Transcript "GPD/TMD Studies with a Future Electron-Ion Collider"

GPD/TMD Studies with a
Future Electron-Ion Collider
Rolf Ent, INT, September 18, 2009
Nuclear Science Goals: How do we understand the visible matter in
our universe in terms of the fundamental quarks and gluons of QCD?
 Explore the structure of the nucleon
(it’s what we are made of)
• Electron-Ion Collider: Status & Current Ideas
• Inclusive DIS Measurement Projections
• Semi-Inclusive DIS Measurement Projections
• Deep Exclusive Measurement Projections & Kinematics
• Summary
EIC science has evolved from new insights
and technical accomplishments over the
last decade or so
•
•
•
•
•
•
•
~1996 development of Generalized Parton Distributions
~1999 high-power energy recovery linac technology
~2000 universal properties of strongly interacting glue
~2000 emergence of transverse-spin phenomenon
~2001 world’s first high energy polarized proton collider
~2003 tantalizing hints of saturation
~2006 electron cooling for high-energy beams
Many recent and ongoing developments: constraints on gluon
polarization, 1st successful test of crab cavities, development of
semi-inclusive DIS framework at NLO, 2nd round of deep exclusive
measurements, Lattice QCD progress, etc., etc.
NSAC 2007 Long-Range Plan
“An Electron-Ion Collider (EIC) with
polarized beams has been embraced
by the U.S. nuclear science
community as embodying the vision
for reaching the next QCD
frontier. EIC would provide unique
capabilities for the study of QCD
well beyond those available at
existing facilities worldwide and
complementary to those planned for
the next generation of accelerators
in Europe and Asia. In support of
this new direction:
We recommend the allocation of
resources to develop accelerator
and detector technology necessary
to lay the foundation for a
polarized Electron Ion Collider.
The EIC would explore the new
QCD frontier of strong color
fields in nuclei and precisely image
the gluons in the proton.”
Why an Electron-Ion Collider?
• Longitudinal and Transverse Spin Physics!
- 70+% polarization of beam and target without dilution
- transverse polarization also 70%!
• Detection of fragments far easier in collider environment!
- fixed-target experiments boosted to forward hemisphere
- no fixed-target material to stop target fragments
- access to neutron structure w. deuteron beams (@ pm = 0!)
• Easier road to do physics at high CM energies!
- Ecm2 = s = 4E1E2 for colliders, vs. s = 2ME for fixed-target
 4 GeV electrons on 60 GeV protons ~ 500 GeV fixed-target
- Easier to produce many J/Y’s, high-pT pairs, jets, etc.
- Easier to establish good beam quality in collider mode
Longitudinal polarization FOM
Target
p
d
fdilution,
Pfixed_target
f2P2fixed_target
f2P2EIC
0.2
0.8
0.03
0.5
0.4
0.5
0.04
0.5
fixed_target
Current Ideas for a Collider
Design Goals for Colliders Under Consideration World-wide
Energies
s
luminosity
ENC@GSI
Up to 3 x 15
180
Few x 1032
(M)EIC@JLab
Up to 11 x 60
150-2650
Few x 1034
Staged
MeRHIC@BNL
Up to 4 x 250
(400-)4000
Close to 1033
Future
ELIC@JLab
Up to 11 x 250
11000
Close to 1035
eRHIC@BNL
Up to 20 x 325
26000
Few x 1033
LHeC@CERN
Up to 70 x 1000
280000
1033
Some of the slides are for a “generic” US version of an EIC:
• polarized beams (longitudinal and transverse, > 70%)
• luminosities of at least 1033
• energies up to 10 x 250, or s = 10000
Present focus of interest (in the US) are the (M)EIC and
Staged MeRHIC versions, with s up to 2650 and 4000, resp.
