# Presentation: 118621

## The eRHIC project atBrookhaven National Laboratory 

## Outline 

**Outline**

- Machine and detector design studies - eRHIC

- Physics case - eRHIC

-   Introduction

-   The RHIC physics program and recent results

## The RHIC collider facility at BNL (1) 

- RHIC facility: Unique collider facility which allows to collide different species (Au-Au and d-Au as well as polarized p-p) at variable beam energy
- Explore the nature of matter under extreme conditions (RHIC relativistic-heavy ion program)
- Explore the nature of the proton spin (RHIC spin physics program)

- Au+Au (d+Au)

- Experiments:
- PHENIX
- STAR
- BRAHMS
- PHOBOS

- Experiments:
- PHENIX
- STAR
- BRAHMS & PP2PP

**Introduction**

## The RHIC collider facility at BNL (2) 

- PHOBOS

- RHIC relativistivic-heavy ion program

- RHIC spin physics program

- RHIC: Two concentric superconducting magnet rings, 3.8km circumference
- Start of construction: January 1991
- First collisions of Au-Au ions: June 2000
- First collision of trans. polarized protons: December 2001
- First collisions of long. polarized protons: May 2003

- Achieved configuration:
- Au+Au:  √s = 130 and 200 GeV
- d+Au: √s = 200 GeV
- p+p: √s = 200 GeV

**Introduction**

## Exploring a new state of matter: “The Quark-Gluon Plasma” 

- Exploring a new state of matter: “The Quark-Gluon Plasma”

- QCD predicts the existence of a color-deconfined medium with quarks and gluons as the relevant degrees of freedom
- Create this new state of matter (QGP) in relativistic heavy-ion collisions:

- Exploring several different signatures is crucial to establish a phase transition from a hadron gas to the quark-gluon plasma
- Those signatures point to different aspects of the phase transition to be explored, e.g. partonic energy loss!
- Partonic energy loss provides a sensitive probe of matter created in relativistic heavy-ion collisions:

- Attenuation of leading particles from jet fragmentation (“Jet quenching”)

- P. Braun-Munzinger, nucl-ex/0007021

- The RHIC physics program and recent results

## The RHIC physics program and recent results

- RHIC results in Au+Au and d+Au collisions

- d+Au

- Au+Au

- d+Au

- Au+Au

- Suppression of inclusive yield in Au-Au collisions is a final-state effect!

## RHIC Spin program (e.g. ΔG) 

- Fundamental question: How is the proton spin  made up?

**Quark Spin**

**Orbital Motion**

-  Where is the spin of the proton then?

- Need: New generation of experiments to explore the spin structure of the proton: polarized proton collisions at RHIC which allows to access directly G in polarized pp collisions!

- At present: G is only poorly constrained from scaling violations in fixed target DIS experiments

-  SMC result: Fraction of proton spin carried by quarks is small:

-  SMC QCD-fit:

- SMC, Phys. Rev. D58 (1998) 112002.

- RHIC spin program:

- Spin structure of the proton (gluon polarization, flavor decomposition, transversity)
- Spin dependence of fundamental interactions
- Spin dependence of fragmentation
- Spin dependence in elastic polarized pp collisions

- Unique multi-year program which has just started...!
- Explore various aspects of the spin structure of the proton in a new domain:

- The RHIC physics program and recent results

## The RHIC physics program and recent results

- AN is found to increase with energy similar to E704 result
- This behavior is also seen by several models which predict non-zero AN values

- Sivers: include intrinsic transverse component, k, in initial state (before scattering takes place)
- Collins: include intrinsic transverse component, k, in final state (after scattering took place)
- Qiu and Sterman: more “complicated QCD calculations” (higher-twist, multi-parton correlations)

- Several approaches beyond the basic “naive QCD calculations” yield non-zero AN values at RHIC energies:

- RHIC results in transverse polarized pp collisions

## Physics case - eRHIC

- General comments on eRHIC

- Explore new QCD regime in eA scattering and polarized ep scattering in collider mode beyond the fixed target DIS era
- Complement current physics program at RHIC (AA/pp  eA/ep)

**Goal of eRHIC project at BNL:**

- Establish a high energy, high intensity polarized electron/positron beam facility at BNL to collide with the existing RHIC heavy ion and polarized proton beam

## Current world status of F2 (unpolarized DIS) and g1 (polarized DIS) data  

- Current world status of F2 (unpolarized DIS) and g1 (polarized DIS) data

- F2 results:

- g1 results:

- 4 orders of magnitude in x!

- 4 orders of magnitude in Q2!

- Good description of F2/g1 data by NLO DGLAP fits
- HERA collider data extended kinematic region towards larger Q2 and low x for F2
- g1 limited by fixed target data at low Q2 and high x

- Limited range in x and Q2!

- Physics case - eRHIC

## Physics case - eRHIC

- eRHIC physics program

- Unpolarized ep scattering:
- Longitudinal structure function FL
- Flavor separation
- Precise direct measurement of the gluon (0.001 < x < 0.5-1)
- Exclusive reactions
- Transition region (Q2  0)
- Polarized ep scattering:
- Polarized structure function of the proton
- Gluon polarization (Complementary efforts at RHIC, COMPASS and HERMES)
- Exclusive reactions
- Deeply-virtual Compton scattering (Orbital angular momentum of quarks)

- 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.

## eRHIC physics program

- Physics case - eRHIC

- Measurements on the gluon polarization at eRHIC:
- Extract gluon polarization in various modes in DIS and photoproduction
- Good precision
- x-range: 0.01 < x < 0.3

- eRHIC Di-Jet
- DATA 2fb**-1**

## Physics case - eRHIC

- Physics program

- eA scattering:
- Study eA scattering for the first time in collider mode
- Influence of nuclear medium within nucleus/nucleon: F2A/F2N
- Gluon distribution within nucleus
- Parton saturation at low-x:
-  Large enhancement of the parton densities / unit area compared to a nucleon, thus access effectively lower values in x then comparable ep mode!

