Masterclass 2008 1

Introduction to hands-on ExerciseAim of the exercise Find out what happens in proton-proton collisions at the LHC as

‘seen’ by the ATLAS detector Categories of Events

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

All the above ‘signals’ are ‘well-known’ processes in addition we added one event from a yet undiscovered particle we

hope to find soon H4e, H4, or Hee

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

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Principle of collider physics

At the LHC you collide protons against protons

The collision energy is used to create particles (E=mc2)

We ‘see’ the end products of the reaction not the reaction itself

We have to deduce what happened in the reaction from end products

Identification of particles in our detector done through their interaction with matter

Our detector is build symmetrically around collision point

It is composed of several layers of detectors, each detector probes a different aspect of the event (= sum of particles produced in collision)

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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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Example: Zee

•Lego plot in - projection of energy deposits in the calorimeters

•Electro-magnetic component in green•Hadronic component in red

•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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Example: Zee

•Lego plot in - projection of energy deposits in the calorimeters

•Electro-magnetic component in green•Hadronic component in red

•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)

•Electro-magnetic calorimeter

•Hadronic calorimeter

•Tracking detector (several sub-systems)

•Electro-magnetic calorimeter

•Hadronic calorimeter

•Muon detector

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To read ‘our’ events•Click on File•Click on ‘Read Event’

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•Look on your results page to find out what is the number of your first event to analyse

•Look on your results page to find out what is the number of your first event to analyse•Now find your first event in list

•Look on your results page to find out what is the number of your first event to analyse•Now find your first event in list•Click open

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Example: Zee

Characteristics:

2 electrons in the event

Example: Zee

Characteristics:

2 electrons in the event•Electron deposit its energy in electro-magnetic calorimeter

Example: Zee

Characteristics:

2 electrons in the event•Electron deposits its energy in electro-magnetic calorimeter•Track in tracking detector in front of shower in calorimeter

Example: Zee

Characteristics:

2 electrons in the event•Electron deposits its energy in electro-magnetic calorimeter•Track in tracking detector in front of shower in calorimeter •No ‘trace’ in other detectors

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Example: Zee•Track in tracking detector have high transverse momentum (pT)

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

Example: Zee•Track in tracking detector have high transverse momentum (pT>10GeV)

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

Example: Zee•Track in tracking detector have high transverse momentum (pT>10GeV)

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Example: Zee•Track in tracking detector have high transverse momentum (pT>10GeV)

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

Example: Zee•Track in tracking detector have high transverse momentum (pT>10GeV)

•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: Zee

•large transverse energy (ET) deposits in electromagnetic calorimeter (ET>10GeV)

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

Example: Zee

•large transverse energy (ET) deposits in electromagnetic calorimeter (ET>10GeV)

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Example: Zee

•large transverse energy (ET) deposits in electromagnetic calorimeter (ET>10GeV)

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

•ET is shown here

Example: Zee

•large transverse energy (ET) deposits in electromagnetic calorimeter (ET>10GeV)

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

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Next event•Click on ‘Next’

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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’

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

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

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

•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

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

•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)

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Example: ZCharacteristics:

2 muons in the event•track in tracking detector

Example: ZCharacteristics:

2 muons in the event•track in tracking detector •tiny ‘traces’ in the calorimeters•track in the muon detector

Example: ZCharacteristics:

2 muons in the event•track in tracking detector •tiny ‘traces’ in the calorimeters

Example: ZCharacteristics:

2 muons in the event

Here:• one in central region

Example: ZCharacteristics:

2 muons in the event

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

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

Example: ZCharacteristics:

2 muons in the event

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Example: WCharacteristics:•1 muon in the event

Example: WCharacteristics:•1 muon in the event•Large missing transverse energy (ET

miss > 10GeV)

•“pick-button” would work as well

•Typically muon and ETmiss

are ‘back-to-back’ (if is in central region)

Example: WCharacteristics:

Example: WCharacteristics:•1 muon in the event•Large missing transverse energy (ET

miss > 10GeV)

•“pick-button” would work as well

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Example: WeCharacteristics:

Example: WeCharacteristics:•1 electron in the event

Example: WeCharacteristics:•1 electron in the event•large missing transverse energy (ET

miss)

•as electron in forward region, electron and ET

miss not ‘back-to-back’

Example: WeCharacteristics:•1 electron in the event•large missing transverse energy (ET

miss)

•as electron in forward region, electron and ET

miss not ‘back-to-back’

•looks like event in side view not well balanced (energy conservation)

Example: WeCharacteristics:•1 electron in the event•large missing transverse energy (ET

miss)

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Example: WeCharacteristics:•1 electron in the event•large missing transverse energy (ET

miss)

•as electron in forward region, electron and ET

miss not ‘back-to-back’

•looks like event in side view not well balanced (energy conservation)

•Hint: check pT of tracks if in doubt!

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Summary so farZ→ee

Two electrons with track PT > 10 GeV

Small Missing ET: Missing ET < 10 GeV

Z→ Two muons with track PT> 10 GeV

Small Missing ET: Missing ET < 10 GeV

W→One muon with track PT > 10 GeV

Large Missing ET: Missing ET > 10 GeV

W→eOne electron with track PT > 10 GeV

Large Missing ET: Missing ET > 10 GeVAll the above events might have some additional low energy particles

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Example: background

Characteristics:

Example: background

Characteristics:

Bundles of particles (jets) are produced•Energy deposited in the electro-magnetic and hadronic calorimeter

Example: background

Characteristics:

Bundles of particles (jets) are produced•Energy deposited in the electro-magnetic and hadronic calorimeter•Several tracks belonging to a jet are found

Example: background

Characteristics:

Bundles of particles (jets) are produced•Energy deposited in the electro-magnetic and hadronic calorimeter•Several tracks belonging to a jet are found •Hint: how to see “same” jet in different projections

•Click on the violet squares •colour change in all projections

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Example: background

Characteristics:

Example: background

Characteristics:

Bundles of particles (jets) are produced•Energy deposited in the electro-magnetic and hadronic calorimeter•Several tracks belonging to a jet are found •Hint: how to see “same” jet in different projections

•Click on the violet squares •colour change in all projections

Example: background

Characteristics:

Bundles of particles (jets) are produced•Energy deposited in the electro-magnetic and hadronic calorimeter•Several tracks belonging to a jet are found •Hint: how to see “same” jet in different projections

•Click on the violet squares •colour change in all projections

Example: background

Characteristics:

Bundles of particles (jets) are produced•Energy deposited in the electro-magnetic and hadronic calorimeter•Several tracks belonging to a jet are found •Hint: how to see “same” jet in different projections

•Click on the violet squares •colour change in all projections

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

• Electron has ONLY electro-magnetic component • Jet has electro-magnetic AND hadronic component

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Example: background

Sometimes you will find electrons in background events (not coming from We or Zee)

Hint: •only one electron not Zee

•small missing ET not We

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Example: background

… or you could find muons in your background events

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Exercise… enough talking …. Let’s start!Click the shortcut to Atlantis on your computerClick on ‘File’ (upper right) and then ‘Read event’Look on your sheet and select the first event indicated on your sheetStudy the event and classify it into 5 different categories

We, W, Zee, Z, backgroundIf you decided what type it is, tick the corresponding box (,,, etc)

Only one tick per event! Go to the next event using ‘Next’classify … tick … next …Once you have analysed 20 events you’re done. Not before!

look at the detector displays or continue and hunt for the Higgs If you don’t manage to classify all events just stop where you are at the end and do the final count Don’t forget there is also one H4, H4e or H2e2 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