS 2006 Confidence Levels Within GRSV framework:  g_STD excluded with 99% CL  g<-0.7 excluded with 90% CL

Renee Fatemi Wayne State University Nuclear Seminar 29  2 comparison with PHENIX 1.STAR and PHENIX are in good agreement 2.Within GRSV framework, at 0.4 GeV 2 /c 2, the total gluon contribution is nearly zero or negative.

Renee Fatemi Wayne State University Nuclear Seminar 30 But beware…conclusions are model dependent! Total integral is larger for GSC BUT sampled fraction is LARGER for GRSV x Really need global analysis + x sensitive measurements!

Renee Fatemi Wayne State University Nuclear Seminar 31 Sample a different range with 500 GeV running Final States 3 4   jet 3 4 Access partonic kinematics via Di-jet and photon-jet Provides mapping of  g(x)

Renee Fatemi Wayne State University Nuclear Seminar 32 Summary From DIS: QUARKS = 20-30% of total proton spin, while the gluon spin is poorly constrained. The RHIC spin program aims to access  G directly STAR inclusive Jets rule out substantial phase space compared to DIS, but cannot be translated easily into a direct  G value. The STAR Spin program is entering a very rich phase of correlation and direct photon measurements, while continuing to expand the p T reach of the inclusive channels. A Global Analysis incorporating the world dataset, along with future precision measurements in x space, are needed to provide a complete and definitive answer.

Renee Fatemi Wayne State University Nuclear Seminar 33 BACKUP

Renee Fatemi Wayne State University Nuclear Seminar 34 BBC measures blue and yellow residual transverse components during longitudinal run (analyzing power 6~7 x ) Spin rotators were adjusted Measure A ∑ in transverse running. Combine with transverse components to set an upper limit on the contribution to the A LL measurement from non-longitudinal polarization components Horizontal spin components similar AA STAR Preliminary Residual Transverse Polarization Systematic

Renee Fatemi Wayne State University Nuclear Seminar 35 BBC coincidence hits in East & West BBCs Relative luminosity systematic calculated from BBC and ZDC asymmetry comparison  A LL (BBC&ZDC) ~ 9.4x10 -3 Relative Luminosity Systematic

Renee Fatemi Wayne State University Nuclear Seminar 36 Background manifests itself as jets with large neutral energy deposit Difference between High Background and Low Background Samples A bg LL Background Removed from analysis Background Fraction Background Asym A LL Systematics: 2005 Background Estimate Jet E EMC /E Tot JP2

Renee Fatemi Wayne State University Nuclear Seminar 37 Beam Gas Background

Renee Fatemi Wayne State University Nuclear Seminar 38 A LL Systematics: Random Pattern Analysis The random pattern analysis randomly creates new spin states for every run random patterns were used. The RMS of the distribution of the  LL s is smaller (within error) than the statistical error, so the systematic error from bunch-dependent correlations is zero.

Renee Fatemi Wayne State University Nuclear Seminar 39 STAR Preliminary False Asymmetry Systematic Check

Renee Fatemi Wayne State University Nuclear Seminar 40 Vogelsang and Stratmann GRSV Inclusive Jet vs pT

Renee Fatemi Wayne State University Nuclear Seminar 41 How RHIC works for 1.Optically pumped Polarized H- source 2. H- source is stripped and pumped into Booster - a fast cycling cyclotron 3. Injected into Alternating Gradient Synchrotron at 2.35 GeV and accelerated to 24.3 GeV 4. Injected into RHIC ring at 24.3 GeV and accelerated to 100 GeV 5.The H- jet target was installed in 2004 to calibrate the CNI polarimeter 6. Two Siberian Snakes are used to preserve polarization of beams 7. Challenge for the future is to overcome expected resonances and preserve polarization beyond beam energies of 100 GeV. 8. CNI provides 10% error 9. Absolute normalization from Jet Target provides 20 % error per beam.

Renee Fatemi Wayne State University Nuclear Seminar 42 Longitudinally polarized lepton-nucleon scattering probes spin structure of the nucleon g 1 (x,Q 2 ) X = % Nucleon Momentum carried by Parton Q 2 = Momentum Transfer of  !Resolution! If Q 2 >> M N then  interacts with only 1 “free” quark with spin anti- aligned with that of the photon Quark Parton Model pQCD +OPE a 0 = ∆  = ∆u+∆u+∆d+ ∆d+∆s+∆s Measured in n and hyperon decay A Quick Review of Nucleon Spin Structure Physics

Renee Fatemi Wayne State University Nuclear Seminar 43 What is Spin? Classical Analogy: The Spinning Top PROTON “It appears to be one of the few places in physics where there is a rule which can be stated very simply, but for which no one has found a simple and easy explanation. The explanation is down deep in relativistic quantum mechanics. This probably means that we do not have a complete understanding of the fundamental principle involved” Feynman said: 1.Spin is an INTRINSIC ATTRIBUTE of all particles 2.Spin is a type of ANGULAR MOMENTUM 3.Spin+Orbital Angular Momentum is CONSERVED 4.Spin is QUANTIZED in units of hbar 5.The world is divided into particles with integer spin values (BOSONS) and half integer spin value (FEMIONS) In Quantum Mechanics:

Renee Fatemi Wayne State University Nuclear Seminar 44 QEDQCD pp  g 8 Color Confinement  Jets! Three-jet events are first direct evidence of gluons observed by TASSO at DESY