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 results

Unique 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 results

Unique 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

part

on

part

icle

dete

ctor

etcp

e

,,

,

πγν ,,

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

“pyth

ia” 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<1

BEMC0<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 model

Pythia 6.203 (CDF Tune A) + GEANT3 + Reconstruction

(r) = fraction of jet pT in sub-cone r

Common jet shape variable

Study HT trigger bias

Study data/MC agreement

Shaded region represents single tower size

HT trigger hot core

Bias decreases with increasing jet pT, well described by MC

04/23/2006Mike Miller 9

Correction factors

( ) ( )( )pythiaTpythia

geantTgeant

T pN

pMpc =

•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 - cone

r = 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 - cone

r = 0.4, 0.2 < η < 0.8

€

CTEQ6, μ = pT (hep - ph/0404057)

04/23/2006Mike Miller 12

Summary and Outlook

Much 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

p

ppresolution

− :

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)

Fra

ctio

nal C

hang

e in

x-s

ectio

n

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 run

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+

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<1

BEMC0<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