GGGG 05/27/2008 5/27/08 The STAR Longitudinal Spin Program Outline: 1) The Spin Puzzle 2) The STAR...

GG

The STAR Longitudinal Spin Program05/27/2008

Outline:

1) The Spin Puzzle

2) The STAR Experiment

3) Inclusive Jet Results

4) Inclusive Hadron Results

5) Coming Attractions

6) Summary

The STAR Longitudinal Spin Program

Jason C. Webb,Valparaiso University

Outline:

1) The Spin Puzzle





6) Summary

GG


The Spin Puzzle The STAR Experiment Inclusive Jets Inclusive Hadrons Coming Attractions Summary

Polarized DIS Measurements

Measurements of the g1p structure function provides

information on quark and antiquark distributions.

D. de Florian et al. Phys. Rev. D71 094018 (2005)

x B J

x B J

Q2=10 GeV2

Only 30% the proton's spincan be attributed to spin of the quarks. The rest must bedue to the spin of the gluonsand orbital motion of thepartons.

The main goal of the STAR Longitudinal Spin Program is to determine thegluon's contribution to the proton's spin, by studying inclusive jet, inclusive hadron, dijet and gamma+jet production.

g1p=

12∑

i

e i2[ qi x qi x ]At leading order:

GG



Polarized Proton-Proton Interactions at RHIC

The Spin Puzzle The STAR Experiment Inclusive Jets Inclusive Hadrons Coming Attractions SummaryThe Spin Puzzle The STAR Experiment Inclusive Jets Inclusive Hadrons Coming Attractions Summary

Gamma+jet:

quark-gluon Comptonscattering dominates

Inclusive hadrons:

mix of partonic subprocesses

Inclusive jets and dijets: Inclusive Measurements: Abundant probe Poor x-resolution (integrates over wide x-range, jet energy scale, frag. functions)

Gamma+jet: Able to reconstruct initial state (LO) kinematics (x1,x2) Good resolution, limited by energy- resolution of EM calorimeters. Rare probe (needs luminosity!) Challenging backgrounds

Dijets: Abundant probe Able to reconstruct initial state (LO) kinematics (x1,x2) Limited x-resolution, depends on jet → parton energy resolution

Several pieces which should “fit together nicely”...

RHIC is the world's first polarized proton-proton collider. Several complementary probes of the gluon's helicity preference are available. The STAR experiment is pursuing several, each with their own experimental advantages and challenges.

GG



Partonic analyzing powers dependon the particular process and scattering angle.

a L L=++

f 1 f 2− +-f 1 f 2

++f 1 f 2 +-

f 1 f 2

Theory: Experimental observables are connected to the parton helicity distributions using pQCD.

Experiment: Longitudinal spin asymmetries access information on the polarized cross sections

pQCD

FragmentationExtract via global fits

Putting the Puzzle Together

(assumes universality of pdfs and ff's.)


AL L=1

PB PY

N−R×N −

N−R×N −

AL L=−−

−−

R= L / L−

GG



Outline:

1) The Spin Puzzle





6) Summary

GG



Detector Overview

Magnet0.5 T SolenoidMinbias Trigger + Luminosity Beam-Beam Counters3.4 < |h| < 5.0

Central TrackingLarge-volume TPC|h| < ~1.5

Electromagnetic CalorimetryBarrel EMC (Pb/Scintilator)

-1 < h < 1Endcap EMC (Pb/Scintilator)1.086 < h < 2.0

Forward Meson Spectrometer (Pb Glass)~2.5 < h < 4.0

Upgrade program increases physics reach: FMS (2008), DAQ1k (2009), FGT (2010), ... Extend measurements to lower x

Bjorken Increase livetime to ~90-95% Improved forward tracking

Level-0 triggers: single calorimetertowers to x = 1x1 jet patchesLevel-2 triggers: tower clusters anddijet coincidence trigger (2006).


GG



The 2005 and 2006 Longitudinal Data Samples

pp 2005 longitudinal

Sampled luminosity: ≈ 1.6 pb-1

Achieved polarizations: PY ≈ P

B ≈ 50%

Inclusive jets, hadrons 0 < < 1

pp 2006 longitudinal

Sampled luminosity: ≈ 4.7 pb-1

Achieved polarizations: PY ≈ P

B ≈ 55%

Inclusive jets -1 < < 1 First dijets

Inclusive +/- -1 < < 1 Inclusive 0 -1 < < 2

` 2005 Dijet Event

RHIC runs in 2005 and 2006 have provideda rich data sample for solving the spinpuzzle.


