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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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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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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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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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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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