Page MenuHomeHEPForge
Files F8724430

No OneTemporary
Actions

View Options

diff --git a/doc/sphinx/HEJFOG.rst b/doc/sphinx/HEJFOG.rst
index 57dd3c0..bd0eddc 100644
--- a/doc/sphinx/HEJFOG.rst
+++ b/doc/sphinx/HEJFOG.rst
@@ -1,300 +1,301 @@
The HEJ Fixed Order Generator
=============================
For high jet multiplicities event generation with standard fixed-order
generators becomes increasingly cumbersome. For example, the
leading-order production of a Higgs Boson with five or more jets is
computationally prohibitively expensive.
To this end, HEJ 2 provides the ``HEJFOG`` fixed-order generator
that allows to generate events with high jet multiplicities. To
facilitate the computation the limit of Multi-Regge Kinematics with
large invariant masses between all outgoing particles is assumed in the
matrix elements. The typical use of the ``HEJFOG`` is to supplement
low-multiplicity events from standard generators with high-multiplicity
events before using the HEJ 2 program to add high-energy
resummation.
Installation
------------
The ``HEJFOG`` comes bundled together with HEJ 2 and the
installation is very similar. After downloading HEJ 2 and
installing the prerequisites as described in :ref:`Installation` the
``HEJFOG`` can be installed with::
cmake /path/to/FixedOrderGen -DCMAKE_INSTALL_PREFIX=target/directory
make install
where :file:`/path/to/FixedOrderGen` refers to the :file:`FixedOrderGen`
subdirectory in the HEJ 2 directory. If HEJ 2 was
installed to a non-standard location, it may be necessary to specify the
directory containing :file:`HEJ-config.cmake`. If the base installation
directory is :file:`/path/to/HEJ`, :file:`HEJ-config.cmake` should be
found in :file:`/path/to/HEJ/lib/cmake/HEJ` and the commands for
installing the ``HEJFOG`` would read::
cmake /path/to/FixedOrderGen -DHEJ_DIR=/path/to/HEJ/lib/cmake/HEJ -DCMAKE_INSTALL_PREFIX=target/directory
make install
The installation can be tested with::
make test
provided that the CT10nlo PDF set is installed.
Running the fixed-order generator
---------------------------------
After installing the ``HEJFOG`` you can modify the provided
configuration file :file:`configFO.yml` and run the generator with::
HEJFOG configFO.yml
The resulting event file, by default named :file:`HEJFO.lhe`, can then be
fed into HEJ 2 like any event file generated from a standard
fixed-order generator, see :ref:`Running HEJ 2`.
Settings
--------
Similar to HEJ 2, the ``HEJFOG`` uses a `YAML
<http://yaml.org/>`_ configuration file. The settings are
.. _`process`:
**process**
The scattering process for which events are being generated. The
format is
:code:`in1 in2 => out1 out2 ...`
The incoming particles, :code:`in1`, :code:`in2` can be
- quarks: :code:`u`, :code:`d`, :code:`u_bar`, and so on
- gluons: :code:`g`
- protons :code:`p` or antiprotons :code:`p_bar`
At most one of the outgoing particles can be a boson, the rest has to be
partonic. At the moment only the Higgs boson :code:`h` is supported. All
other outgoing particles are jets. Multiple jets can be grouped together, so
:code:`p p => h j j` is the same as :code:`p p => h 2j`. There have to be at
least two jets. Further decays of the boson can be added through the
:ref:`particle properties<particle properties: particle: decays>`.
.. _`events`:
**events**
Specifies the number of events to generate.
.. _`jets`:
**jets**
Defines the properties of the generated jets.
.. _`jets: min pt`:
**min pt**
Minimum jet transverse momentum in GeV.
.. _`jets: peak pt`:
**peak pt**
Optional setting to specify the dominant jet transverse momentum
in GeV. If the generated events are used as input for HEJ
resummation, this should be set to the minimum transverse momentum
of the resummation jets. In all cases it has to be larger than
:code:`min pt`. The effect is that only a small fraction of jets
will be generated with a transverse momentum below the value of
this setting.
.. _`jets: algorithm`:
**algorithm**
The algorithm used to define jets. Allowed settings are
:code:`kt`, :code:`cambridge`, :code:`antikt`,
:code:`cambridge for passive`. See the `FastJet