GG


Outline:

1) The Spin Puzzle





6) Summary


GG



Inclusive Jet Production

Midpoint cone algorithm(Adapted from Tevatron II - hep-ex/0005012)

Seed energy = 0.5 GeV

Cone radius in - R=0.4 with 0.2 < < 0.8 (2005) R=0.7 with -0.7 < < 0.9 (2006)

Splitting/merging fraction f=0.5

Simulation reproduces the distribution of energyversus distance from jet thrust axis.

Experimental cross section agrees withNLO pQCD over 7 orders of magnitude


GG



Inclusive Jet Asymmetries (2005)

ARXIV:0710.2048, accepted for publication in PRL

200 GeV0.2 < η < 0.8

0.70Backgrounds

0.94Relative Luminosity

0.1-0.8 (pT dep)Non-longitudinal Polarization

2-5 (pT dep)Reconstruction + Trigger Bias

(x 10 -3)ALL systematics

[-5.4%,+6.7%]pT systematic

GRSV DIS Results from the 2005 run yielded significantnew constraints on g, compared with fitsbased only on DIS measurements.


GG


The 2006 jet asymmetries provide significantnew constraints on g.

GRSV DIS


Inclusive Jet Asymmetries

1st bin ~ 0.5all others ~ 0.1

Backgrounds

0.94Relative Luminosity

~ 0.03

(pT dep)

Non-longitudinal Polarization

[-1,+3]

(pT dep)

Reconstruction + Trigger Bias

(x 10 -3)ALL systematics

6.7%pT systematic

The 2006 results are a significant improvementover the 2005 measurement: Full BEMC Jet finder extends into EEMC Cone radius enlarged to 0.7 Increases in luminosity and polarization

Statistical uncertainties are 3x-4x smaller forhigh pT (pT > 13 GeV).


Inclusive Jet Asymmetries (2006)

GG



Global Analysis -- DSSV

2005

2006


2 distribution as g is varied w/in x-range constrained by the RHIC data. The STAR inclusive jet results provide significant constraints on g.

RHIC constraints

It is interesting to note that the best fit hasa zero-crossing at x ≈ 0.1. Over the nextfew years, STAR's emphasis will shift todijet and gamma+jet measurements, whichwill map out the x-dependence of g.

RHIC pp data have recently been included, along with polarized DIS and semi-inclusive DIS data, in a global fit to the polarizedpdfs. D. de Florian, et al., ARXIV:0804.0422

GG



Outline:

1) The Spin Puzzle





6) Summary

GG



Neutral Pions

Event Reconstruction:

1) Clusters are formed around seed strips in shower-maximum detectors.2) Clusters in orthogonal views associated to form points, and calorimeter energy divided3) Pairs of points reconstructed into p0->gg candidates

BEMC invariant mass spectrum:

Well described by Monte Carlo simulations.Background in the 0 signal region is understood in terms of three components: combinatoric, decays and cluster splitting.

Data

Simulation

10.5 < PT < 16.0 GeV/c

BEMC -1 < < 1

EEMC1<h<2

EEMC invariant mass spectrum:

Phenomenological fits to signal+background,with good chi2/ndf, parameterization whichvaries smoothly as a function of pT. Work underway to improve SMD response.

EEMC SMD


GG



BEMC Coverage: 0 < < 1

Luminosity:0.4 pb-1 (HT) and 44 mb-1 (Minbias)

Good agreement with NLO QCD over sevenorders of magnitude. CTEQ6M pdfs

Kretzer and KKP fragmentation functions

Better agreement w/ KKP

Large scale uncertainties in pQCD

2005 Neutral Pion Cross Section

Point-to-point systematic uncertainties dueto uncertainties in yield extraction.


GG



Neutral Pion Asymmetries in the BEMC

2006 data a significant improvementover 2005:

1) BEMC fully installed2) Increased luminosity3) Increased polarization4) Improved trigger5) Better shielding

Results consistent with PHENIX 2006 preliminary

The run 6 π0 result sees a significant increase in statistical precision as well as a greater reach in PT compared to run 5.

Similar statement applies for run 6 π±.

STAR is planning for a long pp run in 2009. Expecting large increase in FOM with 60% polarization and 50 pb-1


GG


Neutral Pion Asymmetries in the EEMC


Vary fit range 2 – 12

Vary functional form 0.2 – 2

Stat. Uncertainty in fits < 0.2

others under study

Systematic on ALL x10-3

2006 data a significant improvementover 2005:

1) Increased luminosity

2) Increased polarization

3) Improved trigger

4) Better shielding, reduces beam-like

background trigger rate by more than

an order of magnitude.

