masterclass 20081 introduction to hands-on exercise aim of the exercise identify electrons, muons,...

Masterclass 2008 1

Introduction to hands-on ExerciseAim of the exercise Identify electrons, 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 in addition we added one event from a yet undiscovered particle, Higgs, we hope to find soon

Heeee, H, or Hee There will be a surprise prize for those who identifies this event !!!To do the exercise we use the Atlantis visualisation programAs we don’t have data yet, we will use simulations

Masterclass 2008 2

How does a collider work?

Masterclass 2008 3

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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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

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

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

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)

Masterclass 2008 7

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 ‘pick’ •move the pointer to the track and click on it

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


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

Masterclass 2008 11

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



miss > 10GeV)

- Red dashed line in end-on view- Value shown here



miss > 10GeV)

- Red dashed line in end-on view- Value shown here

• Typically electron and ETmiss are ‘back-

to-back’

Masterclass 2008 12

Next event•Click on ‘Next’

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Example: WCharacteristics:

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

miss > 10GeV)


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)



miss > 10 GeV)


• here also some other low momentum tracks around from collision fragments

Masterclass 2008 16

Example: Zee

Characteristics:

2 electrons in the event

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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



Masterclass 2008 18

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•Several tracks belonging to a jet are found

Example: background


•Energy deposited in the electro-magnetic and hadronic calorimeter

Masterclass 2008 19

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

Masterclass 2008 20

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, backgroundThere 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! Go to the next event using ‘Next’classify … tick … next …Once you have analysed 20 events you’re done!

Tell me your resultslook at the detector displays or continue and hunt for the Higgs

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

Don’t forget there is also 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

Masterclass 2008 21

EXTRAS

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Example: Zee•Here’s another one

Example: Zee•Here’s another one•In this example electrons do not look so ‘nice’


•Sometimes it happens that the track is not fully reconstructed and is shortened


•Sometimes it happens that the track is not fully reconstructed and is shortened•Sometimes there might be a track near-by from other collision fragments

Masterclass 2008 23


•Sometimes it happens that the track are not fully reconstructed and are shortened•Sometimes there might be a track near-by from other collision fragments

•Those are typically ‘low’ momentum (few GeV)

masterclass 20081 introduction to hands-on exercise aim of the exercise identify electrons, muons,...

Documents

w e electron track

ways energy e t

transverse energy e

w e characteristics

w e electron deposits

grey e t

way energy

gev example