Upload
estella-wiggins
View
218
Download
0
Embed Size (px)
DESCRIPTION
Frank Simon: Inclusive 0 and A LL in p+p at 200 GeV 3 10/03/2006 The STAR Experiment Magnet 0.5 T Solenoid Triggering & Luminosity Monitor Beam-Beam Counters 3.4 < | | < 5.0 Central Tracking Large-volume TPC | | < 1.5 Calorimetry Barrel EMC (Pb/Scintilator) | | < 1.0 Shower-Maximum Detector …and many other systems not used in the 0 analysis Used Triggers: Minimum Bias (MB): BBC Coincidence, highly prescaled High Tower 1 & 2 (HT1 / HT2): MB + one BEMC cell ( x = 0.05 x 0.05) above threshold (lower threshold trigger prescaled) 2005 run
Citation preview
Longitudinal Spin Asymmetry and Cross Section of Inclusive 0 Production in Polarized p+p
Collisions at 200 GeV
Outline
Introduction Experimental Overview Inclusive Cross Section Neutral Pions in Jets Longitudinal Spin Asymmetry
Frank Simon, MIT, for the STAR Collaboration
Frank Simon: Inclusive 0 and ALL in p+p at 200 GeV 210/03/2006
Introduction Polarized p+p collisions provide sensitivity to gluon polarization in the nucleon
With current statistics the focus is on inclusive measurements (Jets, Pions) large contribution of gg and qg processes to overall cross section => good tool to study gluon polarization, but no constraint of event kinematics
Neutral pions probe the same processes as jets, but with different experimental systematics and effects from fragmentation
relative contributions of subprocesses to inclusive 0 production
W. Vogelsang
Unpolarized measurements of inclusive 0 are of considerable interest: study fragmentation functions via NLO pQCD vs measured cross section comparisons: currently large uncertainty in gluon FF
study fragmentation directly: electromagnetic trigger selects jets with leading 0
gg qg qq
Frank Simon: Inclusive 0 and ALL in p+p at 200 GeV 310/03/2006
The STAR ExperimentMagnet 0.5 T SolenoidTriggering & Luminosity Monitor
Beam-Beam Counters 3.4 < || < 5.0
Central Tracking Large-volume TPC
|| < 1.5 Calorimetry Barrel EMC (Pb/Scintilator)
|| < 1.0 Shower-Maximum Detector
…and many other systems not used in the 0 analysis
Used Triggers: Minimum Bias (MB): BBC Coincidence, highly prescaled High Tower 1 & 2 (HT1 / HT2): MB + one BEMC cell (x = 0.05 x 0.05) above threshold (lower threshold trigger prescaled)
2005 run
Frank Simon: Inclusive 0 and ALL in p+p at 200 GeV 410/03/2006
Neutral Pion Reconstruction 2005 p+p dataset (after rigorous quality cuts): ~ 1.7 pb-1
Trigger & shower maximum detector in 2005 operational only for 0 < < 1, full acceptance -1 < < 1 available for 2006 data
tower size ( x )0.05 x 0.05
0 invariant mass:
€
minv2 = 2E1E2(1− cosθ)
SMD becomes crucial for 0 reconstruction for pt ~ 5 GeV/c (photon separation equal to tower size)
veto calorimeter hits that have a charged track leading to them
0 candidates accepted for 0.1 < y < 0.9 0 has to be able to fire the trigger (but does not have to be the triggering particle) rejection of beam background found with pattern recognition code
Frank Simon: Inclusive 0 and ALL in p+p at 200 GeV 510/03/2006
Neutral Pion Reconstruction
invariant mass spectrum near 0 mass described by: MC 0 line shape low invariant mass background (caused by cluster splitting in the SMD)
combinatoric background & residual fit
Correction factor for cross section determination obtained from PYTHIA & HERWIG simulations
different cuts used for MB and HT triggers
HT1 HT2
Frank Simon: Inclusive 0 and ALL in p+p at 200 GeV 610/03/2006
Inclusive Cross Section
Lsampled: 0.4 pb-1 (HT triggers), 44 b-1 (MB)
Point-to-point systematics from yield extraction
Total systematics dominated by 5% uncertainty in BEMC energy scale, significant contribution from correction factor uncertainty
Compared to NLO pQCD (CTEQ6M pdfs) using KKP and Kretzer fragmentation func. better agreement with KKP large scale uncertainties in pQCD calculations, indicated by choosing different scales for KKP calculations
€
E d3σdp3
= 12πpTΔpTΔy
c N π
Lsampled
Invariant cross section:
consistent with previous results from PHENIX
Frank Simon: Inclusive 0 and ALL in p+p at 200 GeV 710/03/2006
Neutral Pions in Jets STAR is capable of full Jet reconstruction reconstructed are associated with Jets (HT triggered) if the 0 lies within the Jet cone (0.4 in , )
0 direction is strongly correlated with the Jet axis: leading 0 typically within 5° of the Jet axis
<z> defined as the mean ratio of 0 pt to Jet pt
Affected by trigger, depends on pt evolution of cross section and z dependence of the fragmentation function
RMS in , ~ 0.055
Frank Simon: Inclusive 0 and ALL in p+p at 200 GeV 810/03/2006
Double Longitudinal Asymmetry: Overview
