NEW in 2022

The pandemic situation is highly dynamic! Therefore some groups will gather in a lecture hall, other groups will consist of individually connected students. A mixture of both might be in your videoconference! Depending on the situation, please decide with you co-moderators, if you want to upgrade groups to be "panelists" (recommended), so they can share their video and audio. If there are not so many individual participants, it is recommended to make them also "panelist" or to enable them to speak and answer directly. In the "Participants" window you can always enable selected participants to unmute. Please note that panelists might not be able to vote in the polls. When launching the poll, you can choose whether or not panelists are able to participate.


This page provides information for moderators concerning the video conference for the 2022 International Masterclasses. Talks covering the various topics were presented in the moderator orientation).

Video Conference Technical Information

Date and Time

The 2022 International Masterclasses will run from Thursday 24th February until Tuesday 5th April. The Masterclass schedule for the institutes can be found here. The videoconference starts at 16:00 and ends at 17:00 the latest. There is one single exception: On Sat, 5th March, the videoconferece is from 13:00 - 14:00. These are strict time limits. Please log in 30-20 minutes before the official start of your videoconference to meet your co-moderators, set up, sound check, and be ready to start on time. A great help for you might be the one-pager. It is a overview of procedure and will guide your through all tasks.

Videoconference app

All videoconferences will run on Zoom. Due to the pandemic, students in some regions will most likely not be on campus and might not even be in classroom. Our expectation is that many students will connect to the videoconference individually from home. So in contrast to former editions of International Masterclasses moderators might not meet 5 groups of students but up to 200 individual students - or even a mix of groups and individuals. To give moderators more control over who could do what and when, the Zoom conferences will be done in the webinar style.

The Zoom webinar is ideal for a large audience. Although moderators cannot see the high school students, there is a lot of interactivity via the polls and the Q&A function. Nevertheless, if there are not so many individual participants, you might want to enable them to speak and answer directly. In the "Participants" window you can enable selected participants to unmute. Or you can upgrade students or a group in one room to be "panelists", so they can share their video and audio.

Setup Webinars

Each webinar is created by IMC coordinator Uta. You will receive the link/credentials to the webinar 2-3 days before your videoconference.

Starting the Webinar and roles

Moderators with CERN zoom account are "alternative hosts". They have to start the session. Log in at CERN Zoom account: with your credentials. It is important that the alternative hosts are signed into their Zoom accounts on the computer they are using before joining the meeting, otherwise Zoom will not recognize them as alternative hosts.

Moderators without CERN zoom account are "panelists". They cannot start the session!

30 min before the official start time (16:00), the alternative host connects and starts the webinar. Then panelists can connect. At this stage, the webinar is in the mode "practice session". The practice session is only accessible by the host, alternative host, and panelist. The "practice session" allows you to set up and get acquainted with webinar controls before starting your webinar. Settings that should be checked in the “practice phase”:

  • Click “Participants”, choose "Panelists" (left hand side), choose your co-moderator and make her or him "co-host", so they have the same permissions.
  • Establish a communication channel, e.g. Mattermost

Where possible, teams of 3 moderators are sheduled. One person should take over the role of a "technical moderator". Role and responsibilities:

  • Share screen/applications.
  • Monitor Q&A box for questions and read out to moderators.
  • Run Zoom polls.
  • Mute/unmute participants.
  • Play the quiz
  • ...

When you are ready, at 15:55 at latest, you start the webinar (click blue button at the top). From now on, students can join. It might take some time before they are all connected.

  • Share the intro slide, so students can already see what they can expect in the next 60 min.

We created a channel on CERN's Mattermost server which you can use to chat with your co-moderators, you can join it by clicking here (team name is IMC, direct link to Townsquare). You can e.g. create a private chat for a given session, invite your two co-moderators to join and use it during the video conference if you need. You can also ask for technical help or chat with everybody in the channel's Townsquare.

Interactive Zoom tools

Zoom polls

There are pre-created polls in each webinar. You will launch the polls during the session meeting and gather the responses from students.

  • Click Polls in the meeting controls.
  • Select the poll you would like to launch.
  • Click "Launch Poll".
  • The participants in the meeting will now be prompted to answer the polling question(s). You will see the results live.
  • Once you would like to stop the poll, click "End Poll".
  • To share the results to the participants in the meeting, click "Share Results". Participants will then see the results of the polling question(s).
  • Do not forget to click "Stop share results"!

