# Presentation: 646865

## eRHIC: Science and Perspective

-  Introduction
-  Science of eRHIC
-  Realization
-  Summary

*Study of the Fundamental Structure of Matter with an Electron-Ion Collider*
- Deshpande, R. Milner, R. Venugopalan, W. Vogelsang
**hep-ph/0506148, to appear in Ann. Revs. Nucl. Part. Sci.**

- RHIC Planning Meeting       October 29-20, 2005

- Richard G. Milner

## The study of the fundamental structure of matter

- QCD tells us that the nucleon and atomic nuclei are made of pointlike constituents bound by powerful gluon fields
- The valence quark region is well explored experimentally and reasonably well understood theoretically
- Frontier research in QCD demands a concerted experimental effort directed at the role of the gluons and sea quarks
- A new accelerator which directly probes the quarks and gluons is required
- 		Lepton probe	High center of mass energy	High luminosity  precision	Polarized lepton, nucleon	Optimized detectors
- This accelerator is urgently needed to make progress in this field of research and has substantial discovery potential

- RHIC Planning Meeting       October 29-20, 2005

- Richard G. Milner

## Deep inelastic scattering – the experimental cornerstone of QCD

- RHIC Planning Meeting       October 29-20, 2005

- Richard G. Milner

##  Running of the strong coupling αs

- RHIC Planning Meeting       October 29-20, 2005

- Richard G. Milner

## Quark and gluon momentum in proton

- RHIC Planning Meeting       October 29-20, 2005

- Richard G. Milner

## Lattice QCD making significant progress

-   **quenched**
**approximation**

**full QCD**

**agreement with experiment at level of few percent**

**HPQCD**
**hep-lat/0304004**

- RHIC Planning Meeting       October 29-20, 2005

- Richard G. Milner

## Nucleon axial charge in full lattice QCD

**LHPC Collaboration**
**hep-lat/0510062**

- RHIC Planning Meeting       October 29-20, 2005

- Richard G. Milner

## Why a Collider ?

- High Ecm (20 to 100 GeV) 
-   large range of x, Q2
- x range (10-4 to 1):  valence, sea quarks,
-  glue
- Q2 range ( 1 to 1000 GeV2):  utilize
- evolution equations of QCD
- High luminosity ~ 1033 cm-2 s-1
- High polarization ( ~ 70%) of lepton, nucleon achievable
- Complete mass range of nuclear targets
- Collider geometry allows complete reconstruction of final state

- Qmax2 = ECM2 · x

- RHIC Planning Meeting       October 29-20, 2005

- Richard G. Milner

## Why eRHIC?

- RHIC is the world’s first and only polarized proton collider
- In addition, RHIC accelerates heavy ion beams to 100 GeV/nucleon
- eRHIC would capitalize on ~ $ 1 billion investment in RHIC
- RHIC scientific program strongly motivates eRHIC
- Leadership from BNL in evolution of lepton-ion collider since 1999
- eRHIC is viewed at BNL as a necessary and natural upgrade of RHIC after 2010 as the heavy ion and spin programs mature

- RHIC Planning Meeting       October 29-20, 2005

- Richard G. Milner

##   The Electron-Ion Collider (EIC)

- A high luminosity (~1033cm-2s-1) polarized lepton-ion collider is the QCD machine hadronic physicists worldwide require for future research
- Workshops
-         Seeheim, Germany	1997             MIT             2000
- 	    IUCF        		1999             BNL             2002
- 	    BNL          		1999             JLab            2003
- 	    Yale          		2000
- Electron Ion collider (EIC) received very favorable review of science case in US 2001 Nuclear Physics Long Range Plan, with strong endorsement for R&D
- NSAC in March 2003, declared EIC science `absolutely central’ to Nuclear Physics
- DOE Office of Science 20 Year Strategic Plan in 2004: eRHIC identified as a long term (realized ~ 2015) priority

- RHIC Planning Meeting       October 29-20, 2005

- Richard G. Milner

## EIC Steering Committee

- A. Caldwell (MPI Munich)
- A. Deshpande (StonyBrook)
- R. Ent (JLab)
- G. Garvey (LANL)
- R. Holt (ANL)
- E. Hughes (Caltech)
- K.-C. Imai (Kyoto Univ.)
- R. Milner (MIT)
- P. Paul (BNL)
- J.-C. Peng (Illinois)
- S. Vigdor (Indiana Univ.)

