Update History
These update notes describe major updates relative to the baseline
PYTHIA 8.100 version. However, they are less extensive than the
corresponding update notes for PYTHIA 6. There are three main
reasons for this:
- The manual contained on these html/php pages is kept up to date.
(However, the "Brief Introduction" may not always be.)
- 8.1 is a quite new code, so there are many minor changes that,
if all were to be documented, would hide the key ones.
- 8.1 is not yet used for "mission critical" applications,
so there is less need to trace changed behaviour.
Main news by version
- 8.101: 10 November 2007
- New option to initialize with arbitrary beam directions
pythia.init( idA, idB, pxA, pyA, pzA, pxB, pyB, pzB)
- The
LHAevnt
and LHAinit
classes have been
joined into a new LHAup
one, with new options that allow
the writing of a Les Houches Event File.
- 8.102: 6 December 2007
- Limited capability to use two different
Pythia
instances
for signal + pileup event generation, see main19.cc
for an
example.
- Added capability to set beam energy spread
and beam vertex.
Warning: as a consequence, the old Beams
group of
settings has been moved to BeamRemnants
, and
Beams
is now instead used for machine beam parameters.
Therefore also some Main
settings of this character have been
regrouped, as follows:
8.100 setting | has been moved to |
Main:idA |
Beams:idA |
Main:idB |
Beams:idB |
Main:inCMframe |
(Beams:frameType ) |
Main:eCM |
Beams:eCM |
Main:eA |
Beams:eA |
Main:eB |
Beams:eB |
Main:LHEF |
Beams:LHEF |
- 8.103: 22 January 2008
- Updated HepMC conversion routine.
- In the
Event
class the =
and
=+
methods have been overloaded to allow the copying
or appending of event records. Illustrated in main19.cc
.
- 8.104: 14 February 2008
- Updated configure scripts.
- The
SusyLesHouches
class updated to handle
SLHA version 2.
- The
forceHadronLevel()
method introduced for standalone
hadronization.
main15.cc
illustrated how either full hadronization or
only decays of some particles can be looped over for the rest of the
event retained.
- The html and php page formatting improved with
cascading style sheets.
- The static
ErrorMsg
class has been removed and
its functionality moved into the non-static Info
class,
in the renamed Info file.
- 8.105: 24 February 2008
- Further reduction of the use of static, with related code changes.
This should allow to have several almost independent
Pythia
instances. Some static classes still remain, however, notably for
random number generation and particle properties.
- Several minor improvements and new options.
- 8.106: 11 March 2008
- Improved handling of the Higgs width, relevant for massive and thereby
broad resonance shapes.
- 8.107: 17 March 2008
- Correction in the event record, so that the beam particles in line
1 and 2 do not have any mother according to the
motherList
method. Previously the "system" entry in line 0 was counted as their
mother, which gave rise to an unexpected extra vertex in the conversion
to the HepMC format.
- 8.108: 1 May 2008
- Support for HepMC version 1 is removed, to simplify the code and
reflect the evolution of the field.
- Status codes are stored in HepMC only as 1 for existing and 2 for
decayed or fragmented particles (whereas previously the original PYTHIA
codes were used for the latter).
- Parton densities are stored in HepMC as xf(x,Q^2)
rather than the f(x,Q^2) used in (some) previous versions.
- The SusyLesHouches class has ben updated so that reading is fully
compatible with the SLHA2 standard.
- The matrix elements for neutralino pair production have now been
completed and checked.
- A new compilation option
-Wshadow
is introduced and
code is rewritten at all places where this option gave warnings.
- Minor library correction to allow compilation with gcc 4.3.0.
- Ensure that alpha_strong does not blow up, by introducing
a minimal scale somewhat above Lambda_3 (roughly where
alpha_strong = 10).
- New methods
isValence1()
and isValence2()
in the Info
class.
- Protection against division by zero in calculation of decay vertex
(for zero-mass gluons with zero lifetime, where there should be no
displacement).
- 8.109: 6 May 2008
- Inclusion of some first code for rescatterng in multiple interactions;
currently only for internal tryout.
- 8.110: 18 June 2008
- Freeze GRV 94L distribution at small Q^2 to avoid blowup.
- Further evolution of rescattering to include colour reconnection
and more, but not yet FSR or ISR; still only for internal tryout.
- 8.111: 9 July 2008
- Further evolution of rescattering to include FSR (with some issues
still unsolved) but not yet ISR; still only for internal tryout.
- 8.112: 12 September 2008
- The
pythia.readFile(...)
method can now alternatively take
an istream
as argument instead of a filename
.
- Minor bug correction in
PartonLevel.cc
; the bug could
(rarely) give a segmentation fault.
- Resolution of several (but not all) rescattering issues for FSR; still
only for internal tryout.
- 8.113: 2 October 2008
- A new class
PartonSystems
is introduced to
keep track of which partons in the event record belong to which
subcollision system, plus some further information on each subsystem.
It takes over functionality previously found as part of the
Event
class, but leaves room for future growth.
- Development of rescattering in combination with ISR; still only for
internal tryout.
- 8.114: 22 October 2008
- Add capability to link to FastJet, with
main61.cc
as new example.
- Add optional model, wherein an increased pT0 turnoff scale
for MI and ISR is used for above-average active events, i.e. events that
already have several MI's or ISR emissions.
- Rescattering description operational (but still experimental) for case
that FSR is not interleaved, but saved until after MI, ISR and beam remnants
have been handled.