17 march 2004physics with spin krishna kumar university of massachusetts thanks to a. deshpande, r....

17 March 2004 Physics with Spin

Physics with SpinKrishna 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


Outline

• Introduction• Parallel Session Program• Inclusive Scattering• Semi-inclusive scattering• Exclusive scattering• Summary


Historical ContextIt 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!

- 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

Fundamental spin physics experiments over the past 30 years have helped bring about a major change in attitude


Spin and the EIC

•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?!)

Giant strides in the production of intense, highly polarized electron and ion beams


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


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 Werner Vogelsang14:15 - 14:45 Measurement of g1 at the Future Collider and G

from pQCD Evolution of the Structure Function Ernst Sichtermann14:45 - 15:15 Open Charm Production at Colliders Antje Bruell15:15 - 15:45 The Photon Content of Unpolarized and Polarized

Nucleons Asmita Mukherjee15:45 - 16:00 Electroweak and SM Physics at EIC Rolf Ent16:00 - 16:20 Coffee Break

Transversity - Chair: Zein-Eddine Meziani (Temple)16:20 - 16:45 Azimuthal Spin Asymmetries for the Large pt Hadron

Production at eRHIC Yuji Koike16:45 - 17:10 Transversity Measurements at Colliders Naomi Makins17:10 - 17:35 SIDIS and Current Fragmentation Stefan Kretzer


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 Ed Kinney14:25 - 14:50 Polarized Photoproduction at ep Colliders Marco Stratmann14:50 - 15:15 Lambda and Hyperon Physics Naomi Makins15:15 - 15:40 Spatial Distributions of Quarks/Gluons in the Nucleon

at Large Nc Christian Weiss

Angular Momentum - Chair: Latifa Elouadrhiri (JLab)15:40 - 16:05 Quantum Phase-Space Tomography of Quarks

in the Proton Xiangdong Ji16:05 - 16:20 Coffee Break 16:20 - 16:45 Measurement of GPDs at JLab and Future Colliders Harut Avakian16:45 - 17:10 Generalized Parton Distributions at Large x Feng Yuan17:10 - 17:35 Detector Issues N. Smirnov17:35 - 18:00 GPDs and Color Transparency Phenomena Simonetta Liuti


Inclusive DIS

Spin structure functions g1 and g2 describe the spin-dependent cross-sections

Sichtermann, Vogelsang

Precision measurements on 1H, 2H and 3He targets at CERN, DESY and SLAC


Gluon Spin in the Nucleon

€

s = 12

= 12

ΔΣ + Lq + ΔG + LG

€

Σ=0.25 ± 0.1Gluon 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


G from Q2 Evolution of g1Sichtermann

EIC expected improvement in statistical uncertainty on G with analyzed data with 100 pb-1:~3 5 on 250 GeV

~4 10 on 250 GeV~7 20 on 250 GeV

with respect to the present uncertainty of ~0.5

The dream is to produce a similar plot for xg(x) vs x

HERA


Gluon Spin from Open CharmBruell

•Critical, complementary method to obtain G•Simulation work on open charm is just beginning•EIC should provide a clean, high statistics data sample

charm

charm

several stiff kaons in the central regions and a forward electron


Polarized PhotoproductionMukherjee, Stratmann

High Energy Convergence of the GDH sum rule

Direct Photon Resolved Photon

Estimate for a 1 fb-1 data sample

sufficient resolution to tag photoproduction andmeasure jet 4-momentum

Asymmetry


Spin Structure Summary

⎟⎟⎠⎞

⎜⎜⎝⎛

−−⎟⎟⎠⎞

⎜⎜⎝⎛

=−∫∫ ...)(161)()(

21

01

1

01 π

α Qggdxxgdxxg S

V

Anp

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?

: 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?


Polarized Semi-Inclusive DISMakins, Kinney, Kretzer, Koike

Flavor separation of parton distribution functions and fragmentation functions via azimuthal single and double-spin asymmetries with tagged pions and kaons


TransversityMakins

•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


Tomography of the Nucleon• 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

Ji

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


Proton Images at Fixed x

x

y

z

Up-quark densitiesx=0.01

x=0.7x=0.4

Ji


GPDsAvakian, Luiti, Weiss, Yuan

CLAS 5.7 GeV: DVCS SSA

•Resolution (especially t)•Acceptance•Luminosity•Kinematic coverage

EIC Issues(Deconvolution!)

•Can we set a gold standard? •Can moments of GPDs make contact with Lattice QCD?


Detector IssuesN. Smirnov

AEROGEL

HCAL

P/Ae

EMCal

TOF

Outer trackers

Innertrackers

Beam elements

Solenoid

A HERA likeDetector with dedicated PID:>>Time of flight>>Aerogel Ckov

5m

(Not to scale)

Forward detectors including

Roman Pots etc…

AND

Example


Parity Violation (I)Ent

Beyond the Standard ModelLeptoquarksRPV SUSY ExtensionsE6 Z’ Based Extensions

Due to finite Y

1035 /cm2/sSub 0.5% polarimetry


Parity Violation (II)Tofirst order, there is no difference between fixed- target 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


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


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?


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


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.


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


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?


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


Tomography of the NucleonJi

• Wigner operator

• Wigner distribution: “density” for quarks having position r and 4-momentum k (off-shell)

No known experiment can measure this!7-dimensional distribution

17 march 2004physics with spin krishna kumar university of massachusetts thanks to a. deshpande, r....

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