Polarized DIS with Future Polarized Colliders

1
Polarized DIS with Future Polarized Colliders

• Abhay Deshpande
• RIKEN BNL Research Center (RBRC)

Precision Lepton-Nucleon Scattering HERA III
Workshop Munich, December 18th, 2002
RIKEN BNL RESEARCH CENTER
2
Overview

• Introduction to different proposals under
  consideration for polarized DIS
• Physics opportunities with
• -- Polarized HERA, Electron Ion Collider
  (EIC) at BNL
• -- TeslaHERA (THERA) TESLA-N/ELFE_at_DESY
• Status of Polarized Colliders at BNL
• -- Status and comments on EIC
• -- Status of polarized proton beam
  acceleration collisions at BNL
• Summary

3
Deep Inelastic Scattering

• Observe scattered electron/muon hadrons in
  current jets
• Observe spectator or remnant jet

4
Why Collider in the Future?

• Past polarized DIS experiments MOSTLY FIXED
  TARGET
• 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

5
Projects Under Consideration
Machine Lumi/Year Sqrt(s)
Tesla-N (fix target) ELFE at DESY 100 fb-1 10-30 GeV 10 GeV
EIC 4 fb-1 20-100 GeV
Pol. HERA 150 pb-1 300 GeV
Pol. THERA 40-250 pb-1 1-1.5 TeV

• Pol. HERA needs polarized protons (Siberian
  Snakes, polarimeters etc.), Use existing
  detectors(?)
• EIC needs a polarized electron accelerator
  facility at RHIC a new detector
• THERA TESLA-N ELFE need TESLA and polarized
  protons in HERA a new detector

What Physics? ? Luminosity? CM Energy?
6
Kinematic Coverage

• ELFE Q2max 102 GeV2
• xmin 10-2 (1 GeV2)
• TESLA-N Q2max 103 GeV2
• xmin 10-3 (1 GeV2)
• EIC Q2max 104 GeV2
• xmin 10-4 (1 GeV2)
• HERA Q2max 105 GeV2
• xmin 10-5 (1 GeV2)
• THERA Q2max 106 GeV2
• xmin 10-6 (1 GeV2)

20-100 GeV
EIC overlaps with the fixed target experiments
because of the changeable beam energies
7
Luminosity Vs. Center of Mass
EIC has variable -- beam energies -- polarized
light nuclear species ? 100 times HERA
luminosity ? Collisions 2010(?) HERA has -- 3
times larger CM ? Collisions 2007(?) TESLA-N/THER
A -- Need the DESY LC -- Low/High CM -- High/Low
Luminosity ? Collisions 2015(?)
TESLA-N
THERA
8
Scientific Frontiers Future DIS Experiments

• Nucleon Structure polarized unpolarized e-p/n
  scattering
• -- Role of quarks and gluons in the nucleon
• -- Unpolarized quark gluon distributions
• -- Spin structure polarized quark gluon
  distributions
• -- Correlation between partons ? hard
  exclusive processes leading to Generalized Parton
  Distributions (GPDs)
• Nuclear structure unpolarized e-A scattering
• -- Role of quarks and gluons in nuclei
• -- e-p vs. e-A physics in comparison
• 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

EIC e-A Physics
Unpolarized Low x Issues A. Caldwell
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Polarized DIS at Future Facilities
All of them at EIC Pol. HERA
Some at TESLA-N/ELFE

• 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 structure function of the photon from
  photo-production
• Electroweak structure function g5 via W/-
  production
• Flavor separation of PDFs through semi-inclusive
  DIS
• Deeply Virtual Compton Scattering (DVCS) ?
  Gerneralized Parton Distributions (GPDs)
• Transversity
• Drell-Hern-Gerasimov spin sum rule test at high n
• Target/Current fragmentation studies
• etc.
• ? DESY-PROC-1999-03 EIC White-Paper
  BNL-Report-68933 (Feb.2002)

10
Spin structure function g1 at low x
A. D. V. W. Hughes EIC WS at Yale00
Polarized HERA
Polarized EIC
5-7 days of data
3 years of data
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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Polarized Gluon Measurements

• This is the hottest of the experimental
  measurements being pursued at various
  experimental facilities
• -- HERMES/DESY, COMPASS/CERN, E159/E160 at
  SLAC
• -- Low scales poses a potential problem for
  interpretation
• -- TESLA-N?
• -- RHIC Spin (polarized p-p)
• -- Issues of non-DIS scattering
• Deep Inelastic Scattering kinematics of EIC/HERA
• -- Scaling violations (pQCD analysis at NLO)
  of g1 (TESLA-N)
• -- (21) jet production in
  photon-gluon-fusion process
• -- 2-high pT hadron production in PGF
  (TESLA-N)
• Photo-production (real photon) kinematics at
  EIC/HERA
• -- Single and di-jet production in PGF
• -- Open charm production in PGF

12
DG from Scaling Violations of g1
A. D., V. W. Hughes J. Lichtenstadt EIC WS,
Yale00

• 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.)
  /- 1.5 (theory)
• Theory uncertainty dominated by the lack of
  knowledge of the shape of the PDFs in unmeasured
  low x region where EIC data will play a crucial
  role.
• With approx. 1 week of EIC statistical and
  theoretical uncertainties can be reduced by a
  factor of 3-5
• -- coupled to better low x knowledge of spin
  structure function
• -- less sensitivity on factorization
  re-normalization scale variations in fits as new
  data at low x is acquired

?See J. Lichtenstadts talk in this meeting
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Photon Gluon Fusion at EIC

• Direct determination of DG
• -- Di-Jet events
• -- High pT hadrons
• High Sqrt(s) at EIC Pol. HERA
• -- no theoretical ambiguities in
  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

Signal PGF
Background QCD Compton
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Di-Jet events Analysis at NLO
G. Radel, A. De Roeck, EIC WS, Yale00
At Electron Ion Collider 4 fb-1/yr
At HERA 150 pb-1/yr

• Statistical accuracies shown for at 2 EIC
  luminosities and 1 pol. HERA luminosity
• Detector smearing effects considered
• Analysis performed at next to leading order
• Will easily differentiate amongst different DG
  scenarios
• Uncertainty in the first moment of DG will be
  improved by factors of 3
• If combined with g1 NLO analysis effective
  improvement is even more
• EIC will give an absolute uncertainty of about
  3-5 in DG

J. Lichtenstadt, A.D. V. Hughes, EIC WS, Yale00
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Di-Jet World Data for DG/G
G. Radel A. De Roeck, EIC WS, BNL02
EIC Di-Jet DATA 2fb-1

• EIC
• Good precision
• Constrains shape of DG(x)
• HERA
• Lower x access
• Polarization in HERA much more difficult than
  RHIC(?)
• ? D. Barbers talk tomorrow

HERA Di-Jet Data 500 pb-1
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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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PDFs of polarized photon at EIC
M. Stratmann W. Vogelsang, EIC WS, BNL 01

• Stat. Accuracy estimated for
• 1 fb-1 running
• (1 month at EIC including 50 inefficiencies
  of detector)
• Single and double jet asymmetries
• ZEUS acceptance
• Will resolve photons partonic spin contents

Direct Photon Resolved Photon
18
Photon Structure Function at HERA/EIC
M. Stratmann W. Vogelsang,EIC WS, Yale00
Pol. HERA WS, DESY99
EIC 85 pb-1/day
HERA 150 pb-1/yr
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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 HERA EIC
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Measurement Accuracy PV g5 at EIC
J. Contreras A. De Roeck, Pol. HERA WS, DESY99
EIC WS BNL01

• Assumes for EIC (LEFT FIGURE)
• Input GS Pol. PDfs
• xF3 measured by then
• 2 fb-1 luminosity
• Makes the case for e/e- beam facility

• Assumes for HERA (RIGHT FIGURE)
• Input GS polarized PDFs
• xF3 is measured by then
• 1 fb-1 luminosity
• Both e/- beams

21
Drell Hern Gerasimov Spin Sum Rule
S. Bass, A. De Roeck A. Deshpande, EIC WS,
Yale00

• DHG Sum rule
• At EIC n range GeV ? few TeV
• AT HERA 10s of GeV ? 10s 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
• EIC
• -- Q2 10-6 ? 10-2 GeV2
• -- Sqrt(s) 25 ? 85 GeV
• HERA
• -- Q2 10-6 ? 10-3 GeV2
• -- Sqrt(s) 40 ? 250 GeV

22
DGH Spin Sum Rule
S. Bass A. De Roeck
Contribution from EIC/eRHIC and HERA
(1)(2) ?0.5
(1)(4)
(1)(2)?-0.5
(1)(3)
23
Strange Quark Distributions at EIC
HERA, TESLA-N, ELFE
E. Kinney U. Stoesslein, EPIC WS, MIT01

• 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 EIC and
  HERMES (2003-05) and some theoretical curves on
  expectations.

24
Transversity
M. G. Perdekamp, EIC WS, Yale00
TESLA-N, ELFE in HERMES Kinematics
EIC with 80 pb-1 1 day

• Measure helicity flip amplitude d(x,Q2) quark
  transversity
• Does not mix with gluon distributions in its QCD
  evolution
• Measure single spin asymmetries (DIS p0)
• Large acceptance desired
• etalt3.5
• Collins/fragmentation function being measured by
  
• RBRC from ee- at B-factor at BELLE
• ? Expect preliminary results in 03

25
DVCS/Vector Meson Production
ELFE
EIC

• 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
• at HERA, Jlab For ELFE this is
  the principle motivation

26
Deeply Virtual Compton Scattering
A. Sandacz, EIC WS, BNL02 D. Hassel, R. Milner
DVCS has already been seen at HERA New Detector
Techniques at EIC
Roman pots a la PP2PP at RHIC
DVCS study for EIC (preliminary)
10 x 250 GeV
Q2gt 1 GeV2 20ltWlt95 GeV 0.1lttlt1.0 GeV2
Full curve all events Dashed curve accepted
events Q2gt1 GeV2 50K events/fb-1
27
Future Fixed Target DIS at DESY
W.-D. Nowak, Int. WS on Hadron Structure,
Trieste, Feb.2002

• TESLA-N
• -- Use one (positron) arm of TESLA for
  polarized fixed target experiment
• -- Beam energy variable 30-250 GeV
• -- Large Q2 range compared to present fixed
  target experiments
• -- PHYSICS Transversity distributions,
  Polarized Gluon Distribution

• Run in parallel with the ee collider experiments
• Will need
• 1. Polarized source and injector
• 2. Experimental hall and short tunnel
• 3. Beam dump
• Detector design considerations
• Size comparable to COMPASS at CERN
• Good momentum resolution
• Good PID ? RICH, TRD as well as EMCalorimetry

28
ELFE at DESY
W.-D. Nowak, Int. WS on Hadron Structure,
Trieste, Feb.2002 R. Kaiser D. Ryckbosch,
private comm., SPIN2002 at BNL

• ELEF at DESY
• -- Inject electron beam at 30 GeV in modified
  HERA-e
• -- Use HERA as stretcher ring ? extract high
  duty factor
• -- Measurement goal Exclusive reactions with
  high precision
• -- PHYSICS Skewed parton distributions ?
  Orbital angular momenta

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Towards EIC at BNL.

• September 2001 EIC grew out of joining of two
  communities
• 1) polarized eRHIC (ep and eA at RHIC) 10
  GeV e X 250 GeV p or 100 GeV A
• 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 (see DoE Webpage
  for Nuclear Physics Long Range Planning)
• Steering Committee 7 members, one each from BNL,
  IUCF, LANL, LBL, MIT, UIUC, Yale Contact person
  (AD)
• 20 (13 US 7 non-US) Institutes, 100
  physicists 40 accelerator physicists
• See for more details EIC Web-page at
  http//www.bnl.gov/eic
• Annual Meetings MIT Sep.01, BNL Feb.02, BNL(?)
  May/June03
• Subgroups Accelerator WG, Physics WG, Detector
  WG

? EPIC eRHIC EIC
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EIC Layout (present status)

• Proposed by BINP MIT/Bates
• E-ring is ¼ of RHIC ring
• Collisions in ONE interaction region
• Collision energies 5-10 GeV
• Injection linac 2-5 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

EMPTY
PHOBOS
BRAHMS PP2PP
CAD/RF EMPTY
PHENIX
OTHER Ring with 6 IPS (Yale00), Linac-Ring
(Yale00), Linac-Re-circulating ring (BNL01)
STAR
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A Detector for EIC? 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
• DETECTOR DEVELOPMENT JUST BEGINNING Invitation
  to Join!
• -- Some early effort (W. Krasny J.
  Chwastowski, Yale 00 WS)
• -- New effort for modified EIC ring lattice
  to begin BNL/MIT/UIUC/YOU!
• EIC will provide 1) Variable beam energies 2)
  different hadronic species, some of them
  polarized, 3) high luminosity

32
A time line for EIC

• Predictions are very difficult to make,
  especially when they are about the future ---
  Albert E.
• Proposal by 2004-2005
• Expected formal approval 2005-6 Long Range Review
• RD money could start for hardware 2007
• Construction of IR and Detector begin 2007-2008
• 3-5 years for staged detector and IR construction
  without interfering with the RHIC running
• First collisions (2010-2011)???
• If any one knows how to
  do this earlier
• -- I am listening.

