www.yazdparticles.ir
Nov 11, 2010
CERN completes transition to lead-ion running at the LHC
Geneva, 8 November 2010. Four days is all it took for the LHC operations team at CERN to complete the transition from protons to lead ions in the LHC. After extracting the final proton beam of 2010 on 4 November, commissioning the lead-ion beam was underway by early afternoon. First collisions were recorded at 00:30 CET on 7 November, and stable running conditions marked the start of physics with heavy ions at 11:20 CET today.
“The speed of the transition to lead ions is a sign of the maturity of the LHC,” said CERN Director General Rolf Heuer. “The machine is running like clockwork after just a few months of routine operation.”
Operating the LHC with lead ions – lead atoms stripped of electrons - is completely different from operating the machine with protons. From the source to collisions, operational parameters have to be re-established for the new type of beam. For lead-ions, as for protons before them, the procedure started with threading a single beam round the ring in one direction and steadily increasing the number of laps before repeating the process for the other beam. Once circulating beams had been established they could be accelerated to the full energy of 287 TeV per beam. This energy is much higher than for proton beams because lead ions contain 82 protons. Another period of careful adjustment was needed before lining the beams up for collision, and then finally declaring that nominal data taking conditions, known at CERN as stable beams, had been established. The three experiments recording data with lead ions, ALICE, ATLAS and CMS can now look forward to continuous lead-ion running until CERN’s winter technical stop begins on 6 December.
“It's been very impressive to see how well the LHC has adapted to lead ions,” said Jurgen Schukraft, spokesperson of the ALICE experiment. “The ALICE detector has been optimised to record the large number of tracks that emerge from ion collisions and has handled the first collisions very well, so we are all set to explore this new opportunity at LHC.”
“After a very successful proton run, we’re very excited to be moving to this new phase of LHC operation,” said ATLAS spokesperson Fabiola Gianotti. “The ATLAS detector has recorded first spectacular heavy-ion events, and we are eager to study them in detail.”
“We designed CMS as a multi-purpose detector,” said Guido Tonelli, the collaboration’s spokesperson, “and it’s very rewarding to see how well it’s adapting to this new kind of collision. Having data collected by the same detector in proton-proton and heavy-ion modes is a powerful tool to look for unambiguous signatures of new states of matter.”
Lead-ion running opens up an entirely new avenue of exploration for the LHC programme, probing matter as it would have been in the first instants of the Universe’s existence. One of the main objectives for lead-ion running is to produce tiny quantities of such matter, which is known as quark-gluon plasma, and to study its evolution into the kind of matter that makes up the Universe today. This exploration will shed further light on the properties of the strong interaction, which binds the particles called quarks, into bigger objects, such as protons and neutrons.
Following the winter technical stop, operation of the collider will start again with protons in February and physics runs will continue through 2011.
LHC protons 2010: mission accomplished
When we started running the LHC at the end of March, we set ourselves the objective of reaching a luminosity of 1032 by the end of 2010 proton running. Last night, we achieved that goal. The beams that went in at around 2:00am, were colliding with a luminosity of 1.01 ´1032 by 3:38am in both ATLAS and CMS, and had delivered an integrated luminosity of over 2 inverse picobarns to ATLAS, CMS and LHCb by midday today. It’s a great achievement by all concerned to reach this important milestone with over two weeks to spare. The remainder of this year’s proton running will be devoted to maximising the LHC 2010 data set and preparing for 2011 proton running before we switch to lead ions in November.
The significance of this milestone can’t be underestimated, since it is a necessary step on the way to the larger goal of delivering an integrated luminosity of one inverse femtobarn to the experiments by the end of 2011. That’s the amount of data we need to ensure that if nature has put new physics in our path at the LHC’s current collision energy, we’ll have a good chance of seeing it.
At the moment, we’re running the LHC with 248 bunches per beam in a configuration that allows us to go much higher. As 2011 proton running gets underway early next year we’ll continue increasing the number of bunches, since a factor of two or so more luminosity is still needed if we’re to reach our one inverse femtobarn goal. That, however, is for next year. In the meantime, the objective we set ourselves for this year was realistic, but tough, and it’s very gratifying to see it achieved in such fine style.
