diff --git a/config.yml b/config.yml
index 9859b58..8c51e6e 100644
--- a/config.yml
+++ b/config.yml
@@ -1,124 +1,125 @@
# number of attempted resummation phase space points for each input event
trials: 10
# maximum soft transverse momentum fraction in extremal jets
max ext soft pt fraction: 0.1
resummation jets: # resummation jet properties
min pt: 35 # minimum jet transverse momentum
algorithm: antikt # jet clustering algorithm
R: 0.4 # jet R parameter
fixed order jets: # properties of input jets
min pt: 30
# by default, algorithm and R are like for resummation jets
# treatment of he various event classes
# the supported settings are: reweight, keep, discard
# non-resummable events cannot be reweighted
event treatment:
FKL: reweight
unordered: keep
extremal qqx: keep
central qqx: keep
non-resummable: keep
# central scale choice or choices
#
# scales: [125, max jet pperp, H_T/2, 2*jet invariant mass, m_j1j2]
scales: 91.188
# factors by which the central scales should be multiplied
# renormalisation and factorisation scales are varied independently
#
# scale factors: [0.5, 0.7071, 1, 1.41421, 2]
# maximum ratio between renormalisation and factorisation scale
#
# max scale ratio: 2.0001
# import scale setting functions
#
# import scales:
# lib_my_scales.so: [scale0,scale1]
log correction: false # whether or not to include higher order logs
## unweighting setting
## remove to obtain weighted events
# unweight:
+# # type of unweighting (one of 'weighted', 'resummation', 'partial')
# type: partial
# trials: 10000
# max deviation: 0
# event output files
#
# the supported formats are
# - Les Houches (suffix .lhe)
# - HepMC2 (suffix .hepmc)
# - HepMC3 (suffix .hepmc3 or .hepmc)
# TODO: - ROOT ntuples (suffix .root)
#
# An output file's format is deduced either automatically from the suffix
# or from an explicit specification, e.g.
# - Les Houches: outfile
event output:
- HEJ.lhe
# - HEJ_events.hepmc
# to use a rivet analysis
#
# analysis:
# rivet: MC_XS # rivet analysis name
# output: HEJ # name of the yoda files, ".yoda" and scale suffix will be added
#
# to use a custom analysis
#
# analysis:
# plugin: /path/to/libmyanalysis.so
# my analysis parameter: some value
# selection of random number generator and seed
# the choices are
# - mixmax (seed is an integer)
# - ranlux64 (seed is a filename containing parameters)
random generator:
name: mixmax
# seed: 1
# Vacuum expectation value
vev: 246.2196508
# Properties of the weak gauge bosons
particle properties:
Higgs:
mass: 125
width: 0.004165
W:
mass: 80.385
width: 2.085
Z:
mass: 91.187
width: 2.495
# parameters for Higgs-gluon couplings
# this requires compilation with qcdloop
#
# Higgs coupling:
# use impact factors: false
# mt: 174
# include bottom: true
# mb: 4.7
## ---------------------------------------------------------------------- ##
## The following settings are only intended for advanced users. ##
## Please DO NOT SET them unless you know exactly what you are doing! ##
## ---------------------------------------------------------------------- ##
#
# minimum transverse momentum of extremal partons
# deprecated: use "max ext soft pt fraction" instead
# min extparton pt: 30
#
# max events: -1 # Maximal number of fixed order Events to process
# regulator parameter: 0.2 # The regulator lambda for the subtraction terms
diff --git a/doc/sphinx/HEJ.rst b/doc/sphinx/HEJ.rst
index ccdd486..f1fa90e 100644
--- a/doc/sphinx/HEJ.rst
+++ b/doc/sphinx/HEJ.rst
@@ -1,377 +1,414 @@
.. _`Running HEJ 2`:
Running HEJ 2
=============
Quick start
-----------
In order to run HEJ 2, you need a configuration file and a file
containing fixed-order events. A sample configuration is given by the
:file:`config.yml` file distributed together with HEJ 2. Events in the
Les Houches Event File format can be generated with standard Monte Carlo
generators like `MadGraph5_aMC@NLO <https://launchpad.net/mg5amcnlo>`_
or `Sherpa <https://sherpa.hepforge.org/trac/wiki>`_. If HEJ 2 was
compiled with `HDF5 <https://www.hdfgroup.org/>`_ support, it can also
read event files in the format suggested in
`arXiv:1905.05120 <https://arxiv.org/abs/1905.05120>`_.
