School of PARTICLES AND ACCELERATORS

CERN Council looks forward to summer conferences and new members (June 24, 2011)

Geneva, 24 June 2011. At its 159^th session this week, the CERN Council congratulated CERN on the excellent performance of the LHC, and welcomed the news that formal confirmation has been received from the five countries applying for CERN Membership.

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LHC achieves 2011 data milestone - Le LHC atteint son objectif pour 2011 (June 17, 2011)

Geneva, 17 June 2011. Today at around 10:50 CEST, the amount of data accumulated by LHC experiments ATLAS and CMS clicked over from 0.999 to 1 inverse femtobarn, signalling an important milestone in the experiments’ quest for new physics. The number signifies a quantity physicists call integrated luminosity, which is a measure of the total number of collisions produced. One inverse femtobarn equates to around 70 million million¹ collisions, and in 2010 it was the target set for the 2011 run. That it has been achieved just three months after the first beams of 2011 is testimony to how well the LHC is running.

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CERN experiment traps antimatter atoms for 1000 seconds(June 5, 2011)

In a paper published online by the journal Nature Physics today, the ALPHA experiment at CERN reports that it has succeeded in trapping antimatter atoms for over 16 minutes: long enough to begin to study their properties in detail. Full Story

LHC Experiments Present New Results at Quark Matter 2011 Conference(May 23, 2011)

The three LHC experiments that study lead ion collisions all presented their latest results today at the annual Quark Matter conference, held this year in Annecy, France. The results are based on analysis of data collected during the last two weeks of the 2010 LHC run, when the LHC switched from protons to lead-ions. All experiments report highly subtle measurements, bringing heavy-ion physics into a new era of high precision studies. Full Story

Records, results and rumors (April 28, 2011)

The LHC has been colliding stable beams for over eight hours, and the instantaneous luminosity is still higher than the record starting luminosity we announced under a week ago. It’s a sign of how well this magnificent machine is running that last week’s milestone achievement already seems like ancient history. In a week that’s also seen a lot of media interest in a leaked ATLAS note, it’s important for us to stay focused on what really matters for particle physics: delivering plenty of good quality data to the experiments so they can produce reliable peer-reviewed results. Full Story

The AMS detector heads for the International Space Station (April 27, 2011)

The AMS particle detector will take off on 29 April 2011 at 21.47 CEST onboard the very last mission of the space Shuttle Endeavour. AMS, the Alpha Magnetic Spectrometer, will then be installed on the International Space Station from where it will explore the Universe for a period of over 10 years. AMS will address some of the most exciting mysteries of modern physics, looking for antimatter and dark matter in space, phenomena that have remained elusive up to now. Full Story

"6 December 2010"

CERN experiment makes progress towards antihydrogen beams

Geneva, 6 December 2010. The ASACUSA[1] experiment at CERN has taken an important step forward in developing an innovative technique for studying antimatter. Using a novel particle trap, called a CUSP trap, the experiment has succeeded in producing significant numbers of antihydrogen atoms in flight. This result is published today in the journal Physical Review Letters.

Antimatter – or the lack of it – remains one of the biggest mysteries of science. Matter and its counterpart are identical except for opposite charge, and they annihilate when they meet. At the Big Bang, matter and antimatter should have been produced in equal amounts. However, we know that our world is made up of matter: antimatter seems to have disappeared. To find out what has happened to it, scientists employ a range of methods to investigate whether a tiny difference in the properties of matter and antimatter could point towards an explanation.

One of these methods is to take one of the best-known systems in physics, the hydrogen atom, which is made of one proton and one electron, and check whether its antimatter counterpart, antihydrogen, consisting of an antiproton and a positron, behaves in the same way. The challenge is to create antihydrogen atoms, and keep them away from ordinary matter for long enough to study them. ASACUSA’s CUSP trap uses a combination of magnetic fields to bring antiprotons and positrons together to form antihydrogen atoms, and then channel them along a vacuum pipe where they can be studied in flight. So far, only a few antihydrogen atoms have been produced in this way, but the experiment’s ultimate goal is to produce enough to investigate their behaviour in detail with the help of microwaves.

ASACUSA’s approach is complementary to that of the ALPHA experiment, which reported new results in the journal Nature on 17 November. The procedures used to form antihydrogen build on techniques developed by a third antihydrogen experiment at CERN, ATRAP, which pioneered trapping techniques in the 1990s, and is also working on trapping antihydrogen.

“With these alternative methods of producing and eventually studying antihydrogen, antimatter will not be able to hide its properties from us much longer,” said Yasunori Yamazaki of Japan’s RIKEN research centre and a team leader of the ASACUSA collaboration. “There’s still some way to go, but we’re very happy to see how well this technique works.”

