Frank Ellinghaus University of Colorado (for the PHENIX Collaboration) DIS 2008

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

Frank Ellinghaus, University of Colorado

Spin Sum Rule: The latest…

DSSV, arXiv: 0804.0422First “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 scenariosvery 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

( 2 )uu dd ss


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<pT<3 GeV


Invariant cross section

yp

ypN

effefffBRLppd

dE

T

T

recTrigAccT

),(1111

2

13

3

L = integrated Luminosity, based on Vernier scan using the BBC

BR= Branching ratio: 2 photons = 0.3943 ± 0.0026

fAcc = acceptance function from MC (includes smearing)

effTrig (Minimum Bias data) = Trigger efficiency of MB trigger

effTrig (high pT triggered data) = (Trigger effi. MB) x (Trigger effi. high pT

trigger)

effrec = 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 CarloAcceptance 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

dataMC

pT


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

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

preli

mina

ry


Cross section @ 200 GeV

PHENIX Run-05 Preliminary

200 GeV

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

subprocess fraction needed forextraction of G


/ 0

has (slightly) enhanced sensitivityto 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?

gg

...su sd sg

...uu dd ud

ug ug dg dg

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

NRN

NRN

PPA

YBLL

1

L

LR

Relative luminosity R using beam-beam counters

2 < pT < 3 GeV/c

M(MeV)

3 < pT < 4 GeV/c 4 < pT < 5 GeV/c 5 < pT < 6 GeV/c

M(MeV)M(MeV) M(MeV)

r

ArAA

BGLL

BGLL

LL

1

BG

BG

NN

Nr


Access to G: Add the pieces…

2 2~LL gg qg qqA a a q G aG q

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

Measure from DISsubprocess asym+frac (FFs)

p p X

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

0

0 LL LL LLG A A A

0

d d dD D D

0

0 LL LL LLG A A A

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

“Model independent” conclusionpossible once enough data is available.

Fraction of pion production


Comparison to model calculations

0 ,LL LLG A A

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

0 LL LLG A A

• 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

Run-5

q

g q-> 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.

Documents

Frank Ellinghaus University of Colorado (for the PHENIX Collaboration) DIS 2008