Re: Deciphering top quark production at CERN’s Large Hadron Collider

in STEMGeeks7 months ago

Here is another post in response to the task given by @lemouth on the ongoing citizen science project - a project that has to do with the simulation of particle collision using software instead of the real one ongoing at the Large Hadron Collider.

If my mathematics skill is still anything to go by, this should be the 4th task on the project. The previous 3 tasks are as below:

The drill is, that anyone with a PC can participate in the project just by installing some software and following stepwise instructions as they are being spelled out by the instructor. The whole thing might look like a bunch of codes, however, one really does not need any coding knowledge to participate. I am a good example as I got zero knowledge of coding. All the documentation about the project can be found by following the hashtag #citizenscience.

The present task has to do with Deciphering top quark production at CERN’s Large Hadron Collider. This has to do with the analysis of those ‘reconstructed-level events’ as spelled out by Lemouth. So let's get started.

Task 1

The software is started using the following codes:

cd madanalysis5

And the simulated event is imported using:

import ANALYSIS_0/Output/SAF/_defaultset/lheEvents0_0/myevents.lhe.gz as ttbar
set ttbar.xsection = 505.8 (I was able to access my own cross-section value, luckily)

Next is the setting up of Ma5 to normalize the number of collisions recorded during the full run 2 of the LHC and then generating the histogram of the event:

set main.lumi = 140
plot NAPID

The result:

Task 2: Lepton and photon multiplicity

For lepton

define l = l+ l-
plot N(l) 5 0 5
select (l) PT > 20
plot N(l) 5 0 5
plot NAPID


For photon

N(a) 5 0 5
select (a) PT > 20
plot N(a) 5 0 5


Assignment 1: Jet multiplicity

N(j) 5 0 5
select (j) PT > 25
plot N(j) 5 0 8


For b-jets:

N(b) 5 0 5
select (b) PT > 25
plot N(b) 5 0 8

The result:

Why very little variation in the before and after cut figures? Perhaps it is because simulated collisions usually produce large amounts of b-jets - two b-jets actually? I hope my guess is correct :)

Task 3: Selecting a subset of simulated collisions


select N(l)==1

Looking at the effects of the cut on lepton multiplicity
define l = l+ l-
plot N(l) 5 0 5
select (l) PT > 20
plot N(l) 5 0 5
plot NAPID

The result:


What do I expect as a resulting histogram? Is the output in agreement with m expectation? I really have no idea of what to expect, in all sincerity :)

Task 4: Lepton properties

plot PT(l) 25 0 200 [logY]
plot ABSETA(l) 25 0 2.5 [logY]

The result:

There is a bit of variation in these results and those posted by @lemouth (especially in the screenshot on the left). I hope he can explain the reason.

Next is combining two jets:

plot M(j[1] j[2]) 50 0 250 [logY]

The result:

Again, there is a little variation from the result of Lemouth. I await an explanation.

I will leave the last assignment for the pros as I have got no idea how to go about it. I am just glad to follow the project and learn as much as I can while at it.

See you all when the next task drops.

Posted with STEMGeeks


What software are you using to run these simulations?

Posted using Proof of Brain

We use Madanalysis software recommended by @lemouth

Thanks. Looks like a pretty cool tool!

Posted using Proof of Brain

You can check my last four posts carrying the #citizenscience tag to get instructions about how to install those pieces of software and start using them. Our project is always open to new participants ^^


Too mathematically clever for me, but I at least HALF understand it.. 🤪

Half understanding will likely make you top 5% as far particle physics on hive concerned. :)

Did you know my husband's an astrophysicist ? Or at least he studied it before he became a senior physics teacher

@gentleshaid is correct. Understanding half of it makes you one of the top physicists on chain! The next step is to join us in the project ;)

Lol okay I back down and say maybe twenty percent 🤪 ... Or less. I know what the hadron collider does, at least 🤪🤪

Ahaha. I guess I have no way to convince you... Maybe with neutrinos instead of top quarks (as will be done in about 10 days)? ;)

Do you know that joke about neutrinos?

'What do neutrinos and I have in common?'
'Your Mum'

Which is only funny if a guy says it, and is such low level humour that I'm sure you'll forget all about asking me about science.

Damned... I had to look for it on the Internet to understand it (and I didn't find it funny). That's probably a sign of... getting old... Poor me :/

PS: I won't forget ;)

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 7 months ago Reveal Comment