Transcript Physics with Spin Krishna Kumar University of Massachusetts thanks to A. Deshpande, R.

Physics with Spin
Krishna Kumar
University of Massachusetts
thanks to A. Deshpande, R. Ent, E. Hughes, X. Ji, N. Makins, Z-E. Meziani,
and all parallel session speakers
The Second Electron-Ion Collider Workshop,
Jefferson Laboratory
March 17, 2004
17 March 2004
Physics with Spin
Outline
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Introduction
Parallel Session Program
Inclusive Scattering
Semi-inclusive scattering
Exclusive scattering
Summary
17 March 2004
Physics with Spin
Historical Context
It is now common wisdom that lepton scattering experiments are
greatly enhanced by the availability of spin degrees of freedom
Jefferson Laboratory was conceived (I was in undergraduate
school), proposed and approved without polarized beam!
Fundamental spin physics experiments over the past 30
years have helped bring about a major change in attitude
- Beam and target spin greatly increase the scope of anticipated and
unexpected results
- Experimental technology is pushed in ways that benefit other subfields of
science
17 March 2004
Physics with Spin
Spin and the EIC
Giant strides in the production of intense,
highly polarized electron and ion beams
•High electron longitudinal beam polarization
•High light ion beam polarization (longitudinal and transverse)
•High luminosity
•High Center of Mass Energy
•Positron Beam (high luminosity for GPDs?!)
17 March 2004
Physics with Spin
Parallel Session Overview
• Spin (I)
– Inclusive measurements and Gluon spin
• Transversity
– Polarized Semi-Inclusive measurements
• Spin (II)
– Using Spin for Flavor Separation
• Angular Momentum
– Quark Spatial Distributions and GPDs
17 March 2004
Physics with Spin
Parallel Sessions (I)
Monday, March 15, 2004 - VARC 53/55
Spin (I) - Chair: Oscar Rondon (UVa)
14:00 - 14:15
The g1 Structure Function at Low x - Introduction
14:15 - 14:45
Measurement of g1 at the Future Collider and G
from pQCD Evolution of the Structure Function
14:45 - 15:15
Open Charm Production at Colliders
15:15 - 15:45
The Photon Content of Unpolarized and Polarized
Nucleons
15:45 - 16:00
Electroweak and SM Physics at EIC
16:00 - 16:20
Coffee Break
Werner Vogelsang
Ernst Sichtermann
Antje Bruell
Asmita Mukherjee
Rolf Ent
Transversity - Chair: Zein-Eddine Meziani (Temple)
16:20 - 16:45
Azimuthal Spin Asymmetries for the Large pt Hadron
Production at eRHIC
Yuji Koike
16:45 - 17:10
Transversity Measurements at Colliders
Naomi Makins
17:10 - 17:35
SIDIS and Current Fragmentation
Stefan Kretzer
17 March 2004
Physics with Spin
Parallel Session (II)
Tuesday, March 16, 2004 - VARC 53/55
Spin (II) - Chair: Werner Vogelsang (BNL/RBRC)
14:00 - 14:25
Polarized Semi-Inclusive Physics Measurements
at HERMES and Future Prospects at the Colliders
14:25 - 14:50
Polarized Photoproduction at ep Colliders
14:50 - 15:15
Lambda and Hyperon Physics
15:15 - 15:40
Spatial Distributions of Quarks/Gluons in the Nucleon
at Large Nc
Angular Momentum - Chair: Latifa Elouadrhiri (JLab)
15:40 - 16:05
Quantum Phase-Space Tomography of Quarks
in the Proton
16:05 - 16:20
Coffee Break
16:20 - 16:45
Measurement of GPDs at JLab and Future Colliders
16:45 - 17:10
Generalized Parton Distributions at Large x
17:10 - 17:35
Detector Issues
17:35 - 18:00
GPDs and Color Transparency Phenomena
17 March 2004
Physics with Spin
Ed Kinney
Marco Stratmann
Naomi Makins
Christian Weiss
Xiangdong Ji
Harut Avakian
Feng Yuan
N. Smirnov
Simonetta Liuti
Inclusive DIS
Sichtermann, Vogelsang
Spin structure functions g1 and g2 describe
the spin-dependent cross-sections