Aug 12, 2010
LHCNews: ICHEP 2010 conference highlights first results from the LHC
Geneva, 26 July 2010. First results from the LHC at CERN are being revealed at ICHEP, the world’s largest international conference on particle physics, which has attracted more than 1000 participants to its venue in Paris. The spokespersons of the four major experiments at the LHC – ALICE, ATLAS, CMS and LHCb – are today presenting measurements from the first three months of successful LHC operation at 3.5 TeV per beam, an energy three and a half times higher than previously achieved at a particle accelerator.
With these first measurements the experiments are rediscovering the particles that lie at the heart of the Standard Model – the package that contains current understanding of the particles of matter and the forces that act between them. This is an essential step before moving on to make discoveries. Among the billions of collisions already recorded are some that contain 'candidates' for the top quark, for the first time at a European laboratory.
“Rediscovering our ‘old friends’ in the particle world shows that the LHC experiments are well prepared to enter new territory” said CERN’s Director-General Rolf Heuer. “It seems that the Standard Model is working as expected. Now it is down to nature to show us what is new.”
The quality of the results presented at ICHEP bears witness both to the excellent performance of the LHC and to the high quality of the data in the experiments. The LHC, which is still in its early days, is making steady progress towards its ultimate operating conditions. The luminosity – a measure of the collision rate - has already risen by a factor of more than a thousand since the end of March. This rapid progress with commissioning the LHC beam has been matched by the speed with which the data on billions of collisions have been processed by the Worldwide LHC Computing Grid, which allows data from the experiments to be analysed at collaborating centres around the world.
“Within days we were finding Ws, and later Zs – the two carriers of the weak force discovered here at CERN nearly 30 years ago,” said Fabiola Gianotti, spokesperson for the 3000-strong ATLAS collaboration. “Thanks to the efforts of the whole collaboration, in particular the young scientists, everything from data-taking at the detector, through calibration, data processing and distribution, to the physics analysis, has worked fast and efficiently.”
“It is amazing to see how quickly we have ‘re-discovered’ the known particles: from the lightest resonances up to the massive top quark. What we have shown here in Paris is just the first outcome of an intense campaign of accurate measurements of their properties.” said Guido Tonelli, spokesperson for CMS. “This patient and systematic work is needed to establish the known background to any new signal.”
“The LHCb experiment is tailor-made to study the family of b particles, containing beauty quarks,” said the experiment’s spokesperson Andrei Golutvin, “So it’s extremely gratifying that we are already finding hundreds of examples of these particles, clearly pin-pointed through the analysis of many particle tracks.”
“The current running with proton collisions has allowed us to connect with results from other experiments at lower energies, test and improve the extrapolations made for the LHC, and prepare the ground for the heavy-ion runs,” said Jurgen Schukraft, spokesperson for the ALICE collaboration. This experiment is optimized to study collisions of lead ions, which will occur in the LHC for the first time later this year.
Two further experiments have also already benefited from the first months of LHC operation at 3.5 TeV per beam. LHCf, which is studying the production of neutral particles in proton-proton collisions to help in understanding cosmic-ray interactions in the Earth’s atmosphere, has already collected the data it needs at a beam energy of 3.5 TeV. TOTEM, which has to move close to the beams for its in-depth studies of the proton, is beginning to make its first measurements.
CERN will run the LHC for 18-24 months with the objective of delivering enough data to the experiments to make significant advances across a wide range of physics processes. With the amount of data expected, referred to as one inverse femtobarn, the experiments should be well placed to make inroads in to new territory, with the possibility of significant discoveries.
Source: IPM
Europe reaches the top, err, the top reaches Europe
July 23, 2010
It might be a long way to the top, but the LHC experiments are already half-way there. Today at the International Conference on High Energy Physics in Paris, the CMS and ATLAS experiments presented their first top quark candidates. These candidates are collisions that have all the hallmarks of having produced top quarks, but the experiments don’t yet have enough data to be 100% sure that the events created top quarks that decayed into other particles, rather than another type of event.
