Using Jet Asymmetries to Access G at Renee Fatemi Massachusetts Institute of Technology for the STAR Collaboration March 23, 2006 Moriond QCD, La Thuile, Italy 1. Measurements aimed at extraction of G at STAR 2. RHIC Facility and STAR Experiment 3. STAR Jet Algorithm and Jet Characteristics 4. Jet Cross-Section and NLO comparisons 5. Double Spin Jet Asymmetries and implications for G 6 Future Improvements and Measurements STAR STAR
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Renee Fatemi Massachusetts Institute of Technology for the STAR Collaboration
STAR. Using Jet Asymmetries to Access G at. 1. Measurements aimed at extraction of G at STAR 2. RHIC Facility and STAR Experiment 3. STAR Jet Algorithm and Jet Characteristics 4. Jet Cross-Section and NLO comparisons 5. Double Spin Jet Asymmetries and implications for G - PowerPoint PPT Presentation
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Using Jet Asymmetries to Access G at
Renee Fatemi Massachusetts Institute of Technology
for the STAR Collaboration
March 23, 2006 Moriond QCD, La Thuile, Italy
1. Measurements aimed at extraction of G at STAR
2. RHIC Facility and STAR Experiment
3. STAR Jet Algorithm and Jet Characteristics
4. Jet Cross-Section and NLO comparisons
5. Double Spin Jet Asymmetries and implications for G
6 Future Improvements and Measurements
STARSTAR
A Short History of G
€
JPROTON =1
2= ΔSq + ΔG + Lq + LG
€
Sq
€
G Indirectly accessed from DIS via Next-to-Leading order fits
I. Hirai,Kumano and Saito hep-ph/0601087
20-30% proton spin. Data from Fixed Target DIS ep scattering
Limited CM energy range results in large error on G fit.
For Q2=1 GeV2
I.
II.
Need polarized electron-proton collider or direct access to the gluon in order to continue experimental study of G €
G = 0.99 ±−0.311.17
€
G = 0.50 ±1.271.27
II. SMC Collaboration Phys.Rev. D58 (1998) 112002
G=
+ +
No FF! Average over partonic kinematics
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rp
r p → jet + X
No FF! Reconstruct partonic kinematics. Statistically limited until 2006.
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rp
r p → jet + jet
Requires for partonic kinematics
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rp
r p → π + /− + X
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rp
r p → π 0 + X
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DABπ
€
qq + q q
Accessing G at STAR
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ALL =σ ++ −σ +−
σ ++ + σ +−=
ΔfAΔfB × Δσ AB →CX × DC
fA fB ×σ AB →CX × DCfA fB fC
∑
Reconstruction of partonic kinematics
Statistically limited - requires high luminosity
challenging pion background subtraction
€
rp
r p → jet + γ
Inclusive measurements have contributions from several
sub-processes
Understanding of inclusive channels necessary for analysis of clean jet + photon channel
RHIC Complex + STAR Detector
Spin Rotators(transverse/longitudinal)
STAR IR
RHIC
polarimetersSiberian Snakes
Siberian Snakes
PHENIX IR
Colliding 100 GeV beams
Each bunch filled with distinct polarization state
Spin Rotators at STAR IR allow for transverse and longitudinal spin orientation
Bunch Xings every 100-200ns
CNI polarimeters + Hydrogen Jet target provide run by run & absolute polarization
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r p
r p
TPC charged tracks -1.4<<1.4
EMC neutral energy -1 < < 1 (2003-2005 only 0< < 1)
Beam Beam Counters (BBC) provide MINBIAS trigger as well as spin dependent luminosity 3.4 < < 5.0.
High Tower (HT) trigger : Requires 1 tower (0.05 x 0.05) with ET > 2.2-3.4 GeV
= -ln[tan(/2)]
What does a jet at STAR look like?What does it mean to identify a jet with ET=5 GeV at ?
