You can not select more than 25 topics
Topics must start with a letter or number, can include dashes ('-') and can be up to 35 characters long.
65 lines
3.2 KiB
65 lines
3.2 KiB
\begin{longtable}{p{1.5cm}p{12cm}}
|
|
\hline
|
|
\multicolumn{1}{c}{{\textbf{Section} \texttt{scales}}} & \multicolumn{1}{c}{{\textbf{Description}}} \\
|
|
\hline
|
|
\texttt{renscale} &
|
|
This parameter may be used to adjust the value
|
|
of the {\it renormalization} scale. This is the scale
|
|
at which $\alpha_S$ is evaluated and will typically be set to
|
|
a mass scale appropriate to the process ($M_W$, $M_Z$, $m_t$ for
|
|
instance). \\
|
|
\texttt{facscale} &
|
|
This parameter may be used to adjust the value
|
|
of the {\it factorization} scale and will typically be set to
|
|
a mass scale appropriate to the process ($M_W$, $M_Z$, $m_t$ for
|
|
instance). \\
|
|
\texttt{dynamicscale} &
|
|
This character string is used to specify whether
|
|
the renormalization, factorization and fragmentation scales are dynamic, i.e. recalculated
|
|
on an event-by-event basis. If this string is set to `{\tt none}' then the scales
|
|
are fixed for all events at the values specified by {\tt renscale}, {\tt facscale}
|
|
as well as \texttt{fragmentation\_scale} as defined further below.
|
|
|
|
The type of dynamic scale to be used is selected by using a particular string
|
|
for the variable {\tt dynamicscale}, as indicated in Table~\ref{tab:dynamicscales}.
|
|
Not all scales are defined for each process, with program execution halted if
|
|
an invalid selection is made in the input file.
|
|
The selection chooses a reference scale, $\mu_0$. The actual scales used in
|
|
the code are then,
|
|
\begin{equation}
|
|
\mu_{\mathrm{ren}} = \texttt{renscale} \times \mu_0 \;, \qquad
|
|
\mu_{\mathrm{fac}} = \texttt{facscale} \times \mu_0
|
|
\label{eq:dynscale}
|
|
\end{equation}
|
|
Note that, for simplicity, the fragmentation scale (relevant only for processes
|
|
involving photons) is set equal to the renormalization scale.
|
|
In some cases it is possible for the dynamic scale to become very large. This can cause problems
|
|
with the interpolation of data tables for the PDFs and fragmentation functions. As a result if a dynamic scale
|
|
exceeds a maximum of $60$ TeV (PDF) or $990$ GeV (fragmentation) this value is set by default to the maximum.
|
|
\\
|
|
\texttt{doscalevar} &
|
|
|
|
This additional option can be set to \texttt{.true.} to enable scale variation.
|
|
It performs a variation of the scales used in \ref{eq:dynscale} by a factor of
|
|
two so that it surveys the
|
|
additional possibilities,
|
|
\begin{equation*}
|
|
(2\mu_{\mathrm{ren}},2\mu_{\mathrm{fac}}),
|
|
(\mu_{\mathrm{ren}}/2,\mu_{\mathrm{fac}}/2)
|
|
\end{equation*}
|
|
\begin{equation}
|
|
(2\mu_{\mathrm{ren}},\mu_{\mathrm{fac}}),
|
|
(\mu_{\mathrm{ren}}/2,\mu_{\mathrm{fac}}),
|
|
\label{eq:scalevar}
|
|
\end{equation}
|
|
\begin{equation*}
|
|
(\mu_{\mathrm{ren}},2\mu_{\mathrm{fac}}),
|
|
(\mu_{\mathrm{ren}},\mu_{\mathrm{fac}}/2) \,.
|
|
\end{equation*}
|
|
The histograms corresponding to these different choices are included in the output file, from which an
|
|
envelope of theoretical uncertainty may be constructed by the user. \\
|
|
\texttt{maxscalevar} &
|
|
Number of additional scale variation points to choose, can be set to two or six. For two
|
|
it just samples the first two variations as in Eq.~\ref{eq:scalevar}. \\
|
|
\hline
|
|
\end{longtable}
|