e+e- Fixed Target collisions

Hi,

I think that you have issue with the running of alphas (since you are at small scale)
In this case, you do not want it to be running so you can just set it as fix scale.

Cheers,

Olivier

> On 16 Mar 2020, at 12:09, Gabriele Martelli <email address hidden> wrote:
>
> New question #689338 on MadGraph5_aMC@NLO:
> https://answers.launchpad.net/mg5amcnlo/+question/689338
>
> Greatings!! I'm trying to generate 10000 events of Standard Model e+ e- > e+ e- interactions at low energies (no Z boson) with an incoming positron of energy E=550 MeV and an electron target at rest. The problem is that when I compute this process I obtain this message on the terminal:
>
> Survey return zero cross section.
> Typical reasons are the following:
> 1) A massive s-channel particle has a width set to zero.
> 2) The pdf are zero for at least one of the initial state particles
> or you are using maxjetflavor=4 for initial state b:s.
> 3) The cuts are too strong.
> Please check/correct your param_card and/or your run_card.
> Zero result detected: See https://cp3.irmp.ucl.ac.be/projects/madgraph/wiki/FAQ-General-14
>
> I've tried to resolve the kind of problem by inserting some cuts on the minimal lepton momentum but it was helpless. Can someone help me? I'm posting here my run_card and param_card. Thank you!!
>
> PARAM_CARD
> ######################################################################
> ## PARAM_CARD AUTOMATICALY GENERATED BY MG5 FOLLOWING UFO MODEL ####
> ######################################################################
> ## ##
> ## Width set on Auto will be computed following the information ##
> ## present in the decay.py files of the model. ##
> ## See arXiv:1402.1178 for more details. ##
> ## ##
> ######################################################################
>
> ###################################
> ## INFORMATION FOR MASS
> ###################################
> Block mass
> 5 4.700000e+00 # MB
> 6 1.730000e+02 # MT
> 11 5.110000e-04 # Me
> 15 1.777000e+00 # MTA
> 23 9.118800e+01 # MZ
> 25 1.250000e+02 # MH
> ## Dependent parameters, given by model restrictions.
> ## Those values should be edited following the
> ## analytical expression. MG5 ignores those values
> ## but they are important for interfacing the output of MG5
> ## to external program such as Pythia.
> 1 0.000000e+00 # d : 0.0
> 2 0.000000e+00 # u : 0.0
> 3 0.000000e+00 # s : 0.0
> 4 0.000000e+00 # c : 0.0
> 12 0.000000e+00 # ve : 0.0
> 13 0.000000e+00 # mu- : 0.0
> 14 0.000000e+00 # vm : 0.0
> 16 0.000000e+00 # vt : 0.0
> 21 0.000000e+00 # g : 0.0
> 22 0.000000e+00 # a : 0.0
> 24 8.041900e+01 # w+ : cmath.sqrt(MZ__exp__2/2. + cmath.sqrt(MZ__exp__4/4. - (aEW*cmath.pi*MZ__exp__2)/(Gf*sqrt__2)))
>
> ###################################
> ## INFORMATION FOR SMINPUTS
> ###################################
> Block sminputs
> 1 1.325070e+02 # aEWM1
> 2 1.166390e-05 # Gf
> 3 1.180000e-01 # aS
>
> ###################################
> ## INFORMATION FOR YUKAWA
> ###################################
> Block yukawa
> 5 4.700000e+00 # ymb
> 6 1.730000e+02 # ymt
> 15 1.777000e+00 # ymtau
>
> ###################################
> ## INFORMATION FOR DECAY
> ###################################
> DECAY 6 1.491500e+00 # WT
> DECAY 23 2.441404e+00 # WZ
> DECAY 24 2.047600e+00 # WW
> DECAY 25 6.382339e-03 # WH
> ## Dependent parameters, given by model restrictions.
> ## Those values should be edited following the
> ## analytical expression. MG5 ignores those values
> ## but they are important for interfacing the output of MG5
> ## to external program such as Pythia.
> DECAY 1 0.000000e+00 # d : 0.0
> DECAY 2 0.000000e+00 # u : 0.0
> DECAY 3 0.000000e+00 # s : 0.0
> DECAY 4 0.000000e+00 # c : 0.0
> DECAY 5 0.000000e+00 # b : 0.0
> DECAY 11 0.000000e+00 # e- : 0.0
> DECAY 12 0.000000e+00 # ve : 0.0
> DECAY 13 0.000000e+00 # mu- : 0.0
> DECAY 14 0.000000e+00 # vm : 0.0
> DECAY 15 0.000000e+00 # ta- : 0.0
> DECAY 16 0.000000e+00 # vt : 0.0
> DECAY 21 0.000000e+00 # g : 0.0
> DECAY 22 0.000000e+00 # a : 0.0
>
>
>
> RUN_CARD
> #*********************************************************************
> # MadGraph5_aMC@NLO *
> # *
> # run_card.dat MadEvent *
> # *
> # This file is used to set the parameters of the run. *
> # *
> # Some notation/conventions: *
> # *
> # Lines starting with a '# ' are info or comments *
> # *
> # mind the format: value = variable ! comment *
> # *
> # To display more options, you can type the command: *
> # update full_run_card *
