# Presentation: 180153

## A Hurriedly Put-together Spin Discussion onThe Electron Ion Collider Part I

**Abhay Deshpande**

**Polarized e-p and e-A Scattering with a Collider**

***Riken BNL Research Center***

- http://www.phenix.bnl.gov/WWW/publish/abhay/Home_of_EIC

## Crossing the x-Q2 Barrier in DIS: Low-x surprises!

- Elastic e-p scattering (SLAC, 1950s)
-    Q2 ~ 1 GeV2           *Finite Size of proton*
- Inelastic e-p scattering (SLAC, 1960s)
-     Q2 > 1 GeV2            *Parton structure of the proton*
- Inelastic -p scattering off p/d at CERN (1980s)
-     Q2 > 1 GeV2            *Unpolarized EMC effect*
- Inelastic e-p scattering at HERA/DESY (1990s)
-    Q2 > 1 GeV2             *Unexpected rise of F2, Study of pQCD and QCD through various physics processes, diffraction...*

***What NEXT?***

***Low x***

- June 19, 2001                    A Hurried Spin Discussion on the Electron Ion Collider

## Physics with “Spin” full of Surprises!

- Stern & Gehrlach (1921): Space quantization associated with
-                                            direction
- Goudschmidt & Ulhenbeck (1926): Atomic fine structure and
-                                              electron spin magnetic moment
- Stern (1933): Proton anomalous magnetic moment
- Kusch (1947): Electron anomalous magnetic moment
- Prescott & Yale-SLAC Collaboration (1978): EW interference
-                          in polarized e-d DIS, parity non-conservation
- EMC (1989): Proton spin crisis/puzzle                Low x!
- HERMES (1999): ???? Transverse spin asymmetries ????

- June 19, 2001                    A Hurried Spin Discussion on the Electron Ion Collider

## The EIC w.r.t. Other Experimental Facilities

- New kinematic region to be explored
- EIC = eRHIC + EPIC
- Kinematic Reach for DIS:
- High Luminosity!

- June 19, 2001                    A Hurried Spin Discussion on the Electron Ion Collider

## The EIC w.r.t. Other Experimental Facilities

-    Large luminosity and high CM Energy makes EIC unique!

- June 19, 2001                    A Hurried Spin Discussion on the Electron Ion Collider

- Variable CM energy enhances
- its versatility!

## If the EIC is built at RHIC “eRHIC”I. Ben-Zvi et al./S. Peggs et al.

- Use the existing infrastructure and resources of the RHIC at BNL
-       RHIC: Polarized proton beams  50 GeV 250 GeV ?325 GeV
- Exist unused Experimental Hall: The one at 12 o’clock position of the present RHIC reserved for “future major detectors”
- Add a electron LINAC beam energy variable: 3 GeV12 GeV

- RHIC at BNL
- Ring-Linac Design

- Blue ring

- Yellow ring

- Electron
- Linac

- June 19, 2001                    A Hurried Spin Discussion on the Electron Ion Collider

## Topics of Interest for polarized DIS

- Spin structure function g1p/g1n with high precision and at low x
-     ***Bjorken sum rule with high precision***
- G(x,Q2) from pQCD analysis, Di-Jet/high pT hadron events in PGF processes
- Precise determination of s from g1 scaling violations alone...
- Polarized structure of the photon from photo-production studies

- Electroweak structure functions g5(+/-) from W(+/-) production in polarized ep scattering
- Flavor separation of  PDFs through semi-inclusive DIS
- Transversity
- DVCS
- Contribution to GDH sum rule at very high υ
- Tgt/Current fragmentation
- Etc.......
-      Many other measurements

- A robust program which would require a challenging detector design

- June 19, 2001                    A Hurried Spin Discussion on the Electron Ion Collider

- EIC Part II

## Spin Structure Function g1 at low xA. Deshpande et al.

**~5-7 days of data**

**A Unique Measurement! **
**No present/future approved experiment will measure this.**

**3 years of data**

- June 19, 2001                    A Hurried Spin Discussion on the Electron Ion Collider

## Low x Measurement of g1 of the NeutronA. Deshpande et al.

- With He(+2) or Deuteron in hadron ring: g1n measurable
- ~2 weeks of EIC data (only the low x data shown)
- Shown is the present SMC data with various low x scenarios and uncertainties from possible HERA data in 3 years
- Combined with g1p this would enable a “hyperfine” test of Bjorken sum rule which is a fundamental result of QCD (better than 1% accuracy expected)

**EIC 1 inv.fb**

- June 19, 2001                    A Hurried Spin Discussion on the Electron Ion Collider

## First Moment of the G(x)A. Deshpande et al.

- First Moment of the G(x)A. Deshpande et al.

