Spin%20Physics%20with%20eRHIC

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Spin Physics with eRHIC
Spin-2003 Xth Workshop on High Energy Spin
Physics Dubna, September 16-20, 2003

• Abhay Deshpande
• RIKEN BNL Research Center at BNL

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Some spin Low x-high Q2 surprises

• Stern Gehrlach (1921) Space
• quantization associated with direction
• Goudschmidt Ulhenbeck (1926)
• Atomic fine structure electron spin
• magnetic moment
• Stern (1933) Proton anomalous
• magnetic moment 2.79 mN
• Kusch(1947) Electron anomalous
• magnetic moment 1.00119m0
• Prescott Yale-SLAC Collaboration (1978)
• EW interference in polarized e-d DIS,
• parity non-conservation
• European Muon Collaboration (1988/9)
• Spin Crisis/Puzzle
• Transverse single spin asymmetries
• E704, AGS pp scattering, HERMES (1990s)
  RHIC Spin (2001)
• gtgt single spin neutron production(PHENIX)
• gtgt pion production (STAR) at 200 GeV
  Sqrt(S)

• Elastic e-p scattering at SLAC (1950s) ? Q2 1
  GeV2 ? Finite size of the proton
• Inelastic e-p scattering at SLAC (1960s)? Q2 gt 1
  GeV2 ? Parton structure of the proton
• Inelastic mu-p scattering off p/d/N at CERN
  (1980s) ? Q2 gt 1 GeV2 ? Unpolarized EMC effect,
  nuclear shadowing?
• Inelastic e-p scattering at HERA/DESY (1990s)? Q2
  gt 1 GeV2
• ? Unexpected rise of F2 at low x
• ? Diffraction in e-p
• ? Saturation(??)

A facility that does both would be ideal.
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Our knowledge of structure functions
g1
F2
105
10
10
103
1
102
Q2 (GeV2)
Q2 (GeV2)
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Deep Inelastic Scattering
1
2
3

• Observe scattered electron/muon hadrons in
  current jets
• Observe spectator or remnant jet
• gtgt suitably designed detector

Lumi
123 ? 3 exclusive
12 ? 2 semi-inclusive 1
? 1 inclusive
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Why Collider in the Future?

• Past polarized DIS experiments in fixed target
  mode
• Collider has distinct advantages --- Confirmed at
  HERA
• Better angular separation between scattered
  lepton nuclear fragments
• ? Better resolution of electromagnetic probe
• ? Recognition of rapidity gap events (recent
  diffractive physics)
• Better measurement of nuclear fragments
• Higher center of mass (CoM) energies reachable
• Tricky integration of beam pipe interaction
  region -- detector

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Proposals under consideration

• eRHIC at BNL
• A high energy, high intensity polarized
  electron/positron
• beam facility at BNL to collide with the existing
  RHIC
• heavy ion and polarized proton beam would
• significantly enhance RHICs ability to
• probe fundamental and universal aspects of QCD

JLab Upgrade II CEBAF II/ELIC An
Electron-Light-Ion-Collider or/and a 25 GeV Fixed
Target Facility CEBAF II/ELIC will address the
question of precision measurements of nucleon
spin, including the issues related to
generalized parton distributions with its
large luminosities. The collider fixed target
facility will cover complementary x-Q2 ranges
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eRHIC vs. Other DIS Facilities (I)

• New kinematic region
• Ee 5-10 GeV
• Ep 30 250 GeV
• Sqrt(s) 25 100 GeV
• Kinematic reach of eRHIC
• x 10-4 ? 0.7 (Q2 gt 1 GeV2)
• Q2 0 ? 104 GeV
• Polarized e, p and light ion beams -- 70
• Heavy ion beams of ALL elements!
• High Luminosity
• L gt (at least) 1033
• ?up to1034 ? ?? cm-2 sec-1

eRHIC
DIS
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eRHIC ELIC vs. Other DIS Facilities

• eRHIC
• gtgt Variable beam energy
• gtgt p ? U hadron beams
• gtgt Light Ion polarization
• gtgt Large Luminosity
• gtgt Huge Kinematic reach
• ELIC
• gtgt Variable beam energy
• gtgt Light Ion polarization
• gtgt Huge Luminosity

