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The LHC as a photon collider | CMS Experiment

The LHC as a photon collider | CMS Experiment | Tout est relatant | Scoop.it
The Large Hadron Collider is known for smashing together protons. The energy from these collisions gets converted into matter, producing new particles that allow us to explore the nature of our Universe. The protons are not fired at one another individually; instead, they are circulated in bunches inside the LHC, each bunch containing some 100 billion (100,000,000,000) particles. When two bunches cross each other in the centre of CMS, a few of the protons — around 25 or so — will collide with one another. The rest of the protons continue flying through the LHC unimpeded until the next time two bunches cross.

Sometimes, something very different happens. As they fly through the LHC, the accelerating protons radiate photons, the quanta of light. If two protons going in opposite directions fly very close to one another within CMS, photons radiated from each can collide together and produce new particles, just as in proton collisions. The two parent protons remain completely intact but recoil as a result of this photon-photon interaction: they get slightly deflected from their original paths but continue circulating in the LHC. We can determine whether the photon interactions took place by identifying these deflected protons, thus effectively treating the LHC as a photon collider and adding a new probe to our toolkit for exploring fundamental physics.

This kind of proton-tagging has not been possible at the LHC so far. But a new project called the CMS-TOTEM Precision Proton Spectrometer (CTPPS) will soon enable us to study these rare collisions. The project brings together the CMS and TOTEM collaborations, which had previously worked together during the proton-lead collisions of 2013. The CTPPS will be located on either side of CMS, 200 metres away from the interaction point at the centre of the detector.
The physics case for studying photon collisions

The physics of photon collisions has been a topic of some interest for many decades. Indeed, a special meeting in 1978 discussed the prospects of such collisions at LEP, the LHC’s predecessor, which collided electrons with positrons from 1989 until 2000.

“These collisions are very clean as we’re colliding photons, which are elementary particles and not composite ones like protons,” notes Joao Varela, former Deputy Spokesperson for CMS, who is heading the CTPPS project. “It was first proposed to do this type of physics at the LHC with CMS many years ago but the project didn’t materialise then.”

One objective of the CTPPS project is to enable CMS to study quartic gauge couplings. These are interactions where the two photons annihilate upon collision to produce two W bosons: one gets four gauge bosons at the same vertex (see Feynman diagram above). “With the CTPPS, CMS can study whether the distributions and production rates of these interactions are compatible with the Standard Model or not with two orders of magnitude better sensitivity than before,” says Varela.

By locating the CTPPS at 200 metres away from the collision point, it is possible to study a mass region above 200 GeV. If there are new particles with these high masses, the CTPPS also improves CMS’s discovery potential. Varela adds, “Recently, there were two proposals in CMS and one in TOTEM to build such a spectrometer, and we put them together into a single project.”
Design and operation of the spectrometer

The CTPPS relies on objects called “Roman Pots”, which are TOTEM’s speciality. They are cylinders that allow one to move small detectors into the vacuum of the LHC in such a way that there are detectors inside the beam pipe a mere 2 mm from the beam. The tracking detectors of the CTPPS are quite small, with a surface area of 2 cm2. There will be two stations located 10 metres apart on either side of the collision point. Six planes of silicon pixels on each station will detect the track of the flying protons to give direction information. The magnetic field of the LHC’s quadrupoles will serve as the field for the CTPPS.

Once the CTPPS tags deviated protons involved in photon interactions, the CMS detector will collect the data from the collisions themselves, with information about the tagged protons embedded in the same dataset.

The Roman Pots of TOTEM are designed to operate under special LHC runs with a small number of collisions per second. The physics goals of the CTPPS will require the Roman Pots to operate during normal CMS data taking, with the LHC providing an even higher number of collisions per second from 2015 onwards. Before collecting data for physics analyses, the CMS and TOTEM teams will need to demonstrate that this operation is possible and that the CTPPS detectors can be brought very close to the beam without disrupting the beam in the process.

