FROM HERA TO FUTURE ELECTRON-ION COLLIDERS Page: 3 of 7
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FROM HERA TO FUTURE ELECTRON-ION COLLIDERS*
V. Ptitsyn, BNL, Upton, NY 11980, USA
An overview of the proposals of new electron-ion
colliders - e-RHIC at BNL, EIC at JLab and LHeC at
CERN - in the light of experience with HERA is
The year 2007 is the last year of the operation of
lepton-proton collider HERA at DESY. This unique
machine opened for the scientific exploration the area of
physics, which had not been easily accessible with any
other colliders or fixed target experiments. During 15
years of the HERA operation the remarkable results have
been obtained, including the precise data on fine details of
the proton structure, the discovery of very high density of
sea quarks and gluons present in the proton, the detailed
data on electro-weak electron-quark interactions and the
precise measurement of strong interaction coupling
constant . As HERA leaves the scientific exploration
scene, several future projects are under consideration in
the USA and Europe. Those projects intend not only to
extend the knowledge of physics area studied at HERA,
but also to provide the new exploration tools by involving
lepton collisions with heavy ions as well as with polarized
protons and polarized light ions. All of the future lepton-
ion colliders projects are based on the extension of
already existing machines. The JLab considers the
addition of. ion and electron storage rings to the upgraded
CEBAF electron accelerator in order to form the ELIC
collider . BNL seeks to extend capabilities of the
existing RHIC machine by the addition of an electron
accelerator, thus creating the eRHIC machine [3,4].
Correspondingly the LHeC collider has been proposed as
a possible future extension of the LHC at CERN . The
future lepton-ion colliders aim to considerably larger
luminosity of lepton-proton collisions than used at HERA.
Also new colliders will operate in different from HERA
the center-of-mass energy (CME) regions. The eRHIC
and ELIC machines consider their operation at the CME
area of 20 to 100 GeV, with the luminosities ranging in
1032-1034 cm-2sI values. The LHeC goal will be to explore
the collisions at 1.4 TeV CME with the luminosities about
1033 C-2s 1.
Table 1 presents the summary of main beam parameters
for electron-proton collisions for the collider designs
discussed in this paper as well as for HERA. For eRHIC
and ELIC the parameters are shown for the electron-
proton operation mode at the highest design energy.
' Work performed under US DOE contract DE-AC02-98CH1 -886
For a long time the lepton-hadron scattering has been a
very important tool of scientific discovery. The scattering,
presented a clean way to look inside the structures bound
together by strong forces and study the components of
those structures. Before and during HERA era several
fixed target experiments have explored the process of
Deep Inelastic Scattering of leptons on nucleons in order
to gain the knowledge on the nucleon internal structure,
including the structure of the nucleon spin, and to
improve understanding of QCD theory of strong
interactions. After HERA collider had been built,
considerably higher CME gave physicists the opportunity
to investigate structure functions of protons at
considerably better spatial resolution and in the range of
small x values (fractional moment carried by a nucleon
constituent). Besides higher CME, another advantage of a
collider against a fixed target experiment is better
separation of products of a scattering process, which
allows for the complete examination of the final states.
The future lepton-ion colliders aim to continue
exploration of quark-gluon structure of nucleons,
extending kinematic range and adding new dimensions of
that exploration . Collisions of polarized leptons with
polarized proton or light ion beam at eRHIC and ELIC
will contribute into the investigation of the proton and
neutron spin content, which still remains a puzzle. The
examination of the final states will allow to do the
measurements of the structure functions marked by quark
The lepton collisions with heavy ions will provide a
new tool for studies of partonic picture of nuclei and
nuclear binding. The gluon saturation state, the Color
Glass Condensate, can be created and studied in lepton-
heavy ion collisions in eRHIC and ELIC, as well as in
low-x lepton-proton collisions in LHeC.
All studies mentioned above should not only provide
the knowledge of specific structures and states of the
matter but also would improve considerably our
understanding of the QCD theory. Some specific
precision QCD theory tests are also planned as a part of
the lepton-ion collider physic program.
Looking for new physics beyond the Standard Model
the LHeC physics program includes the search and study
of leptoquark particles .
COMMON DESIGN ISSUES
Some issues of the collider design are similar for all
future lepton-ion colliders. The experience from HERA
design and operation is used for various design aspects.
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PTITSYN,V. FROM HERA TO FUTURE ELECTRON-ION COLLIDERS, article, June 25, 2007; United States. (digital.library.unt.edu/ark:/67531/metadc891003/m1/3/: accessed August 21, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.