Protons Spin Gluon Contribution Double Longitudinal Spin Asymmetry

Proton’s Spin Gluon Contribution Double Longitudinal Spin Asymmetry Measurement and Cross-section for Inclusive Jets at sqrt(s)=200 Ge. V in polarized pp collisions Julie Millane Massachusetts Institute of Technology Lake Louise Winter Institute February 2007 Julie Millane

Overview • • • Background Previous results Double Spin Asymmetry Theory Curves Jets STAR experiment at BNL RHIC 2003/2004 Results Preliminary 2005 ALL Measurement 2006 Projections global analysis Julie Millane 2

Parton Distribution Functions • Helicity average • Unpolarized proton structure • f(x) = f+(x) + f-(x) • Quark (q) distribution and Gluon (g) distributions are well know experimentally • Quark and Gluons each carry 50% of the proton momentum • Helicity difference • Polarized proton structure • f(x) = f+(x) - f-(x) • Quark (∆q) distributions: Well known only 0. 003 < x < 0. 8 • Gluon (∆g) distributions: Poorly constrained Julie Millane 3

Proton Spin • • ∆ = ∆u + ∆d + ∆s + …, Quark Contribution G, Gluon Contribution Lzq, Quarks orbital angular momentum Lzg, Gluons orbital angular momentum Julie Millane 4

DIS Results • Polarized DIS experiments: Fraction of proton spin carried by quarks is small • Where is the rest? q SMC QCD-analysis: • G is only poorly constrained from scaling violations in fixed target DIS experiments B. Adeva et al. , SMC Collaboration, Phys. Rev. D 58 (1998) 112002. Julie Millane 5

Spin Asymmetry to find ∆G f f 1 f 2 Julie Millane X 6

Jets parton particle detector • Look for “splashes of energy” in the detector • Add track/tower 4 -momenta Julie Millane 7

Double Spin Asymmetry • P, polarization • N, number of jets • R, relative luminosity Julie Millane 8

Gluon Polarization Measurements • Similar sensitivity of inclusive jet production and inclusive 0 production • Enhanced sensitivity for inclusive production Julie Millane 9

RHIC at BNL • Polarized protons with sqrt(s) = ≤ 500 Ge. V are collided at Brookhaven National Lab on Long Island, NY. • Polarized proton program had first transverse collisions in 2002 and first longitudinal collisions in 2003. • Any combination of longitudinal and transverse polarization is possible at RHIC. Julie Millane 10

Machine Performance Polarization Year (%) Recorded longitudinal luminosity (pb-1) Recorded transverse luminosity (pb-1) 2002 15 0. 3 0. 15 2003 30 0. 3 0. 25 2004 40 -45 0. 4 0 2005 45 -50 3. 1 0. 4 2006 60 8. 5 3. 4/6. 8 Julie Millane 11

RHIC Spin Physics • Longitudinal • Extraction of gluon polarization • Flavor separation of the sea polarization thru W production • Transverse • Quark Transversity • Sivers • Collins Julie Millane 12

STAR Detector • EM Calorimeter • Full jet reconstruction along with TPC • Barrel: 0 < | | < 1 • Endcap: 1. 09 < | | < 2 • 0 < < 2 • Beam-Beam Counter • Time Projection Chamber • • Particle identification Momentum measurement 0 < | | < 1. 4 0 < < 2 Julie Millane • Relative luminosity measurement • Absolute luminosity measurement • Min bias trigger • 3. 4 < | | < 5 • 0 < < 2 13

2003/2004 Inclusive Jet Cross-section • • Min bias and High tower data agree well Agrees within uncertainties to NLO QCD to over 7 orders of magnitude Statistical Errors are usually smaller than plotting symbols Yellow error band is systematic uncertainty • 10% uncertainty on energy scale leads to 50% uncertainty on jet yield • Di-jets and photon jets could reduce this systematic uncertainty B. I. Abelev et al. (STAR Collaboration), Phys. Rev. Lett. 97, 252001 (2006) Julie Millane 14

2003/2004 ALL measurement • Inclusive Jet • Data combined from two runs • Statistics limit results B. I. Abelev et al. (STAR Collaboration), Phys. Rev. Lett. 97, 252001 (2006) Julie Millane 15

2005 Inclusive Jet ALL measurement preliminary curves* G = G G = -G G = 0 GRSV-STD GRSV* 2 /ndf STD 1. 1 G = G 12 G = 0 0. 7 G = -G 1. 4 Systematic error band Julie Millane 16

2003/2004 & 2005 Comparison 2003/2004 STAR Jet ALL 2005 STAR Jet ALL • Results Consistent • Statistical errors improved • p. T range extended preliminary Julie Millane 17

2006 Projections curves* G = G G = -G G = 0 GRSV-STD 2006 STAR Jet ALL 2005 STAR Jet ALL Julie Millane 18

Summary • Cross-section agrees within uncertainties to NLO QCD to over 7 orders of magnitude • 2003/2004 and 2005 ALL measurements are consistent with each other • Measurement contributes significantly to the global ∆G determination Julie Millane 19

Nitty Gritty Details … for those who want to know Julie Millane

2005 Trigger thresholds • Bht 1 • 2. 9 Ge. V/c • Bht 2 • 3. 7 Ge. V/c • Bjp 1 • 4. 6 Ge. V/c • Bjp 2 • 5. 8 - 7. 9 Ge. V/c Julie Millane 21

Particle level jets midpoint-cone algorithm* Simulation detector Data “gea • Search over “all” possible seeds for stable groupings • ts • Check midpoints between jet-jet pairs for stable groupings nt” je particle GEANT parton pythia ia h yt s et • j ” Split/merge jets based on Eoverlap Add track/tower 4 -momenta Correction philosophy “p • Use Pythia+GEANT to quantify detector response • Estimate corrections to go from “detector” to the “particle” level *(hep-ex/0005012) Julie Millane 22

Triggers • Min bias: Coincidence between two scintillation counters • With a min bias trigger many events are recorded that don’t contain jets. • Njets (minb)/ Njets (bht 2) = 3/ 661 • Triggers used for STAR Inclusive Jet ALL determination are (R 6173023) • high tower: 2 (2003/2004, 2005) • jet patch: 2 (2005 only) • High Tower: min bias + a tower registered an ADC above a threshold • Jet Patch: min bias + one of 6 patches ( =1, =1) has an ADC above a threshold Julie Millane 23

2003/2004 Jet ALL Systematics CNI beam polarization 25% scale uncertainty Relative luminosity 0. 009 Non-longitudinal beam < 0. 010 polarization Beam background 0. 003 Trigger bias, jet < 0. 009 reconstruction bias and jet pt resolution Julie Millane 24

2005 Jet ALL Systematics effect (x 10 -3) False Asymmetries <6. 5 Reconstruction + Trigger Bias 2 -12 (p. T dependent) Non-longitudinal Polarization 3 Relative Luminosity 2 Backgrounds <1 Julie Millane 25