“One of the reasons I joined this project,” says Varela, “is to have the possibility of having detector development in a time scale that is in my lifetime. The LHC Phase 1 work is mostly done, while the Phase 2 R&D is for longer-term projects. With the CTPPS, we can make small prototypes and put them in the LHC, and start collecting data relatively quickly.”

The CMS-TOTEM Precision Proton Spectrometer will go into production in 2016.
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Ferney-Voltaire | Cern : la maintenance du LHC va profiter à l’emploi local

Ferney-Voltaire | Cern : la maintenance du LHC va profiter à l’emploi local | Tout est relatant | Scoop.it

À 7h24 exactement, jeudi 14 février, le LHC, plus grand accélérateur de particules du monde, est entré en sommeil. Un arrêt de maintenance normal pour le Centre européen de Recherche nucléaire (Cern) après trois années d’exploitation, qui ont vu la découverte du Boson de Higgs au mois de juillet dernier.

« En fait, l’arrêt aurait même dû intervenir plus tôt. Mais nous avons préféré obtenir le plus de données possibles » explique Frédérick Brodry, chef du département “technologies”. La coupure devrait durer 22 mois, le temps de rattraper les maintenances qui étaient faites chaque année avec le précédent accélérateur. « Cela prend trop de temps de refroidir et réchauffer le LHC. Nous préférons donc les espacer aujourd’hui. »

Après quelques milliards de collisions à la quasi-vitesse de la lumière, les particules élémentaires ont bien mérité ce repos. Mais ce seront bien les seules à ne plus travailler ! Si les physiciens vont continuer à plancher sur les données accumulées, les équipes vont réaliser l’entretien du LHC, l’accélérateur de particules géant. Un chantier impressionnant, même s’il n’y aura pas de transports spectaculaires d’aimants de 15 mètres et 35 tonnes comme il y a pu en avoir au moment de la construction.

1 600 personnes travailleront sur le site

En revanche, il va offrir quantité d’emplois, notamment localement. « Au pic du chantier, à partir de juillet, il y aura environ 1 600 personnes qui travailleront sur la maintenance du LHC, en comptant les 800 habituels du Cern » explique Frédérick Brodry, chef du département “technologies”. Et si cela réclame quelques spécialités plutôt rares dans nos contrées, comme tout ce qui touche la cryogénie (le LHC possède certains équipements qui flirtent avec le zéro absolu, soit -272 degrés !), d’autres au contraire vont fournir du travail localement.

Pour cette grande maintenance, le centre de recherche a en effet besoin de soudeurs, d’électriciens ou encore de logisticiens. Dans l’Ain, les partenaires de l’emploi y ont tout de suite vu une aubaine et ont lancé des politiques de formation à destination des demandeurs d’emploi locaux, notamment ceux qui ont de l’expérience dans l’industrie bellegardienne ou oyonnaxienne. Les agences d’intérim de Haute-Savoie et de l’Ain sont également sur le coup, ainsi que les sous-traitants habituels (Spie, Cégélec, Inéo…), qui vont augmenter leurs effectifs. Un problème : le logement

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Comment déterminer si un objet existe, sans le voir : Boson-spotter’s guide helps you decode the Higgs

Comment déterminer si un objet existe, sans le voir : Boson-spotter’s guide helps you decode the Higgs | Tout est relatant | Scoop.it
The elusive Higgs boson, or something very close, has finally been spotted at CERN’s Large Hadron Collider near Geneva, Switzerland. The next challenge is to pin down whether the new particle...
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Matière noire: pas de modèle, que des hypothèses...

