Exploring%20the%20Spin%20structure%20and%20dynamics%20of%20the%20Proton%20in%20high%20energy%20polarized%20pp%20collisions%20at%20RHIC

1
Exploring the Spin structure and dynamics of the
Proton in high energy polarized pp collisionsat
RHIC
2
Outline

• The STAR detector

• First results in polarized pp collisions

• Future MIT research interests

• Summary and Outlook

• Introduction

3
Introduction

• RHIC Spin program (e.g. ?G)

• Fundamental question How is the proton spin
  made up?

• At present ?G is only poorly constrained from
  scaling violations in fixed target DIS
  experiments

B. Adeva et al., SMC Collaboration, Phys. Rev.
D58 (1998) 112002.

• Need New generation of experiments to explore
  the spin structure of the proton polarized
  proton collisions at RHIC which allows to access
  directly ?G in polarized pp collisions!

? SMC result Fraction of proton spin carried by
quarks is small
RHIC spin program
? Where is the spin of the proton then?
? SMC QCD-fit

• Unique multi-year program which has just
  started!
• Explore various aspects of the spin structure and
  dynamics of the proton in a new domain

• Spin structure of the proton (gluon polarization,
  flavor decomposition, transversity)
• Spin dependence of fundamental interactions
• Spin dependence of fragmentation
• Spin dependence in elastic polarized pp
  collisions

4
Introduction

• Asymmetries

? Measurement of asymmetries (A) Principle
approach to study spin effects
? Ultimately at RHIC, any combination of beam
polarization (longitudinal (/-) /transverse
(?/?)) is possible, which allows to access
different parts of the proton spin structure

• Double longitudinal-spin asymmetry

• Double transverse-spin asymmetry

? Study helicity dependent structure functions!
? Study transverse dependent structure functions!

• Single longitudinal-spin asymmetry

• Single transverse-spin asymmetry

? Study parity violation effects!
? Study left/right asymmetries!

• Statistical significance (FOMfigure-of-merit)

? Single spin asymmetry
? Double spin asymmetry
5
Introduction

• Description of ALL in terms of polarized parton
  distributions

f
f1
f2
Spin asymmetry of sub-process
6
Introduction

• Experimental aspects on asymmetry measurement at
  RHIC AN

• Measurement of AN for forward p0 production at
  STAR

p0
p?(?)
p

• Asymmetry

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Polarized proton collider RHIC

• Overview of RHIC polarized pp collider complex

RHIC pC Polarimeter
Siberian Snakes
BRAHMS PP2PP
PHOBOS
Lmax 2 x 1032 cm-2s-1
70 Beam Polarization
PHENIX
50 lt vs lt 500 GeV
Siberian Snakes
STAR
Spin Rotators
Partial Siberian Snake
2 ? 1011 Pol. Protons / Bunch ? 20 ? mm mrad
FY02 devices
LINAC
Pol. Proton Source 500 mA, 300 ms
BOOSTER
FY03 devices
AGS Internal Polarimeter
AGS
200 MeV Polarimeter
FY03 and beyond
AGS pC Polarimeter
Rf Dipoles
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Polarized proton collider RHIC

• Performance overview

• Installation and commissioning of AGS partial
  snake magnet
• Commissioning of polarized gas jet target (?
  Absolute polarization measurement)
• Commissioning of 250GeV ramp
• Adequate time for commissioning and luminosity
  development

• Commissioning status

• Siberian snake and spin rotator magnets
  successfully commissioned
• Fast polarimeters in AGS/RHIC demonstrated to
  work
• Spin transfer AGS to RHIC demonstrated to work

Rate

• RHIC performance in FY02

BBC MinBias
Polarization
Background Blue beam Background Yellow beam
RHIC SPIN effort is in the very beginning of its
multi-year program!

• Beam energy 100 GeV
• Inst. luminosity ? 5 1029 s-1 cm-2
• Integrated luminosity ? 0.3pb-1
• Polarization ? 0.2 (transverse)
• First trans. spin result!

300k
0.5
RHIC FY03 store 3714 (05/15/03)
Polarization
0.4
200k
0.3

• RHIC performance in FY03

0.2
100k

• Beam energy 100 GeV
• Inst. luminosity ? 2 1030 s-1 cm-2
• Integrated luminosity ? 0.5 pb-1 (trans.) ? 0.4
  pb-1 (long.)
• Polarization ? 0.3 (transverse and longitudinal)
• First ALL measurement!

