Taking a closer look at LHC


  "If there's one thing to do, it's to engage in education".

 George Charpak (Nobel Prize in Physics in 1992).


CERN celebrates 70 years of scientific discovery and innovation.

Large Hadron Collider is the world’s highest energy particle accelerator. LHC (situated in the northwest suburbs of Geneva on the Franco–Swiss border) generates the greatest amount of information that has ever been produced in an experiment before. It is aimed to reveling some of the most fundamental secrets of nature.

Despite the enormous amount of information available about this topic, it is not easy for non-specialists to know where the data come from.

Basically, the purpose of this Website is to help introducing and informing the wider public about the LHC experiment, and some simple physical calculations which take place in all particle accelerators. They can also be used in secondary school classrooms in order to stimulate the curiosity of the students, help them understand the physical concepts of LHC, and they can also be used as an example of the relationship between the cold equations of Physics on the blackboard and the exciting scientific research.

It is important to point out that the calculations that appear on this website are adapted to secondary school level, and in most cases, although they may be useful, they are simply approximations of the correct results.

LHC live

We show below some facts that are of special relevance, appearing in the different Sections of this website the development of the concepts and contents that we consider to be of interest. 

If you are not familiar with the basic concepts of particle physics, we recommend that you first visit the different sections of the general menu of our website.


 CERN highlights in 2023                   


 Taken from CERN WEBSITE


Run 3            

Year 2022, starts LHC Run 3 after a vast programme of works completed during Long Shutdown 2 (LS2). Protons collide at higher energies (13.6 TeV compared to 13 TeV) and with higher luminosities (containing up to 1.8 × 1011 protons per bunch compared to 1.3–1.4 × 1011 ) than in Run 2.

This third experimental phase runs until the end of 2025.

A few weeks after the start of RUN3, several records were already reached.

Some of these are:

.- energy with Pb ions: 6.8 Z TeV (or 2.76 TeV/nucleon)

.- peak luminosity: 2.5·1034

.- pile-up (almost simultaneous collision points) > 100

.- stored energy per beam: ~ 400 MJ

Current schedule foresees Long Shutdown 3 (LS3) to start in 2026, one year later than in the previous schedule, and to last for three instead of 2.5 years (taken from CERN Courier).


In 2012  protons at LHC were running with a beam energy of 4 TeV per proton (8 TeV in collision). At the beginning of 2013, the LHC collided protons with lead ions before going into a long maintenance stop (LS1) until the end of 2014. Running was resumed in 2015 with increased collision 6,5 TeV per proton (13 TeV in collision) and another increase in luminosity. Its maximum total energy of 14 TeV is very close, and after the Long Shutdown 2 (LS2) (2019-2022), in Run 3,  an energy of  6,8 TeV per proton (13,6 TeV in collision) has been already reached (very close to the designed maximum initial energy, 7 TeV per proton)

Higgs Boson                   

One of its main goal has already been achieved in the first phase of operation: to find the Higgs boson

The Nobel prize in Physics 2013 was awarded to François Englert and Peter W. Higgs "for the theoretical discovery of a mechanism that contributes to our understanding of the origin of mass of subatomic particles, and which recently was confirmed through the discovery of the predicted fundamental particle, by the ATLAS and CMS experiments at CERN's Large Hadron Collider."

The ATLAS and CMS collaborations announced their discovery of the particle at CERN on 4 July 2012. This result was further elucidated in 2013.

Candidate Higgs Decay to four muons recorded by ATLAS in 2012 (Image: ATLAS/CERN).

Interesting articles about the Higgs Boson on the tenth anniversary of its discovery are the following:


Precisely on the tenth anniversary of the Higgs Boson discovery, it is a good time to point out that research in Particle Physics is as necessary as it has always been. In this respect, the following article in the journal Nature is highly recommendable

Particle physics isn’t going to die — even if the LHC finds no new particles

Nature. 2022 Jul;607(7917):7-8. doi: 10.1038/d41586-022-01819-4.

