Particle physicist Fabiola Gianotti has become the first woman to head CERN, the organization based in Switzerland that is home to the Large Hadron Collider. She succeeds outgoing director-general Rolf Heuer, who oversaw the laboratory’s operations for the last seven years.
Previously, Gianotti headed the ATLAS collaboration, one of two teams responsible for the discovery of the elusive Higgs boson on July 4, 2012. She quickly became a favorite figure in the media coverage surrounding that achievement — partly because of her gender (only 20% of the ATLAS team were women), and for her elegantly understated style, but also for her good humor.
For instance: Her use of the much-derided Comic-Sans typeface on her Powerpoint slides during that historic announcement was the source of much Internet amusement. Gianotti took the ribbing in stride. She even made an April Fool’s Day decree to make Comic Sans the official document typeface for all of CERN. She was a runner-up for Time magazine’s Person of the Year in 2012.
Gianotti’s father is a retired geologist, while her mother had a passion for music and art. Their daughter, born in 1962, effortlessly straddles both cultural realms, excelling not just in physics, but also music, cooking, and even dance (she trained as a ballerina as a child). “Musical harmony is based on physical principles while in cooking, ingredients must be weighed out with precision,” she told the Guardian in 2014, when her selection as the next director-general of CERN was announced. “At the same time, you have to able to invent, because if one follows the same recipe all the time, you never create anything new.”
Geneva, 14 July 2015. Today, the LHCb experiment at CERN’s Large Hadron Collider has reported the discovery of a class of particles known as pentaquarks. The collaboration has submitted a paper reporting these findings to the journal Physical Review Letters.
“The pentaquark is not just any new particle,” said LHCb spokesperson Guy Wilkinson. “It represents a way to aggregate quarks, namely the fundamental constituents of ordinary protons and neutrons, in a pattern that has never been observed before in over fifty years of experimental searches. Studying its properties may allow us to understand better how ordinary matter, the protons and neutrons from which we’re all made, is constituted.”
Our understanding of the structure of matter was revolutionized in 1964 when American physicist, Murray Gell-Mann, proposed that a category of particles known as baryons, which includes protons and neutrons, are comprised of three fractionally charged objects called quarks, and that another category, mesons, are formed of quark-antiquark pairs. Gell-Mann was awarded the Nobel Prize in physics for this work in 1969. This quark model also allows the existence of other quark composite states, such as pentaquarks composed of four quarks and an antiquark. Until now, however, no conclusive evidence for pentaquarks had been seen.
LHCb researchers looked for pentaquark states by examining the decay of a baryon known as Λb (Lambda b) into three other particles,
a J/ψ- (J-psi),
a proton and
a charged kaon.
Studying the spectrum of masses of the J/ψ and the proton revealed that intermediate states were sometimes involved in their production. These have been named Pc(4450)+ and Pc(4380)+, the former being clearly visible as a peak in the data, with the latter being required to describe the data fully.
“Benefitting from the large data set provided by the LHC, and the excellent precision of our detector, we have examined all possibilities for these signals, and conclude that they can only be explained by pentaquark states”, says LHCb physicist Tomasz Skwarnicki of Syracuse University.
"More precisely the states must be formed of
two up quarks,
one down quark,
one charm quark and
one anti-charm quark.”
Earlier experiments that have searched for pentaquarks have proved inconclusive. Where the LHCb experiment differs is that it has been able to look for pentaquarks from many perspectives, with all pointing to the same conclusion. It’s as if the previous searches were looking for silhouettes in the dark, whereas LHCb conducted the search with the lights on, and from all angles. The next step in the analysis will be to study how the quarks are bound together within the pentaquarks.
“The quarks could be tightly bound,” said LHCb physicist Liming Zhang of Tsinghua University, “or they could be loosely bound in a sort of meson-baryon molecule, in which the meson and baryon feel a residual strong force similar to the one binding protons and neutrons to form nuclei.”
More studies will be needed to distinguish between these possibilities, and to see what else pentaquarks can teach us. The new data that LHCb will collect in LHC run 2 will allow progress to be made on these questions.
1. CERN, the European Organization for Nuclear Research, is the world's leading laboratory for particle physics. It has its headquarters in Geneva. At present, its member states are Austria, Belgium, Bulgaria, the Czech Republic, Denmark, Finland, France, Germany, Greece, Hungary, Israel, Italy, the Netherlands, Norway, Poland, Portugal, Slovakia, Spain, Sweden, Switzerland and the United Kingdom. Romania is a Candidate for Accession. Serbia is an Associate Member in the pre-stage to Membership. Turkey is an Associate Member. India, Japan, the Russian Federation, the United States of America, the European Union, JINR and UNESCO have observer status.
