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Long-standing discrepancy put to rest

Saturday, July 20th, 2013

This morning at the European Physics Society conference in Stockholm, the LHCb experiment operating at the Large Hadron Collider (LHC) CERN brought one more argument to put to rest a long-standing discrepancy that had kept theorists puzzled for nearly two decades.

LHCb presented the most precise measurement to date of the b baryon lifetime. A baryon is a family of composite particles made of three quarks.  For example, protons and neutrons are made of a combination of u and d quarks.  What makes b baryons so special is that they contain a b quark, a much heavier type of quark. Composite particles containing b quarks like B mesons (made of a b and either a u or d quarks) and b baryons are unstable, meaning they have a short lifetime. About one picosecond after being created, they break down into smaller particles.

In theory, both B mesons and b baryons should have approximately the same lifetime. But in the 1990’s, when CERN operated with its previous accelerator called LEP (Large Electron Positron collider), all experiments measured a systematically shorter lifetime for b baryons than B mesons as can be seen on the plot below. Although the LEP experimental errors were quite large, the general trend of lower values was very puzzling since all four experiments (ALEPH, DELPHI, OPAL and L3) were working independently. Lb_lifetime_comparison

The various b baryon lifetime measurements over time from the oldest results at the bottom to the three latest results from the LHC experiments at the top. The measured value has now shifted toward a value of 1.5 picoseconds, as measured for the B mesons.

This prompted theorists to re-examine their calculations and to look for overlooked effects that could explain the difference. Despite all efforts, it was nearly impossible to reconcile the measured b baryon lifetime (somewhere between 1.1 to 1.3 picosecond) with the B meson lifetime at around 1.5 ps.

Nearly a decade later, D0 and CDF, the two experiments from another accelerator, the Tevatron near Chicago, started closing the gap. It took another decade for the LHC experiments to show that in fact, there is no large difference between b baryon and B meson lifetimes.

Already, earlier this year, ATLAS and CMS both reported values in line with the B meson lifetime. With this latest and most precise result from the LHCb experiment, there is now enough evidence to close the case on this two-decade-old discrepancy. LHCb measured the b baryon lifetime to be 1.482 ± 0.018 ± 0.012 ps. Hence, both lifetimes are now measured close to 1.5 picosecond and LHCb calculated their ratio to be 0.976 ± 0.012 ± 0.006, very close to unity as theoretically expected.

One possible explanation is that all LEP experiments were affected by a common but unknown systematic shift or simply, some statistical fluctuation (i.e. bad luck). The exact cause might never be found but at least, the problem is solved. This is a great achievement for theorists who can now rest assured that their calculations were right after all.

Pauline Gagnon

To be alerted of new postings, follow me on Twitter: @GagnonPauline
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Can the LHC solve the dark matter mystery?

Friday, July 12th, 2013

Last part in a series of four on Dark Matter

After reviewing how dark matter reveals its presence through gravitational effects, the lack of direct evidence of interaction with regular matter and the cosmological evidence supporting its existence, here is what the Large Hadron Collider (LHC) at CERN can do.

We can find dark matter with the LHC but only if dark matter interacts with regular matter. Since we do not know how this may happen, we design traps suited for as many beasts as there are theories. Here are a few.


The current theory describing particle physics is the Standard Model. It has been extremely successful, explaining just about everything observed so far. Unfortunately, at higher energy, its equations start to break down.

This is why theorists developed Supersymmetry (or SUSY), building on the Standard Model and extending it further. What is truly remarkable is that this new theory invented to fix the flaws of the Standard Model predicts the existence of particles with the properties expected from dark matter, hence its great popularity.

All would be perfect except that no one has detected any of the many expected supersymmetric particles. This might simply mean that these particles are heavier than the current LHC reach. We will have more chances of discovering them once the LHC resumes in 2015 at much higher energy.

The lightest supersymmetric particle

In the LHC, protons collide, producing large amounts of energy. Since energy, E, and mass, m, are two forms of the same essence as stated by the famous E = mc2, energy can materialise into new particles.  Heavy particles are unstable and quickly decay into lighter ones.

Some variants of SUSY predict that all supersymmetric particles must decay into other supersymmetric particles. Under this assumption, the lightest SUSY particle cannot decay into anything else and remains stable, not interacting with anything else just like dark matter is expected to be.