<http://fastjet.fr/>`_ documentation for a description of these
algorithms.
.. _`jets: R`:
**R**
The R parameter used in the jet algorithm.
.. _`jets: max rapidity`:
**max rapidity**
Maximum absolute value of the jet rapidity.
.. _`beam`:
**beam**
Defines various properties of the collider beam.
.. _`beam: energy`:
**energy**
The beam energy in GeV. For example, the 13
TeV LHC corresponds to a value of 6500.
.. _`beam: particles`:
**particles**
A list :code:`[p1, p2]` of two beam particles. The only supported
entries are protons :code:`p` and antiprotons :code:`p_bar`.
.. _`pdf`:
**pdf**
The `LHAPDF number <https://lhapdf.hepforge.org/pdfsets>`_ of the PDF set.
For example, 230000 corresponds to an NNPDF 2.3 NLO PDF set.
.. _`subleading fraction`:
**subleading fraction**
- This setting is related to the fraction of events, that are not a
- FKL configuration. All possible subleading process are listed in
- :ref:`subleading channels<subleading channels>`. Typically, this
- value should be between 0.01 and 0.1. Note that while this
- parameter influences the chance of generating subleading
- configurations, it generally does not correspond to the actual
- fraction of subleading events.
+ This setting is related to the fraction of events that are not a FKL
+ configuration. All possible subleading process are listed in
+ :ref:`subleading channels<subleading channels>`. This value must be
+ positive and not larger than 1. It should typically be chosen between
+ 0.01 and 0.1. Note that while this parameter influences the chance of
+ generating subleading configurations, it generally does not
+ correspond to the actual fraction of subleading events.
.. _`subleading channels`:
**subleading channels**
-
-Optional parameters to select a specific subleading process, multiple
+ Optional parameters to select a specific subleading process, multiple
channels can be selected at once. If multiple subleading configurations
are possible one will be selected at random for each event, thus each
final state will include at most one subleading process, e.g. either
- :code:`unordered` or :code:`qqx`. The following values are allowed:
-
- - :code:`all`: All channels allowed, default if nothing else set
- - :code:`none`: No subleading contribution, only FKL allowed
- Equivalent to :code:`subleading fraction: 0`
- - :code:`unordered`: Unordered emission allowed
- Unordered emission are any rapidity ordering, where exactly one gluon is
- emitted outside the rapidity ordering required in FKL events. More
- precisely, if at least one of the incoming particles is a quark or
- antiquark and there are more than two jets in the final state,
- :code:`subleading fraction` states the probability that the flavours
- of the outgoing particles are assigned in such a way that an unordered
- configuration arises. Unordered emissions are currently not implemented
- for pure jet production.
- - :code:`qqx`: Production of quark-antiquark pair
- If allowed processes with at least three jets might include a
- quark-antiquark pair, i.e. one quark (in rapidity) next to one antiquark.
- The pair can be at any position in the FKL chain. Similar to above
- :code:`subleading fraction` gives the probability of turning two gluons
- into the quark-antiquark pair. Quark-antiquark pairs are currently only
- implemented for W boson production.
+ :code:`unordered` or :code:`qqx`. Only has an effect if
+ :code:`subleading fraction` is non-zero. The following values are allowed:
+
+ - :code:`all`: All channels allowed. This is the default.
+ - :code:`none`: No subleading contribution, only the leading (FKL)
+ configurations are allowed. This is equivalent to
+ :code:`subleading fraction: 0`.
+ - :code:`unordered`: Unordered emission allowed.
+ Unordered emission are any rapidity ordering where exactly one gluon is
+ emitted outside the rapidity ordering required in FKL events. More
+ precisely, if at least one of the incoming particles is a quark or
+ antiquark and there are more than two jets in the final state,
+ :code:`subleading fraction` states the probability that the flavours
