# Presentation: 264314

## The Longitudinal Spin Program at PHENIX

- Joe Seele for the PHENIX Collaboration
- (University of Colorado at Boulder)
- RHIC User’s Meeting - May 27, 2008

**Notes:**
Thanks to group

## Outline

- Introduction to Spin Puzzle and p+p
- Measurements at PHENIX
- ALLs at 200 GeV and 62.4 GeV
- What have we learned from PHENIX data?
- PHENIX at 500 GeV ... time permitting

- J. Seele - RHIC User's Meeting - 5/27/2008

**Notes:**
Given difficult task of relating a variety of measurements to you in a short 25 minutes

## The Proton Spin Puzzle

- Fairly well measured
- only ~30% of spin

- The proton is viewed as being a “bag” of
- bound quarks and gluons interacting via QCD

- Spins + orbital angular momentum need
- to give the observed spin 1/2 of proton

- J. Seele - RHIC User's Meeting - 5/27/2008

**Notes:**
Proton is a bag of bound quarks and gluons under strictures of QCD
Proton is spin 1/2 object so pieces must come together -> written as “sum rule”
Delta-q is measured, delta-G is not 

## ΔG in Polarized p+p Collisions

- J. Seele - RHIC User's Meeting - 5/27/2008

**Notes:**
P+p collision in factorized pQCD where you have pdfs for initial state, hard partonic cs for scattering, and FFs for final state. 
Write ALL as convolution of polarized pieces, hard partonic helcity asymmetry
ALL has roughly three pieces

## PHENIX

- Central Arms:
-  γ/π0/η detection
- Electromagnetic Calorimeter        (-0.35 < η < 0.35)
- PC3 - Charge Veto
- Charged Particle Detection/ID
- DC
- RICH  (pion ID pT > 4.7 GeV/C)
- Global Detectors:
- Relative Luminosity
- Beam-Beam Counter (BBC)          (+- 3.1 < η < 4.0)
- Zero-Degree Calorimeter (ZDC) (+- 6.9 < η < infinity)
- Local Polarimetry - ZDC

- A rare probes experiment

- J. Seele - RHIC User's Meeting - 5/27/2008

**Notes:**
PHENIX, the beheaded turkey.
Draw attention to beam view and side view
Make distinction between eta and pseudorapidity
Say the arrows are the photons from a eta/pi0 decay to draw attention to the EMCal (most important thing for this measurement) - also point out PC3 used for charge veto
RICH and DC used for charged track reconstruction
Draw attention to BBCs and ZDCs as they are useful for the analysis

## Measuring Helicity Asymmetries

- What to measure :
- N’s - Final state (π,η,γ,”jet”, J/Ψ)
- P’s - Polarization at IR
- R - Relative Luminosity

- PHENIX Central Arms+
- PHENIX Muon Arms

- PHENIX ZDCs+HJet+CNI

- PHENIX ZDCs+BBCs

- <PT/P>=10±2(%)
- <PL/P> =99.48±0.12±0.02(%)

- <PT/P>=14±2(%)
- <PL/P>=98.94±0.21±0.04(%)

| Year | [GeV] | R | ALL |
| --- | --- | --- | --- |
| 2005  | 200 | 1.0e-4 | 2.3e-4 |
| 2006  | 200 | 3.9e-4 | 5.4e-4 |
| 2006  | 62.4 | 1.3e-3 | 2.8e-3 |

- Relative Luminosity

- Local Polarimetry

- run5
- values

- J. Seele - RHIC User's Meeting - 5/27/2008

**Notes:**
Translate asymmetry of helicity dependent cross section into something we measure
Many final states at PHENIX - EM measurements easier at PHENIX
Local pol measured using forward neutron asym (hopefully Han will talk about it)
Rellumi measured using BBCs and uncertainty (primarily from helicity dependent BBC cs) characterized using ZDCs and BBCs

## Luminosity and Polarization

| Year | [GeV] | Long. Luminosity [pb-1] (recorded) | Long. Polarization [%] |
| --- | --- | --- | --- |
| 2003  | 200 | 0.35 | 27 |
| 2004  | 200 | 0.12 | 40 |
| 2005  | 200 | 3.4 | 49 |
| 2006  | 200 | 7.5 | 57 |
| 2006  | 62.4 | 0.08 | 48 |

- J. Seele - RHIC User's Meeting - 5/27/2008

**Notes:**
RHIC - our favorite polarized proton-proton collider
Here’s what PHENIX has recorded for longitudinal p+p collisions

## π0 ALL at 200 GeV

- Large branching ratio to diphoton
- Produced in large quantities
- Strong correlation to gluons in initial state -> See subprocess fractions
- run5/run6 results included in recent DSSV fit

- PRD 76,051106
- PRL 91,241803

- J. Seele - RHIC User's Meeting - 5/27/2008

**Notes:**
PHENIX measures cs to convince us pQCD works (200 to distinguish it from 62.4 data)
98% of pi0s go to 2gamma
Lots of them
Subprocess fractions show strong connection to gluon in initial state
Here’s ALL so far (go through graph carefully)

## π0 ALL at 62.4 GeV

- π0 ALL at 62.4 GeV

- 200 GeV

- 62.4 GeV

- Same effects as 200 GeV π0
- Needs NLL for agreement
- Probes a different range in xb