A typical decay chain is shown above. A supersymmetric quark decays into another SUSY particle, χ2, and a normal quark, q. At the two subsequent stages, an electron or muon (denoted l+ and l) and lighter SUSY particles are produced. The lightest one, in this case a particle called neutralino χ1, cannot decay into anything else and escapes the detector leaving no signal behind.

Seeing the invisible

An event is a snapshot capturing all lighter particles emitted when an unstable particle decays. And within each event, the energy needs to be balanced. So even when a particle flies across the detector leaving no signal, it can still be detected through the energy imbalance in the event. Invisible particles such as the lightest supersymmetric particles can be detected this way.

Both the CMS and ATLAS collaborations have been looking for events containing large amounts of unbalanced energy accompanying a single photon or a single jet (a jet is a bundle of particles made of quarks).


This figure displays an event from the ATLAS experiment containing a single photon (the energy deposit is shown in yellow around 4 o’clock on the left picture) and the missing energy represented by the pink dashed line around 10 o’clock.

This is exactly what an event containing the lightest supersymmetric particle and a photon would look like. But an event containing a Z boson and a photon would look just the same if the Z boson decayed into two neutrinos (other particles that do not interact with the detector).

Unfortunately, nothing has been observed in any of the channels studied so far that is in excess of what is expected from the background, i.e. other known types of events giving similar signatures.

Unlike the direct dark matter searches, the LHC analyses are sensitive to light dark matter particles. Remember the messy plot I showed about direct searches for dark matter? CMS and ATLAS can help clarify the situation, although their results depend on theoretical assumptions when the direct searches don’t.

Below are the CMS results for a search of events containing a single jet and missing energy.  The horizontal axis gives the mass of the dark matter candidate and the vertical axis, the allowed interaction rate with ordinary matter. Everything above the various lines is excluded. CMS (solid red line) exclude light dark matter particles for large interaction rates, a region inaccessible to XENON100, (solid blue curve) the most powerful experiment for direct dark matter searches.


The Higgs boson and dark matter

Another approach to find dark matter relies on some theories that predict that the Higgs boson could decay into dark matter particles. Higgs bosons can be produced with another boson, such as with a Z boson. If the Higgs boson decays to any type of dark matter, we would only see the decay products of the Z and missing energy for the Higgs boson. Searches for such decays have so far not revealed anything above the expected background level. inv-Higgs

A dark parallel world

A group of theorists developed an amazing Theory of Dark Matter incorporating ideas of a Hidden Valley where two worlds would evolve in parallel: our world with Standard Model and the yet undiscovered supersymmetric particles, and a dark world populated with dark particles as depicted below, where each horizontal line represents a particle of a given mass.


The idea is that the LHC could produce heavy supersymmetric particles. These particles would decay in a cascade into lighter ones down to the lightest SUSY one. That particle would be a “messenger” capable of crossing over the Hidden Valley, escaping into the dark sector and becoming invisible to us.

In the dark sector, this particle could decay in a cascade into lighter dark particles until it reaches the lighest supersymmetric dark particle, another messenger capable of tunnelling back to our world where it would reappear into many pairs of electrons or muons.

This may sound like pure science fiction but it is all rooted in sound, but still unproven, physics as a quick check with the original papers cited above will demonstrate.

I was until recently one of the experimentalists looking for signs of this Hidden Valley, selecting events containing regrouped pairs of electrons and muons but so far, nothing has been found.

Experimentalists are still looking, there and in many other places, constantly refining their searches and trying new strategies. If dark matter interacts with matter, we ought to find it.

First part in a Dark Matter series:        How do we know Dark Matter exists?

Second part in a Dark Matter series:   Getting our hands on dark matter

Third part in a Dark Matter series:      Cosmology and dark matter

Pauline Gagnon

To be alerted of new postings, follow me on Twitter: @GagnonPauline
 or sign-up on this mailing list to receive and e-mail notification.


Cosmology and dark matter

Monday, July 8th, 2013

Third part in a series of four on Dark Matter

I have already reviewed how it reveals its presence through gravitational effects and the lack of direct evidence of interaction with regular matter. Let’s now look how cosmological evidence also supports the existence of dark matter.

Galaxy seeds

It is now widely accepted that all matter (dark and visible) started out being uniformly distributed just after the Big Bang. To make a long story short, a rapid expansion followed where the Universe cooled down and particles slowed down enough to form nuclei three minutes after the Big Bang. The first atoms appeared 300 000 years later while galaxies formed between a hundred and a thousand million years later.