“The signal is starting to rise from the background,” notes Tim Christiansen from CMS.
The top quark, the heaviest particle in the Standard Model, was discovered at Fermilab’s Tevatron in 1995. The CDF and DZero experiments on the Tevatron are still busy measuring its properties in detail (one of this morning’s parallel sessions had several talks on its width, mass and likely couplings to particles of and beyond the Standard Model). Now the LHC experiments are joining them on the way to explore the top: both CMS and ATLAS showed selected candidate events of top quark pairs.
Finding top quarks at the LHC is exciting because the top is the last, and heaviest, particle that the LHC needed to add to its list of ‘rediscoveries’. It is also an important partner in the hunt for all sorts of new physics. The better the top and its behavior are understood the easier it will be to distinguish events that involve direct top quark production from events that involve, for example, the Higgs or supersymmetric particles.
http://www.symmetrymagazine.org/breaking/2010/07/23/europe-reaches-the-top-err-the-top-reaches-europe/
Source: ipm
It might be a long way to the top, but the LHC experiments are already half-way there. Today at the International Conference on High Energy Physics in Paris, the CMS and ATLAS experiments presented their first top quark candidates. These candidates are collisions that have all the hallmarks of having produced top quarks, but the experiments don’t yet have enough data to be 100% sure that the events created top quarks that decayed into other particles, rather than another type of event.
“The signal is starting to rise from the background,” notes Tim Christiansen from CMS.
The top quark, the heaviest particle in the Standard Model, was discovered at Fermilab’s Tevatron in 1995. The CDF and DZero experiments on the Tevatron are still busy measuring its properties in detail (one of this morning’s parallel sessions had several talks on its width, mass and likely couplings to particles of and beyond the Standard Model). Now the LHC experiments are joining them on the way to explore the top: both CMS and ATLAS showed selected candidate events of top quark pairs.
Finding top quarks at the LHC is exciting because the top is the last, and heaviest, particle that the LHC needed to add to its list of ‘rediscoveries’. It is also an important partner in the hunt for all sorts of new physics. The better the top and its behavior are understood the easier it will be to distinguish events that involve direct top quark production from events that involve, for example, the Higgs or supersymmetric particles.
http://www.symmetrymagazine.org/breaking/2010/07/23/europe-reaches-the-top-err-the-top-reaches-europe/
Source: ipm
Progress at the LHC
Geneva. 15 July, 2010
A month ago we decided to focus fully on commissioning the LHC beam with the goal of establishing the conditions for routine collisions between bunches at design intensity at an energy of 3.5 TeV per beam. This involved optimizing not only the LHC but also the injection of protons from the SPS. The teams made very good progress and the machine now runs smoothly for physics with multiple bunches of 1011 protons per bunch.
This is an excellent achievement for a machine that is still in its infancy, having produced its first collisions at 3.5 TeV only three and a half months ago.
While there remain issues to understand – as is hardly surprising with a new machine operating in a new energy region – the effort on beam commissioning has certainly paid off. The peak luminosity, which depends on the number of protons per beam and how tightly they are squeezed together, has risen by more than a factor of 1000 to a value of 1.4 x 1030 cm-2 s-1.
Increased luminosity means more collisions and more data for the experiments. Today we are already above an integrated luminosity of 200 nb-1. This puts the experiments in an excellent position to present important results in a new energy region at the major international conference, ICHEP 2010, which starts later next week.
source: IPM
This is an excellent achievement for a machine that is still in its infancy, having produced its first collisions at 3.5 TeV only three and a half months ago.
While there remain issues to understand – as is hardly surprising with a new machine operating in a new energy region – the effort on beam commissioning has certainly paid off. The peak luminosity, which depends on the number of protons per beam and how tightly they are squeezed together, has risen by more than a factor of 1000 to a value of 1.4 x 1030 cm-2 s-1.
