# Presentation: 212417

## Outline :

**Outline **:
***Introduction***
***2005 results***
***2006 results***
***Summary***

***Constraints on ************G through*** ***Longitudinal Double Spin Asymmetry Measurements of Inclusive Jet Production in Polarized p+p Collisions at 200 GeV ***

**The 18****th**** International Symposium on Spin Physics**_**[University of Virginia](http://www.virginia.edu/)**_**October 6-11 2008**

*** **Currently at *Georgia State University*

## Proton Spin Structure

***Proton Spin Structure***

***Spin Crisis :  ******Origin of the proton spin?***

- Polarized DIS ~ 0.3

- Poorly Constrained

*(Leader et al, PRD 75, 074027 (2007))*
- Three recent fits of equal quality:
-  ΔG = 0.13 ± 0.16
-  ΔG ~ 0.006
-  ΔG = -0.20 ± 0.41
- all at *Q*2 = 1 GeV2

## Proton Spin Structure at RHIC

***Proton Spin Structure at RHIC***

-  ***Polarized pp collisions at RHIC ************ New QCD lab:***
***	****** ******strongly interacting probes***
*** ******High ************s and p******T****** make NLO pQCD analysis reliable***
*** ******STAR longitudinal spin program ************ ***
***Gluon polarization distribution***

*** ******Inclusive jet asymmetries are an excellent tool to study gluon polarization: Large cross-sections and relative independence from fragmentation functions***

## STAR Detector Layout

******=0**

******=2**

******= -1**

****** ****= - ln(tan********2)**

- Special interest for spin

***Beam-Beam Counters, ******2<|************|<5***
*** ******Triggering, Luminosity, local Polarimetry***

***Barrel EM Calorimeter, ******−1<************<1****** ***
***Triggering & Calorimetry***

***Time Projection Chamber,  ******|************|<1.4****** ***
***Tracking***

***Endcap EM Calorimeter****** ******1.08<************<2***
*** ******Triggering & Calorimetry***

***STAR Detector Layout***

**Yellow beam**

**Blue beam**

## Inclusive jet cross section & ALL (2003+2004)

*** ******A******LL******jet******  disfavors GRSV-max (************g=g)***

***Inclusive jet cross section & A******LL****** (***2003+2004***)***

*** ******Satisfactory agreement with NLO pQCD over seven orders of magnitude ************  pQCD works!***

***Data are compared to predictions within the GRSV framework  (4 major scenarios)***

## 2005 Inclusive ALLjets Analysis

-  *Dominated by** ****Jet Reconstruction**** **&** ****Trigger Bias ******:***
* **Jet reconstruction bias: ~25% jet resolution and steeply falling jet p**T  **distribution causes measured p**T  **to average 20% larger than true p****T***
* **Trigger bias : each trigger samples the sub-processes (qq/qg/gg) differently.*

***2005 Inclusive A******LL******jets ******Analysis***

*** ******Data well described by MC***

| ALL systematics | (x 10 -3) |
| --- | --- |
| Reconstruction + Trigger Bias | 2-5 (pT dep) |
| Non-longitudinal Polarization | 0.1-0.8 (pT dep) |
| Relative Luminosity | 0.94 |
| Backgrounds | 0.70 |

* **2 pb-1 after run selection *
* **<P**B**P**Y**> ≈ 0.25*
* **2.38 M events** (post-cuts), 50% from newly commissioned ***Jet Patch*** (1x1 rad) trigger*
* **Jet cone radius = 0.4*
* **0.1 < Neutral Energy Fraction < 0.8*
* **0.2 < Jet Detector **** < 0.8*

| pT systematic | [-5.4%,+6.7%] |
| --- | --- |

**Neutral Energy Fraction**

## 2005 Inclusive ALLjets Results

- M. Sarsour, TAMU – ALL for Inclusive Jet Production

***2005 Inclusive A******LL******jets ******Results***

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

*  **Data are compared to predictions within the GRSV framework with several input values of ****G as well as to GS-C.*

