“Tests of Fundamental Symmetries” is a one-day workshop organized jointly by the APS Topical Group on Precision Measurements and Fundamental Constants and the Few-body Topical Group. It will take place in Baltimore, MD on April 10, 2015–the day before the APS April meeting (APR15) begins. It will be held at the Baltimore Convention Center, the site of APR15. The goal of the workshop is to survey forefront efforts in searches for time-reversal and parity violation. Continua a leggere Tests of Fundamental Symmetries
Al CERN di Ginevra sono pronti per lanciare una nuova sfida, ancora più grande. E’ quanto hanno affermato in questi giorni i fisici delle particelle che oggi come non mai ritengono necessaria la costruzione di un nuovo, gigantesco acceleratore, almeno sette volte più potente dell’attuale Large Hadron Collider (LHC) grazie al quale è stato possibile rivelare una particella che tanto assomiglia al bosone di Higgs (post).
Particle physics takes the long-term view. Originally conceived in the 1980s, the LHC took another 25 years to come into being. This accelerator, which is unlike any other, is just at the start of a programme which is expected to run for another 20 years. Even now, as consolidation work aimed at a restart in 2015 continues, detailed plans are being hatched for a large-scale upgrade to increase luminosity and thereby exploit the LHC to its full potential.
The HL (High Luminosity) LHC is CERN1’s number-one priority and will increase the number of collisions accumulated in the experiments by a factor of ten from 2024 onwards.
Even though the LHC programme is already well defined for the next two decades, the time has come to look even further ahead, so CERN is now initiating an exploratory study for a future long-term project centred on a new-generation circular collider with a circumference of 80 to 100 kilometres. A worthy successor to the LHC, whose collision energies will reach 14 TeV, such an accelerator would allow particle physicists to push back the boundaries of knowledge even further. The Future Circular Colliders (FCC) programme will focus especially on studies for a hadron collider, similar to the LHC, capable of reaching unprecedented energies in the region of 100 TeV. The FCC study will be a global venture for particle physics and stems from the recommendation in the European Strategy for Particle Physics, published in May 2013, that a feasibility study be conducted on future fundamental research projects at CERN. It will be conducted over the coming five years and starts with an international kick-off meeting at the University of Geneva from 12 to 15 February. The FCC will thus run in parallel with another study that has already been under way for a number of years, the Compact Linear Collider, or “CLIC”, another option for a future accelerator at CERN. The aim of the CLIC study is to investigate the potential of a linear collider based on a novel accelerating technology. “We still know very little about the Higgs boson, and our search for dark matter and supersymmetry continues. The forthcoming results from the LHC will be crucial in showing us which research paths to follow in the future and what will be the most suitable type of accelerator to answer the new questions that will soon be asked,” says Sergio Bertolucci, Director for Research and Computing at CERN. “We need to sow the seeds of tomorrow’s technologies today, so that we are ready to take decisions in a few years’ time,” adds CERN’s Director for Accelerators and Technology, Frédérick Bordry. The goal of the two studies is to examine the feasibility of the various possible machines, to evaluate their costs and to produce a conceptual design report for the FCC and elaborate on the one already produced for CLIC in time for the next European Strategy update around 2018/2019.
For more information on:
- The European Strategy for Particle Physics
- The HL-LHC
- The FCC
- Message from CERN’s Director General (November 2013)
Nel 1922, il cosmologo russo Alexander Friedmann propose delle soluzioni alle equazioni di campo di Einstein nel caso di un Universo omogeneo, isotropo e non statico. Sotto queste ipotesi, è possibile definire una densità media dell’Universo, ossia una densità di massa-energia e, come lo stesso Friedmann dimostrò a suo tempo, descrivere lo spazio in ogni istante con un solo numero, la curvatura scalare. Da qui si ricavano tre modelli di Universo, detti modelli di Friedmann, in funzione del parametro di curvatura k per cui l’Universo può assumere o una geometria iperbolica (k=-1, aperto), o una geometria euclidea (k=0, piatto), oppure una geometria ipersferica (k=1, chiuso). Dunque, una previsione di questi modelli implica che l’Universo potrebbe un giorno collassare a causa della mutua interazione gravitazionale dovuta alla materia presente nell’Universo, una ipotesi che sembra essere confermata oggi da alcuni calcoli eseguiti da un gruppo di fisici dell’University of Southern Denmark. Il risultato è che il rischio di una possibile contrazione gravitazionale sembra essere molto maggiore di quanto sia stato finora ipotizzato.