Ingredients: Polarization: measured by RHIC polarimeters Relative Luminosity R measured with the STAR BBC & scaler system (relative luminosities for each bunch crossing available)
Spin dependent yields N++, N+- : determined from integration of invariant mass in the signal region after background subtraction
Spin direction in the interaction region verified by the STAR BBCs
€
ALL =σ ++ −σ +−σ ++ +σ +−
= 1P1P2
× N++ − RN+−N++ + RN+−
€
P12P22 ⋅ Ldt∫, FOM ~
€
R = L++L+−
Frank Simon: Inclusive 0 and ALL in p+p at 200 GeV 910/03/2006
Double Longitudinal Asymmetry ALL
constant fit (assumes no pt dependence): ALL = -0.017 +- 0.021
compared to NLO calculations(ignoring systematic errors): GRSV Std: 3 GRSV Max: 10 GRSV Min: 3 GRSV Zero: 2 GRSV max scenario disfavored
overall scale uncertainty from beam polarization measurement not included
Frank Simon: Inclusive 0 and ALL in p+p at 200 GeV 1010/03/2006
ALL Systematic Studies & Errors Parity-Violating Single Spin Asymmetries
Come in through the weak interaction, and are limited to less than 10-4, so they should be consistent with zero at the present level of statistics
Good tool to investigate possible spin dependent background effects or issues with relative luminosities
For 0 all observed single spin asymmetries are within 1 of 0, no systematic assigned
Random Pattern Analysis Asymmetries calculated with randomized bunch patterns no indication of non-statistical effects found
Systematic Errors assigned for remaining Background (from beam background, not removed invariant mass background) pt dependent from 5 x 10-3 to 11 x 10-3
yield extraction (normalization of background model) from 3 x 10-3 to 7 x 10-3
non-longitudinal spin components in beams 3 x 10-3
relative luminosities 2 x 10-3
Frank Simon: Inclusive 0 and ALL in p+p at 200 GeV 1110/03/2006
Comparisons to Published Results
Comparison with published results: STAR 2003/2004 Jets, pt divided by 2 PHENIX 2003/2004 0
Frank Simon: Inclusive 0 and ALL in p+p at 200 GeV 1210/03/2006
Projections for 2006 Data
Significant increase in sampled luminosity Polarization typically ~60% acceptance increase by a factor of 2
significant increase in figure of merit!
Frank Simon: Inclusive 0 and ALL in p+p at 200 GeV 1310/03/2006
Summary First spin result for inclusive 0 production at mid-rapidity from STAR
Inclusive cross section consistent with NLO pQCD calculations KKP fragmentation functions favored over Kretzer set scale uncertainty of pQCD of comparable size as preliminary systematics
Energetic 0 carry a significant fraction of the total transverse momentum of their associated jet
Double longitudinal spin asymmetry disfavors large positive gluon polarization consistent with previous observations with jets and 0 result limited by statistics
Significant increase in figure of merit with the already recorded 2006 data set
Backup
Frank Simon: Inclusive 0 and ALL in p+p at 200 GeV 1510/03/2006
Backup: Systematics: Cross Section Point-to-Point (yield extraction, background subtraction)
Energy scale (5% uncertainty on BSMD gain calibration)
Correction factor (variation of cuts, uncertainty in SMD gain (to a large extend built into MC, additional uncertainties included in systematics), statistical limitation of MC dataset)
Acceptance Stability (changes in electronics status, modeling in MC)
Frank Simon: Inclusive 0 and ALL in p+p at 200 GeV 1610/03/2006
Backup: Systematic Errors on ALL
Bin
remaining Background
Yield Extration
relative Luminosity
non-long. Effects
Total Systematic
stat. Error
1 0.0052 0.0062 0.0022 0.003 0.0089 0.0443
2 0.0052 0.0032 0.0022 0.003 0.0072 0.0291
3 0.0082 0.0047 0.0022 0.003 0.0102 0.0439
4 0.0112 0.0069 0.0022 0.003 0.0137 0.0836
Frank Simon: Inclusive 0 and ALL in p+p at 200 GeV 1710/03/2006
Backup: BEMC 0 Acceptance Photon Candidates (Calorimeter Hits) above 1 GeV requiring information from both SMD planes: Data vs MC
QuickTime™ and aTIFF (LZW) decompressor
are needed to see this picture.QuickTime™ and a
TIFF (LZW) decompressorare needed to see this picture.
Data (all triggers) PYTHIA (no trigger selection)
Data histogram integrates over a running time of 12 days, MC takes the detector status at one specific time within that period
Overall good agreement, detector acceptance reasonably modeled in MC
Frank Simon: Inclusive 0 and ALL in p+p at 200 GeV 1810/03/2006
Backup: BEMC 0 Data/MC Comparison
HT1 triggers4.5 GeV/c < 0 pt
< 4.6 GeV/cblack: datared: Pythia
HT2 triggers7.0 GeV/c < 0 pt
< 7.2 GeV/cblack: datared: Pythia
Preliminary! Limited MC Statistics! 0 properties well reproduced in MC for different pt and triggers