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Measurement of the inclusive jet cross section in p+p collisions at E CM =200 GeV Mike Miller (MIT) For the STAR collaboration
Measurement of the inclusive jet cross section in p+p collisions at ECM=200 GeV
Mike Miller (MIT)For the STAR collaboration
04/23/2006Mike Miller 2
Why study inclusive jet production at RHIC?
RHIC is polarized!Jets provide direct access to gluon helicityLong-term: search for new physics in parity violating di-jet production*
Jet shapes and underlying eventCan extend previous UA1 resultsUnique kinematic niche (Ecm 200-500 GeV, 5<pT<50 GeV)
Can further constrain large-x PDFsBut…
Use tracking + EMCalLower sqrt(s) steeply falling cross sectionMust control E-scale systematic
€
x ≈ 2pTe−y
s → xmax ≈ 0.5
* Eur.Phys.J.C24:149-157,2002
04/23/2006Mike Miller 3
Why study inclusive jet production at RHIC?
RHIC is polarized!Jets provide direct access to gluon helicityLong-term: search for new physics in parity violating di-jet production*
Jet shapes and underlying eventCan extend previous UA1 resultsUnique kinematic niche (Ecm 200-500 GeV, 5<pT<50 GeV)
Can further constrain large-x PDFsBut…
Use tracking + EMCalLower sqrt(s) steeply falling cross sectionMust control E-scale systematic
€
x ≈ 2pTe−y
s → xmax ≈ 0.5
* Eur.Phys.J.C24:149-157,2002
04/23/2006Mike Miller 4
Particle level jets
parto
n
parti
cle
dete
ctor
etcpe
,,,π
γν ,,
gq,
midpoint-cone algorithm*•Search over “all” possible seeds for stable groupings
•Check midpoints between jet-jet pairs for stable groupings
•Split/merge jets based on Eoverlap
•Add track/tower 4-momenta
DataData SimulationSimulation
GEANT
“geant” jets
“pythia” je
ts
Correction philosophy•Use Pythia+GEANT to quantify detector response
•Estimate corrections to go from “detector” to the “particle” level
pyth
ia
*(hep-ex/0005012)
04/23/2006Mike Miller 5
AGSLINACBOOSTER
Polarized Source
Spin RotatorsPartial Snake
Siberian Snakes
200 MeV Polarimeter
AGS Polarimeter Rf Dipole
RHIC pC Polarimeters Absolute Polarimeter (H jet)
PHENIX
PHOBOS BRAHMS & PP2PP
STAR
Siberian Snakes
Helical Partial Snake
Strong Snake
Spin Flipper
2005 Complete!2005 Complete!
Last Week at RHIC peak average design L 2.5 1.2 6.0 P 67% 61% 70%
Luminosity in 1031cm-2s-1
The RHIC complex
04/23/2006Mike Miller 6
2004 p+p commissioning run
pT (track/tower) > 0.2 GeV|vertex-z|<60 cmpT(seed)>0.5 GeV, rcone=0.4, fmerge=0.50.2< ηjet <0.8Neutral energy fraction<0.9(and ET-trig>3.5 GeV/c for HT)
High Tower TriggerBBC coincidence + one tower above thresholdεTrig(η=0.0)=1: ET-tower= 2.5 GeVεTrig(η=0.8)=1: ET-tower= 3.3 GeV
TPC0<φ<2π1< η<1BEMC0<φ<2π0< η<1in situ MIP/e calibration
Sampled luminosity: ~0.16 pb-1
1.4 M High tower (HT) events0.8 M highly pre-scaled minimum bias (MB) events ~220k pT>5 GeV jets in HT sample before cutsCommissioned 1x1 jet patch trigger– main jet trigger in 2005+
04/23/2006Mike Miller 7
2004 EMCal calibration
Limited test-beam calibrationLimited test-beam calibrationin situ calibration of 2400 channels
p+p statistics insufficientp+p statistics insufficient use Au+Au events from earlier in 2004 run (same HV)
Use TPC tracksUse TPC tracks MIPs: relative gainElectrons: energy scale
Set E-scale using 1.8<p<8 GeV/c electronsSingle TowerMIP
€
σTPC ⊗σ EMC ≈17%
04/23/2006Mike Miller 8
Monte Carlo modelPythia 6.203 (CDF Tune A) + GEANT3 + Reconstruction(r) = fraction of jet pT in sub-cone r
Common jet shape variableStudy HT trigger biasStudy data/MC agreement
Shaded region represents single tower sizeHT trigger hot coreBias decreases with increasing jet pT, well described by MC
04/23/2006Mike Miller 9
Correction factors
( ) ( )( )pythiaTpythia
geantTgeant
T pNpM
pc =
•Jet pT resolution ~ 25%•Efficiency of HT trigger changes by 2 orders of magnitude!•Consistent results from both PYTHIA and HERWIG
εjet : decreases c(pT)
resolution: increases c(pT)
εTrig: ~1 e-2 at pT-jet = 5 GeV ~1 at pT-jet = 50 GeV
( ) resolutionpc jettriggerT ⊗⊗εε :
“measured”
“true”
Simulation
04/23/2006Mike Miller 10
Corrected cross section resultsGood agreement between MB and HT dataGood agreement with NLO over 7 orders of magnitudeError bars
statistical uncertainty from dataError band
leading systematic uncertainty10% E-scale uncertainty 50% uncertainty on yieldNeed di-jet, photon-jet to reduce sys. error