CERN is the only laboratory in the world that operates a dedicated low-energy antiproton facility. As far back as 1995, the first nine atoms of antihydrogen were produced at CERN. Then, in 2002, the ATHENA and ATRAP experiments showed that it was possible to produce antihydrogen in large quantities, opening up the possibility of conducting detailed studies. Today, CERN’s antihydrogen experiments are well on the way to investigating this rarest of atoms.

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[1] ASACUSA is an experiment at CERN’s Antiproton Decelerator (AD) facility studying the properties of antimatter. The main thrust of ASACUSA’s research programme to date has been the creation and study of exotic atoms known as antiprotonic helium. Normal helium has two electrons orbiting its nucleus. In an antiprotonic helium atom, one electron has been replaced by an antiproton. Study of such atoms has enabled ASACUSA to measure the mass of antiprotons to very high precision. In total, five experiments use the AD’s low energy antiproton beams. ALPHA and ATRAP focus on studying antihydrogen atoms. AEgIS, an experiment under construction, will study the influence of gravity on antimatter, while ACE is an experiment investigating the effectiveness of antiprotons as a potential treatment for certain forms of cancer.

"26 November 2010"

LHC experiments bring new insight into primordial Universe

Geneva, 26 November 2010. After less than three weeks of heavy-ion running, the three experiments studying lead ion collisions at the LHC have already brought new insight into matter as it would have existed in the very first instants of the Universe’s life. The ALICE experiment, which is optimised for the study of heavy ions, published two papers just a few days after the start of lead-ion running. Now, the first direct observation of a phenomenon known as jet quenching has been made by both the ATLAS and CMS collaborations. This result is reported in a paper from the ATLAS collaboration accepted for publication yesterday in the scientific journal Physical Review Letters. A CMS paper will follow shortly, and results from all of the experiments will be presented at a seminar on Thursday 2 December at CERN. Data taking with ions continues to 6 December.

“It is impressive how fast the experiments have arrived at these results, which deal with very complex physics,” said CERN’s Research Director Sergio Bertolucci. “The experiments are competing with each other to publish first, but then working together to assemble the full picture and cross check their results. It’s a beautiful example of how competition and collaboration is a key feature of this field of research.”

One of the primary goals of the lead-ion programme at CERN is to create matter as it would have been at the birth of the Universe. Back then, the ordinary nuclear matter of which we and the visible Universe are made could not have existed: conditions would have been too hot and turbulent for quarks to be bound up by gluons into protons and neutrons, the building blocks of the elements. Instead, these elementary particles would have roamed freely in a sort of quark gluon plasma. Showing beyond doubt that we can produce and study quark gluon plasma will bring important insights into the evolution of the early Universe, and the nature of the strong force that binds quarks and gluons together into protons, neutrons and ultimately all the nuclei of the periodic table of the elements.

When lead-ions collide in the LHC, they can concentrate enough energy in a tiny volume to produce tiny droplets of this primordial state of matter, which signal their presence by a wide range of measureable signals. The ALICE papers point to a large increase in the number of particles produced in the collisions compared to previous experiments, and confirm that the much hotter plasma produced at the LHC behaves as a very low viscosity liquid (a perfect fluid), in keeping with earlier observations from Brookhaven’s RHIC collider. Taken together, these results have already ruled out some theories about how the primordial Universe behaved.

“With nuclear collisions, the LHC has become a fantastic 'Big Bang' machine,” said ALICE spokesperson Jürgen Schukraft.“In some respects, the quark-gluon matter looks familiar, still the ideal liquid seen at RHIC, but we’re also starting to see glimpses of something new”.

The ATLAS and CMS experiments play to the strength of their detectors, which both have very powerful and hermetic energy measuring capability. This allows them to measure jets of particles that emerge from collisions. Jets are formed as the basic constituents of nuclear matter, quarks and gluons, fly away from the collision point. In proton collisions, jets usually appear in pairs, emerging back to back. However, in heavy ion collisions the jets interact in the tumultuous conditions of the hot dense medium. This leads to a very characteristic signal, known as jet quenching, in which the energy of the jets can be severely degraded, signalling interactions with the medium more intense than ever seen before. Jet quenching is a powerful tool for studying the behaviour of the plasma in detail.

“ATLAS is the first experiment to report direct observation of jet quenching,” said ATLAS Spokesperson Fabiola Gianotti.“The excellent capabilities of ATLAS to determine jet energies enabled us to observe a striking imbalance in energies of pairs of jets, where one jet is almost completely absorbed by the medium. It’s a very exciting result of which the Collaboration is proud, obtained in a very short time thanks in particular to the dedication and enthusiasm of young scientists.”

