Changes between Version 2 and Version 3 of FormFactors


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Timestamp:
Apr 12, 2012, 10:57:36 AM (13 years ago)
Author:
Martin
Comment:

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  • FormFactors

    v2 v3  
    22
    33=== How to add momentum dependent form factors? ===
    4 The easiest way to implement momentum dependent form factors, without changing all the details in the {{{
     4The easiest way to implement momentum dependent form factors, without changing all the details in the
     5{{{
    56matrix.f
    6 }}} files in a process is by adding them in the model files. In particular the {{{
     7}}}
     8files in a process is by adding them in the model files. In particular the
     9{{{
    710couplings.f
    8 }}} can contain momentum dependent form factors. The following steps explain most of the details.
    9    * The first thing you have to do is download the full MG_ME package and untar it. Then, if your model contains new particles and interactions add them to the SM using the Software.UserModel, giving some generic values to the coupling constants. (If your model does not contain new particles and you only want to modify existing interactions, it is enough to make a copy of the {{{
     11}}}
     12can contain momentum dependent form factors. The following steps explain most of the details.
     13   * The first thing you have to do is download the full MG_ME package and untar it. Then, if your model contains new particles and interactions add them to the SM using the Software.UserModel, giving some generic values to the coupling constants. (If your model does not contain new particles and you only want to modify existing interactions, it is enough to make a copy of the
     14{{{
    1015sm
    11 }}} directory to a new directory. )
     16}}}
     17directory to a new directory. )
    1218   * Generate the process you would like to study.
    13    * Go to the =./Source/MODEL/= directory and open the {{{
     19   * Go to the =./Source/MODEL/= directory and open the
     20{{{
    1421couplings.f
    15 }}} file.
    16    * Add (in the setpara subroutine) ''before'' the line {{{
     22}}}
     23file.
     24   * Add (in the setpara subroutine) ''before'' the line
     25{{{
    1726c Start calculating the couplings for HELAS
    18 }}} the following lines to the file: {{{
     27}}}
     28the following lines to the file:
     29{{{
    1930c Momenta of particles in event
    2031      include '../genps.inc'
    2132      double precision pp(0:3,max_particles)
    22       common/momenta_pp/pp }}} This makes sure that the information of the momenta is available in the {{{
    23       common/momenta_pp/pp }}} This makes sure that the information of the momenta is available in the {{{couplings.f}}} file. These momenta can be used to calculate the anomalous (momentum dependent) couplings. The syntax is as follows. All the momenta are saved in an array called pp. The first element is running from 0 to 3, these are the energy, and the x, y and z components of the momentum of a particle (the beam direction is in the z direction) in the center of momentum frame of the event. The second element of the array labels the particles. Only momenta of '''external particles''' are in the array. The labeling is as follows. The first two are the incoming particles, and the others the outgoing numbered according to how the process is written down in the {{{proc_card.dat}}}. For example, if you are studying {{{e+e->Zh>bb~mu+mu-}}} then the first particle will be the positron, the second the electron. The final state particles: b quark, b anti-quark, muon+ and muon- , are 3, 4, 5 and 6 respectively. Hence momentum pp(2,4) is the y-component of the momentum of the b anti-quark in the center of momentum frame of the event. Using these components most anomalous couplings can be implemented by changing the SM values of the couplings in the {{{couplings.f}}} file.
     33      common/momenta_pp/pp
     34}}}
     35This makes sure that the information of the momenta is available in the
     36{{{
     37      common/momenta_pp/pp
     38}}}
     39This makes sure that the information of the momenta is available in the
     40{{{
    2441couplings.f
    25 }}} file. These momenta can be used to calculate the anomalous (momentum dependent) couplings. The syntax is as follows. All the momenta are saved in an array called pp. The first element is running from 0 to 3, these are the energy, and the x, y and z components of the momentum of a particle (the beam direction is in the z direction) in the center of momentum frame of the event. The second element of the array labels the particles. Only momenta of '''external particles''' are in the array. The labeling is as follows. The first two are the incoming particles, and the others the outgoing numbered according to how the process is written down in the {{{
     42}}}