HEJ 2 assumes that the cross section is given by the sum of the event
weights. Depending on the fixed-order generator it may be necessary to
adjust the weights in the Les Houches Event File accordingly.
The processes supported by HEJ 2 are
- Pure multijet production
- Production of a Higgs boson with jets
- Production of a W boson with jets
..
- *TODO* Production of a Z boson or photon with jets
where at least two jets are required in each case. For the time being,
only leading-order events are supported.
After generating an event file :file:`events.lhe` adjust the parameters
under the `fixed order jets`_ setting in :file:`config.yml` to the
settings in the fixed-order generation. Resummation can then be added by
running::
HEJ config.yml events.lhe
Using the default settings, this will produce an output event file
:file:`HEJ.lhe` with events including high-energy resummation.
When using the `Docker image <https://hub.docker.com/r/hejdock/hej>`_,
HEJ can be run with
.. code-block:: bash
docker run -v $PWD:$PWD -w $PWD hejdock/hej HEJ config.yml events.lhe
.. _`HEJ 2 settings`:
Settings
--------
HEJ 2 configuration files follow the `YAML <http://yaml.org/>`_
format. The following configuration parameters are supported:
.. _`trials`:
**trials**
High-energy resummation is performed by generating a number of
resummation phase space configurations corresponding to an input
fixed-order event. This parameter specifies how many such
configurations HEJ 2 should try to generate for each input
event. Typical values vary between 10 and 100.
.. _`max ext soft pt fraction`:
**max ext soft pt fraction**
Specifies the maximum fraction that soft radiation can contribute to the
transverse momentum of each the most forward and the most backward jet. This
setting is needed to regulate an otherwise uncancelled divergence. Values
between around 0.05 and 0.1 are recommended.
.. _`fixed order jets`:
**fixed order jets**
This tag collects a number of settings specifying the jet definition
in the event input. The settings should correspond to the ones used in
the fixed-order Monte Carlo that generated the input events.
.. _`fixed order jets: min pt`:
**min pt**
Minimum transverse momentum in GeV of fixed-order jets.
.. _`fixed order 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.
.. _`fixed order jets: R`:
**R**
The R parameter used in the jet algorithm, roughly corresponding
to the jet radius in the plane spanned by the rapidity and the
azimuthal angle.
.. _`resummation jets`:
**resummation jets**
This tag collects a number of settings specifying the jet definition
in the observed, i.e. resummed events. These settings are optional, by
default the same values as for the `fixed order jets`_ are assumed.
.. _`resummation jets: min pt`:
**min pt**
Minimum transverse momentum in GeV of resummation jets. This
should be between 25% and 50% larger than the minimum transverse
momentum of fixed order jets set by `fixed order jets: min pt`_.
.. _`resummation jets: algorithm`:
**algorithm**
The algorithm used to define jets. The HEJ 2 approach to
resummation relies on properties of :code:`antikt` jets, so this
value is strongly recommended. For a list of possible other
values, see the `fixed order jets: algorithm`_ setting.
.. _`resummation jets: R`:
**R**
The R parameter used in the jet algorithm.
.. _`event treatment`:
**event treatment**
Specify how to treat different event types. The different event types
contribute to different orders in the high-energy limit. The possible values
are :code:`reweight` to enable resummation, :code:`keep` to keep the events as
they are up to a possible change of renormalisation and factorisation scale,
and :code:`discard` to discard these events.
.. _`FKL`:
**FKL**
Specifies how to treat events respecting FKL rapidity ordering. These
configurations are dominant in the high-energy limit.
.. _`unordered`:
**unordered**
Specifies how to treat events with one emission that does not respect FKL
ordering, e.g. :code:`u d => g u d`. In the high-energy limit, such
configurations are logarithmically suppressed compared to FKL
configurations.
.. _`extremal qqx`:
**extremal qqx**
Specifies how to treat events with a quark-antiquark pair as extremal
partons in rapidity, e.g. :code:`g d => u u_bar d`. In the high-energy
limit, such configurations are logarithmically suppressed compared to FKL
configurations. :code:`reweight` is currently only supported for W boson
plus jets production.