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s = 200
“One can usefully define jets down to ET 5 GeV” UA1 Collaboration Nuclear Physics B309 405-425 (1988)
2-particle azimuthal correlations seen at STAR show clear evidence of correlated clusters of particles separated by also known as DIJETS! Real test is collecting these clusters into a “jet” and comparing to NLO pQCD calculations
Simple Jet Definition: A cluster of particles correlated in and that result from the fragmentation and hadronization of scattered partons.
nu
cl-e
x03
06
02
4
€
φ=π
pT (GeV)A. Mischke tomorrow 10:30
STAR Jet Algorithm
i. P of TPC track, EMC tower OR particle used as seed for cluster formation
ii. Cluster P around seed inside Jet Cone Radius = 0.4
iii. Look for additional stable clusters at “midpoint” between two clusters
iv. Merge jets if Energy overlap > 50%
v. Sum of P in each stable cluster forms jet
vi. Require Jet pT > 5 GeV
vii. Same algorithm used for DATA, GEANT and PYTHIA jets
PA
RT
ON
PA
RT
ICL
ED
ET
EC
TO
R
GE
AN
T
JE
TS
DA
TA
J
ET
S
PY
TH
IA
JE
TS
Midpoint Cone Algorithm (hep-ex/0005012)
- Collinear and infrared safe -
DATA JETS GEANT JETS
PYTHIA JETS Corrected Jet Yield = X
Correction factor incorporates detector resolution, and energy losses due to fiducial cuts and undetected neutral energy
Jet Cross-Section Analysis 2004 DATA SAMPLE
~0.15 pb-1 sampled lum
0.8/1.4M MINB/HT events
2004 X-sec Cuts
|vertex| < 60 cm
0.2 < jet < 0.8
Trig ET > 3.5 GeV
Neutral ET / Jet ET<0.9 RA
W p
er-
eve
nt
Yie
ld
Good agreement between DATA and Simulation - PYTHIA 6.205 (CDF Tune A) + GEANT (Geisha)
EmcEt/JetEt (pT > 21.3 GeV/c)
Enhanced neutral energy in jets motivates background cut
Jet Cross-Section Results
B. Jager et.al, Phys.Rev.D70 034010
Two point overlap between HT and MINB show good agreement.
50% systematic shown in yellow band comes from uncertainty in jet energy scale. Need or gamma-jet to reduce this error.
Agreement -within systematics over 7 orders of magnitude!€
π 0
€
C pT( ) =PYTHIA(pT )
GEANT(pT )
Bin migration
Detector and Jet Reconstruction inefficiencyTrigger inefficiency Undetected Neutral Energy
Bin by Bin Correction Factors
Dominant Cross-Section Systematics
* Under Study
* Under Study
* Under Study
Normalization
Pythia slope Statistics of c(pt) Background
BBC TriggerEnergy ScaleF
ract
iona
l Cha
nge
in x
-sec
tion
Fragmentation Function Systematic: Comparison between PYTHIA and HERWIG results in no significant difference in correction factors.
Jet Asymmetry Analysis 2003+2004 DATA Sample
0.3 pb-1 sampled luminosity
<PBPY> = 0.3/0.4 for 03/04
125/162k Jets after cuts 03/04
2003/2004 Cuts
|vertex| < 75/60 cm
0.2 < jet < 0.8
Neutral ET / Jet ET < 0.8/0.9€
ALL =σ ++ −σ +−
σ ++ + σ +−=
1
PB PY
N ++ − RN +−
N ++ + RN +−
bunch crossing#
B
Y
€
R =S++
S+−
S = Scaler board counts from BBC (anti) aligned (+-) ++ helicity states
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−−
Excellent Agreement between 2003/2004 ALL
2003+2004 Jet ALL
First Double Spin Asymmetry from STAR!
ALL is consistent with zero.
Results tend to disfavor the GRSV g=g scenario
Agrees well with previous DIS evaluations
Errors are statistical only
STAR systematic errors ~0.01
Polarization Systematic ~25% not included in figure
A. Single spin Asymmetries consistent with zero as expected
B. Relative Lum Systematic Error
Estimated by comparing BBC scaler results from two different timing cuts.