Q&A on Zoom

The Q&A feature allows students to ask questions during the webinar. Panelists, co-hosts, and host can answer the questions. Students can upvote each other's questions. This should be explained by you!
  • Click Q&A in the webinar controls.
  • Find the question you would like to answer.
  • Click "Answer Live" to answer the question out loud during the webinar.
  • Click "Type Answer" to type out your answer. Type your answer and click "Send".
  • We strongly recommend to dismiss jokes and provocative questions, so they do not get upvoted! Hover over the question that you would like to dismiss and click "Dismiss".
  • Students can upvote a question by clicking the thumbs up icon. Q&A that has been upvoted will automatically be sorted by number of upvotes.

Zoom virtual background for International Masterclasses

You are encouraged to use either the LHC tunnel photo, to be downloaded here, or the customized IMC virtual Zoom background, to be downloaded here. On the Zoom desktop app, navigate to Preferences in the settings menu. On the left side menu, go to Background & Filters. Upload the background by clicking the plus (+) icon to the right of Video Filters. To add or change your virtual background during the meeting, click on the upward arrow (^) next to Start/Stop Video. Click Choose Virtual Background, and select the IMC background.

Procedure and Content Video Conference

Timeline of the video conference


  • 16:00 - 16:10 Welcome & icebreaker, incl. Zoom poll (10')
  • 16:10 - 16:30 Combination & discussion of measurement, incl. Zoom poll (20')
  • 16:30 - 16:50 Open discussion, Zoom Q&A (20')
  • 16:50 - 17:00 Quiz (10')
  • 17:00 Good Bye (01')

Preparation for the video conference

Prepare/upload all the material you will have to share, including:

Make sure you have downloaded what you need onto the desktop (slide and map), you are able to access the tables and results, you know how to share these on Zoom

Masterclass map

At the beginning of the Masterclass during the welcome display a map showing all connecting sites. It can be used to explain to the institutes in which order you will look at their results (e.g. north to south or alphabetical order or similar), to give some more structure to this procedure. The Masterclass organisers will produce a map for each video conference that can be downloaded from the bottom of this page (attachments). Click on the right map for your masterclass and download it to your desktop. Make sure you know what it is called and you are using Zoom to 'share' this so all the institutes can see it.

Table/website for combination of results

The results page must be put onto the shared desktop, these can be found here:

this was used until 2021:
  • ATLAS Z-path
  • ATLAS W-path webpage Top drop down for the combination, and bottom drop down for the histogram.
  • CMS: CIMA admin pages. (Login/Password = Admin/MasterClass.) Choose the date under Masterclasses and then go to the Results button.

Animated quiz

The quiz is played via Kahoot. Students have to open the website (it!) on their PC/phone and enter the PIN which is automatically generated for each game. Alternatively, they can take pen and paper to play along and in the end count how many correct answers did they get.

Moderator which will run the quiz should open the website in their browser (link to quiz 1, backup links quiz 2 or quiz 3). Click "Play as guest" and "Continue as a guest", than check quiz settings (all options should be OFF) and start quiz by clicking on "Classic" mode. You will see the quiz start page that you should share on zoom (browser window or full screen). Ask students to go to and enter the game PIN you see on top of the screen. While waiting for students, you can tell them the rules (7 questions, 4 answers each, 30s to answer, up to 1000 points per answer). Start quiz using "Start" button on top right and go trough questions using "Next" button. All questions have 30s time limit but if all students answer sooner, the timer runs out automatically. After each question you will see the correct answer and a summary of students answer, you can skip the scoreboard that is shown after each question as well.

If you have technical issues with Kahoot, the fallback option is to run old quiz slides and ask students to use pen and paper.

