inclusive jet longitudinal spin asymmetry measurements with polarized p+p collisions at star

1STARSTAR LLWI, Feb 23, 2008 David Staszak UCLA

Inclusive Jet Longitudinal Spin Asymmetry Measurements with Polarized p+p Collisions at STAR

Lake Louise Winter Institute, February 23, 2008

David Staszak (UCLA)

STAR Collaboration


The Proton Helicity Distribution

1/2 = ∆Sq + ∆G + Lq,g

∆Sq: sum of spin contributions from all quarks, anti-quarks

Measured experimentally by DIS in the kinematic range 0.003 < x < 0.8

∆G: contribution from gluons

Gluon Helicity:

G=

We know 20-30% of proton’s total spin

Poorly Constrained from DIS, this is a major goal of the RHIC Spin Group

Lq,g: gluon and quark angular momentum contributions

The future…


Accessing ∆G via ALL

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ALL =Δσ

σ=

σ ++ −σ +−

σ ++ + σ +−∝

ΔfaΔfb

fa fb

ˆ a LL

Several contributing sub-processes: +

Inclusive Jet Signal: High Cross Section + Avoid fragmentation functions

+ +…

B. Jager et. al, Phys Rev D70 034010


G Models

• Many different models of ∆G

• GRSV has set up an inclusive jet/hadron framework to translate ∆G ALL at RHIC energies and STAR kinematics

• GRSV represents a good “first guess”

x·∆G(x)

x·∆

G

x

Vogelsang and Stratmann

Full G integral not covered by STAR acceptance

— GRSV— GS— BB— LSS— AAC— DNSI

Q2=100GeV2/c2


STAR Detector

EM Calorimeter (Pb/Scintillator):• Particle Neutral Energy• Barrel 0<<1 (2003-2005) -1<<1 (2006)• Endcap 1.09<<2.0

Beam-Beam Counter:• MinBias Trigger• Relative Luminosities • 3.4<||<5

Time Projection Chamber:• Charged Tracks PT

• -1.4<<1.4

100 GeV Polarized Proton Beams

All detectors have full azimuthal coverage

EndCapEMC

BBC

EMC Barrel

BBC TPC


Experimentally Measuring ALL

€

€

ALL =1

P1P2

(N ++ + N−−) − R(N +− + N−+)

(N ++ + N−−) + R(N +− + N−+)

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R =L++ + L−−

L+− + L−+

Relative Luminosity R from BBC Coincidence Rates for different Bunch Patterns

Polarization of Beams from CNI Polarimeters taken at set time intervals

Numbers of Jets Nij Reconstructed for Different Bunch Patterns


First Results: 2003+2004 Cross Section and ALL

Published: Phys. Rev. Lett. 97 252001 (2006)

• Limited Statistics• Theory curves based on ∆G parameterizations of DIS data• GRSV-STD is best fit to DIS data

• Agreement within systematics with NLO QCD over 7 orders of magnitude• Theory: B. Jager et. al, Phys Rev D70 034010


Final 2005 ALL

0.2 < < 0.8

- Error bars are statistical only- Grey bands are systematic uncertainty

• Gehrmann-Sterling (GS-C) model calculation inserted into GRSV’s inclusive jet framework Phys.Rev.D53:6100-6109(1996)


ALL Systematics

effect (x 10 -3)

Reconstruction + Trigger Bias

2-5 (pT dependent)

Non-longitudinal Polarization

0.1-0.8 (pT dependent)

Relative Luminosity 0.94

Backgrounds 0.70

pT systematic [-5.4%,+6.7%]

Trigger Bias: The natural interaction mix (gg/qg/qq) can be biased in our sample from our triggers which rely on neutral energy only.

Reconstruction Bias: 25% jet resolution mixed with steeply falling pT spectrum means on average that we over-estimate the jet energy.

Combining PYTHIA partonic information with polarization models of G, we can calculate: ALL(PARTONIC) ALL (GEANT) ALL(GEANT+TRIGGER)

Reconstruction Bias is the difference between ALL(PARTONIC) and ALL (GEANT)

Trigger Bias is the difference between ALL(PARTONIC) and ALL(GEANT+TRIGGER)


GRSV DIS

2005 ALL - ∆G Constraints

*Theoretical Uncertainties not included

GRSV DIS best fit=0.241 = -0.45 to 0.7

PRD 63, 094005 (2001)

Within GRSV framework, G can’t be much larger than STD



2006 Preliminary ALL

- Only Jet Patch Data Shown

• 2 4 pb-1 (more on the way!)

