Electron Ion ColliderA. Accardi, R. Ent, V. Guzey, Tanja Horn, C. Hyde,
A. Prokudin, P. Nadel-Turonski, C. Weiss, …
+ CASA/accelerator team
LRP 2007 JLab User Workshops 2010
INT10-3 program EIC White PaperEIC half recommendation
>500 pages Under construction
EIC: Probing the Sea Quarks and EIC: Probing the Sea Quarks and GluonsGluons
Tanja Horn, Electron Ion Collider, JLab Strategic Planning 2011 2
Why care about sea quarks and gluons
• Structure of proton7̶ Naïve quark model: proton==uud (valence quarks)
7̶ QCD: proton == uud + + + + …
7̶ Proton sea has a non-trivial structure and
Proton is far more than just its up + up+down (valence) quark structure
• QCD and Origin of Mass7̶ 99% of the proton mass/energy is due to the self-
generating gluon field
o Higgs mechanism has almost no role there
7̶ Similarity of mass between proton/neutron arises from fact that gluon dynamics are the same
o Quarks contribute almost nothing
uuu
d
dd ss
valence quarks/gluons
sea quarks/gluonsradiative gluons/sea
• Hadrons in QCD are relativistic many-body systems
– Fluctuating number of elementary quark and gluon constituents
– Rich structure of the wave function
Internal Landscape of the NucleonInternal Landscape of the Nucleon
• Key physical interests– Transverse spatial distribution – Correlations: transverse, longitudinal,
and nuclear modifications– Tests of reaction mechanism
• Components probed in ep scattering:– JLab 12 GeV: valence region– EIC: probes sea quark and gluon
components
3
Q2 ~ xys
Accessible range of energies and resolution, Q2, for probing components of the hadron wave function
Why an Electron-Ion Collider?Why an Electron-Ion Collider?
Tanja Horn, Electron Ion Collider, JLab Strategic Planning 2011 4
• Easier to reach high Center of Mass energies ( )– for colliders (e.g., 4 x 10 x 100=4000 GeV2)
– for fixed target experiments (e.g., 2 x 11 x 0.938=20 GeV2)
sECM 2
peEEs 4
peMEs 2
• Spin physics with high Figure Of Merit (FOM)– Unpolarized FOM = Rate = Luminosity x Cross Section x Acceptance
– Polarized FOM = Rate x (Target Polarization)2 x (Target Dilution)2
– No dilution and high ion polarization (also transverse)
– No current (luminosity) limitations, no holding fields (acceptance)
– No backgrounds from target (Moller electrons)
• Easier detection of reaction products– Can optimize kinematics by adjusting beam energies
– More symmetric kinematics improve acceptance, resolution, particle ID, etc.
– Access to neutron structure with deuteron beams ( )
Target fdilution,
fixed_target
Pfixed_target f2P2fixed_target f2P2
EIC
p 0.2 0.8 0.03 0.5
d 0.4 0.5 0.04 0.5
0pp
Science of an EIC: Explore and Understand Science of an EIC: Explore and Understand QCDQCD
5
• Map the spin and spatial quark-gluon structure of nucleons7̶ Image the 3D spatial distributions of gluons and sea quarks through exclusive J/Ψ, γ (DVCS) and
meson production
7̶ Measure ΔG, and the polarization of the sea quarks through SIDIS, g1, and open charm production
7̶ Establish the orbital motion of quarks and gluons through transverse momentum dependent observables in SIDIS and jet production
• Discover collective effects of gluons in nuclei7̶ Explore the nuclear gluon density and coherence in shadowing through
e + A → e‘ + X and e + A → e‘ + cc + X
7̶ Discover novel signatures of dynamics of strong color fields in nuclei at high energies in e + A → e’ + X(A) and e + A → e’ + hadrons + X
7̶ Measure gluon/quark radii of nuclei through coherent scattering γ* + A → J/Ψ + A
• Understand the emergence of hadronic matter from quarks and gluons− Explore the interaction of color charges with matter (energy loss, flavor dependence, color
transparency) through hadronization in nuclei in e + A → e' + hadrons + X
− Understand the conversion of quarks and gluons to hadrons through fragmentation of correlated quarks and gluons and breakup in e + p → e' + hadron + hadron + X
[INT10-3 2010]
Needs high luminosity and range of energies
3D partonic picture of the nucleon
Information about 3D partonic picture is encoded in Generalized Parton Distributions and Transverse Momentum Dependent Distributions
TransverseMomentum Dependentdistributions
GeneralizedParton Distributions
Wigner distribution
SIDIS DES
J/Ψ, φ
Transverse Spatial Imaging through Transverse Spatial Imaging through
GPDsGPDs
Tanja Horn, Electron Ion Collider, JLab Strategic Planning 2011
Mesons select definite charge, spin, flavor component of GPD
EIC enables a comprehensive program of transverse imaging of gluons and sea quarks
pointlike? π, ρ, K, K*
Λ, Σ
γ
BMN *
√s~140 GeV
d+d
dd=ALU
√s~30 GeV
ep → e'π+n
~100 days, ε=1.0, L=1034 s-1cm-2
ep → e'K+Λ
[Geraud, Moutarde, Sabatie 10+, INT10-3 report]
[Horn et al. 08+, INT10-3 report]
EIC: singlet quark size from deeply virtual compton scattering
EIC: Imaging of strange sea quarks!