ELIC-Jlab
TESLA-N
eRHIC
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Scientific Frontiers Open to eRHIC
ELIC

• Nucleon Structure polarized unpolarized e-p/n
  scattering
• -- Role of quarks and gluons in the nucleon
• gtgt Unpolarized quark gluon
  distributions, confinement in nucleons
• gtgt Spin structure polarized quark
  gluon distributions
• -- Correlation between partons
• gtgt hard exclusive processes leading to
  Generalized Parton Distributions (GPDs)
• Meson Structure
• -- Mesons are goldstone bosons and play a
  fundamental role in QCD
• Nuclear structure unpolarized e-A scattering
• -- Role of quarks and gluons in nuclei,
  confinement in nuclei
• -- e-p vs. e-A physics in comparison and
  variability of A from d?U
• Hadronization in nucleons and nuclei effect of
  nuclear media
• -- How do partons knocked out of nucleon in
  DIS evolve in to colorless hadrons?
• Partonic matter under extreme conditions
• -- e-A vs. e-p scattering study as a
  function of A

ELIC
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Unpolarized DIS e-p at eRHIC

• Large(r) kinematic region already covered at HERA
  but additional studies at eRHIC are possible
  desirable
• Uniqueness of eRHIC high luminosity, variable
  Sqrt(s), He3 beam, improved detector
  interaction region
• Will enable precision physics
• -- He3 beams ? neutron structure ? d/u as
  x?0,
• dbar(x)-ubar(d)
• -- precision measurement of aS(Q2)
• -- precision photo-production physics
• -- precision gluon distribution in x0.001 to
  x0.6
• -- slopes in dF2/dlnQ2
• -- flavor separation (charm and strangeness)
• -- exclusive reaction measurements
  
• -- nuclear fragmentation region measurements
  

1 1 1 1 1 2 2,3 2,3
Luminosity Requirement
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Polarized DIS at eRHIC
1 1 1 1 1,2 1 1,2 3 1 1 2,3

• Spin structure functions g1 (p,n) at low x, high
  precision
• -- g1(p-n) Bjorken Spin sum rule better than
  1 accuracy
• Polarized gluon distribution function DG(x,Q2)
• -- at least three different experimental
  methods
• Precision measurement of aS(Q2) from g1 scaling
  violations
• Polarized s.f. of the photon from
  photo-production
• Electroweak s. f. g5 via W/- production
• Flavor separation of PDFs through semi-inclusive
  DIS
• Deeply Virtual Compton Scattering (DVCS)
• gtgt Gerneralized Parton Distributions (GPDs)
• Transversity
• Drell-Hern-Gerasimov spin sum rule test at high n
• Target/Current fragmentation studies
• etc.

Luminosity Requirement
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Proton g1(x,Q2) low x eRHIC
AD, V.W.Hughes
eRHIC 250 x 10 GeV Luminosity 85 inv. pb/day
Fixed target experiments 1989 1999 Data
10 days of eRHIC run Assume 70 Machine Eff.
70 Detector Eff.
Studies included statistical error detector
smearing to confirm that asymmetries are
measurable. No present or future approved
experiment will be able to make this measurement
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Low x measurement of g1 of Neutron
AD, V.W.Hughes

• With polarized He3
• 2 weeks of data at eRHIC
• Compared with SMC(past) possible HERA data
• If combined with g1 of proton results in Bjorken
  sum rule test of better than 1-2 within a couple
  of months of running

EIC 1 inv.fb
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Polarized Gluon Measurement at eRHIC

• This is the hottest of the experimental
  measurements being pursued at various
  experimental facilities
• -- HERMES/DESY, COMPASS/CERN, RHIC-Spin/BNL
  E159/E160 at SLAC
• -- Reliability from applicability of pQCD
  without doubt leaves only RHIC
• Measurements at eRHIC will be complimentary with
  RHIC
• Deep Inelastic Scattering kinematics at eRHIC
• -- Scaling violations (pQCD analysis at NLO)
  of g1 ? First moment of DG
• -- (21) jet production in
  photon-gluon-fusion process ?
• -- 2-high pT hadron production in PGF
  ?
• Photo-production (real photon) kinematics at
  eRHIC
• -- Single and di-jet production in PGF
• -- Open charm production in PGF
• ELIC measurements possible but in limited
  kinematic range and would
• result in considerable scale dependences in
  interpretation.

