# Presentation: 913195

## eRHIC: Physics, Design & Status

**Abhay Deshpande**
**RIKEN BNL Research Center at BNL**

**RIKEN High pT Workshop**
**December 5th , 2003**

- A

## Some spin & Low x-high Q2 surprises...

- Stern & Gehrlach (1921) Space:
-        quantization associated with direction
- Goudschmidt & Ulhenbeck (1926):
-        Atomic fine structure & electron spin
-        magnetic moment
- Stern (1933) Proton anomalous
-        magnetic moment 2.79 ****N
- Kusch(1947) Electron anomalous
- magnetic moment 1.00119****0
- Prescott & Yale-SLAC Collaboration (1978)
-        EW interference in polarized e-d DIS,
-        parity non-conservation
**European Muon Collaboration (1988/9) **
**       ****Spin Crisis/Puzzle**
- Transverse single spin asymmetries:
-       E704, AGS pp scattering, HERMES (1990s) RHIC Spin (2001)
-       >> single spin neutron production(PHENIX)
-       >> pion production (STAR) at 200 GeV Sqrt(S)

- Elastic e-p scattering at SLAC (1950s)   Q2 ~ 1 GeV2   Finite size of the proton
- Inelastic e-p scattering at SLAC (1960s) Q2 > 1 GeV2  Parton structure of the proton
- Inelastic mu-p scattering off p/d/N at CERN (1980s)  Q2 > 1 GeV2  Unpolarized EMC effect, nuclear shadowing?
- Inelastic e-p scattering at HERA/DESY (1990s) Q2 > 1 GeV2
-       Unexpected rise of F2 at low x
-       Diffraction in e-p
-       Saturation(??)

- A facility that does both would be ideal....

- Further, we now are wiser in
- planning a detector design to
- observe these new/surprising
- physics!

- Abhay Deshpande

- high pT workshop

## Deep Inelastic Scattering

- Observe scattered electron/muon & hadrons in current jets
- Observe spectator or remnant jet
-   >> suitably designed detector...

- [1]

- [3]

- [2]

- [1]+[2]+[3]    [3]  exclusive
- [1]+[2]          [2] semi-inclusive
- [1]                [1] inclusive

- Lumi

- Abhay Deshpande

- high pT workshop

## Why Collider in the Future?

- Past polarized DIS experiments: in fixed target mode
- Collider has distinct advantages --- Confirmed at HERA
- Better angular separation between scattered lepton & nuclear fragments
-      Better resolution of electromagnetic probe
-      Recognition of rapidity gap events (recent diffractive physics)
- Better measurement of nuclear fragments
- Higher center of mass (CoM) energies reachable
***Tricky integration of beam pipe – interaction region -- detector***

- Abhay Deshpande

- high pT workshop

## Proposal under consideration

**eRHIC at BNL**
- A high energy, high intensity polarized electron/positron
- beam facility at BNL to collide with the existing RHIC
- heavy ion and polarized proton beam would
- significantly enhance RHIC’s ability to
- probe fundamental and universal aspects of QCD

-  Linac+e-ring+RHIC
-         Linac+Ring Design (backup)
-  Linac+e-ring outside RHIC tunnel
-  Main design 10 GeV e beams,
-        5 GeV possible
-  e-facility OUTSIDE the RHIC tunnel
-  Operations do NOT interfere with
-        RHIC operations

- Abhay Deshpande

- high pT workshop

## eRHIC vs. Other DIS Facilities (I)

**eRHIC**

- DIS

- New kinematic region
- Ee = 5-10 GeV
- Ep = 30 – 250 GeV
- Sqrt(s) = ~25 – 100 GeV
- Kinematic reach of eRHIC
-     x   = 10-4  ~0.7  (Q2 > 1 GeV2)
-     Q2 = 0  104 GeV
- Polarized e, p and light ion beams  -- ~70%
- Heavy ion beams of ALL elements!
- High Luminosity
-     L  > (at least) 1033 cm-2 sec-1