How did the Universe change from being a gigantic cloud of uniformly distributed matter to containing large structures?  Dark matter is probably the one to be blamed.

Dark matter is heavier than regular matter and slowed down earlier. Small quantum fluctuations eventually turned into small lumps of dark matter. These lumps attracted more dark matter under the effect of the gravitational attraction, in a very slow snowball effect. Since dark matter also interacts very weakly, these planted seeds survived well through the stormy moments of the early Universe.

Once matter cooled off as the Universe expanded, it started accumulating on the lumps of dark matter. Hence, dark matter planted the seeds for galaxies. “All this could have happened without dark matter, although it would have taken much more time,” explains Alexandre Arbey, theorist at CERN.

Simulating the formation of the Universe

Not convinced? Nowadays, scientists can reproduce this process using computer simulations. As a starting point, they inject into their models how much matter and dark matter there was right after the Big Bang. The observations of the cosmic microwave background provide these estimates. Then they let it evolve under the attractive effect of gravity and the repulsive effect of the Universe expansion.

All these guesses must converge to reproduce the amount of dark matter leftover today, a quantity called the “relic abundance”. If all is properly tuned, scientists can recreate the whole evolution of the Universe in fast motion from the moment of the Big Bang until today.computer-simulation

The results are striking as can be seen on the three pictures above. These computer-generated images show the distribution of dark matter 470 million years after the Big Bang, then 2.1 and 13.4 billion years later (today). Dark matter first formed small lumps, then long filaments and finally large-scale structures appeared.

Scientists from the French National Centre for Scientific Research (CNRS) just released an amazing video showing how they are now using these mega simulations in the hope to discriminate against different dark matter and dark energy models by comparing these images with current observations.

Cold dark matter

Another way to figure out which theory of dark matter best fits the reality was provided last month by a group of scientists working with the Subaru telescope. They studied the distribution of dark matter in fifty galaxy clusters. Averaging all the data, they found that the dark matter density gradually decreases from the centre of the clusters to their diffuse outskirts.

This new evidence conforms to the predictions of cold dark matter theory (CDM), which states that dark matter is made of slow moving particles. Hot dark matter candidates like neutrinos would be made of particles moving close to the speed of light.


Cold dark matter theory predicts that central regions of galaxy clusters have a lower dark matter density while individual galaxies have a higher concentration parameter.

Unexplained signals from outer space

Astronomers are not just providing clues to the mystery of dark matter but also raising questions.  For example, a decade ago, the INTEGRAL-SPI experiment found an intense gamma ray source at 511 keV coming from the galactic centre, exactly where dark matter is most concentrated. This value of 511 keV is precisely the energy corresponding to the electron or positron mass.


This smelled incredibly like dark matter particles annihilating or decaying into pairs of electron and positron, which in turn can annihilate into gamma rays as depicted on the diagrams above. Unfortunately, nowadays the excitement has somewhat wound down since theorists have a hard time reconciling its characteristics with numerous other observations.

Several satellite experiments (HEAT, PAMELA and FERMI) have observed an excess of positrons in cosmic rays. A positron is the antimatter counterpart of the electron. Given matter prevails over antimatter in the Universe (otherwise, we and the galaxies would not be there), astrophysicists have to figure out where these positrons come from.

Many theorists have attempted to explain this in terms of astronomical phenomena but the jury is still out. Could this be the first concrete sign of dark matter? The AMS experiment on-board the International Space Station has already shown that they have high quality data and could provide a definitive answer very soon.

Dark matter remains a mystery but this field is fast evolving. In my next blog, I will look at what the Large Hadron Collider (LHC) at CERN could do after restart in 2015.

First part in a Dark Matter series:       How do we know Dark Matter exists?

Second part in a Dark Matter series:  Getting our hands on dark matter

Third part in a Dark Matter series:     Cosmology and dark matter

Fourth part in a Dark Matter series:  Can the LHC solve the Dark Matter mystery?

Pauline Gagnon

To be alerted of new postings, follow me on Twitter: @GagnonPauline
 or sign-up on this mailing list to receive and e-mail notification.




Getting our hands on dark matter

Monday, July 1st, 2013

Second part in a series of four on Dark Matter

In a previous blog, I reviewed the many ways dark matter manifests itself through gravitational effects. But to this day, nobody has managed an unambiguous direct observation of dark matter.

This is not surprising given we are talking about a completely different and totally unknown type of matter, something not made of quarks and leptons like all visible matter (humans, planets, stars and galaxies).