Shape of DG(x)
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DG from Scaling Violations of g1
AD, V.W.Hughes, J.Lichtenstadt

• World data (today) allows a NLO pQCD fit to the
  scaling violations in g1 resulting in the
  polarized gluon distribution and its first
  moment.
• SM collaboration, B. Adeva et al. PRD (1998)
  112002
• DG 1.0 /- 1.0 (stat) /- 0.4 (exp. Syst.)
  /- 1.4 (theory)
• Theory uncertainty dominated by the lack of
  knowledge of the shape of the PDFs in unmeasured
  low x region where eRHIC data will play a crucial
  role.
• ? lack of knowledge of the functional form or
  shape of the gluon pdf
• With approx. 1 week of eRHIC statistical and
  theoretical uncertainties can be reduced by a
  factor of 3
• -- coupled to better low x knowledge of spin
  structure
• -- less dependence on factorization
  re-normalization scale in fits as new data is
  acquired

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Photon Gluon Fusion at eRHIC

• Direct determination of DG
• -- Di-Jet events (21)-jet events
• -- High pT hadrons
• High Sqrt(s) at eRHIC
• -- no theoretical ambiguities regarding
  interpretation of data
• Both methods tried at HERA in un-polarized gluon
  determination both are successful!
• -- NLO calculations exist
• -- H1 and ZEUS results
• -- Consistent with scaling violation F2
  results on G
• Scale uncertainties at ELIC large

Signal PGF
Background QCD Compton
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Di-Jet events at eRHIC Analysis at NLO
G. Radel A. De Roeck, AD, V.W.Hughes,J.Lichtenst
adt

• Stat. Accuracy for two luminosities
• Detector smearing effects considered
• NLO analysis
• Excellent ability to gain information on the
  shape of gluon distribution

• Easy to differentiate different DG scenarios
  factor 3 improvements
• in 2 weeks
• If combined with scaling violations of g1
  factors of 5 improvements
• in uncertainties observed in the same time.
• Better than 3-5 uncertainty can be expected
  from eRHIC DG program

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Di-Jet at eRHIC vs. World Data for DG/G
G. Radel, A. De Roeck,AD

• Good precision
• Clean measurement in x range 0.01lt x lt 0.3
• Constrains shape of DG(x)
• Polarization in HERA much more difficult than
  RHIC.

eRHIC Di-Jet DATA 2fb-1
ELIC
DG from scaling violations gt xmin 10-5 at
HERA gt xmin 10-4 at eRHIC
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Polarized PDFs of the Photons

• Photo-production studies with single and di-jet
• Photon Gluon Fusion or Gluon Gluon Fusion (Photon
  resolves in to its partonic contents)
• Resolved photon asymmetries result in
  measurements of spin structure of the photon
• Asymmetries sensitive to gluon polarization as
  well but we will consider the gluon polarization
  a known quantity!

Direct Photon
Resolved Photon
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Photon Spin Structure at eRHIC
M. Stratmann, W. Vogelsang
eRHIC

• Stat. Accuracy estimated for
• 1 fb-1 running
• (2 weeks at EIC)
• Single and double jet asymmetries
• ZEUS acceptance
• Will resolve photons partonic spin contents

Direct Photon Resolved Photon
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Parity Violating Structure Function g5

• This is also a test

• Experimental signature is a huge
• asymmetry in detector (neutrino)
• Unique measurement
• Unpolarized xF3 measurements
• at HERA in progress
• Will access heavy quark
• distribution in polarized DIS

For eRHIC kinematics
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Measurement Accuracy PV g5 at eRHIC
J. Contreras, A. De Roeck

• Assumes
• Input GS Pol. PDfs
• xF3 measured by then
• 4 fb-1 luminosity
• Positrons Electrons in eRHIC ? g5()
• gtgt reason for keeping the option of positrons
  in eRHIC

