# Presentation: 571934

## UMass Amherst

**UMass Amherst**

**Christine Aidala**

**June 15, 2006**

*Accessing Transversity via Collins and Interference Fragmentation at RHIC*

**QCDN-06, Rome**

## Increasing Interest in Transverse Spin Physics at RHIC

- Progress in e+e- and DIS measurements as well as theory allows us to learn more and more from p+p results
- 2006 run (ends June 26): Both PHENIX and STAR dedicated a significant fraction of beam time to transversely polarized collisions
- Transverse spin physics competes with longitudinal spin program (g)
- PHENIX: 2.7 pb-1 sampled at ~55% polarization
- STAR: 6.8 pb-1 sampled at ~60% polarization
- (Compare to < 1 pb-1 total for all previous runs combined)
- Transverse running allows for qualitatively different physics results from RHIC spin program

- C. Aidala, QCD-N06, June 15, 2006

## Transverse Spin at RHIC

- Results from STAR, PHENIX, and BRAHMS from 2002-2005 data sets presented by S. Heppelmann
- Additional transverse data taken this year by all three experiments
- Future running only with STAR and PHENIX detectors

- Longitudinal or transverse spin

- Longitudinal or transverse spin

- C. Aidala, QCD-N06, June 15, 2006

## Avenue to Transversity at RHIC

- Present and near-term: High-precision inclusive AN and jets (S. Heppelmann’s talk)
- Mid-term: Collins and IFF (this talk)
- Long-term: Drell-Yan (M. Grosse Perdekamp’s talk)
- Parallel effort on spin-dependent FF’s at BELLE (R. Seidl’s talk)

- C. Aidala, QCD-N06, June 15, 2006

## Transversity from Collins Effect

*Transversity from Collins Effect*

*Jet*

- Proton
-  Structure

- Hard Scattering
-      Process

- Collins
- Fragmentation

*Jet*

- J. Collins, Nucl.Phys. B396 (1993)161

- transversity
- distributions

- pQCD

- PDFs

- Collins FF

*Jet axis*

- C. Aidala, QCD-N06, June 15, 2006

## Transversity from Interference Fragmentation

*Jet*

*Jet*

- Proton
-  Structure

- Hard Scattering
-      Process

- Interference
- Fragmentation

- Jian Tang , Thesis MIT, June 1999

- R. Jaffe, X.Jin, J. Tang Phys. Rev. D57 (1999)5920

- X. Ji, Phys. Rev. D49 (1994)114

- J. Collins, S. Heppelmann, G. Ladinsky,
- Nucl.Phys. B420 (1994)565

*Transversity from Interference Fragmentation*

- IFF

- transversity
- distributions

- pQCD

- PDFs

- A. Bianconi, S. Boffi, R. Jakob, M. Radici, Phys. Rev. D62 (2000) 034009

- C. Aidala, QCD-N06, June 15, 2006

## PHENIX Detector Overview 

**Central arms**
**Photons, electrons, identified charged hadrons**
**|********| < 0.35**
****** ****= 180 degrees**
**Forward muon arms**
**Track and identify muons**
**1.2 < |********| < 2.4**
****

- Fine segmentation and high rate but limited acceptance

- C. Aidala, QCD-N06, June 15, 2006

## PHENIX: EMCal-RICH Trigger

- Rare probes experiment—trigger capabilities essential!
- 4x4 tower overlapping energy sum, 3 threshold settings
- 1.4 GeV used for most 0 studies since 2003
- 2x2 tower non-overlapping energy sum, threshold ~ 0.6 GeV
- Used in conjunction with RICH to form an electron trigger

- Mid-rapidity trigger on electromagnetic energy

- C. Aidala, QCD-N06, June 15, 2006

## PHENIX: IFF Using 0++-

*PHENIX: IFF Using ****0**+****+-*

- RUN 6 achieved: 2.7 pb-1, 55% Polarization
- RUN 7 projected: 5.0 pb-1, 65% Polarization

- 

- Simple error estimates using PYTHIA + PHENIX acceptance + 1.4 GeV
- photon trigger threshold.  0.5 < minv < 1.0 GeV/c2

- (Note Run 7 Beam Use Proposal
- still under discussion)

- R. Seidl

- pT pair (GeV/c)

- Tang: hep-ph/9807560

- Theory curve a particular model prediction for RHIC at 200 GeV:
-   q(x) = | q(x) +  q(x) | (Soffer bound)
-  IFF from phase-shift analysis

- Studies also underway for development of a high-pT charged pion trigger for 2008, which would greatly improve  IFF measurements.