- J. Seele - RHIC User's Meeting - 5/27/2008

**Notes:**
And here’s our 62.4 data! 
Cross section needs NLL for good description (too low energy)
Graphics shows rough x_bj range for measurements.  200 gets more glue.. 62.4 gets more quarks
And the 62.4 ALL vs. NLO theory (NLL theory will be in paper.. Soon!)
And compared to 200 GeV data... vs xT now..  (put xt formula in there)

## η ALL at 200 GeV

- η ALL at 200 GeV

- Produced ~1/2 as much as π0
- 40% diphoton branching ratio
- Different wavefunction from π0
- Stronger correlation to gluon/strange
- Will be important at 500 GeV -> photon merging at higher pT

- J. Seele - RHIC User's Meeting - 5/27/2008

**Notes:**
Eta detected same ways as pi0... 40% BR though .. Here’s the cross section (published run3 result)
Different wf should give sentivities to different partons -> stronger strange/glue (can see glue in subprocess frac)
Important at 500 GeV -> no merging until much higher pT
And the ALL!

## π+/π- ALL at 200 GeV

- Produced in large quantities
- No trigger at PHENIX
- Cross section being calculated for these pTs

- FFs should pick out different flavor mixtures -> good for consistency

- J. Seele - RHIC User's Meeting - 5/27/2008

**Notes:**
No cross section for these pts for charged pions yet (working on it!)
No “real” trigger at PHENIX (would be greate if we had one)
At this high pT so RICH can identify them
Again different FFs will give different sensitivities

## Cone ALL at 200 GeV

- Similar to a jet measurement -> uses cone algorithm
- Produced copiously, but no jet trigger at PHENIX
- Theory is “corrected” to be more representative the cone sampling.
- Not statistically separate from π and η measurements

- J. Seele - RHIC User's Meeting - 5/27/2008

**Notes:**
PHENIX’s version of jet measurement. Cone algorithm used to give a cluster of particles) pT_cone is their vector summed pT
Hard to combine with other measurements since it uses the high pT photon trigger
And ALL

## Direct Photons

- Sensitive to sign and magnitude of delta-G
- No FF convolution
- A rare probe - lacks statistical power

- Run3 PRL 98,012002

- Run5

- J. Seele - RHIC User's Meeting - 5/27/2008

**Notes:**
This is PHENIX’s “golden “ channel.
Any asymmetry is roughly proportional to Delta-G... no FF convolution
Rare probe though... needs much more lumi
No result, but if we get a run9 in order with what we asked for here is expected precision

## Constraint from Measurements

- A series of constrained fits were done by Vogelsang and Stratmann in the GRSV model.
- They constrained the integral of ΔG at the input scale.

- Time to incorporate all measurements into the
- global fits

- J. Seele - RHIC User's Meeting - 5/27/2008

**Notes:**
What does all this data tell us though? Not all the data has been incorporated into a global fit yet.
Explain the toy model here.
Shown here are the pi0, eta, and cone and the sum of the pi0 and eta (cone too dependent so it isn’t combined)
If we then include the charged pions (notice the scale) we find a bit of a disagreement in the pi+’s case (nothing wild but still something)

## Advertisement for other Long. 

- J/Ψ_x0003_ production connected to heavy flavor production

- Spin correlated transverse momentum (OAM) may contribute to jet kT (Meng Ta-chung et al., Phys. Rev. D40, 1989)
- Calculate helicity asymmetry of kT in di-hadron correlations

- J. Seele - RHIC User's Meeting - 5/27/2008

**Notes:**
Didn’t have time to really go through these but PHENIX has J/Psi A_LL measurement as well. Needs much more data
And a kT helicity asymmetry which may be related to orbital angular momentum in the nucleon.

## xb Coverage for Different Energies

- Coverage for sqrt(s) = 500 GeV

- Coverage for sqrt(s) = 200 GeV

- Coverage for sqrt(s) = 62.4 GeV

- J. Seele - RHIC User's Meeting - 5/27/2008

**Notes:**
A slide about “into the future”!!!
More people shows our expectations for results in the future but I don’t really have time for that
Here is what 200 GeV has coveregd in x-space
Here’s what 62.4 roughly covered
And here’s roughly what 500 GeV will cover
Now I asked from a standpoint of Delta-G “What could more 62 GeV data due for us?” ... recent DSSV peaks in roughly the same range as where the 62.4 data has good coverage. Perhaps lower energy running isn’t a bad thing? And complementarily, Drell-Yan may be possible at 62.4 GeV as well (constrain sea quarks...)

## 500 GeV Program and W Physics

- W’s decay then measure e,μ

- J. Seele - RHIC User's Meeting - 5/27/2008

## Forward Muons at PHENIX

- J. Seele - RHIC User's Meeting - 5/27/2008

## Conclusions

- PHENIX ALL measurements are pushing forward along many fronts
- Measurements are luminosity hungry!
- Need to put the current measurements into a global fit -> Daniel’s Talk Next
- Stay tuned for PHENIX Transverse Spin Results -> Han’s Talk

- J. Seele - RHIC User's Meeting - 5/27/2008

**Notes:**
PHENIX has measured A_LLs in many species but they need more luminosity
Need to see their impact -> See Daniel’s talk next
Only “half” of program -> See Han’s talk this afternoon