Increased luminosity means more collisions and more data for the experiments. Today we are already above an integrated luminosity of 200 nb-1. This puts the experiments in an excellent position to present important results in a new energy region at the major international conference, ICHEP 2010, which starts later next week.
source: IPM
The first two months at 3.5 TeV per beam
Geneva 2 June
Two months is a very short time in the life of a major particle physics project, but a lot can happen in that time as the LHC has shown since 30 March. Colliding beams at 3.5 TeV was an important milestone, a start to the LHC physics programme, but it was just a single step on a very long journey. Since then, we’ve lengthened our stride, and are progressing well towards the key objectives for 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 1034 and the objective for 2010 is to reach 1032.
Two months is a very short time in the life of a major particle physics project, but a lot can happen in that time as the LHC has shown since 30 March. Colliding beams at 3.5 TeV was an important milestone, a start to the LHC physics programme, but it was just a single step on a very long journey. Since then, we’ve lengthened our stride, and are progressing well towards the key objectives for 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 1034 and the objective for 2010 is to reach 1032.
All this was achieved during physics running, leading to incredible progress being made by the experiments. They have been running with 90% efficiency, a remarkable achievement for devices of such complexity. Billions of collisions have been recorded and successfully dispatched for analysis via the LHC Computing Grid. The rediscovery of the Standard Model, which is necessary before we can confidently say we’re ready for new physics, is well underway. There are even some intriguing observations about the properties of collisions at this new energy. As a measure of their success to date, the experiments have already published or submitted over a dozen papers to peer reviewed journals and conferences based on LHC collision data.
Physics running is interspersed with periods of machine development essential for further progress to be made. As a foretaste of what the experiments can expect over the next two months, the LHC operations team has notched up some impressive results over the last few machine development sessions. The first of these was to inject bunches with more than the LHC’s design intensity and collide them at 450 GeV. There’s nothing new about 450 GeV, but it’s an important milestone nevertheless since the difficulty of colliding bunches increases with intensity. By comparison, adding extra bunches is a relatively easier task. The icing on the cake of last week’s machine development came when design intensity bunches were brought into collision at 3.5 TeV on 26 May.
Behind this great progress is a guiding principle of caution. The masters of ceremony are those responsible for the systems that protect the LHC and the experiments from stray beam particles. Collimators absorb particles that wander from their intended orbits before they can impinge on LHC magnets or sensitive detector elements, while the LHC beam dump system is there to extract the beams safely in case of need. Any increase in intensity has to be approved by the LHC machine protection teams, and progress is incremental. Each increase in intensity, and therefore stored energy in the machine, is a learning process for the machine protection teams and only when they are ready do increases in intensity happen.
With all eyes on the amount of data being delivered to the experiments, it would be easy to overlook some of the pioneering systems that make the LHC possible. When I asked someone in the CERN Control Centre last week about the cryogenics, they replied that it’s working so well they’d almost forgotten it was there. For the operators of the world’s largest cryogenic installation that’s quite a compliment. And for anyone wondering whether large-scale cryogenics may have broader applications, the LHC is proving to be an interesting test case.
The same goes for the vacuum systems. Beam lifetimes of 1000 hours have been posted, which is truly exceptional for any particle accelerator. Of course, we don’t keep beams for that long: there are many reasons why beams are extracted long before they reach their theoretical lifetimes. So far in the LHC, the longest fill for physics has been 30 hours, which well exceeds my expectations for the first months of running.
A lot can happen in two months, and we are well on course to achieving our 2010 objectives for the LHC. The fact that the LHC’s availability for operation is already over 60% is testimony to the skills and professionalism of all those who operate the machine and its supporting infrastructure, and it is perhaps the one statistic that has made all the others possible. As I write, we’ve recently completed a rather frustrating weekend, with a short circuit in a cable terminal of an electrical cabinet stopping us from running. By Monday morning, however, we’d recovered and will resume LHC running tomorrow after a scheduled technical stop. Glitches such as this are a fact of life in a working lab, and do not detract from the fact that we have much to be pleased with from these two months. As the figures I’ve quoted above illustrate, however, we still have a long way to travel. My congratulations go to all involved with this great scientific adventure.