Nevertheless, just as the quarks and leptons are the building blocks of visible matter, physicists expect dark matter is also made of fundamental particles, albeit dark particles. So we need to catch dark matter particles interacting in some way with particles of regular matter.

So far, all we know is that dark matter reacts to gravitation but not to electromagnetism since it does not emit any light. Maybe it interacts with ordinary matter through the weak nuclear force, the one responsible for radioactive decays. Dark matter would then be made of weakly interacting particles.

Weakly Interacting Massive Particles

One popular hypothesis is that dark matter particles would be WIMPs, which stands for Weakly Interacting Massive Particles. How often can WIMPs interact with matter? It should be less than 0.1 times per year per kilogram of sensitive material in the detector, depending on the WIMP mass.

The detection principle is simple: once in a while, a WIMP will strike a nucleus in one of the detector’s atoms, which will recoil and induce a small recordable vibration.


From Lauren Hsu’s review talk at ICHEP 2012.

The vertical axis shows the number of times a dark particle transfer a given amount of energy to a nucleus. The more massive the detector and the longer you operate it, the higher are the chances of recording a collision.

The detector material also matters as seen on the plot above: collisions are more energetic, hence easier to detect,  with Germanium (Ge) than with heavier nuclei like Xenon (Xe), but the total number of collisions is higher with the latter material.

These detectors are placed deep in mines or tunnels to block cosmic rays that would induce false signals in the detector. Eliminating all sources of background is the biggest challenge facing these experiments.

Dark matter wind

If the Universe is full of dark matter, we on Earth should feel a wind of dark particles as we travel around the Sun. This rate is evaluated to be of the order of a million particles per square centimetre per second for a WIMP ten times heavier than a proton.

And just like a cyclist riding on a circular track on a windy day, we should feel a head wind of dark matter particles in June and a tail wind in December since there is a greater concentration of dark matter in the centre of the galaxy.



Imagine now a detector operating on Earth and sensitive to WIMPs. The variations in the wind intensity would be detected as an annual modulation in the number of dark matter particles hitting the detector throughout the year.

This is exactly what the DAMA/LIBRA experiment claims to observe for more than a decade now as shown on the plot below. Their signal is loud and clear (8.9 sigma) but unfortunately, refuted by several experiments.

DAMA-LIBRAThe number of events recorded by DAMA/LIBRA as a function of time (more than 10 years) shows a clear annual modulation.

Three other experiments have also reported signals: CoGent sees a faint modulation while both CRESST and CDMS observed a few events in excess of the expected background.

All would be great if these four experiments would all agree on the characteristics of the dark matter particle but that is unfortunately not the case.

Many theorists have deployed heroic efforts to devise new models to explain why some experiments see a signal while others do not, but no model is widely accepted yet. The situation remains terribly confusing as can be appreciated from the plot below.


The vertical axis represents the possible rate at which a dark matter particle could interact with regular matter while the horizontal axis gives the mass of the hypothetical dark particle. The areas in solid colours delimit the possible values obtained by the four experiments having a signal. Only CoGent and CDMS agree.

The lines show the limits placed on the allowed dark matter interaction rate and mass by some of the experiments that reported no signal. All values above those lines are excluded, meaning the null experiments are in direct contradiction with the four groups that reported a signal.

As frustrating as this might seen, it is in fact not surprising given the complexity of these experiments. It could be due to experimental flaws or there might be a theoretical explanation.

Many experiments are collecting more data and new ones are being built. With theorists and experimentalists being hard at work, hopefully there will soon be a breakthrough.

First part in a Dark Matter series:       How do we know Dark Matter exists?

Second part in a Dark Matter series:  Getting our hands on dark matter

Third part in a Dark Matter series:     Cosmology and dark matter

Fourth part in a Dark Matter series:  Can the LHC solve the Dark Matter mystery?

Pauline Gagnon

To be alerted of new postings, follow me on Twitter: @GagnonPauline
 or sign-up on this mailing list to receive and e-mail notification.

Further information:

Hangout with CERN: The Dark Side of the Universe

TED Ed clip: Dark matter: The matter we can’t see

TED talk by Pat Burchat: Shedding light on dark matter



How do we know Dark Matter exists?

