Why can't I change width in LHC_HZZ_POWHEG example?

[Generic User (don't modify these fields)]

Hi,

I have been trying to run LHC_HZZ_POWHEG example, playing with higgs parameters. I tried adding

MASS[25]=400.
WIDTH[25]=29.2

to both (run) or (model) sections of the run card but width parameter seems to be not picked up.

****************** Higgs parameters ****************
 *                                                  *
 *   mass(H) =  400.00      width(H) =  0.24080E+02 *
 *                                                  *
 *              Br( H -> b bbar)  =   0.00075 	    *
 *              Br( H -> tau tau) =   0.00003 	    *
 *              Br( H -> W W)	  =   0.68108       *
 *              Br( H -> Z Z)	  =   0.31814       *
 *              Br( H -> gam gam) =   0.00000 	    *
 ****************************************************

Am I missing something obvious? I am using 1.3.1 with MCFM-6.0.

Thanks, Sami

[marek]

Due to the modified structure of MCFM-6.0 the current interface only works with a (modified) MCFM-5.8. Unfortunately, the installation script is missing from the tarball, I therefore attached it to this thread. Alternatively, you could use the internal one-loop matrix element library for this process by switching to "Loop_Generator Internal" in the process block and add "Internal" to the ME_GENERATORS list. Could you please test, if this works for you? Thanks, Marek

[Generic User (don't modify these fields)]

Hello Marek,

Sorry for late reply. I already found the script you added from a friend and I applied the same changes to MCFM-6.0 when I was running. Anyway I did compile MCFM-5.8 with your script and a fresh compilation of Sherpa-1.3.1 using that. However result didn't change (the value is changed though)

 ****************** Higgs parameters ****************
 *                                                  *
 *   mass(H) =  400.00      width(H) =  0.19335E-01 *
 *                                                  *
 *              Br( H -> b bbar)  =   0.9330        *
 *              Br( H -> tau tau) =   0.0426        *
 *              Br( H -> W W)     = 848.2202        *
 *              Br( H -> Z Z)     = 396.2104        *
 ****************************************************

Do you have any idea why it is not changed? Is width parameter useless for MCFM interface?

Thanks, Sami

[marek]

Hello Sami,

although MCFM allows for setting the EW parameters explicitely (where you have to care about consistency yourself) it does however recalculate the Higgs width. This is accounted for in our interface where the Higgs propagator is reweighted to the width you set in Sherpa. So, the width you set is correctly taken into account, as stated in the Sherpa particle properties listing in the beginning of the run. Similarly, MCFM calculates the nlo correction only in the infinite top-mass limit. Our interface then corrects this to the top mass dependence you set in Sherpa.

Again, as an alternative circumventing these a posteriori corrections, using the internal nlo matrix element, as described above, treats the Higgs width and the top mass dependence as set from the beginning.

Hope this helps, Marek