# Presentation: 124448

## Measuring Orbital Angular Momentum through Jet kT

- Douglas Fields
*University of New Mexico/RBRC*

- Jan Rak, Rob Hobbs, Imran Younus

- Douglas Fields

- 6/2/2005

## Idea came from me trying to understand Siver’s effect 
Quantum Fan Level Description
This is a double spin asymmetry
This is for longitudinally polarized protons
Rotating partons around spin direction
Two classes of collisions:
Like helicity, i.e.,

Un-like helicity, i.e.,

- Quantum Fan Level Description
- This is a double spin asymmetry
- This is for longitudinally polarized protons
- Rotating partons around spin direction
- Two classes of collisions:
- Like helicity, i.e.,
- Un-like helicity, i.e.,

- Basic Picture

- Douglas Fields

- 6/2/2005

## Like Helicity(Positive on Positive Helicity)

- Integrate over b, left
- with some residual kT

- Measure jet

- Douglas Fields

- 6/2/2005

## Un-like Helicity(Positive On Negative Helicity)

- Integrate over b, left
- with some *different*
- residual kT

- Douglas Fields

- 6/2/2005

## History

- Talked to many people – Werner pointed me to a paper by Meng Ta-chung et al.
- “Experiment B” – similar idea, only for Drell-Yan

- Douglas Fields

- 6/2/2005

## From Meng Ta-Chung et al.Phys Rev. D40, p769, (1989)

- kTR

- kPR

- Douglas Fields

- 6/2/2005

## From Meng Ta-Chung et al.Phys Rev. D40, p769, (1989)

- From Meng Ta-Chung *et al.**Phys Rev. D40, p769, (1989)*

- kTR

- kPR

- kTR

- kPR

- Like Helicity

- Un-like Helicity

- Douglas Fields

- 6/2/2005

## From Meng Ta-Chung et al.Phys Rev. D40, p769, (1989)

- From Meng Ta-Chung *et al.**Phys Rev. D40, p769, (1989)*

- This paper makes the following assumptions:
- Uniform spherical density F(b,θP,θT)
- kPR~kTR~kR (no dependence on b, θP, θT.)
- Then,

- Evaluated numerically

- Douglas Fields

- 6/2/2005

## How Large an Effect Can We Expect?

- Douglas Fields

- 6/2/2005

## Pause For Feedback

- Need theoretical guidance!
- Would be nice to have experimental handle on impact parameter:
- Multiplicity
- Forward or central
- Underlying event...
- but, not explicitly necessary.

- Douglas Fields

- 6/2/2005

## How do we measure kt?

- Intra-jet pairs angular width :	N   jT
- Inter-jet pairs angular width : A  jT  kT

- 0 - h  azimuthal correlation functions

- Trigger 0

- Douglas Fields

- 6/2/2005

## PHENIXDetector Overview

- East Arm
- tracking:
- DC, PC1, TEC, PC3
- electron & hadron ID:
- RICH,TEC/TRD,
- TOF, EMCal
- photons:
- EMCal

- West Arm
- tracking:
- DC,PC1, PC2, PC3
- electron ID:
- RICH,
- EMCal
- photons:
- EMCal

- Douglas Fields

- 6/2/2005

## π0 Identification

- PHENIX has central arm EMCal with electron rejection in RICH.
- Used shower profile cut.
- Good S/B at higher pt (>2GeV).

- Douglas Fields

- 6/2/2005

## Charged Particles

- Tracks in the Drift Chamber
- Hits in the Pad Chambers
- RICH veto for low momentum
- Shower shape cut at high momentum

- Douglas Fields

- 6/2/2005

## Correlation Functions

- dNreal  Δφ distribution from particles in the same event
- dNmixed  Δφ distribution from particles in different  events with similar vertex position
- Norm =
- Fit to two gaussians plus a constant term

-  3.0<pT<4.0

- Fit = const + Gauss(0)+Gauss()

-  1.5<pT<2.0

- Intra-jet pairs angular width :	N   jT
- Inter-jet pairs angular width : A  jT  kT

- Douglas Fields

- 6/2/2005

## Jet Kinematics

- Douglas Fields

- 6/2/2005

## How accurately can we measure <kt>?

-        is extracted from           and fragmentation functions which are extracted from the inclusive distributions.

- Douglas Fields

- 6/2/2005

## How accurately can we measure Δ<kt>?

- How accurately can we measure Δ<kt>?

- ZT uncertainties should cancel in the difference
- Bunch Shuffling in Run3 (PHENIX)
- δ Δ<kt> ~ 80MeV

- Douglas Fields

- 6/2/2005

## For Run5

- ~10-20 times more statistics than Run3
- Statistical errors smaller by factor of 3-5
- Polarization in Run5 ~55%
- Effect larger by factor of ~5 (PY*PB) than Run3

- Douglas Fields

- 6/2/2005

## Summary

- We can make a measurement of the double-longitudinal spin dependence of jet <kT>.
- This may be sensitive to orbital angular momentum.
- These effects (if really there) may also influence the double-longitudinal cross-section asymmetry.
- Need theoretical guidance...

- Douglas Fields

- 6/2/2005