Identifying Particles in the ATLAS Detector at the LHC
We will ask the students to scan a mix of various physics events and classify them in the following categories
- W->mu nu
- W->e nu
- Z->mu mu
- Z->e e
- QCD dijet events
To do this we use the ATLANTIS events display. The Atlantis setup was tailored to make it simpler and better looking for the
students by Mark Stockton from Birmingham. Many thanks to Mark!
At RAL we typically have 80 students per hands-on session, and two students work together.
The aim of the exercise is to classify events in the different categories: W->enu, W->munu, Z->ee, Z->mumu and background events
from jet production. To make it a bit more fun 1 Higgs->4l event is added to the sample. The group which finds this event will get a small prize e.g. an ATLAS 3D viewer.
Each student will get 20 events to analyse. In case they are fast they are allowed to look as well at the other events to chase for the Higgs and obtain the prize.
After the students have finished the results from each group are collected and we calculate together the ratio of W->enu/W->munu
and the ratio of Z/W production and compare with the predictions.
This will teach the student some basics how the detector works, e.g. what kind of 'traces' the different particles leave in the various detectors (e, mu, jet, missing transverse energy). They will need to learn how to select events via their signatures.
Computer set-up
On each computer running under windows (linux would work as well) ATLANTIS will be installed. There is a special version with its
own configuration file together with the events available in the
Masterclass download zip file.
Note, there are 500 events in this zip file, which is 460MB.
Unzip the file, install it on your windows machine and create a shortcut to the Desktop.
Paperwork
For the exercise, you will need some introductory slides, a results page per group, instructions for tutors etc. Here
is what we need for the RAL exercice
- introductory ppt slides:
This will teach the students how to identify the various categories of events in the detector and familisarise them with some Atlantis basics.
- result page per group: This page tells the students which
set of events they have to analyse. Per event there is one box to tick per event category. The students have to tick (exactly) one box
- overall result sheet:
On this excel sheet the main tutor will collect the results from the various groups. Then he'll look together with the student at the ratio of W->enu/W->munu and the ratio
of W/Z production which is approximately 10:1 (main effects: branching ratio, electro-weak couplings).
- Atlantis instructions:
summary of the main Atlantis command the student will need to do the exercise.
- summary sheet of the various event signatures:
in this sheet you find one event per category with some basic information how to identify them.
- Overview sheet on how to identify electrons, muons
and missing ET and which questions to ask yourself to identify the different type of signatures
- cheat sheet for tutors: this
sheet will tell the tutors which run number corresponds to each event type.
Preparation for the exercise
At RAL there is a series of lectures to introduce the students to particle physics. This year more emphasis will be put on
how a collider experiment work and on how to detect particles in the detector. This years LHC lecture can be found
here in ppt format. However,
as the first set of students will do the exercise prior to this lecture, some basic details about collider physics and on how
a detector work can be found as well in the
introductory ppt slides,
which will be shown before the students start the exercise. In there the basics on how to use Atlantis is covered as well.
In the tutorial room Atlantis is already launched and the first event a given group has to analyse is displayed. This saves
a bit of time. The summary sheet and the additonal sheets for the students is distributed.
Exercise
Each group of two students gets 20 events. The first group is asked to go through event 1-20, the 2nd group to use event
21-40 etc. Each group uses another set of events. Next to each computer the students will find their
result page, some
Atlantis instructions,
and a summary of the various signatures
they have to identify. Now they have 30 min for the exercise. Then we ask them to stop and sum up the events per category.
If they didn't finish analysing the 20 events, this doesn't matter. If they manage to finish scanning the events ahead of
time, they can look at the other events and hunt for the Higgs.
The tutors go around and help the students using ATLANTIS and help them classifying the events. In our trials the most
complicated part is the distinction between electrons and jets. In case of doubt the tutor can look at the run number
displayed. From the run number the type of event is known, so he can 'cheat' a bit if in doubt. None of our students
looked at the run number. Note the Higgs event is Event_116 (H->2e2mu).
Results
After the exercise each group is asked how many events they found per category. The main tutor fills in the results in the
overall result sheet.
Note, the lower part should be covered for this part. Then once all the results are collected, scroll down a bit and show
the measured results for the ratio of W->enu/W->munu, Z->ee/Z->mumu (not much stat, so make people aware of this) and
the ratio of W/Z production which is approx. 10:1 (main factors, couplings, branching ratio). Then at last you ask, if
someone found the Higgs. If yes, show the event to everyone and give the prize. In our case it's an Atlas 3d viewer.
Feedback
If you have any feedback concerning the exercise or want more information, please send a mail to Monika.Wielers@cern.ch
Last updated: April 2, 2008 M. Wielers