## General comments on eRHIC

- Essential features eRHIC:
- High luminosity:  ≈ 1 · 1033 cm-2 sec-1 (ep) / ≈ 1 · 1031 cm-2 sec-1 (eA)
- High polarization (polarized e, p and light ion beams):  ≈ 70%
- Heavy ion beams of several elements
- High (variable) energy: Ee ≈ 5 - 10 GeV, Ep ≈ 50 - 250GeV
- Variable center-of-mass energy (ep): 30 – 100 GeV
- Kinematic reach: x ≈ 10-4 - 0.7 (Q2 > 1 GeV2)
- Optimal detector for physics to be explored at eRHIC                                    (Lessons from HERA!)

- Machine and detector studies - eRHIC

- Current electron ring design:
- Proposed by BINP & MIT-Bates + BNL with input from DESY (IR design under active discussion)
- e-ring is approximately 1⁄4 of RHIC ring
- So far: Collisions in one interaction region (Multiple detectors are under consideration)
- Full energy injection using polarized electron source and 10 GeV energy linac
- Longitudinal polarization using local spin rotators
- Possible collisions points: IP12, IP2 and IP4

## Machine and detector studies - eRHIC

|  | Electron beam | Proton (ion) beam |
| --- | --- | --- |
| Number of particles per bunch | 1x1011  | 1x1011  p
1x109 Au |
| Collision frequency | 28.15 MHz (~ 35ns bunch crossing) |  |
| Number of bunches | 90-120 | 360 |
| Beam-beam parameter | 0.05 | 0.005 |

|  | 250p/10e | 50p/5e | 100Au/10e | 100Au/5e |
| --- | --- | --- | --- | --- |
| Normalized 96% ion emittance,
π mm mrad  | 14.5 | 14.5 | 6 | 6 |
| IP beta (ions), cm | 26 | 26 | 25 | 50 |
| Electron rms emittance, nm | 23 | 46 | 18 | 36 |
| IP beta (electrons), cm | 10 | 25 | 12 | 12 |
| Luminosity, 1033 cm-2s-1 | 1 | 0.2 | 0.01 | 0.005 |

- Beam parameter limits assumed for a realistic design

- eRHIC parameters for different configurations

- eRHIC machine parameters

## Machine and detector studies - eRHIC

- TESLA-N

- eRHIC

- ELIC-Jlab

- eRHIC in comparison to other facilities

- eRHIC features:
- Variable beam energy
- p and ion beams
- Proton and light ion polarization
- Large luminosity
- Huge kinematic reach

## Requirements on a future eRHIC detector  

- Basic requirements:
- Measure precisely scattered electron (Kinematics of DIS reaction)
- Tag electrons under small angles (Study of transition region)
- Measure hadronic final state (Kinematics, jet studies, flavor tagging, fragmentation studies, particle ID)
- Zero-degree photon detector to control radiative corrections and in e-A physics to tag nuclear de-excitations
- Missing ET for events with neutrinos in the final state (W decays)
- Tagging of forward particles (Diffraction and nuclear fragments)

- Machine and detector studies - eRHIC

## Machine and detector studies - eRHIC

- GEANT simulation started of a central detector geometry
- Study of synchrotron radiation background is underway (Contacts to DESY colleagues)
- Crucial: Forward and rear tagging devices and acceptance limitation of inner machine elements

- eRHIC detector design studies

- Ee=10 GeV

- Ep=250 GeV

## Past:
Series of workshops
Before 2001:
Indiana/MIT: EPIC 
eRHIC
Merge to EIC: EIC = eRHIC + EPIC (Sept. 2000)
White paper (March 2001)
EIC workshop (Febr. 2002)
“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 ( JLAB-ELIC 3)

Present:
Potential next large-scale project at BNL beyond RHIC
Beam cooling for RHIC already within eRHIC machine budget
Strong intention to have a dedicated eRHIC group at BNL soon 
WWW-page: http://www.bnl.gov/EIC
eRHIC: Zero-th Design Report (Physics + Accelerator Lattice)  Requested by BNL Management by January 2004

- Series of workshops
- Before 2001:
- Indiana/MIT: EPIC
- eRHIC
- Merge to EIC: EIC = eRHIC + EPIC (Sept. 2000)
- White paper (March 2001)
- EIC workshop (Febr. 2002)
*“*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 ( JLAB-ELIC 3)
- Present:
- Potential next large-scale project at BNL beyond RHIC
- Beam cooling for RHIC already within eRHIC machine budget
- Strong intention to have a dedicated eRHIC group at BNL soon
- WWW-page: _http://www.bnl.gov/EIC_
- eRHIC: Zero-th Design Report (Physics + Accelerator Lattice)  Requested by BNL Management by January 2004

**Outlook - eRHIC**

## Future:

Series of CDR’s:
Rough institutional responsibility, interests and functionality of detector by 2005/2006 (CD0)
Detector R&D money could start for hardware by approx. 2007 (CD1)
Ring, IR, Detector design document by approx. 2008 (CD2)
Final Design ready by approx. 2010 (CD3)  Begin construction

First collisions in approx. 10 years from now...!

- Series of CDR’s:
- Rough institutional responsibility, interests and functionality of detector by 2005/2006 (CD0)
- Detector R&D money could start for hardware by approx. 2007 (CD1)
- Ring, IR, Detector design document by approx. 2008 (CD2)
- Final Design ready by approx. 2010 (CD3)  Begin construction
- First collisions in approx. 10 years from now...!

**Outlook - eRHIC**