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Drell Hern Gerasimov Spin Sum Rule
S.D.Bass, A. De Roeck,AD

• DHG Sum rule
• At eRHIC range GeV ? few TeV
• Although contribution from to the this sum rule
  is small, the high n behavior is completely
  unknown and hence theoretically biased in any
  present measurements at
• Jefferson Lab., MAMI, BNL

• Inclusive Photo-production
• measurement
• Using electron tagger in
• RHIC ring
• Q2 10-6 ? 10-2 GeV2
• Sqrt(s) 25 ? 85 GeV

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DVCS/Vector Meson Production

• Hard Exclusive DIS process
• g (default) but also vector mesons possible
• Remove a parton put another back in!
• ? Microsurgery of Baryons!

• Claim Possible access to skewed or off forward
  PDFs?
• Polarized structure Access to quark orbital
  angular momentum?
• On going theoretical debate experimental effort
  just beginning

--A. Sandacz AD
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Strange Quark Distributions at eRHIC
U. Stoesslein, E. Kinney

• After measuring u d quark polarized
  distributions. Turn to s quark (polarized
  otherwise)
• Detector with good Particle ID pion/kaon
  separation
• Upper Left statistical errors for kaon related
  asymmetries shown with A1 inclusive
• Left Accuracy of strange quark distribution
  function measurements possible with eRHIC and
  HERMES (2003-05) and some theoretical curves on
  expectations.

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Highlights of e-A Physics at eRHIC

• Study of e-A physics in Collider mode for the
  first time
• QCD in a different environment
• Clarify reinforce physics studied so far in
  fixed target e-A m-A experiments including
  target fragmentation
• QCD in x gt 1/(2mNRN) 0.1
  (high x)
• QCD in 1/(2mNRA) lt x lt 1/(2mNRN)
  0.1 (medium x)
• Quark/Gluon shadowing
• Nuclear medium dependence of hadronization
• . And extend in to a very low x region to
  explore
• saturation effects or high density partonic
  matter also called the Color Glass Condensate
  (CGC)
• QCD in x lt 1/(2mNRA) 0.01
  (low x)

See www.bnl.gov/eic for further details
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Using Nuclei to Increase the Gluon Density

• Parton density at low x rises as
• Unitarity ? saturation at some
• In a nucleus, there is a large enhancement of the
  parton densities / unit area compared to a
  nucleon
• Example
• Q24 (GeV/c)2
• ?lt 0.3
• A 200
• Xep10-7 ? for ? XeA 10-4
  

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A Detector for eRHIC ? A 4p Detector

• Scattered electrons to measure kinematics of DIS
• Scattered electrons at small (zero degrees) to
  tag photo production
• Central hadronic final state for kinematics, jet
  measurements, quark flavor tagging, fragmentation
  studies, particle ID
• Central hard photon and particle/vector detection
  (DVCS)
• Zero angle photon measurement to control
  radiative corrections and in e-A physics to tag
  nuclear de-excitations
• Missing ET for neutrino final states (W decays)
• Forward tagging for 1) nuclear fragments, 2)
  diffractive physics
• At least one second detector could be rolled
  in from time to time.
• under consideration
• eRHIC will provide 1) Variable beam energies 2)
  different hadronic species, some of them
  polarization, 3) high luminosity

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Moving Towards eRHIC.

• September 2001 EIC grew out of joining of two
  communities
• 1) polarized eRHIC (ep and eA at RHIC)
• BNL, UCLA, YALE and people from DESY
  CERN
• 2) Electron Poliarized Ion Collider (EPIC)
  3-5 GeV e X 30-50
• GeV polarized light ions
• Colorado, IUCF, MIT/Bates, HERMES
  collaborators
• February 2002 White paper submitted to NSAC Long
  Range Planning Review ? Received enthusiastic
  support as a next RD project
• Steering Committee 8 members, one each from BNL,
  IUCF, LANL, LBL, MIT, UIUC, Caltech, JLAB, Kyoto
  U. Contact person (AD)
• 20 (13 US 7 non-US) Institutes, 100
  physicists 40 accelerator physicists Recent
  interest from HERA
• See for more details EIC/eRHIC Web-page at
  http//www.bnl.gov/eic
• Subgroups Accelerator WG, Physics WG Detector
  WG
• E-mails BNL based self-registered email servers
  list yourselves!