## Limits on ΔG from 2005 jet results

*** ******Significant new constraints on ************G when compared to predictions derived from one global fit to DIS data***

**Theoretical uncertainties not included*

- G > 0.45 95% [2]
- G > 0.3 66% [1]
- DIS best fit = 0.24 with ~1 range from -0.45 to 0.7 at input scale
***  ******PRD 63, 094005 (2001)***

***Limits on ******Δ******G from 2005 jet results***

## There are many other global analyses of the polarized DIS data

- M. Sarsour, TAMU – ALL for Inclusive Jet Production

***There are many other global analyses of the polarized DIS data***

***Other global analyses***

***Bjorken  x***

***Many predictions for A******LL****** vs. p******T***
***Is the sensitivity unique to GRSV?***

***x*****Δ*****g*****(*****x*****) at**
***Q*****2**** = 10 GeV****2**

## The STAR data exclude a broad range of models that have ΔG larger than that in GRSV-std
The counterexample is GS-C, which is negative at large x, has a node near x ~ 0.1, and has a large first moment at small x

***The STAR data exclude a broad range of models that have ******Δ******G larger than that in GRSV-std***
***The counterexample is GS-C, which is negative at large x, has a node near x ~ 0.1, and has a large first moment at small x***

***Comparison to other global analyses***

## Run 2006 Data

***Run 2006 Data***

***Improved FOM***
*Luminosity :**	**	**	**2 **** 4.7 pb**-1*
*Polarization: **	**	**	**50% **** 60% (online polarization)*
*Barrel EMC **** coverage: **	**[0,1] **** [-1,1]*
***In addition***
*Jet Cone Radius: 0.4 **** 0.7*
*-0.7 < ****jet axis **< 0.9*
*Neutral Energy Fraction < 0.85*
*Increased trigger thresholds*
*Inclusion of Endcap EMC towers*
*Improved tracking at large |****|*
*Shielding from backgrounds*

## Trigger Bias

***Trigger Bias***
-  *(Dominates A**LL** Systematics)*

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

*Maximum deviation determines A**LL** systematic*
*Confidence level calculations take account of any residual*

## Estimating the non-jet background

**Charged Energy Fraction**

***Estimating the non-jet background***

- Data

- Monte Carlo

*Non-jet backgrounds stand out in the data as single-jet events that have a small charged energy fraction*

- Data

**Charged Energy Fraction**

**Charged Energy Fraction**

*  **Isolate the background in the ratio of mono-jet to di-jet events vs. charged energy fraction*

## Effects of Residual Transverse Polarization

***Effects of Residual Transverse Polarization***

***Measured sensitivity to transversely polarized protons***

***BBC measurements of residual transverse components during longitudinal run (analyzing power 6~7 x 10******-3******)***

**Spin rotators were adjusted**

***Combine them to set an upper limit on the contribution to the A******LL****** measurement from non-longitudinal polarization components***

**Horizontal spin components similar**

**A******

**STAR Preliminary**

*~10**-4*

## Single transverse spin Asymmetry, AN

* **Beam gas background ,  ****A**N **< 4x10**-4*
* **Instrumental asymmetries **** 10**-4*
* **Expect trigger and reconstruction bias comparable to that for A**LL** (few x 10**-3**). Detailed calculation requires a model*

***Single transverse spin Asymmetry, A******N***

**  ****A****N****  is *****consistent with zero***

## 2006 Inclusive ALLjets

- M. Sarsour, TAMU – ALL for Inclusive Jet Production

***2006 Inclusive A******LL******jets***

-  Using jet patch trigger (x = 1x1 patch of towers) only
-  ***Statistical uncertainties are 3-4 times smaller than 2005 in high p******T****** region (p******T******>13 GeV/c)***

**GRSV curves with cone radius 0.7 and -0.7 < ******** < 0.9**

| ALL systematics | (x 10 -3) |
| --- | --- |
| Reconstruction + Trigger Bias | [-1,+3]
 (pT dep) |
| Non-longitudinal Polarization | ~ 0.03
 (pT dep) |
| Relative Luminosity | 0.94 |
| Backgrounds | 1st bin ~ 0.5
Else ~ 0.1 |

