Standard-Model Parameters
The strong coupling
Currently the only class in this category is AlphaStrong
,
which is used to provide a first- or second-order running
alpha_strong (or, trivially, a zeroth-order fixed one).
Formulae are the standard ones found in [Eid04]. The starting
alpha_strong value is defined at the M_Z mass scale.
The Lambda values are matched at the b and c
flavour thresholds, such that alpha_strong is continuous,
using an approximate iterative method for second-order matching.
Since we allow alpha_strong to vary separately for
hard processes, timelike showers, spacelike showers and multiple
interactions, the relevant values are to be set in each of these classes.
The alpha_strong calculation is initialized by
init( value, order)
, where value
is the alpha_strong value at M_Z and order
is the order of the running, 0, 1 or 2. Thereafter the value can be
calculated by alphaS(scale)
, where
scale
is the Q^2 scale in GeV^2.
For applications inside shower programs, a second-order alpha_s
value can be obtained as the product of the two functions
alphaS1Ord(scale)
and alphaS2OrdCorr(scale)
,
where the first gives a simple first-order running (but with the
second-order Lambda) and the second the correction factor,
below unity, for the second-order terms. This allows a compact handling
of evolution equations.
The weak mixing matrix
The absolute values of the Cabibbo-Kobayashi-Maskawa matrix elements are
set by the following nine real values - currently the CP-violating phase
is not taken into account in this parametrization. It is up to the user
to pick a consistent unitary set of new values whenever changes are made.
parameter name="StandardModel:Vud" default="0.9745" min="0.973" max="0.976"
The V_ud CKM matrix element.
parameter name="StandardModel:Vus" default="0.224" min="0.218" max="0.230"
The V_us CKM matrix element.
parameter name="StandardModel:Vub" default="0.0037" min="0.002" max="0.006"
The V_ub CKM matrix element.
parameter name="StandardModel:Vcd" default="0.224" min="0.218" max="0.230"
The V_cd CKM matrix element.
parameter name="StandardModel:Vcs" default="0.9737" min="0.972" max="0.975"
The V_cs CKM matrix element.
parameter name="StandardModel:Vcb" default="0.0415" min="0.033" max="0.040"
The V_cb CKM matrix element.
parameter name="StandardModel:Vtd" default="0.0094" min="0.004" max="0.020"
The V_td CKM matrix element.
parameter name="StandardModel:Vts" default="0.040" min="0.030" max="0.050"
The V_ts CKM matrix element.
parameter name="StandardModel:Vtb" default="0.9991" min="0.998" max="0.9995"
The V_tb CKM matrix element.
Electroweak couplings
In addition, this section contains a few further parameters that should
normally not be touched.
parameter name="StandardModel:alphaEMfix" default="0.00729735"
min="0.00729" max="0.00730"
Fixed alpha_em value used in QED vertices.
parameter name="StandardModel:sin2thetaW" default="0.232"
min="0.225" max="0.240"
The weak mixing angle.
Eventually will appear a running alpha_em.