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).

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.

In 2012  protons were running with a beam energy of 4 TeV. At the beginning of 2013, the LHC collided protons with lead ions before going into a long maintenance stop until the end of 2014. Running was resumed in 2015 with increased collision 6,5 TeV per protón and another increase in luminosity. Its maximum total energy of 14 TeV is already very close, and probably it will be probably reached during RUN 3 after the Long Shutdown 2 (LS2) (2019-2020).

One of its main goal has already been reached: 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).

 Another important achievement comes from the LHCb Collaboration, March 2021, which hints a potential Violation of Lepton Flavor 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, should the SM hold. However, LHCb has very recently measured this ratio to be 0.846+0.044-0.041  (then 0.80<RK<0.89 , aprox). This indicates that the decay to electrons is slightly more likely than that to muons. The result deviates with respect to the SM with a statistical significance of ~3 standard deviations, which is not enough to claim a "discovery", but provides "evidence" that the SM might be wrong when describing how leptons behave in nature.

The ratio between muon and electron decays of B+ mesons to a kaon and a pair of leptons as measured by LHCb and other experiments (Babar and Belle). The SM expectation is showed by the dashed line.


More information:



Other important achievements:

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.

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.

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. 

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.

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.

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.

... and to know what is coming see beyond LHC 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 today, 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

The calculations 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.

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. Currently, he is in USC Particle Physics Department ("Ramon y Cajal", Spanish Postdoctoral Senior Grants).

Ramon Cid Manzano, 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 is PhD for Santiago University (USC).



CERN Directory

CERN Experimental Program

Theoretical physics (TH)

CERN Physics Department

CERN Scientific Committees

CERN Structure

CERN and the Environment



Detector CMS

Detector ATLAS

Detector ALICE

Detector LHCb

Detector TOTEM

Detector LHCf

Detector MoEDAL



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

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