Matière noire: pas de modèle, que des hypothèses... | Tout est relatant | Scoop.it

Lors de la dernière journée de la Conférence Internationale sur la Physique des Hautes Energies, on a fait le point sur la matière noire. Comme plusieurs d’entre vous le savent, nous sommes tous: nous-mêmes, la terre, les étoiles et les galaxies faits d’atomes. Ces atomes émettent de la lumière lorsqu’ils sont excités, ce qui permet aux astronomes d’étudier l’univers. Mais toute cette matière ne compte que pour 4% du contenu total de l’univers alors que la matière noire en fait 22%. Les 74% restant viennent d’énergie d’un type inconnu surnommée « énergie noire. »

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Le côté obscur de la matière noire

Le côté obscur de la matière noire | Tout est relatant | Scoop.it
Un astronome argumente un dossier noir de la physique en traitant d’arnaques et d’impostures la matière noire et l’énergie noire, deux des piliers de l’explication actuelle du fonctionnement de l’univers.

 

L’histoire de la physique est jalonnée de notions plus ou moins fumeuses qui servent, un temps, à boucher les trous des théories de l’époque. La plus célèbre de ces béquilles scientifiques est sans doute l’éther. Parmi les plus récentes, pourrait bien figurer la matière noire. Suite aux derniers travaux des chercheurs dans ce domaine, l’Express titre: «Matière noire: ils ont cartographié l'invisible». Invisible? Certes. D’autant que la matière noire est hautement hypothétique.

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Doubts raised about certainty of Higgs-boson find

Doubts raised about certainty of Higgs-boson find | Tout est relatant | Scoop.it
IT's not the god particle. It's just a naughty little anomaly. Or so a group of doubting scientists would have us believe.

The claim comes barely a week after scientists from the world's most expensive experiment - the Large Hadron Collider - announced what they claim was the discovery of a "missing" particle that adds mass to matter (the Higgs-boson, or so-called "god" particle).

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Future LHC super-magnets pass muster

Future LHC super-magnets pass muster | Tout est relatant | Scoop.it

In the past four years, scientists at the Large Hadron Collider have accomplished unprecedented feats of physics, all with their particle accelerator working at half its design capacity.

The future is looking even brighter, literally.

Last week the US LHC Accelerator Research Program, or LARP, successfully tested a new type of magnet required to boost the power of the LHC—or the luminosity of its particle beams—by a factor of 10.

LARP is a collaboration among the US Department of Energy’s Brookhaven, Fermi, Lawrence Berkeley and SLAC national laboratories, working in partnership with CERN.

The improved magnets are one of the most critical components in a series of LHC upgrades that will be implemented over the next ten years. In the accelerator, magnets squeeze and focus beams of charged particles, directing them to a point of high-energy collision inside a detector. The new magnets, along with other upgrades, will allow the LHC to collect a larger amount of data at higher energies, making it possible to search for more massive potentially hidden particles than ever before.

Lucio Rossi, leader of the high luminosity project at CERN, says the improved LHC could illuminate unexplored corners of physics.

If you enter a dark room with only a candle, the room will be dim, and the candle will soon burn out, he says. But if you have a high-powered flashlight, not only can you see more of the room, but you also have enough time to get a good look around.

“Thanks to this magnet, we will have more collisions, more statistics and more rare events,” Rossi says. “If there is physics beyond the Standard Model, these magnets will shed light on it.”

Like the magnets that currently steer particles through the LHC, the new magnets are superconducting. A superconductor is a material that allows electric current to flow without resistance, creating a strong magnetic field.

The current LHC magnets are made of a metal alloy called niobium titanium. While they have performed remarkably well, there’s a limit to the amount of magnetic field they can sustain—and they’ve gone almost as far as they can go.

For the LHC to continue pushing the boundaries of high-energy physics, physicists plan to switch to magnets made out of niobium tin. Niobium tin has a greater tolerance to heat than niobium titanium, which means it has a larger window of superconductivity and can sustain a higher magnetic field longer.

However, there’s a catch; although niobium tin is a better superconducting material, it’s brittle and sensitive to strain.

“Think of a steel wire you would use for home repairs,” says Berkeley Lab’s GianLuca Sabbi, who directed the development of the new magnets. “You can bend it, and it won’t break. This is the case for niobium titanium, but niobium tin is more like glass.”

