Transcript Document

Physics & Status of eRHIC
A
Workshop on Hadron Structure & Spectroscopy
Compass 2004, Paris
March 3, 2004
Abhay Deshpande
Stony Brook University
RIKEN BNL Research Center
Some spin & Low x-high Q2 surprises…
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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)
>> single spin neutron production(PHENIX)
>> pion production (STAR) at 200 GeV Sqrt(S)
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Elastic e-p scattering at SLAC (1950s)
 Q2 ~ 1 GeV2  Finite size of the
proton
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Inelastic e-p scattering at SLAC
(1960s) Q2 > 1 GeV2  Parton
structure of the proton
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Inelastic mu-p scattering off p/d/N at
CERN (1980s)  Q2 > 1 GeV2 
Unpolarized EMC effect, nuclear
shadowing?
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Inelastic e-p scattering at HERA/DESY
(1990s) Q2 > 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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Deep Inelastic Scattering
[1]
[2]
[3]
•Observe scattered electron/muon
[1]
•Observe spectator or remnant jet
[1]+[2]
•Obersve current jet as well
[1]+[2]+[3]
Lumi
>> suitably designed detector…
[1]+[2]+[3]  exclusive
[1]+[2]
 semi-inclusive
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[1]
 inclusive
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
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Tricky integration of beam pipe – interaction region -- detector
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L. Bland, this Conferences
Relativistic Heavy Ion Collider
RHIC pC Polarimeters
BRAHMS & PP2PP (p)
Absolute Polarimeter
(H jet)
Lmax  2 1032 s 1cm 2
70% Polarizati on
PHENIX (p)
50 
s  500 GeV
STAR (p)
Siberian Snakes
Spin Rotators
Partial Siberian Snake
LINAC
BOOSTER
Pol. Proton Source
500 mA, 300 ms
2  1011 Pol. Protons / Bunch
e = 20 p mm mrad
AGS
200 MeV Polarimeter
AGS Internal Polarimeter
Rf Dipoles
RHIC accelerates heavy ions to 100 GeV/A
and polarized protons to 250 GeV
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An ideal machine for
studying QCD!
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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 RHIC’s ability to
probe fundamental and universal aspects of QCD
•10 GeV linac + e-ring + RHIC
•e-ring NOT in RHIC tunnel
• Other options: linac+RHIC
• Nominal 10 GeV polarized
electron/positron beams:
-- Collisions with 5 GeV e
• One IR considered so far,
but plan > 1 detectors
Additional detectors and
IRs not ruled out
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eRHIC vs. Other DIS Facilities (I)
• Ee = 5-10 GeV
• Ep = 30 – 250 GeV
• Sqrt(s) = ~25 – 100 GeV
eRHIC
• Kinematic reach of eRHIC
x = 10-4  ~0.7 (Q2 > 1 GeV2)
Q2 = 0  104 GeV
• Polarized e, p ~70%
• Polarized light ion beams: He
DIS
• Un-polarized heavy ion beams of
ALL elements up to Uranium with
EBIS source
• High Luminosity
L ~ 1033 cm-2 sec-1
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eRHIC vs. Other DIS Facilities
eRHIC:
ELIC-Jlab
TESLA-N
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Variable beam energy
p  U hadron beams
Light Ion polarization
Large Luminosity
Huge Kinematic reach
eRHIC
ELIC at Jlab:
(Electron-Light Ion
Collider)
>> Variable beam energy
>> p, d & He polarization
>> Huge Luminosity
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Scientific Frontiers Open to eRHIC
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Nucleon Structure: polarized & unpolarized e-p/n scattering
-- Role of quarks and gluons in the nucleon
>> Unpolarized quark & gluon distributions, confinement in nucleons
>> Spin structure: polarized quark & gluon distributions
-- Correlation between partons
>> hard exclusive processes leading to Generalized Parton Distributions (GPD’s)
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Meson Structure:
-- Mesons are goldstone bosons and play a fundamental role in QCD
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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
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Hadronization in nucleons and nuclei & effect of nuclear media
-- How do partons knocked out of nucleon in DIS evolve in to colorless hadrons?
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Partonic matter under extreme conditions
-- e-A vs. e-p scattering; study as a function of A
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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)
[1]
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precision measurement of aS(Q2)
precision photo-production physics
precision gluon distribution in x=0.001 to x=0.6
slopes in dF2/dlnQ2 (Transition from QCD --> pQCD)
flavor separation (charm and strangeness)
exclusive reaction measurements
nuclear fragmentation region measurements
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[1]
[1]
[1]
[1]
[2]
[2,3]
[2,3]
Luminosity
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Requirement
Polarized DIS at eRHIC
[1]
• 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)
[1]
-- at least three different experimental methods
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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)
>> Gerneralized Parton Distributions (GPDs)
Transversity
Drell-Hern-Gerasimov spin sum rule test at high n
Target/Current fragmentation studies
… etc….
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[1]
[1]
[1,2]
[1]
[1,2]
[3]
[1]
[1]
[2,3]
Luminosity
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Requirement
AD, V.W.Hughes
Proton g1(x,Q2) low x eRHIC
Fixed target experiments
1989 – 1999 Data
eRHIC 250 x 10 GeV
Luminosity = ~85 inv. pb/day
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 12
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experiment will be able to make this measurement
AD, V.W.Hughes
Low x measurement of g1 of Neutron
• With polarized He3
• ~ 2 weeks of data at eRHIC
• Compared with:
EIC 1 inv.fb
– 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
BNL/Stony Brook, Caltech, MIT effort for R&D on He beams near future
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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
• 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
Shape of DG(x)
-- (2+1) jet production in photon-gluon-fusion process 
-- 2-high pT hadron production in PGF
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• Photo-production (real photon) kinematics at eRHIC
-- Single and di-jet production in PGF
-- Open charm production in PGF
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AD, V.W.Hughes, J.Lichtenstadt
DG from Scaling Violations of g1
• 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. Jaffe’s 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. Ridolfi’s 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 x=10-4).