In this Sept. 10, 2008 file photo, European Center for Nuclear Research (CERN) scientists control computer screens showing traces on Atlas experiment of the first protons injected in the Large Hadron Collider (LHC) during its switch on operation in CERN's control room, near Geneva, Switzerland.
The recent identification of a long-theorized particle provides strong evidence of a new form of matter.
Scientists working on the Large Hadron Collider, the most powerful particle collider in the world, verified the existence of a particle called Z(4430) last week, according to New Scientist. Previously, physicists had reasoned that the particle could exist but had yet to observe it.
Discovery of any new particle is an important step for scientists, but Z(4430) is viewed with particular importance — it is evidence of a new type of matter called a tetraquark.
Quarks are among the most basic building blocks of matter. Combinations of different types of quarks produce protons and neutrons. Although quarks typically bind together in groups of two or three, scientists had theorized that four quarks could be combined to form a different type of matter: the tetraquark.
"With the existence of tetraquarks, it is possible for neutrons within the core to interact strongly enough to create tetraquarks. This could even lead to the production of pentaquarks and hexaquarks, or even that quarks could interact individually without being bound into color neutral particles. This would produce a hypothetical object known as a quark star."
GOOGLE NOW OFFERS YOU A PEEP INTO THE MACHINE THAT'S PROBING THE SECRETS OF THE BIG BANG AND HOW THE UNIVERSE WORKS. IT'S COLORFUL!
You may think Google's engineers are smart, but they're rather outclassed by the small town's worth of physicists, engineers, and mathematicians who populate CERN, Europe's amazing research facility that's home to the Large Hadron Collider. Now CERN has graciously opened its doors to Google's Street View. This means that you, too can take a walk around the rooms and structures where scientists are trying to unravel the secrets of everything.
CERN is enormous, so it took the Street View team about two weeks to image the whole thing back in 2011. The image archives are extensive as a result, letting you walk around the curving tunnels that contain the particle accelerator at the heart of the LHC and even to peep at the various experiments inserted in its beam, including the ones used to find the Higgs boson.
CERN - Large Hadron Collider tunnel. Photo: Google
It's the sort of facility that you will find fascinating--your writer has long dreamed of visiting, having been lucky enough to spend hundreds of hours strolling around a mere 100-meter synchrotron, a small toy compared to the LHC. Once you've enjoyed peeping at CERN, why don't you do a little reading about what goes on there?
Candidate events in the CMS SM Higgs Search. CMS, 13 May 2012, 21.08. A typical candidate event including two high-energy photons.
HIG-13-002 Event 1: Event recorded with the CMS detector in 2012 at a proton-proton centre-of-mass energy of 8TeV. The event shows characteristics expected from the decay of the SM Higgs boson to a pair of Z bosons, one of which subsequently decays to a pair of electrons (green lines and green towers) and the other Z decays to a pair of muons (red lines). The event could also be due to known Standard Model background processes. Image 1 of 16. HIG-13-002 Event 1: Event recorded with the CMS detector in 2012 at a proton-proton centre-of-mass energy of 8 TeV. The event shows characteristics expected from the decay of the SM Higgs boson to a pair of Z bosons, one of which subsequently decays to a pair of electrons (green lines and green towers) and the other Z decays to a pair of muons (red lines). The event could also be due to known Standard Model background processes. Image: CERN, CMS
Geneva, 14 March 2013. At the Moriond Conference today, the ATLAS and CMS collaborations at CERN1’s Large Hadron Collider (LHC) presented preliminary new results that further elucidate the particle discovered last year. Having analysed two and a half times more data than was available for the discovery announcement in July, they find that the new particle is looking more and more like a Higgs boson, the particle linked to the mechanism that gives mass to elementary particles. It remains an open question, however, whether this is the Higgs boson of the Standard Model of particle physics, or possibly the lightest of several bosons predicted in some theories that go beyond the Standard Model. Finding the answer to this question will take time.
Whether or not it is a Higgs boson is demonstrated by how it interacts with other particles, and its quantum properties. For example, a Higgs boson is postulated to have no spin, and in the Standard Model its parity – a measure of how its mirror image behaves – should be positive. CMS and ATLAS have compared a number of options for the spin-parity of this particle, and these all prefer no spin and positive parity. This, coupled with the measured interactions of the new particle with other particles, strongly indicates that it is a Higgs boson.