Wednesday, June 26th, 2013

First part in a series of four on Dark Matter

Some of you may have heard of dark matter, this mysterious type of matter that no one can see but makes 27% of the content of the Universe while visible matter (you, me, all stars and galaxies) accounts for only 5%. How do we know it really exists? In fact, its existence is confirmed in many different ways.

disk dark matter

Galactic clusters

Fritz Zwicky, a Swiss astronomer, was the first to suspect the existence of dark matter in 1933. He was trying to measure the mass of a galactic cluster (a group of several galaxies) using two different methods. He tried to infer this mass from the speed of the galaxies. Just like kids on a merry-go-round have to hold on to avoid being ejected, galaxies are held together in a spinning galactic cluster by the gravitational force provided by the matter it contains. If there were not enough matter to create this force, the galaxies would simply scatter.

He then compared his result with the mass evaluated from the light the galaxies shed. He realised that there was way more matter in the cluster than what was visible. This matter of an unknown type generated a gravitational field without emitting light. Hence its name, dark matter.

Velocity curves of spinning galaxies

But it was not until the 1970’s that an American astronomer, Vera Rubin, measured the speed of stars in rotating galaxies accurately enough to convince the scientific community. She observed that stars in spinning galaxies were all rotating at roughly the same velocity, no matter their distance to the galactic centre. This is in contradiction with Kepler’s law that describes the rotation of planets around the Sun.

A planet located further from the Sun rotates slower, following the curve labelled A in the graph below. However, Vera Rubin showed instead that stars in a spinning galaxy followed curve B. This was as if the stars were not rotating around the visible centre of the galaxy but around many unknown centres, all providing additional gravitational attraction. This could only happen if huge amounts of invisible matter filled the entire galaxy and beyond.


Gravitational lensing

One striking dark matter detection technique is called “gravitational lensing”.  It is based on the way that large concentrations of matter (visible or dark) create gravitational fields strong enough to distort space.

Imagine a stretched bed sheet where we toss a ping-pong ball. The ball will simply roll following the surface of the sheet. But if you drop some heavy object in the middle of the sheet, the ball will still follow the sheet surface but will now move on a curve.


Light behaves the same way in space. An empty space, void of any matter is just like a stretched sheet. There, light moves in a straight line. In the presence of a massive object such as a star or a galaxy, the space is deformed and light follows the curvature of the distorted space.


(Adapted from Pat Burchat’s TED talk)

Light coming from a distant galaxy will bend when passing near a massive clump of dark matter as shown above. The galaxy will appear shifted, as if coming from different places (images on top and bottom). In three dimensions, all diverted light will form a ring as seen on the photo below taken by the Hubble telescope. In case the galaxy and the observers are not perfectly aligned, only small arcs form.


(Photo credit NASA)

This technique is now powerful enough to produce maps of the dark matter distribution in the Universe.

Cosmic microwave background

Astrophysicists can even infer how much dark matter exists by studying the cosmic microwave background. This is relic radiation dating back to when the Universe was barely 380,000 years old. This fossil light has been travelling around for more than 13 billion years and now reaches us coming from all and no direction in particular.

The map of the Universe below was drawn using data taken by the Planck satellite. It shows hotter spots corresponding to where first dark matter then visible matter started forming lumps, providing the seeds for galaxies. Nowadays, scientists believe dark matter acted as a catalyst in galaxy formation.


(Photo credit Planck experiment)

The microwave background radiation can be decomposed just like sound from a musical instrument can be broken into harmonics. From the features of its “power spectrum”, i.e. the amount of radiation associated to each frequency, astrophysicists can calculate the quantity of dark matter contained in the Universe.

Today, we have numerous and convincing proofs of the presence of dark matter but see it only indirectly through its gravitational effects. How about direct evidence? This will be my next topic. But beware: there’s hot debate in the scientific community on how to interpret the various direct detection results.

Second part in a Dark Matter series:    Getting our hands on dark matter

Third part in a Dark Matter series:       Cosmology and dark matter

Fourth part in a Dark Matter series:    Can the LHC solve the Dark Matter mystery?

Pauline Gagnon

To be alerted of new postings, follow me on Twitter: @GagnonPauline
 or sign-up on this mailing list to receive and e-mail notification.

 For more information:

Hangout with CERN: The Dark Side of the Universe

TED Ed clip: Dark matter: The matter we can’t see

TED talk by Pat Burchat: Shedding light on dark matter



How to find a needle in 78 haystacks?

Friday, June 21st, 2013

The Large Hadron Collider (LHC) started a vast consolidation program in March 2013 that will last well into 2015. Everybody at CERN on the accelerators or the experiments is now working hard to complete all needed tasks in time.