-- less dependence on factorization & re-normalization scale in fits
as new
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data is acquired
Photon Gluon Fusion at eRHIC
Signal: PGF
• “Direct” determination of DG
-- Di-Jet events: (2+1)-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
Background
QCD Compton
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• Both methods tried at HERA in unpolarized gluon determination &
both are successful!
-- NLO calculations exist
-- H1 and ZEUS results
-- Consistent with scaling
violation F2 results on G
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G. Radel & A. De Roeck,
AD, V.W.Hughes,J.Lichtenstadt
Di-Jet events at eRHIC: Analysis at NLO
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Stat. Accuracy for two
luminosities
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Detector smearing
effects considered
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NLO analysis
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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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Polarized PDFs of the Photons
• Photo-production studies with single and di-jet
Direct Photon
Resolved Photon
• 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!
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M. Stratmann, W. Vogelsang
Photon Spin Structure at eRHIC
• Stat. Accuracy
estimated for
1 fb-1 running
(2 weeks at eRHIC)
• Single and double jet
asymmetries
• ZEUS acceptance
• Will resolve photon’s
partonic spin
contents
Direct Photon
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Resolved Photon
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Parity Violating Structure Function g5
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This is also a test
• Experimental signature is a huge
asymmetry in detector (neutrino)
• Unique measurement
• Unpolarized xF3 measurements For eRHIC kinematics
at HERA in progress
• Will access heavy quark
distribution in polarized DIS
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J. Contreras, A. De Roeck
Measurement Accuracy PV g5 at eRHIC
Assumes:
1.
Input GS Pol. PDfs
2.
xF3 measured by
then
3.
4 fb-1 luminosity
Positrons & Electrons in
eRHIC  g5(+)
>> reason for keeping
the option of
positrons in eRHIC
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U. Stoesslein, E. Kinney
Strange Quark Distributions at eRHIC
• 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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DVCS/Vector Meson Production
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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.
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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 > [1/(2mNRN) ] ~ 0.1
(high x)
QCD in: [1/(2mNRA)] < x < [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 < [1/(2mNRA)] ~ 0.01
(low x)
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See: www.bnl.gov/eic for further details
E665, NMC, SLAC Experiments
DIS in Nuclei is Different!
F2D/F2A
Regions of:
• Fermi smearing
• EMC effect
• Enhancement
• Shadowing
• Saturation?
Regions of shadowing and
saturation mostly around Q2
~1 GeV2
Low Q2!
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An e-A collision at eRHIC can be
at significantly higher Q2
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The Saturation Region…
• As parton densities grow,
standard pQCD break down.
• Even though coupling is
weak, physics may be nonperturbative 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
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E. Iancu, L. McLerran,R. Venugopalan, et al.
A Color Glass Condensate??
• 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
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Interaction Region Design….early ideas…
Budker/MIT Proposal
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B. Parker’s (BNL) Proposal
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A Possible Lay Out of the Collider at BNL
10GeV
e
5-10 GeV
IP12
IP10
p
IP2
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RHIC
IP8
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Proposed by BNL, MIT/Bates + BNL + DESY
E-ring is 1/3 the size of RHIC ring
Collision energies Ee=5-10 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
IP4
IP6
e-cooling
R&D needed & started
OTHER : Ring with 6 IPS, Linac-Ring,
Linac-Re-circulating ring
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Where do electrons and quarks go?
q,e
10 GeV x 250 GeV

p
1770
1600
100
10 GeV
5 GeV
5 GeV
scattered electron
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scattered quark
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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)
scattered electron
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At eRHIC:
Measure electron energy with
tracker (< 20 GeV, large kin. region)
Dp/p ~ 0.005-0.0001 (2-4T Magnet)
Design low noise calorimeter
Crystal or SPACAL
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Electron, Quark Kinematics
p
scattered electron
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
q,e
5 GeV x 50 GeV
scattered quark
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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
• 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
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Whitepaper 2001/2
Detector Design (I)… others expected
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Whitepaper 2001/2
Detector Design (I)… others expected
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Detector Design II --- HERA like…
Hadronic Calorimeter
5m
Outer trackers
2.5m
EM Calorimeter
Inner trackers
Nearest beam elements 1m
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A. Deshpande, N. Smirnov
Detector Design II: HERA like…+ PID
HCAL
EMCal
Solenoid
AEROGEL
TOF
Beam elements
7m
P/A
e
Inner
trackers
5m
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Outer trackers
A HERA like
Detector with
dedicated PID:
>>Time of flight
>>Aerogel Ckov
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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!
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Present Activities
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Accelerator & IR Design WG:
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Physics & MC WG:
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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
BNL, Colorado U., Jlab, LBL, MIT, UIUC (scientists/faculty+students)
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
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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)
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A possible time line for eRHIC…
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“Absolutely Central to the field…” NSAC 2001-2 Long Range Planning
document summary; high on R&D 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
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eRHIC: Zero-th Design Report (Physics + Accelerator Lattice)
 Requested by BNL Management: Ready February 2004.
 e-cooling R&D money started (with RHIC II) some DOE+some 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--> 5 years for staged detector and IR construction without interfering
with the RHIC running
• First collisions with limited detector (2012/13)???
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