- RHIC Planning Meeting       October 29-20, 2005

- Richard G. Milner

## eRHIC will be a unique accelerator

**eRHIC will be a unique accelerator**

- RHIC Planning Meeting       October 29-20, 2005

- Richard G. Milner

## Scientific Highlights

- nucleon structure	sea quarks and glue	spin and flavor structure	new parton distributions
- Meson structure
- 		, K are Goldstone Bosons of QCD
- 		essential to nuclear binding
- hadronization	evolution of parton into hadron	process in nuclei of fundamental interest
- nuclei	role of partons	initial conditions for relativistic heavy ion collisions
- matter under extreme conditions	saturation of parton distributions	new phenomena, e.g. colored glass condensate

- RHIC Planning Meeting       October 29-20, 2005

- Richard G. Milner

## The Spin Structure of the Nucleon

**The Spin Structure of the Nucleon**

- Bjorken Sum Rule
- From NLO-QCD analysis of DIS measurements ...
- 	ΔG = 1.0±1.2
- quark polarization Δq(x)
- 	first 5-flavor separation from 	HERMES
- transversity δq(x)
- 	a new window on quark spin
- 	azimuthal asymmetries from     	HERMES and JLab
- gluon polarization ΔG(x)
- 	RHIC-spin and COMPASS will 	provide some answers!
- orbital angular momentum L
- 	how to determine?  GPD’s ?

- 1⁄2 = 1⁄2  + G + Lq + Lg

- ΔΣ ≈ 0.2

- RHIC Planning Meeting       October 29-20, 2005

- Richard G. Milner

## Inclusive spin-dependent DIS

- RHIC Planning Meeting       October 29-20, 2005

- Richard G. Milner

## QCD Test: Bjorken Sum Rule

-  Γ1p -  Γ1n = 1/6 gA [1 + Ο(αs)]
-  Sum rule verified to ±10%
-  eRHIC can approach ±1%
-                            **G. Igo**
**     ****Precision QCD test**

- RHIC Planning Meeting       October 29-20, 2005

- Richard G. Milner

## Polarized parton densities of the proton

**Bl****ümlein and Böttcher**

- SU(3) flavor
- symmetry
- assumed

- RHIC Planning Meeting       October 29-20, 2005

- Richard G. Milner

## HERMES Flavor Decomposition of Quark Spin

- Semi-inclusive
- DIS

- RHIC Planning Meeting       October 29-20, 2005

- Richard G. Milner

**Gluon polarization data from COMPASS**

- 2002+3 data analysis; as much again in 2004 on disk

- RHIC Planning Meeting       October 29-20, 2005

- Richard G. Milner

## Gluon polarization from STAR

- STAR preliminary 2003+4 results for double longitudinal spin asymmetry ALL  versus jet pT in p + p → jet + X, compared with NLO pQCD

**New more precise data from PHENIX**

- RHIC Planning Meeting       October 29-20, 2005

- Richard G. Milner

## Spin structure function gp1 at low x

**x   = 10****-4**** ******** 0.7**
**Q****2**** = 0 ******** 10****4**** GeV**
**eRHIC 250 x 10 GeV**
**Lumi=85 inv. pb/day**

**x   = 10****-3**** ******** 0.7**
**Q****2**** = 0 ******** 10****3**** GeV**
**Fixed target experiments**
**1989 – 1999 Data**

- 10 days of eRHIC run
- Assume: 70% Machine Eff.
-                70% Detector Eff.

- RHIC Planning Meeting       October 29-20, 2005

- Richard G. Milner

## eRHIC determination of polarized quarks and anti-quarks

**Kinney and St****össlein**

- RHIC Planning Meeting       October 29-20, 2005

- Richard G. Milner

## Gluon polarization from di-jets in LO for eRHIC

**Deshpande et al.**

- RHIC Planning Meeting       October 29-20, 2005

- Richard G. Milner

## Parity violating lepton scattering

-  requires a positron beam
-  determines new combinations of Δu, Δd, Δs etc.
-  analog sum rule to Bjorken

**A. Deshpande**

- RHIC Planning Meeting       October 29-20, 2005

- Richard G. Milner

## Saturation: the Color Glass Condensate

- RHIC Planning Meeting       October 29-20, 2005

- Richard G. Milner

## Using Nuclei to Increase the Gluon Density

- Parton density at low x rises as
- Unitarity  saturation at some
- In a nucleus, there is a large enhancement of the parton densities / unit area compared to a nucleon
-      Example
- 			Q2=4 (GeV/c)2
- 		                < 0.3
- 		           A = 200
-            Xep=10-7   for  XeA = 10-4

