1. Introduction to hands-on Exercise
Aim of the exercise
Find out what happened in proton-proton collisions at the LHC as ‘seen’ by the ATLAS detector
Categories
We
W
Zee
Z
Background from jet prod. (those might look like an electron)
All the above ‘signals’ are ‘well-known’ processes, in addition we added one event from a never seen particle we hope to find soon
H4e, H4, or H2e2
There will be a prize for the group who identifies this event !!!
To do the exercise we use the Atlantis visualisation program
As we don’t have data yet, we will use simulations
Masterclass 2008

2. Principle of collider physics
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 build symmetrical around the collision point
It is composed of several layers of detectors, each detector probes a different aspect of the event
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.
Neutrinos are only detected indirectly via ‘missing energy’ not recorded in the calorimeters
Muon detector
Measure charge and momentum of muons
Masterclass 2008

4. Example: Zee End-on view of the detector (x-y-projection)
Warning: Only particles reconstructed in central region shown here (otherwise the particles in te forward would cover the view)!
Side view of the detector (R-z-projection)
Particles in central and forward region are shown
Lego plot in - projection of energy deposits in the calorimeters
Electro-magnetic component in green
Hadronic component in red
Masterclass 2008

5. 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
Masterclass 2008

6. To read ‘our’ events Click on File Click on ‘Read Event’
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7. Now find your first event and open it Click open
Look on your summary sheet to find out which is your first event to analyse
Now find your first event and open it
Click open
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8. Electron deposit its energy in electro-magnetic calorimeter
Example: Zee
Characteristics:
2 electrons in the event
Example: Zee
Characteristics:
2 electrons in the event
Electron deposit its energy in electro-magnetic calorimeter
Example: Zee
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: Zee
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
Masterclass 2008

9. Track in tracking detector have high transverse momentum (pT>10GeV)
Example: Zee
Track in tracking detector have high transverse momentum (pT>10GeV)
To see this yourself,
click on ‘pick’
Example: Zee
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: Zee
Track in tracking detector have high transverse momentum (pT>10GeV)
Masterclass 2008

10. Track in tracking detector have high transverse momentum (pT>10GeV)
Example: Zee
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: Zee
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
Masterclass 2008

11. move the pointer to the ‘cluster’ and click on it Example: Zee
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: Zee
large transverse energy (ET) deposits in electromagnetic calorimeter (ET>10GeV)
Masterclass 2008

12. move the pointer to the ‘cluster’ and click on it
Example: Zee
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
Example: Zee
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
Masterclass 2008

13. Next event
Click on ‘Next’
Masterclass 2008

14. In this example electrons do not look so ‘nice’ Example: Zee
Here’s another one
In this example electrons do not look so ‘nice’
Example: Zee
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
Example: Zee
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: Zee
Here’s another one
Masterclass 2008

15. In this example electrons do not look so ‘nice’
Example: Zee
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)
Masterclass 2008

16. forward particles not in end-on projection! Example: Z
Characteristics:
2 muons in the event
Here:
one in central region
one in forward region
forward particles not in end-on projection!
Example: Z
Characteristics:
2 muons in the event
track in tracking detector
Example: Z
Characteristics:
2 muons in the event
track in tracking detector
tiny ‘traces’ in the calorimeters
Example: Z
Characteristics:
2 muons in the event
track in tracking detector
tiny ‘traces’ in the calorimeters
track in the muon detector
Example: Z
Characteristics:
2 muons in the event
Here:
one in central region
Example: Z
Characteristics:
2 muons in the event
Masterclass 2008

17. Large missing transverse energy (ETmiss > 10GeV)
Example: W
Characteristics:
1 muon in the event
Large missing transverse energy (ETmiss > 10GeV)
pick would work as well
Example: W
Characteristics:
1 muon in the event
Large missing transverse energy (ETmiss > 10GeV)
Pick would work as well
Typically muon and ETmiss are ‘back-to-back’ (if  is in central region)
Example: W
Characteristics:
1 muon in the event
Example: W
Characteristics:
Masterclass 2008

18. large missing transverse energy (ETmiss) Example: We
Characteristics:
1 electron in the event
large missing transverse energy (ETmiss)
Example: We
Characteristics:
1 electron in the event
large missing transverse energy (ETmiss)
as electron in forward region, electron and ETmiss not ‘back-to-back’
Example: We
Characteristics:
1 electron in the event
large missing transverse energy (ETmiss)
as electron in forward region, electron and ETmiss not ‘back-to-back’
looks like event in side view not well balanced (energy conservation)
Example: We
Characteristics:
1 electron in the event
Example: We
Characteristics:
Masterclass 2008

19. large missing transverse energy (ETmiss)
Example: We
Characteristics:
1 electron in the event
large missing transverse energy (ETmiss)
as electron in forward region, electron and ETmiss not ‘back-to-back’
looks like event in side view not well balanced (energy conservation)
Hint: check pT of tracks if in doubt!
Masterclass 2008

20. Bundles of particles (jets) are produced
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: sometimes it’s not so obvious if it’s a jet or an electron
Click on the violet square (colour change)
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
Example: background
Characteristics:
Masterclass 2008

21. Bundles of particles (jets) are produced
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: sometimes it’s not so obvious if it’s a jet or an electron
Click on the violet squares (colour change)
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: sometimes it’s not so obvious if it’s a jet or an electron
Click on the violet squares (colour change)
look at composition of hadronic and electro-magnetic energy in lego plot
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: sometimes it’s not so obvious if it’s a jet or an electron
Click on the violet squares (colour change)
look at composition of hadronic and electro-magnetic energy in lego plot
Look at the side-view
Masterclass 2008

22. only one electron (not from Zee) small missing ET (not from We)
Example: background
Sometimes you will find electrons in background events (not coming from We or Zee)
Hint:
only one electron (not from Zee)
small missing ET (not from We)
Masterclass 2008

23. … or you could find muons in your background events
Example: background
… or you could find muons in your background events
Masterclass 2008

24. Exercise … enough talking …. Let’s start
Click the shortcut to Atlantis on your computer
Click on ‘File’ (upper right) and then ‘Read event’
Look on your sheet and select the first event indicated on your sheet (e.g. Event_126.xml)
Study the event and classify it into 5 different categories
We, W, Zee, Z, background
If you decided what type it is, tick the corresponding box (,,, whatever you like)
Go to the next event using ‘Next’
classify … tick … next …
Don’t forget there is also one H4, H4e or H2e2 in the whole sample and there’s a prize waiting….
Once you have analysed 25 events you’re done
Now you can look at the detector displays or look at more events and hunt for the Higgs
At the end we will do the final summary together
Hint: there will be many more W produced compared to Z’s
Masterclass 2008