Precision measurements on 1H,
2H and 3He targets at CERN,
DESY and SLAC
17 March 2004
Physics with Spin
Gluon Spin in the Nucleon
1 1
s    Lq  G  LG
2 2
 0.25 0.1
Gluon contribution is likely to be substantial:
Profound implications for our basic understanding of the nucleon which
must be directly measured by experiment

RHIC Spin
and COMPASS experiments will provide the first
precise measurements towards this goal
The gold standard: measure G from a variety of experiments,
where the dominant theoretical input is NLO QCD and residual
model dependence is negligible and non-controversial
17 March 2004
Physics with Spin
G from Q2 Evolution of g1
Sichtermann
EIC expected improvement in
statistical uncertainty on G with
analyzed data with 100 pb-1:
HERA
~3 5 on 250 GeV
~4 10 on 250 GeV
~7 20 on 250 GeV
with respect to the present
uncertainty of ~0.5
17 March 2004
Physics with Spin
The dream is to produce a
similar plot for xg(x) vs x
Gluon Spin from Open Charm
Bruell
charm
charm
several stiff kaons in the central
regions and a forward electron
•Critical, complementary method to obtain G
•Simulation work on open charm is just beginning
•EIC should provide a clean, high statistics data sample
17 March 2004
Physics with Spin
Polarized Photoproduction
Mukherjee, Stratmann
Estimate for a 1 fb-1 data sample
Asymmetry
sufficient resolution to tag photoproduction and
measure jet 4-momentum
High Energy Convergence of the GDH sum rule
Direct Photon
Resolved Photon
17 March 2004
Physics with Spin
Spin Structure Summary
The final design parameters of the EIC must
guarantee multiple, precision measurements of G
Should a high precision test of the Bjorken Sum Rule be pursued?
2




1
g

(
Q
)
p
n
A
S
0 g1 ( x)dx  0 g1 ( x)dx  6  gV 1    ...
1
1
: requires a careful evaluation of systematics of polarimetry
New information on the polarized photon’s partonic content
What can be gained by precision studies of g2?
17 March 2004
Physics with Spin
Polarized Semi-Inclusive DIS
Makins, Kinney, Kretzer, Koike
Flavor separation of parton distribution functions and
fragmentation functions via azimuthal single and
double-spin asymmetries with tagged pions and kaons
17 March 2004
Physics with Spin
Transversity
Makins
•transverse polarization introduces a new structure fn. h1
•Cannot be accessed by inclusive scattering
•Information on transverse quark distribution in the nucleon
•The first moment of h1 yields the nucleon’s tensor charge
The most favorable spin configuration is an unpolarized
beam on a transversely polarized target
While first measurements are being carried out at HERMES and new
measurements will be carried out Jefferson Lab and spin RHIC, EIC
will be a laboratory where transversity will be extracted with reduced
theoretical uncertainty
17 March 2004
Physics with Spin
Tomography of the Nucleon
Ji
• A framework to extract 3-D spatial information of quarks in a nucleon at
rest
• Generate Wigner (quantum phase-space) distributions
• Obtain proton images at fixed x
• Direct connection to GPDs through Fourier Transforms
Ultimate strategy:
•Data on various hard exclusive processes
•Deconvolution and global fits to obtain GPDs
•Further constraints from Lattice QCD
•Obtain tomographic 3-D pictures of the nucleon
•Understand origins of mass and spin structure
17 March 2004
Physics with Spin
Proton Images at Fixed x
Ji
Up-quark densities
x=0.01
z
y
x
x=0.4
17 March 2004
x=0.7
Physics with Spin
GPDs
Avakian, Luiti, Weiss, Yuan
CLAS 5.7 GeV: DVCS SSA
EIC Issues
(Deconvolution!)
•Resolution (especially t)
•Acceptance
•Luminosity
•Kinematic coverage
•Can we set a gold standard?