“The preliminary results with the full 2012 data set are magnificent and to me it is clear that we are dealing with a Higgs boson though we still have a long way to go to know what kind of Higgs boson it is.” said CMS spokesperson Joe Incandela.
"The beautiful new results represent a huge effort by many dedicated people. They point to the new particle having the spin-parity of a Higgs boson as in the Standard Model. We are now well started on the measurement programme in the Higgs sector," said ATLAS spokesperson Dave Charlton.
Image 4 of 16. HIG-13-004 Event 1: Event recorded with the CMS detector in 2012 at a proton-proton centre-of-mass energy of 8 TeV. The event shows characteristics expected from the decay of the SM Higgs boson to a pair of τ leptons. Such an event is characterised by the production of two forward-going jets, seen here in opposite endcaps. One of the τs decays to a muon (red lines on the right) and neutrinos, while the other τ decays into a charged hadron and a neutrino
To determine if this is the Standard Model Higgs boson, the collaborations have, for example, to measure precisely the rate at which the boson decays into other particles and compare the results to the predictions. The detection of the boson is a very rare event - it takes around 1 trillion (1012) proton-proton collisions for each observed event. To characterize all of the decay modes will require much more data from the LHC.
Footnote(s):
1. CERN, the European Organization for Nuclear Research, is the world's leading laboratory for particle physics. It has its headquarters in Geneva. At present, its member states are Austria, Belgium, Bulgaria, the Czech Republic, Denmark, Finland, France, Germany, Greece, Hungary, Italy, the Netherlands, Norway, Poland, Portugal, Slovakia, Spain, Sweden, Switzerland and the United Kingdom. Romania is a candidate for accession. Cyprus, Israel and Serbia are associate members in the pre-stage to membership. India, Japan, the Russian Federation, the United States of America, Turkey, the European Commission and UNESCO have observer status.
A proton collides with a lead nucleus, sending a shower of particles through the CMS detector.
CREDIT: CERN
Collisions between particles inside the Large Hadron Collider atom smasher have created what looks like a new form of matter.
The new kind of matter is called color-glass condensate, and is a liquidlike wave of gluons, which are elementary particles related to the strong force that sticks quarks together inside protons and neutrons (hence they are like "glue").
Scientists didn't expect this kind of matter would result from the type of particle collisions going on at the Large Hadron Collider at the time. However, it may explain some odd behavior seen inside the machine, which is a giant loop where particles race around underneath Switzerland and France.
When scientists sped up protons (one of the building blocks of atoms) and lead ions (lead atoms, which contain 82 protons each, stripped of their electrons), and crashed them into each other, the resulting explosions liquefied those particles and gave rise to new particles in their wake. Most of these new particles, as expected, fly off in all directions at close to the speed of light. [Photos: The World's Largest Atom Smasher (LHC)]
But recently scientists noticed that some pairs of particles were flying off from the collision point in correlated directions.
"Somehow they fly at the same direction even though it's not clear how they can communicate their direction with one another. That has surprised many people, including us," MIT physicist Gunther Roland, whose group led the analysis of the collision data along with Wei Li of Rice University, said in a statement.
A similar flight pattern is seen when two heavy particles, such as lead and lead, crash into each other. In this case, the collisions create what's called quark-gluon plasma — a superhot soup of particles similar to the state of the universe just after the Big Bang. This soup can sweep particles in the same direction, explaining why their flight directions would be correlated.
But quark-gluon plasma isn't possible with lead-proton collisions, like the ones in the new study. Now researchers think a different state of matter, the color-glass condensate, may act in a similar way. The color-glass condensate's dense swarm of gluons may also sweep particles off in the same direction, suggested Brookhaven National Laboratory physicist Raju Venugopalan, who first predicted the substance, which may also be seen after proton-proton collisions.
The mechanism may depend on a weird quirk of particles called quantum entanglement. Two particles can be entangled so that they retain a connection even after they are separated, and an action on one reverberates on the other.
Entangled gluons in the color-glass condensate could explain how particles flying away from the collision point might share information about their flight direction with each other, Venugopalan said.
The intriguing phenomenon was not expected to result from the LHC's run of proton-lead collisions, which was meant to serve as a reference point for comparison to other types of collisions.
"You don't expect quark-gluon plasma effects" with lead-proton collisions, Rolandsaid. "It was supposed to be sort of a reference run — a run in which you can study background effects and then subtract them from the effects that you see in lead-lead collisions.
The findings will be detailed in an upcoming issue of the journal Physical Review B.