- RHIC Planning Meeting       October 29-20, 2005

- Richard G. Milner

## Gluon Momentum Distribution from DIS

- RHIC Planning Meeting       October 29-20, 2005

- Richard G. Milner

## RHIC Data consistent with Gluon Saturation

- RHIC Planning Meeting       October 29-20, 2005

- Richard G. Milner

## Longitudinal structure function FL

-  Extracted from scaling violations of
-    F2
-  Experimentally can be determined
-    directly
-  Highly sensitive to effects of gluon
-  With precise enough F2 and FL one
-    can extract the coefficient λ of the
-    saturation scale
-  Logarithmic derivatives of F2 and FL
-    with Q will be sensitive to CGC

- RHIC Planning Meeting       October 29-20, 2005

- Richard G. Milner

## Quarks in a Nucleus

- “EMC Effect”

- Space-Time Structure of Photon

- F2A/F2D

-            10-4       10-3       10-2      10-1          1

- x

- Can pick apart the spin-flavor structure of EMC effect by technique of flavor tagging, in the region where effects of the space-time structure of hadrons do not interfere (large !)

- Nuclear attenuation negligible
- for  > 50 GeV hadrons escape
- nuclear medium undisturbed

- RHIC Planning Meeting       October 29-20, 2005

- Richard G. Milner

## eRHIC projections for nuclear quark distributions 

**T. Sloan**

**1 pb****-1**

- RHIC Planning Meeting       October 29-20, 2005

- Richard G. Milner

## Sea-Quarks and Gluons in a Nucleus

- Drell-Yan  No Nuclear Modifications to
-  	      Sea-Quarks found at x ~ 0.1
-        Where is the Nuclear Binding?

- Flavor tagging can also (in principle)
- disentangle sea-quark contributions

- Constraints on possible nuclear
- modifications of glue come from
- 1) Q2 evolution of nuclear ratio of
-     F2 in Sn/C (NMC)
- 2) Direct measurement of J/Psi
-      production in nuclear targets

- Compatible with EMC effect?
- Precise measurements possible of
-  Nuclear ratio of Sn/C (25 GeV)
-  J/Psi production (ELIC)

- F2

- G

- RHIC Planning Meeting       October 29-20, 2005

- Richard G. Milner

## Nuclear Binding

- Natural Energy Scale of QCD: O(100 MeV)
- Nuclear Binding Scale O(10 MeV)
- Does it result from a complicated detail of near cancellation of strongly attractive and repulsive terms in N-N force, or is there another explanation?

- How can one understand
- nuclear binding in terms
- of quarks and gluons?

- Complete spin-flavor structure
- of modifications to quarks and
- gluons in nuclear system may be
- best clue.

- RHIC Planning Meeting       October 29-20, 2005

- Richard G. Milner

## eRHIC - machine design aspects

- First detailed document (252 pages) reporting on the eRHIC accelerator and interaction region (IR) design studies
- Collaborative effort between BNL, MIT-Bates, BINP and DESY
- Goal:
- Develop an initial design for eRHIC
- Investigate accelerator physics issues most important to its design
- Evaluate luminosities that could be achieved with minimal R&D effort including IR design
- Identify specific R&D extensive accelerator aspects which could lead to significantly higher luminosities
- Review planned in June 2005

- http://www.bnl.gov/eic/

**See talk by V. Ptitsyn**

- RHIC Planning Meeting       October 29-20, 2005

- Richard G. Milner

## eRHIC: ring-ring design

- Collisions at 12 o’clock interaction region
- 10 GeV, 0.5 A e-ring with 1/3 of RHIC circumference (similar to PEP II HER)
- Inject at full energy 2 – 10 GeV
- Existing RHIC interaction region allows for typical asymmetric detector (similar to HERA or PEP II detectors)

- Required modifications
-      of RHIC:
-  Electron cooling
-  Increase of total current
-    120 → 360 bunches
- Additional spin rotators

- RHIC Planning Meeting       October 29-20, 2005

- Richard G. Milner

## eRHIC

**eRHIC**
**e-/e+ Ring Parameters**
**10 GeV electrons – 250 GeV protons**

- Type your question here and then click Search.

