SUSY Processes
The implementation of SUSY processes is currently still in a development
stage, so careful case-by-case validations against other codes are
strongly recommended and should be considered mandatory.
Please notify the authors (peter.skands@cern.ch)
of any significant deviations (i.e., larger than 10%). In some cases,
limited preliminary validations have
already been carried out by the authors. This is remarked on process by
process below.
Here is collected processes involving supersymmetric particle
production, with the exception of the (extended) Higgs sector.
Since the number of separate but closely related processes is so big,
there will not be switches for each separate process but only for a
reasonable set of subgroups. However, the general
switches SUSY:idA and SUSY:idB may be used in
conjunction with any of these groups to provide some additional
flexibility to concentrate on processes involving only specific (s)particle
final states, see below.
Important note:
In order to simulate SUSY processes it is required to read in the
couplings and masses relevant for the scenario to be studied. This
is done with the help of the SUSY Les Houches Accord (SLHA), including
the SLHA2 extensions and generalizations. (Internally, the SLHA2
conventions are used. SLHA1 spectra are automatically translated into
SLHA2 notation during initialization.) The
reading of a relevant SLHA file must be set up, as described
on this page.
Note also that lepton and photon initial states are not yet available. Only
quark/gluon-initiated 2->2 processes have been implemented. Likewise, direct
slepton production has not yet been implemented (i.e., 2->2 processes
involving sleptons in the final state). Sleptons will of course still be
produced through cascade decays of heavier (s)particles.
Finally, note that these cross sections will be correctly folded with open
branching fractions of cascade decays, but at present any difference between
particle and antiparticle decay tables is not taken into account. This
possibility will be included in a future update.
flag SUSY:all
(default = off)
Common switch for production of supersymmetric particles, i.e.
particles with R-parity -1.
mode SUSY:idA
(default = 0; minimum = 0)
Option to limit the sum over possible outgoing states in SUSY
2 -> 2 processes to ones including a specific particle
identity code. The default corresponds to summing over all possible
indices. A non-zero value of SUSY:idA selects only processes
that contain the state corresponding to that particular particle identity
code in the fundamental 2 -> 2 scattering process (symmetrized
over particle/antiparticle). It is the user's responsibility to ensure
that (a subset of) the processes be to simulated actually include this
particle at the 2 -> 2 level; thus, asking for the lightest
neutralino (code 1000021) to be present in a squark-squark production
process will give no match.
mode SUSY:idB
(default = 0; minimum = 0)
As for SUSY:idA, but requires an additional particle
with PDG code SUSY:idB to be present in the 2->2
process. Thus, using SUSY:idA and SUSY:idB
a specific subprocess can be selected. Again only the absolute sign is
used, i.e. the summation over particle and antiparticle is retained.
Gluino Pair Production
flag SUSY:gg2gluinogluino
(default = off)
Pair production of gluinos by gluon-gluon initial states. Does not
depend on flavour violation. This cross section has been validated against
Pythia 6 for SPS1a.
flag SUSY:qqbar2gluinogluino
(default = off)
Pair production of gluinos by quark-antiquark annihilation and
t-channel squark exchange. So far, these cross sections assume the
squark CKM is aligned with the quark CKM and that all quantities are
real, so effects of non-minimal flavour violation and/or CP violation
are not yet included. This cross section has been validated against
Pythia 6 for SPS1a.
Associated Squark-Gluino Production
flag SUSY:qg2squarkgluino
(default = off)
Associated production of a squark with a gluino. Only implemented for the
flavor-diagonal case. These cross sections have been validated against
Pythia 6 for SPS1a. Note: these cross sections are so far
limited to the SLHA1 flavor structure. They will not give correct results if
used with an SLHA2 spectrum.
Squark Pair Production
flag SUSY:gg2squarkantisquark
(default = off)
Pair production of a scalar quark together with a scalar antiquark by
gluon annhilation via s-channel gluon exhange, t- and u-channel squark
exchange, and the direct 4-point coupling.
The cross section expression follows
[Boz07] and has been validated against Pythia 6.
flag SUSY:qqbar2squarkantisquark
(default = off)
Pair production of a scalar quark together with a scalar antiquark
by quark-antiquark annihilation.
For same-isospin ~q~q* production (i.e., ~u~u*, ~u~c*, ...),
the s-channel gluon, photon, and Z and
t-channel gluino contributions have so far been implemented (i.e., the
t-channel neutralino contributions are neglected).
For opposite-isospin ~q~q* production (~u~d*, ~u~s*, ...),
the s-channel W and t-channel gluino
contributions have been implemented (i.e., the t-channel neutralino
contributions are neglected).