L 2 x 1030 cm-2 s-1
0.1
0.0
0600 0800
1000 1200


Time of Day
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The STAR detector

• Overview

• Upgrade program of the STAR experiment for the
  first polarized proton collisions (FY02/FY03)
• Beam-Beam Counter (BBC) (2 lt ? lt 5)
• Relative luminosity measurement
• Rejection of beam-gas event in pp collisions
• Minimum bias trigger
• Beam tuning to make collisions at STAR
• Luminosity monitor
• Forward-Pion Detector (FPD) (3 lt ? lt 4)
• Electromagnetic calorimeter system Prototype
  setup of 3 Pb-glass arrays and 1 Pb-scintillator
  calorimeter east side for FY02
• Upgrade in FY03 Pb-glass array on EAST/WEST
• Energy and shower profile measurement (?0 ? ??)
• Event yield for Forward ?0 production
• Commissioning of EM-calorimeter modules and
  trigger (Barrel -1 lt ? lt 1 Endcap 1.09 lt ? lt
  2)
• Commissioning of spin scaler system

FPD East
FPD West
BBC East
BBC West
7.5m
7.5m
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The STAR detector

• STAR calorimeter system Endcap and Barrel

Completion and full exploitation of STAR barrel
and endcap calorimeter system crucial for STAR
SPIN program!
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First results in polarized pp collisions

• STAR BBC luminosity monitoring

Luminosity BBC EW counts
Bunch Crossing

• Abort gaps ? beam-gas background!

Polarization pattern at STAR Spin Up
Spin Down Unpolarized
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First results in polarized pp collisions

• First measurement of AN for forward p0 production
  at RHIC

• AN is found to increase with energy similar to
  E704 result (?s 20 GeV (10 X smaller than at
  RHIC), 0.5 lt pT lt 2.0 GeV)
• This behavior is also seen by several models
  which predict non-zero AN values

• Several approaches beyond the basic naive QCD
  calculations yield non-zero AN values at RHIC
  energies

• Sivers include intrinsic transverse component,
  k?, in initial state (orbital momentum) (before
  scattering takes place)
• Collins include intrinsic transverse component,
  k?, in final state (transversity) (after
  scattering took place)
• Qiu and Sterman (Initial-state twist-3)/Koike
  (final-state twist-3) more complicated QCD
  calculations (higher-twist, multi-parton
  correlations)

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Future MIT research interests

• Access ?G in polarized pp collisions

• ?G sensitivity in polarized pp collisions

• High-pT (prompt) photon production
• Jet production
• Heavy-flavor production

• Access ?G Double longitudinal-spin asymmetry ALL

• Theoretical advantage of RHIC

W. Vogelsang, M. Strattmann
? Study helicity dependent structure functions!

• Measurement of ALL requires

1. N(-) Spin dependent event yield
2. R Relative luminosity
3. P Beam polarization

• FOM ( Figure-Of-Merit)

? Smaller scale dependence at RHIC compared to
HERMES/COMPASS!
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Future MIT research interests

• The golden channel at RHIC Quark-Gluon Compton
  scattering

• ALL for QGC scattering interpreted in LO QCD

• Polarized cross-section is strongly peaked when
  photon is emitted in direction of incident quark
• Best determination of ?G for final-state photon
  to initial-state quark

Gluon polarization
pQCD result for QGC scattering
Measured asymmetry from polarized DIS

• Note QGC scattering dominates over competing
  background process

• Reconstruction of initial-state partonic
  kinematics

• Event-by-event determination of pT,? (photon
  energy), ?? (photon direction) and ?jet (jet
  direction) allows to reconstruct

• Large x quark (large quark polarization) analyzes
  small-x gluons (gluon-rich)
• Asymmetric QGC scattering (forward boost in
  direction of incident quark)

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Future MIT research interests

• Quark-Gluon Compton scattering Prospects at STAR
  

• Simulated ALL at two different RHIC
  center-of-mass energies

• Multi year program at RHIC which requires
• High luminosity
• High polarization
• ?s 200 / 500GeV

• Combined data sample at 200 GeV and 500 GeV is
  essential to minimize extrapolation errors in
  determining ?G

Accuracy 0.5

• Ultimately Global analysis of various ?G!