The CMS collaboration presented the most precise measurement of the effective leptonic electroweak mixing angle.

April, 2024.

The CMS collaboration presented (2024 Rencontres de Moriond conference) the most precise measurement of the effective leptonic electroweak mixing angle performed at a hadron collider to date, in good agreement with the prediction from the Standard Model.

The electroweak mixing angle is a key element of these consistency checks. It is a fundamental parameter of the Standard Model, determining how the unified electroweak interaction gave rise to the electromagnetic and weak interactions through a process known as electroweak symmetry breaking. At the same time, it mathematically ties together the masses of the W and Z bosons that transmit the weak interaction. So, measurements of the W, the Z or the mixing angle provide a good experimental cross-check of the Model.

First observation of photons-to-taus in proton-proton collisions by CMS.

March, 2024

The CMS collaboration announces the observation of two photons creating two tau leptons in proton–proton collisions. It is the first time that this process has been seen in proton–proton collisions, which was made possible by using the precise tracking capabilities of the CMS detector.


 Candidate event of a process γγ →ττ process in proton–proton collisions.

It is also the most precise measurement of the tau's anomalous magnetic moment and offers a new way to constrain the existence of new physics.

Taken from CMS Collaboration Website

Precise test of lepton flavour universality in W-boson decays into muons and electrons.

March, 2024

ATLAS Collaboration: Precise test of lepton flavour universality in W-boson decays into muons and electrons in pp collisions at √s=13 TeV with the ATLAS detector. (58th Rencontres de Moriond 2024)

A fundamental axiom of the Standard Model is the universality of the couplings of the different generations of leptons to the electroweak gauge bosons. The measurement of the ratio of the decay rate of W bosons to electrons and and muons, R(μ/e), constitutes an important test of this axiom. Using 140 fb−1 of proton–proton collisions recorded with the ATLAS detector at a centre-of-mass energy of 13 TeV, ATLAS Collaboration reported a measurement of this quantity from di-leptonic events where the top quarks decay into a W boson and a bottom quark.

The measured value of R(μ/e) is 0.9995 ± 0.0045 is in agreement with the hypothesis of universal lepton couplings as postulated in the Standard Model. This is the only such measurement from the Large Hadron Collider, so far, and obtains twice the precision of previous measurements in other laboratories.

More here...

Observation of the  Bc+ J/ψ J/ψ π+ π0 decay

January, 2024

LHCb Collaboration: The first observation of the Bc+ →J/ψ π+ π0 decay is reported with high significance using proton-proton collision data, corresponding to an integrated luminosity of 9 fb−1, collected with the LHCb detector at centre-of-mass energies of 7, 8, and 13 TeV.

The Bc+ (composed of two heavy quarks, b and c) is the heaviest meson that can only decay through the weak interactions, via the decay of one heavy constituent quark. The decay of Bc+ into a J/ψ and a π+π0 pair has never been observed before, mainly because the precise reconstruction of the low-energy π0 meson through its decay into a pair of photons is very challenging in an LHC proton-proton collision environment.

 Diagram for the decays of the Bc+ meson into the J/ψ meson and light hadrons

  The large number of b-quarks produced in LHC collisions and the excellent detector allows LHCb to study the production, decays and other properties of the Bc+ meson in detail. Since the Bc+ discovery by the CDF experiment at the Tevatron collider (Fermilab-Chicago), 18 new Bc+ decays have been observed (with more than five standard deviations), all of them by LHCb.

An exabyte of disk storage at CERN

September, 2023

CERN disk storage capacity passes the threshold of one million terabytes of disk space

CERN’s data store not only serves LHC physics data, but also the whole spectrum of experiments and services needing online data management.

More here ...

The first observation of neutrinos at LHC.

August 2023.

