18-02-2009
The FERMI observatory has discovered the most energetic gamma-ray burst ever detected

The Fermi gamma-ray space telescope  [1] has detected the most violent gamma-ray burst ever recorded; a gigantic explosion marking the death of a massive star. Light from this explosion, captured by the Fermi observatory on September 16th 2008, had taken 12.2 billion years to reach Earth. Hence, it must have been produced at a time when the Universe was just 1.5 billion years old.  The total amount of energy released makes this the most violent explosion observed in the Universe since the Big Bang. Observed by the Fermi on scales covering more than six decades in energy, this gamma-ray burst demonstrated exceptional properties. Clouds of charged particles were catapulted out during the explosion, at a speed equal to 99.9% of the speed of light! This work, the result of the international Fermi collaboration, with partners from CEA-Irfu, was published on February 19th 2009 in the journal Science express.

16-11-2009

For more than 20 years, solid niobium has had the monopoly on high-gradient applications of superconducting radio frequency (SRF) cavities for particle accelerators. But it will soon have reached its limits. It was only recently that A. Gurevich, a theoretician from Florida State University, put forward a theory explaining the reasons behind niobium's success and a way of breaking its monopoly. Until now, this theoretical model had never been experimentally demonstrated. This has now changed for a collaborative project between IRFU (Saclay) and INAC (Grenoble) has just made this vital step towards new acceleration technology.

23-12-2009

Monday, 23 November 2009, marked the first particle beam collision inside the large detectors of the LHC. ALICE saw its first collisions at an energy of 900 GeV, enabling it to check for correct operation of the 18 large detectors which comprise it. Since 27 November, with just a few days worth of data, the collaboration has even published an article confirming some existing measurements.

The group from the IRFU, who are responsible for the dimuon arms, had to await more stable beam conditions in order to see their detectors reacting to the data coming from the collisions and, on 6 December, all the gaseous detectors were able to be powered up. The traces from the first muons could be successfully reconstructed, to the great satisfaction to all the team. They are now eager to begin collecting more data after the planned restart in February 2010.

05-05-2009

At the end of March 2009, the ALICE Muon Spectrometer took cosmic rays over a period of two weeks. The ALICE group at Saclay2 was closely involved in the design, development, construction and installation of a part of the chambers of this Spectrometer3. The purpose of the cosmic ray test was to check the performance of the entire system, from acquisition to reconstruction of the data. The acquisition system readout about a million channels and the data was recorded on the computing grid. Almost 15,000 tracks were reconstructed under conditions close to those of the real experiment. The cosmic test was a success, demonstrating the performance and the stability of the spectrometer chambers. It also revealed some weak points of the system. Tests are currently underway to correct the observed defaults.

Another cosmic test is planned for August, a few weeks before the first LHC beam injections, involving all ALICE detectors.

 

 

Contacts:

Alberto BALDISSERI

Hervé BOREL

21-04-2009

It has now been more than two years that Antares1, the underwater telescope installed in the depths of the abyssal plains 2500 m under the Mediterranean, is scanning the skies through the Earth in search of neutrinos. Over a thousand of them have already been observed until today, making it possible to establish the first views of the heavens to search for high-energy cosmic neutrinos, particles that may be able to teach us more about the most violent phenomena in the Universe.

 

 

Neutrinos are particles that interact very little with matter. Emitted by the most violent cataclysms of the Universe, they could prove that these phenomena are responsible for cosmic rays, mainly protons, which are constantly bombarding the Earth. These protons actually reach us after having been diverted from their paths by intergalactic magnetic fields, which prevents us from identifying their origin.

 

Their very weak interaction with matter makes neutrinos hard to detect. This problem can only be overcome by using enormous detectors, shielded against the cosmic rays. Antares, installed off the coast of Toulon, is protected against this radiation by a natural shield - 2000 m of water. Work on the detector took two years and its deployment was achieved in May 2008. Today 885 "eyes", together with the electronic equipment designed and built by CEA-IRFU (Institute of Research into the Fundamental Laws of the Universe) to read and process the data, are strung out in groups of threes along 12 flexible lines 450 m high. These lines are higher than the Eiffel Tower and are anchored to the seabed covering an area as large as four football fields.

23-12-2009

Since the accident which occurred on the LHC accelerator several days after its commissioning in 2008, the ATLAS collaboration has been impatient to observe "true" events produced at the centre of the detector, and to make the equipment function under real conditions. On 23 November, following several days of tests with a single beam, Atlas recorded its first proton-proton collisions, at the injection energy into the LHC (450 GeV per beam, i.e. 900 GeV in the centre of mass reference frame of the collision). Analysis has then been able to reconstruct known unstable particles by detecting their disintegration products, demonstrating that the detectors and associated software are functioning correctly. The Atlas group, from the Particle Physics Department at IRFU, has also been able to check the behaviour of the muon detector sub-systems and the electromagnetic calorimetry, for which it is responsible. Collisions at 2.38 TeV (1.19 TeV per beam) were recorded before the LHC shutdown on 16 December, establishing a new world-record as of the most powerful particle accelerator in the world. The LHC will start up again in February 2010 after a short technical break aiming to produce collisions with higher energies and at higher intensity. Dark matter may be made of new particles, which could be produced in the high-energy proton-proton collisions at LHC. In this case Atlas would be able to discover them.

27-12-2009

Since the restart of the LHC on 20 November, CMS has taken advantage of the excellent operating performance of the collider to record a large amount of useful data. This is now being used to check its correct operation and calibration. During this period, CMS has demonstrated the stability of the detectors' working conditions as well as the efficiency of the data analysis system, which sends data from the detector to analysis teams around the world, and this in spite of very rapidly changing beam conditions.

