Hypatia (Hybrid Pupil’s Analysis Tool for Interactions in atlas)

When two protons collide head on in the LHC, many particles are created out of the collision energy.

The ATLAS (A Toroidal LHC Apparatus) particle Detector is one of the 4 main particle detectors positioned around the 27 km LHC ring. At 46 m long, 25 meters wide and 25 meters high, the barrel-shaped ATLAS detector is the largest of its kind to be built. Its purpose is to identify the secondary particles produced in collisions, and to measure their positions in space, their charges, speed, mass and energy. To do this, ATLAS has many cylindrical layers or ‘sub-detectors’, each having a particular role in the reconstruction of collisions. A magnet system is included to separate the different particles according to their charge and to allow the measurement of their momentum.

Reference for ATLAS: http://www.atlas.ch/etours_exper/index.html

For examples of particle tracks in the ATLAS detector see http://atlas.physicsmasterclasses.org/en/index.htm



HYPATIA enables the analysis of the results of the p-p head-on collisions. We are interested in events where Z bosons and Higgs bosons are produced out of the collision energy. Unfortunately both particles have such very short lifetimes, they decay into secondary particles within 10 ^-22 seconds. One can only deduce their temporary existence by the secondary particles that they decay into.

For example, Z bosons decay into electron positron pairs or muon – antimuon pairs. Higgs can decay into photon pairs, or 4 leptons.

Access HYPATIA online http://hypatia.iasa.gr/en/index.html

or Load HYPATIA 7.3 onto each computer using : http://hypatia.phys.uoa.gr/Downloads/Hypatia_7.3_Masterclass_c.zip

Demonstrate to the class, using some typical cases how to identify (a) an electron positron event, (b) a two photon event, (c) a 4 lepton event. Also show them what a background event may look like.

See below: A Higgs Boson decays into two Z Bosons which each decay into two leptons. Because the Higgs, and Z boson are neutral, the charged particles produced must conserve charge, and therefore cancel each other out.

Here is a 2 photon event: candidate for Higgs.

From http://www.physics.utoronto.ca/students/outreach/poptor/20130112_Session2POPTOR_HYPATIA_jkeung-1.pdf

What to do step by step:

1 In HYPATIA, for each collision event, try to find signs of the existence of particles such as (a) Z boson, by hunting for an electron positron pair or a muon antimuon pair, (b) a Higgs boson by hunting for a photon pair, (c) a Higgs boson by hunting for 2 lepton pairs ( 2 lepton pairs (e+ e- e+ e-, or e+ e- u+ u-, or u+ u- u+ u-) .

2 If you cannot find such particle pairs the event might be a background event. Use the pointing tools and particle information in HYPATIA to make your decision.

Make up a tally sheet for recording the results of analysing each event.

3. If you believe you see the decay products of one of the particles above, pick the corresponding tracks or objects and insert them into the HYPATIA Invariant Mass table.

a. If you find a pair of electrons or a pair of muons tracks you

might have found a Z boson or the much lighter J/Psi or Upsilon particle.

b. If you are lucky to see 2 pairs of leptons, insert them both;

you may have a Higgs candidate decaying to 4 leptons.

c. If you believe you have found a Higgs boson decaying to a pair of photons, pick both photons and insert them into the HYPATIA invariant mass table.

4. If you believe the collision resulted in a background event (no pair

of leptons with opposite electric charges and no pairs of photons),

ignore the event and proceed to the next one.”

5. Utilise the HYPATIA histogram functions to see the spread of masses captured.

Lead classroom discussions on identification of the particles. Assist them with knowledge of the J/Psi meson mass = 3 Gev/c, the Upsilon meson mass = 10 Gev/c, the Z boson mass = 91 Gev/c. And if there is a mass centered on 125 Gev/c it may be a Higgs Boson.

Your lessons should prove successful, if enough time has been allocated to ensure our students have a clear idea of what the ATLAS detector is designed to find, and how to select the tracks shown by HYPATIA. Our students should then find the HYPATIA exercise analysing real LHC data stimulating, and gain an insight into particle physics research.

HYPATIA was developed by Professor Christine Kourkoumelis and her team from the University of Athens. The acronym is deliberately constructed to honour Hypatia the great female philosopher, astronomer and mathematician of Alexandria in the 4^th century AD.

Additional Reference : http://indico.cern.ch/getFile.py/access?contribId=95&resId=1&materialId=slides&confId=61942

At CERN HST Summer Programme, I was part of a ten person work group who decided to explore how to use HYPATIA in the classroom. We worked together for 3 days and gained assistance via email from Christine Kourkoumelis, as well as from a friendly University lecturer from USA, Phil Rubin (George Mason University) who was at CERN with some of his students.

The other team members are:

Roberta Balestrino from Italy, Tyra Batista Luna from the Dominican Republic, Ralf Benherzig from Germany, Jose Caballero from the Netherlands, Olivia Fischer from Austria, Jason Jennings from Canada, Gonzaga Mpamizo from Uganda, Maria Ntouma from Greece and Miriam Simralova from Slovakia.