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Global Perspective and Efforts
In the USA, JLab will receive a major upgrade in beam
energy within the next 4 years. New detectors and beam
lines complement this. The GlueX experiment will probe
similar physics to PANDA, but in the light-quark sector
just below the charm threshold. It is optimized to
look for hybrid states with strange quarks. An upgraded
CLAS12 experiment will study light baryon spectroscopy
at higher masses. In Japan, spectroscopy of strange
particles will also be done using the kaon beams at the
JPARC facility.
BELLE will continue running after a major upgrade of
the accelerator and the detector. The expected increase
in data rate by a factor of 100 will allow the possible
discovery of new phenomena exploiting the same techniques
as currently used but with greatly increased
sensitivity. This should not be a competitor for PANDA
in the field of precision hadron physics, provided the time
scales stay more-or-less as they are. SuperBELLE, coming
online 2014-15, will take several years to accumulate
the required statistics of several thousand events for a
final state to determine its quantum numbers from a
partial wave analysis. PANDA will be able to accumulate
sufficient data much faster. The inherent problems of
being limited by detector resolution or being constrained
to a specific decay chain will remain as disadvantages
for SuperBELLE compared to an antiproton facility.
The BESIII experiment in China has started data taking
and will dominate the traditional spectroscopy of the
charmonium states that are accessible at e + e – colliders.
The volume of the data it will produce and the quality
of the detector make it a major step forward in hadron
physics.
Theoretical groups from all over the world have started
to work together to address the difficult problems of
hadron physics and non-perturbative QCD. Regular
meetings are scheduled and common proposals to
funding agencies are beginning to appear.
4.1.5 Hadronic Interactions
Recent Achievements
and Hot Topics
The interactions between hadrons play a crucial role
in shaping our understanding of QCD. They are also at
the heart of the second manifestation of strong QCD –
the formation of atomic nuclei and other exotic forms
of strongly interacting matter. With the advent of EFTs
and progress in lattice QCD, supplemented by phenomenological
studies and the many high quality data from
various laboratories world-wide, the study of hadronic
interactions is developing into precision science.
Arguably the most advanced analyses have been performed
for interactions between mesons, in particular
between pions. Here, combining chiral perturbation theory
at two-loop order with dispersive techniques has led
to predictions of the S-wave ππ scattering lengths with
the astonishing precision of 2% – truly a benchmark calculation.
These scattering lengths are now being tested
in various experiments and also by lattice calculations
(see Figure 8). It is fascinating to see how pion physics
has become a precision laboratory both theoretically
and experimentally.
The extension of these studies to the simplest reaction
involving strange quarks, elastic πK scattering in
the threshold region, has not yet achieved such precision.
On the theoretical side, loops including the heavier
strange quark have more pronounced effects, and on
the experimental side, the database is not yet sufficient.
Furthermore, lattice calculations have not yet reached an
accuracy comparable to that of the ππ case. However,
Figure 8. Experimental and theoretical results for the S-wave ππ
scattering lengths.
Perspectives of Nuclear Physics in Europe – NuPECC Long Range Plan 2010 | 73