# Definition of drjj parameter in the run card

Dear MadGraph experts,

I am trying to check my own numerical computation of a total cross section for a p p > j j process

against a total cross section from MadGraph.

In MadGraph I generate events for p p > j j process (where j = g u d s c u~ d~ s~ c~) .

I do not use Pythia and 0 = ickkw and drjj = 0.1

Now if I do not impose any cuts on distance between jets in my code I am getting agreement between my code and MadGraph.

(My code just does a numerical Monte-Carlo integration of analytical expression for cross section integrand as a function of y_1, y_2 and pT).

However if impose a cut on a distance between jets in my code deltaR >= 0.1 I am starting to get a disagreement between MadGraph and my calculations.

I define deltaR as

deltaR = sqrt(deltaEta2 + deltaPhi^2)

where deltaE = y1 - y3 and deltaPhi = 2 * ( atan(exp(-y1) - atan(exp(-2) )

last expression for deltaPhi follows from the connection between pseudorapidity and an an angle between particle and a beem pipe y = -ln ( tan(teta / 2)).

Moreover if I set drjj = 3.0 in my code I am getting a zero cross section and in MadGraph I still capable to generate events and calculate a cross section...

I suspect that I do not really understand how drjj is defined in MadGraph ..

So my questions are:

Could you please tell me how drjj is define in MadGraph?

And is there any difference between drjj in case when one switch on showering ?

Is there any difference in the definition of drjj for two jet final state and three (or four) jet final states ?

Is there any difference between definition of drjj, drll, draj and all these parameters in run card?

Thank you very much!

With best regards,

Oleh

## Question information

- Language:
- English Edit question

- Status:
- Solved

- Assignee:
- No assignee Edit question

- Solved by:
- oleh

- Solved:
- 2017-12-13

- Last query:
- 2017-12-13

- Last reply:
- 2017-12-13

Hi,

> Could you please tell me how drjj is define in MadGraph?

So in madgraph the cuts is done in file SubProcesses/cuts.f around line 440:

> c DeltaR min & max cuts

> c

> do i=nincoming+

> do j=i+1,nexternal

> if(debug) write (*,*) 'r2(',i, ',' ,j,')='

> if(debug) write (*,*) dsqrt(r2min(

> if(r2min(

> tmp=r2(

> notgood=(tmp .lt. r2min(j,i)).or.

> $ (r2max(j,i).ge.0d0 .and. tmp .gt. r2max(j,i))

> if (notgood) then

> if(debug) write (*,*) i,j,' -> fails'

> passcuts=.false.

> return

> endif

> endif

> enddo

> enddo

As you can see here this is the same function called for drjj, drll, draj.

the definition of r2min(j,i) and r2max(j,i) are done inside setcuts.f:

with the following lines:

Note that the value of r2min is printed in the log of each individual channel of integration.

The definition of the r2 function is done in Source/

> DOUBLE PRECISION FUNCTION R2(P1,P2)

> c******

> c Distance in eta,phi between two particles.

> c******

> IMPLICIT NONE

> c

> c Arguments

> c

> double precision p1(0:3),p2(0:3)

> c

> c External

> c

> double precision rap,DELTA_PHI

> external rap,delta_phi

> c-----

> c Begin Code

> c-----

> R2 = (DELTA_

> RETURN

> END

The function DELPHI is defined in line 162 of the same file:

> DOUBLE PRECISION FUNCTION DELTA_PHI(P1, P2)

> c******

> c Returns separation in phi of two particles p1,p2

> c******

> IMPLICIT NONE

> c

> c Arguments

> c

> double precision p1(0:3),p2(0:3)

> c

> c Local

> c

> REAL*8 DENOM, TEMP

> c-----

> c Begin Code

> c-----

> DENOM = SQRT(P1(1)**2 + P1(2)**2) * SQRT(P2(1)**2 + P2(2)**2)

> TEMP = MAX(-0.99999999D0, (P1(1)*P2(1) + P1(2)*P2(2)) / DENOM)

> TEMP = MIN( 0.99999999D0, TEMP)

> DELTA_PHI = ACOS(TEMP)

> END

and the function rap is defined in line 95 (again same file)

> DOUBLE PRECISION FUNCTION rap(p)

> c******

> c Returns rapidity of particle with p in the CM frame

> c Note that it only applies to p-p collisions

> c******

> IMPLICIT NONE

> c

> c Arguments

> c

> double precision p(0:3)

> c

> c Local

> c

> double precision pm

> c

> c Global

> c

> include 'maxparticles.inc'

> include 'run.inc'

>

> double precision cm_rap

> logical set_cm_rap

> common/

> data set_cm_rap/.false./

>

> c-----

> c Begin Code

> c-----

> if(.not.set_cm_rap) then

> print *,'Need to set cm_rap before calling rap'

> stop

> endif

> c pm=dsqrt(

>

> pm = p(0)

> if (pm.gt.abs(p(3))) then

> rap = .5d0*dlog(

> else

> rap = -1d99

> endif

> end

> And is there any difference between drjj in case when one switch on showering ?

No. But be carefull about the following parameter:

But note that in presence of MLM matching/merging (ickkw=1) we assume those cuts to be zero. (you should see that in the log actually).

(to be 100% sure please check the log of any channel of integration)

> Is there any difference in the definition of drjj for two jet final state and three (or four) jet final states ?

No

> Is there any difference between definition of drjj, drll, draj and all these parameters in run card?

No

Cheers,

Olivier

> On Dec 12, 2017, at 18:08, oleh <email address hidden> wrote:

>

> New question #661631 on MadGraph5_aMC@NLO:

> https:/

>

> Dear MadGraph experts,

>

> I am trying to check my own numerical computation of a total cross section for a p p > j j process

> against a total cross section from MadGraph.

>

> In MadGraph I generate events for p p > j j process (where j = g u d s c u~ d~ s~ c~) .

> I do not use Pythia and 0 = ickkw and drjj = 0.1

>

> Now if I do not impose any cuts on distance between jets in my code I am getting agreement between my code and MadGraph.

> (My code just does a numerical Monte-Carlo integration of analytical expression for cross section integrand as a function of y_1, y_2 and pT).

>

> However if impose a cut on a distance between jets in my code deltaR >= 0.1 I am starting to get a disagreement between MadGraph and my calculations.

>

> I define deltaR as

> deltaR = sqrt(deltaEta2 + deltaPhi^2)

> where deltaE = y1 - y3 and deltaPhi = 2 * ( atan(exp(-y1) - atan(exp(-2) )

>

> last expression for deltaPhi follows from the connection between pseudorapidity and an an angle between particle and a beem pipe y = -ln ( tan(teta / 2)).

>

> Moreover if I set drjj = 3.0 in my code I am getting a zero cross section and in MadGraph I still capable to generate events and calculate a cross section...

>

> I suspect that I do not really understand how drjj is defined in MadGraph ..

>

> So my questions are:

> Could you please tell me how drjj is define in MadGraph?

>

> And is there any difference between drjj in case when one switch on showering ?

>

> Is there any difference in the definition of drjj for two jet final state and three (or four) jet final states ?

>

> Is there any difference between definition of drjj, drll, draj and all these parameters in run card?

>

> Thank you very much!

>

> With best regards,

> Oleh

>

>

>

>

> --

> You received this question notification because you are an answer

> contact for MadGraph5_aMC@NLO.

oleh (fedkevych) said : | #2 |

Dear Oliver,

thank you very much!

You helped me a lot!

PS I just found an error in implementation of deltaR in my code.

Now my computations agree with MAdGraph.

With best regards,

Oleh