4 GeV e x 250 GeV p – 100 GeV/u Au
MeRHIC
2 x 60 m SRF linac
s = (400-) 4000
3 passes, 1.3 GeV/pass
Polarized e-gun
Beam dump
3 pass
4 GeV
ERL
MeRHIC
Medium Energy eRHIC
STAR
V.N. Litvinenko, RHIC S&T Review, July 23, 2009
@ IP2 of RHIC
Up to 4 GeV e- x 250 GeV p
L ~ 1032-1033 cm-2 sec -1
90% of hardware can be reused
A High-Luminosity (M)EIC at JLab
(M)EIC
Coverage
Legend:
MEIC = EIC@JLab
1 low-energy IR (s ~ 200)
3 medium-energy IRs
(s < 2600)
ELIC = high-energy EIC@JLab
(s = 11000)
(limited by JLab site)
Use CEBAF “as-is” after 12-GeV Upgrade
s ~ 2500 sufficient to transcend into
region of large rise of gluon density
Approximate
staged EIC
coverage
Electron-Ion Collider – further info
• EIC (eRHIC/ELIC) webpage: http://web.mit.edu/eicc/
• Upcoming meeting: January 10-12, 2010 @ Stony Brook
• 2nd joint BNL/JLab EIC Advisory Committee meeting:
November 2 + 3, 2009 (@JLab)
• Week-long meeting at the INT, intermixed with the
ongoing JLab 12-GeV program: Oct. 19-23
(dedicated to physics of staging options)
2010: long INT program dedicated to science @ EIC
• Weekly meetings at both BNL and JLab
• Series of topical workshops planned in 2010
Where does the spin of the proton
originate?
Input from DIS, SIDIS, pp (RHIC)
and Global Fits…
De Florian, Sassot, Stratmann and Vogelsang,
Phys. Rev. Lett. 101, 072001 (2008)
DG < 0.1?
(constrained in narrow region of x only)
Where does the spin of the proton
originate?
Generalized Parton Distributions provide access to total quark contribution to
proton angular momentum in (deep) exclusive processes: e + N  e’ + N + X
½ = Jq + Jg = ½ DS + Lq + Jg
e
k
H(x,x,t), E(x,x,t), . .
“Generalized Parton Distributions”
Accessible through deep exclusive
reactions (and Lattice QCD)
k'
*

q
q'
p
p'
Quark angular momentum (Ji’s sum rule)
1

1
1
J q   J g   xdx H q ( x, x ,0)  Eq ( x, x ,0)
2
2 1

X. Ji, Phy.Rev.Lett.78,610(1997)
Where does the spin of the proton
originate?
(disconnected diagrams not yet included)
… and input from Lattice QCD on
GPD moments (also from deep
exclusive scattering)
LHPC Collaboration,
Phys. Rev. D77, 094502 (2008)
Lu and Ld separately quite
substantial (~0.15), but cancel
(polarized) e-p at medium energies
• Exclusive processes and GPDs
– Deeply-Virtual Meson Production: spin/flavor/spatial quark structure
(Q2 ~ 10 GeV2)
– DVCS: helicity GPDs, spatial quark and gluon imaging
• Charm as direct probe of gluons
– J/ψ, exclusive: spatial distribution of gluons
– D Λc, open charm (including quasi-real D0 photoproduction for ΔG)
• Semi-inclusive DIS
– Flavor decomposition: q ↔ q, u ↔ d, strangeness s, s
– TMDs: spin-orbit interactions from azimuthal asymmetries, pT
dependence
– Target fragmentation and fracture functions
• Inclusive DIS
– ΔG and Δq+Δq from global fits (+ RHIC-spin, COMPASS, JLab 12 GeV)
– Neutron structure from spectator tagging in D(e,e’p)X
Luminosity Considerations for EIC
• Luminosity of 1x1033 cm-2 sec-1
eRHIC: x =
10-4 @ Q2 = 1
ELIC : x =
10-4 @ Q2 = 1
12 GeV: x = 4.5x10-2 @ Q2 = 1
• One day  50 events/pb
• Supports Precision Experiments
Q2 (GeV2)
Lower value of x scales as s-1
• DIS Limit for Q2 > 1 GeV2 implies
x down to 1.0 times 10-4
• Significant results for 200
events/pb for inclusive scattering
• If Q2 > 10 GeV2 required for Deep
Exclusive Processes can reach x
down to 1.0 times 10-3
eRHIC,
ELIC
(W2 > 4)
W2<4
x
Include low-Q2 region
• Typical cross sections factor 1001,000 smaller than inclusive
scattering
• Significant results for 20,000200,000 events/pb  high
luminosity essential
Staging example: s ~ 1000  x = 1.0x10-3@Q2=1
The Gluon Contribution to the Proton Spin
(Antje Bruell, Abhay Deshpande, RE)
at small x
Superb sensitivity
to Dg at small x!
Example for s = 4200
The Gluon Contribution to the Proton Spin
Dg/g
(Antje Bruell, RE)
Projected data on Dg/g with an
EIC, via  + p  D0 + X
K- + p+
assuming vertex separation of 100 mm.
Advantage: measurements
directly at fixed Q2 ~ 10
GeV2 scale!
