# Presentation: 883485

## Transverse Spin2008 RHIC Spin Plan UpdateL. Bland, M. Grosse-Perdekamp, F. Yuan

- Outline
- Goals
- Recent Transverse Spin Developments
- Future Opportunities for Transverse Spin at RHIC
-  Transverse spin Drell Yan production
-  Transverse spin  + jet production
-  Future transversity studies at RHIC

## RHIC Spin GoalsUnderstanding the Origin of Proton Spin

- Understanding the origin of proton spin helps to understand its structure

## Developments Since 2007 Update

- Final results from STAR and BRAHMS
- Improved theoretical understanding of Sivers mechanism
- New experimental capabilities

## Final ResultsxF dependence of AN for forward  production

- Even though the kinematics of the SIDIS measurement and the forward  data have little overlap, it is possible to account for most of the features of the RHIC data by calculations based on phenomenological fits to the SIDIS data

## Final ResultspT dependence of AN for forward  production

- Final ResultspT dependence of AN for forward  production

- A key feature of the RHIC data that cannot be explained is the *p*T dependence at fixed *x*F.  Calculations based only on the Sivers mechanism require *A*N to decrease with increasing *p*T.  This trend is not what is observed.

## Recent DevelopmentsImproved Understanding of Sivers Mechanism

- Two requirements...
-   spin-correlated kT dependence in proton  orbital motion
-   a relative phase between amplitudes
- The phase in SIDIS is a simple final-state, attractive color-charge interaction
- The phases in p+p are in general complicated, and lead to cancellations for transverse spin effects for mid-rapidity dijet production
- Firm predictions for future p+p ...
- Transverse spin effects for Drell-Yan production arise from a simple initial-state, repulsive color-charge interaction
- Transverse spin effects for +jet arise primarily from a simple initial-state, repulsive color-charge interaction

## Recent DevelopmentsIncreased Acceptance for Forward Calorimetry

- Recent DevelopmentsIncreased Acceptance for Forward Calorimetry

- Factor of ~20 increase in forward calorimetry acceptance in change from Forward Pion Detector to Forward Meson Spectrometer

## Future OpportunitiesTransverse Spin Asymmetries for the DY Processhttp://spin.riken.bnl.gov/rsc/write-up/dy-final.pdf

- Following luminosity developments planned for RHIC-II and detector upgrades, it is expected that a transverse spin DY measurement could be completed in two 10-week runs in 2015 and 2016

## Future OpportunitiesTransverse Spin Asymmetries for the DY ProcessBenchmarking

- Future OpportunitiesTransverse Spin Asymmetries for the DY ProcessBenchmarking

- Clustering and shower-shape analysis that were developed for the forward pion detector have been adapted and applied to run-8 data from the FMS.  (*Inset*) Mass distribution from all pairs after clustering and shower shape analysis.  The analysis is applied to events where the total energy deposited in the FMS is Etot>20 GeV and 20 < *p*z,tot < 25 GeV/c.  The  peak is being used to calibrate the energy scales of individual FMS cells.  The tail of the pair mass distribution extends to large mass.  Peak positions, widths and signal-to-background ratios will be strongly influenced by the ongoing calibration efforts.

## Future OpportunitiesTransverse spin for forward +jetTest of predictive power of theory (A. Bacchetta et al. PRL 99 (2007) 212002) 

- Future OpportunitiesTransverse spin for forward +jetTest of predictive power of theory (A. Bacchetta et al. PRL **99** (2007) 212002)

- Restricting the measurement of the forward photon to E>35 GeV at <>=3.2 produces a signal:background ratio of 2.1.

## Future OpportunitiesTransverse spin for forward +jetTest of predictive power of theory

- 104 useable forward photon + jet coincidences are expected in a 30 pb-1 data sample with 60% beam polarization

## Future OpportunitiesProbing TransversityCollins Mechanism / Interference Fragmentation

- Future OpportunitiesProbing TransversityCollins Mechanism / Interference Fragmentation

- Single spin asymmetries for – (red) and   (blue) and –  hadron pairs as a function of the invariant mass of the hadron pair. The data points correspond to the statistical errors expected with 16 pb–1 and 65% polarization in run 9.

## Backup

## STAR Results vs. Di-Jet Pseudorapidity Sum

***STAR Results vs. Di-Jet Pseudorapidity Sum***
***Run-6 Result***

## Sivers in SIDIS vs Drell Yan

- Important test at RHIC of the _fundamental QCD prediction_ of the_ _non-universality of the Sivers effect!
- requires very high luminosity (~ 250pb-1)

**Transverse-Spin Drell-Yan Physics at RHIC**
- L. Bland, S.J. Brodsky, G. Bunce, M. Liu, M. Grosse-Perdekamp, A. Ogawa, W. Vogelsang, F. Yuan
- _[http://spin.riken.bnl.gov/rsc/write-up/dy_final.pdf](http://spin.riken.bnl.gov/rsc/write-up/dy_final.pdf)_

## Non-universality of Sivers Asymmetries:

**Simple QED**
**example:**

**DIS: attractive**

**Drell-Yan: repulsive**

**Same in**** ****Q****C****D****:**

**As a result:**

_**Non-universality**_** of Sivers Asymmetries:**
**Unique Prediction of Gauge Theory !**

## Rapidity and Collision Energy

**Large rapidity acceptance required to probe valence quark Sivers function**

## Benchmarking Simulations

**p+p ******** J/********+X ******** *****l*****+*****l*********+X, ********s=200 GeV**

*e**e*
- ||<0.35

****
- 1.2<||<2.2

**J/******** is a critical benchmark that must be understood before Drell-Yan**

- PHENIX,
- hep-ex/0611020

## Dilepton Backgrounds

**J/******

******’**

****

**Drell-Yan**

**Isolation needed to discriminate open heavy flavor from DY**