- Abhay Deshpande

- high pT workshop

## eRHIC vs. Other DIS Facilities

**eRHIC vs. Other DIS Facilities**

**eRHIC:**
- >> Variable beam energy
- >> **p ******** U hadron beams**
- >> Light Ion  polarization
- >> Large Luminosity
- >> **Huge Kinematic reach**
**ELIC:****electron-light ion collider at Jlab**
- >> Variable beam energy
- >> Light Ion polarization
- >> **Huge Luminosity**

- TESLA-N

- eRHIC

- ELIC-Jlab

- Abhay Deshpande

- high pT workshop

## Scientific Frontiers Open to eRHIC

**Nucleon Structure:** polarized & unpolarized e-p/n scattering
-     -- Role of quarks and gluons in the nucleon
-          >> Unpolarized quark & gluon distributions, confinement in nucleons
-          >> Spin structure: polarized quark & gluon distributions
-     -- Correlation between partons
-          >> hard exclusive processes leading to Generalized Parton Distributions (GPD’s)
**Meson Structure:**
**    ****-- **Mesons are goldstone bosons and play a fundamental role in QCD
**Nuclear structure:** unpolarized e-A scattering
-     -- Role of quarks and gluons in nuclei, confinement in nuclei
-     -- e-p vs. e-A physics in comparison   and variability of A: from dU
**Hadronization in nucleons and nuclei** **& effect of nuclear media**
-     -- How do partons knocked out of nucleon in DIS evolve in to colorless hadrons?
**Partonic matter under extreme conditions**
-     -- e-A vs. e-p scattering; study as a function of A

- Abhay Deshpande

- high pT workshop

## Unpolarized DIS e-p at eRHIC

- Large(r) kinematic region already covered at HERA but additional studies at eRHIC are possible & desirable
- Uniqueness of eRHIC: high luminosity, variable Sqrt(s), He3 beam, improved detector & interaction region
- Will enable precision physics:
-     -- He3 beams  neutron structure  d/u as x0,
-         dbar(x)-ubar(d)
-     -- precision measurement of S(Q2)
-     -- precision photo-production physics
-     -- precision gluon distribution in x=0.001 to x=0.6
-     -- slopes in dF2/dlnQ2   ***(Transition: QCD-to-pQCD & low x)***
-     -- flavor separation (charm and strangeness)
-     -- exclusive reaction measurements
-     -- nuclear fragmentation region measurements

- [1]
- [1]
- [1]
- [1]
- [1]
- [2]
- [2,3]
- [2,3]

- Luminosity
- Requirement

- Abhay Deshpande

- high pT workshop

## Polarized DIS at eRHIC

- Spin structure functions g1 (p,n) at low x, high precision
-     -- g1(p-n): Bjorken Spin sum rule better than 1% accuracy
- Polarized gluon distribution function ****G(x,Q2)
-     -- at least three different experimental methods
- Precision measurement of S(Q2) from g1 scaling violations
- Polarized s.f. of the photon from photo-production
- Electroweak s. f. g5 via W**+/-** production
- Flavor separation of PDFs through semi-inclusive DIS
- Deeply Virtual Compton Scattering (DVCS)
-     >> Gerneralized Parton Distributions (GPDs)
- Transversity
- Drell-Hern-Gerasimov spin sum rule test at high 
- Target/Current fragmentation studies
- ... etc....

- [1]
- [1]
- [1]
- [1]
- [1,2]
- [1]
- [1,2]
- [3]
- [1]
- [1]
- [2,3]

- Luminosity
- Requirement

- Abhay Deshpande

- high pT workshop

## Our knowledge of structure functions

*F**2*

*g**1*

***Q******2****** (GeV******2******)***

***Q******2****** (GeV******2******)***

***10******5***

***10***

***10******2***

***1***

***10***

***10******3***

- Abhay Deshpande

- high pT workshop

## Proton g1(x,Q2) low x eRHIC

- eRHIC 250 x 10 GeV
- Luminosity = ~85 inv. pb/day

- Fixed target experiments
- 1989 – 1999 Data

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

**Studies included statistical error & detector smearing to confirm **
**that asymmetries are measurable.  ****No present or future approved **
**experiment will be able to make this measurement**

