Dire Expert Settings

  1. Further QCD and QED photon shower settings
  2. Further dark photon shower settings
  3. Matching and merging settings
  4. Other experimental merging settings
  5. Color factors
  6. Configurable timelike splitting kernels
One purpose of Dire is to have a numerical tool that can be compared to analytic resummation techniques as well as possible. Thus, some settings are available to facilitate theory comparisons. In an experimental production run, these paramaters should not be changed from their default values.

Further QCD and QED photon shower settings

flag  Dire:QED:doForcePosChgCorrelators   (default = off)
If on, this requires all QED splitting functions to use positive charge correlators. This especially means that some (otherwise in principle allowed) splittings are forbidden. This switch is only included to compare to other methods.

parm  Dire:QED:pTminForcePos   (default = -1.0)
This parameter determines the minimal evolution variable above which the above scheme of positive-only charge correlators is employed. On top of possible scaling factors for the arguments of the running QCD coupling, Dire also offers different functional forms of the argument itself. All of these functional forms reduce to a relative transverse momentum in the soft collinear limits, but differ for hard emissions.

mode  DireTimes:alphasScheme   (default = 0)

option 0 : The evolution variable is used as argument of the strong coupling.
option 1 : The collinear transverse momentum is used as argument.
option 2 : The eikonal factor sij sjk / sik for the splitting (ij),k -> i,j,k is used.

mode  DireSpace:alphasScheme   (default = 0)

option 0 : The evolution variable is used as argument of the strong coupling.
option 1 : The collinear transverse momentum is used as argument.
option 2 : The eikonal factor sij sjk / sik for the splitting (ij),k -> i,j,k is used.

Further dark photon shower settings

Dark photon emissions/splittings in Dire can be enabled with the following switches. It is worth noting that dark-photon radiation is handled very similar to QED/QCD radiation.

flag  TimeShower:U1newShowerByL   (default = off)
If on, then final state leptons are allowed to radiate dark photons.

flag  TimeShower:U1newShowerByQ   (default = off)
If on, then final state quarks are allowed to radiate dark photons.

flag  SpaceShower:U1newShowerByL   (default = off)
If on, then incoming leptons are allowed to radiate dark photons.

flag  SpaceShower:U1newShowerByQ   (default = off)
If on, then incoming quarks are allowed to radiate dark photons.

Dark photon emission rates are govered by several parameters.

parm  Dire:U1new:alphaX   (default = 1.0)
The coupling of the dark photon to (ficticious) dark-sector particles.

Matching and merging settings

Dire offers some functionality for matrix-element + parton shower merging. The currently most advanced of the available schemes are iterated matrix element corrections in the "MOPS" scheme. The details of the scheme are goverened by the following settings.

flag  Dire:doMECs   (default = off)
If on, matrix-element corrections for the first few splittings are used.

word  Dire:MG5card  
The ME corrections in Dire rely on code produced by MadGraph5. The initialization of this code requires a Madgraph parameter card. This setting should give the full path to such a "param_card". Without this input, the code will abort.

mode  Dire:nFinalMaxMECs   (default = -1)
If set, this limits the amount of matrix element corrections to final-state particle counts below this value. Any negative value means that ME corrections are applied for each splitting for which ME code is available.

parm  Dire:pTminMECs   (default = 1.0)
The minimal evolution scale value (in GeV) for which ME corrections should be applied. A negative value means no restriction.

parm  Dire:QminMECs   (default = 1.0)
The minimal of all two-particle momentum invariants (in GeV) for which ME corrections should be applied. Non-negative values mean that all two-particle invariants are calculated, and if any is below this parameter, then ME corrections are not attempted. The corresponding change in the emission rate is relected in the probability of clustering histories used for MECs, such that subsequent ME corrections still recover the correct distribution.

flag  Dire:suppressLargeMECs   (default = off)

word  Dire:MEplugin  
name of the plugin library to use for matrix element corrections.

