recent phenix results on and production in polarized pp collisions at rhic at s=200 gev frank...
TRANSCRIPT
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
Frank Ellinghaus, University of Colorado
: 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
Frank Ellinghaus, University of Colorado
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
Frank Ellinghaus, University of Colorado
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
Frank Ellinghaus, University of Colorado
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
Frank Ellinghaus, University of Colorado
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
Frank Ellinghaus, University of Colorado
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
Frank Ellinghaus, University of Colorado
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 %
Frank Ellinghaus, University of Colorado
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)
Frank Ellinghaus, University of Colorado
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
Frank Ellinghaus, University of Colorado
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
Frank Ellinghaus, University of Colorado
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
Frank Ellinghaus, University of Colorado
/ 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.
Frank Ellinghaus, University of Colorado
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!)
Frank Ellinghaus, University of Colorado
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
Frank Ellinghaus, University of Colorado
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
Frank Ellinghaus, University of Colorado
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
Frank Ellinghaus, University of Colorado
+, –, 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
Frank Ellinghaus, University of Colorado
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
Frank Ellinghaus, University of Colorado
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: