Physics

1
Physics Status of eRHIC
A
Workshop on Hadron Structure Spectroscopy Compas
s 2004, Paris March 3, 2004

• Abhay Deshpande
• Stony Brook University
• RIKEN BNL Research Center

2
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.
3
Deep Inelastic Scattering
1
2
3

• Observe scattered electron/muon
  1
• Observe spectator or remnant jet
  12
• Obersve current jet as well
  123
• gtgt suitably designed detector

Lumi
123 ? exclusive 12
? semi-inclusive 1 ?
inclusive
4
Why Collider in Future?

• Past polarized DIS experiments in fixed target
  mode
• Assuming highly polarized beams. There are no
  dilution factors as in polarized targets of
  fixed target experiments
• Collider has other 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
Relativistic Heavy Ion Collider
L. Bland, this Conferences
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
An ideal machine for studying QCD!
RHIC accelerates heavy ions to 100 GeV/A and
polarized protons to 250 GeV
6
Proposal 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

• 10 GeV linac e-ring RHIC
• e-ring NOT in RHIC tunnel
• Other options linacRHIC
• Nominal 10 GeV polarized
• electron/positron beams
• -- Collisions with 5 GeV e
• One IR considered so far,
• but plan gt 1 detectors
• Additional detectors and
• IRs not ruled out

7
eRHIC vs. Other DIS Facilities (I)

• 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 70
• Polarized light ion beams He
• Un-polarized heavy ion beams of ALL elements up
  to Uranium with EBIS source
• High Luminosity
• L 1033 cm-2 sec-1

eRHIC
DIS
8
eRHIC 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 at Jlab
• (Electron-Light Ion Collider)
• gtgt Variable beam energy
• gtgt p, d He polarization
• gtgt Huge Luminosity

ELIC-Jlab
TESLA-N
eRHIC
9
Scientific Frontiers Open to eRHIC

• 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 un-polarized 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

10
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 (Transition from QCD
  --gt pQCD)
• -- flavor separation (charm and strangeness)
• -- exclusive reaction measurements
  
• -- nuclear fragmentation region measurements
  

1 1 1 1 1 2 2,3 2,3
Luminosity Requirement
11
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
  1-2 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
12
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
13
Low x measurement of g1 of Neutron
AD, V.W.Hughes

• With polarized He3
• 2 weeks of data at eRHIC
• Compared with
• SMC(past)
• If HERA were to be polarized (now hypothetical)
• 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
BNL/Stony Brook, Caltech, MIT effort for RD on
He beams near future
14
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
• Measurements at eRHIC will be complimentary with
  RHIC and a significant next step compared to the
  fixed target DIS experiments
• 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

Shape of DG(x)
15
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.
• (Recall R. L. Jaffes talk)
• 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
• unknown shape of the PDFs in unmeasured low x
  region where eRHIC data will play a crucial role
• Factorization and renormalization scales (mF
  mR) (G. Ridolfis talk)
• 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 function
• (measurements to x10-4).
• -- less dependence on factorization
  re-normalization scale in fits as new
• data is acquired

16
Photon Gluon Fusion at eRHIC

• Direct determination of DG
• -- Di-Jet events (21)-jet events
• -- High pT hadrons
• (C. Bernet, COMPASS)
• In fixed tgt exp scale uncertainties large
• High Sqrt(s) 100 GeV, 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

Signal PGF
Background QCD Compton
17
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

18
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
19
Photon Spin Structure at eRHIC
M. Stratmann, W. Vogelsang

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

Direct Photon Resolved Photon
20
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
21
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

22
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.

23
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 et al.
24
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
25
DIS in Nuclei is Different!
E665, NMC, SLAC Experiments

• Regions of
• Fermi smearing
• EMC effect
• Enhancement
• Shadowing
• Saturation?
• Regions of shadowing and saturation mostly around
  Q2 1 GeV2
• An e-A collision at eRHIC can be at significantly
  higher Q2

F2D/F2A
Low Q2!
26
The Saturation Region

• As parton densities grow, standard pQCD break
  down.
• Even though coupling is weak, physics may be
  non-perturbative due to high field strengths
  generated by large number of partons.
• A new state of matter???

An e-A collider/detector experiment with high
luminosity and capability to have different
species of nuclei in the same detector would be
ideal ? Need the eRHIC at BNL
27
A Color Glass Condensate??
E. Iancu, L. McLerran,R. Venugopalan, et al.

• At small x, partons are rapidly fluctuating
  gluons interacting weakly with each other, but
  still strongly coupled to the high x parton color
  charges which act as random static sources of
  COLOR charge
• ? Analogous to spin GLASS systems in
  condensed matter a disordered spin state coupled
  to random magnetic impurities
• Gluon occupation number large being bosons they
  can occupy the same state to form a CONDENSATE
• ? Bose Einstein condensate leads to a huge
  over population of ground states
• A new state matter(??) Color Glass Condensate
  (CGC) at high energy density would display
  dramatically different, yet simple properties of
  glassy condensates

28
Interaction Region Design.early ideas
Budker/MIT Proposal
B. Parkers (BNL) Proposal
29
A Possible Lay Out of the Collider at BNL

• Proposed by BNL, MIT/Bates BNL DESY
• E-ring is 1/3 the size of RHIC ring
• Collision energies Ee5-10 GeV
• Injection linac 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
• Two detector designs under consideration

e-cooling
RD needed started
OTHER Ring with 6 IPS, Linac-Ring,
Linac-Re-circulating ring
30
Where do electrons and quarks go?
q,e
?
p
10 GeV x 250 GeV
1770
1600
100
10 GeV
5 GeV
5 GeV
900
scattered electron
scattered quark
31
Electron kinematics some details
10 GeV x 250 GeV

• At HERA
• Electron method Dx/x DE/(y.E)
• Limited by calorimeter resolution
• ?Hadron method
• Limited by noise in calorimeter
• (E_noise/E_beam)
• At eRHIC
• Measure electron energy with
• tracker (lt 20 GeV, large kin. region)
• Dp/p 0.005-0.0001 ?(2-4T Magnet)
• ?Design low noise calorimeter
• ?Crystal or SPACAL

scattered electron
32
Electron, Quark Kinematics
q,e
?
5 GeV x 50 GeV
p
scattered electron
scattered quark
33
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
• Presently interest in at least one other
  specialized detector how to?
• under consideration
• eRHIC will provide 1) Variable beam energies 2)
  different hadronic species, some of them
  polarization, 3) high luminosity

34
Detector Design (I) others expected
Whitepaper 2001/2
35
Detector Design (I) others expected
Whitepaper 2001/2
36
Detector Design II --- HERA like
Hadronic Calorimeter
Outer trackers
5m
2.5m
Inner trackers
EM Calorimeter
Nearest beam elements 1m
37
Detector Design II HERA like PID
A. Deshpande, N. Smirnov
HCAL
EMCal
Solenoid
AEROGEL
TOF
A HERA like Detector with dedicated PID gtgtTime
of flight gtgtAerogel Ckov
Beam elements
7m
P/A
e
Inner trackers
5m
Outer trackers
38
Moving Towards eRHIC.

• September 2001 eRHIC 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, US-HERMES
  collaborators
• Steering Committee 8 members, one each from BNL,
  IUCF, LANL,MIT, UIUC, Caltech, JLAB, Kyoto U.
  Stony Brook
• 20 (13 US 7 non-US) Institutes, 100
  physicists 40 accelerator physicists Recent
  interest from HERA (low x, low Q2 physics)
• 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!

39
Present Activities

• Accelerator IR Design WG
• BNL-MIT/Bates collaboration on e-ring design
• BNL-JLAB collaboration on linac design
• Weekly meetings, monthly video meetings
• Synchroton radiation in IR focus group BNL, Iowa
  State U.
• ZDR Ready by February 2004 External Review
  March04
• Physics MC WG
• BNL, Colorado U., Jlab, LBL, MIT, UIUC
  (scientists/facultystudents)
• Meet every three months
• Setup MC generators start studies of physics
  processes including detector acceptances
• Will iterate with the detector/IR design and
  provide guidance on the final detector design
• Detector Design Will be taken up in detail in
  the coming year
• Basic functionality of ZEUS/H1 detectors adjusted
  for different energy
• Additional acceptances in forward backward
  region (low Q2, low x)
• Specialized particle ID for lower center of mass
  energy physics
• Integration of electron beam polarimetry in the
  IR
• Selection of detector technology coupled to the
  interests of various institutions
• Meetings 2004 January (BNL), March 15-17 at Jlab
  (EIC2004), Fall 2004(?), December(BNL)

40
A possible time line for eRHIC

• 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
• One of the 28 must-do science projects by US DoE
  in the next 20 years
• eRHIC Zero-th Design Report (Physics
  Accelerator Lattice)
• ? Requested by BNL Management Ready February
  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 design studies could start for hardware
  2008 (CD1) (DoE now?)
• Ring, IR, Detector design(s) ready 2009(CD2)
• Final Design Ready 2010 (CD3) ? begin
  construction
• 2--gt 5 years for staged detector and IR
  construction without interfering with the RHIC
  running
• First collisions with limited detector
  (2012/13)???