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                  *       Update notes       *
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                  *    HYDJET version 2.4    *
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                 (Last updated 1 February 2019) 
 
HYDJET version 2.4 is a direct continuation of previous versions. 

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HYDJET2.4: 1 February 2019

1. The strength of the elliptic and triangular flow fluctuations 
   for soft component can be specified now by user in RunInputHydjet 
   file with the new parameters 'fKeps2' and 'fKeps3' respectively.
2. Option to switch on/off elliptic, triangular and quadrangular 
   modulations of the collective velocity profile for the alternative 
   scenario of anisotropic flow treatment is introduced. It is controlled 
   by the new parameters 'fRhou2', 'fRhou3' and 'fRhou4' respectively. 
3. The bug related with the sometimes incorrect update of the 
   particle coordinate information is fixed.
4. Several technical improvements have been done over the code to achieve 
   better compatibility with latest Root versions and C++/Fortran 
   compilers.

HYDJET2.3: 30 November 2015

1. The additional elliptic and triangular flow fluctuations for soft 
   component are introduced via event-by-event Gaussian smearing of 
   the spatial anisotropy parameters.

HYDJET2.2: 17 December 2013

1. The triangular flow for soft component is introduced via a special 
   modulation of the freeze-out hypersurface. Third Fourier harmonic of 
   azimuthal particle distribution appears relatively to new angle 'psiv3' 
   (randomly distributed with respect to the direction of the impact 
   parameter, and stored in array SERVICEEV at InitialStateHydjet.cxx). 

2. The treatment of quadrangular flow for soft component is improved.


HYDJET2.1: 6 July 2009

1. Option to get output from full particle history for PYTHIA/PYQUEN generated 
   particles (including partons and strings) is introduced. It is controlled by 
   the new flag: 
   fIedit=1 - only final state particles are presented in event output, 
   fIedit=0 - full particle history from PYTHIA/PYQUEN is produced.
   By default the full particle history is not produced, fIedit(D=1).

2. Option to produce thermal charmed particles (J/Psi and D mesons) is introduced. 
   Total number of c-quarks is calculated with PYTHIA, and then thermal charmed 
   hadrons are generated within the statistical hadronization model. 
   It is controlled by the new flag: 
   fIcharm=0 -  thermal charm production is switched off, 
   fIcharm>=1 - thermal charm production is switched on), 
   By default thermal charmed particle production is switched off, fIcharm(D=1).
   The new input parameters fMuC (chemical charm potential) and fCorrC (charmness 
   enhancement factor) are inroduced. If fCorrC less than zero then is is calculated.

3. The decays of PYTHIA/PYQUEN generated particles are performed by PYTHIA decayer by 
   default (instead of FASTMC decayer used before), mstj(21)(D=1).

4. Decay channels for K0 mesons are specified in "tabledecay.data" for FASTMC decayer. 
   K0 is decayed in K0S(50%) and K0L(50%). K0S is further decayed, while K0L is 
   considered stable.

5. Decay channels for J/Psi, D0+, D0-, D0 and D0-bar mesons are defined in 
   "tabledecay.data" for FASTMC decayer. Only 2- and 3-body decays from PYTHIA 
   tables are introduced meaning 77% of full branching for D0+ and D0- mesons, 
   65% for D0 mesons and 12% for J/psi (the e+e- and mu+mu- channels). 
   Other decay channels of J/Psi and D mesons are not produced. 

6. Most of the PYTHIA particle codes are added into the particle definition list
   "particles.data" to accomodate the full particle history.

7. In the output tree, the "Daughter1Index", "Daughter2Index" and "Daughter3Index"
   branches were removed. Instead, the "FirstDaughterIndex" and "LastDaughterIndex"
   branches are introduced keeping the index of the first and last daughter, 
   respectively. In the particle list, all daughter particles for a given particle
   are stored consecutively. If a particle has no daughters than these branches are
   -1. Some PYTHIA/PYQUEN particles have daughters but their first and last daughter
   indexes are -1. This happens for some PYTHIA status codes because PYTHIA keeps 
   colour flow information instead of the daughter indexes. So the mother index can 
   be used to reconstruct particle history if needed up to this level.

   In the output tree, the "pythiaStatus" branch was added. This will keep the
   PYTHIA status code k(i,1) for each particle from the hard component of HYDJET++ 
   (see PYTHIA manual for the code definitions). Particles from the soft component 
   (type=1) have pythiaStatus=-1.

   In the output tree, the "final" branch was added. This is an integer branch keeping 1 
   for final state particles and 0 for decayed particles. This flag can be used for 
   particles from both hard and soft components. Final state particles can be    determined 
   also in a more complicated way. For particles from hard component (type=1), the  final 
   state particles must have pythiaStatus=1 and zero daughters. For particles from soft 
   component (type=0), the final state particles must have zero daughters.

8. Makefile is modified. Now single Makefile is used for both root tree and histogram output. 
   By default Makefile uses g77 as fortran compiler. If g77 is not found, Makefile switches 
   to gfortran.

9. The file with default input parameters for c.m.s energy 2.76 A TeV "RunInputHydjetLHC2760" 
   is added (3 March 2011).