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CalcHEP past, present and future

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					CalcHEP: past, present and future


                        Alexander Belyaev
Southampton University & Rutherford Accelerator LAB




                WHEPP-X Chennai, India, 09/01/08



Alexander Belyaev, “CalcHEP: past, present and future”, WHEPPX, Jan 9 2008   1
                                   OUTLINE
Introduction into CalcHEP
Startup guide
    Installation
     symbolic session
     numerical session, kinematical distributions, event generation
Introduction of new model (LanHEP) and advanced features
New recent features, interface with MC generators
Outlook




Alexander Belyaev, “CalcHEP: past, present and future”, WHEPPX, Jan 9 2008   2
                              Practical points
 Questions/Comments:
  Please send me your e-mails: belyaev@soton.ac.uk

 Some useful Manuals
http://www.hep.phys.soton.ac.uk/~belyaev/manual

 Homeworks/exercises:                                  Homework#xx




  Alexander Belyaev, “CalcHEP: past, present and future”, WHEPPX, Jan 9 2008   3
              Introduction to CalcHEP
Author
  Alexander Pukhov
Idea
   The effective study of HEP phenomenology passing at
    high level of automation from your favorite model to
   physical observables such as decay width, branching
   ratios, cross sections kinematic distributions, ...
Analogous packages (ME generators):
  http://www.ippp.dur.ac.uk/montecarlo/BSM/
  http://www-theory.lbl.gov/tools/
 CompHEP (Boos et al)
 MadGraph/MadEvent (Maltoni, Stelzer)
 Grace/Helas (Fujimoto et al)
 FeynArts/FeynCalc/FormCalc (T.Han et al)
   recent: O'mega (Moretti, Ohl, Reuter)
Alexander Belyaev, “CalcHEP: past, present and future”, WHEPPX, Jan 9 2008   4
     Features/Limitations of CalcHEP
Any process within any model! Decay and scattering

Tree-level processes

Squared Matrix Element calculation
   no spin information for outgoing particles – spin
   averaged amplitude
Limit on number of external legs and number of
diagrams
   official limit – 6 , unofficial – none
    limit is set from the practical point: 2 -> 6 (1->7) :
   is the essential time limit
   number of diagrams ~ 100-200:
   time and disk-space limit

Alexander Belyaev, “CalcHEP: past, present and future”, WHEPPX, Jan 9 2008   5
    Quick start with CompHEP/CalcHEP:
       practical notes on installation
 Download code and read manual

http://www.ifh.de/~pukhov/calchep.html

http://theory.sinp.msu.ru/~pukhov/calchep.html

      tar -zxvf calchep_2.x.x.tgz
      cd calchep_2.x.x
      make
 Creating working directory
       From calchep_2.x.x directory:
     ./mkUsrDir ../work_calc

Homework#1: Install CalcHEP
 Alexander Belyaev, “CalcHEP: past, present and future”, WHEPPX, Jan 9 2008   6
  CalcHEP structure: symbolic part




Alexander Belyaev, “CalcHEP: past, present and future”, WHEPPX, Jan 9 2008   7
                        Starting CalcHEP
cd ../work_calc

 Files:
bin -> /home/belyaev/tmp/calchep_2.x.x/bin
calchep*
calchep.ini
models/
results/
tmp/

Start:
./calchep




 Alexander Belyaev, “CalcHEP: past, present and future”, WHEPPX, Jan 9 2008   8
  Model and parameters
funcxx.mdl, lgrngxx.mdl, prtclsxx.mdl, varsxx.mdl

  Particle decays
Higgs boson decay as an example:
parameter dependence, implementation width into
funcxx.mdl as a dependent parameter
Homework#2
Calculate SM Higgs boson Decay width




  Alexander Belyaev, “CalcHEP: past, present and future”, WHEPPX, Jan 9 2008   9
         Details          of symbolic session



   hadron/composite particle scattering
   unknown particle are assumed to be composite:
   'p' consists of u,U,d,D,s,S,c,C,b,B,G
    wild cards/names for outgoing particles
    'H -> 2*x'
   one can non-trivially exclude intermediate particles
     'W+ > 2, A>1, Z>3'
   particle width can be calculated 'on-fly'
     '!wtop' , i.e. '!' symbol should be used in the prt table



Alexander Belyaev, “CalcHEP: past, present and future”, WHEPPX, Jan 9 2008   10
CalcHEP Structure: numerical part




Alexander Belyaev, “CalcHEP: past, present and future”, WHEPPX, Jan 9 2008   11
    Process                                         as an example(1)
 PDFs




 QCD scale




 kinematical cuts, regularization, setting distributions



Alexander Belyaev, “CalcHEP: past, present and future”, WHEPPX, Jan 9 2008   12
    Process                                         as an example(2)
adaptive MC integration and phase-space mapping




Alexander Belyaev, “CalcHEP: past, present and future”, WHEPPX, Jan 9 2008   13
   Homework#3
   1. Calculate WbB production rates at Tevatron and LHC
   for PT b-jet > 20 GeV, b-Jet separation > 0.5,
   max pseudorapidity < 3
   2. Plot Invariant mass distributions for bb-pair,
   and Wb pairs for PT b-jet > 20 GeV and PT b-jet > 40 GeV




Alexander Belyaev, “CalcHEP: past, present and future”, WHEPPX, Jan 9 2008   14
                           Even generation




Alexander Belyaev, “CalcHEP: past, present and future”, WHEPPX, Jan 9 2008   15
  Useful scripts for numerical session(1)
     your working directory
bin -> /home/belyaev/comphep/calchep_2.x.x/bin/
calchep*
calchep.ini
models/
results/
tmp/
     cycle over subprocesses
  you need to exit from the numerical session first!
  ../bin/subproc_cycle
  needs 2 parameters like run_vegas
 1: total integrated luminosity
 2: limit for number of events to generate

  ../bin/subproc_cycle 100 10000
  #Subprocess 1 (u, D' -> W+, b, B) Cross section = 1.1739E+02
  #Subprocess 2 (D', u -> W+, b, B) Cross section = 1.1603E+02
  Total Cross Section 233.42 [pb] see details in prt_xx - prt_xx files




  Alexander Belyaev, “CalcHEP: past, present and future”, WHEPPX, Jan 9 2008   16
 Useful scripts for numerical session(2)
 calchep_2.x.x/bin/ directory:
 useful scripts/codes

subproc_cycl            ../bin/subproc_cycle 2 1000 2 1000
sum_distr               ../bin/sum_distr distr_2 distr_3 > distr_sum
show_distr              ../bin/show_distr distr_sum
tab_view                ../bin/tab_view < tab_1.txt
events2tab
gen_events
name_cycle
pcm_cycle

                                                           Homework#4
                                                           learn how to use:
                                                           1) gen_events
                                                           2) events2tab
                                                           3) tab_view



 Alexander Belyaev, “CalcHEP: past, present and future”, WHEPPX, Jan 9 2008    17
     Useful scripts for numerical session(2)
 events2tab
Parameters:
1- name of variable,
2- minimum limit,
3- maximum limit,
4- number of bins(<=300).
 File with events must be passed to input. For example:
  ../bin/events2tab T3 1 100 200 < events_1.txt >tab.txt
  ../bin/tab_view < tab.txt

     name_cycle
1:   Name of parameter
2:   Initial value
3:   Step
4:   Number of steps




     Alexander Belyaev, “CalcHEP: past, present and future”, WHEPPX, Jan 9 2008   18

				
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