# Presentation: 401841

## 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_x0001_

- Several contributing sub-processes:

- +

**Inclusive Jet Signal: High Cross Section + Avoid fragmentation functions**

- +

- +...

*B. Jager et. al, Phys Rev D70 034010*

**Notes:**
Low PT dominated by gg and qg on left plot
_x0005_High asymmetries near mid-rapidity on right plot => STAR’s acceptance

## G Models

- 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

- Full G integral not covered by STAR acceptance

**—  ****GRSV**
**—  ****GS**
**—  ****BB**
**—  ****LSS**
**—  ****AAC**
**—  ****DNSI**

*Q**2**=100GeV**2**/c**2*

## 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

**EndCap**
**EMC**

**BBC**

**EMC **
**Barrel**

**BBC **

**TPC**

## Experimentally Measuring ALL

- 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

- 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 p**T** 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)

## 2005 ALL - ∆G Constraints

- 2005 ALL - ∆G Constraints

**Theoretical Uncertainties not included*

*GRSV DIS best fit=0.24*
*1**** = -0.45 to 0.7*
*PRD 63, 094005 (2001)*

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

## 2006 Preliminary ALL

- 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

- parton

- particle

- detector

- Jet Reconstruction
-  Midpoint Cone Algorithm
-  0.5 GeV_x0005_ 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 ~ 0.5
Else ~ 0.1 |

| pT systematic | 6.7% |
| --- | --- |

## Jet Reconstruction and Trigger Bias

***Step 1:  Use PYTHIA+GEANT to estimate the p******T****** shift from detector jets to particle jets***

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

**Particle jets**
**Shifted detector jets**
**Detector jets**

***Step 3: Choose the largest difference for each jet p******T****** 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**

- ALL(R3 + 0.001) - ALL (R3)

- R3(BBC) - R3(ZDC)

- ALL(R3 - 0.001) - ALL (R3)

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

## Background Systematic

- Background manifests itself  as jets with large neutral energy deposit

- AbgLL

- Background Fraction

- Background Asym

- Jet EEMC/ETot

**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)