[Rivet] Fwd: [bug #33077] Outgoing Z boson not stored in hard process vertex

James Monk jmonk at fnal.gov
Tue Feb 5 17:12:46 GMT 2008


Rivet will need HepMC 2.03.04 or later in order for the  
VetoedFinalState projection to work properly (see below)

Begin forwarded message:

> From: "noreply [Lynn Garren]" <noreply-savannah at cern.ch>
> Date: 5 February 2008 17:08:19 GMT
> To: Lars Sonnenschein <Lars.Sonnenschein at cern.ch>, Lynn Garren <garren at fnal.gov 
> >, James Monk <jmonk at hep.ucl.ac.uk>, Andreas Pfeiffer <andreas.pfeiffer at cern.ch 
> >, Pere Mato <pere.mato at cern.ch>
> Subject: [bug #33077] Outgoing Z boson not stored in hard process  
> vertex
>
>
> This is an automated notification sent by LCG Savannah.
> It relates to:
> 		bugs #33077, project HepMC - a C++ Event Record for Monte Carlo  
> Generators
>
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> LATEST MODIFICATIONS of bugs #33077:
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> Update of bug #33077 (project hepmc):
>
>                  Status:                    None => Fixed
>             Open/Closed:                    Open => Closed
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>    _______________________________________________________
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> Follow-up Comment #3:
>
> The fix for this has been made available by Atlas.  It is in cvs now  
> and will
> be available in the forthcoming releases 2.01.10 and 2.03.04.
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> OVERVIEW of bugs #33077:
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> URL:
>  <http://savannah.cern.ch/bugs/?33077>
>
>                 Summary: Outgoing Z boson not stored in hard process  
> vertex
>                 Project: HepMC - a C++ Event Record for Monte Carlo
> Generators
>            Submitted by: None
>            Submitted on: 2008-01-29 15:32
>                Category: None
>                Severity: 3 - Normal
>                Priority: 5 - Normal
>              Item Group: None
>                  Status: Fixed
>                 Privacy: Public
>             Assigned to: sonne
>        Originator Email: jmonk at hep.ucl.ac.uk
>             Open/Closed: Closed
>         Discussion Lock: Any
>
>    _______________________________________________________
>
>
> Hi,
>
> I've been trying to remove (from a Rivet projection) the decay  
> products of
> the Z boson in some fortran Herwig Drell-Yan events.  The obvious  
> way to do
> this is to look through the ancestors of the lepton's production  
> vertex for a
> Z.  When I tried this I noticed there weren't very many events with  
> final
> state leptons connected to a Z (or gamma), so I compared the hepevt  
> common
> from Herwig with the HepMC record.  I found that the HepMC record is  
> missing
> the Z that is present in the hepevt common:
>
> (hepevt):
> ***** HEPEVT Common Event#: 1, 235 particles (max 10000) ***** Double
> Precision
> 4-byte integers, 8-byte floating point numbers, 10000-allocated  
> entries.
> Indx Stat Par- chil-       (  P_x,       P_y,       P_z,     
> Energy,       M )
>
>      ID  ents dren    Prod (   X,         Y,         Z,        cT)
> [mm]
> ________________________________________________________________________________
>   1 +101    0    0    (        0,         0,       300,       300,
> 0.938)
>    +2212    0    0    (        0,         0,         0,         0)
>   2 +102    0    0    (        0,         0,      -300,       300,
> 0.938)
>    -2212    0    0    (        0,         0,         0,         0)
>   3 +103    1    0    (        0,         0,         0,       600,
> 600)
>       +0    2    0    (        0,         0,         0,         0)
>   4 +121    6    9    (        0,         0,      46.5,      46.5,
> 0.32)
>       +2    6    9    (        0,         0,         0,         0)
>   5 +122    6   14    (        0,         0,     -45.2,      45.2,
> 0.32)
>       -2    6   14    (        0,         0,         0,         0)
