# Presentation: 855148

## Recent PHENIX results on   and  production in polarized pp collisions at RHIC at s=200 GeV

- Frank Ellinghaus
- University of Colorado
- (for the PHENIX Collaboration)
- DIS 2008
- April 7-11, London, UK

## Spin Sum Rule: The latest...

- DSSV, arXiv: 0804.0422
- First “global” (DIS+SIDIS+pp) analysis!

- HERMES, arXiv: 0802.2499

- Gluons carry half the momentum.
- Do they carry half the spin?

- G small in measured range.
- Gluon orbital momentum?
- Contribution at small or large x?

- PHENIX 0 (large gg contribution) does not constrain negative gluon scenarios
- very well -> charged pions, direct photons

##  : enhanced sensitivity to G and s?

-  DIS -> s small and negative
-  SIDIS HERMES (PRL 92:012005,2004**)**    -> s zero or small and positive for x>0.03
-  Latest HERMES result (arXiv:0803.2993) ** **-> s zero or small and positive for x>0.03

-  DSSV uses latest FFs from DSS, both fits include the HERMES SIDIS Data
-   -> node at about 0.02
-  DNS also included (HERMES) SIDIS, but has less flexible func. form and
-   uses (quite different) FFs from KKP and Kretzer

**Size of ********s important for total quark spin contribution ******

## PHENIX Detector

## The PHENIX Detector for Spin Physics

- Central Detector:
-  detection
- Electromagnetic Calorimeter:
-      PbSc + PbGl,  < |0.35|,  = 2 x 90
-  
- Drift Chamber
- Ring Imaging Cherenkov Detector
- Muon Arms:
- J
- Muon ID/Muon Tracker ()
-  
- Electromagnetic Calorimeter (MPC)
- Global Detectors:
- Relative Luminosity
- Beam-Beam Counter (BBC)
- Zero-Degree Calorimeter (ZDC)
- Local Polarimetry - ZDC

## PHENIX longitudinally polarized pp Runs

| Year | s [GeV] | Recorded L | Pol [%] | FOM (P4L) |
| --- | --- | --- | --- | --- |
| 2003 (Run-3)  | 200 | .35 pb-1 | 27 | 1.5 nb-1 |
| 2004 (Run-4) | 200 | .12 pb-1 | 40 | 3.3 nb-1 |
| 2005 (Run-5) | 200 | 3.4 pb-1 | 49 | 200 nb-1 |
| 2006 (Run-6) | 200 | 7.5 pb-1 | 55 | 690 nb-1  |
| 2006 (Run-6) | 62.4 | .10 pb-1  | 48 | 5.3 nb-1  |

##  reconstruction via  decay

- Energy asymmetry cut: E1-E2 / E1+E2 < 0.7
- pT > 2 GeV
- |zvertex| < 30 cm
- Fit:Gauss+Pol3

**2<p****T****<3 GeV**

## Invariant cross section

- L = integrated Luminosity, based on Vernier scan using the BBC
- BR= Branching ratio:   2 photons = 0.3943 ± 0.0026
*f**Acc* = acceptance function from MC (includes smearing)
*eff**Trig* (Minimum Bias data) = Trigger efficiency of MB trigger
*eff**Trig* (high pT triggered data) = (Trigger effi. MB) x (Trigger effi. high pT
-          trigger)
*eff**rec* = Correct for  loss due to photon conversion (~6% in PBSC,
-            ~8% in PbGl) x loss due to cut on shower shape (~4%)
- N = number of reconstructed 

## facc from Monte Carlo

- Acceptance and smearing correction from MC
- (also accounts for dead regions in EmCal, minimum cuts on photon energies,...)