Questions and correct answers:

  • Question 1: Which particle is the mediator of the strong force? C. Gluon
  • Question 2: How much of our universe is matter or energy of which we know nothing about? A. 95.1 %
  • Question 3: What is the power consumption of the LHC? The same as... B. GVA canton
  • Question 4: What does the Higgs field do? D. Solve the origin on mass
  • Question 5: Which of the following inventions was driven by particle physics research at CERN? D. All of the above
  • Question 6: During a long LHC run, the proton beams might circulate for up to 10 hours. How far will these protons have travelled (assuming they have not interacted)? B. The distance from CERN to Neptune and back
  • Question 7: Which is the most common elementary particle in your body? A. Up-quark
The average human body (70 kg) mainly consists of: 44 kg Oxygen, 14 kg Carbon, 7 kg Hydrogen For each Oxygen and Carbon atom: u=d, as they have the same number of protons and neutrons (let´s not talk about C13, C14, O18...). Each Hydrogen atom has 2u and 1d. 7 kg of Hydrogen = 7000 mol, that means a huge number of atoms. Iron or Potassium atoms for example have more neutrons than protons, but they are far less abundant. The human body contains 170 g Potassium (4,3 mol) and 3 g Iron (0,05 mol). This can not compensate for the over-abundance of up-Quarks from Hydrogen.

Welcome & icebreaker

During the welcome you can start the first Zoom polls (4 questions) to have some interaction with the students. (old link to welcome questions are here.

Discussion of combined results with students

Students will have already discussed their results on a local level. Now you should display and discuss the combined results. Possible questions are listed below. To interact with students, you can launch a Zoom poll for each question (see below the prepared questions and answers). This will give you more food to discuss. You can also encourage students to type a short answer in the chat.

If there are not so many participants, you might want to enable them to speak and answer directly. In the "Participants" window you can enable selected participants to unmute.

Physics Discussion of the Measurement

ATLAS Z path

General information on ATLAS Z path

See moderators-document for description: PDF, or DOC, OPloT link

For each question, show the plot indicated with the question.

Question 1


Moderator discussion: Explain what a peak is, point out Z boson peak at 90 GeV.

Poll question: Do you see any peaks here that you would not expect?

  • Yes
  • No
  • I’m not sure

Moderator discussion: Explain that the low mass peaks correspond to the J/psi and upsilon resonances and that the peaks at 1 TeV and 1.5 TeV correspond to simulated Z’ and Graviton events that we hid in the data!

Question 2


Poll question: Do you see a peak corresponding to the Higgs boson?

  • Yes
  • No
  • Maybe, but I’d need more data to be sure

Moderator discussion: Explain about statistical limitations of the measurements and that H->yy is a very rare process.

Question 3


Moderators discussion: Explain that you’re now showing the results scaled up to a much larger amount of data and that now the Higgs (brown histogram) is visible over the background (green histogram)

Poll question: Do you think we could see the peak here even if it had the same color as the background?

  • Yes
  • No
  • Not sure

Moderators discussion: Explain that it depends on how accurately we can measure the background processes, but in this case this is the same size as the dataset that we did discover the Higgs in, so we could identify it.

Question 4


Moderators discussion: Explain the plot and that we’re now looking for Higgs bosons decaying to two Z bosons (that subsequently decay to electrons and muons).

Poll question: Why are there more events with electrons than muons?

  • The Z boson decays to electrons more often than muons
  • Muons don’t interact in the detector very often
  • Other particles are ‘faking’ the electrons

Moderator discussion: Explain that the Z boson decays to e+e- and mu+mu- at equal rates, but muons leave a very distinctive signature in the detector while electrons are easier to fake.

Question 5


Moderator discussion: Show the “ll+4l+yy” plot and zoom into the high mass region (not the “ll+4l+yy overview” plot, as it does not allow one to select the range)

Poll question: Why don’t we see the particle at 1000 GeV in the 4-lepton and diphoton distributions?

  • It has the wrong mass
  • It has the wrong spin
  • It has the wrong charge

Moderator discussion: Explain that observing how a particle decays can give us lots of information about its properties. In this case we can deduce that the particle at 1000 GeV must have spin=1 (Z’) while the particle at at 1500 GeV has spin=2 (graviton).


A great animation for the evolution of the Higgs->gammagamma signal and for the Higgs->ZZ. These demonstrations can help with explaining to students who claim they have discoverd the Higgs, that they probably will need more statistics.

ATLAS W-path

General information on ATLAS W path

Students´ tasks include:

  • Explore the structure of the proton by counting the number of W+ and W- events in W candidate events: Students identify W candidate events, decay products and (if possible) their electric charge, calculate ratio R±
  • Search for the Higgs in l+νl-ν + 0,1 Jets final state (1000 real data events containing l+νl-ν + 0,1 Jets were mixed with a selection of 11000 real data events from 2011 (W candidate events and background). Students identify WW candidate events and measure the opening angle Δφll between both electrically charged leptons in transverse plane.