> #*********************************************************************
> #
> #*********************************************************************
> # Tag name for the run (one word) *
> #*********************************************************************
> tag_1 = run_tag ! name of the run
> #*********************************************************************
> # Number of events and rnd seed *
> # Warning: Do not generate more than 1M events in a single run *
> #*********************************************************************
> 10000 = nevents ! Number of unweighted events requested
> 0 = iseed ! rnd seed (0=assigned automatically=default))
> #*********************************************************************
> # Collider type and energy *
> # lpp: 0=No PDF, 1=proton, -1=antiproton, 2=photon from proton, *
> # 3=photon from electron *
> #*********************************************************************
> 0 = lpp1 ! beam 1 type
> 0 = lpp2 ! beam 2 type
> 0.55 = ebeam1 ! beam 1 total energy in GeV
> 0 = ebeam2 ! beam 2 total energy in GeV
> #*********************************************************************
> # Beam polarization from -100 (left-handed) to 100 (right-handed) *
> #*********************************************************************
> 0.0 = polbeam1 ! beam polarization for beam 1
> 0.0 = polbeam2 ! beam polarization for beam 2
>
>
> #*********************************************************************
> # PDF CHOICE: this automatically fixes also alpha_s and its evol. *
> #*********************************************************************
> nn23lo1 = pdlabel ! PDF set
> 230000 = lhaid ! if pdlabel=lhapdf, this is the lhapdf number
> # To see heavy ion options: type "update ion_pdf"
> #*********************************************************************
> # Renormalization and factorization scales *
> #*********************************************************************
> False = fixed_ren_scale ! if .true. use fixed ren scale
> False = fixed_fac_scale ! if .true. use fixed fac scale
> 91.188 = scale ! fixed ren scale
> 91.188 = dsqrt_q2fact1 ! fixed fact scale for pdf1
> 91.188 = dsqrt_q2fact2 ! fixed fact scale for pdf2
> -1 = dynamical_scale_choice ! Choose one of the preselected dynamical choices
> 1.0 = scalefact ! scale factor for event-by-event scales
> #*********************************************************************
> # Type and output format
> #*********************************************************************
> False = gridpack !True = setting up the grid pack
> -1.0 = time_of_flight ! threshold (in mm) below which the invariant livetime is not written (-1 means not written)
> average = event_norm ! average/sum. Normalization of the weight in the LHEF
> # To see MLM/CKKW merging options: type "update MLM" or "update CKKW"
>
> #*********************************************************************
> #
> #*********************************************************************
> # handling of the helicities:
> # 0: sum over all helicities
> # 1: importance sampling over helicities
> #*********************************************************************
> 0 = nhel ! using helicities importance sampling or not.
> #*********************************************************************
> # Generation bias, check the wiki page below for more information: *
> # 'cp3.irmp.ucl.ac.be/projects/madgraph/wiki/LOEventGenerationBias' *
> #*********************************************************************
> None = bias_module ! Bias type of bias, [None, ptj_bias, -custom_folder-]
> {} = bias_parameters ! Specifies the parameters of the module.
> #
> #*******************************
> # Parton level cuts definition *
> #*******************************
> #
> #
> #*********************************************************************
> # BW cutoff (M+/-bwcutoff*Gamma) ! Define on/off-shell for "$" and decay
> #*********************************************************************
> 15.0 = bwcutoff ! (M+/-bwcutoff*Gamma)
> #*********************************************************************
> # Standard Cuts *
> #*********************************************************************
> # Minimum and maximum pt's (for max, -1 means no cut) *
> #*********************************************************************
> 0.050 = ptl ! minimum pt for the charged leptons
> -1.0 = ptlmax ! maximum pt for the charged leptons
> {} = pt_min_pdg ! pt cut for other particles (use pdg code). Applied on particle and anti-particle
