Hidden Valley Processes
This Hidden Valley (HV) scenario has been developed specifically
to allow the study of visible consequences of radiation in a
hidden sector, by recoil effect. A key aspect is therefore that
the normal timelike showering machinery has been expanded with a
third kind of radiation, in addition to the QCD and QED ones.
These three kinds of radiation are fully interleaved, i.e.
evolution occurs in a common pT-ordered sequence.
The scenario is described in [Car10].
Particle content and properties
For simplicity we assume that the HV contains an unbroken SU(N)
gauge symmetry. This is used in the calculation of production cross
sections. These could be rescaled by hand for other gauge groups.
mode
HiddenValley:Ngauge
(default = 3
; minimum = 1
)
is U(1) for Ngauge = 1
, is SU(N) if
Ngauge > 1
. Note that pair production cross sections
contains a factor of Ngauge
for new particles
in the fundamental representation of this group.
A minimal HV particle content has been introduced. Firstly, there is
a set of 12 particles that mirrors the Standard Model flavour
structure, and is charged under both the SM and the HV symmetry groups.
Each new particle couples flavour-diagonally to a corresponding SM
state, and has the same SM charge and colour, but in addition is in
the fundamental representation of the HV colour, as follows:
Dv
, identity 4900001, partner to the normal
d
quark;
Uv
, identity 4900002, partner to the normal
u
quark;
Sv
, identity 4900003, partner to the normal
s
quark;
Cv
, identity 4900004, partner to the normal
c
quark;
Bv
, identity 4900005, partner to the normal
b
quark;
Tv
, identity 4900006, partner to the normal
t
quark;
Ev
, identity 4900011, partner to the normal
e
lepton;
nuEv
, identity 4900012, partner to the normal
nue
neutrino;
MUv
, identity 4900013, partner to the normal
mu
lepton;
nuMUv
, identity 4900014, partner to the normal
numu
neutrino;
TAUv
, identity 4900015, partner to the normal
tau
lepton;
nuTAUv
, identity 4900016, partner to the normal
nutau
neutrino.
Collectively we will refer to these states as Fv
;
note, however, that they need not be fermions themselves.
In addition the model contains the HV gauge particle, either
a HV gluon or a HV photon, but not both; see Ngauge
above:
gv
, identity 4900021, is the massless
gauge boson of the HV SU(N) group;
gammav
, identity 4900022, is the massless
gauge boson of the HV U(1) group.
Finally, there is a new massive particle with only HV charge sitting
in the fundamental representation of the HV gauge group:
qv
, identity 4900101.
The typical scenario would be for pair production of one of the
states presented first above, e.g. g g -> Dv Dvbar.
Such a Dv can radiate gluons and photons like an SM quark,
but in addition HV gluons or HV photons in a similar fashion.
Eventually the Dv will decay like Dv -> d + qv.
The strength of this decay is not set as such, but is implicit in
your choice of width for the Dv state.
Thereafter the d and qv can radiate
further within their respective sectors. The fate of the
qv, gv or gammav, once formed,
is not considered further: they remain invisible.
Only the spin of the HV gluon or HV photon is determined unambiguously
to be unity; for the others you can make your choice.
mode
HiddenValley:spinFv
(default = 1
; minimum = 0
; maximum = 2
)
The spin of the HV partners of the SM fermions, e.g.
Dv, Uv, Ev and nuEv.
option
0 : spin 0.
option
1 : spin 1/2.
option
2 : spin 1.
mode
HiddenValley:spinqv
(default = 0
; minimum = 0
; maximum = 1
)
The spin of qv when the Fv (the HV partners of
the SM fermions) have spin 1/2. (While, if they have spin 0 or 1,
the qv spin is fixed at 1/2.)
option
0 : spin 0.
option
1 : spin 1.
parm
HiddenValley:kappa
(default = 1.
)
If the Fv have spin 1 then their production
cross section depends on the presence of ananomalous magnetic dipole
moment, i.e. of a kappa different from unity. For other spins
this parameter is not used.
You should set the Fv and qv masses appropriately,
with the latter smaller than the former two to allow decays.
Production processes
flag
HiddenValley:all
(default = off
)
Common switch for the group of all hard Hidden Valley processes,
as listed separately in the following.
flag
HiddenValley:gg2DvDvbar
(default = off
)
Pair production g g -> Dv Dvbar.
Code 4901.
flag
HiddenValley:gg2UvUvbar
(default = off
)
Pair production g g -> Uv Uvbar.
Code 4902.
flag
HiddenValley:gg2SvSvbar
(default = off
)
Pair production g g -> Sv Svbar.
Code 4903.
flag
HiddenValley:gg2CvCvbar
(default = off
)
Pair production g g -> Cv Cvbar.
Code 4904.
flag
HiddenValley:gg2BvBvbar
(default = off
)
Pair production g g -> Bv Bvbar.
Code 4905.
flag
HiddenValley:gg2TvTvbar
(default = off
)
Pair production g g -> Tv Tvbar.
Code 4906.
flag
HiddenValley:qqbar2DvDvbar
(default = off
)
Pair production q qbar -> Dv Dvbar
via intermediate gluon.