For a report on ABC's Catalyst program (http://www.abc.net.au/catalyst/), I visited the Large Hadron Collider in Switzerland to find out what is being done now that the Higgs Boson has been discovered.
Although its mass has been measured around 125-126 GeV most of the other properties of the particle remain unknown. Its spin appears to be 0 or 2 but more results are required to nail this down. If it is the standard model Higgs, the spin should be 0, resulting in a fairly symmetric distribution of decay products in the detectors.
We may know this year if it's not the standard model Higgs - this would be the case if it doesn't decay into specific particles with the expected frequency. However if it is the standard model Higgs, it may take many more years to be certain. The large hadron collider will be shut down in 2013 for upgrades so that higher energies up to 14 TeV can be tested. Right now the LHC is operating at 8 TeV. The next announcement is expected in December.
LHC data confirm discovery, but not identity, of Higgs-like entity.
The ATLAS detector (above) and its rival CMS have both seen a clear signal of a new, Higgs-like particle. CLAUDIA MARCELLONI/CERN
Physicists in Europe will present evidence of an entirely new particle on Wednesday,Nature has learned. But more data will be needed to officially confirm whether it is indeed the long-awaited Higgs boson — the particle thought to be behind the mass of all the others.
Even as rumours fly in the popular media, physicists have begun quietly cheering at CERN, the European particle-physics lab near Geneva in Switzerland. “Without a doubt, we have a discovery,” says one member of the team working on the ATLAS experiment, who wished to remain anonymous. “It is pure elation!”
For nearly half a century, physicists have predicted the existence of a particle that helps to endow others with mass. Named after theoretical physicist Peter Higgs, the boson is the upshot of a mathematical trick that unites the electromagnetic and weak nuclear forces into a single ‘electroweak’ interaction. It is considered the final, crucial piece of the standard model of particle physics.
Physicists working on ATLAS saw hints of a Higgs particle last year (see: 'Detectors home in on Higgs boson' ), but the first solid results from the full 2012 data set arrived last week. The signal was seen in the decay of a Higgs-like particle into two high-energy photons — one of the cleanest ways to glimpse a Higgs among the hundreds of trillions proton–proton collisions recorded in the Large Hadron Collider (LHC). The data contained “a significant excess" of collision events at a mass of around 125 gigaelectronvolts, the ATLAS researcher told Nature, which is the same value suggested by last year's data. The same signal is present in other Higgs decay channels, too, such as those in which the new Higgs-like particle decays into four leptons.
ATLAS's chief rival, the CMS experiment, also sees significant Higgs evidence in its 2012 data, according to a physicist there, who asked not to be named because both ATLAS and CMS have strict embargoes in place. “In practice you would have to be monstrously sceptical not to be convinced by what we have now,” the source says. "But the final decisions on what to say on Wednesday are still being made."
Weighing in
Physicists have maintained that they will not announce the discovery of the Higgs until the signal surpasses 5 sigma, meaning that it has just a 0.00006% chance of being wrong. The ATLAS and CMS experiments are each seeing signals between 4.5 and 5 sigma, just a whisker away from a solid discovery claim. The results are also consistent with an analysis from the mothballed Tevatron collider, which was presented today at Fermilab in Batavia, Illinois.
CERN's head of communications, James Gillies, confirmed that four of the theorists who dreamt up the Higgs mechanism in the 1960s — François Englert, Carl Hagen, Peter Higgs and Gerald Guralnik — will be present at Wednesday's seminar, but he declined to be drawn on what will be announced. "Things are still evolving here," he says. "Until the spokespersons of the ATLAS and CMS collaborations stand up in front of the audience, it's premature to speculate."
Physicists will now turn their attention to understanding the new particle. Crucially, they will want to know whether it behaves like a mass-giving Higgs, and more specifically whether it behaves like the Higgs predicted in the standard model. One important task will be to carefully measure the different ways that the particle is produced and decays inside the LHC detectors. The rates could be altered by the existence of exotic new particles not predicted by the standard model that would interfere with the underlying quantum mechanical behaviour.
“Fine, there is something there — a resonance," says Martinus Veltman, emeritus professor at the University of Michigan in Ann Arbor, who shared the 1999 Nobel Prize in Physics for his work on the standard model. “Now we have to find out if it has all the properties that the Higgs is supposed to have.”Nature doi:10.1038/nature.2012.10932
In this Sept. 10, 2008 file photo, European Center for Nuclear Research (CERN) scientists control computer screens showing traces on Atlas experiment of the first protons injected in the Large Hadron Collider (LHC) during its switch on operation in CERN's control room, near Geneva, Switzerland.
