Parçacıkları Tanıma

Programın gösterdiği proton-proton çarpışmalarını analiz edebilmemiz için, elektronları ( ve pozitronları) , müonları( ve karşıt-müonları), nötrinoları ve hadronik parçacıkları ve jetleri nasıl tanımlayabileceğimizi bilmemiz gerekir. Resim galerisinde parçacıkları tanımlamanın nasıl çalıştığı gösterilecektir.



  • This signature is generated by an electron. The particle has left a track (yellow/green) in the inner detector, indicating that it carries an electric charge. It has deposited all its energy within the electromagnetic calorimeter, as seen by the small green boxes in that region. Since there are no entries in the hadronic calorimeter or the muon chambers, the particle is identified as an electron or positron.
  • The other event contains either two electrons, two positrons, or an electron and a positron. The tracks through all three inner detectors and the green boxes representing the energy deposits in the electromagnetic calorimeter are clearly visible and easy to recognize.
  • How can you determine whether it’s an electron or a positron? You can simply click on the track in the event display. By doing so, the information for the selected track will appear below in the window. This info display provides details about the selected track, starting with the type of event object (in this case, a particle track). The next parameters include the azimuthal angle (φ), pseudo-rapidity (η), and the transverse momentum (pT). Additionally, it shows the particle’s electric charge (e.g., Charge: +1 for a positron). Based on the charge, we can identify the particle as a positron. This version improves clarity and readability.


  • In this event display one sees a track (yellow line) in the inner detector, small energy depositions in both the electromagnetic as well the hadronic calorimeter, and blue lines in the muon chambers. It is a muon (or an anti-muon), the only particle that goes through the whole detector and thereby leaves signals in all shells.
  • You can load Muon Spectrometer Geometry (Endcap) to see that blue tracks are in the area of it. You can also adjust geometries opacity from top tools menu.
  • In the side view, the individual entries in the muon chambers are represented as orange crosses. All of the crosses inside one chamber are connected by an orange line, which symbolizes the track of the muon in this chamber. Connecting all orange tracks in mind will show you the path of the muon through the outer layers of the ATLAS detector Muon or anti-muon? The same procedure that we described in the electron/positron section provides the result: In this event display, a muon is pictured (charge: -1).


  • How does one recognize a neutrino?
    Neutrinos don't interact with even a single component of the ATLAS detector. They neither interact with the tracking detector, nor the calorimeters, nor the muon chambers.

    How can one therefore detect something what one cannot see?
    Since all quarks and gluons move along the beam axis before the proton-proton collision all of their velocity components at right angles to the beam (perpendicular) and therefore the so called total transverse momentum is zero. Due to momentum conservation the total transverse momentum (the vectorial sum of the transverse momenta of all particles) has to be zero after the collision as well. If the measurements contradict this, it is assumed that particles carrying transverse momentum leave ATLAS without being detected (e.g. one or more neutrinos which have (in sum) exactly this missing transverse momentum).

    In the ATLAS detector, the missing transverse momentum is determined by the energy deposited in the calorimeters. When there is an imbalance within this energy distribution – which is called missing transverse momentum – this suggests a neutrino which was produced during the collision.

    In the tracer event display, the missing transverse momentum is shown as a red dashed line. This line depicts the direction of the energy imbalance.
  • In this event, an electron and a neutrino were produced nearly exclusively. Since these two particles are kind of the only ones that have been produced the total transverse momentum is split between these two due to the conservation of momentum. That is why the neutrino with its share of the transverse momentum flies away from the electron in the nearly opposite direction.

    The missing momentum can be observed by clicking on the red dashed line in the event display. The information window will display the missing transverse energy (ET) value. If the missing transverse energy is high (greater than 20 GeV), it’s likely that a neutrino was produced. Smaller missing transverse momenta, around 10-20 GeV, may be due to measurement uncertainties in the detector.


  • In this event display so called jets are shown. Each jet consists of a bundle of several particles. The electrically charged particles cause tracks in the inner detector whereas the neutral ones don't. If you extrapolate the tracks you will find many entries in the calorimeters. Other depositions nearby cannot be assigned to a track because they were caused by electrically neutral particles. Especially the hadronic calorimeter contains many entries. This can be explained by the way jets form. Every jet is the result of a gluon, quark, or antiquark that is ejected from the proton during the collision. Big amounts of energy are at work in order to overcome the huge binding forces holding the gluons and (anti-)quarks in the proton together. A part of this energy is used to create new quark-antiquark pairs which move in the approximately same direction and bind each other to form new particles – so called hadrons. These hadrons constitute the jets that are shown as purple cones in this picture to make the easily recognisable.
  • By default, jets are not activated in the event display scene. You can load them by opening the event menu from the top tools menu and selecting the jets checkbox.

    Aklınızda bulundurun: İç dedektörde izler bırakan ve elektromanyetik ve özellikle hadronik kalorimetrelerde girişimler yapan saçılmış olan parçacıklar kuarklara, karşıt-kuarklara, gluonlara ve jetlere indirgenebilirler.