Other experimental merging settings

The following settings are currently under investigation and not used in the code.

flag  Dire:doMerging   (default = off)
This switch should be considered experimental. If on, this simply ensures that the merging machinery can be accessed. The type of merging can then be further specified with the switches below.

flag  Dire:doMOPS   (default = off)
This flag switches on the handling of unordered configurations necessary in the MOPS merging method.

flag  Dire:doMEM   (default = off)
This flag switches on the possibility to classify input configurations according to the HYTRESS hypothesis testing scheme.

parm  MEM:WidthH   (default = -1.0)
This parameter allows to set the Higgs-boson width parameter used to calculate Higgs hypothesis likelihoods in the HYTREES scheme.

flag  Dire:doGenerateSubtractions   (default = off)
This flag allows to retrieve differential real-emission parton-shower counter-terms necessary for MC@NLO matching directly from a shower call.

flag  Dire:doGenerateMergingWeights   (default = off)
This flag allows to switch on/off the generation of CKKW-L-type reweighting factors by the merging machinery.

flag  Dire:doSingleLegSudakovs   (default = off)
This flag allows to retrieve no-emission probabilities from the parton showers on a leg-by-leg basis. The default definition of no-emission probabilities is instead based on the evolution of a state as as a whole.

flag  Dire:doExitAfterMerging   (default = off)
If on, this switch will allow to terminate the event processing once the calls to the merging machinery have been executed.

flag  DireTimes:DecaysAsShower   (default = off)
If on, then shower-generated particles that are classified as resonances can also decayed directly within the final-state parton-shower evolution.

flag  DireSpace:DecaysAsShower   (default = off)
If on, then shower-generated particles that are classified as resonances can also decayed directly within the initial-state parton-shower evolution.

Color factors

The expert user may also want to change the color factors used by QCD showering. This can be done using the settings

parm  DireColorQCD:TR   (default = -1.0)
Changes TR used by Dire. Any negative value means that consistent defaults are used.

parm  DireColorQCD:CA   (default = -1.0)
Changes CA used by Dire. Any negative value means that consistent defaults are used.

parm  DireColorQCD:NC   (default = -1.0)
Changes NC used by Dire. Any negative value means that consistent defaults are used.

parm  DireColorQCD:CF   (default = -1.0)
Changes CF used by Dire. Any negative value means that consistent defaults are used.

Configurable timelike splitting kernels

For in-depth theory comparisons, changed splitting kernels can be necessary. Thus, the user can customize the soft, collinear and finite behavior of timelike splitting probabilities to a large extent by changing the coefficients of mock-up series expansions and by exponential factors. A publication discussing these options is in preparation.

flag  DireTimes:useBackboneGluons   (default = off)
This flag ensures that the recoil in radiation off gluons that trace back to the core process is handled identical to that off hard-process quarks, as is relevant for theoretical quark-gluon discrimination studies.

flag  DireTimes:doGeneralizedKernel   (default = off)
If enabled, then the user may reconfigure timelike splitting kernels.

Please find below all changeable coefficients.

pvec  DireGeneralizedKernel:softCoeffs:Dire_fsr_qcd_1->1&21   (default = {0.,1.,0.,0.})

pvec  DireGeneralizedKernel:softExps:Dire_fsr_qcd_1->1&21   (default = {0.,0.,0.,0.})

pvec  DireGeneralizedKernel:kappaCoeffs:Dire_fsr_qcd_1->1&21   (default = {0.,0.,0.,0.})

pvec  DireGeneralizedKernel:kappaExps:Dire_fsr_qcd_1->1&21   (default = {0.,0.,0.,0.})

pvec  DireGeneralizedKernel:collCoeffs:Dire_fsr_qcd_1->1&21   (default = {0.,1.,0.,0.})

pvec  DireGeneralizedKernel:collExps:Dire_fsr_qcd_1->1&21   (default = {0.,0.,0.,0.})