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Present Lay Out of the Collider at BNL

• Proposed by BINP MIT/Bates BNL
• with input from DESY
• E-ring is ¼ of RHIC ring
• Collisions in one interaction region
• gtgt Multiple detectors under consideration
• Collision energies Ee5-10 GeV
• Injection linac 2-10 GeV
• Lattice based on superbend magnets
• Self polarization using Sokolov Ternov Effect
  (14-16 min pol. Time)
• IP12, IP2 and IP4 are possible candidates for
  collision points

e-cooling
RD needed started
OTHER Ring with 6 IPS, Linac-Ring,
Linac-Re-circulating ring
NSAC Subcommittee Evaluation March 03 1 Science,
2 for Readiness
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ELIC vs. Other DIS Facilities (I)

• Jlab ELIC High luminosity measurements
  EXCLUSIVE measurements and associated physics at
  intermediate x Q2
• Ee 3-5 (7) GeV
• Ep 30 100 (150) GeV
• Sqrt(s) 20 45 (65 ??) GeV
• Kinematic reach of ELIC
• x 10-3 ? 0.8 (Q2 gt 1 GeV2)
• Q2 0 ? 6 x102 GeV
• Polarized e, p, light ion beams
• -- 70 polarization
• High Luminosity
• L gt 1033 ? up to1035 cm-2 sec-1

eRHIC
ELIC
DIS
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JLAB/ELIC Layout
L. Merminga/R. Ent
One accelerating one decelerating pass through
CEBAF
NSAC Subcommittee Evaluation March 03 1 Science,
3 for Readiness
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JLAB/ELIC Aggressive R D Launched
L. Merminga

• Conceptual development
• gtgt Circulator ring ? to reduce the high
  current polarized photo-injector and ERL
  requirement
• gtgt Highest luminosity limits
• Analysis and simulations
• gtgt electron cooling and short bunches
• gtgt beam-beam physics
• gtgt energy recovery linac physics
• Experimental research effort
• gtgt CEBAF-ERL to address ERL issues in large
  scale systems
• gtgt JLAB FEL (10mA), Cornell/JLAB Prototypes
  (100 mA), BNL Cooling Prototype (100mA) to
  address high current ERL issues.

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A possible time line for eRHIC

• Predictions are very difficult to make,
  especially when they are about the future ---
  Albert E.
• Absolutely Central to the field NSAC 2001-2
  Long Range Planning
• document summary high on RD
  recommendation projects.
• Highest possible scientific recommendation from
  NSAC Subcommittee
• February/March 2003, Readiness Index 2 (
  JLAB-ELIC 3)
• eRHIC Zero-th Design Report (Physics
  Accelerator Lattice)
• ? Requested by BNL Management January 2004
• ? e-cooling RD money started (with RHIC II)
  some DOEsome BNL internal
• FOLLOWING THIS TIME LINE FOR GETTING READY
  (FUTURE)
• Expected formal approval 2005-6 Long Range
  Review (Ready CD0)
• Detector RD money could start for hardware 2007
  (CD1)
• Ring, IR, Detector design(s) 2008(CD2)
• Final Design Ready 2009 (CD3) ? begin
  construction
• 3/5 years for staged detector and IR
  construction without interfering with the RHIC
  running
• First collisions (2011)???

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Luminosity Comparison Table
L. Merminga(Jlab)) V. Ptiitsyn(BNL)
JLAB/ELIC
eRHIC
Parameter Units Design Design
e- Ions
Energy GeV 5 50/100
Electron Cooling - - Yes
Circulator Ring - Yes -
Luminosity cm-2 sec-1 6x1034 / 1x1035 6x1034 / 1x1035
Iave A 2.5 2.5
fc MHz 1500 1500
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Scale Dependence NLO/LO K factor
M. Stratmann W. Vogelsang