EIC: Gluon size from J/ and electroproduction (Q2 > 10 GeV2)
40<W2<60 GeV2
[Weiss INT10-3 report]
80<W2<100 GeV2
-t (GeV2)
Cro
ss s
ectio
n
3<Q2<6 GeV2
1.6E-3 < xB < 2.5E-3
√s~140 GeV
~30 days, L=1034 s-1cm-2
√s~30 GeV
~100 days, ε=1.0, L=1034 s-1cm-2
-t (GeV2)
Only a small subset of the (x,Q2) landscape has been mapped here:
terra incognitaGray band: present “knowledge” of TMDs with current experimental data
Dark gray band: EIC (1)
Exact kT distribution presently poorly known!Mapping of kT distribution is crucial to our understanding of interplay of collinear and 3D partonic pictures
[Prokudin, Qian, Huang]
An EIC with good luminosity & high transverse polarization is the optimal tool to study this!
Image the Transverse Momentum of the Quarks
[Prokudin, Qian, Huang]
3D partonic picture is encoded in TMDs
Nucleon Structure: Orbital
MotionGoal: explore quark/gluon orbital motion and its polarization dependence through both deep exclusive and semi-inclusive multi-dimensional processes
Can we learn about orbital motion from a comprehensive approach based on TMDs, GPDs, etc., even if model-dependent?
Potential new insight from jets or p’T of target fragmentation?
EIC: wide kinematic range low to high pT
Gluons in Nuclei
NOTHING!!!
What do we know about gluons in a nucleus?
Ratio of gluons in lead to deuterium
• EIC: access gluons through FL (needs variable energy) and dF2/dln(Q2)
• Knowledge of gluon PDF essential for quantitative studies of onset of saturation
Hadronization: Parton propagation in matter
EIC: Explore the interaction of fast color charges with matter
pT2 vs. Q2
-Time scales for color neutralization tCN and hadron formation tF
- eA/A complementary to jets in AA: cold vs. hot matter
EIC: Understand the conversion of color charge to hadrons through fragmentation and breakup
[Accardi, Dupre INT10-03 Report]
Le
e’*
+
pT
pT2 = pT
2(A) – pT2(2H)
Comprehensive studies possible:• wide range of energy v = 10-100 GeV move hadronization inside/outside nucleus, distinguish energy loss and attenuation• wide range of Q2: QCD evolution of fragmentation functions and medium effects• Hadronization of charm, bottom Clean probes with definite QCD predictions• High luminosity Multi-dimensional binning and correlations• √s > 30: jets and their substructure in eA
C. Weiss
s
• For large or small y, uncertainties in the kinematic variables become large
Range in yQ2 ~ xys
Range in s
Range of kinematics
• Detecting only the electron ymax
/ ymin
~ 10
• Also detecting all hadrons ymax
/ ymin
~ 100
– Requires hermetic detector (no holes)
• Accelerator considerations limit smin
– Depends on smax
(dynamic range)
• At fixed s, changing the ratio Ee / E
ion can for
some reactions improve resolution, particle identification (PID), and acceptance
C. WeissC. Weiss
valence quarks/gluons
non-pert. sea quarks/gluons
radiative gluons/sea
[Weiss 09]
s
To cover the physics we need…To cover the physics we need…
12
Vacuum fluct.