“It is truly amazing to be looking, albeit on a microscopic scale, at the conditions and state of matter that existed at the dawn of time,” said CMS Spokesperson Guido Tonelli. “Since the very first days of lead-ion collisions the quenching of jets appeared in our data while other striking features, like the observation of Z particles, never seen before in heavy-ion collisions, are under investigation. The challenge is now to put together all possible studies that could lead us to a much better understanding of the properties of this new, extraordinary state of matter"

The ATLAS and CMS measurements herald a new era in the use of jets to probe the quark gluon plasma. Future jet quenching and other measurements from the three LHC experiments will provide powerful insight into the properties of the primordial plasma and the interactions among its quarks and gluons.

With data taking continuing for over one more week, and the LHC already having delivered the programmed amount of data for 2010, the heavy-ion community at the LHC is looking forward to further analysing their data, which will greatly contribute to the emergence of a more complete model of quark gluon plasma, and consequently the very early Universe.

"17 November 2010"

Antimatter atoms produced and trapped at CERN

Geneva, 17 November 2010. The ALPHA experiment at CERN[1] has taken an important step forward in developing techniques to understand one of the Universe’s open questions: is there a difference between matter and antimatter? In a paper published in Nature today, the collaboration shows that it has successfully produced and trapped atoms of antihydrogen. This development opens the path to new ways of making detailed measurements of antihydrogen, which will in turn allow scientists to compare matter and antimatter.

The antihydrogen programme goes back a long way. In 1995, the first nine atoms of man-made antihydrogen were produced at CERN. Then, in 2002, the ATHENA and ATRAP experiments showed that it was possible to produce antihydrogen in large quantities, opening up the possibility of conducting detailed studies. The new result from ALPHA is the latest step in this journey.

Antihydrogen atoms are produced in a vacuum at CERN, but are nevertheless surrounded by normal matter. Because matter and antimatter annihilate when they meet, the antihydrogen atoms have a very short life expectancy. This can be extended, however, by using strong and complex magnetic fields to trap them and thus prevent them from coming into contact with matter. The ALPHA experiment has shown that it is possible to hold on to atoms of antihydrogen in this way for about a tenth of a second: easily long enough to study them. Of the many thousands of antiatoms the experiment has created, ALPHA’s latest paper reports that 38 have been trapped for long enough to study.

"For reasons that no one yet understands, nature ruled out antimatter. It is thus very rewarding, and a bit overwhelming, to look at the ALPHA device and know that it contains stable, neutral atoms of antimatter,” said Jeffrey Hangst of Aarhus University, Denmark, spokesman of the ALPHA collaboration. “This inspires us to work that much harder to see if antimatter holds some secret.”

In another recent development in CERN’s antimatter programme, the ASACUSA experiment has demonstrated a new technique for producing antihydrogen atoms. In a paper soon to appear in Physical Review Letters, the collaboration reports success in producing antihydrogen in a so-called Cusp trap, an essential precursor to making a beam. ASACUSA plans to develop this technique to the point at which beams of sufficient intensity will survive for long enough to be studied.

“With two alternative methods of producing and eventually studying antihydrogen, antimatter will not be able to hide its properties from us much longer,” said Yasunori Yamazaki of Japan’s RIKEN research centre and a member of the ASACUSA collaboration. “There’s still some way to go, but we’re very happy to see how well this technique works.”

“These are significant steps in antimatter research,” said CERN Director General Rolf Heuer, “and an important part of the very broad research programme at CERN.”

Full information about the ASACUSA approach will be made available when the paper is published.

For further information on ALPHA experiment, please read here:

http://cerncourier.com/cws/article/cern/30577

"8 November 2010"

The next major milestone came on 19 April with a ten-fold increase in luminosity – in other words, the machine started delivering ten times as many collisions to the experiments in a given period of time than had previously been possible. This came about thanks to two simultaneous developments: firstly the number of particles in each bunch was doubled, and secondly the beam size at the interaction point was squeezed down. The term you’ll hear used to describe the beam size at the interaction point is called beta-star, and the smaller the beta, the better. Before squeeze, beta is 11 m at ATLAS and CMS. The ultimate goal is to reduce it to 0.55 m. Today, we’re running with a beta of 2 m. That may not sound very small, and that’s because it’s not the size of the beam: beta is the distance from the interaction point that the beam is twice the size it is at the interaction point. What’s important for physics is that the lower the beta, the smaller the beam at the interaction point. With beta of 2 m, the beam is just 45 microns across at the interaction point, a quarter the width of a human hair, and its cross section is about five times smaller than with a beta of 11 m.

Four weeks of running under these conditions led to significant quantities of data being accumulated by the experiments, and then came the next big step. Over the weekend of 22 May, we started to run with 13 bunches in each beam.