The experimental collaborations are currently deploying huge efforts on many fronts. One major task is preparing to deal with the increased data volume the revamped LHC will bring in 2015.

The LHC will resume at higher energy and luminosity, i.e. more intense beams. For the LHCb experiment, since it operates at constant luminosity, higher energy will translate into more tracks per event and almost twice the signal rate. Same situation for the other experiments, ALICE, CMS and ATLAS, but they will also have higher luminosity, meaning having to cope with more collisions occurring simultaneously every time bunches of protons collide in the LHC, making it increasingly difficult to disentangle each recorded event.


To give you an idea, here are three snapshots captured by the ATLAS detector in successive years. The event on the left was taken at low luminosity at the start of the LHC. Very few collisions happened at the same time yielding very few tracks per event as seen on the picture.

Then in 2011, the average number of simultaneous collisions increased to around 12 (centre) and reached up to 40 by the end of 2012 (right).  In 2015, there will be between 60 and 80 superimposed collisions in each event depending on the operating scheme that will be retained. The challenge will be to extract a collision of interest from the huge quantity of tracks in each event.

Hence, much effort is spent improving the simulation, calibration and reconstruction of such events. Physicists are building on the existing techniques to be able to cope with the expected data volume.


The picture above shows a zoomed view of an event in the centre of the CMS detector where 78 proton-proton collisions took place simultaneously (the bright dots on the horizontal axis). The scale here is a few centimetres.

Here, each track corresponds to a charged particle. And each and every one of these tracks must be associated with only one vertex, namely, the point in space where it was created in a proton collision. This way, only the tracks associated to the main collision point will be retained to reconstruct the event.

In the picture above, most tracks come from collisions where the protons barely grazed each other and can be ignored. Only the energetic collisions have a chance to produce the heavy and rare particles we are interested in.

In parallel, all groups are using the opportunity of the shutdown to replace or repair electronic modules, power supplies and other components that failed or showed signs of deterioration during the past three years. New sub-detectors are even being added to increase the detectors performance. For example, the CMS collaboration is extending its muon detector coverage and the ATLAS experiment is adding a fourth layer on its pixel detector. LHCb is replacing its beam pipe and ALICE is doing major upgrades to its calorimeters.

But the main effort for all LHC experiments is still to finalize all analyses using the full data collected so far. Everyone seems to be following my mother’s advice: We must tirelessly revisit our work until it is perfect. (Cent fois sur le métier, remettez votre ouvrage). This is precisely what is happening right now. Each aspect of the data analysis is revisited to reach the full potential of the current data set: calibration, particle identification, background evaluation and signal extraction.

Every collaboration already has dozens of new results ready for the upcoming major summer conferences such as the European Physics Society meeting in mid-July.

Pauline Gagnon

To be alerted of new postings, follow me on Twitter: @GagnonPauline
 or sign-up on this mailing list to receive and e-mail notification.



Investing in science is worth every penny

Monday, June 10th, 2013

Politicians are faced with hard choices. How should they spend public money? Investing in science is an excellent choice not only for the long-term but also for immediate returns.

Of course, if you are asking what will the Higgs boson put on humanity’s plate, the answer is easy: nobody knows. When the finance minister asked Michael Faraday about the practical value of electricity in 1850, he had an idea, but he replied: “One day sir, you may tax it.”

At least, the discovery of the Higgs boson means that we now have a complete theory to explain how visible matter works. Hence, humanity can go to bed knowing a little more about the Universe we live in.

But there are plenty of indirect returns stemming from all the research activities in particle physics. Many of them have just been summarised in a new brochure called “Accelerating science and innovation – Societal benefits of European research in particle physics”.

The brochure was presented by CERN to European science and technology ministers last week of May in Brussels on the occasion of a special meeting of the CERN Council hosted by the European Commission.

The World Wide Web, invented at CERN more than 20 years ago, is estimated to have stimulated €1.5 trillion in annual commercial traffic. This is 1500 times larger than the billion CHF spent on research annually at CERN.

Around 10,000 accelerators using technology developed for particle physics are now in operation for medical use in hospitals worldwide.

Thanks to physics, X-rays and radiotherapy are used everyday for cancer treatment and medical imaging. Hadron therapy, where protons or carbon ions are used instead of photons as in conventional radiotherapy, is the latest promising technique developed recently and is set to greatly improve therapy for certain types of cancer. Such accelerators developed in collaboration with CERN are already in used by MedAustron in Austria and CNAO in Italy.