While neutrinos are estimated to be some of the most abundant particles in the universe, observing them has so far proved to be highly challenging, as the probability that they will interact with other matter is very low.

Neutrinos are produced very abundantly in proton colliders such as the LHC, however, up to now, these neutrinos had never been directly observed.
The FASER and SND@LHC collaboration are two distinct research efforts, both utilizing the LHC at CERN. Recently, these two efforts independently observed the first collider neutrinos, which could open important new avenues for experimental particle physics research.

More in ...

ATLAS sets record precision on Higgs boson’s mass.

July 2023.

Taken from CERN Website.

The mass of the Higgs boson is not predicted by the Standard Model and must therefore be determined by experimental measurement. Its value governs the strengths of the interactions of the Higgs boson with the other elementary particles as well as with itself. A precise knowledge of this fundamental parameter is key to accurate theoretical calculations which, in turn, allow physicists to confront their measurements of the Higgs boson’s properties with predictions from the Standard Model. Deviations from these predictions would signal the presence of new or unaccounted-for phenomena.

The new ATLAS measurement combines two results: a new Higgs boson mass measurement based on an analysis of the particle’s decay into two high-energy photons (the “diphoton channel”) and an earlier mass measurement based on a study of its decay into four leptons (the “four-lepton channel”).

The new measurement in the diphoton channel, which combines analyses of the full ATLAS data sets from Runs 1 and 2 of the LHC, resulted in a mass of 125.22 billion electronvolts (GeV) with an uncertainty of only 0.14 GeV (0.09%).

First evidence of the rare decay of the Higgs boson into a Z boson and a photon.

May 2023.

The Standard Model predicts that, if the Higgs boson has a mass of around 125 GeV, approximately 0.15% of Higgs bosons will decay into a Z boson and a photon.

But some theories that extend the Standard Model predict a different decay rate. Measuring the decay rate therefore provides valuable insights into both physics beyond the Standard Model and the nature of the Higgs boson.

In a new study, ATLAS and CMS have now joined forces to maximise the outcome of their search. By combining the data sets collected by both experiments during the second run of the LHC, which took place between 2015 and 2018, the collaborations have significantly increased the statistical precision and reach of their searches.

This collaborative effort resulted in the first evidence of the Higgs boson decay into a Z boson and a photon. The result has a statistical significance of 3.4 standard deviations, which is below the conventional requirement of 5 standard deviations to claim an observation. The measured signal rate is 1.9 standard deviations above the Standard Model prediction.



Candidate events from ATLAS (left) and CMS (right) for a Higgs boson decaying into a Z boson and a photon, with the Z boson decaying into a pair of muons.
(Image: CERN) 

Another important achievement comes from the LHCb Collaboration, December 2022, on the Principle of Universality of Lepton Flavor.

The international LHCb collaboration presented on 20 December new measurements of decays that provide one of the most accurate tests to date of a key property of the Standard Model of particle physics, known as lepton flavour universality.

The weak interaction, as described by the Standard Model (SM), is supposed to act equally for all the leptons. This means that decays involving, e.g., muons or electrons should have equal probabilities (with small corrections due to the different masses of these leptons). An example of such decays are B+→ (K+μ+μ-) and  B+→ (K+e+e-), in which a beauty meson decays to a pair of leptons, accompanied by a K meson. Following the reasoning above, if one measures the probability of both decays and then makes the ratio (RK) of these probabilities one would theoretically expect a value very close to 1. Previous studies of these decays have shown significant differences from theoretical predictions, potentially due to the effects of new particles or forces.

The results announced in Dec 2022, which exceed previous comparisons, are in perfect agreement with the Principle of universality of leptonic flavour.

See more…

More updated information (August 2023) on this issue can be found here.

