exploring the spin structure of the proton with two-body partonic scattering at rhic
DESCRIPTION
STAR. Exploring the Spin Structure of the Proton with Two-Body Partonic Scattering at RHIC. For the. J. Sowinski. Collaboration. Few Body 2006 8/24/06. Where does the proton’s spin come from?. u. u. d. p is made of 2 u and 1 d quark. S = ½ = S S q. - PowerPoint PPT PresentationTRANSCRIPT
Exploring the Spin Structure of the Proton with Two-Body Partonic Scattering at
RHIC
J. Sowinski
STARSTAR
For the
Collaboration
Few Body 2006 8/24/06
2
Where does the proton’s spin come from?
u u
d
p
Sz = ½ = ½ + G + Lzq + Lz
g
p is made of 2 u and 1d quark
S = ½ = Sq
Explains magnetic moment of baryon octet
BUT partons have an x distribution and there are sea quarks and gluons
Check via electron scattering and find quarks carry only ~1/3 of the proton’s spin!
3
CTEQ5M
SMC Analysis, PRD 58, 112002 (1998)
First Moments at Q02=1 GeV2:
(MS) = 0.19 ± 0.05 ± 0.04
(AB) = 0.38
G(AB) = 0.99
(just one example of many)
+ 0.03 + 0.03 + 0.03- 0.03 - 0.02 - 0.05
+ 1.17 + 0.42 + 1.43- 0.31 - 0.22 - 0.45
—
Gluons carry ~1/2 the momentum (mass)!
Maybe we shouldn’t be surprised thatquarks carry only ~1/3 of proton’s spin
G is poorly constrained, even solutions with zero crossing allowed
Parton Distribution Functions
4
A ~ P P a LL g part LL^
pQCD
MeasureKnow from DIS
“G”
G via partonic scattering from a gluon
• Dominant reaction mechanism
• Experimentally clean reaction mechanism
• Large a• But jet and 0 rates are
sufficient to give significant G const. in first RHIC pol. p data
Prefer
LL^
-jet coinc. rare
STARSTAR
Heavy flavor rare
Jets and 0s
ALL = ++ - +-
++ + +-
5
The Relativistic Heavy Ion Collider
PHENIXSTAR
Brahmspp2pp
PHOBOS
~4 km circ. Collider
Heavy ions• Au-Au• Lighter ions• Asymmetric d-Au
4+ detectors• STAR• PHENIX• PHOBOS• Brahms• pp2pp (p-p only)
The first polarized p-p collider!
500GeV24GeV s
Retired
6
Dramatic Improvements in Polarized Beam Dramatic Improvements in Polarized Beam Performance Performance 2003 2006 >
2 orders of magnitude improvement in FOM = P 4L relevant to 2-spin asymmetries!
Factor ~ 5--6 remains to reach “enhanced design” goals
BRAHMS
PHENIX
AGS
BOOSTER
Spin Rotators(longitudinal polarization)
Solenoid Partial Siberian Snake
Siberian Snakes
200 MeV PolarimeterAGS Internal Polarimeter
Rf Dipole
RHIC pC PolarimetersAbsolute Polarimeter (H jet)
AGS pC Polarimeters
Strong Helical AGS Snake
Helical Partial Siberian Snake
Spin Rotators(longitudinal polarization)
Spin flipper
Siberian Snakes
STAR
PHOBOS
Pol. H- SourceLINAC
Absolute Pbeam calibration to ~ 5% goal in progress
STAR s = 200 GeV pp Sampled
Luminosities
7
The STAR Detector at RHIC
At the heart of STAR is the world’s largest Time Projection Chamber
STARSTAR
STAR Detector• Large solid angle• Not hermetic• Tracking in 5kG field• EM Calorimetry• “Slow” DAQ (100Hz)• Sophisiticated triggers
8
200320042005
Detector
=0
Forward Pion Detector
Endcap EM Calorimeter
Beam-Beam Counters
Time Projection Chamber
-2<η< 2
Barrel EM Calorimeter
-1<η< 1
1<η< 2-4.1<η< -3.3
2<|η|< 5
Solenoidal MagneticField 5kG
=2= -1
Tracking
Lum. Monitor Local Polarim.