- C. Aidala, QCD-N06, June 15, 2006

## STAR Detector Overview

- -1 <  < 1

- 0 <  < 1

- 1 <  < 2

- 2.2 < || < 5

- || ~3.3/3.7/4.0

- Collins and IFF measurements possible

- C. Aidala, QCD-N06, June 15, 2006

## STAR: Collins

- With upgraded Forward Pion Detector installed in 2006 run, sensitivity to 0 position in forward jets
- Separate Collins vs. Sivers in observed 0 asymmetry
- Simulation and data analysis underway to understand how precisely jet axis can be determined with FPD++
- Forward Meson Spectrometer to be installed for 2007 run will provide 0 pair measurements as well as fully contained jets
- Continuous EMCal coverage  < 4.0

- 2006

- C. Aidala, QCD-N06, June 15, 2006

## STAR: IFF

*STAR: IFF*

- Interference fragmentation
- measurement for h+h- possible
- with 2006 data
- Like PHENIX measurement, sensitive to transversity with IFF available as input, e.g. from BELLE
- Proposal by Bacchetta and Radici (PRD 90, 094032 (2004)) to measure IFF *directly in unpolarized p+p collisions* using dijets
- Level-2 dijet trigger available
- Based on energy deposit in EMCal  trigger-side jet (most often) has leading 0
-  0-charged hadron pair measurement possible
- Several million dijet events collected in 2006
- Can look at this analysis this year

- C. Aidala, QCD-N06, June 15, 2006

## Longer-Term Future

- End of 200 GeV running mid-Run-09 (2009): Plan for ~31 pb-1 transverse data at PHENIX
- Sub-percent statistical errors up to pT ~ 8 GeV/c for 0+ IFF
- RHIC-II (M. Grosse Perdekamp’s talk)

- C. Aidala, QCD-N06, June 15, 2006

## Summary and Prospects

- Increased interest in transverse spin physics at RHIC  better prospects for more beam time with transverse polarization
- Possible to access transversity distribution via Collins effect at STAR and IFF at PHENIX and STAR
- May get first results this year or next
- Belle measurements of Collins FF and IFF will provide important input for p+p studies
- Also possible to measure IFF directly in (unpolarized) p+p through dijets at STAR

- RHIC results, alongside e+e- and DIS measurements, will constitute an important part of a global analysis to understand transversity.

- C. Aidala, QCD-N06, June 15, 2006

## Extra Slides

- C. Aidala, QCD-N06, June 15, 2006

## PHENIX: pT -pTJet Correlation

- Jet transverse momentum determined by outgoing partons in Pythia
- (entries 7 or 8, depending on proximity to pair momentum)
- Nearly linear behaviour between jet transverse momentum and that of pion pair

- p±p0

- pT pair (GeV/c)

- pT jet (GeV/c)

- C. Aidala, QCD-N06, June 15, 2006

## STAR Jet Cross Section

- C. Aidala, QCD-N06, June 15, 2006

## RHIC Specifications

- 3.83 km circumference
- Two independent rings
- Up to 120 bunches/ring
- 106 ns crossing time
- Energy:
- Up to 500 GeV for p-p
- Up to 200 GeV for Au-Au(per N-N collision)
- Luminosity
- Au-Au: 2 x 1026 cm-2 s-1
-    p-p   : 2 x 1032 cm-2 s-1 (_*polarized*_)

- C. Aidala, QCD-N06, June 15, 2006

## STAR Excellent Coverage for (Di-)Jets

- L2
- jet

- C. Aidala, QCD-N06, June 15, 2006

##  STAR Triggered on Di-Jet Found On-line

- 

- =0o

- L2 algo
- result

* **STAR Triggered on Di-Jet Found On-line*

- Comparison with off-line  similar

_**L2 di-jet logic:**_
-  5500 EMC towers
-  sliding jet patches
-  jet size : 0.6x0.6 (x)
-  jet1 Et>3.6, jet 2 Et>3.3 GeV
-  decision :  60 muSec/event
-  event rate ~8 Hz