33
RHIC Accelerator Complex
RHIC pC Polarimeters

Absolute Polarimeter (H jet)
Siberian Snakes
Spin Rotators
2 ? 1011 Pol. Protons / Bunch e 20 p mm mrad
Partial Siberian Snake
LINAC
BOOSTER
Pol. Proton Source 500 mA, 300 ms
AGS
AGS Internal Polarimeter
200 MeV Polarimeter
Rf Dipoles
RHIC accelerates heavy ions to 100 GeV/A and
polarized protons to 250 GeV
34
RHIC Polarimetry
E950 Experiment at AGS (1999) ???
RHIC Polarimetry Now
BNL,Kyoto,RBRC,RIKEN,Yale
35
Siberian Snakes
BNL, RBRC, RIKEN
Effect of depolarizing resonances averaged out
by rotating spin by large angles on each turn

4 helical dipoles ? S. snake 2 snakes in each
ring -- axes orthogonal to each other
36
Successful Operation of the Snake
Blue Ring, Run 1 (2000-2001)

• Injection with Spin Flipped Asymmetry Flipped
• Adiabatically Snake on Horizontal polarization
• Accelerate equivalent to 180o rotation 180o
  rotated

Successful Single Snake Operation !
37
Polarization in Run 2 (January 2002)
Yellow Ring
Blue Ring

38
Why low polarization? ? AGS!
Source Improvement

New AGS SNAKE 2004-5
Ramp up Spead
Injection 1st Year
AGS power generator failure ½ ramp up speed 2x
resonance effect
39
Machine Performance Expectations
RUN proton/bunch x109 bunch Beta (m) Emittance (pmm) Luminosity 1030 cm-2s-1 Pol. ()
2001- 2002 70 55 3 25 1.8 15-25
2002-2003 100 112 1 25 16 45-55
2005- ? 112 1 ? ? 70-80
Design 200 112 1 20 80 70

40
A Case for Polarized Colliders Excellent!

• The polarized EIC and HERA for e-N scattering
  will enable the polarized DIS studies of nucleons
  in a completely new x-Q2
• -- A robust physics program exists with pros
  and cons w.r.t. high luminosity of EIC and higher
  CM energy of HERA
• If we are lucky HERA II finds Physics Beyond SM,
  polarized HERA will be imperative to understand
  the chiral properties of the object(!)
• -- Polarized THERA program will be
  concentrated around this
• Physics with variable Sqrt(s) at EIC will include
  in addition
• -- inclusive physics in DIS as well as
  photo-production regime
• -- semi-inclusive physics with good particle
  ID
• -- exclusive physics leading to DVCS, DES
  and further to GPDs
• -- study of evolution of any of the pdfs
  when necessary
• Proof of high energy polarized proton beam is at
  hand with RHIC Spin
• Primary physics program for TESLA-N/ELFE will
  limit itself to already explored x-Q2 coverage,
  but with significantly enhance statistical
  accuracy with huge luminosities hence allowing
  detailed studies of exclusive reactions, possibly
  leading to angular momenta in q and g

41
Some spin Low x/High Q2 surprises

• Elastic e-p scattering SLAC (1950s) ? Q2 1 GeV2
  ? Finite size of the proton
• Inelastic e-p scattering SLAC (1960s) ? Q2 gt 1
  GeV2 ? Parton structure of the proton
• Inelastic m-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(??)

• 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 (1989) Spin
  Crisis/Puzzle
• E704, AGS pp scattering, HERMES (1990s)
  Transverse spin asymmetries (??)
• RHIC Spin (2001) Transverse spin asymmetries (??)

42
Thanks..

• Many people were listed along with their work for
  various polarized HERA and Electron Ion Collider
  Workshops.
• -- Many more participated but can not be
  mentioned.
• TESLA-N, ELFE W.D.Nowak, R. Kaiser, D.
  Ryckbosch
• EIC Accelerator Issues V. Ptytsin and the EIC
  Accelerator group (BNL/MIT-Bates)
• Initial versions of some transparencies shown in
  this talk were prepared with A. De Roeck(CERN)
  for previous workshops and presentations for
  polarized HERA and making the case for EIC