LHCb makes its first dataset available to the public

December 2022: the LHCb collaboration has made data from LHC Run1 available to the public for the first time, allowing anyone in the world to carry out research.
“The data collected at LHCb is a unique legacy to humanity, especially since no other experiment covers the region LHCb looks at,” said Sebastian Neubert, leader of the LHCb open data project. “It has been obtained through a huge international collaborative effort, which was funded by the public. Therefore the data belongs to society.”

CERN Open Data Portal.

Another very important research topic, in which LHC should play an important role, is the measurement of the muon's magnetic moment value. In this field we should refer to the Muon g-2 Experiment (Fermilab) which searches for telltale signs of new particles and forces by examining the muon’s interaction with a surrounding magnetic field. By precisely determining the magnetic moment of the muon and comparing with similarly exact theoretical predictions, the experiment is sensitive to new physics lurking in the subatomic quantum fluctuations surrounding the muon. The strong evidence announced in 2021, by Muon g-2 Experiment, that muons deviate from the Standard Model calculation might hint at exciting new physics. Muons act as a window into the subatomic world and could be interacting with yet undiscovered particles or forces (taken from Muon g-2 News).

Tomado de Fermilab-Twitter

See more on this experiment here.

More updated information (2023) on this issue can be found here.

New hadrons. With data from Run 1 and Run2 phases, more than half a hundred hadrons have been discovered (66 new hadrons have been announced by July 2022). (See more at Patrick Koppenburg-Website)

Most of them have been discovered in the LHCb experiment.

On 5 July 2022, four new discoveries were announced:


Other important achievements:

March 2023. The ATLAS and CMS collaborations have both observed the simultaneous production of four top quarks, a rare phenomenon that could hold the key to physics beyond the Standard Model. More information...

March 2023. First Physics Results from FASER The FASER collaboration reports the first direct observation of neutrino interactions at a particle collider experiment. Neutrino candidate events are identified in a 13.6 TeV center-of-mass energy pp collision data set of 35.4 fb1 using the active electronic components of the FASER detector at the Large Hadron Collider. See more...

In January 2022, LHCb Collaboration announced the Measurement of the W boson mass.The W boson mass is measured using proton-proton collision data at s = 13 TeV corresponding to an integrated luminosity of 1.7 fb1 recorded during 2016 by the LHCb experiment. The W boson mass was determined to be:

mw = 80354 ± 23stat± 10exp± 17theory ± 9PDFMeV,

where uncertainties correspond to contributions from statistical, experimental systematic, theoretical and parton distribution function sources. The measurement agrees well with the prediction of the global electroweak fit and with previous measurements.

 However, the Collider Detector at Fermilab (CDF) Collaboration reported in April 2022 a precise measurement of the W boson mass extracted from data taken at the Tevatron particle accelerator (Fermilab), and, surprisingly, the researchers found that the mass of the boson was significantly higher: 80,433.5 ± 9.4 MeV/c2. The result deviates from the standard model, but it is an experimental measurement that will have to be validated by future experiments, for example at the Large Hadron Collider (LHC).

 Mass W Boson


 Nature, 2022 May; 605(7911):604-607


In March 2019 (Rencontres de Moriond), the LHCb collaboration at CERN has presented for the first time, the matter–antimatter asymmetry known as CP violation in a particle dubbed the D0 meson. To observe this CP asymmetry, the LHCb researchers used the full dataset delivered by the Large Hadron Collider (LHC) to the LHCb experiment between 2011 and 2018 to look for decays of the D0 meson (this meson is made of a charm quark and an up antiquark and its antiparticle, the anti-D0, into either kaons or pions). CP violation is an essential feature of our universe, necessary to induce the processes that, following the Big Bang, established the abundance of matter over antimatter that we observe in the present-day universe. So far, CP violation has only been observed in particles containing a strange or a bottom quark.

24 October 2018, protons performed their last lap of the track. At 6 a.m., the beams from fill number 7334 were ejected towards the beam dumps. It was the LHC’s last proton run from now until 2021, as CERN’s accelerator complex will be shut down from 10 December to undergo a full renovation. For the next weeks the collider will master lead ions (lead atoms that have been ionised, meaning they have had their electrons removed). The collisions of lead ions allow studies to be conducted on quark-gluon plasma, a state of matter that is thought to have existed a few millionths of a second after the Big Bang.

