Progress concerning R-parity violating SUSY
*---------------------------------------------------------
R. Galea
"Status on SUSANA Development"
*---------------------------------------------------------
Raphael detailed the improvements he implemented
together with T.Jones in the SUSANA version used
by Zeus experiment. We remind here that SUSANA is an
event generator for the resonant squark production
decaying into a quark and a neutralino, followed by
the neutralino decay into one lepton and 2 jets
(H.Dreiner, J. Butterworh).
The neutralino is assumed to be a pure photino.
The main two improvements implemented are :
o choose e-/e+ in initial state
o implementation of Initial and Final state Partons Showers
Distributions showing the effect of PS on mass spectrum
have been shown and compared to what is obtained with
SPYTHIA.
*---------------------------------------------------------
E. Perez
"Improvements of e-p SUSYGEN : Beyond the
resonant squark production"
*---------------------------------------------------------
At the last WG80 meeting, SUSYGEN allowed to treat
resonant squark production followed by any Rp-violating
or gauge decay of the squark.
But, for e.g. the process :
e + quark -> quark + neutralino,
t-channel and u-channel diagrams also exist ! :
e u
\ tilde{u}_L /
\________________/ => s-channel
/ \
/ \
d chi^0
e
----------------------- chi^0
|
|
| tilde{e}_L => t-channel
|
d |
----------------------- u
e
----------------------- u
|
|
| tilde{d}_R => u-channel
|
d |
----------------------- chi^0
The t and u channels for quark + neutralino production are
now implemented in SUSYGEN. The most important is the
selectron t-channel exchange, which interferes positively
with the s-channel. The enhancement of the cross section
can reach ~ 30% for light selectrons. For example, with
squarks=200 GeV, photino-like neutralino = 40 GeV, lambda'=0.5 :
sigma(e- u -> d chi0) = 16.2 pb for selectron=60 GeV
sigma(e- u -> d chi0) = 12 pb for selectron very heavy
In comparison with SUSANA generator, the full mixing of the
neutralino is here taken into account. Due to the different
couplings when the neutralino is not a pure photino,
the effect on the cross section is sizeable.
For the next meeting, the t-channel sneutrino exchange
should as well be included for e + q -> q + chargino.