> {} = pt_max_pdg ! pt cut for other particles (syntax e.g. {6: 100, 25: 50})
> #*********************************************************************
> # Minimum and maximum E's (in the center of mass frame) *
> #*********************************************************************
> 0.0 = ej ! minimum E for the jets
> 0.0 = eb ! minimum E for the b
> 0.0 = ea ! minimum E for the photons
> 0.050 = el ! minimum E for the charged leptons
> -1.0 = ejmax ! maximum E for the jets
> -1.0 = ebmax ! maximum E for the b
> -1.0 = eamax ! maximum E for the photons
> -1.0 = elmax ! maximum E for the charged leptons
> {} = e_min_pdg ! E cut for other particles (use pdg code). Applied on particle and anti-particle
> {} = e_max_pdg ! E cut for other particles (syntax e.g. {6: 100, 25: 50})
>
> #*********************************************************************
> # Maximum and minimum absolute rapidity (for max, -1 means no cut) *
> #*********************************************************************
> 2.5 = etal ! max rap for the charged leptons
> 0.0 = etalmin ! main rap for the charged leptons
> {} = eta_min_pdg ! rap cut for other particles (use pdg code). Applied on particle and anti-particle
> {} = eta_max_pdg ! rap cut for other particles (syntax e.g. {6: 2.5, 23: 5})
> #*********************************************************************
> # Minimum and maximum DeltaR distance *
> #*********************************************************************
> 0.4 = drll ! min distance between leptons
> -1.0 = drllmax ! max distance between leptons
> #*********************************************************************
> # Minimum and maximum invariant mass for pairs *
> #*********************************************************************
> 0.050 = mmll ! min invariant mass of l+l- (same flavour) lepton pair
> -1.0 = mmllmax ! max invariant mass of l+l- (same flavour) lepton pair
> {} = mxx_min_pdg ! min invariant mass of a pair of particles X/X~ (e.g. {6:250})
> {'default': False} = mxx_only_part_antipart ! if True the invariant mass is applied only
> ! to pairs of particle/antiparticle and not to pairs of the same pdg codes.
> #*********************************************************************
> # Minimum and maximum invariant mass for all letpons *
> #*********************************************************************
> 0.050 = mmnl ! min invariant mass for all letpons (l+- and vl)
> -1.0 = mmnlmax ! max invariant mass for all letpons (l+- and vl)
> #*********************************************************************
> # Minimum and maximum pt for 4-momenta sum of leptons *
> #*********************************************************************
> 0.050 = ptllmin ! Minimum pt for 4-momenta sum of leptons(l and vl)
> -1.0 = ptllmax ! Maximum pt for 4-momenta sum of leptons(l and vl)
> #*********************************************************************
> # Inclusive cuts *
> #*********************************************************************
> 0.050 = xptl ! minimum pt for at least one charged lepton
> #*********************************************************************
> # Control the pt's of leptons sorted by pt *
> #*********************************************************************
> 0.050 = ptl1min ! minimum pt for the leading lepton in pt
> 0.050 = ptl2min ! minimum pt for the second lepton in pt
> -1.0 = ptl1max ! maximum pt for the leading lepton in pt
> -1.0 = ptl2max ! maximum pt for the second lepton in pt
> #*********************************************************************
> # maximal pdg code for quark to be considered as a light jet *
> # (otherwise b cuts are applied) *
> #*********************************************************************
> 4 = maxjetflavor ! Maximum jet pdg code
> #*********************************************************************
> #
> #*********************************************************************
> # Store info for systematics studies *
> # WARNING: Do not use for interference type of computation *
> #*********************************************************************
> False = use_syst ! Enable systematics studies
> #
> systematics = systematics_program ! none, systematics [python], SysCalc [depreceted, C++]
> ['--mur=0.5,1,2', '--muf=0.5,1,2', '--pdf=errorset'] = systematics_arguments ! see: https://cp3.irmp.ucl.ac.be/projects/madgraph/wiki/Systematics#Systematicspythonmodule
> # Syscalc is deprecated but to see the associate options type'update syscalc'
>
>
>
>
>
>
>
>
> --
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