Question 1


Moderator discussion: Show the combination/summary table and explain to the students what they are looking at.

Poll question: How did the final result change when we did the combination?

  • Nothing changed
  • It became more precise (smaller error)
  • It became less precise (larger error)
  • We found dark matter

Moderator discussion: Discuss briefly why this ratio is 1.5 (and not 1) and what this tells us about the structure of the proton (should have been covered in detail earlier in the day).

Question 2

Moderator discussion: Staying with the same table, point out to the students the official ATLAS measurement

Poll question: Is our result compatible with the results measured in ATLAS?

  • Yes
  • No
  • Not sure

Moderator discussion: Talk about statistical compatibility of the results (N.B. the students’ measurement should agree with the ATLAS one, within uncertainties, but doesn’t always!)

Question 3


Moderator discussion: Show histogram from the second drop-down menu, explain what is being plotted (angle between two leptons) and that the black points represent the data measured by the students.

Poll question: What do the blue and green areas mean?

  • Higgs bosons
  • Nothing - it’s just to make the plot look pretty
  • They represent the processes that we expect to occur in the data

Moderator discussion: Explain that these are the predictions we get from the Standard Model about how many events to expect. Blue is what we expect from real WW events, and green is from other processes (ttbar, Z) that can mimic this process.

Question 4


Moderators discussion: Stay on the same plot, and show the Higgs contribution (red) by checking into the appropriate checkbox and click on "submit". Explain that you’re now showing the results with the Higgs contribution included?

Poll question: Can we claim a Higgs discovery?

  • Yes
  • No
  • Not sure

Moderators discussion: In this case, no, we can’t claim the Higgs. Explain about how we would need more data in order to say for sure that the Higgs is there.


  • Animations for Higgs -> WW can be found here.


General information on CMS measurement

An introduction to the CMS measurement can be found here. The topic of the Measurement is W and Z bosons with additional particles to be found and studied. Students will use iSpy-webgl and CIMA to find/create:

  • Ratios e/mu and W+/W-
  • Mass of Z from dilepton plot
  • J/Psi and Y peaks in dilepton plot
  • Study 4-lepton mass plot with possible Higgs, ZZ, Z-gamma.
Key Activites of Students, Mentors, and Moderators

Students will:

  • Distinguish W from Z boson candidates from event displays
  • Use curvature of lepton tracks to distinguish W+ from W-
  • Distinguish electron from muon events
  • Transfer the following data to mentors by way of CIMA: Numbers of electron and muon events, Numbers of W+ and W- candidates, Invariant masses particle candidates in 2- and 4-lepton events.
Mentors (or their assistants) at the institutes will:
  • Show students Institute result for ratios e/nu and W+/W-, discuss significance (find in CIMA student pages)
  • Show the mass plot of Z and H candidates in CIMA where they can be found (find in CIMA student pages)
  • Discuss mass plots with students (J/Psi, Upsilon, Z, Z-gamma, H, and ZZ in 2- and 4-lepton mass histograms.)
  • Numbers of electron and muon events, Numbers of W+ and W- candidates, ratios, and Mass plot will be visible to moderators in CIMA.

For more detailed instructions, see:

To share results

  • Go to the CIMA admin pages. (Login/Password = Admin/MasterClass)
  • Choose the date under Masterclasses and then go to the Results button.

Question 1


Moderator discussion: Share Combined Mass Histograms (overall mass histograms) with the students. Explain that the top plot shows the two-lepton mass, for events with two electrons or muons in them.

Poll question: What do the peaks in the two-lepton mass distribution represent?

  • Particles that have decayed to two leptons
  • A problem with the detector electronics
  • Random noise

Moderator discussion: Explain that we can see the J/psi, Upsilon and Z (point with cursor to each one) and that calculating the mass of the lepton pair tells us the mass of the particle.

Question 2

Moderators discussion: Explain that bottom plot shows the 4-lepton mass, and that, analogously to the 2-lepton plot, peaks in the distribution can tell us about the particles that were produced. In this case we can (hopefully!) see two narrow peaks corresponding to the mass of Zy and Higgs masses, and a broad cluster of events which we expect to be ZZ events.