- Abhay Deshpande

- high pT workshop

## Low x measurement of g1 of Neutron

**Low x measurement of g****1**** of Neutron**

- With polarized He3
- ~ 2 weeks of data at eRHIC
- Compared with SMC(past) & possible HERA data
**If combined with g1 of proton results in Bjorken sum rule test of better than 1-2% within a couple of months of running**

**EIC 1 inv.fb**

- Abhay Deshpande

- high pT workshop

## Polarized Gluon Measurement at eRHIC

- This is the hottest of the experimental measurements being pursued at various experimental facilities:
-     -- HERMES/DESY, COMPASS/CERN, RHIC-Spin/BNL & E159/E160 at SLAC
-      -- Reliability from applicability of pQCD without doubt leaves *only RHIC*
- Measurements at eRHIC will be complimentary with RHIC
- Deep Inelastic Scattering kinematics at eRHIC
-     -- Scaling violations (pQCD analysis at NLO) of g1   ***First moment of ************G***
-      -- (2+1) jet production in photon-gluon-fusion process 
-      -- 2-high pT hadron production in PGF                         
- Photo-production (real photon) kinematics at eRHIC
-     -- Single and di-jet production in PGF
-      -- Open charm production in PGF

***Shape of  ************G(x)***

- Abhay Deshpande

- high pT workshop

## Photon Gluon Fusion at eRHIC

- “Direct” determination of ****G
-      -- Di-Jet events: (2+1)-jet events
-      -- High pT hadrons
- High Sqrt(s) at eRHIC
-      -- no theoretical ambiguities regarding interpretation of data
- Both methods tried at HERA in un-polarized gluon determination & both are successful!
-      -- NLO calculations exist
-      -- H1 and ZEUS results
-      -- Consistent with scaling violation F2 results on G

- Signal: PGF

- Background
- QCD Compton

- Abhay Deshpande

- high pT workshop

## Polarized PDFs of the Photons

- Photo-production studies with single and di-jet
- Photon Gluon Fusion or Gluon Gluon Fusion (Photon resolves in to its partonic contents)
- Resolved photon asymmetries result in measurements of spin structure of the photon
- Asymmetries sensitive to gluon polarization as well... but we will consider the gluon polarization “a known” quantity!

- Direct Photon

- Resolved Photon

- Abhay Deshpande

- high pT workshop

## Parity Violating Structure Function g5

- This is also a test

**For eRHIC kinematics**

-  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

- Abhay Deshpande

- high pT workshop

## Highlights of e-A Physics at eRHIC

- Study of e-A physics in Collider mode for the first time
- QCD in a different environment
- Clarify & reinforce physics studied so far in fixed target e-A & **-A experiments including target fragmentation
-      QCD in:   x > [1/(2mNRN) ] ~ 0.1                        (high x)
-      QCD in:   [1/(2mNRA)] < x < [1/(2mNRN)] ~ 0.1 (medium x)
-      Quark/Gluon shadowing
-      Nuclear medium dependence of hadronization
- .... And extend in to a very low x region to explore:
-      saturation effects or high density partonic matter also called the Color Glass Condensate (CGC)
-      QCD in:  x < [1/(2mNRA)] ~ 0.01                        (low x)

- See: _[www.bnl.gov/eic](http://www.bnl.gov/eic)_   for further details

- Abhay Deshpande

- high pT workshop

## DIS in Nuclei is Different! 

**Regions of:**
-  Fermi smearing
-  EMC effect
-  Enhancement
-  Shadowing
-  Saturation?
- Regions of shadowing and saturation mostly around Q2 ~1 GeV2
- An e-A collision at eRHIC can be at significantly higher Q2

- F2D/F2A

- Low Q2!

- E665, NMC, SLAC Experiments

- Abhay Deshpande

- high pT workshop

## Statistical Precision at eRHIC for e-A

- High precision at eRHIC shown statistical errors for 1 pb-1
- Recall: eRHIC will ~85 pb-1 per day
- NMC data F2(Sn/D)
- eRHIC’s Q2 range between 1 and 10 GeV2
- Will explore saturation region!

**eRHIC**

- Abhay Deshpande

- high pT workshop

## The Saturation Region...

- As parton densities grow, standard pQCD break down.
- Even though coupling is weak, physics may be non-perturbative due to high field strengths generated by large number of partons.
- A new state of matter???