The CNAO accelerator used for hadron therapy developed in partnership with CERN provides a more efficient way to kill cancerous cells.

Even antimatter research is put to good use. The ACE experiment performed at CERN’s antimatter facility showed that antiprotons could be powerful in destroying tumours.

Particle physics at CERN has helped produce more efficient solar energy panels and is now developing desk-top accelerators to enable hospitals to produce locally their own single doses of radioactive isotopes as needed.

CERN engineers are testing high temperature superconducting cables of magnesium diboride. This kind of research could lead to electricity being carried over large distances without energy loss.


The solar panels used by the Geneva airport for heating use a technology created to improve the vacuum in CERN accelerators beam pipes.

Accelerator technology is also used for various industrial clean-up projects. In trials in Texas, electron beams have converted highly infectious sewage sludge into safe-to-handle agricultural fertiliser. Efforts are also underway with the n-TOF facility at CERN to transmute highly radioactive nuclear waste into safe materials.

These are but a few of the many applications stemming from research conducted in particle physics facilities. Not to mention training a supply of people ready for technological challenges, stimulating students and teachers interest and igniting enthusiasm for physics all over the world.

So it was great news last week that CERN Council adopted the European Strategy for Particle Physics at its special meeting hosted by the European Commission. The benefits are multiplied when nations pool their efforts and resources in the pursuit of fundamental knowledge.

Pauline Gagnon

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Disability and diversity at work

Friday, May 31st, 2013

National diversity has always been CERN‘s forte. With people coming from 99 different nationalities, CERN is a unique working place. However CERN recently realised that much more could be done to welcome not only people from all over the world but also people of different genders, ages, abilities, sexual orientation and ethnic origin.

This is why the Diversity office was recently created and has already started shaking some old beliefs by organizing a series of special seminars.

This week, CERN welcomed Dr Tom Shakespeare, an outstanding speaker who overcame many barriers. Bearing his surname, he said laughing, was more challenging than suffering from a growth-impairing disease and being paraplegic. But just like his unproven but most likely famous ancestor, Tom has a knack with language and captivated his audience with a lecture on how working places would benefit from being more welcoming to people having all sorts of disabilities, be they physical or mental. His key message was that people are more disabled by society than by their own minds or bodies.



“Disability is an issue of human rights and equality”, he said, “not disease”.  He went on talking about several famous physicists who made great contributions to physics despite having some form of disability. Isaac Newton was a highly anxious and insecure person probably suffering from either autism, Asperger or Tourette syndrome. Albert Einstein’s difficulties in school may have stemmed from dyslexia while Paul Dirac had some form of neurological difference giving him an eccentric and peculiar personality. In particular, he showed a compelling video where Stephen Hawking, one of the most celebrated astrophysicists, talks about his life, explaining how he was able to become so successful despite his disease, and where he gives his full support to the World Report on Disability.

This World Health Organisation report shows that one billion people in the world have some form of disabilities. This means just about 15% of all people have some level of impairment affecting the way they move, talk, hear, see, behave or think. “You might not have any disability now but most of you are at risk of developing one as you age”, Tom told the audience.

He insisted on the importance for a work place to adapt to people’s handicaps, and not the other way around, such as to enable every individual to contribute to their full potential. Neurodiversity can in fact be seen as an opportunity instead of a challenge. People with attention deficit disorder, Asperger syndrome or autism for example can contribute in their own unique ways.

He gave very valuable and simple tips on proper etiquette on how to treat disabled people with respect and dignity: don’t stare; don’t make assumption, just ask; treat the person as a human being and not a disease (like talk about a person who is blind rather than “the blind” or “the quadriplegic”); address the person directly not their parent or carer, and give them a chance to speak for themselves. Finally, ask questions about things you need to know and not just because you are curious.

Pauline Gagnon

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CERN to host its first TEDx

Tuesday, April 23rd, 2013

The first TEDxCERN event will take place on 3 May 2013, under the theme ‘Multiplying Dimensions’, at the Globe of Science and Innovation with a Live Webcast at the CERN Main Auditorium and at the TEDxCERN site. Partner institutes all over the world will be hosting live simulcast and tickets are available for people in the Geneva area interested to attend the event at CERN.

Going beyond particle physics, the event, organized with the support of Rolex, will provide a stage for the expression of science in multiple disciplines, unveiling bold, new insights into emerging research and innovations that may fundamentally shape the course of things to come.

