CERN
Let’s take a look at one of the largest labs in the world. (
The Large Hadron Collider (LHC) is a giant scientific facility located 100m under the Earth’s surface, near Geneva on the border of France and Switzerland. It is the most advanced particle accelerator in CERN and is used by scientists in order to study the basic particles ofmatter.
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ATLAS is a very big basic particle physics experiment that is performed in the LHC atCERN.
The ATLAS detector studies the proton collisions in extremely high energies, in order to collect information about the fundamental forces of the Universe which have governed it since the very first moment of its existence. Among the mysteries studied within ATLAS are the identification of the origins of mass, the existence of more dimensions, the unification of the fundamental forces as well as proof of the existence of dark matter.
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Basicparticles
Molecules consist of atoms, which are the smallest unit of matter with characteristic properties, and are the chemical elements. Atoms in their turn consist of protons, neutrons andelectrons.
Protons and neutrons consist of other smaller particles, called quarks. Up to now, leptons (one of them is the electron) and quarks (it is thought there are six of them) are considered to be the basic particles ofmatter.
Each kind of lepton and quark has its corresponding anti-particle: a particle of equal mass but opposite charge andspin.
LeptonsElectron(e-) / muon(μ-) / Tau(τ-)
Electron neutrino(νe) / Muon neutrino(νμ) / Tau neutrino(ντ)
Relatedquestions
1.Does momentum depend on the direction ofspeed?
2.What is an insulatedsystem?
3.What does “conservation of momentum” mean inreality?
4.During a collision is the kinetic energymaintained?
5.How are basic particlescategorised?
6.Are new particles produced during a particlecollision?
7.What kind of research is done atCERN?
8.What is the objective of the ATLASexperiment?
Vectoraddition
Scalar and vectorsizes
Scalar sizes can be fully described only by measuring them. For vector sizes to be fully identified, we need to know both their extent and direction. To perform mathematical operations with vectors their direction must be taken intoaccount.
Vectoraddition
In order to add two or more vectors, we must place them sequentially so that the end of the first one rests on top of the next one, being careful not to alter the vector’s angle. The beginning of the total vector is the beginning of the first vector and its end is the end of the lastone.
If all vectors have a common starting point, then we can use the parallelogram rule to addthem:
From the ending point of each vector we draw a parallel to the second vector. The point where the two parallels intersect is the end of the sum vector. This method is suitable for adding only two vectors at atime.
Vectoranalysis
In physics there is often a need to resolve a vector into orthogonal components. To do this, we implement the following procedure. We draw two dotted lines from the end of the vector, parallel to the axis x'x and y'y respectively. The point where the two dotted lines intersect is the end of the correspondingcomponent.
Theexperiment
Open the ΗΥΡΑΤΙΑ program and follow the steps below to perform theexercise.
1.Select the file “JiveXML_5104_20655.xml” (use the buttons “Previous Event” and “Next Event”) to see the data on the collision we want to study. If the file is not displayed in the fact list, save it on your local computerfrom“ReadingandAssignments”.Select“File”→“Readeventlocally”,findthefileandopenit.
2.In “Track Momenta Window” select the “Simulated” card to see the simulations of all the trajectories you willstudy.
3.Draw the momentum vectors for each particle. First, find the angle and the magnitude based on the data of the table in the “Track MomentaWindow”:
a.Convert the angle (φ) for each particle from radians to degrees and enter them in the corresponding column of the followingtable.
b.If the magnitudes of all momentum vectors (column P[GeV]) are too big, you have to draw them all to scale. In order to normalise your values, divide them all by the smallest value.Add the results in the “Students worksheet” file that you will find in “readings andassignments”.
4.Based on your calculations, draw the correspondingvectors.
5.Draw the vector of the resultant momentum according to your estimations, as well as the vector ofthe remaining momentum (non-accuratesolution).
