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<!--
//==============================================================================
// overview.html
//
// Copyright (C) 2010-2013 Tobias Toll and Thomas Ullrich
//
// This file is part of Sartre version: 1.1
//
// This program is free software: you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation.
// This program is distributed in the hope that it will be useful,
// but without any warranty; without even the implied warranty of
// merchantability or fitness for a particular purpose. See the
// GNU General Public License for more details.
// You should have received a copy of the GNU General Public License
// along with this program. If not, see <http://www.gnu.org/licenses/>.
//
// Author: Thomas Ullrich
// Last update:
//
$Date: 2013-05-29 21:25:21 +0100 (Wed, 29 May 2013) $
//
$Author: thomas.ullrich@bnl.gov $
//==============================================================================
-->
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PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "DTD/xhtml1-strict.dtd">
<
html
xmlns
=
"http://www.w3.org/1999/xhtml"
xml:lang
=
"en_US"
lang
=
"en_US"
>
<
head
>
<
title
>
Sartre - Overview
</
title
>
<
meta
http-equiv
=
"Content-type"
content
=
"text/html; charset=UTF-8"
/>
<
link
href
=
"sartre.css"
rel
=
"stylesheet"
type
=
"text/css"
/>
</
head
>
<
body
>
<
table
border
=
"0"
cellpadding
=
"0"
cellspacing
=
"0"
width
=
"100%"
>
<
tr
>
<
td
width
=
"120"
align
=
"left"
valign
=
"top"
><
img
src
=
"images/sartreLogo.png"
alt
=
""
border
=
"0"
align
=
"right"
/></
td
>
<
td
width
=
"10"
>
</
td
>
<
td
align
=
"left"
valign
=
"middle"
class
=
"postheader"
><
a
href
=
"index.html"
><
font
color
=
"#004faf"
>
Home
</
font
></
a
>
·
<
a
href
=
"overview.html"
><
font
color
=
"#004faf"
>
Overview
</
font
></
a
>
·
<
font
color
=
"#004faf"
>
<
a
href
=
"usersGuide.html"
>
Users
Guide
</
a
></
font
>
·
<
a
href
=
"referenceGuide.html"
><
font
color
=
"#004faf"
>
Reference Guide
</
font
>
</
a
></
td
></
tr
>
</
table
>
<
h1
class
=
"title"
>
Overview
</
h1
>
<
p
>
Sar
<
em
>
t
</
em
>
re is an event generator for exclusive diffractive vector
meson production and DVCS in
<
em
>
ep
</
em
>
and
<
em
>
e
</
em
>
A collisions based
on the dipole model. It can also describe so called Ultra Peripheral Collisions (UPC)
at hadron-hadron colliders.
Sar
<
em
>
t
</
em
>
re describes the processes:
<
br
>
<
em
>
e p
</
em
>
→
<
em
>
e' V p',
<
br
>
e A
</
em
>
→
<
em
>
e' V A',
<
br
>
p p
</
em
>
→
<
em
>
p' V p',
<
br
>
p A
</
em
>
→
<
em
>
p' V A',
<
br
>
A A
</
em
>
→
<
em
>
A' V A',
</
em
>
<
br
>
where V = J/
ψ
,
φ
,
ρ
,
γ
. Most common nuclei
are included. Sar
<
em
>
t
</
em
>
re
is not a stand-alone program but a set of C++ classes and C functions
that form the API. It is up to the user to provide the main program.
This scheme gives the user the maximum flexibility to filter, select,
and store events in whatever format is most convenient for her/him.
However, a rather complete example main program is provided to get
the ball rolling. Since Sar
<
em
>
t
</
em
>
re is quite modular, certain
classes can be used individually for specific purposes, e.g. for
numeric calculations of cross-sections or to calculate the kinematics
of final state particles for a given set of
<
i
>
x
</
i
>
,
<
i
>
t
</
i
>
,
and
<
i
>
Q
<
sup
>
2
</
sup
></
i
>
.