Poll question: Can we claim a discovery of the Higgs boson from this result?

  • Yes
  • No
  • Maybe, but I’d need more data to be sure

Moderators discussion: Explain about requirements for claiming a “discovery” and that in this case we can see hints of the Higgs, but we’d need more data to be sure.

Question 3


Moderator discussion: Share with students: Combined Results (Overall e/mu and W+/W- results). Explain what is shown in the table

Poll question: What did you expect the ratio of electron events to muon events to be (approximately)?

  • 0.5
  • 1.0
  • 2.0

Moderators discussion: Explain that W bosons are equally likely to decay to electrons as they are do muons, so we would expect that this ratio is = 1. If the student measurements do not have this result, suggest some reasons why this could be the case (electrons harder to identify in the detector than muons - maybe some teams selected more jets as electrons, or rejected some electrons because they thought they were jets).

Question 4

Moderators discussion: Show the ratio of W+ to W- events in the same table.

Poll question: Why do we observe more W+ bosons than W- bosons?

  • There are 2 up quarks (charge = +⅔) and one down quark (charge = -⅓) in a proton so there is more chance to make positively charged W bosons
  • W- bosons don’t decay to electrons and muons at the same rate as W+ bosons do
  • Some new particle is being produced that only decays to W+

Moderator discussion: Explain what this ratio tells us about the structure of the proton.

ALICE - Looking for strange particles

Questions that will be used in the Zoom polls

* Q1: Are kaons
  • Baryons?
  • Mesons?

* Q2: Are Lambdas

  • Baryons?
  • Mesons?

* Q3: Why does the invariant mass have a width and is not a delta function?

  • Because some of the detectors were not working properly
  • Because of the intrinsic resolution of the detectors

* What causes the background in the invariant mass distributions of kaons?

  • The two pions do not originate from the same kaon but appear as coming from the same secondary vertex
  • One or both pions have been misidentified
  • Both of the above

Scenarios (Questions to be used in the non-webinar-style, when only groups connect)

  • Why are the two tracks of each V0 curved in opposite directions?
  • Why is the radius of curvature of the proton bigger than that of the pion in Λ decays?
  • Why don’t you see the Λ or the K0 before their decay?
  • Why does the Λ not decay to two pions, like the K0?
  • Why does the invariant mass have a width and is not a delta­function?

General information on ALICE - Looking for strange particles

The updated document (version 2022) can be found at

Topic of the measurement

• Identify strange particles (V0s : Ks, Λ, anti-Λ) from their decay pattern, combined with calculation of their invariant mass.

• Find number of Ks, Λ, anti-Λ for different centrality regions for lead-lead data.

• Calculate yields for Ks, Λ, anti-Λ and strangeness enhancement factors by comparing to proton-proton data.

What the students do in each institute Visual analysis Using a simplified version of the ALICE event display based on ROOT, they identify and classify strange particles (V0s : Ks, Λ, anti-Λ) from their decay pattern, combined with invariant mass calculation. Each group of 2 or 3 students looks at 15 events. At the end of this first part, the tutor merges the results of all groups and produces invariant mass plots for Ks, Λ, anti-Λ. During the videoconference, they can give the mass values and width of the peaks. Large scale analysis - Find V0s in different centrality regions in PbPb collision Students analyse large datasets, by running a programme that selects V0s, calculates the invariant mass and produces an invariant mass plot; each group of 2 or 3 students is assigned a centrality region and they have to find the number of Ks, Λ, anti-Λ in this region. To do this, they have to fit curves to the combinatorial background (2nd degree polynomial) and the peak (Gaussian) and subtract.

Calculation of particle yields and strangeness enhancement factors Each group reports the number of Ks, Λ, anti-Λ they found in the centrality class that they have analysed. The results for the whole class are entered in a spreadsheet as the following

The number of events in each centrality region is given in the spreadsheet.

The number of participating nucleons in the collision, Npart, which is correlated with the centrality, is also given in the table for each centrality class.

The number of particles measured is less than the number of particles produced; to find the latter we need to take into account the efficiency; efficiency values, for Ks, Λ and anti-Λ, have been estimated and are given in the table.