The first collisions on 30 March were done with one bunch per beam, and the ultimate goal is to reach 2808, so there’s still some way to go. Nevertheless, we set a new luminosity record that weekend of 2 ´ 10²⁹. To put that in context, we achieved 10²⁷ on 30 March, the design figure for the LHC is 10³⁴and the objective for 2010 is to reach 10³².

Geneva, 31 May 2010. Researchers on the OPERA experiment at the INFN[1]’s Gran Sasso laboratory in Italy today announced the first direct observation of a tau particle in a muon neutrino beam sent through the Earth from CERN[2], 730km away. This is a significant result, providing the final missing piece of a puzzle that has been challenging science since the 1960s, and giving tantalizing hints of new physics to come.

Geneva March 9, The LHC is already over a week into its 2010 run, and the start of physics at 7 TeV is just around the corner. Last week, participants at the annual La Thuile workshop in Italy had the chance to take stock of what lies in store for the LHC’s first physics run. They learned that there’s a great sense of anticipation here at CERN and at particle physics labs around the globe, and for good reason – we’re about to open up the biggest range of potential new discovery that particle physics has seen in over a decade.

Our objective over the next 18 to 24 months is to deliver one inverse femtobarn of data to the experiments. In other words, enough data to make significant advances across a wide range of physics channels.

Take supersymmetry. ATLAS and CMS will each have enough data to significantly extend today’s sensitivity to new discoveries. Experiments today are sensitive to some supersymmetric particles with masses up to about 400 GeV. An inverse femtobarn at the LHC pushes that up to about 800 GeV. This means that in the next two years, the experiments at the LHC will explore as much territory in their quest for SUSY as has been covered in the history of particle physics to date. In other words, the LHC has a real chance over the next two years of discovering supersymmetric particles, possibly elucidating the nature of the dark matter that accounts for about a quarter of the mass and energy of the Universe.

The Higgs particle is another example. The last word that CERN had to say on the matter came from LEP almost ten years ago. In the last year of LEP running there were tantalising signs that the Higgs might have made an appearance but all we could say for sure was that the Higgs must have a mass above about 115 GeV. Since then, the Tevatron has done great work towards ruling out some of the mass range that the Higgs could inhabit. With an inverse femtobarn of data from the LHC, the combined analyses of ATLAS and CMS will be able to explore a wide mass range, and there’s even a chance of discovery if the particle has a mass near 160 GeV.

At the more exotic end of the potential discovery spectrum, LHC experiments will be sensitive to new massive particles that could herald the presence of extra dimensions. Discoveries up to masses of 2 TeV will be possible, whereas today’s reach is around 1 TeV.

All this makes now a very good time to be a particle physicist, and in particular a student of particle physics. Some 2500 graduate students are eagerly awaiting data from all the LHC experiments, ALICE, ATLAS, CMS, LHCb, LHCf and TOTEM. They’re a privileged group, set to produce the first PhD theses at the new high-energy frontier.

Two years of continuous running is a tall order both for the LHC operators and the experiments, but it will be well worth the effort. By abandoning CERN’s traditional annual operational cycle we’re increasing the overall running time and discovery potential over the next three years. This run will be followed by preparations for 14 TeV collisions in a single shutdown and another major advance into new territory as great as the one we are on the threshold of achieving.

A long run now is the right decision for the LHC and for the experiments. It gives the machine people the time necessary to prepare carefully for the work that’s needed before allowing 14 TeV. And for the experiments, 18 to 24 months will bring enough data across all the potential discovery areas to firmly establish the LHC as the world’s foremost facility for high-energy particle physics.

Yesterday evening at 18:03, the LHC ended its first full period of operation in style. Collisions at 2.36 TeV recorded since last weekend have set a new world record and brought to a close a successful first run. The LHC has now been put into standby mode, and will restart in February 2010 following a short technical stop to prepare for higher energy collisions and the start of the main research programme.

A technical stop is needed to prepare the LHC for higher energy running in 2010. Before the 2009 running period began, all the necessary preparations to run up to a collision energy of 2.36 TeV had been carried out. To run at higher energy requires higher electrical currents in the LHC magnet circuits. This places more exacting demands on the new machine protection systems, which need to be readied for the task. Commissioning work for higher energies will be carried out in January, along with necessary adaptations to the hardware and software of the protection systems that have come to light during the 2009 run.

The success of the 2009 run is down to the skill and dedication of every one of you. Congratulations and thanks to you all.