• Uncertainties in xDg smaller than 0.01
• Measure 90% of DG (@ Q2 = 10 GeV2)
RHIC-Spin
Access to Dg/g is also possible from the g1p measurements
through the QCD evolution, and from di-jet measurements.
Flavor Decomposition @ EIC
10
5 on 50
250EIC
EICprojected
projecteddata
data
quark polarization Dq(x)
first 5-flavor separation
Du > 0
100 days
at 1033
Dd < 0
Lower x ~ 1/s
5 on 50 
s = 1000
10 on 250 
s = 10000
(Ed Kinney,
Joe Seele)
-3
10
10-3
-2
10
10-2
10
10-1-1 xx
Bj
Bj
Precisely image the sea quarks
Spin-Flavor Decomposition of the Light Quark Sea
| p
>
u
=
u
+
u
d
u
d
RHIC-Spin region
u
u
u
+
u
d
d
d
+ … Many models
predict
Du > 0, Dd < 0
100 days at 1033
100 days at 1033
New Spin Structure Function: Transversity
dq(x) ~
(in transverse
basis)
-
• Nucleon’s transverse spin content
 “tensor charge”
• No transversity of Gluons in
Nucleon  “all-valence object”
• Chiral Odd  only measurable in
semi-inclusive DIS
 first glimpses from HERMES
 COMPASS 1st results: ~0 @ low x
 valence region only?
 Future: Flavor decomposition
(started by Anselmino et al.)
Need (high) transverse ion polarization
(Naomi Makins, Ralf Seidl)
Correlation between Transverse Spin and
Momentum of Quarks in Unpolarized Target
(Harut Avakian, Antje Bruell)
All Projected Data
Perturbatively
Calculable at
Large pT
Assumed
100 days
of 1035
luminosity
Vanish like
1/pT (Yuan)
ELIC
Sivers effect: Pion electroproduction
(Harut Avakian)
GRV98, Kretzer FF (4par)
S. Arnold et al
arXiv:0805.2137
M. Anselmino et al
arXiv:0805.2677
GRV98, DSS FF (8par)
•EIC measurements at small x will pin down sea contributions to Sivers function
Sivers effect: Kaon electroproduction
(Harut Avakian)
EIC
CLAS12
•At small x of EIC Kaon relative rates higher, making it ideal place to study
the Sivers asymmetry in Kaon production (in particular K-).
•Combination with CLAS12 data will provide almost complete x-range.
Sivers effect: sea contributions
(Harut Avakian)
GRV98, DSS FF
M. Anselmino et al
arXiv:0805.2677
GRV98, Kretzer FF
S. Arnold et al
arXiv:0805.2137
•Negative Kaons most sensitive to sea contributions.
•Biggest uncertainty in experimental measurements (K- suppressed at large x).
SIDIS – kT Dependence
Final transverse momentum of the
detected pion Pt arises from convolution
of the struck quark transverse momentum
kt with the transverse momentum
generated during the fragmentation pt.
Pt = pt + z kt
+ O(kt2/Q2)
Linked to framework of Transverse
Momentum Dependent Parton Distributions
This workshop (Anselmino):
Get rid of convolution by measuring jets
 Map kt dependence directly
Sets a lower threshold in s:
Assume jet requires 50 GeV energy and
2 GeV transverse energy  Ecm ~ 30-50?
What Ecm and Luminosity are needed
for Semi-Inclusive DIS Processes?
• Find that 100 days of measurements with a luminosity of
1033 is in general sufficient (for pT < 1 GeV)
• Useful to include lower-energies to improved data quality
at larger x values (~ 0.1)
• Include higher energies (Ecm = 30-50) to access jets (and
diffraction)
• but, for SIDIS need multiple conditions: Longitudinal,
Transverse, 1H, 2H, 3He, heavy A, low, high Ecm
1033 really seems minimum
 full program requires (n times 100 days)
• simulations at large pT were done assuming 1035 luminosity
 Likely needs more than 1033 luminosity
What Ecm and Luminosity are needed
for Deep Exclusive Processes?
New Roads:
 r and f Production give access
to gluon GPD’s at small x (<0.2)
 Deeply Virtual Meson
Production @ Q2 > 10 GeV2
Well suited processes for the EIC
 transverse spatial distribution
of gluons in the nucleon
Can we do such measurements at fixed x in the valence quark region?