Sooner or later a radical shift in the forces of the Universe will cause every little particle in it to become extremely heavy. Everything, every grain of sand on Earth, every planet in the Solar System and every galaxy, will become millions of billions times heavier than it is now, and this will have disastrous consequences: the new weight will squeeze all material into a small, super hot and super heavy ball, and the Universe as we know it will cease to exist. This violent process is called a phase transition and is very similar to what happens when, for example water turns to steam or a magnet heats up and loses its magnetization. The phase transition in the Universe will happen if a bubble is created where the Higgs-field associated with the Higgs-particle reaches a different value than the rest of the Universe. If this new value results in lower energy and if the bubble is large enough, the bubble will expand at the speed of light in all directions. All elementary particles inside the bubble will reach a mass, that is much heavier than if they were outside the bubble, and thus they will be pulled together and form supermassive centers. “Many theories and calculations predict such a phase transition, but there have been some uncertainties in the previous calculations. Now we have performed more precise calculations, and we see two things: 1) yes, the Universe will probably collapse, and 2) a collapse is even more likely than the old calculations predicted“, says Jens Frederik Colding Krog of the Center for Cosmology and Particle Physics Phenomenology (CP ³ – Origins) at University of Southern Denmark and co-author of an article on the subject in the Journal of High Energy Physics. “The phase transition will start somewhere in the Universe and spread from there. Maybe the collapse has already started somewhere in the Universe and right now it is eating its way into the rest of the Universe. Maybe a collapsed is starting right now right here here. Or maybe it will start far away from here in a billion years. We do not know”, says Jens Frederik Colding Krog. More specifically he and his colleagues looked at three of the main equations that underlie the prediction of a phase change. These are about the so-called beta functions, which determine the strength of interactions between for example light particles and electrons as well as Higgs bosons and quarks. So far physicists have worked with one equation at a time, but now the physicists from CP3 show that the three equations actually can be worked with together and that they interact with each other. When applying all three equations together the physicists predict that the probability of a collapse as a result of a phase change is even greater than when applying only one of the equations.
The theory of phase transition is not the only theory predicting a collapse of the Universe. Also the so-called Big Crunch theory is in play.
This theory is based on the Big Bang, the formation of the Universe. After the Big Bang all material was ejected into the Universe from one small area, and this expansion is still happening. At some point, however, the expansion will stop and all the material will again begin to attract each other and eventually merge into a small area again. This is called the Big Crunch. “The latest research shows that the Universe’s expansion is accelerating, so there is no reason to expect a collapse from cosmological observations. Thus it will probably not be Big Crunch that causes the Universe to collapse“, says Jens Frederik Colding Krog.
Although the new calculations predict that a collapse is now more likely than ever before, it is actually also possible, that it will not happen at all.
It is a prerequisite for the phase change that the Universe consists of the elementary particles that we know today, including the Higgs particle. If the Universe contains undiscovered particles, the whole basis for the prediction of phase change disappears. “Then the collapse will be canceled”, says Jens Frederik Colding Krog. In these years the hunt for new particles is intense. Only a few years ago the Higgs-particle was discovered, and a whole field of research known as high-energy physics is engaged in looking for more new particles. At CP3 several physicists are convinced that the Higgs particle is not an elementary particle, but that it is made up of even smaller particles called techni-quarks. Also the theory of supersymmetry predicts the existence of yet undiscovered particles, existing somewhere in the Universe as partners for all existing particles (superparticles). According to this theory there will be a selectron for the electron, a fotino for the photon, etc. While the physical results discussed in the article were partially established earlier in the literature, the work of the Danish based researchers deals with the mathematical foundations of the technique used among other things also to determine the stability of the Universe. In their work the researchers assumed valid the current knowledge of the Standard Model interactions augmented by the discovery of the Higgs and the latest mathematical constraints.
University of Southern Denmark: Collapse of the universe is closer than ever before
Con il termine “nuova fisica” si intende un nuovo campo di ricerca che tenta di spiegare quei fenomeni della natura che i fisici non sono ancora in grado di descrivere. Oggi, sta prendendo piede sempre più l’idea in base alla quale l’Universo può essere caratterizzato da una struttura diversa rispetto a quanto previsto dagli attuali modelli o teorie. In tal senso, un gruppo di fisici hanno avviato uno studio che avrà lo scopo di aiutare gli scienziati a rendere più facile, almeno in parte, la comprensione di alcuni fenomeni della fisica fondamentale.
“New physics is about searching for unknown physical phenomena not known from the current perception of the Universe. Such phenomena are inherently very difficult to detect“, explains Matin Mojaza from CP3-Origins. Together with colleagues Stanley J. Brodsky from Stanford University in the U.S. and Xing-Gang Wu from Chongqing University in China, Mojaza has now succeeding in creating a new method that can make it easier to search for new physics in the Universe (post).
The method is a so called scalesetting procedure, and it fills out some empty, but very important, holes in the theories, models and simulations, which form the basis for all particle physics today.