parm  DireGeneralizedKernel:finCoeffs:Dire_fsr_qcd_1->1&21   (default = -2.0)

pvec  DireGeneralizedKernel:softCoeffs:Dire_fsr_qcd_1->21&1   (default = {0.,1.,0.,0.})

pvec  DireGeneralizedKernel:softExps:Dire_fsr_qcd_1->21&1   (default = {0.,0.,0.,0.})

pvec  DireGeneralizedKernel:kappaCoeffs:Dire_fsr_qcd_1->21&1   (default = {0.,0.,0.,0.})

pvec  DireGeneralizedKernel:kappaExps:Dire_fsr_qcd_1->21&1   (default = {0.,0.,0.,0.})

pvec  DireGeneralizedKernel:collCoeffs:Dire_fsr_qcd_1->21&1   (default = {0.,1.,0.,0.})

pvec  DireGeneralizedKernel:collExps:Dire_fsr_qcd_1->21&1   (default = {0.,0.,0.,0.})

parm  DireGeneralizedKernel:finCoeffs:Dire_fsr_qcd_1->21&1   (default = -2.0)

pvec  DireGeneralizedKernel:softCoeffs:Dire_fsr_qcd_21->21&21a   (default = {0.,1.,0.,0.})

pvec  DireGeneralizedKernel:softExps:Dire_fsr_qcd_21->21&21a   (default = {0.,0.,0.,0.})

pvec  DireGeneralizedKernel:kappaCoeffs:Dire_fsr_qcd_21->21&21a   (default = {0.,0.,0.,0.})

pvec  DireGeneralizedKernel:kappaExps:Dire_fsr_qcd_21->21&21a   (default = {0.,0.,0.,0.})

pvec  DireGeneralizedKernel:collCoeffs:Dire_fsr_qcd_21->21&21a   (default = {0.,1.,0.,0.})

pvec  DireGeneralizedKernel:collExps:Dire_fsr_qcd_21->21&21a   (default = {0.,0.,0.,0.})

parm  DireGeneralizedKernel:finCoeffs:Dire_fsr_qcd_21->21&21a   (default = -2.0)

pvec  DireGeneralizedKernel:softCoeffs:Dire_fsr_qcd_21->21&21b   (default = {0.,1.,0.,0.})

pvec  DireGeneralizedKernel:softExps:Dire_fsr_qcd_21->21&21b   (default = {0.,0.,0.,0.})

pvec  DireGeneralizedKernel:kappaCoeffs:Dire_fsr_qcd_21->21&21b   (default = {0.,0.,0.,0.})

pvec  DireGeneralizedKernel:kappaExps:Dire_fsr_qcd_21->21&21b   (default = {0.,0.,0.,0.})

pvec  DireGeneralizedKernel:collCoeffs:Dire_fsr_qcd_21->21&21b   (default = {0.,1.,0.,0.})

pvec  DireGeneralizedKernel:collExps:Dire_fsr_qcd_21->21&21b   (default = {0.,0.,0.,0.})

parm  DireGeneralizedKernel:finCoeffs:Dire_fsr_qcd_21->21&21b   (default = -2.0)

pvec  DireGeneralizedKernel:collCoeffs:Dire_fsr_qcd_21->1&1a   (default = {0.,1.,0.,0.})

pvec  DireGeneralizedKernel:collExps:Dire_fsr_qcd_21->1&1a   (default = {0.,0.,0.,0.})

parm  DireGeneralizedKernel:finCoeffs:Dire_fsr_qcd_21->1&1a   (default = 0.0)

pvec  DireGeneralizedKernel:collCoeffs:Dire_fsr_qcd_21->1&1b   (default = {0.,1.,0.,0.})

pvec  DireGeneralizedKernel:collExps:Dire_fsr_qcd_21->1&1b   (default = {0.,0.,0.,0.})

parm  DireGeneralizedKernel:finCoeffs:Dire_fsr_qcd_21->1&1b   (default = 0.0)