     43file. These momenta can be used to calculate the anomalous (momentum dependent) couplings. The syntax is as follows. All the momenta are saved in an array called pp. The first element is running from 0 to 3, these are the energy, and the x, y and z components of the momentum of a particle (the beam direction is in the z direction) in the center of momentum frame of the event. The second element of the array labels the particles. Only momenta of '''external particles''' are in the array. The labeling is as follows. The first two are the incoming particles, and the others the outgoing numbered according to how the process is written down in the
     44{{{
    2645proc_card.dat
    27 }}}. For example, if you are studying {{{
     46}}}
     47. For example, if you are studying
     48{{{
    2849e+e->Zh>bb~mu+mu-
    29 }}} then the first particle will be the positron, the second the electron. The final state particles: b quark, b anti-quark, muon+ and muon- , are 3, 4, 5 and 6 respectively. Hence momentum pp(2,4) is the y-component of the momentum of the b anti-quark in the center of momentum frame of the event. Using these components most anomalous couplings can be implemented by changing the SM values of the couplings in the {{{
     50}}}
     51then the first particle will be the positron, the second the electron. The final state particles: b quark, b anti-quark, muon+ and muon- , are 3, 4, 5 and 6 respectively. Hence momentum pp(2,4) is the y-component of the momentum of the b anti-quark in the center of momentum frame of the event. Using these components most anomalous couplings can be implemented by changing the SM values of the couplings in the
     52{{{
    3053couplings.f
    31 }}} file.
    32    * As a final step you have to make sure that the {{{
     54}}}
     55file.
     56These momenta can be used to calculate the anomalous (momentum dependent) couplings. The syntax is as follows. All the momenta are saved in an array called pp. The first element is running from 0 to 3, these are the energy, and the x, y and z components of the momentum of a particle (the beam direction is in the z direction) in the center of momentum frame of the event. The second element of the array labels the particles. Only momenta of '''external particles''' are in the array. The labeling is as follows. The first two are the incoming particles, and the others the outgoing numbered according to how the process is written down in the
     57{{{
     58proc_card.dat
     59}}}
     60. For example, if you are studying
     61{{{
     62e+e->Zh>bb~mu+mu-
     63}}}
     64then the first particle will be the positron, the second the electron. The final state particles: b quark, b anti-quark, muon+ and muon- , are 3, 4, 5 and 6 respectively. Hence momentum pp(2,4) is the y-component of the momentum of the b anti-quark in the center of momentum frame of the event. Using these components most anomalous couplings can be implemented by changing the SM values of the couplings in the
     65{{{
     66couplings.f
     67}}}
     68file.
     69   * As a final step you have to make sure that the
     70{{{
    3371setpara
    34 }}} subroutine is called on an event-by-event basis, by adding to the {{{
     72}}}
     73subroutine is called on an event-by-event basis, by adding to the
     74{{{
    3575run_card.dat
    36 }}} the line {{{
     76}}}
     77the line
     78{{{
    3779T        = fixed_couplings  ! if .false. calc. coupl. for every event
    38 }}}just after the line where you can set the scale factor. For an example {{{
     80}}}
     81just after the line where you can set the scale factor. For an example
     82{{{
    3983run_card.dat
    40 }}} look [attachment:run_card.dat here].
     84}}}
     85look [attachment:run_card.dat here].
    4186
    4287
    43 Note that it might be interesting to make a new model for every process you want to study. In that case, instead of modifying the {{{
     88Note that it might be interesting to make a new model for every process you want to study. In that case, instead of modifying the
     89{{{
    4490couplings.f
    45 }}} file in the =./Source/MODEL/= directory, you could change the one in the =./Models/newmodel/= directory. Doing it this way has the clear advantage of being able to regenerate your process, without having to change the {{{
     91}}}
     92file in the =./Source/MODEL/= directory, you could change the one in the =./Models/newmodel/= directory. Doing it this way has the clear advantage of being able to regenerate your process, without having to change the
     93{{{
    4694couplings.f
    47 }}} file every time, which makes it less error prone. (Make sure that you also save a copy of the {{{
     95}}}
     96file every time, which makes it less error prone. (Make sure that you also save a copy of the
     97{{{
    4898proc_card.dat
    49 }}} in the model directory so that you won't forget for which process you created this model.)
     99}}}
     100in the model directory so that you won't forget for which process you created this model.)
    50101
    51102-- Main.RikkertFrederix - 20 Jul 2008