To ensure conservation of momentum and energy, the final state for each deuteron production channel is required to have at least two final products, where one product is a deuteron. This is in contrast to the traditional coalescence model of [Scd63] and [Kap80] where typically only a deuteron is produced from a two-body initial state and so momentum and energy are not conserved. Here, a modified coalescence model can be used where the final state can be specified as a deuteron and a photon.

The default deuteron production setup is taken from [Dal15], where 8 production channels are defined:

*p+ n0 → gamma 2H**p+ n0 → pi0 2H**p+ n0 → pi0 pi0 2H**p+ n0 → pi+ pi- 2H**p+ p+ → pi+ 2H**p+ p+ → pi+ pi0 2H**n0 n0 → pi- 2H**n0 n0 → pi- pi0 2H*

`DeuteronProduction`

class performs the deuteron
production, first building all valid two-particle combinations, then
determining whether the combinations bind, and finally performing an
isotropic decay of the bound state into the specified final state.
`HadronLevel:DeuteronProduction = on`

,
you can regulate the detailed behaviour with the following settings.
**Warning**: changed `mvec`

and `wvec`

values
must be provided as a comma-separated list enclosed in braces,
`{...}`

.

`parm `

** DeuteronProduction:norm **
(`default = `

; **119.6**`minimum = 1`

)

An overall unitless multiplicative normalization scale to increase the
maximum used when sampling the differential cross-sections. Increasing
this scale decreases the cross-section for deuteron production. Using
the default model, the maximum differential cross-section is *3.2
mb* with the *n0 n0 → pi- 2H* and *p+ p+ → pi+
2H* channels. To convert the fit values from table VIII of
[Dal15] into this multiplicative normalization factor, take
*1/(value from table * maximum cross-section)*. For example,
the ALICE 7 TeV deuteron fit with a *1/σ _{0}* of
2.63 inverse barn, the multiplicative normalization is 119.6.

`wvec `

** DeuteronProduction:channels **
(`default = `

)**{2212 2112 > 22, 2212 2112 > 111, 2212 2112 > 111 111, 2212 2112 > 211 -211, 2212 2212 > 211, 2212 2212 > 211 111, 2112 2112 > -211, 2112 2112 > -211 111}**

List of the deuteron production channels to include of the form
*initial states > final states * where *initial
states* are the PDG particle IDs of the initial state particles to
combine (there must be two), and *final states* are the PIDs of
the final state particles, excluding the deuteron. There must be one
or more final state particles in addition to the deuteron. The
products of each channel are space separated, while the channels are
comma separated.

`mvec `

** DeuteronProduction:models **
(`default = `

)**{1, 2, 3, 3, 2, 3, 2, 3}**

List of the parameterization mode for each deuteron production channel
specified by `DeuteronProduction:channels`

. The parameters
for each of the channels is specified with
`DeuteronProduction:parms`

. The length of this vector must
be the same as `DeuteronProduction:channels`

.
`option `

** 0** : the coalescence model, *p _{1}
θ(p_{0} - k)*, a step function with two
parameters:

`option `

`option `

`option `

`wvec `

** DeuteronProduction:parms **
(`default = `

)**{1.28 2.3034605532591175 -93.663463313902028 2565.3904680353621 -25594.100560137995 143513.10872427333 -503572.89020794741 1149248.0196165806 -1723683.9119787284 1679348.7891145353 -1019888.5470232342 349840.35161061864 -51662.760038375141 -5.1885266705385051 2.9195632726211609, 85 1.34 1.77 0.38 0.096, 2.85519622e+06 1.31114126e+01 2.96145497e+03 5.57220777e+00 1.46051932e+06, 6.46455516e+06 1.05136338e+01 1.97924778e+03 5.36301369e+00 6.04534114e+05 2.54935423e+15 1.65669163e+01 2.32961298e+07 1.11937373e+01 2.86815089e+16, 170 1.34 1.77 0.38 0.096, 5.09870846e+15 1.65581228e+01 2.33337076e+07 1.13304315e+01 2.86815089e+16, 170 1.34 1.77 0.38 0.096, 5.09870846e+15 1.65581228e+01 2.33337076e+07 1.13304315e+01 2.86815089e+16}**

The parameters needed for the model of each channel. The parameters
for each channel are space separated, while the channels are separated
by commas. The length of this vector must be the same as
`DeuteronProduction:channels`

. Note, to match the parameters
of [Dal15] these parameters give differential cross-sections in
*μb* not *mb*.

`parm `

** DeuteronProduction:kMin **
(`default = `

)**1e-1**

The minimum bracketing value of *k* (in *GeV*) when maximum
finding. For the default *p n → gamma 2H* production model
the cross-section diverges at low *k*, but the probability of
producing two nucleons with low *k* suppresses this divergence.

`parm `

** DeuteronProduction:kMax **
(`default = `

)**5**

The maximum bracketing value of *k* (in *GeV*) when maximum
finding.

`parm `

** DeuteronProduction:kTol **
(`default = `

)**1e-4**

The minimum relative tolerance in *k* required when maximum
finding.

`mode `

** DeuteronProduction:kSteps **
(`default = `

)**100**

The number of steps to sample in *k* when calculating the
initial grid for maximum finding.