+ of the outgoing particles are assigned in such a way that an unordered
+ configuration arises. Unordered emissions are currently not implemented
+ for pure jet production.
+ - :code:`qqx`: Production of a quark-antiquark pair. In the leading
+ (FKL) configurations all partons except for the most backward and
+ forward ones are gluons. If the :code:`qqx` channel is allowed,
+ :code:`subleading fraction` gives the probability of emitting a
+ quark-antiquark pair in place of two gluons that are adjacent in
+ rapidity. Quark-antiquark pairs are currently only implemented for
+ W boson production.
.. _`unweight`:
**unweight**
This setting defines the parameters for the partial unweighting of
events. You can disable unweighting by removing this entry from the
configuration file.
.. _`unweight: sample size`:
**sample size**
The number of weighted events used to calibrate the unweighting.
A good default is to set this to the number of target
`events`_. If the number of `events`_ is large this can
lead to significant memory consumption and a lower value should be
chosen. Contrarily, for large multiplicities the unweighting
efficiency becomes worse and the sample size should be increased.
.. _`unweight: max deviation`:
**max deviation**
Controls the range of events to which unweighting is applied. A
larger value means that a larger fraction of events are unweighted.
Typical values are between -1 and 1.
.. _`particle properties`:
**particle properties**
Specifies various properties of the different particles (Higgs, W or Z).
This is only relevant if the chosen `process`_ is the production of the
corresponding particles with jets. E.g. for the `process`_
:code:`p p => h 2j` the :code:`mass`, :code:`width` and (optionally)
:code:`decays` of the :code:`Higgs` boson are required, while all other
particle properties will be ignored.
.. _`particle properties: particle`:
**Higgs, W+, W- or Z**
The particle (Higgs, |W+|, |W-|, Z) for which the following
properties are defined.
.. |W+| replace:: W\ :sup:`+`
.. |W-| replace:: W\ :sup:`-`
.. _`particle properties: particle: mass`:
**mass**
The mass of the particle in GeV.
.. _`particle properties: particle: width`:
**width**
The total decay width of the particle in GeV.
.. _`particle properties: particle: decays`:
**decays**
Optional setting specifying the decays of the particle. Only the decay
into two particles is implemented. Each decay has the form
:code:`{into: [p1,p2], branching ratio: r}`
where :code:`p1` and :code:`p2` are the particle names of the
decay product (e.g. :code:`photon`) and :code:`r` is the branching
ratio.
Decays of a Higgs boson are treated as the production and subsequent
decay of an on-shell Higgs boson, so decays into e.g. Z bosons are not
supported.
.. _`scales`:
**scales**
Specifies the renormalisation and factorisation scales for the output
events. For details, see the corresponding entry in the HEJ 2
:ref:`HEJ 2 settings`. Note that this should usually be a
single value, as the weights resulting from additional scale choices
will simply be ignored when adding high-energy resummation with HEJ 2.
.. _`event output`:
**event output**
Specifies the name of a single event output file or a list of such
files. See the corresponding entry in the HEJ 2
:ref:`HEJ 2 settings` for details.
.. _`RanLux init`:
.. _`random generator`:
**random generator**
Sets parameters for random number generation. See the HEJ 2
:ref:`HEJ 2 settings` for details.
.. _`analysis`:
**analysis**
Specifies the name and settings for a custom analysis library. This
can be useful to specify cuts at the fixed-order level. See the
corresponding entry in the HEJ 2 :ref:`HEJ 2 settings`
for details.
.. _`Higgs coupling`:
**Higgs coupling**
This collects a number of settings concerning the effective coupling
of the Higgs boson to gluons. See the corresponding entry in the
HEJ 2 :ref:`HEJ 2 settings` for details.

File Metadata

Mime Type
text/x-diff
Expires
Mon, Jan 20, 11:30 PM (1 d, 12 h)
Storage Engine
blob
Storage Format
Raw Data
Storage Handle
4234128
Default Alt Text
(12 KB)

Event Timeline