Agree with NLO calculation within systematic uncertainty
€
midpoint - coner = 0.4, 0.2 < η < 0.8
€
CTEQ6, μ = pT (hep - ph/0404057)
04/23/2006Mike Miller 11
Corrected cross section resultsGood agreement between MB and HT dataGood agreement with NLO over 7 orders of magnitudeError bars
statistical uncertainty from dataError band
leading systematic uncertainty10% E-scale uncertainty 50% uncertainty on yieldNeed di-jet, photon-jet to reduce sys. error
Agree with NLO calculation within systematic uncertainty
UA1 at 200 GeV
€
midpoint - coner = 0.4, 0.2 < η < 0.8
€
CTEQ6, μ = pT (hep - ph/0404057)
04/23/2006Mike Miller 12
Summary and OutlookMuch work to develop methods and techniques for jet triggering, reconstruction, and analysesFirst glimpse:
Significant pT reach (~50 GeV/c)Agreement within large systematics with NLO calculations
A few primary issues under study:Luminosity determinationRefined corrections NLO clustering scheme
Goal:Bring 2004 (and 2003) analyses to efficient closure
Bright Future2005: first real p+p run 3 pb-1 collected2006: first dedicated p+p run (goal 15 pb-1) with complete EMCal and commissioned jet and di-jet triggers
QCD jet physics at RHIC:coming of age
04/23/2006Mike Miller 13
Backup slides
04/23/2006Mike Miller 14
Consider detector response (measured) to known input (true)
trueT
measT
trueT
pppresolution −
:
Simulation: ~25% ± 5% for 10<pT<50 GeV/c
Consistent number derived from (modest) sample of di-jet events
Choose bin width = resolution
“geant jets” “pythia jets”
Response FunctionResponse Function
Simulation
pT (measured)
17 < pT(thrown) < 21 GeV/c
reco Bin = thrown bin: 35-40% reco Bin = thrown ± 1: ~80%
Motivates use of bin-by-bin Motivates use of bin-by-bin correction factorcorrection factor
04/23/2006Mike Miller 15
* Under Study
* Under Study
* Under Study
Dominant systematic uncertainty estimatesDominant systematic uncertainty estimates
Normalization
Pythia slope Statistics of c(pt) Background
BBC TriggerEnergy Scale
•Dominant uncertainty: 10% change in ECal ~40% change in yield•More under long term study (see last slide)
Frac
tiona
l Cha
nge
in x
-sec
tion
04/23/2006Mike Miller 16
Consider detector response (measured) to known input (true)
“geant jets” “pythia jets”
Response & bin quality factors
Simulation
Simulation
04/23/2006Mike Miller 17
Consider detector response (measured) to known input (true)
“geant jets” “pythia jets”
Bins of width 1-sigma “purity” of ~35% over range on the diagonal.
Motivates application of bin-by-bin correction factors.
Response & bin quality factors
Simulation
Simulation
04/23/2006Mike Miller 18
Charged Track Momentum p/p TPC 1%
Charged Track Inefficiency 10% x 60% jet 6%*
Neutral Tower Energy Gain/Gain = 10% 40% in yield
Neutral Energy Inefficiency ∑ET from n+K0L/S+++ν 6-10%*
MIP Subtraction 10% Correction to Jet ET 1%
Fiducial Detector Effects Edges/Dead regions 2%
Jet calculation 1 tower = =0.05 3%
Background Trigger Background trigger +MINBIAS event 5% in yield
Background Energy Jet + underlying Background 0
Underlying Event Work in Progress NA
Fragmentation Comparison to HERWIG ongoing NA
* Included in Correction Factor
Jet Energy Scale Systematics
04/23/2006Mike Miller 19
Theory Systematics
Changing the pdf Changing the scale
04/23/2006Mike Miller 20
2004 p+p commissioning runSampled luminosity: ~0.16 pb-1
1.4 M High tower (HT) events0.8 M highly pre-scaled minimum bias (MB) events ~220k pT>5 GeV jets in HT sample before cutsCommissioned 1x1 jet patch trigger– main jet trigger in 2005+
pT (track/tower) > 0.2 GeV|vertex-z|<60 cmrcone=0.4, fmerge=0.50.2< ηjet <0.8Neutral energy fraction<0.9(and ET-trig>3.5 GeV/c for HT)
High Tower TriggerBBC coincidence + one tower above thresholdεTrig(η=0.0)=1: ET-tower= 2.5 GeVεTrig(η=0.8)=1: ET-tower= 3.3 GeV
TPC0<φ<2π1< η<1BEMC0<φ<2π0< η<1in situ MIP/e calibration
AGS
PHOBOS BRAHMS
PHENIXSTAR
RHIC: unique pp collider designed for 70% beam polarization and 50<√s<500 GeV
Runs: 03/04 “commissioning”, 2005/2006 physics running
04/23/2006Mike Miller 21
Data vs. MC
04/23/2006Mike Miller 22
Data vs. MC
Red pythia + gstarBlack dataAll error bars statistical
High tower triggerpt (jet) >10 GeV/c
04/23/2006Mike Miller 23
Data vs. MC
Red pythia + gstarBlack dataAll error bars statistical
High tower triggerpt (jet) >10 GeV/c