Analysis-Discussion
1.Why did you normalise the momentum vector magnitudes? Why did you divide them by the smallest momentum value? Would there be any difference if you divided by another number? How does this normalisation affect yourresults?
2.Based on the vector analysis, calculate the magnitude of the complete momentum as well as the corresponding vector angle. Make sure you use the initial values and not the normalisedones.
3.What error sources arethere?
4.Is the complete momentum you calculated for the level x-y zero? If no, whynot?
5.Is the principle of momentum maintenance valid? If yes, why did you come up with a non-zero momentum?
6.Does the vector you drew for the neutron fit with the corresponding vector in thedetector simulation?
7.Based on the exercise you did and the answers you gave to the previous questions, write ashort report following the formprovided.
About
Brief description: Students will determine the resultant momentum of all particles detected during ahadron collision and will calculate the magnitude and momentum of the residualvector.
Connection with thecurriculum:
Greece: 1st Grade Upper Secondary School Physics, Chapters 1 3, §1.2 and § 3.2 of the text book. Teachingtargets:
1.Learn the principle of the conservation ofmomentum.
2.Practise addingvectors.
3.Measure vector angles and convert radians to angledegrees.
4.Learn about research in the field of basic particle physics. Age: 15 – 18 – Time required: 2½ teachingunits
Technicalrequirements:
1.Computers with an Internetconnection
2.Data analysis tool,HYPATIA
a.Save HYPATIA-v4 from thewebpage
b.Decompress the saved file and save the extracted file directly onto your computer’s hard disk inC:\
c.Double click on the “Hypatia 4.jar” file to open theprogram.
Note: This program requires installing the Java Runtime Environment (version 1.4 or newer) software, which you may find here:
Preparing students: Mass, speed, acceleration, power, energy and the way all these are connected, i.e. Newton’s laws, should have already been discussed inclass.
Students also learn the difference between scalar and vectorsizes.
Note: The theory presented in “Theory behind the experiment” concerns the relevant exercise in the guide and does not constitute a full theoreticalapproach.
Key words: mass, speed, acceleration, energy, collision, principle of the conservation of momentum, radians, degrees,vector
Author(s): ThanosLeontios
Additionalinformation
Description ofequipment
1.Open the program and show its basicfunctions.
Image 1. The HYPATIA data analysistool
a.Inertial masseswindow
b.List of trajectories included in the present HYPATIAfile
c.Canvaswindow
Use the magnifying glass in each part to magnify the image. When a trajectory is selected, it becomeswhite.
d.Name of file whichappears
e.Transverse view of the detector showing alltrajectories
f.Longitudinal view of the detector showing alltrajectories
g.3D energy diagram for the x-yplane
h.Detected trajectorieswindow
Contains all the recorded data for the trajectoriesdetected.
i.File navigationoption
j.List of recorded trajectories with the correspondingdata
k.Controlwindow
You can change the view settings for a file or add filters to the projection oftrajectories.
2.Describe the different parts of the ATLAS detector to yourstudents
Image 2. An example of how the various particles are detected in different parts of the detector. Note that the neutral particles leave their mark only in the calorimeters. Therefore, their trajectories appear only in the red and green parts and not in the inner part of thedetector.
Image 3. Representation of an ATLAS detector
The various layers are positioned concentrically, circling the area of thecollision.
Starting from the interaction point (the point where the protons and antiprotons collide with each other) and moving outward, the parts of the ATLAS detector are asfollows:
Trajectory detector (or inner detector) (green, brown): It is the innermost part of ATLAS and consists of three sub-detectors designed to detect charged particles. The neutral particles (e.g. photons) pass through this region without being detected. All the charged particles interact with the detector but they pass through theoretically without any change in their direction or theirenergy.
Image 4. The innerdetector.