- pQCD analysis of g1 structure function at NLO gives the first moment of the polarized gluon distribution. Present value and uncertainty is: (at Q2 = 1 GeV2)
-                        1.0         (stat)       (exp.sys.)      (theory/low-x)
- Major source of uncertainty from low x unmeasured region: Theory completely unconstrained in this region.
- If EIC data is obtained and the analysis is repeated, the theoretical uncertainties improve by factors of 3-5; the statistical uncertainty improves by even bigger factors.

**+1.0              + 0.4                         +1.4          **

**- 0.4              - 0.2                          - 0.5**

**Complimentary determination of ********G to that from**
**RHIC Spin**

- June 19, 2001                    A Hurried Spin Discussion on the Electron Ion Collider

## Other methods to get GPhoton-Gluon-Fusion (PGF)

- Photon Gluon Fusion in DIS:
-              Di-Jet events
-              2-High-pT hadron events
- At high Sqrt(s) the theoretical interpretation is without ambiguities or uncertainties!
- Method already tried at HERA
-      --  NLO calculations exist
-      -- G(x,Q2) extracted and published (H1 & ZEUS)
-      -- Consistent with G(x,Q2) from
-      pQCD analysis of F2

- Signal: PGF

- Background
- QCD Compton

- June 19, 2001                    A Hurried Spin Discussion on the Electron Ion Collider

## Result of Di-Jet analysis at NLOG. Radel et al./A.Deshpande et al.

- Easy to differentiate between different scenarios of G: Improves G by factor of ~3
- Combined analysis: Di-Jet + pQCD analysis of g1:G constrained by these two together further improves the uncertainties by additonal factor of ~3
-                   **Effectively factors of 10 improvement in ********G can be expected!**

-   Statistical accuracy
-   shown for EIC
-   for 2 luminosities
-   Detector smearing effects
-   studied
-  NLO analysis for Di-Jet
-  Included

- June 19, 2001                    A Hurried Spin Discussion on the Electron Ion Collider

## Polarized Parton Distribution of the Photon

- Photoproduction studies with single and di-jet and one and 2 high pT opposite charged hadrons.
- At high enough energies the photon can resolve itself into its parton content
- With polarized protons asymmetries related to the spin structure of the photon can be extracted! **A UNIQUE measurement! **
**Asymmetries sensitive to the gluon structure as well!**

- Resolved Photon

- Direct Photon

- June 19, 2001                    A Hurried Spin Discussion on the Electron Ion Collider

## Spin structure of polarized photon!M. Stratmann & W. Vogelsang

- Statistical uncertainty with 1 inv.fb.
- ~2wks running for EIC
- Single and double jet asymmetries
- ZEUS Acceptance cuts
- Will resolve the photon spin structure easily!

- Direct Photon                            Resolved Photon

- June 19, 2001                    A Hurried Spin Discussion on the Electron Ion Collider

## Parity Violating Structure Functions g5

- Parity Violating Structure Functions g5

- Unique measurement with EIC
- Identified by missing neutrino momentum: huge asymmetry in detector
- Complementary measurement to RHIC SPIN

**For EIC kinematics**

- June 19, 2001                    A Hurried Spin Discussion on the Electron Ion Collider

## Measurement Accuracy PV g5 with EICJ. Contreras et al.

- Assume:
- 1) Input GS Polarized PDFs
- 2) xF3 is measured
-     well by that time
- 3) 4fb-1 luminosity
-     (~1.5 months run)
- If e+ and e- possible
-  then one can have
-  g5(+) as well.
- Separate flavors
- Delta u, Delta d etc.

- June 19, 2001                    A Hurried Spin Discussion on the Electron Ion Collider

## “Formal” Status of EIC

- The Electron Ion Collider was presented to the US Nuclear Science Advisory Committee’s (NSAC) Long Range Planning (LRP) Town hall Meetings from October 2000 to April 2001
- At the final NSAC meeting in Santa Fe, NM the project was rated at the top in the projects needing “immediate R&D funding”.
- R&D principally needed for the Electron-Cooling of the hadron beam to achieve the high luminosities. This is COMMON and NECESSARY for RHIC-II Stage as well! Money also needed for R&D for detector & interaction region design/development,  and for high intensity polarized electron source.
- Depending on the US DoE funding levels in the present administration, the R&D money expected(!) in the FY03 DoE budget at the earliest.

- June 19, 2001                    A Hurried Spin Discussion on the Electron Ion Collider

## Immediate Plans/Action Items

- Steering committee is in the making
- People from about 15 institutes have contributed to the NSAC White-paper preparation and have shown interest in pursuing the EIC  More have shown interest in joining the effort
- Moving towards a Collaboration: “EICC”
- Meeting at BNL or IUCF sometime in November or December 2001: 5th Meeting on EIC
- Open invitation to the spinners and QGP-ers at RHIC to join.