• BEMC fully instrumented, EEMC towers included

• 50 55% Beam Polarization

• Increased trigger thresholds better statistics at high pT

2006 Improvements

-0.7 < < 0.9


2006 Preliminary ALL

* GRSV-STD excluded with 99% CL

* g < -0.7 excluded with 90% CL


Summary and Outlook

Inclusive jet channel is one way in which the RHIC Spin Group is able to access ∆G

2005 and 2006 inclusive jet results are a significant contribution to global understanding of ∆G

500pp GeV running is on the horizon expanded x-range

From STAR, Di-jet and Gamma-Jet measurements are on the way. Gamma-Jet can measure G(x) as a function of x, whereas Inclusive Jet can only measure an integrated x-range.

A global analysis of worldwide measurements is necessary to come to a definitive answer for ∆G


Backup Slides


Comparison: 2006 - 2005 ALL


Model Dependent ALL Curves



STAR Jet Reconstruction and Triggering

part

onpa

rtic

lede

tect

or

etcp

e

,,

,

πγν ,,

gq,

Jet Reconstruction • Midpoint Cone Algorithm• 0.5 GeV seed energy• 0.4 Cone Radius (2005), 0.7 C.R. (2006)

hep-ex/0005012

2005/2006 Trigger Mix• MinBias - BBC Coincidence• HighTower - ∆x = .05x.05 EMC patch above threshold• JetPatch - ∆x = 1x1 EMC patch above threshold


Data/MC Comparison

PRL 97, 252001 (2006)


2006 Systematic Uncertainties

effect (x 10 -3)

Reconstruction + Trigger Bias

[-1,+3] (pT dependent)

Non-longitudinal Polarization

~0.03(pT dependent)

Relative Luminosity

0.94

Backgrounds 1st bin ~ 0.5Else ~ 0.1

pT systematic 6.7%


Jet Reconstruction and Trigger Bias

Step 1: Use PYTHIA+GEANT to estimate the pT shift from detector jets to particle jets

Step 2: Simulate the difference in ALL between detector and particle jets for various gluon polarization scenarios

Particle jetsShifted detector jetsDetector jets

Step 3: Choose the largest difference for each jet pT bin


Single Spin Asymmetries


Relative Luminosity Systematic

Calculated using the BBC:

Cross-checked using theZero Degree Calorimeter (ZDC),another luminosity monitor

Difference (below) interpreted as a systematic on the relative luminosity

Difference between BBC and ZDC is 0.001

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R3 =Lparallel

Lantiparallel

ALL(R3 + 0.001) - ALL (R3)

R3(BBC) - R3(ZDC)

ALL(R3 - 0.001) - ALL (R3)

Systematic estimated as the difference betweenALL(R3) and ALL(R3 ± 0.001)


Background Systematic

Background manifests itself as jets with large neutral energy deposit

Difference between High Background and Low

Background Samples 05.0<bgf AbgLL

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Abg = 0.00837 ± 0.00639

Background

Removed from analysis

( ) ( ) ( ) ( )( )Tbg

TbgLLTbgTLL

Tmeas

pf

pApfpApA

LL +

×+=

1

Background Fraction Background Asym Jet EEMC/ETot

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ALLEMF>0.8 = 0.00837 ± 0.00639€

fbkg = 0.0014 ± 0.0012

JP2


Non-longitudinal Beam Polarization Systematic

Non-longitudinal beam polarization changes ALL:

To bound this effect,

Calculate A from transverse data: |A |

0.1

Estimate the beam transverse polarization component Local polarimetry (BBC up-down and left-right asymmetries)

€

δA LLAΣ =|tanθB tanθ Y cos φY − φ B( ) A Σ |

€

⇒ |δA LLAΣ | ≤ 0.003

inclusive jet longitudinal spin asymmetry measurements with polarized p+p collisions at star

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