Geneva, 23 November 2009. Today the LHC circulated two beams simultaneously for the first time, allowing the operators to test the synchronization of the beams and giving the experiments their first chance to look for proton-proton collisions. With just one bunch of particles circulating in each direction, the beams can be made to cross in up to two places in the ring. From early in the afternoon, the beams were made to cross at points 1 and 5, home to the ATLAS and CMS detectors, both of which were on the lookout for collisions. Later, beams crossed at points 2 and 8, ALICE and LHCb.

“It’s a great achievement to have come this far in so short a time,” said CERN Director General Rolf Heuer. “But we need to keep a sense of perspective–there’s still much to do before we can start the LHC physics programme.”

Beams were first tuned to produce collisions in the ATLAS detector, which recorded its first candidate for collisions at 14:22 this afternoon. Later, the beams were optimised for CMS. In the evening, ALICE had the first optimisation, followed by LHCb. The attached file shows the first collision candidate in CMS. It was reported at 19:40.

“This is great news, the start of a fantastic era of physics and hopefully discoveries after 20 years' work by the international community to build a machine and detectors of unprecedented complexity and performance," said ATLAS spokesperson Fabiola Gianotti.

“The events so far mark the start of the second half of this incredible voyage of discovery of the secrets of nature,” said CMS spokesperson Tejinder Virdee.

“It was standing room only in the ALICE control room and cheers erupted with the first collisions,” said ALICE spokesperson Jurgen Schukraft. “This is simply tremendous.”

“The tracks we’re seeing are beautiful,” said LHCb spokesperson Andrei Golutvin, “we’re all ready for serious data taking in a few days time.”

These developments come just three days after the LHC restart, demonstrating the excellent performance of the beam control system. Since the start-up, the operators have been circulating beams around the ring alternately in one direction and then the other at the injection energy of 450 GeV. The beam lifetime has gradually been increased to 10 hours, and today beams have been circulating simultaneously in both directions, still at the injection energy.

Next on the schedule is an intense commissioning phase aimed at increasing the beam intensity and accelerating the beams. All being well, by Christmas, the LHC should reach 1.2 TeV per beam, and have provided good quantities of collision data for the experiments’ calibrations.

Geneva, 20 November 2009.
Particle beams are once again circulating in the world’s most powerful particle accelerator, CERN*’s Large Hadron Collider (LHC). This news comes after the machine was handed over for operation on Wednesday morning. A clockwise circulating beam was established at ten o'clock this evening. This is an important milestone on the road towards first physics at the LHC, expected in 2010.

“It’s great to see beam circulating in the LHC again,” said CERN Director General Rolf Heuer. “We’ve still got some way to go before physics can begin, but with this milestone we’re well on the way.”

The LHC circulated its first beams on 10 September 2008, but suffered a serious malfunction nine days later. A failure in an electrical connection led to serious damage, and CERN has spent over a year repairing and consolidating the machine to ensure that such an incident cannot happen again.
“The LHC is a far better understood machine than it was a year ago,” said CERN’s Director for Accelerators, Steve Myers.“We’ve learned from our experience, and engineered the technology that allows us to move on. That’s how progress is made.”

Recommissioning the LHC began in the summer, and successive milestones have regularly been passed since then. The LHC reached its operating temperature of 1.9 Kelvin, or about -271 Celsius, on 8 October. Particles were injected on 23 October, but not circulated. A beam was steered through three octants of the machine on 7 November, and circulating beams have now been re-established. The next important milestone will be low-energy collisions, expected in about a week from now. These will give the experimental collaborations their first collision data, enabling important calibration work to be carried out. This is significant, since up to now, all the data they have recorded comes from cosmic rays. Ramping the beams to high energy will follow in preparation for collisions at 7 TeV (3.5 TeV per beam) next year.

Particle physics is a global endeavour, and CERN has received support from around the world in getting the LHC up and running again.

“It’s been a herculean effort to get to where we are today,” said Myers. “I’d like to thank all those who have taken part, from CERN and from our partner institutions around the world.”

A press conference will be held at CERN, at the Globe of Science and Innovation, at 2pm on Monday 23 November, and webcast at:
http://webcast.cern.ch/. Submit your questions to @CERN via Twitter. We cannot guarantee that all questions will be answered.

Follow LHC progress on twitter at www.twitter.com/cern
For photos, video and latest information see:
http://press.web.cern.ch/press/lhc-first-physics/
Contact : http://press.web.cern.ch/press/ContactUs.html

Harvard physicist Cumrun Vafa tells scientists at the Large Hadron Collider that the discovery of a predicted, long-lived particle during research there would be the first experimental confirmation of string theory.

http://news.harvard.edu/gazette/story/2009/11/a-line-on-string-theory/?