Data are consistent w/ ALL

(0)=0. Statistical precision comparable to

midrapidity results Result is an important step towards

measuring ALL

in the gamma+jet

channel.


GG



1.0 GeV/c

pion band

Charged Pions

pp 2005 data analysis:

- Trigger selection: Minbias || JP1 || JP2- -1 < < 1- |z

vertex| < 60cm (BBC timing)

Particle ID performed using dE/dx of charged

particle tracks w/in the TPC tracking volume.

Events w/in -1 < N < +2 from the mean of the

pion energy loss band are selected for analysis.

Deflection of the track in the magnetic field

determines charge of the pion.


GG



Trigger Bias {3.0 – 7.3}, pT dependent

Non-longitudinal Polarization 3.0

Relative Luminosity 2.2

Particle Identification 1.7

Beam Background 0.3

Systematic on ALL x10-3

Charged Pions

Preliminary Results 2005

Differences in + vs fragmentation allow for

the determination of the sign of g.

Trigger-bias on ALL

estimated using Pythia+

GEANT simulation, and GRSV pdfs

Preliminary results disfavor large gluon

polarization (GRSV max).

Analysis of 2006 data underway.


GG



Outline:

1) The Spin Puzzle





6) Summary

GG



Dijet Measurements

x1 2 =1

s pT3e

±3 pT4e± 4 x2

x1

pT4 , 4

pT3 , 3For dijets (and any 2 → 2 process), theinitial state kinematics can be determinedfrom final state observables (assumes LO).

Data is well described by simulations. Cross section and asymmetry analysis in progress.


M =s x1 x 2 y= 12

log x1

x2

= 1234

GG



Dijet Projections for 50 pb-1 with <P> = 60%

Significant new constraints from dijets expected in upcoming run(s).

Plot compares anticipated statisticalprecision to several fits for four different kinematic regions.

Inclusives 2005/6 Constraints from dijets


DSSV

GG



Gamma+Jet Measurements

x1 2 =1

spT e± e

± jet

x2

x1 pT ,

jet

Simulated x-gluon resolution

As with dijets, the gamma+jet channel allows us to reconstruct the initial state kinematics. The x-resolution is only limited by the calibration of thecalorimeters and intrinsic k

T.

W. Vogelsang Backgrounds present a significant experimental challenge. At pT = 10 GeVs/b is 1/10, and gets worse as one goesto lower pT. Isolation cuts and pT matchingwith the awayside jet can reduce thebackground significantly, but further discrimination power is required.


GG




Gamma+jet channel is still a work in progress.

Isolation cuts - require E

T / E

Tcone > 0.99

Plot compares data (3.1 pb-1) to MC simulations of g+jet signal anddijet backgrounds (scaled to 3.1 pb-1) after same set of cuts applied.

S/B ratio after isolation is smaller than the 1/3 expected from originalsimulations. Work underway to improve isolation cuts.

Planned upgrade (FGT) will also improve the isolation cuts.

GG




Analysis of the transverse shower shapeswill provide additional discrimination. Realevents are compared with a “library”of photon shapes, obtained from in situmeasurements of decays.


GG


Outline:

1) The Spin Puzzle





6) Other measurements (time

permitting)

7) Summary


GG



Summary

The STAR inclusive jet measurements from 2005/6 have already provided significant constraints on g.

Inclusive hadron measurements can provide complementary information

- fragmentation functions connect pT to x

- additional sensitivity to sign of g in +/- channel

Over the next few years we will begin to map out the x-dependence of g using two complementary methods:

- High statistics: dijets- High resolution: +jet coincidences

The STAR inclusive jet measurements from 2005/6 have already provided significant constraints on g.

Inclusive hadron measurements can provide complementary information

- fragmentation functions connect pT to x

- additional sensitivity to sign of g in +/- channel

Over the next few years we will begin to map out the x-dependence of g using two complementary methods:

- High statistics: dijets- High resolution: +jet coincidences

GG


GG



The 2005 and 2006 Longitudinal Data Samples

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

Backup slides to be added

GGGG 05/27/2008 5/27/08 The STAR Longitudinal Spin Program Outline: 1) The Spin Puzzle 2) The STAR...

Documents

Transcript of GGGG 05/27/2008 5/27/08 The STAR Longitudinal Spin Program Outline: 1) The Spin Puzzle 2) The STAR...