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.