 

22-04-2009

Since researchers have been confronting the standard model of particle physics with experimentation, nothing has been able to shake it. Of all particles it describes, only the Higgs Boson has not yet been discovered. But the standard model is probably not the ultimate theory: it does not cover gravitation and numerous experimental observations remain unexplained.

A new invariance, called supersymmetry, was suggested during the 1970s. It associates particles with different spins (integer spin bosons and half-integer spin fermions). It is possible to create supersymmetric extensions of the standard model, elegantly resolving the mathematical problems that emerge during calculation of the Higgs Boson mass.

 

D01 experiment accumulating data from Fermilab's Tevatron (United States) just published2 results relating to the Higgs Boson research needed for supersymmetric extensions to the standard model. All currently available data has been analysed, representing more than one and a half billion events.

 

Finding a supersymmetric light Higgs 

In the Tevatron, a high-energy proton-antiproton collider, large quantities of Higgs Bosons could be produced if they are sufficiently light. A useful channel for detecting them is their production associated with a bottom quark3 (b), H0b. In 90% of cases, supersymmetric light Higgs Bosons are supposed to disintegrate into two bottom quarks. That is why research in this area is based on identifying those events involving at least three jets4 resulting from bottom quarks in the final state.

 

 

 

06-04-2009

 

 

Until the advent of the LHC, the Tevatron at the Fermi National Accelerator Laboratory, Fermilab (close to Chicago, USA), will remain the world's most powerful collider and the only location where the top1 quark can be produced.

The DØ experiment recently published2 results on the measurement of the rate of production of top-antitop quark pairs. This quantity, which is dependent on the value taken for the mass of the top quark, enables a prediction to be made for that mass using the standard model3. The top quark, which was discovered at Fermilab in 1995, remains the subject of very active research. Methods of analysis and the quantity of data are forever improving, which is resulting in subsequent improvements in the accuracy of the measurement of the top quark mass.  The precise measurement of this value, combined with results from other precision measurements, enables the most probable mass of the Higgs Boson to be estimated. Hence improved measurements of the mass of the top quark is tightening the vice in the search for the Higgs boson.

 

02-06-2009

The second phase of the Double Chooz international experiment officially began on Wednesday 20 May. The Declaration of Intent signed by the four partners (CEA, CNRS, EDF, Champagne-Ardenne Region) is the first step in the plan to build a second detector devoted to neutrino research next to the Chooz nuclear power plant.

Prior to signing the DOI, the participants visited the site of the first detector, currently under construction. By the end of the year, the detector should pick up the first neutrinos emitted by the plant and attempt to measure the disappearance of primary flux neutrinos. The second detector, which will be operational two years from now, will provide precise measurements of the flux and spectrum of the neutrinos emitted and greatly enhance measurement control and precision.

 

 

 

 

Contact

 

Thierry LASSERRE

16-11-2009

 

Work on a new clean room, begun in July 2007 at the Saclay accelerator platform, has just been completed. The new clean room will be officially opened on 24 November 2009 and will replace the chemical facilities and clean room of IRFU's Accelerators, Cryogenics and Magnetism Division (SACM) located at L'Orme, which could no longer undergo all the improvements required to keep pace with current development work. A hall in building 124 (previously the Saturne laboratory) has therefore been renovated to accommodate the future facilities and equipment compatible with future accelerator research requirements and collaborative projects with industrial partners interested in the control of superconducting cavity systems.

02-06-2009
A research team has just published the most precise measurement ever of the rate of gravitational collapse supernovae observed in the Universe 3.7 billion years ago

 

The Supernova Legacy Survey (SNLS) team at the Canada-France-Hawaii Telescope facility has just obtained the world's best measurement of the explosion rate of massive stars when the Universe was only 10 billion years old. A research team at IRFU's particle physics department at the CEA-Saclay centre worked on the first three years of SNLS data to obtain this result, which makes a crucial contribution to our understanding of the origins and evolution of chemical elements in the interstellar medium. The measurement seems to show that there are two to four times fewer supernovae today than 3.7 billion years ago. Could the Universe be burning out?

 

 

 

Contacts:

 

 

Nathalie PALANQUE-DELABROUILLE

James RICH

Vanina RUHLMAN-KLEIDER

 

14-09-2009

 

 

Engineers and physicists from IRFU have successfully assembled and commissioned three large chambers designed to reconstruct charged particle tracks. The chambers will characterize the neutrino beam used in the T2K (Tokai to Kamiokande) experiment. They are the first large Time Projection Chambers (TPCs) to be equipped with micromesh gas detectors (Micromegas). The chambers have a very large sensitive area (nearly 9m²) and a correspondingly high number of electronic channels (124,000). IRFU built the entire detection system of the three TPCs, comprising 72 Micromegas detectors and all the front-end electronics. Engineers from SEDI, a department specialised in detector, electronics and information technology, specially designed a new chip called AFTER and two printed circuit boards for sending digitised signals to the acquisition system via an array of 72 gigabit optical links. The three chambers were tested with a particle beam at TRIUMF in Canada and have been installed in JPARC (Tokai, Japan) at the end of 2009.


The first beam and cosmic ray tests demonstrated that tracks could be reconstructed with the required degree of precision. This achievement represents a major step forward in the construction of a vital detector for the T2K experiment.

 

The TPC are now detecting tracks produced by neutrino interaction in the near detector of T2K and provide superior information to measure the momentum and to identify these particles. 


 

Contacts:

 

Alain DELBART

Marco ZITO

 

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