.. _`central qqx`:
**central qqx**
Specifies how to treat events with a quark-antiquark pair central in
rapidity, e.g. :code:`g g => g u u_bar g`. In the high-energy limit, such
configurations are logarithmically suppressed compared to FKL
configurations. :code:`reweight` is currently only supported for W boson
plus jets production.
.. _`non-resummable`:
**non-resummable**
Specifies how to treat events where no resummation is possible. Only
:code:`keep` or :code:`discard` are valid options, *not* :code:`reweight`
for obvious reasons.
.. _`scales`:
**scales**
Specifies the renormalisation and factorisation scales for the output
events. This can either be a single entry or a list :code:`[scale1,
scale2, ...]`. For the case of a list the first entry defines the
central scale. Possible values are fixed numbers to set the scale in
GeV or the following:
- :code:`H_T`: The sum of the scalar transverse momenta of all
final-state particles
- :code:`max jet pperp`: The maximum transverse momentum of all jets
- :code:`jet invariant mass`: Sum of the invariant masses of all jets
- :code:`m_j1j2`: Invariant mass between the two hardest jets.
Scales can be multiplied or divided by overall factors, e.g. :code:`H_T/2`.
It is also possible to import scales from an external library, see
:ref:`Custom scales`
.. _`scale factors`:
**scale factors**
A list of numeric factors by which each of the `scales`_ should be
multiplied. Renormalisation and factorisation scales are varied
independently. For example, a list with entries :code:`[0.5, 2]`
would give the four scale choices (0.5μ\ :sub:`r`, 0.5μ\ :sub:`f`);
(0.5μ\ :sub:`r`, 2μ\ :sub:`f`); (2μ\ :sub:`r`, 0.5μ\ :sub:`f`); (2μ\
:sub:`r`, 2μ\ :sub:`f`) in this order. The ordering corresponds to
the order of the final event weights.
.. _`max scale ratio`:
**max scale ratio**
Specifies the maximum factor by which renormalisation and
factorisation scales may difer. For a value of :code:`2` and the
example given for the `scale factors`_ the scale choices
(0.5μ\ :sub:`r`, 2μ\ :sub:`f`) and (2μ\ :sub:`r`, 0.5μ\ :sub:`f`)
will be discarded.
.. _`log correction`:
**log correction**
Whether to include corrections due to the evolution of the strong
coupling constant in the virtual corrections. Allowed values are
:code:`true` and :code:`false`.
.. _`unweight`:
**unweight**
- Unweight events. Valid options are
-
- - :code:`weighted`: Generate weighted events. Default, if nothing else
- specified.
- - :code:`resummation`: Unweight only resummation events. Each set of
- resummation events coming of *one Fixed Order event* are unweighted
- separately. This can greatly reduce the number of resummation events,
- speeding up analysis and shrinking file size.
+ Settings for unweighting events. Unweighting can greatly reduce the
+ number of resummation events, speeding up analyses and shrinking
+ event file sizes.
+
+ .. _`type`:
+
+ **type**
+ How to unweight events. The supported settings are
+
+ - :code:`weighted`: Generate weighted events. Default, if nothing
+ else specified.
+ - :code:`resummation`: Unweight only resummation events. Each set
+ of resummation events coming from *a single fixed order event*
+ are unweighted separately according to the largest weight in the
+ current chunk of events.
+ - :code:`partial`: Unweight only resummation events with weights
+ below a certain threshold. The weight threshold is determined
+ automatically in a calibration run prior to the usual event
+ generation.
+
+ .. _`unweight: trials`:
+
+ **trials**
+ Maximum number of trial resummation events generated in the
+ calibration run for partial unweighting. This option should only
+ be set for partial unweighting.
+
+ If possible, each trial is generated from a different input
+ fixed-order event. If there are not sufficiently many input
+ events, more than one trial event may be generated for each of
+ them and the actual number of trial events may be smaller than
+ requested.
+
+ Increasing the number of trials generally leads to better
+ unweighting calibration but increases the run time. Between 1000
+ and 10000 trials are usually sufficient.