In the spreadsheet, there are embedded formulas to calculate:

Yield : the number of particles (of a certain type) produced per interaction = Nparticles(produced)/Nevents = Nparticles(measured)/(efficiency x Nevents)

Strangeness enhancement: the particle yield normalised by the number of participating nucleons in the collision, and properly normalised by the yield in proton-proton collisions at the same collision energy.

Ks-Yield(pp) = 0.25 /interaction Λ-Yield(pp) = 0.0615 /interaction ; the same for anti-Λ <Npart> = 2 for pp

NOTE: the above yields for Ks and Λ refer to proton-proton collisions at 2.76 TeV (same energy as for Pb-Pb collisions, 2.76 TeV per nucleon pair); they have been calculated by interpolation, between measured Ks and Λ yields at 900 GeV and 7 TeV [internal ALICE notes].

With all this information a spreadsheet like the following is produced with the information for Ks, Λ and anti-Λ.


Embedded in the spreadsheet is a scatter plot, showing the enhancement factors for Ks, Λ and anti- Λ versus the number of participants.


The results of all institutes can be accessed at the url (until 2021 :

Inside this folder, there is an example spreadsheet, results-example.xls

Each institute fills in a spreadsheet with the name results-inst_name-xxxxxx.xls ( inst_name is the name of the institute, e.g. CERN, Nantes, Heidelberg… xxxxxx is the date, e.g. 03032015)

DISCLAIMER : The results in this example – and the results produced by this analysis – are based on a small dataset selected for this measurement and on a number of assumptions and simplifications; therefore they may differ from official ALICE results.

Institutes’ report and comments

Starting from 2017 the institutes no longer give a report of the results during the videoconference. This new concept was introduced because it was considered too repetitive reporting basically the same things up to five times.

By going to the google docs folder as described in the previous section, the moderator should bring to the screen and show the spreadsheet with the institute’s results, including scatter plot. He 'she can comment. Possible comments :

The number of Ks, Lambda and antiLambda (and the calculated yield) is higher for more central collisions and decreases as we go to less central collsions. This is expected since, in the most central ones, up to ~400 nuclei in total interact, which results in thousands of particles produced per collision.

Strangeness enhancement is observed (ratio >1). Ratio=1 would mean that there is no difference between collisions of nucleons of the lead nuclei and collisions of protons.

Show ALICE results.


The students have only measured Λ (1 strange quark); Their measurement is in agreement with the ALICE results, within errors. (In addition, assumptions were made about the efficiency – real life analysis takes much longer – things were simplified here to complete the measurement).

The other particles shown on the plot have higher content of s-quarks: the Ξ has 2, the Ω 3. Strangeness enhancement increases with the number of strange quarks in the baryon. Note

If there is a problem with accessing google docs, the institutes can use excel spreadsheets with embedded scatter plots on their local computer. They can then show them by screen sharing.

Additional information can be found at the URL

the text describing the measurement also “Instructions to the Institutes”

Temperature Calculation

An additional comment can be made by the moderators on the calculation of temperature from particle ratios, along the lines:

Our observation of the number of produced Lambdas and Kaons can serve as a thermometer of the matter which is produced in the collision.

If you had measured Lambdas + Anti_Lambdas and K0s per event in the 0-5% centrality Pb-Pb events and then corrected for detection efficiency (pt-integrated), you would have obtained the following values (preliminary ALICE analysis results, not yet published):

NK0s = 123.9 ± 7 (which is the dN/dy per event) NΛ = 28.8 ± 3

We then put the NK0s in relation with the number of produced pions per event. The following value has been measured for the 0-5% centrality Pb-Pb event

Nπ+ = 792.1 ± 44.1

We form the ratio and obtain

NK0s / Nπ+ = 0.156 ± 0.012 NΛ / Nπ+ = 0.036 ± 0.004

From the plot below we can then roughly judge at which temperatures the particles were produced:


The curves are produced with a so-called thermal model. It relates the relative abundance of particles with the temperatures in the fireball. Very roughly speaking, it shows that the production of particle of mass mi is proportional to ~ exp(-mi/T). We can see this also in the plot showing that the heavier lambdas are produced less often than the lighter kaons. Thus, our observation of the number of produced Lambdas and Kaons can serve as a thermometer of the matter which is produced in the collision. Our results show that the temperature of the fireball is somewhere between 120 MeV and 180 MeV corresponding to roughly 1.74×1012 K (compared to 5.778 K on the surface of the sun -- factor 1 billion). Within 2σ the two ratios are even in agreement with a single temperature.