Source: IPM
Jun 16, 2010
CERN Press Release - Particle Chameleon Caught in the act of Changing
31 May 2010
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.
The neutrino puzzle began with a pioneering and ultimately Nobel Prize winning experiment conducted by US scientist Ray Davies beginning in the 1960s. He observed far fewer neutrinos arriving at the Earth from the Sun than solar models predicted: either solar models were wrong, or something was happening to the neutrinos on their way. A possible solution to the puzzle was provided in 1969 by the theorists Bruno Pontecorvo and Vladimir Gribov, who first suggested that chameleon-like oscillatory changes between different types of neutrinos could be responsible for the apparent neutrino deficit.
Several experiments since have observed the disappearance of muon-neutrinos, confirming the oscillation hypothesis, but until now no observations of the appearance of a tau-neutrino in a pure muon-neutrino beam have been observed: this is the first time that the neutrino chameleon has been caught in the act of changing from muon-type to tau-type.
Antonio Ereditato, Spokesperson of the OPERA collaboration described the development as: “an important result which rewards the entire OPERA collaboration for its years of commitment and which confirms that we have made sound experimental choices. We are confident that this first event will be followed by others that will fully demonstrate the appearance of neutrino oscillation".
"The OPERA experiment has reached its first goal: the detection of a tau neutrino obtained from the transformation of a muon neutrino, which occurred during the journey from Geneva to the Gran Sasso Laboratory,” added Lucia Votano, Director Gran Sasso laboratories. “This important result comes after a decade of intense work performed by the Collaboration, with the support of the Laboratory, and it again confirms that LNGS is a leading laboratory in Astroparticle Physics”.
The OPERA result follows seven years of preparation and over three years of beam provided by CERN. During that time, billions of billions of muon-neutrinos have been sent from CERN to Gran Sasso, taking just 2.4 milliseconds to make the trip. The rarity of neutrino oscillation, coupled with the fact that neutrinos interact very weakly with matter makes this kind of experiment extremely subtle to conduct. CERN’s neutrino beam was first switched on in 2006, and since then researchers on the OPERA experiment have been carefully sifting their data for evidence of the appearance of tau particles, the telltale sign that a muon-neutrino has oscillated into a tau-neutrino. Patience of this kind is a virtue in particle physics research, as INFN President Roberto Petronzio explained:
“This success is due to the tenacity and inventiveness of the physicists of the international community, who designed a particle beam especially for this experiment,” said Petronzio. “In this way, the original design of Gran Sasso has been crowned with success. In fact, when constructed, the laboratories were oriented so that they could receive particle beams from CERN”.
At CERN, neutrinos are generated from collisions of an accelerated beam of protons with a target. When protons hit the target, particles called pions and kaons are produced. They quickly decay, giving rise to neutrinos. Unlike charged particles, neutrinos are not sensitive to the electromagnetic fields usually used by physicists to change the trajectories of particle beams. Neutrinos can pass through matter without interacting with it; they keep the same direction of motion they have from their birth. Hence, as soon as they are produced, they maintain a straight path, passing through the Earth's crust. For this reason, it is extremely important that from the very beginning the beam points exactly towards the laboratories at Gran Sasso.
‘This is an important step for neutrino physics,” said CERN Director General Rolf Heuer. “My congratulations go to the OPERA experiment and the Gran Sasso Laboratories, as well as the accelerator departments at CERN. We’re all looking forward to unveiling the new physics this result presages.”
While closing a chapter on understanding the nature of neutrinos, the observation of neutrino oscillations is strong evidence for new physics. In the theories that physicists use to explain the behaviour of fundamental particles, which is known as the Standard Model, neutrinos have no mass. For neutrinos to be able to oscillate, however, they must have mass: something must be missing from the Standard Model. Despite its success in describing the particles that make up the visible Universe and their interactions, physicists have long known that there is much the Standard Model does not explain. One possibility is the existence of other, so-far unobserved types of neutrinos that could shed light on Dark Matter, which is believed to make up about a quarter of the Universe’s mass.
