What is the difference between b and j in Reco level

Dear Safinaz,

> I'm studying the following process p p > b b~ a a. I'd like to plot the
> invariant mass of the b b~ pair at the reconstruction level .. but when
> I make display_particles I found j (quarks after have been clustered in
> jets- ex: hadrons ), and (b) may be refer for b- tagging jet, so do I
> use M(j[1] j[2]) or M(b[1] b[2]) ?
What is a b-jet and a jet depends on what is in your event sample. In the reco level, a jet will be considered as a b jet only if it has a b-tagged properties. Whether this property is there depends on how you have simulated your signal.

>
> I made a small check that plotted N(b) which found almost centred at
> zero and N(j) which peaked around 2 as expected, is this means I should
> use "j" not "b" ?
This means that most of your jets are non-b-tagged. Nothing more nothing less.

> But I found some other problem with "j", I used pp > h > aa and pp > h >
> b b~ as backgrounds and plotted the transverse energy of the diphoton ET
> (a[1] a[2]) pair and the jet pair ET (j[1] j[2]), in ET (a[1] a[2]) pp
>> h > b b~ appeared at zero and only pp > h > aa was the background
> for the signal pp > 2 a 2b as expected , while when plotting ET (j[1]
> j[2]) both pp > h > b b~ and pp > h > aa had a distribution , I don't
> get why pp > h > aa appears here ? while in ET (b[1] b[2]) it didn't
> appear at all..
Parton showering effects?

> So shortly when dealing on Reco level with b-quarks do I use "j" or "b"
> ?
As I said above, it depends on what you have done for your simulation.

> If it "j" as in N(b) and N(j), why photons appears in jets plots ? how
> to avoid that ?
A jet is not a photon… I do not understand that.

Cheers,

Benjamin

Dear Dr. Benjamin,

Thanks for your reply ..

>> What is a b-jet and a jet depends on what is in your event sample. In the reco level, a jet will be considered as a b jet only if it has a b-tagged properties. Whether this property is there depends on how you have simulated your signal.

I'm used PGS detector simulator implemented in MadGraph5 . There where I generated .lhco file

>> This means that most of your jets are non-b-tagged. Nothing more nothing less.

I don't understand that, if N(j) is peaked around 2 as in the event sample while N(b) around zero, does not that mean MadAnalysis recognized the initial b- quarks as "j" not "b" ?

>> Parton showering effects ?

So do are my results are right like that ?
I just read in some paper that some times jets misidentified as photons, so photons should be isolated, [for instance in : arXiv:1606.03833v1 [hep-ex] page 5] .. so is this needs to use DELTAR in MA ? but in PGS card (the detector simulator I used in MG) the photon should be isolated in a cone of radius R as mentioned in the referred paper ..

Regards,
Safinaz

Hi Safinaz,

>>> This means that most of your jets are non-b-tagged. Nothing more nothing less.
>
> I don't understand that, if N(j) is peaked around 2 as in the event
> sample while N(b) around zero, does not that mean MadAnalysis recognized
> the initial b- quarks as "j" not "b" ?
Check your LHCO file. You may have no b-jets inside.

>
>
>>> Parton showering effects ?
>
> So do are my results are right like that ?
> I just read in some paper that some times jets misidentified as photons, so photons should be isolated, [for instance in : arXiv:1606.03833v1 [hep-ex] page 5] .. so is this needs to use DELTAR in MA ? but in PGS card (the detector simulator I used in MG) the photon should be isolated in a cone of radius R as mentioned in the referred paper ..
If you use PGS, thise means that you must have used either pythia or herwig for showering and hadronization, haven't you? Therefore you have jets in the final state.

I do not know much about PGS. Therefore, I cannot tell you what is done internally, in particular regarding b-tagging.

Regards,

Benjamin

>> Check your LHCO file. You may have no b-jets inside. .

That's true, actually this looks strange for me .. any why i'll try to check it again .

Regards,
Safinaz