- Up to 10% acceptance in PbSc for  at high pT

- data

- MC

***p******T***

## Photon/MB Trigger Efficiency

- Photon trigger efficiency roughly stable from 4 GeV on (high pT photon trigger threshold is set to 1.4 GeV)

- Minimum Bias (MB) trigger efficiency about 80 %

##  cross section

-  Run 6  cross section analysis in progress, goes up to 20 GeV!
-  No  fragmentation functions (FFs) in the literature!
-  Enables extraction of FFs from e+e- data and this (large range in pT) pp
-   result (  gluon FFs).
-  Extraction uses method/code from DSS (de Florian, Sassot, Stratmann,
-    PRD75, 2007) 

##  FFs - Data

| Experiment | System | Energy (GeV) | # Points |
| --- | --- | --- | --- |
| ALEPH ’92 | e+e- | 91.2  | 8 |
| ALEPH ’00 | e+e- | 91.2 | 18 |
| ALEPH ‘02 | e+e- | 91.2 | 5 |
| L3 ‘92 | e+e- | 91.2 | 3 |
| L3 ’94 | e+e- | 91.2 | 8 |
| OPAL | e+e- | 91.2 | 9 |
| ARGUS | e+e- | 10 | 6 |
| CELLO | e+e- | 35 | 4 |
| HRS | e+e- | 29 | 13 |
| JADE ’85 | e+e- | 34.4 | 1 |
| JADE ‘’90 | e+e- | 34.9 | 3 |
| MARK II | e+e- | 29 | 7 |
| PHENIX 2 | p+p | 200 | 12 |
| PHENIX 3 | p+p | 200 | 6 |
| PHENIX ’05 prelim. | p+p | 200 | 19 |

##  FFs - Comparison

- Describes e+e- data very well over a large range in energies.

- Will include low-energy high-precision
- (prelim.) BABAR data and PHENIX RUN 6 cross
- section (25 data points out to 20 GeV) soon.
- Hope for HERMES SIDIS data......

- preliminary

## Cross section @ 200 GeV

- NLO pQCD calculation ( = pT) by M. Stratmann
- (uses this  FF, so more a self-consistency check)

-  subprocess fraction needed for
- extraction of G

##  / 0 

-  has (slightly) enhanced sensitivity
- to gg (when compared to 0) as
- expected

-  Enhanced gg contribution leads to
-   larger asymmetries than for 0
-  sizeable differences in the asymmetry
-   only for max/min scenarios
-  With G small in currently measured
-   region the difference between 
-   and  asymmetries is small compared
-   to the current stat. error.

## Access to s?

- Up to 10% contribution from strange quarks....
- (Caution: Potentially large uncertainty on s-quark FF due to absence of SIDIS data!)

## Inclusive  Asymmetries in pp  X

- Relative luminosity R using beam-beam counters

## Access to G: Add the pieces...

- Access to polarized gluon distribution function via double helicity asymmetry in inclusive polarized pp scattering:

***from DIS***

***subprocess asym+frac (FFs)***

- Max and min scenarios excluded by 

## Cross section - pQCD applicability

- RUN5  200 GeV -- 0

-  Charged pion cross section so far only
-    extracted from MB triggered data set;
-    PID with TOF
-    ->low pT only
-  Also charge separated cross sections
-   extracted by PHENIX
-  “high” pT triggered (EmCal+RICH) data set;
-    charged pions begin firing the RICH at
-    pT~4.7 GeV,
-    cross section extraction in progress ...

**PRD76:051106,2007**

-  0: pQCD seems at work, with still
-    sizeable scale uncertainties for
-    pT<5 GeV

## +, –, 0 and the sign of G

- Especially in the region where qg scattering is dominant (pT > 5 GeV),
- the increasing contribution of d quarks (d<0)                           leads to:

- “Model independent” conclusion
- possible once enough data is
- available.

## Comparison to model calculations

-  Charge separated FFs (DSS, PRD75, 2007)  available using SIDIS data (HERMES
-   preliminary); Calculations by W. Vogelsang

-  New Run 6 (2006) result in agreement with Run 5 (2005)

-  More data needed-> Projection for Run 9 (2009) w/o maybe additional higher pT point

## Direct Photons  at s=200 GeV

- Direct Photons  at s=200 GeV

- Run-5

- -> small unc. from FFs
- -> better access to sign of G (q times G)

- Theoretically clean “Golden Channel” is luminosity hungry...

- Dominated by qg Compton:

## Summary

- Charged pion and  data are getting ready to be included in (the next round of) global QCD fits, thanks to new/improved FFs....some more data needed too.