  • ALICE published results on strangeness enhancement:


Scenarios (Questions for 5 groups)

  • Visual analysis: where do the clusters come from that are not associated with a reconstructed track?
  • Visual analysis: did you observe more positively or negatively charged particle tracks? Why is this so?
  • Visual analysis: why do most of the produced particles have low momenta?
  • What is a reconstruction efficiency and why is it important?
  • What is the difference between R_CP and R_AA?
  • Why is R_AA < 1 consistent with energy loss in a quark-gluon plasma?

General information on ALICE R_AA measurement

For a description see the manual of the measurement: PDF. Further information can be found in the guide for tutors and the moderators' manual.


Instructions for the LHCb exercise can be found on this link together with merging script at the bottom of the software section. The exercise was moved from local version to web in 2022 so some instructions might be outdated.

The exercise has two parts: searching for D_0 in LHCb events and measuring its reconstructed mass; measuring the lifetime in a larger sample of events using selection cuts. Students will normally discuss combine results within their institute and discuss them before the videoconference. Local organizers should send moderators their results by 15:00 on the day of videoconference (json files with invariant masses and a single lifetime value). Moderators than merge the data to prepare a gif of D_0 mass distribution and a plot with lifetime measured by institutes and the PDG value. For remote MC in 2021, moderators can shorty discuss the plots and run zoom polls (questions below) or ask studnents to write to chat their findings. Sometimes institutes ask one or few students to present/share their results.

If there is an expert from pit which connects, we recommend to keep the physics discussion short to allow for long enough cavern tour and Q&A session.

Example moderator discussion and questions that will be used in the Zoom polls

Here is an example of physics discussion, you can adjust it and pick which poll questions in zoom you want to use. 4 polls seem about right to keep students engaged and stick to time (do not use all 6 questions).

Moderators discussion: Introduce measurement, say now we merge data from all groups and show the combined plot of D0 invariabt mass distribution

* Q1: How did the D0 mass distribution change with more data?

  • Nothing changed
  • The D0 peak became clearer
  • The D0 peak became less clear (more background or more fluctuations)
  • We found dark matter

Moderators discussion: Discuss statistics and importance of collecting large datasets

* Q2: What can cause the background in the invariant mass distributions?

  • The pion and kaon do not originate from the D0 but appear as coming from the same secondary vertex
  • The pion and/or kaon have been misidentified
  • Both reasons can contribute

Moderators discussion: Show the lifetime plot

* Q3: Did your result of lifetime agree with the world average value listed in PDG tables?

  • Yes, it was exactly the same value
  • Yes, within uncertainty
  • No

Moderators discussion: Usually they measure larger lifetime than PDG. You can discuss the sources of bias, using more cuts and better selection in real analyses etc.

* Q4: How much data would you need to be as precise as the current world average? As example take yor your error ~5 fs, PDG world average error ~1 fs.

  • Two times
  • Five times
  • Twenty-five times

Moderators discussion: You can discuss statistics, future experiments etc.

* Q5: Is it a good idea to measure D0 lifetime by more than one experiment?

  • Yes, it can show if some measurement has bias
  • No, our results are always correct
  • It depends if you have time

(Q5 can be used if there is one institute with value very different from others)

* Q6: What experimental effects might cause a difference between the measured lifetime and the world average?

  • A mis-aligned detector
  • Choosing the wrong proton-proton collision point as the D0’s starting vertex
  • Human error
  • All of the above

Social Media


Please tweet about the Masterclasses! Our account is @physicsIMC. Use the hashtag #physicsIMC and #LHCIMC

International Day of Women and Girls in Science (Feb 11)

The program of the day is available here. A presentation on the situation of women in physics can be shown, available as pptx or pdf.

NEW in 2021

*There have been significant changes to the format of the masterclasses in response to the pandemic situation! There are 3 important changes: First: Moderators will not sit together. Second: Individual students could also participate in the video conference, not just groups. This is the case when students cannot visit school. Third: Zoom, CERN´s official video-conference service, will be used. Please follow the trainings carefully, even (especially!) if you are an experienced moderator!*

Click for information that was "new" in previous years.

NEW in 2020

The CMS Masterclass has been updated for 2020 to include 4-lepton events and separate dilepton and 4-lepton mass plots.