“At TEDxCERN, we are opening the door to a multiverse of scientific disciplines, showcasing the many ways that science is present in all our lives,” said Sergio Bertolucci, Director for Research and Scientific Computing at CERN. With the aim of inspiring young people to become a part of the new generation of scientists, TEDxCERN will also be webcast at participating institutes around the globe. The event will have special hosts, including Nobel laureate George Smoot.

Four short animation movies specially made for the occasion will be presented on that day including this on the origin of the Universe.

TED is a nonprofit organization devoted to Ideas Worth Spreading. Started as a four-day conference in California 26 years ago, TED has grown to support those world-changing ideas with multiple initiatives. At TED, the world’s leading thinkers and doers are asked to give the talk of their lives in 18 minutes. Talks are then made available, free, at TED.com. For example, a talk not to be missed is (my thesis adviser) Pat Burchat’s stunning performance on the nature of dark matter and dark energy.

TEDx is a program of local, self-organized events that bring people together to share a TED-like experience. At a TEDx event, TEDTalks video and live speakers combine to spark deep discussion and connection in a small group. These local, self-organized events are branded TEDx, where x = independently organized TED event. The TED Conference provides general guidance for the TEDx program, but individual TEDx events are self-organized. (Subject to certain rules and regulations.)

The speakers for TEDxCERN range from pioneers to young scientists: Londa Schiebinger, historian, on gendered innovation; Chris Lintott, on how to discover a planet from your sofa; Hiranya Peiris, winner of the 2012 Royal Astronomical Society Fowler Prize, on the early universe; Marc Abrahams, MC of the Ig Nobel Awards and editor of the Annals of Improbable Research, on why all good — and some bad — research is improbable; Eliezer Rabinovici and Zehra Sayers on SESAME, a ground breaking research project in the Middle East that is bringing together Israeli, Jordanian, Palestinian, Turkish, Pakistani, and Iranian scientists; Brittany Wenger, 18-year-old scientist and Grand Prize Winner 2012 Google Science Fair, on Research and Inspiration; Becky Parker, winner of the first RAS Patrick Moore Medal, on why you are never too young to be a research scientist; Gian Giudice, theoretical physicist, on what the current Higgs measurement could mean for the future of the Universe and Alison Lester, an ATLAS physicist, will talk about chasing fundamental particles at CERN.

The full program and the biographies of the speakers can be found on TEDxCERN site.

The organizing team hopes to inspire, encourage, and celebrate scientific thinking through these talks, and above all, convey that science matters to everyone.

Pauline Gagnon

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(Based on CERN press release)



Higgs boson lottery: when CERN plays April Fools jokes

Tuesday, April 9th, 2013

For April first, I wrote that CERN was to give away ten Higgs bosons in a gesture to thank the public for its incredible interest in CERN’s scientific research. About 1500 people eagerly entered the lottery. Most of them wrote very enthusiastic notes, explaining how much they would love one and how much it would mean to them. Many people were not completely fooled but played along just as eagerly.

It was great fun to have a chance to play an April Fools joke that got people all over the world. Entries came from places as diverse as Pakistan, Rwanda, Finland, Canada, Australia, China and Portugal. This shows the incredible interest the Higgs boson has generated on all continents.

I used a random number generator to select the winners who are from Mexico, UK, USA, Belarus (3), Russia (3), Kazakhstan and The Netherlands. Nearly half the entries came from Belarus or Russia, where a popular news agency ran the story. People fell for it even though as everyone knows: “Первого апреля никому не верю!” (On April first, do not trust anyone).

Even some physics students fell for it, so strong was their desire to get their own Higgs boson. Granted, using CERN’s fame is cheating a bit, giving any claim a lot of clout. But many played along: one tried to bribe me with a magnetic monopole, while another promised to feed it only the best particles. Another woman said she already had lots of antimatter and would know how to properly care for a Higgs boson. One physics student said that given the short lifetime of a Higgs boson, he might end up with just two W or Z bosons. One person expressed how great it was for CERN to share. Some asked for a Higgs bosun, bozzon or bison. A guy told me how much this would help him win his girlfriend’s heart as he was about to propose to her. A very disappointed student replied physicists were cruel when he realized it was a joke. But I hope he changed his mind when he found out he was one of the 10 lucky winners.

Custom-made Higgs bosons recently escaped from the Particle Zoo and are on their way to their new home, where all the winners said they would warmly welcome them.

Pauline Gagnon

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