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 We W Zee 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 H4e, H4, or H2e2 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
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
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
Example: Zee 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
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
To read ‘our’ events Click on File Click on ‘Read Event’ Masterclass 2008
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 Masterclass 2008
Electron deposit its energy in electro-magnetic calorimeter 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 Masterclass 2008
Track in tracking detector have high transverse momentum (pT>10GeV) 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) 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) Masterclass 2008
Track in tracking detector have high transverse momentum (pT>10GeV) 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 Masterclass 2008
move the pointer to the ‘cluster’ and click on it 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) Masterclass 2008
move the pointer to the ‘cluster’ and click on it 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 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 Masterclass 2008
Next event Click on ‘Next’ Masterclass 2008
In this example electrons do not look so ‘nice’ 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 Sometimes there might be a track near-by from other collision fragments 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 Masterclass 2008
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 Sometimes there might be a track near-by from other collision fragments Those are typically ‘low’ momentum (few GeV) Masterclass 2008
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
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
large missing transverse energy (ETmiss) Example: We Characteristics: 1 electron in the event large missing transverse energy (ETmiss) Example: We Characteristics: 1 electron in the event large missing transverse energy (ETmiss) as electron in forward region, electron and ETmiss not ‘back-to-back’ Example: We 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: We Characteristics: 1 electron in the event Example: We Characteristics: Masterclass 2008
large missing transverse energy (ETmiss) Example: We 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
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
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
only one electron (not from Zee) small missing ET (not from We) Example: background Sometimes you will find electrons in background events (not coming from We or Zee) Hint: only one electron (not from Zee) small missing ET (not from We) Masterclass 2008
… or you could find muons in your background events Example: background … or you could find muons in your background events Masterclass 2008
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 We, W, Zee, 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 H4, H4e or H2e2 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