NEW in 2019

Everything is stable. No new elements have been introduced... besides the use of VidyoConnect instead of VidyoDesktop. Updated instructions in the relevant sections!

NEW in 2018

There is one improvement: To streamline the discussion of measurements sets of questions have been developed which should be used by the moderators. There are 5 scenarios for ATLAS and CMS measurements. Each scenario consists of a plot or table and relevant question(s) that students are supposed to answer. The scenarios can be found in the section Physics Discussion of the Measurement

-- KateShaw -17-Feb-2013

-- KateShaw - 01-Nov-2011

Topic attachments
I Attachment History Action Size Date Who Comment
Microsoft Word filedoc ALICE-moderators2022.doc r1 manage 570.0 K 2022-02-16 - 17:09 DespinaHatzifotiadou instructions for moderators for ALICE - strange particles - version 2022
PDFpdf ALICE-moderators2022.pdf r1 manage 411.0 K 2022-02-16 - 17:10 DespinaHatzifotiadou instructions for moderators for ALICE - strange particles - version 2022
JPEGjpg LHC-tunnel-144-dpi.jpg r1 manage 755.6 K 2022-01-26 - 14:57 UtaBilow LHC tunnel photo as virtual background for Zoom
PDFpdf List_of_welcome_questions.pdf r1 manage 15.6 K 2012-02-20 - 23:46 UtaBilow  
Unknown file formatdocx One_pager_for_moderators-2022.docx r1 manage 16.9 K 2022-02-09 - 22:26 UtaBilow One pager for moderators
PDFpdf One_pager_for_moderators-2022.pdf r1 manage 112.7 K 2022-02-09 - 22:27 UtaBilow  
PNGpng VCTimeline_new.png r1 manage 49.5 K 2017-02-07 - 19:45 KatharineLeney Timeline image
JPEGjpg Zoom-background.jpg r1 manage 130.8 K 2021-02-22 - 14:17 UtaBilow customized IMC virtual background for Zoom
Unknown file formatpptx answersheet-2017-en.pptx r1 manage 103.1 K 2017-01-30 - 14:31 UtaBilow answersheet quiz
PNGpng cima-admin-mass.png r1 manage 41.8 K 2020-02-14 - 16:11 KennethCecire  
PNGpng cimaratios.png r1 manage 23.8 K 2020-02-14 - 16:34 KennethCecire  
PNGpng combination_4l.png r1 manage 50.8 K 2018-02-05 - 15:31 MagnarBugge  
PNGpng combination_gg.png r1 manage 53.1 K 2018-02-05 - 15:31 MagnarBugge  
PNGpng combination_gg3.png r1 manage 49.9 K 2018-02-05 - 15:31 MagnarBugge  
PNGpng combination_highMass.png r1 manage 71.2 K 2018-02-05 - 15:31 MagnarBugge  
PNGpng combination_ll.png r1 manage 55.6 K 2018-02-05 - 15:31 MagnarBugge  
PDFpdf intro-slide-IMC-2021.pdf r1 manage 180.4 K 2021-02-06 - 22:05 UtaBilow intro slide to be shown at the very beginning of the webinar
Unknown file formatpptx intro-slide-IMC-2021.pptx r1 manage 1099.3 K 2021-02-06 - 22:05 UtaBilow intro slide to be shown at the very beginning of the webinar
JPEGjpg map-04-04-2022-ATLAS.jpg r1 manage 1425.0 K 2022-04-03 - 16:39 UtaBilow map
JPEGjpg map-05-04-2022-ATLAS.jpg r1 manage 1424.7 K 2022-04-03 - 16:39 UtaBilow map
JPEGjpg map-05-04-2022-CMS.jpg r1 manage 1415.2 K 2022-04-03 - 16:39 UtaBilow map
PDFpdf pres-women-in-physics-2022.pdf r1 manage 915.7 K 2022-02-10 - 17:39 UtaBilow  
Unknown file formatpptx pres-women-in-physics-2022.pptx r1 manage 2347.9 K 2022-02-10 - 17:39 UtaBilow  
Unknown file formatpptx quiz-2017-en.pptx r2 r1 manage 14215.1 K 2017-01-31 - 15:48 UtaBilow quiz
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Topic revision: r440 - 2022-04-03 - UtaBilow
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