Particle Physics Masterclass 2015

Computer Workshop

http://atlas.physicsmasterclasses.org/en/wpath_teilchenid2.htm

http://www.ep.ph.bham.ac.uk/twiki/bin/view/General/MinervaResources

http://atlas-minerva.web.cern.ch/atlas-minerva/

Minerva is a Masterclass tool allowing students to learn more about the physics that goes on in the ATLAS detector at the LHC. Currently, Minerva has two scenarios. One a tried and tested, well established exercise, where students must analyse events, using information from all parts of the detector to identify W and Z bosons. Another is an exercise where students must find the decay products of neutral strange particles, which will eventually culminate in the calculation of the mass and lifetime of the strange particle.

The aim of the exercise was to identify particles in the ATLAS detector at the LHC.

Identify electrons (e), muons (m), neutrinos(n) in the ATLAS detector

Types of Events (“particles produced in one collision”)

Do W and Z decay equally often in electrons and muons?

Students scanned a mix of various physics events and classified them in the following categories

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Background from jet production (which might look like W or Z event)

All the above events are ‘well-known’ processes

Data came from 2010 LHC collisions!

In addition one event was added which was a candidate Higgs event, it may appear as:

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After the students finished the results from each group were collected and the ratio of

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was calculated and the ratio of Z/W production was compared with the predictions.

To do the exercise the Atlantis visualisation program was used

https://indico.cern.ch/event/0/session/4/contribution/168/material/paper/1.pdf

http://www.hep.ucl.ac.uk/atlas/atlantis/

Principle of collider experiment

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The LHC collide protons against protons

The collision energy is used to create particles

The particles created in the detector are identified. This done through their interaction with matter

Only the end products of the reaction can be ‘seen’ not the reaction itself. A deduction needs to be made about what happened from this.

A detector is built symmetrically around the collision point. It is composed of several layers of detectors; each detector probes a different aspect of the event

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The exercise

The first event to be analysed was already displayed

The students had to study each event and classify it into 5 different categories

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Many more W’s are produced compared to Z events

Note: in reality there many more background events than here

The students were given some additional sheets to help them

They had to decide what type it was and tick the corresponding box

Only one tick per event!

When everything was done the totals were added up.

If the students had finished their 20 events they could hunt for the Higgs by looking at other set(s) of events

There is only one Higgs event

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in the whole sample

At the end a final summary was done and the group looked at the ratio

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and the ratio W/Z production together

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The photographs show the year 13 students doing the analysis. Unfortunately they were not able to find the Higgs Boson this year. Just as well CERN found it in 2012.

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