>   6 +120    4    7    (    -5.18,     -2.02,      1.28,      91.9,
> 91.7)
>      +23    5    8    (        0,         0,         0,         0)
>      ^^^^
>
> (HepMC)
> GenParticle: 1 ID:2212 (P,E)=0,0,300,300.001 Stat:101 PV:0 EV:-2 Pol: 
> (-0,0)
> F:0
> GenParticle: 2 ID:-2212 (P,E)=0,0,-300,300.001 Stat:102 PV:0 EV:-3  
> Pol:(-0,0)
> F:0
> GenParticle: 3 ID:2 (P,E)=0,0,46.4977,46.4988 Stat:121 PV:-2 EV:-1  
> Pol:(-0,0)
> F:0
> GenParticle: 4 ID:-2 (P,E)=0,0,-45.2188,45.2199 Stat:122 PV:-3 EV:-1
> Pol:(-0,0) F:0
> GenParticle: 5 ID:14 (P,E)=6.63997,-1.33916,45.9957,46.4918 Stat:123  
> PV:-1
> EV:-4 Pol:(-0,0) F:0
> GenParticle: 6 ID:-14 (P,E)=-6.63997,1.33916,-44.7168,45.2269 Stat: 
> 124 PV:-1
> EV:-5 Pol:(-0,0) F:0
> GenParticle: 7 ID:2 (P,E)=-2.94741,-0.764536,48.0059,47.5284 Stat: 
> 141 PV:-1
> EV:-6 Pol:(-0,0) F:0
> GenParticle: 8 ID:21 (P,E)=2.07153,0.266261,6.91286,7.26033 Stat:2  
> PV:-6
> EV:-7 Pol:(-0,0) F:0
> GenParticle: 9 ID:21 (P,E)=0.875875,0.498275,5.94509,6.07635 Stat:2  
> PV:-6
> EV:-8 Pol:(-0,0) F:0
> ....
> GenParticle: 231 ID:22 (P,E)=-0.125745,-0.17355,-13.4178,13.4195  
> Stat:1
> PV:-119 EV:0 Pol:(-0,0) F:0
>
> So there is no pdg_id 23 particle in the HepMC record and it  
> contains four
> fewer particles than the hepevt record.
>
> Comparing to ATLAS' implementation of IO_HERWIG
> (http://atlas-sw.cern.ch/cgi-bin/viewcvs-atlas.cgi/offline/Simulation/HepMC/src/IO_HERWIG.cxx?view=markup 
> )
> I see that ATLAS have added a section of code especially to retain  
> the boson
> at the hard vertex (line 148-169):
>
> //BPK-> index_hard retained if it is a boson
> 	    int index_hard = 0;
> 	    for ( int i = 1; i <=HEPEVT_Wrapper::number_entries(); i++ ) {
> 	      if ( HEPEVT_Wrapper::status(i)==120 ) index_hard=i;
> 	      if ( index_hard!=0 ) break;
> 	    }
> 	
> 	    if ( index_hard!=0) {
> 	      hard_vtx->add_particle_out( hepevt_particle[index_hard] );
> 	      GenVertex* hard_vtx2 = new GenVertex();
> 	      hard_vtx2->add_particle_in( hepevt_particle[index_hard] );
> 		  for ( int i = 1; i <= HEPEVT_Wrapper::number_entries(); ++i ) {
> 		if (  HEPEVT_Wrapper::first_parent(i)==index_hard ) {
> 		  hard_vtx2->add_particle_out( hepevt_particle[i] );
> 		}
> 	      }
> 	      evt->set_signal_process_vertex( hard_vtx );
> 	      evt->set_signal_process_vertex( hard_vtx2 );
> 	    }
> 	    else {
> 	      evt->set_signal_process_vertex( hard_vtx );
> 	    }
>
> Is it intentional that HepMC removes the Z boson from the event  
> record (if
> so, why?) or is this a bug in the official HepMC that ATLAS have  
> fixed in
> their private implementation?
>
> thanks,
>
> James
>
>
>
>    _______________________________________________________
>
> Follow-up Comments:
>
>
> -------------------------------------------------------
> Date: 2008-02-05 17:08              By: Lynn Garren <garren>
> The fix for this has been made available by Atlas.  It is in cvs now  
> and will
> be available in the forthcoming releases 2.01.10 and 2.03.04.
>
> -------------------------------------------------------
> Date: 2008-01-29 16:59              By: Anonymous
> I saw this behaviour both with the current 2.03.03 version and the  
> previous
> 2.02.01 that I had been using.
>
> James
>
> -------------------------------------------------------
> Date: 2008-01-29 16:54              By: Lynn Garren <garren>
> Which version of HepMC?
>
>
>
>
>
>
>    _______________________________________________________
>
> Carbon-Copy List:
>
> CC Address                          | Comment
> ------------------------------------+-----------------------------
> 466                                 | -COM-
> jmonk at hep.ucl.ac.uk                 | -SUB-
>
>
>
>
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> ======================================================================
>
> This item URL is:
>  <http://savannah.cern.ch/bugs/?33077>
>
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