25 July 2018, for the very first time, operators injected not just atomic nuclei but lead “atoms” containing a single electron into the LHC. This was one of the first proof-of-principle tests for a new idea called the Gamma Factory, part of CERN’s Physics Beyond Colliders project.

In March 2018, at the 53rd annual Rencontres de Moriond conference, taking place between 10 and 24 March 2018 in La Thuile in the Aosta Valley in Italy, ATLAS and CMS have unveiled a suite of new measurements of the properties of the scalar boson associated with the Brout-Englert-Higgs field. These results come from the examination of data from proton-proton collisions at an energy of 13 TeV that the LHC delivered in 2015 and 2016. The data sets used by ATLAS and CMS each contained around two million Higgs bosons, of which around 10,000 were readily accessible to the detectors.

12 October 2017, for eight hours, LHC was accelerating and colliding Xenon nuclei, allowing the large LHC experiments, ATLAS, ALICE, CMS and LHCb, to record xenon collisions for the first time.


6 July 2017, at the EPS Conference on High Energy Physics in Venice, the LHCb experiment at CERN’s Large Hadron Collider has reported the observation of Ξcc++(Xicc++) a new particle containing two charm quarks and one up quark. The existence of this particle from the baryon family was expected by current theories, but physicists have been looking for such baryons with two heavy quarks for many years. The mass of the newly identified particle is about 3621 MeV, which is almost four times heavier than the most familiar baryon, the proton, a property that arises from its doubly charmed quark content. It is the first time that such a particle has been unambiguously detected.

... and to know what is coming see HL-LHC: High Luminosity and also The Future Circular Collider.

CERN Council appoints  Fabiola Gianotti  for second term of office as CERN Director General (Nov 2019)

At its 195th Session (Nov 2019), the CERN Council selected Fabiola Gianotti, as the Organization’s next Director-General, for her second term of office. Gianotti’s new five-year term of office goes from 1 January 2021 to Decembrer 2025. This is the first time in CERN’s history that a Director-General has been appointed for a full second term.


For the bibliography used when writing each Section in this Website please go to the References Section

We reiterate that the calculationscalculations that you will be finding in this Website are adapted from the Physics of Secondary School and in most cases they are just very simple approaches to the correct results.

Besides the Sections of this Website, it may be interesting to take a look at other websites which give simple description of Particle PhysicsFor exampleAn Introduction To Particle Physics or other ones that you can find in the section Education of this website.

This Website has received the permissión of CERN to use informations, data, texts and images from CERN websites. The use on this Website of the various materials from publications produced by CERN is strictly in accordance with CERN's terms of use.

The rest of images, graphs, etc., not belonging to ushave been taken as "fair use" qualification, but, please, let us know if that is not the case.

Glossary with an alphabetical list of particle physics terms is included in the last section of this website.




Xabier Cid Vidal, PhD in experimental Particle Physics for Santiago University (USC). Research Fellow in experimental Particle Physics at CERN from January 2013 to Decembre 2015. He was until 2022 linked to the Department of Particle Physics of the USC as a "Juan de La Cierva", "Ramon y Cajal" fellow (Spanish Postdoctoral Senior Grants), and Associate Professor. Since 2023 is Senior Lecturer in that Department.(ORCID).

Ramon Cid Manzano, until his retirement in 2020 was secondary school Physics Teacher at IES de SAR (Santiago - Spain), and part-time Lecturer (Profesor Asociado) in Faculty of Education at the University of Santiago (Spain). He has a Degree in Physics and in Chemistry, and he is PhD for Santiago University (USC) (ORCID).



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 For the bibliography used when writing this Section please go to the References Section

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