-  Luminosity limited by beam-beam tune shifts:
- ξi = 0.0065   ξe = 0.08
- Luminosity assumes collisions
- at two other IPs
-  Dedicated operations yields
- Luminosity ~ 1033 cm-2 s-1

- RHIC Planning Meeting       October 29-20, 2005

- Richard G. Milner

## eRHIC: linac-ring design 

**eRHIC: linac-ring design**

- Two possible designs are presented in the ZDR
- Electron beam is transported to collision point(s) directly from superconducting energy recovery linac (ERL)
- Features:
- Higher luminosity (~ X 5) possible
- Rapid reversal of electron polarization
- Machine elements free region approx. 5m
- Simpler IR region design: Round beams possible
- Multiple interaction regions
- No positrons

- RHIC Planning Meeting       October 29-20, 2005

- Richard G. Milner

## eRHIC: interaction region design 

-        - ZDR assumes IR region with zero crossing angle
- Crab-crossing scheme considered (rotate ion bunch into direction of electron beam): However, required deflecting RF voltage: V=14.4MV  factor 10 larger then for KEKB crab cavities so excluded for now.
- Initial design: dipole winding in the superconducting electron low- quadrupoles
- Limitation: 1m machine element free region

- RHIC Planning Meeting       October 29-20, 2005

- Richard G. Milner

## Review of eRHIC ZDR

- Detailed technical review of both ring-ring and linac-ring designs by Machine Advisory Committee in June 2005
- Excellent technical criticism
- Status of the present design studies is not yet advanced enough to make a decision
- Ring-ring: challenging project, can be extrapolated from to-day’s experience and technology.  Suggests pursuing ring-ring design as first priority with goal to develop a CDR
- Linac-ring: much more attractive regarding luminosity.  Requires successful extrapolations on a number of fronts that are beyond what can be achieved to-day.  Requires intensive R&D.
- Concentrate first on R&D which is useful to ring-ring **and **ring-linac options, e.g. ERL prototype, cooling of ion beams, and beam dynamics.

- RHIC Planning Meeting       October 29-20, 2005

- Richard G. Milner

## eRHIC lepton ring vs. PEP-II rings

- Ring type:		all are collider lepton rings
- Energy range: 		5~10 GeV vs. 3-9 GeV
- Beam currents:   	0.5 ~1A  vs. 1.5 ~ 3 A
- 		similar bunch current, PEP-II has more bunches
- Beam dimensions:  	comparable
- 		emit.: ~50 nm rad,  beta_ave: ~15 m (arc, rf)
- Collective effects:	similar
- In general, technical approaches are very similar.

- RHIC Planning Meeting       October 29-20, 2005

- Richard G. Milner

## RF :  	90% from PEP-II with minimum modifications
Magnet/power supply:  		~ 50 % from PEP-II
Feedback:   			100%
Beam diagnostics / control:   	~ 50%
Vacuum:    	now we count it as 20% ~ 30% 
Injector: 		design not clear at this point. 

A large amount of PEP-II components could be used for the eRHIC lepton ring.
A preliminary estimate shows that we may save 20% to 30% of cost by using PEP-II components.  More detailed studies underway.

- Magnet/power supply:  		~ 50 % from PEP-II
- Feedback:   			100%
- Beam diagnostics / control:   	~ 50%
- Vacuum:    	now we count it as 20% ~ 30%
- Injector: 		design not clear at this point.
- A large amount of PEP-II components could be used for the eRHIC lepton ring.
- A preliminary estimate shows that we may save 20% to 30% of cost by using PEP-II components.  More detailed studies underway.

**D. Wang/Bates**

**Preliminary conclusions**

- RHIC Planning Meeting       October 29-20, 2005

- Richard G. Milner

## eRHIC - Detector design 

**General purpose unpolarized/polarized **
**                 ****ELECTR****on-****A**
- - compact central detector with specialized
-    forward/rear tagging detectors
- - required free region ± 3m

-  **Forward detector  unpolarized eA**
-  specialized detector system to detect
-   complete final state in eA collisions
- - Require dfree region ± 5 m

-  Common detector subsystems
-  R&D coherent with heavy ion
-   detector upgrades

**See talk by B. Surrow**

- RHIC Planning Meeting       October 29-20, 2005

- Richard G. Milner

## eRHIC realization

- Science case must be strengthened and sharpened
- Accelerator case must be developed so that the science can be made to happen in a timely fashion
- eRHIC must be presented coherently in the context of future RHIC plans
- It is essential to energize and organize the hadronic community worldwide in support of eRHIC
- We expect a new Long Range planning exercise within the next several years
- We have to be ready to argue for eRHIC in the context of other communities arguing strongly for other priorities

- RHIC Planning Meeting       October 29-20, 2005

- Richard G. Milner

## Summary

- A high luminosity lepton-ion collider offers a very exciting future for the study of the fundamental structure of matter
- eRHIC appears to be a very attractive means to realize it in a cost-effective and timely way
- It is essential to develop the most powerful eRHIC case with a sense of urgency

- RHIC Planning Meeting       October 29-20, 2005

- Richard G. Milner