Code 4911.
flag
HiddenValley:qqbar2UvUvbar
(default = off
)
Pair production q qbar -> Uv Uvbar
via intermediate gluon.
Code 4912.
flag
HiddenValley:qqbar2SvSvbar
(default = off
)
Pair production q qbar -> Sv Svbar
via intermediate gluon.
Code 4913.
flag
HiddenValley:qqbar2CvCvbar
(default = off
)
Pair production q qbar -> Cv Cvbar
via intermediate gluon.
Code 4914.
flag
HiddenValley:qqbar2BvBvbar
(default = off
)
Pair production q qbar -> Bv Bvbar
via intermediate gluon.
Code 4915.
flag
HiddenValley:qqbar2TvTvbar
(default = off
)
Pair production q qbar -> Tv Tvbar
via intermediate gluon.
Code 4916.
flag
HiddenValley:ffbar2DvDvbar
(default = off
)
Pair production f fbar -> Dv Dvbar
via intermediate gamma*/Z^*.
Code 4921.
flag
HiddenValley:ffbar2UvUvbar
(default = off
)
Pair production f fbar -> Uv Uvbar
via intermediate gamma*/Z^*.
Code 4922.
flag
HiddenValley:ffbar2SvSvbar
(default = off
)
Pair production f fbar -> Sv Svbar
via intermediate gamma*/Z^*.
Code 4923.
flag
HiddenValley:ffbar2CvCvbar
(default = off
)
Pair production f fbar -> Cv Cvbar
via intermediate gamma*/Z^*.
Code 4924.
flag
HiddenValley:ffbar2BvBvbar
(default = off
)
Pair production f fbar -> Bv Bvbar
via intermediate gamma*/Z^*.
Code 4925.
flag
HiddenValley:ffbar2TvTvbar
(default = off
)
Pair production f fbar -> Tv Tvbar
via intermediate gamma*/Z^*.
Code 4926.
flag
HiddenValley:ffbar2EvEvbar
(default = off
)
Pair production f fbar -> Ev Evbar
via intermediate gamma*/Z^*.
Code 4931.
flag
HiddenValley:ffbar2nuEvnuEvbar
(default = off
)
Pair production f fbar -> nuEv nuEvbar
via intermediate gamma*/Z^*.
Code 4932.
flag
HiddenValley:ffbar2MUvMUvbar
(default = off
)
Pair production f fbar -> MUv MUvbar
via intermediate gamma*/Z^*.
Code 4933.
flag
HiddenValley:ffbar2nuMUvnuMUvbar
(default = off
)
Pair production f fbar -> nuMUv nuMUvbar
via intermediate gamma*/Z^*.
Code 4934.
flag
HiddenValley:ffbar2TAUvTAUvbar
(default = off
)
Pair production f fbar -> TAUv TAUvbar
via intermediate gamma*/Z^*.
Code 4935.
flag
HiddenValley:ffbar2nuTAUvnuTAUvbar
(default = off
)
Pair production f fbar -> nuTAUv nuTAUvbar
via intermediate gamma*/Z^*.
Code 4936.
Timelike showers
One key point of this HV scenario is that radiation off the
HV-charged particles is allowed. This is done by the standard
final-state showering machinery. (HV particles are not produced
in initial-state radiation.) All the (anti)particles Fv
and qv have one (negative) unit of HV charge. That is,
radiation closely mimics the one in QCD. Both QCD, QED and HV
radiation are interleaved in one common sequence of decreasing
emission pT scales. Each radiation kind defines a set of
dipoles, usually spanned between a radiating parton and its recoil
partner, such that the invariant mass of the pair is not changed
when a radiation occurs. This need not follow from trivial colour
assignments, but is often obvious. For instance, in a decay
Qv -> q + qv the QCD dipole is between the q and
the hole after Qv, but qv becomes the recoiler
should a radiation occur, while the role of q and qv
is reversed for HV radiation.
This also includes matrix-element corrections for a number
of decay processes, with colour, spin and mass effects included
[Nor01]. They were calculated within the context of the
particle content of the MSSM, however, which does not include spin 1
particles with unit colour charge. In such cases spin 0 is assumed
instead. By experience, the main effects come from mass and colour
flow anyway, so this is not a bad approximation. (Furthermore the
MSSM formulae allow for gamma_5 factors from wave
functions or vertices; these are even less important.)
An emitted gv can branch in its turn,
gv -> gv + gv. This radiation may affect momenta
in the visible sector by recoil effect, but this is a minor
effect relative to the primary emission of the gv.
flag
HiddenValley:FSR
(default = off
)
switch on final-state shower of gv or gammav
in a HV production process.
parm
HiddenValley:alphaFSR
(default = 0.1
; minimum = 0.0
)
fixed alpha scale of gv/gammav emission; corresponds to
alpha_strong of QCD or alpha_em of QED. For
shower branchings such as Dv -> Dv + gv the coupling is
multiplied by C_F = (N^2 - 1) / (2 * N) for an
SU(N) group and for gv -> gv + gv by N.
parm
HiddenValley:pTminFSR
(default = 0.4
; minimum = 0.1
)
lowest allowed pT of emission. Chosen with same default
as in normal QCD showers.