The cross section expressions follow [Boz07]
and should thus be valid also in the case of non-minimal flavour
violation and/or CP violation. These cross sections have been validated
against Pythia 6 for SPS1a,
for ~t1~t1*, ~t2~t2*, ~b1~b1*, ~b2~b2*, and ~b1~b2* (+c.c.) production.
For ~t1~t2* (+c.c.),
there is currently a factor 2 between Pythia 6 and this implementation;
pending resolution. The FLV and CPV cases have not yet been validated.
flag SUSY:qqbar2squarkantisquark:gluonOnly
(default = off)
When switched on this flag switches off all but the s-channel
gluon contribution in the
calculation of same-isospin squark-antisquark production cross
sections. Intended for reference only. For the most
accurate physics simulation, leave this flag in the off
position.
flag SUSY:qq2squarksquark
(default = off)
Pair production of scalar quarks (squark-squark and its charge
conjugate process; for squark-antisquark production see above)
by t- and u-channel gluino, neutralino, and
chargino exchange. The cross section expressions follow [Boz07]
and should thus be valid also in the case of non-minimal flavour
violation and/or CP violation. Note: Pythia 6 only included the gluino exchange
contribution, which typically dominates due to the size of the strong
coupling; for counterchecks,
the flag SUSY:qq2squarksquark:gluinoOnly
below can be switched on to eliminate the chargino and neutralino
contributions. These cross sections have been validated against Pythia 6 for
SPS1a, for ~b1~b1, ~b1~b2, and ~b2~b2 production, with 5-10% differences
observed.
flag SUSY:qq2squarksquark:gluinoOnly
(default = off)
When switched on this flag causes the t- or u-channel
neutralino and chargino contributions to be ignored in the
calculation of squark pair production cross sections. Intended for reference
only. For the most
accurate physics simulation, leave this flag in the off
position.
Neutralino and Chargino Pair Production
flag SUSY:qqbar2chi0chi0
(default = off)
Pair production of neutralinos by quark-antiquark annihilation. With
four neutralino species this gives ten separate processes, codes
1201 - 1210. The cross section expressions follow [Boz07] and
should thus be valid also in the case of non-minimal flavour
violation and/or CP violation. These cross sections have been validated
against Pythia 6 for SPS1a and against the code
XSUSY (based on [Boz07]) for a non-minimal FLV case.
Validation of CPV cases has not yet been carried out.
flag SUSY:qqbar2chi+-chi0
(default = off)
Associated chargino-neutralino production by quark-antiquark
annihilation. With four neutralino species, two chargino ones, and
maintaining charge conjugate proceeses separate, this gives 16
separate processes, codes 1221 - 1236. The cross section expressions
follow [Boz07] and should thus be valid also in the case of
non-minimal flavour violation and/or CP violation. These cross sections have
been validated against Pythia 6 for SPS1a and against the code
XSUSY (based on [Boz07]) for a non-minimal FLV case. Validation of
CPV cases has not yet been carried out.
flag SUSY:qqbar2chi+chi-
(default = off)
Pair production of charginos by quark-antiquark annihilation. With
two chargino species and maintaining mutually charge conjugate
processes separate, this gives four separate processes, codes
1241 - 1244. The cross section expressions follow [Boz07]
and should thus be valid also in the case of non-minimal flavour
violation and/or CP violation. These cross sections have
been validated
against Pythia 6 for SPS1a and against the code
XSUSY (based on [Boz07]) for a non-minimal FLV case. Validation of
CPV cases has not yet been carried out.
Associated Neutralino/Chargino + Squark/Gluino Production
flag SUSY:qg2chi0squark
(default = off)
Pair production of neutralinos from quark-gluon initial states.
The cross section expressions follow [Boz07] and
should thus be valid also in the case of non-minimal flavour
violation and/or CP violation. Note: these cross sections are in a
development stage and have not yet been validated.
flag SUSY:qg2chi+-squark
(default = off)
Associated chargino-squark production from quark-gluon initial states.
annihilation. The cross section expressions
follow [Boz07] and should thus be valid also in the case of
non-minimal flavour violation and/or CP violation. Note: these cross sections
are in a development stage and have not yet been validated.
flag SUSY:qqbar2chi0gluino
(default = off)
Associated neutralino-gluino production by quark-antiquark
annihilation. Status: not implemented yet.
flag SUSY:qqbar2chi+-gluino
(default = off)
Associated chargino-gluino production by quark-antiquark
annihilation. Status: not implemented yet.
Slepton Production
No 2->2 slepton pair production or associated slepton production
cross sections have been implemented yet.