“With this method we can eliminate much of the uncertainty in theories and models of today“, says Matin Mojaza. Many theories and models in particle physics today has the problem that they, together with their predictions, provide some parameters that scientists do not know how to set. “Physicists do not know what values they should give these parameters. For example, when we study the Standard Model and see these unknown parameters, we cannot know whether they should be interpreted as conditions that support or oppose to the Standard Model, this makes it quite difficult to study the Standard Model accurately enough to investigate its value”, explains Matin Mojaza. With the new approach researchers can now completely clean their models for the unknown parameters and thus become better at assessing whether a theory or a model holds water.
The Standard Model has for the last 50 years been the prevailing theory of how the Universe is constructed. According to this theory, 16 (17 if we include the Higgs particle) subatomic particles form the basis for everything in the Universe.
But the Standard Model is starting to fall short, so it is now necessary to look for new physics in the Universe. One of the Standard Model’s major problems is that it cannot explain gravity, and another is that it cannot explain the existence of dark matter, believed to make up 25 percent of all matter in the Universe. In addition, the properties of the newly discovered Higgs particle, as described in the Standard Model, is incompatible with a stable Universe. “A part of the Standard Model is the theory of quantum chromodynamics, and this is one of the first things, we want to review with our new method, so that we can clean it from the uncertainties“, explains Matin Mojaza. The theory of quantum chromodynamics predicts how quarks (such as protons and neutrons) and gluons (particles that keeps quarks in place inside the protons and neutrons) interact. Matin and his Chinese and American colleagues now estimate that there may be a basis for reviewing many scientific calculations to clean the results from uncertainties and thus obtain a more reliable picture of whether the results support or contradict current models and theories. “Maybe we find new indications of new physics, which we would not have exposed if we had not had this new method”, says Matin Mojaza.
He believes that the Standard Model needs to be extended so that it can explain the Higgs particle, dark matter and gravity.
One possibility in this regard is to examine the so-called technicolor theory, and another is the theory of supersymmetry. According to the supersymmetry theory, each particle has a partner somewhere in the Universe (these have not yet been found though). According to the technicolor theory there is a special techni-force that binds so-called techni-quarks, which can form other particles, perhaps this is how the Higgs particle is formed. This could explain the problems with the current model of the Higgs particle. Also Rolf-Dieter Heuer, director of CERN in Switzerland, where the famous 27 km long particle accelerator, the LHC, is situated, believes that the search for new physics is important. According to him, the Standard Model cannot be the ultimate theory, and it is only capable of describing about 35 percent of the Universe. Like CP3-Origins, also CERN has put focus on weeding out old theories and search for new physics, this happening in 2015, when the accelerator starts up again (post).
I rivelatori LHCb e CMS situati presso l’acceleratore LHC del CERN di Ginevra hanno permesso di realizzare la prima e definitiva osservazione di una particella, denominata mesone Bs, che decade in due muoni. Questi risultati presentano delle implicazioni importanti per la ricerca di nuove particelle ed interazioni fondamentali, anche se si tratta di un altro colpo per coloro che sperano di rivelare le prime tracce della supersimmetria. Nonostante la fisica attuale spieghi solo il 5% del contenuto materia-energia dell’Universo, le cosiddette particelle supersimmetriche rappresentano una delle tante categorie di particelle candidate a spiegare la materia scura, che costituisce quasi il 27% del contenuto materia-energia dell’Universo.
According to professor Tara Shears, from the University of Liverpool’s Department of Physics, this observation is one of the rarest processes in fundamental physics and represents a fantastic confirmation of the Standard Model of particle physics. She explains: “It is one of the most frustrating confirmations we’ve ever had. We know our theory is incomplete, and this ultra-rare decay may give us clues as to what might replace it. But what this discovery tells us is that there are no signs yet of our best alternative, a theory called supersymmetry (SUSY)“.
We haven’t ruled out SUSY entirely, but we’ve definitely dismissed many of the most popular versions of it. We know that there must be new physics, but it’s starting to look like this might be stranger than we’d imagined.
The decay observed at LHCb and CMS is predicted to be extremely rare in the Standard Model, with a Bs meson only decaying into two muons about 3 times in every billion. However, if ideas like SUSY are correct than the chances of the decay can be significantly increased or even suppressed. Hundreds of millions of collisions take place every second at the LHC, each one producing hundreds of new particles that leave electrical signals in the giant detectors. Physicists from LHCb and CMS trawled through two years’ worth of data, searching untold trillions of collisions for signs of two muons coming from a Bs meson. Professor Shears said: “It takes an enormous amount of data and hard work to sift out this tiny signal, and an incredibly precise particle detector to allow us to recognise the distinct experimental signature it leaves inside LHCb. Key to this is the VErtex LOcator (VELO), a precision silicon detector, at the core of LHCb, which physicists at the University of Liverpool designed and built. This detector is capable of resolving distances a fraction of a hair’s breadth in size, a precision which is needed to measure the distinctive flight distance inside LHCb that allows us to identify a Bs meson“. Neither LHCb nor CMS alone had enough data to announce a formal discovery, but when their results were formally combined the signal passed the all-important “five sigma” level, above which a discovery can be declared. This result is certainly not the end of the road for ideas like supersymmetry, which has many different versions, so many in fact that it is almost always possible to contort it so that it agrees with experimental data. However, combined with the recent discovery of the Higgs boson (post), whose mass is larger than predicted by many SUSY theories, this new result may force SUSY into such baroque configuration that the original motivation, a natural description of nature, is lost. Professor Shears added: “We’ve used all the data that LHC has delivered to us so far to make this measurement. What’s wonderful, and a very strong result, is that the CMS experiment has also performed the measurement on a completely separate dataset and seen the same thing. It’s a remarkable confirmation“.