Calorimeters: When a particle (charged or not) enters the calorimeter it collides with the detector’s dense material. This collision gives rise to a series of other particles and almost all the energy of the original particle is absorbed by the calorimeter. Because of this, the calorimeter is inserted after the internal probe, so as to record the trajectory of the particle before it is absorbed. The calorimeters measure energy and have two differentparts:
•The electromagnetic calorimeter (grey/green): measures the total energy of e+, e- and photons. Therefore, if one is looking for electrons, their trajectory stops in the calorimeters.
Image 5. The electromagnetic calorimeter and the hadronic calorimeter.
•The hadronic calorimeter (red) measures the total energy of hadrons (such as protons and neutrons).
The only particles with the ability to penetrate the detectors and the calorimeters and continue towards the muon detector are muons andneutrinos.
Detectors / muon spectrometers: This is the outer layer of the detector (blue). Muons are the only charged particles that penetrate the hadron calorimeter almost unaffected and reach the muon detector. Their trajectories are the only ones recorded in the outermost layer of the muondetector.
Particles that are not detected: Neutrinos interact very weakly with matter, thus are not detected at all. Their presence can be confirmed by measuring the “lost”momentum.
Image 6. The muondetector.
Residual energy / momentum: This is the energy and the momentum needed for the principles of maintaining momentum and energy toapply.
In the LHC the initial momentum along the beams is unknown because the hadrons’ energy is continuously exchanged between the particles, and therefore the residual energy cannot be measured. However, the initial momentum vertically to the beam distribution line is zero. Therefore, the existence of a non-zero momentum implies the existence of residual momentum and energy (Etmiss). The residual momentum is represented in the image of the detector with a dotted line indicating the direction of the “lost”momentum.
Magnets: Τhe ATLAS detector is located in a powerful magnetic field which bends the trajectories of charged particles. The fields are generated by four kinds of magnets – three toroidal shaped ones and a tubular one (not shown in the representation). The positively and negatively charged particles are directed in opposite directions by the same magnetic field. The curvature and direction of the particle’s trajectory are used to determine the momentum and charge of aparticle.
(Source:
Form and guidelines for the projectwriting
Name(s), class,section
SummaryTheabstractshouldsummarisebrieflyandclearlytheproject’s content. It should clearly explain to the reader what information can be drawn from the project. The most important elements of the summary are the presentation of the problem and the project’s contribution. It should be between 70 and 120words.
Introduction – Descriptionof theproblem
The introduction must consist of two paragraphs: in the first one the general problem should be presented and commented on. The second should illustrate the focus of the project. Typically the second paragraph should start with a phrase like “The aim of this project isto…”.
Hypothesis –InitialideaIn the hypothesis and original concept sectionpreliminary
assumptions and projections based on the current knowledge on the topic should be presented. Thebasic
concepts and definitions that are essential for the understanding of the problem should also beanalysed.
ExperimentalsetupIn this section, the experimental setup andeverything
concerning materials, equipment or software used for the experiment should bedescribed.
Performing the experiment
Here the experiment performed is presented in detail. Authors should provide a detailed description of every step of the experiment, including the measurements they undertook and the way they didit.
DataanalysisIn the analysis data section, the data deducedfromtheexperiment performed are presented and all calculations based on them are carried out. All results must be necessarily accompanied by a percentage error between the experimental and the theoreticalvalue.
Commenting on the results
The authors present their observations on the results obtained. They comment on their findings. If some of the results are incorrect they should indicate the possible sources oferror.
ConclusionTheconclusionshouldbrieflystate the originalproblemandthegeneralcontent of the project. It should be a standalone piece, that is, by reading this alone, the reader should be able to get the gist of the project’s main idea without having to read it all. Usually, the conclusion ends with a paragraph describing possible extensions of this project and presents future relevantstudies.
SourcesAt the end of theproject,referenceshouldbemadeto allsourcesofinformation. If the source is a website, the link must be given. If the source is a book the title, the author and the publishing house shouldbe
named.