The first CMS beam splashes was detected on November 7th 2009.
Beam splashes are when a beam is threaded part-way through the LHC ring, then deliberately collided with a closed collimators, 150m upstream of the CMS experiment. The secondary particles are produced by the interaction of the beam with the collimator, most of them are absorbed, with the exception of the muons and neutrinos. CMS can detect muons, and what is seen is a huge splash of activity, shown in this event display. The little red lines are reconstructed muon tracks, blue dots are raw hits, and the yellow/blue starburst in the center is the calorimeter energy. It can be said that the beam is coming from the right-hand side of the detector ("LHC beam-1", the clockwise direction around the ring).
more:
http://cmsdoc.cern.ch/cms/performance/FirstBeam/cms-e-commentary09.htm

The LHC will run for the first part of the 2009-2010 run at 3.5 TeV per beam, with the energy rising later in the run. That’s the conclusion that we’ve just arrived at in a meeting involving the experiments, the machine people and the CERN management. We’ve selected 3.5 TeV because it allows the LHC operators to gain experience of running the machine safely while opening up a new discovery region for the experiments.

The developments that have allowed us to get to this point are good progress in repairing the damage in sector 3-4 and the related consolidation work, and the conclusion of testing on the 10000 high-current electrical connections last week. With that milestone, every one of the connections has been tested and we now know exactly where we stand.

The latest tests looked at the resistance of the copper stabilizer that surrounds the superconducting cable and carries current away in case of a quench. Many copper splices showing anomalously high resistance have been repaired already, and the tests on the final two sectors revealed no more outliers. That means that no more repairs are necessary for safe running this year and next.

The procedure for the 2009 start-up will be to inject and capture beams in each direction, take collision data for a few shifts at the injection energy, and then commission the ramp to higher energy. The first high-energy data should be collected a few weeks after the first beam of 2009 is injected. The LHC will run at 3.5 TeV per beam until a significant data sample has been collected and the operations team has gained experience in running the machine. Thereafter, with the benefit of that experience, we’ll take the energy up towards 5 TeV per beam. At the end of 2010, we’ll run the LHC with lead-ions for the first time. After that, the LHC will shut down and we’ll get to work on moving the machine towards 7 TeV per beam

The foreseen shutdown work on the LHC is proceeding well, including the powering tests with the new quench protection system. However, during the past week vacuum leaks have been found in two "cold" sectors of the LHC. The leaks were found in sectors 8-1 and 2-3 while they were being prepared for the electrical tests on the copper stabilizers at around 80 K. In both cases the leak is at one end of the sector, where the electrical feedbox, DFBA, joins Q7, the final magnet in the sector.

Unfortunately, the repair necessitates a partial warm-up of both sectors. This involves the end sub-sector being warmed to room temperature, while the adjacent sub-sector "floats” in temperature and the remainder of the sector is kept at 80 K. As the leak is from the helium circuit to the insulating vacuum, the repair work will have no impact on the vacuum in the beam pipe. However the intervention will have an impact on the schedule for the restart. It is now foreseen that the LHC will be closed up and ready for beam injection by mid-November.

The end of a Council week is a good opportunity to bring you up to date with the status of the LHC, and I'm pleased to say that we had a good deal of positive news to report to the delegations today. The bottom line is that we remain on course to restart the LHC safely this year, albeit currently about 2-3 weeks later than we'd hoped at Chamonix.

This Council week has seen many important developments for our future. I am particularly pleased that Council approved the Medium Term Plan and budget for 2010 as presented by the management. This is a strong vote of confidence in all of you. The President of Council is reporting on Council business in this issue of the Bulletin, so I will focus on the status of the LHC.

A tremendous amount of work has been done to understand fully the splices in the LHC's superconducting cable and copper stabilizers. One of these splices was the root cause of the incident last September that brought the LHC to a standstill. We've learned a great deal since then. It's mostly good news but there's also plenty of food for thought. The good news is that all the measurements done so far indicate that we will be ready by September or October to run the LHC safely in the range 4-5 TeV per beam. The food for thought is that the same tests tell us that before we can run safely above 5 TeV, more work is needed. This will be carried out in future shutdown periods.

Many of you will have heard, or seen on the LHC web pages, that we're warming up sector 4-5. This will give us increased confidence that we fully understand the splices. We're warming up this sector because we have developed a new non-invasive technique for investigating the splices. The sector has been measured at a temperature of 80 K, indicating at least one suspect splice. By warming the sector, the results of the test can be checked at room temperature, allowing us to confirm the reliability of the test at 80 K. If the 80 K measurements are confirmed, any suspect splices in this sector will be repaired. More importantly, validation of the 80K measurements will allow the splice resistance in the last three sectors to be measured at this temperature, thereby avoiding the time needed for re-warming. When these measurements are done, we'll have to balance energy against time: 4 TeV should require no further repairs, for example, whereas 5 TeV could call for more work. The measurements in these last three sectors will allow us to make that decision, determining the initial operating energy of the LHC in the range 4-5 TeV, and the start date for the first run.

