Perspectives of Nuclear Physics in Europe - European Science ...

4.1 Hadron Physics
European and Global Perspectives
In Europe there are several major institutes with active
experimental research programmes in hadron-structure
physics. In France, there are CEA/Saclay and INP at
Orsay, and also the Universities of Clermont-Ferrand
and Grenoble which are involved at MAMI, at JLab in the
USA, and in the CERN COMPASS programme. The same
is true of several institutes in Italy, namely the INFN sections
at Frascati, Torino, Trieste, Pavia, Ferrara, Genova
and Trento. There is a long-standing collaboration and
exchange among these institutes, which will definitely be
continued and intensified. The contribution of British universities
at Glasgow and Edinburgh to hadron-structure
explorations is substantial. The Universities of Bonn and
Darmstadt are running electron accelerators comparable
to the MAMI facility at Mainz. Mainz University has initiated
a discussion on teaming up with Bonn University
and the Research Centre Jülich for an ambi tious new
project at GSI/FAIR, the Electron-Nucleon Collider (ENC).
Studies for such a collider using the HESR are being
pursued with the aim of establishing a common physics
programme, which could be pursued as an international
project. CERN with its COMPASS programme at the
SPS recently invited the hadron community to submit
new proposals for fixed-target experiments. In the
USA, there is a rich hadron-structure programme at the
Brookhaven National Laboratory, including studies of
the proton spin at the RHIC collider. The high energy of
that machine means that cross sections for electroweak
processes are large and can be used to extract hadron
structure information. In addition RHIC is making plans
for a future electron-nucleon collider (eRHIC, MEeRHIC,
EIC). MIT Bates has stopped data taking at its electron
linac/storage ring complex and is now pursuing the EIC
project. JLab at Newport News in Virginia currently operates
the 6 GeV CEBAF accelerator and has a future
programme on structure and spectroscopy of hadrons
based around an upgrade of the existing accelerator
complex to 12 GeV beam energy. It is also pursuing
possible electron-nucleon collider projects at different
levels (ELIC). Another approach to hadron structure physics
is provided by the current e + e - facilities at Frascati
(Daphne), Beijing (BEPC), and at Tskuba (KEK B-Factory
with the Belle experiment).
and much more. This information will be partly complementary
to space-like observable studies at other
accelerator facilities. In the meantime, the continuation
of the rich hadron structure experimental and theoretical
programme at the various current accelerator facilities
should therefore be of the highest importance.
A new high-luminosity, high-polarisation electronnucleon
collider with a centre-of-mass energy larger than
10 GeV would allow a precise determination of parton
distributions, generalised parton distributions and transverse
momentum distributions over a wide Q 2 range.
This would also lead to much improved knowledge of
the spin and flavour space-time structure of quarks and
gluons inside the nucleon. In addition to the reconstruction
of the momentum dependent spatial distribution of
quarks and gluons inside the nucleon, the transverse spin
distribution could be precisely measured, as well as the
longitudinal spin distribution of quarks and gluons and
the quark angular momentum.
Electron-nucleon colliders for hadron structure are
currently under discussion at different places in the US
(MEeRhic at BNL and medium energy ELIC at JLab) as
well as in Europe (ENC at GSI/FAIR). The ENC would use
the HESR ring at FAIR for polarised protons and add an
3.3 GeV electron beam, yielding a centre-of-mass energy
of about 14 GeV with high polarisation and a luminosity
of about 6 10 32 cm -2 s -1 . A moderately modified PANDA
detector would be used. A feasibility study for both the
physics programme and the high luminosity accelerator
has recently started.
Structure and spectroscopy of hadrons reveal complementary
aspects of strong interaction physics using
different methods and particle beams. An electronnucleon
collider as a future upgrade to FAIR would allow
the spectroscopy studies using PANDA experiment to
be complemented by an advanced nucleon-structure
programme.
Medium- and Long-Term Strategy
The development of the FAIR facility at GSI is of the
highest priority for the tuture of the field. The PANDA
experiment at the HESR storage ring is primarily a
spectroscopy experiment, but will allow precise determinations
of many nucleon structure observables as
well, such as time-like form factors, time-like generalised
parton distributions, transverse momentum distributions
68 | Perspectives of Nuclear Physics in Europe – NuPECC Long Range Plan 2010