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, and, to a lesser extent, to primary school pupils and teachers. 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.

Through several sections and many sub-sections (CERN, LHC, PHYSICS at the LHC, Detectors, Standard Model, Education, Links, News ... ) we approach the contents that we believe should be known by non-specialists who are interested in Particle Physics, CERN and the LHC.

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.

We also present below the most recent news on particle physics produced at CERN. In the News section  section you will find news from previous years.

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 the authors of this website, have been taken as "fair use" qualification, but, please, let us know if that is not the case, and they will be removed immediately.

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.

In the Referencias Section you can find many articles and books dealing with different aspects of Particle Physics, CERN and the LHC. In addition, in this other Section you can consult the articles that the authors of this website have published on these issues with an essentially outreaching intention.

We also present below the most recent news on particle physics produced at CERN. In the More News  section you will find news from previous years.ite.


 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:



R E C E N T   N E W S

IGFAE and CERN join together in ‘Instruments of Vision’, an exhibition by artist Armin Linke.

June-August 2024

From 21 June to 28 August 2024, the IGFAE presents the exhibition Instruments of Vision by the artist Armin Linke. The project is the result of the IGFAE's collaboration with Arts at CERN, on the occasion of the IGFAE's 25th anniversary and the 70th anniversary of the founding of CERN.

More here...

ATLAS releases 65 TB of open data for research.

July, 2024

The ATLAS Experiment at CERN has made two years’ worth of scientific data available to the public for research purposes. The data include recordings of proton–proton collisions from the Large Hadron Collider (LHC) at a collision energy of 13 TeV. This is the first time that ATLAS has released data on this scale, and it marks a significant milestone in terms of public access and utilisation of LHC data.

More here...

The rarest hyperon decay ever observed.

July, 2024

The LHCb collaboration reported the observation of the hyperon Σ+→pμ+μ- rare decay. A hyperon is a particle containing three quarks including one or more strange quarks.

Rare decays of known particles are a promising tool for searching for physics beyond the Standard Model (SM) of particle physics. In the SM, the Σ+→pμ+μ- process is only possible through “loop diagrams”: rather than the decay happening directly, intermediate states need to be exchanged in a “loop”.

 A Feynman diagram illustrating the Σ+→pμ+μ- decay in the Standard Model

In quantum field theory, the probability of such a process occurring is the sum of the probabilities of all possible particles exchanged in this loop, both known and unknown. This is what makes such a process sensitive to new phenomena. If a discrepancy between the experimental measurement and theoretical calculations was observed, it could be caused by a contribution from some unknown particles. These particles could either be exchanged in the loop or mediate this decay directly, interacting with the quarks and then decaying into a pair of muons. In the latter case the new particle would leave a footprint in the properties of the two muons.

More here...

“Spooky action at a distance” between the heaviest particles.

June, 2024

In a new measurement, the CMS collaboration examines, for the first time, the spin entanglement of a top quark and a top antiquark that are simultaneously produced at a very high speed with respect to each other. The two particles are therefore far apart before decaying, i.e., their distance is larger than what can be covered by information transferred at the speed of light. The correlation between the spins of the quark and of the antiquark is measured by looking at the angular distributions of their decay products.


Confirming the quantum entanglement between the heaviest fundamental particles, the top quarks, has opened up a new avenue to explore the quantum nature of our world at energies far beyond what is accessible, e.g., in quantum optics. The large production rate of top quark pairs at the LHC provides a gigantic data sample of top quarks, offering a unique opportunity for these studies.

Taken from CMS Collaboration

More here...

 Accelerator Report: Already a fifth of the way there.

15 May, 2024 (by Rende Steerenberg)

The whole CERN accelerator complex and its associated experimental facilities have been fully operational for some time now, so the time is ripe to review the first part of this year’s run and look forward to what is still to come.

At the LHC, first collisions with just a few bunches occurred on 6 April. Meaningful physics data taking can only begin when collisions take place with at least 1200 bunches per beam, and this milestone was reached on 14 April. It means that, out of the 147 days allocated to proton-proton collisions this year, 32 have already been completed, representing just over 20% of the 2024 proton run.

During these initial 32 days, the LHC machine was available 67.2% of the time with stable beams in collision 45.2% of the time. The goal is to achieve a stable beam time ratio of at least 50%.

Luminosity production is also progressing according to schedule, as can be seen in the graph below.

So far, the integrated luminosity collected has reached 17.5 fb-1, which is nearly 20% of the 2024 target of 90 fb-1. To reach this target, is needed an average of about 0.8 fb-1 per day. Recently it has seen a record production of 1.23 fb-1 in just 24 hours, which demonstrates the LHC’s impressive potential to meet and possibly even exceed the target.

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.

Measurement of the W-boson mass and width (Γ𝑊) with the ATLAS detector.

April 2024.

Proton-proton data recorded by the ATLAS detector in 2011, at a centre-of-mass energy of 7 TeV, have been used for an improved determination of the W-boson mass and a first measurement of the W-boson width at the LHC.

A particle's width is directly related to its lifetime and describes how it decays to other particles. If the W boson decays in unexpected ways, such as into yet-to-be-discovered new particles, these will influence the measured width.

Using proton-proton collision data at an energy of 7 TeV collected during Run 1 of the LHC, ATLAS measured the W-boson width as 2202 ± 47 MeV. This is the most precise measurement to date made by a single experiment, and—while a bit larger—it is consistent with the Standard-Model prediction to within 2.5 standard deviations .

The updated measurement of the W-boson mass is 80367 ± 16 MeV, which improves on and supersedes the previous ATLAS measurement using the same dataset. The measured values of both the mass and the width are consistent with the Standard-Model predictions.

More here...

LHCb collab: Measurement of D0− D0 mixing and CP violation in D0➝ K+π− decays.

March, 2024

At a seminar held March 26 at CERN, the LHCb collaboration at the Large Hadron Collider (LHC) presented the results of its latest search for matter–antimatter asymmetry in the oscillation of the neutral D meson, which, if found, could help shed light on the mysterious matter–antimatter imbalance in the universe.

D0 mesons oscillations are identified as small changes in the flavour mixture (matter or antimatter) of the D0 mesons as a function of the time at which they decay. The Kπ decay, reported today, is one of the best channels to study this mixing

The results are consistent with previous studies, confirming the matter–antimatter oscillation of the neutral D meson and showing no evidence of CP violation in the oscillation. The findings call for future analyses of this and other decays of the neutral D meson using data from the third run of the LHC and its planned upgrade, the High-Luminosity LHC.

More here...


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.

More news...

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

Fabiola Gianotti, CERN Director General.

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 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 documents or websites which give simple description of Particle PhysicsFor exampleAn Introduction To Particle Physics or A brief introduction to Particle Physics or other ones that you can find in the section Education of this website. Please note that some of these documents or websites are not up to date, but we believe that they still provide good information to get started in particle physics.

We insist that 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 the authors of this website, have been taken as "fair use" qualification, but, please, let us know if that is not the case, and they will be removed immediately.


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 a Degree 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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