University of Liverpool: CERN latest data shows no sign of supersymmetry – yet
- Ultra-rare decay confirmed in LHC (bbc.co.uk)
- Rare Particle Discovery Dims Hopes for Exotic Theories (livescience.com)
- Bs on the frontiers (quantumdiaries.org)
Physicists operating an experiment located half a mile underground in Minnesota reported this weekend that they have found possible hints of dark-matter particles. The Cryogenic Dark Matter Search experiment has detected three events with the characteristics expected of dark matter particles, MIT graduate student Kevin McCarthy reported at the American Physical Society meeting in Denver on April 13.
“There’s a limited amount one can really say from just three events” McCarthy says. “But it certainly warrants some further investigation”. A statistical fluctuation of the experimental background is likely to produce three or more events resembling this result a little over 5 percent of the time. However, all three of these events have energies more like those expected of a low-mass dark-matter particle, something that should happen by chance only 0.19 percent of the time. This consideration brings the result to a higher confidence level, around 3 sigma. These odds might give one a reason to feel optimistic, but they do not pass the criterion physicists use to claim a discovery, so CDMS scientists say they’re staying reserved until they’ve conducted more analysis. CDMS results from 2010 included two potential dark-matter particles in a higher mass range, but physicists ruled out those candidates with further study. The latest result does bring new intrigue to the hunt for dark matter. The best fit with the result would be a dark-matter particle with a mass of 8.6 GeV. This seems to align with some interpretations of recent results from the CoGeNT dark matter experiment and from the Fermi Gamma-Ray Space Telescope. But the CDMS result contradicts indications from the experiment currently leading the field, the XENON experiment. “There’s been an interesting back-and-forth between experiments” says CDMS Spokesperson Blas Cabrera of Stanford University and SLAC National Accelerator Laboratory. “To investigate this hint, we’ll certainly need more data. If a signal persists, it will need to be replicated by other experiments with different technologies before it is accepted by the community”. CDMS collaboration members expect to shed more light on the result themselves later this year with new data they are taking using detectors of a different material, germanium as opposed to silicon. If a dark-matter particle passed through, it could knock against the nucleus of an atom in the detector, releasing a small amount of energy as charge and heat. Scientists keep the detector cold and shielded from cosmic rays underground in order to best watch for such a signal. They study interactions of non-dark-matter particles to rule out background noise. CDMS scientists were surprised this result came from its lighter silicon detectors and not its heavier germanium detectors. When they designed their experiment in the early 2000s, they included the silicon ones only to verify results from the germanium. Scientists expected they would need the bulkier detectors to register the nuclear recoil from massive dark-matter particles, predicted to weigh about 100 times the mass of a proton. However, in the past couple of years, new theories and experimental results have attracted physicists’ attention to the idea of low-mass dark-matter particles—only about 10 times as massive as a proton. The idea for a high-mass dark-matter particle comes mainly from the theory of supersymmetry, which posits that each of the particles we know has a more massive partner particle. The idea of a low-mass dark-matter particle comes mainly from a theory that has only recently begun to gain currency, that of a “dark sector” made up of many types of dark particles and forces. “If there is a dark sector, it could be just as complex as the ordinary matter sector”, says CDMS physicist Bernard Sadoulet of Lawrence Berkeley National Laboratory and the University of California, Berkeley. “Finding low-mass dark-matter particles would not rule out the theory of supersymmetry, but “it’s hard to reconcile it with at least the most vanilla flavors of of the theory”, says CDMS Project Manager Dan Bauer of Fermilab. The year 2013 should be an interesting one in the search for dark matter.
CDMS: Dark Matter Search Results from CDMS-II Silicon Detectors SLAC: Cryogenic Dark Matter Search Adds New Intrigue with Latest Result
E. Figueroa-Feliciano's presentation at Light Dark Matter 2013
K. McCarthy's presentation at APS
B. Cabrera's Panofsky Prize presentation at APS
B. Sadoulet's Panofsky Prize presentation at APS