This shows you the differences between two versions of the page.
Both sides previous revision Previous revision Next revision | Previous revision Next revision Both sides next revision | ||
2017:groups:tools:lhe [2017/06/12 17:01] leif.lnnblad |
2017:groups:tools:lhe [2017/06/12 17:40] leif.lnnblad |
||
---|---|---|---|
Line 6: | Line 6: | ||
It has been claimed that the shower starting/veto scales need to be more flexible. Something like that is already included in the Pythia8 which interprets eg. an attribute ''pt_start_3="42"'' in a ''<scales>'' tag as the starting scale of particle 3. These attributes are in addition to the ''mups'' defined in the current version together with ''mur'' and ''muf''. | It has been claimed that the shower starting/veto scales need to be more flexible. Something like that is already included in the Pythia8 which interprets eg. an attribute ''pt_start_3="42"'' in a ''<scales>'' tag as the starting scale of particle 3. These attributes are in addition to the ''mups'' defined in the current version together with ''mur'' and ''muf''. | ||
- | After the discussions on Saturday it was agreed that much of the complications of scale settings for individual particles must in any case be handled through specialized hooks into the parton shower, the interface of which is determined by the individual parton shower, with different implementations done by the respective matrix element providers. For this to work smoothly there is nevertheless a need to formalise the information that goes into the event file. | + | After discussions it was agreed that much of the complications of scale settings for individual particles must in any case be handled through specialized hooks into the parton shower, the interface of which is determined by the individual parton shower, with different implementations done by the respective matrix element providers. For this to work smoothly there is nevertheless a need to formalise the information that goes into the event file. |
The suggestion is to allow subtags named ''<scale>'' with the content specifying a special scale in GeV. This tag can have a number of attributes: | The suggestion is to allow subtags named ''<scale>'' with the content specifying a special scale in GeV. This tag can have a number of attributes: | ||
Line 17: | Line 17: | ||
== Splitting up the LHE file == | == Splitting up the LHE file == | ||
- | The current way of specifying the cross section is not sufficient for some matrix element generators. Requests has been made to be able to report the number of tried events in addition to the ones accepted and actually present in the file. Further more, for practical reasons, there was a request to have the possibility to report the cross section in a separate file, since when starting writing a file, the cross section is not always fully known (this is the case in HepMC where the current best estimate of the cross section is reported for each event. In addition, it is in some cases desirable to divide up a huge LHE file into several smaller ones containing equivalent events. It was therefore decided to allow to split up LHE files into one file containing the ''<init>'' with all information run information, and a list of files containing only ''<event>''s. For this we introduced a new ''<eventfiles>'' tag which may contain an arbitrary number of ''<eventfile>'' tags. The ''<eventfiles>'' tag does not have attributes, while for the ''<eventfile>'' the following may be specified. | + | The current way of specifying the cross section is not sufficient for some matrix element generators. Requests has been made to be able to report the number of tried events in addition to the ones accepted and actually present in the file. Further more, for practical reasons, there was a request to have the possibility to report the cross section in a separate file, since when starting writing a file, the cross section is not always fully known (this is the case in HepMC where the current best estimate of the cross section is reported for each event. In addition, it is in some cases desirable to divide up a huge LHE file into several smaller ones containing equivalent events. It was therefore decided to allow to split up LHE files into one file containing the ''<init>'' with all information run information, and a list of files containing only ''<event>''s. For this we introduced a new ''<eventfiles>'' tag which may contain an arbitrary number of ''<eventfile>'' tags. The ''<eventfiles>'' tag does not have attributes and must be in the ''<init>'' block. The ''<eventfile>'' the following may be specified. |
- | * ''name'' is the name of the file containing ''<event>''s | + | * ''name'' (mandatory) is the name of the file containing ''<event>''s. This would preferably be a relative filename with respect to the directory where the file containing the ''<init>'' block resides. |
- | * ''neve'' given the number of | + | * ''nevent'' is the number of ''<event>''s in the file. |
+ | * ''ntries'' is the number of attempts the ME generator needed to produce the events in the file. (see below). | ||
- | The first is an ammendment to the ''<event>'' tag where an attribute ''ntries'' can be given to indicate the number of tries the matrix element generator used before producing the event. If absent, ''ntries="1"'' is assumed. | + | == Cross section information == |
- | + | ||
- | The other suggestion is to allow for supplying ''<xsecinfo>'' tags inside an ''<event>'' block to indicate that the original ''<xsecinfo>'' (given in the ''<init>'' block) is updated. In addition the ''<xsecinfo>'' is given an new optional attribute ''ntries'' given the number of attempts used to produce the number of events indicated in the ''neve'' attribute. | + | |
+ | As noted above some ME generator needs to report the number of attempts needed to generate the ''<event>''s in the LHE file, to get the proper statistics. In addition the for LHE files with weight variations, the cross section information may be needed for each weight variation. To handle the we propose additional attributes for the ''<xsecinfo>'' tag and that several ''<xsecinfo>'' tags may be given in the ''<init>'' block. The previously defined attributes were | ||
+ | * ''neve'' (mandatory) is the number of events in the file. | ||
+ | * ''totxsec'' (mandatory) the total cross section of all the processes in the file. | ||
+ | * ''maxweight'' the largest of the weights of the events in the file. | ||
+ | * ''meanweight'' the average of the weights of the events in the file. | ||
+ | * ''negweights'' is set ''true'' if the file contains negative weights. | ||
+ | * ''varweights'' is set ''true'' if the file contains variable weights. | ||
+ | It is now suggested to add the following attributes | ||
+ | * ''ntries'' is the number of attempts made before accepting the ''neve'' events in the file. | ||
+ | * ''xsecerr'' is the estimated statistical uncertainty on ''totxsec''. | ||
+ | * ''weightname'' the name of the weight variation to which this ''<xsecinfo>'' tag corresponds. If not given, the default ''XWGTUP'' weight is implied. | ||
+ | == Documentation and sample code == | ||
+ | It was agreed that the changes proposed are significant enough to bump the version number of LHE to 4.0. It was also agreed that the LHE accord must be better documented and that there should be one well-defined place to find this documentation. | ||
+ | Since version 3 of the HepMC event record now comes with sample LHEF code and the option of including LHE information in the HepMC files, it is natural to keep this code up-to-date, and that documentation also is distributed with HepMC3. HepMC3 can be obtained from [[https://gitlab.cern.ch/hepmc/HepMC3]] | ||