[1] Italy's national nuclear physics institute, INFN (Istituto Nazionale di Fisica Nucleare), supports, coordinates and carries out scientific research in subnuclear, nuclear and astroparticle physics and is involved in developing related technologies. The institute operates in conjunction with universities and is involved in the wider international debate as well as in cooperation programs. The Institute was established by physicists in Milan, Padua, Rome and Turin on 8 August 1951with a view to pursuing and furthering the research started by Enrico Fermi's team of researchers during the 1930s. In over 50 years, INFN has gradually extended and currently includes thirty detachments, four national laboratories and a data processing centre. Furthermore, the area outside Pisa is host to the gravitational observatory EGO, jointly developed by INFN and the French national research centre. As many as 5000 contribute to the institute's endeavours; 2000 of whom are directly employed by it, 2000 university staff and more than one thousand among students and scholarship holders.
[2] CERN, the European Organization for Nuclear Research, is the world's leading laboratory for particle physics. It has its headquarters in Geneva. At present, its Member States are Austria, Belgium, Bulgaria, the Czech Republic, Denmark, Finland, France, Germany, Greece, Hungary, Italy, Netherlands, Norway, Poland, Portugal, Slovakia, Spain, Sweden, Switzerland and the United Kingdom. India, Israel, Japan, the Russian Federation, the United States of America, Turkey, the European Commission and UNESCO have Observer status.
Source: IPM.ir
The first two months at 3.5 TeV per beam
2 June 2010
Geneva 2 June
Two months is a very short time in the life of a major particle physics project, but a lot can happen in that time as the LHC has shown since 30 March. Colliding beams at 3.5 TeV was an important milestone, a start to the LHC physics programme, but it was just a single step on a very long journey. Since then, we’ve lengthened our stride, and are progressing well towards the key objectives for 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 1034 and the objective for 2010 is to reach 1032.
Two months is a very short time in the life of a major particle physics project, but a lot can happen in that time as the LHC has shown since 30 March. Colliding beams at 3.5 TeV was an important milestone, a start to the LHC physics programme, but it was just a single step on a very long journey. Since then, we’ve lengthened our stride, and are progressing well towards the key objectives for 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 1034 and the objective for 2010 is to reach 1032.
All this was achieved during physics running, leading to incredible progress being made by the experiments. They have been running with 90% efficiency, a remarkable achievement for devices of such complexity. Billions of collisions have been recorded and successfully dispatched for analysis via the LHC Computing Grid. The rediscovery of the Standard Model, which is necessary before we can confidently say we’re ready for new physics, is well underway. There are even some intriguing observations about the properties of collisions at this new energy. As a measure of their success to date, the experiments have already published or submitted over a dozen papers to peer reviewed journals and conferences based on LHC collision data.
Physics running is interspersed with periods of machine development essential for further progress to be made. As a foretaste of what the experiments can expect over the next two months, the LHC operations team has notched up some impressive results over the last few machine development sessions. The first of these was to inject bunches with more than the LHC’s design intensity and collide them at 450 GeV. There’s nothing new about 450 GeV, but it’s an important milestone nevertheless since the difficulty of colliding bunches increases with intensity. By comparison, adding extra bunches is a relatively easier task. The icing on the cake of last week’s machine development came when design intensity bunches were brought into collision at 3.5 TeV on 26 May.
Behind this great progress is a guiding principle of caution. The masters of ceremony are those responsible for the systems that protect the LHC and the experiments from stray beam particles. Collimators absorb particles that wander from their intended orbits before they can impinge on LHC magnets or sensitive detector elements, while the LHC beam dump system is there to extract the beams safely in case of need. Any increase in intensity has to be approved by the LHC machine protection teams, and progress is incremental. Each increase in intensity, and therefore stored energy in the machine, is a learning process for the machine protection teams and only when they are ready do increases in intensity happen.
With all eyes on the amount of data being delivered to the experiments, it would be easy to overlook some of the pioneering systems that make the LHC possible. When I asked someone in the CERN Control Centre last week about the cryogenics, they replied that it’s working so well they’d almost forgotten it was there. For the operators of the world’s largest cryogenic installation that’s quite a compliment. And for anyone wondering whether large-scale cryogenics may have broader applications, the LHC is proving to be an interesting test case.
