Berlin 2005 – wissenschaftliches Programm
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HK: Physik der Hadronen und Kerne
HK 31: Elektromagnetische und Hadronische Proben
HK 31.2: Vortrag
Dienstag, 8. März 2005, 16:45–17:00, TU MA004
In Search of the Nature of the γγ Line at 2mπ in pp → pp γγ and its relation to ππ Production ∗ — •M. Bashkanov, H. Clement, E. Doroshkevich, M. Kaskulov, O. Khakimova, F. Kren, R. Meier, T. Skorodko, and G. J. Wagner — Physikalisches Institut, Universität Tübingen
At CELSIUS-WASA pp collisions with the emission of
γγ, π, ππ, η have been measured exclusively with
4 to 6
overconstraints. In the Mγγ spectrum a small, narrow line
has
been observed at Mγγ=2mπ. In search of the nature of this
line we have investigated a variety of scenarios. Aside from the
possibility
that this line is real,
the only realistic alternative is a scenario, where γs originating
from π0π0 production merge into common γ clusters. This
merger
scenario is only effective if the π0s move parallel, i.e.,
Mπ0π0≈ 2mπ0. A peculiar enhancement is indeed
observed
in Mπ0π0 right at threshold. However, reconstruction of the
π0π0 parent spectrum by MC simulations in the merger scenario leads
to the postulate of a threshold enhancement in Mπ0π0,
which is an order of magnitude larger
than the actual observed one. In order to shed
more light onto this problem we have investigated
pd →3Heππ along with its γγ channel.
In Mπ0π0 we again find a threshold enhancement, which is even
much larger than in pp collisions. Since in all cases
the Mπ+π− spectra behave normal, these observations indicate a
strong isospin breaking between π0π0 and π+π− thresholds.
We investigate the possibility that both observations in Mπ0π0
and Mγγ are related by a dynamic σ.
∗ supported by BMBF (06 TU 201), DFG
(Europ. Graduiertenkolleg) and Landesforschungsschwerpunkt (Quasiteilchen)