Labinformation:
In order to conduct this exercise, the data analysis tool HYPATIA will be used. It has been created solely for educational purposes by the University of Athens and the Institute of Physics of Belgrade. HYPATIA has been designed to analyse real data from the ATLAS experiment conducted at the Large Hadron Collider at CERN. Students will measure the momentum of various particles and by using the conservation of momentum principle they will discover the existence of particles whose trajectory has not beendetected.
Further information:
Lab exercise #1: Conservation of momentum during particlecollision
- Generalinformation
Brief description: Students will determine the resultant momentum of all particles detected during a hadron collision and will calculate the size and momentum of the residualvector.
Connection with thecurriculum:
Greece: 1st Grade of High School Physics, Chapters 1 3, § 1.2 and § 3.2 of thetextbook.
Teachingtargets:
1.Learn about the conservation of momentumprinciple.
2.Practise addingvectors.
3.Measure vector angles and convert radians to angledegrees.
4.Learn about research in the field of basic particlephysics.
Age:15-18
Time required: 2½ teachingunits
Technicalrequirements:
1.Computers with an Internetconnection
2.HYPATIA data analysis tool-
-save version HYPATIA-v4 from the webpage
-Decompress the file you saved and then save the extracted file directly to your computer hard disk inC:\
-Double click on the “Hypatia 4.jar” file to open theprogram.
Notice: The program requires installing the Java Runtime Environment software (version 1.4 or newer). which can be found here:
Students’ preparation: Mass, speed, acceleration, power, energy and the way all these are connected, i.e. Newton’s laws, should have already been discussed inclass.
Students also learn the difference between scalar and vectorsizes.
Note: The theory presented in “Theory behind the experiment” concerns the relevant exercise in the guide and does not constitute a full theoreticalapproach.
Key words: mass, speed, acceleration, energy, collision, principle of the conservation of momentum, radians, degrees,vector
- Activitydescription
B.1Activities for elicitingquestions
Intereststimulation
You could begin your lesson by discussing with your students about CERN and the experiments conducted there. You could focus on the following two subjects, in order to attract theirattention:
- The Large Hadron Collider(LHC@CERN)
A gigantic scale scientific tool located 100 metres below the surface of the Earth near Geneva, Switzerland, on the premises of CERN. It extends beyond the border between Switzerland and France. It is a particle accelerator – particles are the building blocks of the material world. It is expected to revolutionise the way we understand nature, from the microcosm to the infiniteuniverse.
Two beams of subatomic particles (hadrons) – either protons or lead ions – travel in opposite directions inside the circular accelerator, gaining energy in each round. Physicists use the LHC to reproduce the conditions that existed in the universe immediately after the big bang, causing the head-on collision of the two beams. Teams of physicists from around the world analyse the particles produced by the collision, using special detectors in a number of experiments conducted with theLHC.
Show the following videos to yourstudents:
-CERN in 3minutes
-LHC in 10minutes
-ATLAS – From dream toreality
Theabovevideoscanbefoundonthe“LearningwithATLAS@CERN”homepage,(
- Simulation of particle collision (proton-antiprotoncollision)
Use the following videos to explain to your students how particle collisions happen in the LHC and why scientists conduct theseexperiments.
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The LHC is the largest and most powerful particle accelerator in the world and the most recent addition to the accelerator system at CERN. It consists of superconducting magnets and a number of systems which accelerate particles, maximising their energy as they move within the 27km acceleratorring.
Within the accelerator two particle beams travel, in opposite directions to each other, at a speed close to the speed of light. These beams travel in different rings which are completely empty and as they travel in these they accelerate while their energy increases through the application of a strong electromagnetic field generated by superconducting magnets. These magnets are made of special materials, suitable for use in such conditions without causing resistances or losses in energy. In order to minimise energy losses, the magnets are cooled at -271oC, i.e. near absolute zero! For this reason most of the accelerator is connected to a cooling system with liquid helium for cooling the magnets and theperipherals.