The Bulletin will continue to keep you up to date with LHC progress, and if you are interested in a full report, Steve Myers at CERN and Jim Strait at Fermilab will be making detailed presentations on 2 July. Steve's presentation will be webcast at http://www.cern.ch/webcast.

Geneva, 30 April 2009. The 53rd and final replacement magnet for CERN's Large Hadron Collider (LHC) was lowered into the accelerator's tunnel today, marking the end of repair work above ground following the incident in September last year that brought LHC operations to a halt. Underground, the magnets are being interconnected, and new systems installed to prevent similar incidents happening again. The LHC is scheduled to restart in the autumn, and to run continuously until sufficient data have been accumulated for the LHC experiments to announce their first results.

"This is an important milestone in the repair process," said CERN's Director for Accelerators and Technology, Steve Myers. "It gets us close to where we were before the incident, and allows us to concentrate our efforts on installing the systems that will ensure a similar incident won't happen again."

The final magnet, a quadrupole designed to focus the beam, was lowered this afternoon and has started its journey to Sector 3-4, scene of the September incident. With all the magnets now underground, work in the tunnel will focus on connecting the magnets together and installing new safety systems, while on the surface, teams will shift their attention to replenishing the LHC's supply of spare magnets.

In total 53 magnets were removed from Sector 3-4. Sixteen that sustained minimal damage were refurbished and put back into the tunnel. The remaining 37 were replaced by spares and will themselves be refurbished to provide spares for the future.

"Now we will split our team into two parts," explained Lucio Rossi, Deputy head of CERN's Technology Department. "The main group will carry out interconnection work in the tunnel while a second will rebuild our stock of spare magnets."

The LHC repair process can be divided into three parts. Firstly, the repair itself, which is nearing completion with the installation of the last magnet today. Secondly, systems are being installed to monitor the LHC closely and ensure that similar incidents to that of last September cannot happen again. This work will continue into the summer. Finally, extra pressure relief valves are being installed to
release helium in a safe and controlled manner should there be leaks inside the LHC's cryostat at any time in the machine's projected 15-20 year operational lifetime.

The CERN Management today confirmed the restart schedule for the Large Hadron Collider resulting from the recommendations from the Chamonix workshop. The new schedule foresees first beams in the LHC at the end of September this year, with collisions following in late October. A short technical stop has also been foreseen over the Christmas period. The LHC will then run through to autumn next year, ensuring that the experiments have adequate data to carry out their first new physics analyses and have results to announce in 2010. The new schedule also permits the possible collisions of lead ions in 2010.

This new schedule represents a delay of 6 weeks with respect to the previous schedule which foresaw LHC "cold at the beginning of July". The cause of this delay is due to several factors such as implementation of a new enhanced protection system for the busbar and magnet splices, installation of new pressure relief valves to reduce the collateral damage in case of a repeat incident, application of more stringent safety constraints, and scheduling constraints associated with helium transfer and storage.

In Chamonix there was consensus among all the technical specialists that the new schedule is tight but realistic.

The enhanced protection system measures the electrical resistance in the cable joints (splices) and is much more sensitive than the system existing on 19 September.

The new pressure relief system has been designed in two phases. The first phase involves installation of relief valves on existing vacuum ports in the whole ring. Calculations have shown that in an incident similar to that of 19 September, the collateral damage (to the interconnects and super-insulation) would be minor with this first phase.

The second phase involves adding additional relief valves on all the dipole magnets and would guarantee minor collateral damage (to the interconnects and super-insulation) in all worst cases over the life of the LHC. One of the questions discussed in Chamonix was whether to warm up the whole LHC machine in 2009 so as to complete the installation of these new pressure relief valves or to perform these modifications on sectors that were warmed up for other reasons. The Management has decided for 2009 to install relief valves on the four sectors that were already foreseen to be warmed up. The dipoles in the remaining four sectors will be equipped in 2010.

Many issues were tackled in Chamonix this week, and important recommendations made. Under a proposal submitted to CERN management, we will have physics data in late 2009, and there is a strong recommendation to run the LHC through the winter and on to autumn 2010 until we have substantial quantities of data for the experiments. With this change to the schedule, our goal for the LHC's first running period is an integrated luminosity of more than 200 pb-1 operating at 5 TeV per beam, sufficient for the first new physics measurements to be made. This, I believe, is the best possible scenario for the LHC and for particle physics.

There were discussions in Chamonix between accelerator and detector physicists on several important issues. Agreements were reached whereby teams drawing from both communities will work together on important subjects, such as the detailed analysis of measurements made during testing of magnets on the surface.

