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The LHC as a photon collider | CMS Experiment

The LHC as a photon collider | CMS Experiment | Tout est relatant |
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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Japan selects candidate site for linear collider

Japan selects candidate site for linear collider | Tout est relatant |
A site evaluation committee has recommended a location for the proposed International Linear Collider, if it is built in Japan.


In a press conference this morning, the Japanese high-energy physics community's site evaluation committee for the proposed International Linear Collider announced its recommendation: If the 19-mile-long, next-generation particle collider is built in Japan, it should be located in the Kitakami mountains of the Iwate and Miyagi prefectures.

The ILC, considered a next step after the Large Hadron Collider, would accelerate and collide electrons and their antiparticles, positrons, at an energy of 500 billion electronvolts. The clean collisions of these elementary particles could reveal information obscured in the complexity of collisions between composite particles—protons, which are made up of quarks and gluons—in the LHC.

The ILC site evaluation committee of Japan made its choice following a careful evaluation of two finalist candidate sites: the Kitakami mountains and the Sefuri mountains of the Saga and Fukuoka prefectures. The decision was made based on the sites’ geology, infrastructure and ability to support the thousands of researchers who would move to the area.

The global ILC collaboration published its official blueprint for the collider in June, marking the end of several years of research and development. With the design finished and a possible site chosen, the ILC council will now work to promote the selection—as well as the project as a whole—among the Japanese government and the other countries considering making the project a reality.

Some 2000 scientists, including particle physicists, accelerator physicists and engineers, around the world are involved in the linear collider project, developing the tools and technologies needed to build the most advanced collider ever.

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Research pair find 5.9 year cycle of oscillations in length of day

Research pair find 5.9 year cycle of oscillations in length of day | Tout est relatant |

A pair of researchers, Richard Holme of the University of Liverpool in the U.K. and Olivier de Viron of the University of Paris, in France has found that the length of Earth’s days follows a cyclic oscillation pattern every 5.9 years. As the two describe in their paper published in the journal Nature, the variations in day length were discovered as part of a study examining day-length over the past 50 years.

The time it takes the Earth to spin once around its axis varies by milliseconds on any given day. This is due to the impact of weather patterns, ocean currents and other factors. But the Earth is also subject to other forces that can cause the length of day to vary over the long term or even for short “jumps” of time. In this new effort, the researchers looked at data from the past 50 years and then filtered out those short term forces that cause daily fluctuations in day-length. In so doing, they found what they describe as a ten year “decadally varying trend” a 5.9 year cycle of day-length oscillations and times when the planet seems to jerk, temporarily changing the length of the days that follow.
Unlike the ten year trend (believed to be caused by changes in the Earth’s core) and the episodic jerks (scientists have detected 10 such events since 1969) the 5.9 year cycle was unexpected. Every 5.9 years, they claim, the planet undergoes a period of several months where the length of each day is longer or shorter than “normal.” The researchers don’t know what causes the cycle but suspect it has something to do with the core-mantle boundary.
Scientists are also interested in learning more about the episodic jerks that alter day-length for several months at a time—this new research has revealed that during each event, the Earth’s geomagnetic field undergoes a similar effect. Scientists don’t know why either occurs, but suspect they are connected.

Research into Earth’s day-length changes as well as studies seeking to better understand the true makeup of the planet are not just academic pursuits—gains in understanding are used by geologists and engineers in mining and exploration efforts.

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Japanese team sees gamma-ray pulse before lightning flash

Japanese team sees gamma-ray pulse before lightning flash | Tout est relatant |

Physicists in Japan have made the best study yet of the gamma rays that are produced in the minutes leading up to a lightning flash. In addition, the team also observed for the first time emissions that ended abruptly less than a second before the exact moment the flash occurs. The finding provides important information about the relationship between the mysterious atmospheric accelerators that produce the gamma rays and the lightning that we see in the sky.
Physicists have known for some time that gamma rays are sometimes produced when lightning strikes. Indeed, gamma-ray pulses from thunderclouds that vary in length from sub-millisecond to several minutes have been detected for the last 30 years. Most researchers agree that there are two types of bursts: very short, higher-energy bursts that coincide with lightning; and longer, lower-energy pulses that are sometimes not associated with a specific lightning event. While all of these bursts are thought to be created when charged particles are accelerated by the huge electric fields that build up in a thundercloud, the exact mechanism – or mechanisms – that produce them remains a mystery.
In this latest study, Harufumi Tsuchiya of the RIKEN High-energy Astrophysics Laboratory and colleagues at several other Japanese institutes looked at data collected in 2010 by the Gamma-Ray Observation of Winter THunderclouds (GROWTH) experiment at the Kashiwazaki-Kariwa nuclear power plant. The experiment includes several different gamma-ray detectors that are used in tandem with plastic detectors – the latter ensuring that charged particles such as muons are not mistaken for gamma rays. The system detected gamma rays at energies between 40 keV and 30 MeV…..

