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3. Research Infrastructures and Networking
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Proposed accelerator layout to convert the HESR into a double-polarised proton-antiproton collider. Polarised antiprotons are produced
in the Antiproton Polariser Ring (APR) and then injected in the (COSY-like) Cooler Synchrotron Ring (CSR). Polarised protons will circulate
in the HESR.
A dedicated r.f.-system must be incorporated into
HESR to allow for multi bunch operation (h=100) at collision
energy. A bunch length s L ≤ 0.3m is foreseen to avoid
luminosity reduction by the hourglass effect. Another
extension of the HESR r.f.-system is required by the task
of accumulating a sufficient number of polarised bunches
at injection energy which leads to strong space charge
forces at this stage.
PAX at FAIR
A new chapter in studies of hadron physics will unfold
with the advent of a polarised antiproton beam provided
an efficient method for polarising antiprotons can be
demonstrated. The PAX Collaboration is performing
dedicated experiments to investigate the feasibility of
the only viable method demonstrated so far that could
yield a beam of polarised antiprotons, which is spinfiltering
of a stored beam by selective loss and selective
spin-flip through repetitive interaction with a polarised
internal target. Should this investigation be successful,
a natural implementation of polarised antiprotons might
be foreseen at the FAIR facility. The PAX Collaboration
has suggested to convert HESR into an asymmetric
polarised proton – polarised antiproton collider and to
study double polarised antiproton-proton reactions.
The physics case for experiments with polarised antiprotons
comprises:
• Double polarised antiproton-proton Drell-Yan reactions,
which are entirely dominated by the annihilation
of valence quarks in the proton with the valence
antiquarks in the antiproton. The measured double
spin-asymmetry A TT will allow the first direct measurement
of the still undetermined leading order (twist 2)
transversity structure function of the nucleon. No other
existing or future facility will be ever able to measure
the transversity in a competitive way directly.
• Measurements of the moduli and absolute phases
of the electromagnetic form-factors in the time-like
region, providing an independent way of testing the
Rosenbluth separation in the time-like region;
• Measurements of double-polarised proton-antiproton
hard scattering to be compared to the analogue pp
measurement, the asymmetry of which represents the
largest ever measured asymmetry in hadron physics,
and for which a theoretical interpretation is still missing;
52 | Perspectives of Nuclear Physics in Europe – NuPECC Long Range Plan 2010