==== README ====

The scalar leptoquark pair-production processes provided in this package correspond to four simplified models in which only one or two types of leptoquarks are enabled:

  - S1 model:
    * LQ_S1: pair production of the S1 final state
  - R2 model:
    * LQ_R2_r2-1_p53: pair production of the R2^{+5/3} mass eigenstate
    * LQ_R2_r2-2_p23: pair production of the R2^{+2/3} mass eigenstate
  - R2 + S3 model:
    * LQ_R2S3_r2-1_p53: pair production of the R2^{+5/3} mass eigenstate
    * LQ_R2S3_r2-2_p23: pair production of the R2^{+2/3} mass eigenstate
    * LQ_R2S3_s3-1_p23: pair production of the S3^{+2/3} mass eigenstate
    * LQ_R2S3_s3-2_m13: pair production of the S3^{-1/3} mass eigenstate
    * LQ_R2S3_s3-3_m43: pair production of the S3^{-4/3} mass eigenstate
  - S1 + S3 model:
    * LQ_S1S3_s1: pair production of the S1 mass eigenstate
    * LQ_S1S3_s3-1_p23: pair production of the S3^{+2/3} mass eigenstate
    * LQ_S1S3_s3-2_m13: pair production of the S3^{-1/3} mass eigenstate
    * LQ_S1S3_s3-3_m43: pair production of the S3^{-4/3} mass eigenstate

If you would like to compute predictions for a different model containing any of the scalar leptoquark states S1, S1tilde, R2, R2tilde, and S3, please contact us.


=== PREREQUISITES ===

POWHEG-BOX-V2: https://powhegbox.mib.infn.it/
LHAPDF: https://lhapdf.hepforge.org/
COLLIER: https://collier.hepforge.org/

Note: The lhapdf-config script must be accessible globally (i.e. by adding to the PATH variable the installation path of LHAPDF).

The scalar leptoquark pair-production codes have been tested with POWHEG-BOX-V2 revision 3479, LHAPDF version 6.3.0, and COLLIER version 1.2.3.


=== INSTALLATION ===

Before compiling the processes, the paths to the POWHEG-BOX-V2 and COLLIER installations have to be provided. This can be done by modifying the Makefile in the corresponding process folder and changing the lines:

   PWHGPATH=../..
   COLLIERPATH=/path/to/COLLIER

Note: If this folder (LQ_processes_PWHGBOX) is already inside the POWHEG-BOX-V2 directory, then only the COLLIERPATH variable has to be adapted.

In a specific process folder, the executable file can be compiled by typing

  make pwhg_main

or, e.g., by using 4 cores to speed up the compilation process

  make -j4 pwhg_main

after which the executable pwhg_main should be created. It is not necessary to modify the core POWHEG-BOX files as detailed in appendix B of the paper, since the modified files are already provided with each process.

Note: If you are using the gcc compiler version 10 or above, it might be necessary to add the following line to the Makefile

  FFLAGS=-fallow-argument-mismatch

right after line 36,

  ifeq ("$(COMPILER)","gfortran")

at the top of the file.


=== RUNNING ===

To run a fixed-order calculation for a certain process, switch to the testrun-lhc folder of the process, adapt the powheg.input for POWHEG-BOX related settings such as, e.g.:
  - the PDF set and ID by (un)commenting or modifying the lines starting with lhans1 and lhans2,
  - the centre-of-mass energy of each proton beam by changing the values of ebeam1 and ebeam2,
  - the fixed-order accuracy by changing the flag bornonly (bornonly 1: LO, bornonly 0: NLO),
  - the factorisation and renormalisation scale multipliers facscfact and renscfact,

as well as the param_card.dat for:
  - the masses of the leptoquarks which can be found under Block MASS, starting from the line with the ID 770,
  - the Yukawa couplings of the leptoquark in the specific model which can be found under the BLOCK MGUSER; the indices of the components are given in the comments to the right of each line (with each component being split into a real and imaginary part denoted by _real and _imag).

To run the code with the current settings, type from the testrun-lhc directory

  ../pwhg_main

and press enter. When the run finishes, the total cross section will be output on the terminal window in the line starting with

  total (btilde+remnants) cross section in pb

together with a numerical Monte Carlo integration error (which, if necessary and in case it is too large, can be reduced by adapting the number of integration calls ncall2 and iterations itmx2 and to a lesser degree by the corresponding settings for the creation of the integration grid ncall1 and itmx1 in the powheg.input file). The results will also be written to the file pwg-stat.dat.

In the folder Cards of each process, additional parameter cards with the settings to compute the predictions for the benchmark points of tables 1-3 as in the paper are provided.

Note: In order to be able to reproduce the results of the paper for high leptoquark masses, the flag ''negativepdfs'' has been added to the ''powheg.input'' file, which, when set to 1, overrides the default behaviour of the POWHEG-BOX of setting negatively valued PDFs to zero. Furthermore, parton showering is not yet supported, please only use the codes to compute fixed-order NLO predictions.