</
p
>
<
p
>
The heart of Sar
<
em
>
t
</
em
>
re is an implementation of the bSat and
bCGC dipole models developed by H. Kowalski, L. Motyka, and G. Watt
[
<
a
href
=
"references.html#ref_kmw"
>
1
</
a
>
,
<
a
href
=
"references.html#ref_wk"
>
2
</
a
>
].
We extended the models to also describe
<
em
>
e
</
em
>
A collisions
making Sar
<
em
>
t
</
em
>
re the first
generator to describe this class of processes. Saturation is introduced
in the bSat model through an exponential term in the scattering
amplitude. In order to study the impact of saturation on the production
cross-section we construct a non-saturated version of
the bSat model, bNonSat, by linearizing the dipole cross-section.
</
p
>
<
p
>
To calculate and generate the total cross-sections, rather complex
integrations have to be performed for each phase-space point (in
<
em
>
e
</
em
>
A
around 1000 4D integrals each) rendering an on-the-fly calculation while
generating events impractical. Therefore, we calculate the first
and second moments of the amplitudes, for both longitudinally and
transversely polarized photons separately, and store the results
in look-up tables. These calculations are very time consuming and were performed
on the US Science Grid. The tables are contained in the Sar
<
em
>
t
</
em
>
re
distribution. The
look-up tables are three dimensional in
<
em
>
Q
<
i
><
sup
>
2
</
sup
></
i
>
,
W
<
i
><
sup
>
2
</
sup
></
i
>
,
</
em
>
and
<
em
>
t
</
em
>
. There is a set of four look-up
tables for each species of produced vector meson or DVCS, and for each species
of colliding nucleus. Currently we provide tables based on the bSat and bNonSat
models.
</
p
>
<
p
>
Sar
<
em
>
t
</
em
>
re thus consist of two parts: an event generator
part and a table generator part. Most users will only use the former.
The API and example programs to generate tables are included in the
distribution
although we do not recommend to engage in this enterprise unless
you have massive CPU time available. The event generator part using
the pre-calculated tables is able to simulate millions of events in
a matter of minutes on a standard computer.
</
p
>
<
p
>
This is the first release of Sar
<
em
>
t
</
em
>
re and we tried hard to
provide sufficient documentation for the user to get started. However,
things evolve and many parts might not be as well documented as
they should be. Please feel free to contact the authors in this case.
We will try to continuously improve the documentation.
</
p
>
<
p
>
The best
way to get started is to use the provided example main program
(
<
code
>
sartreMain.cpp
</
code
>
) and runcard (
<
code
>
sartreRuncard.txt
</
code
>
) and have a look
at the
<
a
href
=
"usersGuide.html"
><
font
color
=
"#004faf"
>
Users Guide
</
font
></
a
>
. Instead of starting from scratch, it is probably
more efficient to use the example and modify it to suit your needs.
For advanced users or users who want to get more out of the generator
than the example program provides we refer to the
<
a
href
=
"referenceGuide.html"
><
font
color
=
"#004faf"
>
Reference Guide
</
font
></
a
>
that explains the various classes in the API in more detail.
</
p
>
<
p
>
Sar
<
em
>
t
</
em
>
re relies heavily on components (4-vectors, numeric tools,
and more) of
existing packages such as ROOT and GSL that need to be present in
order build and run it. Making use of existing package reduces the
code to the essential parts needed and makes things easier to maintain
and modify.
</
p
>
<
p
>
<
p
>
</
p
>
<
address
><
div
align
=
"center"
>
<
table
border
=
"0"
cellspacing
=
"0"
width
=
"100%"
><
tbody
><
tr
class
=
"address"
>
<
td
align
=
"left"
width
=
"40%"
>
</
td
>
<
td
align
=
"center"
width
=
"20%"
>
</
td
>
<
td
align
=
"right"
width
=
"40%"
><
div
align
=
"right"
><
br
>
Last Update:
<!-- #BeginDate format:Am1 -->
January 14, 2013
<!-- #EndDate -->
</
div
></
td
>
</
tr
></
tbody
></
table
></
div
></
address
>
</
body
></
html
>
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