Important to disentangle flavor and spin…
fixed x: s ~ s/Q2 (Mott) x
1/Q4 (hard gluon exchange)2
s
L
Q2 reach
DVCS
Q2 reach
(e,e’p)
12-GeV
21
1035
=7
=7
EIC example
1000
3 x 1034
~100
~17
GPDs and Transverse Imaging
Deep exclusive measurements in ep/eA with an EIC:
diffractive:
transverse gluon imaging
non-diffractive:
quark spin/flavor structure
J/y, ro,  (DVCS)
p, K, r+, …
[ or J/y, f, r0
p, K, r+, … ]
Describe correlation of longitudinal momentum
and transverse position of quarks/gluons 
Transverse quark/gluon imaging of nucleon
(“tomography”)
GPDs and Transverse Gluon Imaging
Goal: Transverse gluon imaging of nucleon over wide range of x: 0.001 < x < 0.1
Requires: - Q2 ~ 10-20 GeV2 to facilitate interpretation
- Wide Q2, W2 (x) range
- luminosity of 1033 (or more) to do differential measurements in Q2, W2, t
Q2 = 10 GeV2 projected data
(Andrzej Sandacz)
EIC enables gluon imaging!
Simultaneous data at
other Q2-values
GPDs and Transverse Gluon Imaging
Or more…
Differential DVCS
measurements at
moderate-large Q2
(> 10 GeV2),
moderate x (~0.05)
and t ~ 1 GeV2
would benefit from
luminosities larger
than 1033
At small x (large W):
s ~ G(x,Q2)2
Simultaneous measurements over large range in x, Q2, t at EIC!
Diffractive Channels: Transverse Gluon Imaging
,
Two-gluon exchange dominant
for J/y, f, r production at
large energies  sensitive to
gluon distribution squared!
LO factorization ~ color dipole
picture  access to gluon spatial
distribution in nuclei
Fit with ds/dt = e-Bt
Measurements at DESY of diffractive
channels (J/y, f, r, ) confirmed
the applicability of QCD factorization:
• t-slopes universal at high Q2
• flavor relations f:r
Unique access to
transverse gluon
imaging at EIC!
Exclusive Processes: EIC Potential
and Simulations
• Diffractive channels
- data/experience from HERA: p (DVCS), r0p, fp, J/Yp
- DVCS simulations by A. Sandacz et al., see e.g.
http://web.mit.edu/eicc/SBU07/index.html
- Found to be feasible with luminosity of 1033
• Non-diffractive channels
- New territory for collider!
- Much more demanding in luminosity: 1034 minimum?
- Physics closely related to JLab 6/12 GeV
- quark spin/flavor separations, nucleon/meson structure
- Feasibility study of p+n, p0p, K+L
- T. Horn, A. Bruell, V. Guzey, and C. Weiss
Extend to Quark Imaging:
Non-Diffractive Channels
Simulation for charged p+
production, assuming 100 days
at a luminosity of 1034, with 5
on 50 GeV (s = 1000)
• V. Guzey, Ch. Weiss:
Regge model
• T. Horn: π+ empirical
parameterization
Pushes for lower and
more symmetric energies
(to obtain sufficient DMx)
Γ dσ/dt (mb/GeV2)
- New territory for collider!
- Much more demanding in luminosity (see example)
- Physics closely related to JLab 6/12 GeV
- quark spin/flavor separations
- nucleon/meson structure
(Tanja Horn,
Antje Bruell,
Christian Weiss)
10<Q2<15
15<Q2<20
35<Q2<40
Extend to Quark Imaging:
Non-Diffractive Channels
Rate estimate for KΛ
Using an empirical fit to
kaon electroproduction
data from DESY and JLab
assuming 100 days at a
luminosity of 1034, with
5 on 50 GeV (s = 1000)
10<Q2<15
15<Q2<20
35<Q2<40
(Tanja Horn,
David Cooper)
Pushes for lower and
more symmetric energies
(to obtain sufficient DMx)
and luminosity > 1034
0.01<x<0.02
0.02<x<0.05
0.05<x<0.1
Consistent with earlier back-ofthe-envelope scaling arguments
1H(e,e’π+)n
MEIC@JLab
4 on 12 GeV2
– Kinematics
MEIC@JLab
4 on 60 GeV2
MEIC@JLab
11 on 60 GeV2
~ ENC@GSI
Staged eRHIC
4 on 250 GeV2
Staged eRHIC
2 on 250 GeV2
1H(e,e’π+)n
4 on 12
(Tanja Horn)
4 on 250
– Pion Kinematics – P
4 on 60
11 on 60
2 on 250
Lower proton
energies better
to map cones
around hadrons
for deep
exclusive and
SIDIS. Also
better for DM
resolution and
particle Id.