pQCD radiation
EIC: Critical EIC: Critical CapabilitiesCapabilities
But we get there in different ways:Input passed on to INT10-03 program:
• Base EIC Requirements per Executive Summary INT Report:• range in energies from √s ~ 20 to √s ~ 70 & variable• fully-polarized (>70%), longitudinal and transverse• ion species up to A = 200 or so• high luminosity: about 1034 e-nucleons cm-2 s-1
• multiple interaction regions• upgradable to higher energies (√s ~ 150 GeV)
Proton Energy (GeV)
Lu
min
osi
ty (
x10
32)
eRHIC-1, Ee=5 GeV
Ee=5 GeV
Ee=10 GeV
14
Exclusive Meson Production
√s=31.6 GeV √s=44.7 GeV √s=100GeV
Mom
entu
m (
GeV
/c)
Mom
entu
m (
GeV
/c)
Mom
entu
m (
GeV
/c)
Lab Scattering angle (rad) Lab Scattering angle (rad) Lab Scattering angle (rad)
Q2 > 10 GeV2 → events of interest for imaging studies
Exclusive measurements at very high CM energy require detection of high energy mesons over a very small angular range
Best momentum resolution for symmetric or nearly symmetric collisions
Ep = 250 GeVEp = 30 GeV
Δθ=1-2˚ Δθ<0.3˚
Better t-resolution with lower proton energy and more symmetric kinematics
Nuclear Science: Map t between tmin and 1 (2) GeV2
Must cover between 1-5 deg Should cover between 0.5-5 deg Like to cover between 0.2-7 deg
t ~ Ep22 Angle recoil baryons = t½/Ep
[Horn 08+, INT10-3 report]
e- Beamp/A Beam
solenoid
electron FFQs50 mrad
0 mrad
ion dipole w/ detectors
ions
electrons
IP
ion FFQs
2+3 m 2 m 2 m
• Detect particles with angles below 0.5o.
detectors
Central detector
EM
Ca
lorim
ete
r
Ha
dro
n C
alo
rime
ter
Mu
on
De
tect
or
EM
Ca
lorim
ete
r
Solenoid yoke + Muon DetectorTOF
HT
CC
RIC
H
RICH or DIRC/LTCC
Tracking
2m 3m 2m
4-5m
Solenoid yoke + Hadronic Calorimeter • Very-forward detector, Large dipole bend @ 20 meter from IP allows for very-small angle detection (<0.3o)
MEIC: FullFull Acceptance Detector
7 meters
• Detect particles with angles down to 0.5o. Need 1-2 Tm dipole.
GEANT4 model
EIC: Design ParametersEIC: Design Parameters Base EIC Requirements per Executive Summary INT Report:
• highly polarized (>70%) electron and nucleon beams- longitudinally polarized electron and nucleon beams- transversely polarized nucleon beams
• ion species from deuterium to A = 200 or so• center of mass energies from √s ~ 20 to √s ~ 70 GeV & variable
- electron energies above 3 GeV to allow efficient electron trigger- proton energy adjustable to optimize particle identification
• upgradeable to center of mass energy of about √150 GeV• high luminosity ~1034 e-nucleons cm-2 s-1
- optimal luminosity in √s ~ 30-50 region- luminosity ≥1033 e-nucleons cm-2 s-1 in √s ~ 20-70 region
• multiple interaction regions• integrated detector/interaction region
- non-zero crossing angle of colliding beams- crossing in ion beam to prevent synchrotron background- ion beam final focus quads at ~7 m to allow for detector space- bore of ion beam final focus quads sufficient to let particles pass through up to
t ~ 2 GeV2 (t ~ Ep2Q2)
• positron beam desirable16
MEIC : Medium Energy
EICUse CEBAF “as-is” after the 12-GeV Upgrade
polarimetry
low-energy IP
medium-energy IPs
Three compact rings:• 3 to 11 GeV electron• Up to 12 GeV/c proton (warm)• Up to 100 GeV/c proton (cold)
Proton Energy (GeV)
Lu
min
osi
ty (
x10
32)
eRHIC-1, Ee=5 GeV
Ee=5 GeV
Ee=10 GeV
EIC Realization Imagined
Activity Name 2010 2011 2012 2013 2014 2015 2016 2017 2018 2019 2020 2021 2022 2023 2024 2025
12 Gev Upgrade
FRIB
EIC Physics Case
NSAC LRP
EIC CD0
EIC Machine Design/R&D
EIC CD1/Downsel
EIC CD2/CD3
EIC Construction
Note: 12 GeV LRP recommendation in 2002 – CD3 in 2008
(Mont@INT)
19
SummarySummary
• Collider environment provides tremendous advantages – polarization
– Target fragmentation
• EIC is needed to completely understand nucleon structure and the role of gluons in nuclei
• EIC is a mature project– Designs ongoing at JLab and BNL
– White paper for next LRP under construction
– Accelerator R&D funds have been allocated
– Joint detector R&D projects have started
• EIC is the ultimate tool to study sea quarks and gluons– Sea quarks and gluons play a prominent role in nucleon structure