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Future MIT research interests

• Prospects on constraining ?G from inclusive jet
  production in RUN4 (FY04)

• Simulation based on Pythia including trigger and
  and jet reconstruction efficiencies
• Assume Coverage of EMC (barrel)
  ? 0 lt F lt 2p and 0 lt ? lt 1
• Jet Trigger ET gt 5 GeV over at least one patch
  (?? 1) X (?F 1)
• Jet reconstruction Cone algorithm
  (seed 1GeV, R 0.7)
• Polarization 40 - Luminosity 3pb-1

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Future MIT research interests

• W production Flavor dependence

• W production in pp collisions probes flavor
  structure of QCD sea analogous to deep-inelastic
  scattering
• Polarized proton beams allow the measurement of
  (the expected large) parity violation in W
  production
• Forward e detection (?Asymmetric partonic
  collisions!) gives direct access to probe the
  underlying quark (anti-quark) polarization which
  is dominated at RHIC by u/d quarks

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Future MIT research interests

• Inner and forward tracking upgrade at STAR

• Experimental issues for W case
• ee- charge sign determination (Select W/W-)
• e/h discrimination (Full EEMC capabilities
  crucial!)
• Trigger High pT single EM-cluster in BEMC/EEMC
  tower

• Formulated as long-term goal in STAR Decadal
  Upgrade Plans to BNL Management
• Main physics motivation W physics (Polarized pp
  program) and Heavy Quark production (Au-Au and
  polarized pp program)
• MIT kick-off meeting on inner/forward tracking
  upgrade November 7-8, 2003
• Overview of physics case, possible tracking
  layout and technology choices (Pixel/GEM/Silicon)
• Discussion on upgrade strategy, staging of
  various projects and overall organization
• Profit from MIT LNS silicon laboratory and
  MIT-BATES (Proposal of a GEM facility!) to
  strongly participate in the STAR tracking upgrade
  
• New STAR Working Group (MIT, LBL, IUCF, Yale,
  BNL, CalTech,) on STAR tracking upgrade
  Simulation and design work ? Aim for a proposal
  by summer 2005!

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Future MIT research interests

• Timeline (Machine and detector upgrade)

RHIC RUN NEW EQUIPMENT TO
STAR/RHIC SPIN

New AGS warm snake H gas jet RF spin flipper
BEMC preshower EEMC SMD preshower completed
FPD New strong AGS cold snake Completed BEMC,
EEMC (incl. postshower) Evtl. forward hadron
calorimeter Work to achieve full design L and
Pbeam ?s 500 GeV commissioning STAR TOF
barrel Improved STAR inner/forward tracker
Test L improvement schemes calibrate Pbeam to
10 continue ALL(jets)
Calibrate Pbeam to 5 improve L
Collins frag. with forward ?0s more ALL(jets)
first look at ?jet ALL(? jet), transversity
measurements at mid-rapidity, at ?s 200 GeV
FY04 FY05 FY0607 FY0809
ALL(? jet), AL(W) at ?s 500 GeV
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Summary and Outlook

• RHIC Spin program at BNL
• First successful polarized proton collisions ever
  at RHIC (transverse and longitudinal)
• Successful upgrade and commissioning of various
  new STAR components for the first polarized
  proton run at RHIC
• Unique opportunity to explore the spin structure
  of the proton in a new unexplored regime at RHIC
  over the next years. Focus on
• Gluon polarization
• Flavor decomposition
• This requires various accelerator, polarimeter
  and detector components to be completed (High
  polarization and luminosity ? Continuous pp
  running and development crucial)!
• Profit from infra-structure at MIT-LNS and
  MIT-BATES towards STAR tracking upgrade

?A very exciting time is ahead of us to explore
the spin structure of the proton at RHIC and to
establish a new ep/eA facility at BNL!

• Future eRHIC program at BNL
• Explore new QCD regime in eA (high parton density
  saturation phenomena) and polarized ep
  scattering (complement ongoing RHIC physics
  activities)
• Unique opportunity to establish such a QCD
  facility at BNL!