This presents some serious technical challenges because making a traditional superconducting magnet requires drawing the alloy into thin wires, gathering those wires into high current cables and then tightly winding them into an accelerator coil. If scientists took these steps, niobium tin would shatter.

US LHC Accelerator Research Program scientists get around this issue by following a clever recipe. First, they coil the “raw” ingredients of niobium tin—the metals that combine to create it—and then put the whole device into a special furnace for a high temperature heat treatment, which melds the components into a superconductor with the desired shape already intact.

At this point, it becomes sensitive to strain, so the scientists fill all the gaps and voids with an epoxy, which glues the brittle material together, providing the support the fragile wires need to withstand the harsh environment of the LHC.

The new technology has applications beyond high-energy physics. Plans are already in motion to incorporate these magnets into medical practices such as imaging and cancer treatment.

As the LHC continues to be streamlined, physicists hope to see further beyond the veil, piecing together the truth behind dark matter, dark energy, extra dimensions and other mysteries. At this scale of luminosity, previously undiscovered particles may even begin to appear.
- See more at: http://www.symmetrymagazine.org/article/july-2013/future-lhc-super-magnets-pass-muster#sthash.HIZmS9vf.dpuf

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The man who built the LHC

The man who built the LHC | Tout est relatant | Scoop.it
The Large Hadron Collider (LHC) in Geneva is the arguably most famous experiment on Earth. It’s also, by many measures, the largest; a particle collider 27km in circumference and 100m underground, it took 16 years to build and cost £6bn.
The LHC was built to answer some of the burning questions facing particle physicists. Within the massive tunnels, protons travelling at near-light-speed collide with each other, and the physicists examine the resulting debris to try to work out what is going on. Hundreds of researchers scour the data for evidence of the Higgs boson, embraced by the media as “the God particle”. The Higgs, if it is found, would explain why everything around us has mass.
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Le boson de Higgs a deux «papas» belges

Le boson de Higgs a deux «papas» belges | Tout est relatant | Scoop.it
Le physicien Peter Higgs reconnaît lui-même devoir partager la paternité de « sa » particule avec plusieurs collègues, aux premiers rangs desquels deux Belges, Richard Brout et François Englert. Fr...
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Timberlake: Higgs boson, not in America

Timberlake: Higgs boson, not in America | Tout est relatant | Scoop.it

Nationalism nowadays is generally an inadequate mentality. It estranges one nation from an ever globalizing world. A world that will need to work together to accomplish great things.But I need to admit, it was a bittersweet moment when I heard that CERN's Large Hadron Collider in Geneva discovered a Higgs boson like particle with nearly 100 percent accuracy on America's Independence Day.

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For Cost of One Month of Iraq War, 'God Particle' Could Have Been U.S. Triumph

For Cost of One Month of Iraq War, 'God Particle' Could Have Been U.S. Triumph | Tout est relatant | Scoop.it

The discovery of the Higgs boson subatomic particle, announced this week, is one of the biggest triumphs in the history of science. The discovery was announced by scientists at the CERN, the research center in Switzerland that operates the Large Hadron Collider (LHC), the massive particle accelerator that detected the Higgs boson.

Once upon a time, most big scientific breakthroughs like this were made in the U.S. But in an era of declining science budgets and fewer science degrees awarded, America is increasingly no longer the leader in cutting-edge science.

The Large Hadron Collider cost around $8 billion. Although that sounds like a steep price tag, it's important to keep this figure in perspective. After all, during the Iraq War, the U.S. was typically spending $8 billion every month in that disastrous and unnecessary conflict.

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La particule sans Dieu - The godless particle

La particule sans Dieu - The godless particle | Tout est relatant | Scoop.it

The way the Higgs got the divine title is something of a joke in the world of physics. Originally, the story goes, they called it the "goddamn" particle because it was so freakin' hard to find. But then there was this book, written by Nobel Prize laureate physicist Leon Lederman. His publishers balked at the blasphemy. So the future bestseller was titled "The God Particle" -- and the public bit bigtime.

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