Pythia6 MSEL problem

Greetings,
I was trying to use MSEL(62), however, when I initialized pythia, I got an error saying no processes selected. I then set MSEL(0) and attempted to set the relevant processes (461-479) manually. Unfortunately, I got an error: “requested subprocess 461 not existing.” Trying several other processes, I got the same error, both inside this range and outside. Some processes, seem to work fine.

I have the latest versions of the pythia6 and root installed from source.

Any suggestions would be appreciated.

Thanks,
Matt Walker

Could you send a short script (running) showing the problem?

Rene

If I do:

root [5] TPythia6 pythia;
root [6] pythia.SetMSEL(62);
root [7] pythia.Initialize(“CMS”,“p”,“p”,200.0);

then stripping general initialize output I get:
"1****************** PYINIT: initialization of PYTHIA routines *****************

==============================================================================
I I
I PYTHIA will be initialized for a p on p collider I
I at 200.000 GeV center-of-mass energy I
I I

Error: no subprocess switched on.
Execution stopped."

and then root exits.

Matt

Similarly, if I try to turn on the processes manually (here only process 461):
root [2] TPythia6 pythia;
root [3] pythia.SetMSEL(0);
root [4] pythia.SetMSUB(461,1);
root [5] pythia.Initialize(“CMS”,“p”,“p”,200.0);

1****************** PYINIT: initialization of PYTHIA routines *****************

==============================================================================
I I
I PYTHIA will be initialized for a p on p collider I
I at 200.000 GeV center-of-mass energy I
I I

Error: requested subprocess 461 not existing.
Execution stopped!

Matt

I cannot reproduce your problem. I get the following output:

[code]==============================================================================
I I
I PYTHIA will be initialized for a p on p collider I
I at 200.000 GeV center-of-mass energy I
I I

******** PYMAXI: summary of differential cross-section maximum search ********

      ==========================================================
      I                                      I                 I
      I  ISUB  Subprocess name               I  Maximum value  I
      I                                      I                 I
      ==========================================================
      I                                      I                 I
      I   96   Semihard QCD 2 -> 2           I    2.2418D+03   I
      I  461   g + g  -> bb~[3S1(1)] + g     I    5.1611D-06   I
      I                                      I                 I
      ==========================================================

****** PYMULT: initialization of multiple interactions for MSTP(82) = 4 ******
pT0 = 1.41 GeV gives sigma(parton-parton) = 8.33D+01 mb: accepted

****** PYMIGN: initialization of multiple interactions for MSTP(82) = 4 ******
pT0 = 1.41 GeV gives sigma(parton-parton) = 5.04D+01 mb: accepted

root [4] ************* PYINIT: initialization completed **********************[/code]

This is with pythia version 6.409

Rene

Apparently, I was not using the most up to date pythia*.f file.

Thanks for your help.