Since the incident, enormous progress has been made in developing techniques to detect any small anomaly. These will be used in order to get a complete picture of the resistance in the splices of all magnets installed in the machine. This will allow improved early warning of any additional suspicious splices during operation. The early warning systems will be in place and fully tested before restarting the LHC.

Another important topic for the future was the radiation hardness of electronics installed in the service areas and the tunnel. For many years, particle detector electronics have been designed to cope with events such as loss of beam into the detectors. Until now, this has not been necessary for the accelerators, but will become so when the LHC moves to higher beam intensity and luminosity. Again, with detector and accelerator physicists working closely together, the experience gained from the detectors can be applied to the LHC itself.

As the Bulletin reported on 30 January, opening up a magnet in which an anomalously high electrical resistance was measured made the reason for the anomaly immediately obvious - a splice had not been correctly made. This is one of two such splices that were identified in the five sectors tested, and as a result the magnet containing the second will also be removed from the tunnel for repair. Since resistance tests can only be conducted in cold magnets, three sectors remain to be tested: sector 3-4 where the original incident occurred and the sectors on either side. Within sector 3-4, the 53 magnets that are being replaced in the tunnel will all be tested before cool down, and the sectors either side will be cooled down early enough to intervene if necessary with no impact on the schedule. This leaves around 100 dipole magnets that we'll not be able to test until September and a correspondingly small chance that we may find further bad splices that will need to be repaired before operation starts.

The Chamonix workshop involved a lot of work by many people. Much progress has been made, and the management now has all it needs to make an informed decision next Monday on LHC restart. I'd like to thank all those involved, and I will be writing to you again early next week to let you know our decision.

A meeting, chaired by Jos Engelen, on the LHC schedule took place on Tuesday afternoon. Participating were the LHC Project Leader, Lyn Evans, the incoming Director of Accelerators and Technology, Steve Myers, the LHC coordinator, M. Ferro-Luzzi, and the Spokespersons and Technical Coordinators of the LHC experiments.

Information was presented on the LHC schedule that reflected present understanding. An official presentation is being prepared for the CERN Council in December. The schedule outlined below is therefore still subject to changes.
Extracts from the summary of the meeting are given below.

A lot of progress has been made in developing diagnostic procedures (calorimetry) and tools to make sure that no other bad splices are 'hidden' in the machine

Moving out magnets affected by the incident has started. It is foreseen to remove 39 dipoles, including 6 (3 at each side) in a buffer zone. These magnets should not be affected but will be re-tested just to confirm that the limits of the affected region are understood.

All magnets to be brought to the surface should be out before the Christmas shutdown. By then 20 dipoles should already be back in the machine.
The plan is to install the first dipole (from the set of spares) already this week.

The test bench (for cold testing) is a limiting factor. Capacity to be ramped up after connection of 18 kW plant (now 6 kW) in February 2009.

Last magnet should be back in end of March 2009; whole machine cold again beginning of July. Meaning optimistically first beam in the machine end of July.

Many activities are going on in parallel in the tunnel, but are not (and should not come) on the critical path (work on flanges, relief valves, cabling)

Point of concern of experiments: access conditions in experimental caverns and service caverns. Is being looked into by/ with Safety Commission.

Lyn Evans has been invited to give a talk on the status of the machine on the Monday morning of the December CMS Week.

LHC physics data taking gets underway at new record collision energy of 8TeV

(April 5, 2012)

CERN experiment makes spectroscopic measurement of antihydrogen

(March 7, 2012)

LHCb experiment squeezes the space for expected new physics

(March 5, 2012)

Update on the OPERA Result

(February 22, 2012)

LHC to run at 4 TeV per beam in 2012

(February 13, 2012)

ATLAS and CMS experiments present Higgs search status

(December 13, 2011)

CMS/ATLAS combination on the SM Higgs Searches
(November 18, 2011)

OPERA experiment update

(November 18, 2011)

CERN has 2020 vision for LHC upgrade
(November 16, 2011)

LHC proton run for 2011 reaches successful conclusion

(October 31, 2011)

CERN supports European Year of Volunteering through Citizen Cyberscience Centre

News in Persian

CERN experiment weighs antimatter with unprecedented accuracy

LHC experiments present their latest results at Europhysics Conference on High Energy Physics

(July 21, 2011)

New two-particle correlations observed in the CMS detector at the LHC
The CMS Collaboration at CERN released today a paper entitled “Observation of Long-Range Near-Side Angular Correlations in Proton-Proton Collisions” that details signs of a new phenomenon in proton interactions.

News: 26 October 2009

Particles are back in the LHC!