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The man who built the LHC

The man who built the LHC | Tout est relatant |
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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Why Earth's Inner and Outer Cores Rotate in Opposite Directions

Why Earth's Inner and Outer Cores Rotate in Opposite Directions | Tout est relatant |


The Earth's magnetic field controls the direction and speed at which Earth's inner and outer cores spin, even though they move in opposite directions, new research suggests.

Scientists have long suspected that Earth's magnetic field — which protects life from harmful space radiation — drifts in a slightly westerly direction. That theory was established in the 1690s, when geophysicist Edmund Halley (the same Halley who spotted the eponymous comet) sailed aboard a research vessel through the South Atlantic Ocean and collected enough compass readings to identify this shift.

By the mid-20th century, geologists had gathered further evidence for this drift and had determined that the westerly rotation of the magnetic field exerts a force on the liquid outer core— composed of a molten mix of iron and nickel — that causes it to rotate in a westerly direction. Decades later, geophysicists used deep seismic data to determine that the inner core — a solid iron-nickel alloy that is about the size of the moon — rotates in an easterly direction, at a greater speed than the rotation of the Earth itself.

But, until now, scientists have regarded these rotations within the two layers of the core as separate, with no relation to each other.   

Now, researchers at the University of Leeds in England have found a common link between the two rotations by creating a computer model that shows how the rotation of the Earth's magnetic field can both pull the liquid outer core in a westerly direction while also exerting an opposite force on the inner core that causes an easterly rotation.

"Previously, there have been these two independent observations, and there has not been a link between them," study co-author Philip Livermore, of the University of Leeds, told LiveScience's OurAmazingPlanet. "We argue that the magnetic field itself is pushing on the outer core, and there is an equal and opposite push on theinner core."

The Earth's magnetic field — created by the convection of hot liquid metal within the outer core — undergoes slight fluctuations roughly every decade. The inner core's rotation rate has also been shown to fluctuate on a similar timescale. These new results help explain why these two phenomena occur on the same timescale, since one has now been shown to affect the other, the researchers say.

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Experimental realization of an optical second ...

Experimental realization of an optical second ... | Tout est relatant |

Progress in realizing the SI second had multiple technological impacts and enabled further constraint of theoretical models in fundamental physics.
Caesium microwave fountains, realizing best the second according to its current definition with a relative uncertainty of 2–4 × 10−16, have already been overtaken by atomic clocks referenced to an optical transition, which are both more stable and more accurate. Here we present an important step in the direction of a possible new definition of the second.
Our system of five clocks connects with an unprecedented consistency the optical and the microwave worlds. For the first time, two state-of-the-art strontium optical lattice clocks are proven to agree within their accuracy budget, with a total uncertainty of 1.5 × 10−16.
Their comparison with three independent caesium fountains shows a degree of accuracy now only limited by the best realizations of the microwave-defined second, at the level of 3.1 × 10−16….

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Future LHC super-magnets pass muster

Future LHC super-magnets pass muster | Tout est relatant |

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:

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Cet homme a-t-il percé le secret de la matière noire ? Peut-être...

Cet homme a-t-il percé le secret de la matière noire ? Peut-être... | Tout est relatant |

La science vient d’inaugurer un nouvel instrument de communication: le sourire. C’est en effet l’indication principale donnée par Samuel Ting, prix Nobel de physique en 1976 avec Burton Richter, pour la découverte d’une nouvelle particule subatomique, lors de la conférence annuelle de l’American Association for the Advancement of Science qui s’est tenue du 14 au 18 février 2013 à Boston.

Pressé de questions sur les résultats engrangés par le spectromètre AMS arrimé sur la Station spatiale internationale (ISS) depuis le 19 mai 2011, Sam Ting, professeur au MIT et principal responsable de l’expérience qui a coûté 1,5 milliard de dollars, est resté très évasif.

Il s’est contenté de laisser entendre que les résultats obtenus donneront aux hommes une meilleure idée de ce qu’est la matière noire. Car c’est bien de cela qu’il s’agit. Rien de moins.

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Le côté obscur de la matière noire

Le côté obscur de la matière noire | Tout est relatant |
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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