1H(e,e’π+)n
4 on 12
(Tanja Horn)
– Electron Kinematics – P
4 on 250
4 on 60
11 on 60
2 on 250
More
symmetric
and lower
energies
are better
for energy
resolution
1H(e,e’π+)n
– Neutron Kinematics – t
Want 0 < t < 1 GeV!
4 on 12
DQ = 5
(Tanja Horn)
4 on 60
DQ = 1.3
dt/t ~ t/Ep  lower Ep better
4 on 250
DQ = 0.3
Conclusion: deep exclusive charged meson production
will likely require proton energies up to 60 GeV or so.
 s ~ 1000
 @Q2 = 10 GeV2 access down to x = 0.01
 Drives large detector space (MeRHIC: 20 m ~ (M)EIC: 18m)
Summary - I
Fundamental requirements of EIC:
• Range of energies, 10 < Ecm < 50? And variable!
• Need to also be able to run at more symmetric energies
• High polarization, both longitudinal and transverse
• Optimize luminosity and detection fraction together
• Exact luminosity required for many processes complicated
- Depends on x, Q2 and pT phase space to cover
- Depends on multi-dimensional binning & statistics
- Depends on which physics processes will be of
highest scientific value – opinions differ
• Next slide: an attempt at a science/luminosity matrix
for the FULL (?) EIC science potential
(note that this requires an iteration process,
for now several versions are worked upon)
JLAB6&12
HERMES
EW
1035
ENC@GSI
Luminosity [cm-2 s-1]
COMPASS
(M)EIC
1034
MeRHIC
DES
1033
JETS
SIDIS
DIS
1032
10
DIFF
100
Saturation
10000
1000
s [GeV2]
100000
Summary - II
Both BNL and JLab have emphasized staging ideas for an
EIC as their immediate priority:
• MeRHIC: 400 < s < 4000, L close to 1033
• (M)EIC : 100 < s < 2600, L few times 1034
Processes requiring most luminosity are:
deep exclusive pion and kaon (!) electroproduction
large pT semi-inclusive DIS
electroweak studies
Processes driving to a center-of-mass energy of 30-50 are:
jet production (to map quark transverse momentum?)
factorization? diffraction (Ecm > 40?)
But, deep exclusive charged meson production drives more
symmetric energies and Ecm of 10-30
The EIC will indeed allow a unique GPD & TMD program
Optimization of such EIC remains, with your input, ongoing!
Four Electron-Ion Collider Facilities Considered
EICx2: L > 1x1033 cm-2s-1
Ecm = 20-100+ GeV
• Variable energy range
• Polarized and heavy ion beams
• High luminosity in energy region
of interest for nuclear science
Nuclear science goals:
• Explore the new QCD frontier:
strong color fields in nuclei
• Precisely image the sea-quarks
and gluons to determine
the spin, flavor and spatial
structure of the nucleon.
ENC@GSI:
L ~ few x 1032 cm-2 s-1
Ecm = 13 GeV
LHeC: L = 1.1x1033 cm-2s-1
Ecm = 1.4 TeV
• Add 70-100 GeV electron ring to
interact with LHC ion beam
• Use LHC-B interaction region
• High luminosity mainly due to
large ’s (= E/m) of beams
High-Energy physics goals:
• Parton dynamics at the TeV scale
- physics beyond the
Standard Model
- physics of high parton
densities (low x)
• Add 3 GeV electron accelerator
to interact with FAIR ion beam
Nuclear science goal:
• Precisely image the sea-quark and
gluon structure of the nucleon.
(M)EIC@JLab Interaction Region Concept
IR1: General Purpose detector
(but not diffractive/low-Q2?)
IR3: Diffractive/Low-Q2 detector
Medium
Energy IP
Snake
Insertion
60°
p
Low
Energy IP
e
IR2: Polarimetry etc.
IR Regions:
+/- 9 meter
IR4: Low Energy detector
Medium Energy:
30-60 on 3-5 (11)
Low Energy:
12 on 3-5
[sqrt(s) only factor of three
higher than 12-GeV program]
Reaching Saturation: EIC Options
Energies
s
sEIC/sHERA
11 x 24
1050
1/96
1.51
4
4 x 100
1600
1/63
1.71
6
10 x 100
4000
1/25
2.25
15
Energies for
heavy-ion beams
boost in
“virtual” x reach
gluon density boost over HERA
over HERA at Q2 = const
G ~ A1/3 x s0.3
(A = 208)