The same goes for the vacuum systems. Beam lifetimes of 1000 hours have been posted, which is truly exceptional for any particle accelerator. Of course, we don’t keep beams for that long: there are many reasons why beams are extracted long before they reach their theoretical lifetimes. So far in the LHC, the longest fill for physics has been 30 hours, which well exceeds my expectations for the first months of running.
A lot can happen in two months, and we are well on course to achieving our 2010 objectives for the LHC. The fact that the LHC’s availability for operation is already over 60% is testimony to the skills and professionalism of all those who operate the machine and its supporting infrastructure, and it is perhaps the one statistic that has made all the others possible. As I write, we’ve recently completed a rather frustrating weekend, with a short circuit in a cable terminal of an electrical cabinet stopping us from running. By Monday morning, however, we’d recovered and will resume LHC running tomorrow after a scheduled technical stop. Glitches such as this are a fact of life in a working lab, and do not detract from the fact that we have much to be pleased with from these two months. As the figures I’ve quoted above illustrate, however, we still have a long way to travel. My congratulations go to all involved with this great scientific adventure.
source: IPM.ir
May 29, 2010
سمينارهاي هندسه
با سلام
متأسفانه به دليل عدم استقبال دوستان گرام يدر دانشكده و ساعت بسيار نامناسبي كه در اختيارم قرار دادند سمينارهاي هندسه و نسبيت و ذرات را به زمان ديگري موكول ميكنم. البته تا حدودي مطالبي در 6 جلسه گفته شده كه اگر ادامه پيدا كرد در ادامه ِ مطالب فبلي است.
متأسفانه به دليل عدم استقبال دوستان گرام يدر دانشكده و ساعت بسيار نامناسبي كه در اختيارم قرار دادند سمينارهاي هندسه و نسبيت و ذرات را به زمان ديگري موكول ميكنم. البته تا حدودي مطالبي در 6 جلسه گفته شده كه اگر ادامه پيدا كرد در ادامه ِ مطالب فبلي است.
Apr 29, 2010
ATLAS Experiment Reports Its First Physics Results from the LHC
March 2010
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Almost 20 years since the inception of the ATLAS detector, the labors of 3000 scientists along with large numbers of engineers and other support staff have found fruition in the earliest results. These results demonstrate that this mammoth detector (seven stories tall and twice as long) works almost flawlessly. It is a great achievement that a 7000 tonne detector – with 3000 km of cables and close to 100 million channels to be read out – has successfully measured particle tracks with a precision of 0.001 centimeters so quickly.
In later stages, ATLAS will focus on rare events and filter out less interesting events. This first paper reports on results with the “trigger” set to accept almost all events (this setting is called “minimum bias”). The paper reports results for the number of charged particles per collision and its dependence on several variables such as the particles’ momentum perpendicular to the beam.
The results from over 300,000 proton-proton collisions were compared with sophisticated computer simulations and with results from other experiments at the same collision energy. These comparisons demonstrate that the ATLAS detector performs remarkably well even at these early stages of the research. The inner detector of ATLAS (which follows the tracks of the charged particles emerging from the collisions) was key to the measurements. Data from the inner detector matched the simulations excellently.
Tom LeCompte, the Physics Coordinator for ATLAS, commented that: “It's particularly gratifying that our result be published now, on the eve of the LHC beginning its multi-year program of the highest energy collisions in the world. Teamwork was essential in being able to produce a physics result this quickly, especially with a brand new detector as complex as ATLAS.”
This first ATLAS paper with physics results represents a major milestone for the experiment at the Large Hadron Collider. It demonstrates the enormous potential for making major discoveries in the years ahead.
ATLAS spokesperson, Fabiola Gianotti, noted that "This first paper is very special for all of us, as it marks the beginning of a very exciting era of physics results and hopefully great discoveries. I am particularly delighted by the fact that the analysis described in this paper was mainly done by students and young post-docs. We are all very proud of these achievements."
M. Barnett
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