CMS WZH Masterclass

The LHC and the new physics

It is a time of exciting new discoveries in particle physics.

At CERN, the LHC is now in Run 3, with its highest collision rates and energies yet. At the same time, there are new questions as the few experimental results vary from the highly reliable Standard Model.

The LHC and CMS are where we need to be to explore these new mysteries.

LHC@CERN

~27 km circumference

~100 m underground

Protons circulate in opposite directions

Up to 14 TeV collision energy

The LHC and the new physics

The Compact Muon Solenoid (CMS)

Protons collide inside CMS

The LHC accelerates protons to almost 7500 times the energy equivalent of their mass. The protons circulate in opposite directions and collide in the center of CMS.

But protons are not just particles: they are more like bags of quarks and gluons. When protons collide, all sorts of very short-lived particles can be made from all that energy.

What do the protons tell us?

We learn from what proton collisions produce:

W bosons give us clues to the proton structure…and they also present a mystery.

Z bosons decay (sort of) like lighter particles but are also needed to sort out Higgs data.

Higgs bosons, well, are Higgs bosons, the new kid on the block!

Artist’s image of a proton from CERN Courier. Learn more here and even more here.

One-lepton events

The + or – charged W boson enables radioactive decay by transforming neutrons into protons.

It decays into a neutrino and another lepton. Since CMS cannot detect the neutrino directly, we can call this a one-lepton event.

Two-lepton events

The Z boson is a neutral cousin of the W. It enables the “weak neutral current”.

It decays into two leptons of the same type but opposite charge – electron and positron or muon and antimuon. It has other decay paths but we are not looking for these.

Four-lepton events

The Higgs boson is an expression of the field that gives other particles mass.

One decay mode of the Higgs is into two Z bosons, which themselves promptly decay. Thus we can get 2 muons and 2 electrons or 4 muons or 4 electrons.

Decay summary

iSpy event display for CMS

1, 2, or 4 leptons?

Which of these events is 1-, 2-, or 4-lepton? Which flavors of leptons? What else do you see?

Note Tracks (reco) turned OFF.

1, 2, or 4 leptons?

Which of these events is 1-, 2-, or 4-lepton? Which flavors of leptons? What else do you see?

Note Inverted Colors and increased ECal Barrel opacity.

1, 2, or 4 leptons?

Which of these events is 1-, 2-, or 4-lepton? Which flavors of leptons? What else do you see?

1, 2, or 4 leptons?

Which of these events is 1-, 2-, or 4-lepton? Which flavors of leptons? What else do you see?

CMS Instrument for �Masterclass Analysis (CIMA)

Enter data on each event:

CMS Instrument for �Masterclass Analysis (CIMA)

CIMA makes mass histograms automatically:

CMS Instrument for �Masterclass Analysis (CIMA)

CIMA tabulate data for key ratios:

Calculate e/mu and W+/W- !

New: Publish results!

Any group of students who have participated in a masterclass may make a report of their results up to one week after. Students:

• Create a report using Claims, Evidence, and Reasoning.:
• Post their report online or save it as a file of some sort (100 MB limit). 
• Make the report available via the Google form at https://forms.gle/KiScZ5j2zL3tiWan9 or by email. 
• The actual report can be in any form that works for your group, as long as it can be put online.

Masterclass reports are encouraged but optional.

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Learn more: https://quarknet.org/mc-comm (scroll down).

Parting words…