•Can moments of GPDs make contact with Lattice QCD?
17 March 2004
Physics with Spin
Detector Issues
N. Smirnov
Example
HCAL
EMCal
Solenoid
AEROGEL
(Not to scale)
TOF
Beam elements
P/A
e
Inner
trackers
5m
17 March 2004
A HERA like
Detector with
dedicated PID:
>>Time of flight
>>Aerogel Ckov
AND
Forward detectors
including
Roman Pots etc…
Outer trackers
Physics with Spin
Parity Violation (I)
Ent
Beyond the Standard Model
E6 Z’ Based Extensions
e
u
RPV SUSY Extensions
u
u
e
Due to finite Y
1035 /cm2/s
Sub 0.5% polarimetry
17 March 2004
u
~
d
Z’
e
e
Leptoquarks
Physics with Spin
e
LQ
u
e
u
Parity Violation (II)
Tofirst order, there is no difference between fixedtarget DIS and collider DIS for such a measurement
•y dependence, perhaps gain in systematics
•More selective x range: better theory control
Why even bother after HERA measurements?
Any new physics signature can be characterized as a contact interaction at “low” energy
The goal of “low” energy experiments is to characterize all
chiral combinations with all initial and final state fermions
The goal is NOT to find the first signature of new
physics and go to Stockholm
The goal is to help our LHC colleagues, who are likely
to be staring at a tantalizing, low statistics signal
17 March 2004
Physics with Spin
Parity Violation (III)
The g5 structure function
• 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
Worth doing even if no positron beam
17 March 2004
Physics with Spin
Parity Violation (wild)
The partonic structure of the Z boson?
Suppose you had enough luminosity to see the PV Asymmetry at low Q2
Would one learn something new about the partonic content of the photon?
What is the correct description to think about this process?
17 March 2004
Physics with Spin
Polarized Sources
• Polarized electron sources (polarization and
intensity) are not a technical hurdle
• Likely the same thing for proton sources
• Some work on 2H at BNL
• Precision inclusive physics requires polarized
3He. This is a new technical challenge
17 March 2004
Physics with Spin
Polarimetry
• Electron polarimetry at 0.5% likely doable in
10 years
• If sub-0.5% is required, this is a major,
independent effort
– Beyond the Standard Model?
• Proton polarimetry will reach ~5% at the
RHIC spin program
– Bjorken sum rule test needs sub-5%?
• 2H and 3He polarimetry? We need to start
thinking about this.
17 March 2004
Physics with Spin
Back to Physics…..
• Inclusive DIS
– EIC is the ultimate gluon spin machine
– Close the book on longitudinal spin structure
• Semi-Inclusive DIS
– New window into spin structure
– Transversity, flavor separation, fragmentation…..
• Exclusive DIS
– Deconvolve experimental data to extract GPDs?
– GPDs provide full description of the nucleon?
– Conceptual understanding of nucleon structure?
• The focus should be to make as much contact with Lattice QCD as
possible
17 March 2004
Physics with Spin
A Look Forward
• RHIC spin and Jlab physics will push a
significant component of the required
experimental technology
• We will also learn a whole lot about how to
analyze EIC data while grappling with
analysis issues at these facilities
• Key question: What is the optimum center of
mass energy range and luminosity range?
– You could make a strong case for 2 machines!
– How many detectors should we plan for?
17 March 2004
Physics with Spin
Closing Thoughts
• Phew! That was hard!
• I learnt a lot! (Did you?)
• We in this room know that there is an extraordinary
opportunity to further our understanding of the nucleon
with an EIC
• To make headway on funding outside this room, we need
to focus our combined efforts on bringing a coherent case
to the rest of the science community
• Spin physics will play a critical role, both in strengthening
the physics case and in communicating our field to the
public
17 March 2004
Physics with Spin
Tomography of the Nucleon
Ji
• Wigner operator
• Wigner distribution: “density” for quarks having position r
and 4-momentum k (off-shell)
7-dimensional distribution
No known experiment can measure this!
17 March 2004
Physics with Spin