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

**200 GeV**
**-0.7 < ******** < 0.9**

## Limits on ΔG from 2006 jet results

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

**Theoretical uncertainties not included*

***Limits on ******Δ******G from 2006 jet results***

*** ******Run 2006 data provides even stronger constraints on gluon polarization***

## The first global NLO analysis to include inclusive DIS, SIDIS, and RHIC pp data on an equal footing
Finds a node in the gluon distribution near x ~ 0.1, but with the opposite phase from GS-C

***The first global NLO analysis to include inclusive DIS, SIDIS, and RHIC pp data on an equal footing***
***Finds a node in the gluon distribution near x ~ 0.1, but with the opposite phase from GS-C***

- de Florian et al., PRL **101**, 072001 (2008)

***DSSV – first global analysis with polarized jets***

***STAR***

##  NLO pQCD describes inclusive jet cross section at RHIC

 Within GRSV framework, 2005 results constrain G to less than 65% of the proton spin with 90% confidence

 Significant increase in precision in Run 2006 data provides even stronger constraints on gluon polarization

 STAR inclusive Jets rule out substantial phase space but do not yet determine sign of G

 STAR inclusive Jets results are in good agreement with other competitive measurements

 STAR inclusive jets play a significant role in the first global NLO analysis to consider DIS, SIDIS, and RHIC data together

  Over the next few years, STAR di-jet measurements will provide direct information about Δg(x)

***Summary***

*** ******NLO pQCD describes inclusive jet cross section at RHIC***
*** ******Within GRSV framework, 2005****** results constrain ************G to less than 65% of the proton spin with 90% confidence***
*** ******Significant increase in precision in Run 2006 data provides even stronger constraints on gluon polarization***
*** ******STAR inclusive Jets rule out substantial phase space but do not yet determine sign of ************G***
*** ******STAR inclusive Jets results are in good agreement with other competitive measurements***
*** ******STAR inclusive jets play a significant role in the first global NLO analysis to consider DIS, SIDIS, and RHIC data together***
-   ***Over the next few years, STAR di-jet measurements will provide direct information about ******Δ******g(x)***

## Back up

***Back up***

**AGS**

**LINAC**

**BOOSTER**

- Pol. Proton Source
- 500 A, 300 s

**Spin Rotators**

- Partial Siberian Snake

- Siberian Snakes

- 200 MeV Polarimeter

- AGS Internal Polarimeter

- Rf Dipoles

- RHIC pC Polarimeters

- Absolute Polarimeter
-              (H jet)

- 2  1011 Pol. Protons / Bunch
-  = 20  mm mrad

*RHIC accelerates heavy ions to 100 GeV/A *
*and polarized protons to 250 GeV*

***Solenoidal Tracker At RHIC****** ******(******STAR******)***

## Jet pT Scale Corrections & Systematics

***Jet p******T****** Scale Corrections & Systematics***
-  *(Resolution and Efficiency)*

***Largest effects are Detector Related:***
*Inefficiency: ~10%  +  Resolution:  ~25%*

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

## Relative luminosity Systematic

***Relative luminosity Systematic***

- Relative luminosity systematic is calculated from comparisons between the BBC and ZDC asymmetries

*********A******LL******Rel. Lum***

## False Asymmetries

***False Asymmetries***

**STAR Preliminary**

**STAR Preliminary**

**  *****Consistent with zero***

## ALL vs. Run Index

***A******LL****** vs. Run Index***

***STAR Preliminary***

## 2005 and 2006 Inclusive ALLjets

***2005 and 2006 Inclusive A******LL******jets***

*** ******Consistency between 2005 and 2006 A******LL******jets***
*** ******2006 A******LL******jets****** extends the precision to higher p******T****** region***

## M. Sarsour, TAMU – ALL for Inclusive Jet Production