+
+ .. _`unweight: max deviation`:
+
+ **max deviation**
+ Controls the range of events to which unweighting is
+ applied. This option should only be set for partial unweighting.
+
+ A larger value means that a larger fraction of events are
+ unweighted. Typical values are between -1 and 1.
.. _`event output`:
**event output**
Specifies the name of a single event output file or a list of such
files. The file format is either specified explicitly or derived from
the suffix. For example, :code:`events.lhe` or, equivalently
:code:`Les Houches: events.lhe` generates an output event file
:code:`events.lhe` in the Les Houches format. The supported formats
are
- :code:`file.lhe` or :code:`Les Houches: file`: The Les Houches
event file format.
- :code:`file.hepmc2` or :code:`HepMC2: file`: HepMC format version 2.
- :code:`file.hepmc3` or :code:`HepMC3: file`: HepMC format version 3.
- :code:`file.hepmc` or :code:`HepMC: file`: The latest supported
version of the HepMC format, currently version 3.
.. _`random generator`:
**random generator**
Sets parameters for random number generation.
.. _`random generator: name`:
**name**
Which random number generator to use. Currently, :code:`mixmax`
and :code:`ranlux64` are supported. Mixmax is recommended. See
the `CLHEP documentation
<http://proj-clhep.web.cern.ch/proj-clhep/index.html#docu>`_ for
details on the generators.
.. _`random generator: seed`:
**seed**
The seed for random generation. This should be a single number for
:code:`mixmax` and the name of a state file for :code:`ranlux64`.
.. _`analysis`:
**analysis**
Name and Setting for the event analyses; either a custom
analysis plugin or Rivet. For the first the :code:`plugin` sub-entry
should be set to the analysis file path. All further entries are passed on
to the analysis. To use Rivet a list of Rivet analyses have to be
given in :code:`rivet` and prefix for the yoda file has to be set
through :code:`output`. See :ref:`Writing custom analyses` for details.
.. _`vev`:
**vev**
Higgs vacuum expectation value in GeV. All electro-weak constants are derived
from this together with the `particle properties`_.
.. _`particle properties`:
**particle properties**
Specifies various properties of the different particles (Higgs, W or Z). All
electro-weak constants are derived from these together with the :ref:`vacuum
expectation value<vev>`.
.. _`particle properties: particle`:
**Higgs, W or Z**
The particle (Higgs, |W+| or |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.
.. _`Higgs coupling`:
**Higgs coupling**
This collects a number of settings concerning the effective coupling
of the Higgs boson to gluons. This is only relevant for the
production process of a Higgs boson with jets and only supported if
HEJ 2 was compiled with `QCDLoop
<https://github.com/scarrazza/qcdloop>`_ support.
.. _`Higgs coupling: use impact factors`:
**use impact factors**
Whether to use impact factors for the coupling to the most forward
and most backward partons. Impact factors imply the infinite
top-quark mass limit.
.. _`Higgs coupling: mt`:
**mt**
The value of the top-quark mass in GeV. If this is not specified,
the limit of an infinite mass is taken.
.. _`Higgs coupling: include bottom`:
**include bottom**
Whether to include the Higgs coupling to bottom quarks.
.. _`Higgs coupling: mb`:
**mb**
The value of the bottom-quark mass in GeV. Only used for the Higgs
coupling, external bottom-quarks are always assumed to be massless.
Advanced Settings
~~~~~~~~~~~~~~~~~
All of the following settings are optional. Please **do not set** any of the
following options, unless you know exactly what you are doing. The default
behaviour gives the most reliable results for a wide range of observables.
.. _`min extparton pt`:
**min extparton pt**
Specifies the minimum transverse momentum in GeV of the most forward and the
most backward parton. Its value should be slightly below the minimum
transverse momentum of jets specified by `resummation jets: min pt`_. This
setting got superseded by `max ext soft pt fraction`_ and will be removed in
future versions.
.. _`max events`:
**max events**
Maximal number of (input) Fixed Order events. HEJ will stop after processing
`max events` many events. Default considers all events.
.. _`regulator parameter`:
**regulator parameter**
Slicing parameter to regularise the subtraction term, called :math:`\lambda`
in `arxiv:1706.01002 <https://arxiv.org/abs/1706.01002>`_. Default is 0.2