- 2005 data event

_**L0  di-jet logic:**_
-  BBC East.West
-  Etot >14 GeV
-  hardwired jet patches
-  jet size : 1x1 (x)
-  one jet Et>4.0 GeV
-  event rate ~120 Hz

**L0-L2 logic benefits:**
-  large acceptance combined with trigger rejection power
-  full statistics on-line trigger monitoring of EMC
-  compact trig info saved for each event

- -1

- 0

- +2

- =180o

- =360o

- ~180 o
- back-to-back di-jet

- Z=Et/GeV

- Jet  is weighted
- with EM ET

- C. Aidala, QCD-N06, June 15, 2006

**Notes:**
Presented data only from d-jet L2 trigger, one of several contributiong to STAr di-jets

## Forward Pion Detector at STAR

*Forward Pion Detector at STAR*

** ****24 layer Pb-Scintillator Sampling     ****	****Calorimeter **
** ****12 towers**
** ****Shower-Maximum Detector  - 2 orthogonal layers of 100 x 60 strips **
** ****2 Preshower Layers**

**Top-Bottom-South Detectors**
** ****4x4 array of Lead-Glass **
** ****No Shower Max**
** ****Used for systematic error studies**
**TRIGGER****  ****E****DEP**** > 15 GeV**

- C. Aidala, QCD-N06, June 15, 2006

**Notes:**

In QCD AN for single-inclusive reaction is power suppressed as 1/ Pion pT in the hard scale. Makes calculations complicated. 
Talk about how difficult to disentangle Sivers from Qu and Sterman twist 3 effects. Also Collins effect plays a role here.
“Boer,Mulders and Pijlman, Nucl.Phys. B 667(2003)

## 2006 − Forward Pion Detector++

- Large enough
- to integrate over a jet cone
- for direct photon isolation cuts

- C. Aidala, QCD-N06, June 15, 2006

## 2007 and Beyond – Forward Meson Spectrometer

-   FMS will provide full azimuthal
-    coverage for range 2.5  η  4.0
- •  Broad acceptance in              plane
-    for inclusive                        production
-   Broad acceptance for              and
-                from forward jet pairs to probe
-    low-*x* gluon density

*2007 and Beyond – Forward Meson Spectrometer*

- C. Aidala, QCD-N06, June 15, 2006

## 2006 STAR Di-Jet Events

*2006 STAR Di-Jet Events*

- Reconstructed di-jets from
-  EM calorimeter only trigger data:

- Stuck high bit in one tower

- Jet 1

- Jet 2

-  vs. 2

- Transverse EM energy

- 3,000,000
- di-jets

- C. Aidala, QCD-N06, June 15, 2006

**Notes:**
Power of STAR

## 2006 – Physics Goals

- ♦  Forward jet shape                 ♦  Asymmetry for jet-like events
- ♦                             mapping     ♦             ?
- ♦  Inclusive/direct photon measurements

**FPD++**

- 5/15 GeV summed energy threshold
- for large/small cells

- hardware-level calibration

- The data taken should allow most of the goals
- to be met; analysis is in progress

- C. Aidala, QCD-N06, June 15, 2006

## IFF Asymmetries vs pT:  ± 

- [Tang:hep-ph9807560]

-   p0 – Trigger 1.4 GeV Photons
-  0.5 < minv < 1 GeV
-  Calculated jet pT from pion pair (PYTHIA)

- RUN 6: 2.7 pb-1, 55% Polarization
- RUN 7: 5.0 pb-1, 65% Polarization

- 200 GeV

- 500 GeV

- May be possible to draw some
- early conclusions from 2007 data

- Theory curve by [Tang:hep-ph9807560]:
-  dq(x) = | q +  Dq(x) | (Soffer bound)
-  IFF from Phase-shift analysis

- C. Aidala, QCD-N06, June 15, 2006