http://lhcb-public.web.cern.ch/lhcb-public/
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
Puzzling antimatter
For many years, the absence of antimatter in the Universe has tantalised particle physicists and cosmologists: while the Big Bang should have created equal amounts of matter and antimatter, we do not observe any primordial antimatter today. Where has it gone? The LHC experiments have the potential to unveil natural processes that could hold the key to solving this paradox.
If the Universe contained antimatter regions, we would be able to observe intense fluxes of photons at the boundaries of the matter/antimatter regions. “Experiments measuring the diffuse gamma-ray background in the Universe would be able to observe these light emissions”, confirms Antonio Riotto of CERN's Theory group. “In the absence of such evidence, we can conclude that matter domains are at least the size of the entire visible Universe”, he adds.
What caused the disappearance of antimatter in favour of matter? “In 1967, the Russian physicist Andrej Sakharov pointed out that forces discriminating between matter and antimatter, called “CP-violating” effects, could have modified the initial matter-antimatter symmetry when deviations from the thermal equilibrium of the Universe occured”, says Antonio Riotto. In the cold Universe today, we can only observe very rare CP-violating effects in which Nature prefers the creation of matter over antimatter. Following their discovery in the decays of K-mesons containing strange quarks, they have now also been observed in the decays of B mesons, which contain bottom quarks.
Today, scientists think that the early Universe might have gone through a transition phase in which the thermodynamic equilibrium was broken, when the density of the Universe was very high and the average temperature was one billion or more times that inside the Sun. "Some physicists think that this might have happened through the formation of ‘bubbles’ which have progressively expanded, thus ‘imposing’ their new equilibrium on the whole pre-existent Universe", explains Antonio Riotto. Whatever the real dynamics of this phase actually were, the important thing is that one particle of matter in every 10 billion survived, while all the others annihilated with the corresponding antiparticles.
How can the LHC help to solve the mystery? By studying rare decays, experiments can bring us more accurate information about phenomena related to CP-violation involving both known and new particles, such as mesons containing both bottom and strange quarks. Moreover, if new supersymmetric particles are discovered at the LHC, some of the possible scenarios leading to a non-equilibrium phase could find experimental support. "If the LHC finds a Higgs boson with a mass less than about 130 GeV, and if this discovery comes with the detection of a light supersymmetric particle called ‘stop‘, this could be the experimental proof that the non-equilibrium phase happened through the formation of bubbles", concludes Antonio Riotto.
In any case, since the disappearance of primordial antimatter cannot be explained by the current Standard Model theory, it is clear that we have to look for something new. Scientists are exploring different avenues but, given the fact that what we observe represents only about 4% of the total energy and matter that the Universe is made of, one can guess that part of the key to solving the antimatter mystery could be held in the yet unknown part of the Universe. With its very high discovery potential, the LHC will certainly help shed light on the whole issue.
The LHC is not alone in the search for the solution to the antimatter mystery. BaBar at SLAC in the US and BELLE at KEK in Japan have measured decays of B-mesons in detail , and the Tevatron experiments CDF and D0 are also exploring CP-violation effects. Later this year, the AMS (Alpha Magnetic Spectrometer) experiment will be docked to the International Space Station (ISS) and will start looking for evidence of antimatter particles resulting from the decay of dark matter.
francesco.poppi
Course on the Physics of Accelerators
http://accelerator.ipm.ac.ir/doc/HelmutWiedemann.pdf
Helmut Wiedemann
Stanford University, USA
April 26 - May 19, 2010
سخنراني دكتر خلخالي در مورد رفتار فضا در هندسه ناجابهجايي
http://math.ipm.ac.ir/Monthly_Colloquium/Khalkhali.pdf
جلسهي پنجم هندسه ذرات و كيهانشناسي
اين جلسه به دليل وقت كم جلسهي قبلي و عدم استقبال دوستان عزيز، به قسمت دم نرسيد كه به جبران آن موضوعات جلسهي پنجم در تاريخ 11 ارديبهشت به آدرس و ساعت مذكو ردر پوستر (پستهاي را نگاه كنيد) به قرار زير است:
بخش اول:
تعريف منيفلد
نكات و مثالهايي در اين زمينه
بخش دوم:
تقارن گسسته و اعداد كوانتمي و نقض
CP
با سپاس
فرهاد ذكاوت
CP
با سپاس
فرهاد ذكاوت
Apr 19, 2010
جلسهي چهارم هندسه، نسبيت و ذرات
اين جلسه ساعت 16.50 در كلاس 107 دانشكدهي شيمي در همان طبقهي دوم روبروي فيزيك برگزار ميشود.
موضوعات:
section one:
linear algebra
Group theory
tensors
......................
section 2:
Diffrentiable Manifolds and tensonrs:
Manifolds
One-forms
Fiber Bundles
Apr 8, 2010
جلسهي دوم هندسه در فيزيك
با سلام خدمت دوستان گرامي
جلسهي دوم هندسه در فيزيك با موضوع پايههاي هندسه و معرفي توپولوژي شنبه ساعت 5 تا 7 برگزار خواهد شد. با همكاري انجمن فيزيك برآن هستم ساعت سمينارها را به زمان مناسبتري تغيير دهم تا دوستان علاقهمند بتوانند شركت كنند.
قابل ذكر است با پيش فرضهاي اين جلسه از جلسهي 3 وارد مباحث رياضيفيزيك خواهيم شد. لذا دوستان گرامي كه جلسات بعدي خواهند آمد بايد قبلاً با بعضي اصطلاحات آشنا باشند. منابع هر جلسه اعلام ميشود.
با سپاس
فرهاد ذكاوت
قابل ذكر است با پيش فرضهاي اين جلسه از جلسهي 3 وارد مباحث رياضيفيزيك خواهيم شد. لذا دوستان گرامي كه جلسات بعدي خواهند آمد بايد قبلاً با بعضي اصطلاحات آشنا باشند. منابع هر جلسه اعلام ميشود.
با سپاس
فرهاد ذكاوت
Apr 4, 2010
The First LHC Collisions at 7 TeV
30 March 2010
The Particles and Accelerators department of IPM is one of the 35 institutes around the world which are marking this event by taking part in its live broadcast. The broadcast will take place in the CMS room of IPM's Larak campus through direct connection to CERN. The live broadcast will start at 11 AM local time.
Source: IPM>Cern
CERN has announced that on March 30th it will attempt the first 7 TeV collisions at its Large Hadron Collider (LHC). This very important event, in fact marks, the beginning of LHC's physics programme to test and explore the Standard Model of particle physics, looking for its missing pieces (Higgs boson) or for evidence showing the way for going beyond this model. So far the highest energy achieved in particle collisions has been that of FermiLab accelerator at 1.9 TeV, and a 7 TeV collision by itself constitutes a landmark in the history of high energy experiments. Each of the 3.5 TeV beams were already successfully circulated around the 27 km circumference of LHC on March 19th.
The Particles and Accelerators department of IPM is one of the 35 institutes around the world which are marking this event by taking part in its live broadcast. The broadcast will take place in the CMS room of IPM's Larak campus through direct connection to CERN. The live broadcast will start at 11 AM local time.
Source: IPM>Cern
On the threshold of new territory
13 March 2010
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.
Source: IPM>Cern
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.
Source: IPM>Cern
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