- An e-A collider/detector experiment with high luminosity and
- capability to have different species of nuclei in the same detector
- would be ideal...  Need the eRHIC at BNL

- Abhay Deshpande

- high pT workshop

## A Color Glass Condensate??

- At small x, partons are rapidly fluctuating gluons interacting weakly with each other, but still strongly coupled to the high x parton color charges which act as random static sources of COLOR charge
-      Analogous to spin GLASS systems in condensed matter: a disordered spin state coupled to random magnetic impurities
- Gluon occupation number large, being bosons they can occupy the same state to form a CONDENSATE
-       Bose Einstein condensate leads to a huge over population of ground states
- A new “state matter”(??): Color Glass Condensate (CGC) at high energy density would display dramatically different, yet simple properties of glassy condensates

- E. Iancu, J.J-MarianL. McLerran,R. Venugopalan, et al.

***And now Color Quantum Liquid!!! (CQL)???***

- Abhay Deshpande

- high pT workshop

## Signatures of Saturation/CGC (I)

- Structure functions F2(x,Q2), dF2/dlnQ2, dF2/dlnx
-     - dF2/dlnQ2 at fixed x at high Q2 is the gluon distribution
-     - CGC vs. conventional pQCD predict very different
-     - Gluon measurements using semi-inclusive... di-jet final states
-     - eRHIC will differentiate them easily for protons and heavy nuclei
- Longitudinal structure function FL = F2 – 2xF1
-        - Provide independent gluon distribution measurement
-     - Needs variable electron beam energy  Possible at eRHIC
- Measurement of nuclear shadowing
-     - Quark shadowing (F2A/A*F2N) in fixed target experiments observed
-     - Gluon shadowing (GA/A*GN) indirect evidence only... pQCD at NLO
-     - This is expected to be severe at low x and high Q2
-     - Ideal measurement for eRHIC

***Spin vs. un-polarized measurements in same detector***

- Abhay Deshpande

- high pT workshop

## Signatures of CGC (II)

- Shadowing and diffraction:
-     Relation between nuclear shadowing and diffraction will be very different at high parton density media... eRHIC will study this systematically as a function of A of the nuclei.
- Hard Diffraction
-      Large rapidity gap between current and target fragmentation region. At HERA 7% cross section diffractive.
-      In e-A at eRHIC, diffractive processes may contribute 30-40% to the total cross section.
- Coherent & Inclusive vector meson production:
-     For light vector mesons diff. Cross section. = 0.5 (inclusive)
-     Heavy vector mesons this decreases...finally reaching 1/lnQ2
-     eRHIC will measure for different nuclei, Jcross sections

***Detector: emphasis for forward physics!***

- Abhay Deshpande

- high pT workshop

## Present Lay Out of the Collider at BNL

- Proposed by BINP & MIT/Bates + BNL
-      with input from DESY
- E-ring is 1/3 of RHIC ring; linac ~500m
- Collisions in one interaction region
-      **>> Multiple detectors under consideration**
- Collision energies Ee=5-10 GeV
- Injection linac 10 GeV
- Lattice based on “superbend” magnets
- Self polarization using Sokolov Ternov Effect: (14-22 min pol. Time)
**IP12, IP2 and IP4 are possible candidates for collision points**

**OTHER :** Ring with 6 IPS, Linac-Ring,
- Linac-Re-circulating ring

-  e-cooling

**R&D needed & started**

- Abhay Deshpande

- high pT workshop

## A Detector for eRHIC  A 4 Detector

- Scattered electrons to measure kinematics of DIS
- Scattered electrons at small (~zero degrees) to tag photo production
- Central hadronic final state for kinematics, jet measurements, quark flavor tagging, fragmentation studies, particle ID
- Central hard photon and particle/vector detection (DVCS)
- ~Zero angle photon measurement to control radiative corrections and in e-A physics to tag nuclear de-excitations
- Missing ET for neutrino final states (W decays)
- Forward tagging for 1) nuclear fragments, 2) diffractive physics
- “At least one” second detector could be “rolled” in from time to time....
-      ...under consideration
- eRHIC will provide: 1) Variable beam energies 2) different hadronic species, some of them polarization, 3) high luminosity

