masterclass 20141 introduction to hands-on exercise aim of the exercise identify electrons (e),...

Masterclass 2014 1

Introduction to hands-on ExerciseAim of the exercise Identify electrons (e), muons (), neutrinos() in the ATLAS detector Types of Events (“particles produced in one collision”) We W Zee Z Background from jet production (which might look like W or Z event) All the above events are ‘well-known’ processes Data from 2010 LHC collisions! Aim of the exercise: Do W and Z decay equally often in electrons and

muons? In addition we added one event which is a candidate Higgs event, it may

appear as: Heeee, H, or Hee There will be a mystery prize for the first group to identify this event !!!To do the exercise we use the Atlantis visualisation program

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Principle of collider experiment

At the LHC you collide protons against protons

The collision energy is used to create particles

Identify created particles in our detectors

Done through their interaction with matter

We can only ‘see’ the end products of the reaction not the reaction itself and then have to deduce what happened from this

Our 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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How it works…

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How to detect particles in a detector

Tracking detector−Measure charge and momentum of charged particles in magnetic field

Electro-magnetic calorimeter−Measure energy of electrons, positrons and photons

Hadronic calorimeter−Measure energy of hadrons (particles containing quarks), such as protons, neutrons, pions, etc.

Muon detector−Measure charge and momentum of muons

Neutrinos are only detected indirectly via ‘missing energy’ not recorded in the calorimeters

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•End-on view of the detector (x-y projection)

•Warning: Only particles reconstructed in central region shown here (otherwise the particles in the forward would cover the view)!

•Side view of the detector (R-z projection)

•Particles in central and forward region are shown

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•Tracking detector (several sub-systems)•Tracking detector (several sub-systems)

•Electro-magnetic calorimeter

•Tracking detector (several sub-systems)


•Hadronic calorimeter

•Tracking detector (several sub-systems)


•Hadronic calorimeter

•Muon detector

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Detail• we cannot measure the whole event energy because energy is lost in very forward region (beam-pipe)

• better measurement: “side-way” component

• typically “interesting” collisions contain particles with big “side-ways” energies

Example: WeCharacteristics:- Electron with high “side-way” or transverse energy- Neutrino measured indirectly via large missing “side-way” or transverse energy

Electron identification• Electron deposits its energy in electro-magnetic calorimeter

• Note, what you see here are the energy deposits in space. • length gives magnitude, but everything is within this calorimeter!

Electron identification• Electron deposits its energy in electro-magnetic calorimeter•Track in tracking detector in front of shower in calorimeter

Electron identification• Electron deposits its energy in electro-magnetic calorimeter•Track in tracking detector in front of shower in calorimeter •No ‘trace’ in other detectors (electron stops in electro-magnetic calorimeter)

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Example: We•Electron track in tracking detector has high “side-ways” or transverse momentum (pT>10GeV)

•To see this yourself,


•To see this yourself,•click on ‘pick’


•To see this yourself,•click on ‘hand’ •move the pointer to the track and click on it

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•To see this yourself,•click on ‘hand’ •move the pointer to the track and click on it•Selected track becomes grey


•To see this yourself,•click on ‘hand’ •move the pointer to the track and click on it•Selected track becomes white

•pT is shown here

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Example: We• Electron deposits large “side-ways” energy (ET) in electro-magnetic calorimeter (ET>10GeV)

•To see this yourself,


•To see this yourself•move the pointer to the ‘purple square’ and click on it

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•To see this yourself•move the pointer to the ‘purple square’ and click on it•Selected ‘square’ becomes grey


•To see this yourself•move the pointer to the ‘purple square’ and click on it•Selected ‘square’ becomes grey

•ET is shown here

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Example: WeCharacteristics:• Electron with high “side-way” energy

- We now know how to identify them!


- We now know how to identify them!• Neutrino measured indirectly via large missing “side-way” or transverse energy (ET

miss > 10GeV)



miss > 10GeV)

-Red dashed line in end-on view -Not shown if value very small!-Note the thickness corresponds to the magnitude of ET

miss



miss > 10GeV)

-Red dashed line in end-on view -Not shown if value very small!

•Typically electron and ETmiss are ‘back-

to-back’



miss > 10GeV)

-Red dashed line in end-on view -Not shown if value very small!

• Value shown here

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Next event•Click on ‘Next’

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Example: WCharacteristics:

Example: WCharacteristics:• Large missing “side-way” energy (ET

miss > 10GeV)

Example: WCharacteristics:• Large missing “side-way” energy (ET

miss > 10 GeV)

• 1 muon with high track “side-way” momentum (pT>10GeV)

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Muon identificationMuon identification• Track in muon detector

Muon identification• Track in muon detector • Track in tracking detector

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Example: WCharacteristics:• Large missing “side-ways” energy (ET

miss > 10 GeV)

• 1 muon with high track “side-way” momentum (pT>10GeV)

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Example: Zee

Characteristics:

2 electrons in the event

Example: ZeeExample: Zee

Characteristics:

2 electrons in the event•here also some other low momentum tracks around from collision fragments

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Example: ZCharacteristics:

2 muons in the event



Here:• one in central region



Here:• one in central region• one in forward region

•Particles in forward region are not seen in “end-on” projection! Only in “side” projection



Here:• one in central region• one in forward region

•Particles in forward region are not seen in “end-on” projection! Only in “side” projection•Always look at side view to get the complete picture!

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Example: background

Characteristics:• Does not contain We, W, Zee, Z

Example: background

Characteristics:• Does not contain We, W, Zee, Z• Typically bundles of particles (jets) are produced

Example: background


•Energy deposited in the electro-magnetic and hadronic calorimeter

Example: background


•Energy deposited in the electro-magnetic and hadronic calorimeter•Several tracks belonging to a jet are found

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Remember: •Sometimes it’s not so obvious if it’s a jet or an electron

• Electron stops in electro-magnetic calorimeter,

so has ONLY electro-magnetic component • Jet goes also in hadronic calorimeter,

so has electro-magnetic AND hadronic component

Remember: • Sometimes it’s not so obvious if it’s a jet or an electron



so has electro-magnetic AND hadronic component • Also note: sometimes jets might be produced in

addition to the W and Z bosons In this case this is not a background event!

Remember: • Sometimes it’s not so obvious if it’s a jet or an electron



so has electro-magnetic AND hadronic component • Missing “side-ways” energy can be also present in background events but typically it’s small

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Exercise: let’s start!The first event you have to analyse is already displayedStudy each event and classify it into 5 different categories

We, W, Zee, Z, backgroundMany more W’s are produced compared to Z eventsNote: in reality there many more background events than here

There are some additional sheets to help you next to your computerWhen you decide what type it is, tick the corresponding box (,,)

Only one tick per event! Once you have analysed 20 events you’re done! Just add up the totals.If you don’t manage to classify all events do not worry!

just stop where you are at the end and do the final count If you finish your 20 events you can hunt for the Higgs by looking at other set(s) of events – ask a demonstratorThere is only one Higgs event (H, Heeee or Hee) in the whole sample and there’s a prize waiting…. At the end we will do the final summary and look at the ratio We/W, Zee/Z and the ratio W/Z production together

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“Candidate” HiggsHopefully many of you found the candidate Higgs event.

On an event-by-event basis we can’t say for sure “this was a Higgs”

Discovery is made in a statistical manner:

masterclass 20141 introduction to hands-on exercise aim of the exercise identify electrons (e),...

Documents

event energy

energy deposits

collision energy

missing energy

event slide

muon detector measure

created particles

z event