€
δALL = 0.009
C.Random Fill Pattern Analysis 1. Randomly assign spin patterns to 56 bunches.
2. Recalculate ALL - fit with line
3. Repeat 400x and histogram fit
4. RMS of histogram is on order of ALL statistical error indicating no systematic associated with a specific bunch
AL
L
Run ID Fit Mean
p0=0.007613 ±0.0169RMS= 0.0164
Asymmetry Systematics II2004
(det)<1
bg
Jet EEMC/ETot
4. Background Asymmetry - showers from beam scraping results in jets with an excess of neutral energy. Estimate systematic effect on ALL by calculating background fraction (fBG) and asymmetry (ALL
BG).
Jet EEMC/ETot>0.9(det)<1
AbgLL 2004
€
ALL
meas pT( ) =ALL pT( ) + f BG pT( ) × ALL
BG pT( )1+ f BG pT( )
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f BG = 0.05
ALLBG ≈ 0.06 ± 0.03
δbgALL< 0.003
5. Trigger Bias - The HT trigger can alter the “natural” weight of contributions from gg,qg,qq. Use GRSV std + CTEQ5L to simulate ALL and estimate systematic due to A) subprocess changes B) detector bias C) bin migration
δTRGALL< 0.006 PYTHIA jets
High Tower jets
ALL
• PYTHIA - HT
Simulations
Future Results
I. Use of new Jet Patch trigger in 2005 increased jet reconstruction efficiency, reduced trigger bias and reduced the size of trigger efficiency corrections for Jet cross-section measurements
II. Longer dedicated runs will increase statistics
Increased Statistics will allow STAR to distinguish between gluon senarios.
2005 Projections from data on tape
2005 HT1
2005 JP1
C (
pT)
PYTHIA Simulations
Summary First Jet Results from STAR reflect several years of work on
Detector Design, Trigger Algorithms, Jet Algorithms and Luminosity Monitoring tools.
Jet X-seci. Understand Detector/Trigger enough to provide good agreement
between Simulation/Dataii. Agreement within systematics for NLO pQCD calculationsiii. Future possibilities - access to high x PDFs + jet shape analysisiv. Motivates application of Jet Algorithm in this energy regime to jet
asymmetry measurements. Jet Asymmetry
i. First double spin asymmetry results are consistent with zero.ii. This measurement is in full agreement with previous DIS evaluations of
the gluon polarizationiii. Initial measurements are statistics limited.
2003+2004 results reflect statistics from limited preliminary runs. Inclusive predictions from 2005+2006 statistics indicate the ability to discriminate between gluon scenarios.
BACKUP SLIDES
pp Run 2002 2003 2004 2005
>2006
CM Energy 200 GeV 200 GeV 500 GeV
<Pb> and direction at
STAR0.15 T
0.30 T/L 0.40 L 0.45 L/T 0.7 L/T 0.7 L/T
Lmax [ 1030 s-1cm-2 ] 2 6 6 16 80 200
Lint [pb-1 ] at STAR 0.3 0.5 / 0.4 0.4 5 320 800
Stable polarization direction - transverseLongitudinal polarization at STAR/Phenix
AGS Heclical Partial Snake
Number of bunches: 55 - 1122x1011 protons/bunch (max)
PHOBOS
Jet Cross-Section Results
€
1
dΩ
dσ
dpT
=1
2π ⋅0.6⋅
1
ΔpT
⋅1
L ⋅dt∫⋅
1
c pT( )⋅
dN
dpT
€
1
L ⋅dt∫=
σ BBC ⋅εvertMB
NMB−eventsaccepted
hep-ph/0404057
Due to size of systematic errors connected with small c(pT) at low pT bins only use HT data > 7 GeV
Two point overlap between HT and MINB show good agreement.
50% systematic shown in yellow band comes from uncertainty in jet energy scale. Need or gamma-jet to reduce this error.
Agreement (within systematics) over 7 orders of magnitude!€