Triggering
Triggering
= - ln(tan(/2)
STARSTAR
9
STARSTAR
What is a jet?
Midpoint Cone Algorithm• Add 4 momenta of tracks and
towers in cone around seed• R = 0.4 (, ) year < 2006• Split and merge for stable groups
part
onpa
rtic
lede
tect
or
etcp
e
,,
,
GE
AN
Tpy
thia
q,g
Use Monte Carlo to correct data for comparison to theory
(Resolution, trigger, efficiency, fragmentation …)
10
2003 + 2004 ResultsJet Shape
• (r) = Fraction of jet pT in sub-cone r
• Study of trigger bias• Study of data/MC
agreement• High Tower trigger • Bias decreases with pT
Cross Section Correction Factors
• MinBias correction ~ 1• Corrections (1/c(pT) can be
large for High Tower data
STARSTAR
11
• Sampled luminosity: ~0.16 pb-1
• Good agreement between minbias and high tower data
• Good agreement with NLO over 7 orders of magnitude – slope
• Good agreement with NLO magnitude within systematic uncertainty
• Error bars: Statistical uncertainty from data
• Systematic error band
Leading systematic uncertainty
10% E-scale uncertainty 50% uncertainty on yield
• Out of cone hadronizaton and underlying event ~25% corr. not shown
First inclusive jet cross section result at RHIC
2004 p+p run
STARSTARhep-ex0608030
12
jet cone=0.4 0.2<jet<0.8
2004 Prelim.2003 Prelim.
STARSTAR
First ALL Measurement for Inclusive Jet Production
Submitted for publication
• 2003 (pol.~0.3) + 2004 (pol. ~ 0.4) total 0.4 pb-1
• Total systematic uncertainty ~0.01▪ Backgrounds▪ Relative Luminosity▪ Residual transverse
asymmetries▪ Beam Polarization▪ Trigger Bias
STARSTAR
Inclusive Jets: LO (W. Vogelsang)
fra
cti
on
pT/GeV
hep-ex0608030
13
Current Constraints on G
Fit to STAR ALLjet
vs. assumed G at input scale: W. Vogelsang
Fit to PHENIX ALL
vs. assumed G at input scale: W. Vogelsang
Photon-gluon fusion results:
COMPASS, HERMES, SMC photon-gluon fusion studies ~ comparable G constraints to 2003+4 STAR jets and 2005 PHENIX 0 ALL
14
Projections from Collected Data
L = 6 pb-1 P=0.6
G=G
GRSV-std
G=-G G=0
2005 Data• Jet patch triggers• Enhanced EM
calorimeter coverage
2006 Data• Software triggers• Full EM
calorimeter coverage -1<<2 including trigger
• DiJets• Direct -jet
sample
STARSTAR
15
Next Step is to Explore g(x)
• Exploit 2 body kinematics • Detect and jet in coinc.
• Measure jet, E and • Extract x1, x2 and *
• Assume larger of x1 and x2 = xquark
• Assume lesser = xgluon
• Make cut that one x > 0.2
jet
Simulated data set
• Large data sets at 200 and 500 GeV• 500 GeV => low x• Overlap gives same x with different
pT to check scaling• Di-Jets
• Similar kinematics• Less selective for gluons• Lower sensitivity but larger cross
section than -jets
Large coincident solid angle is crucial
16
Conclusions• RHIC has made tremendous progress in
delivering polarized protons over past few years
• Initial inclusive jet ALL results are providing significant constraints on G
• Much better jet statistics are already in hand from 2005 and 2006 data
• Future studies with di-Jets and -jet coinc. are expected to probe the shape, g(x)
STARSTAR