- Abhay Deshpande

- high pT workshop

## Detector Design (I)... others expected

- Abhay Deshpande

- high pT workshop

## Detector Design II

- 5m

- 5m

**Inner tracker**

**Outer tracker**

- HCAL

- EMCAL

- e

- p/A

- Tool setup by B. Surrow

- Abhay Deshpande

- high pT workshop

## Moving Towards eRHIC....

- September 2001: eRHIC grew out of joining of two communities:
-      1) polarized eRHIC (ep and eA at RHIC)
-          BNL, UCLA, YALE and people from DESY & CERN
-       2) Electron Poliarized Ion Collider (EPIC) 3-5 GeV e X 30-50
-          GeV polarized light ions
-          Colorado, IUCF, MIT/Bates, HERMES collaborators
- February 2002: White paper submitted to NSAC Long Range Planning Review  Received enthusiastic support as a next R&D project
- Steering Committee: 8 members, one each from BNL, IUCF, LANL, LBL, MIT, UIUC, Caltech, JLAB, Kyoto U.+ Contact person (AD)
**~20 (~13 US + ~7 non-US) Institutes, ~100 physicists + ~40 accelerator physicists... ****Recent interest from HERA**
- See for more details: EIC/eRHIC  Web-page at **“http://www.bnl.gov/eic” **
**Subgroups: Accelerator WG, Physics WG + Detector WG**
- E-mails: BNL based self-registered email servers... list yourselves!

- Abhay Deshpande

- high pT workshop

## Present Activities

**Accelerator & IR Design WG:**
- BNL-MIT/Bates collaboration on e-ring design
- BNL-JLAB collaboration on linac design
- Weekly meetings, monthly video meetings
- Constant communication with Detector/Physics WG
- ZDR Ready by January 2004: Outside BNL Review March04
**Physics & MC WG:** (Theorists/Experimentalists: Welcome to Join!)
- BNL, Colorado U., Jlab, LBL, MIT, UIUC (researchers+students)
- Meet every three months
- Setup MC generators start studies of physics processes including available detector acceptances
- Will iterate with the detector/IR design and provide input guidance on the final detector design
**Detector Design:** Will be taken up in detail in the coming year
- 2004 Meetings: January(BNL), **April(Jlab),** August(??), Nov/Dec(BNL)

- Abhay Deshpande

- high pT workshop

## QCD & Hadronic Physics Experiments around the world 

- HERA: H1, ZEUS, HERMES
- End data taking ~2006
- End analysis ~2008/9
- Groups looking for construction & physics projects, of course there is LHC... but...
- CERN: COMPASS
- Future beyond 2007/8 uncertain for polarized DIS program
- Results ready by 2007/8
- SLAC: EXXX
- Spin & parity violation programs nothing beyond 2003
- RHIC II: RHIC Spin
- Up to 2012/13(?)
- RHIC II heavy ion program how much beyond this date?

***eRHIC construction 2017???!!***

- Abhay Deshpande

- high pT workshop

## A possible time line for eRHIC...

*“**Absolutely Central to the field...”  NSAC 2001-2 Long Range Planning*
*       **document summary; high on R&D recommendation projects.*
*Highest possible scientific recommendation from NSAC Subcommittee*
*      **February/March 2003, Readiness Index 2*
***One of the 28 “must-do” projects in the DOE’s list***
- eRHIC: Zero-th Design Report (Physics + Accelerator Lattice)
-      Requested by BNL Management: **January 2004**
-      e-cooling R&D money started (with RHIC II) some DOE+some BNL internal
**FOLLOWING THIS TIME LINE FOR GETTING READY:**
- Expected **“formal” approval 2005-6 Long Range Review**  (Ready CD0)
- Detector R&D money could start for hardware 2008 (CD1)
- Ring, IR, Detector design(s) 2009(CD2)
- Final Design Ready 2010 (CD3)  begin construction
- ~3/5  years for **staged detector and IR construction without interfering with the RHIC running**
***First collisions with partial detector: 2012/13(???)***

- Abhay Deshpande

- high pT workshop