Another one bites the dust. Or “Super-B? What Super-B?” November 28, 2012Posted by apetrov in Uncategorized.
Tags: charm physics, particle physics, Super-B experiment
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Studies of New Physics require several independent approaches. In the language of experimental physics it means several different experiments. Better yet, several accelerators that have detectors that study similar things, but produce results with different systematic and statistical uncertainties. For a number of years that was how things were: physicists searched for New Physics in high-energy experiments where new particles could be produced directly (think TeVatron or LHC experiments), or low-energy, extremely clean measurements that explored quantum effects of heavy new physics particles. In other words, New Physics could also be searched for indirectly.
As a prominent example of the later approach, detectors BaBar at SLAC (USA) and Belle at KEK (Japan) studied decays of copiously produced B-mesons in hopes to find glimpses of New Physics in quantum loops. These experiments measured many Standard Model-related parameters (in particular, confirming the mechanism of CP-violation in the Standard Model) and discovered many unexpected effects (like new mesons containing charmed quarks, as well as oscillations of charm mesons). But they did not see any effects that could not be explained by the Standard Model. A way to go in this case was to significantly increase luminosity of the machine, thereby allowing for very rare processes to be observed. Two super-flavor factories (those machines are really like factories, churning out millions of B-mesons) were proposed, the Belle-II experiment at KEK and a new Super-B factory at the newly-created Cabibbo Lab in Frascatti, Italy. I have already written about the Cabibbo Lab.
It appears, however, that Italian government decided today that it cannot fund the Super-B flavor factory. Tommaso Dorigo reported it in his blog this morning. Here is more hard data: there is a press release (in Italian) from the INFN that basically tells you that “economic conditions… were incompatible with the costs of the project evaluated.” Which is another way of saying that Italian government is not going to fund it. This follows by the news from the PhysicsWorld saying the same thing.
Many physicists have been expressing doubts that the original Super-B plan, which was, in my opinion, very bold, could be executed within the proposed time frame. Yet, physicists pressed on… that is until this morning’s announcement. Reality of our world sets in — there is not enough money for basic research…
So, is Higgs finally here? July 4, 2012Posted by apetrov in Uncategorized.
Today is a big day at CERN. There are two collaborations that presented their latest results on the search of the Higgs boson. Did they finally discover the Higgs boson?
Let’s first figure out what it all means? What two collaborations? What is Higgs boson? And, most importantly, what do we mean by “discovered”?
First things first. The two collaborations that I’m talking about are CMS and ATLAS, two huge detectors and hundreds of professors, postdocs and graduate students working to get and work the data that come out of it. The collaborations looked at almost three years (although 2010 does not really count and 2012 is still going — but with fantastic pace) and found signals of the Higgs boson, a particle that was predicted to be there in the minimal Standard Model.
Why is that we need Higgs boson and why is it there? The Standard Model of particle physics is described by its symmetries — or the symmetry group (SU(2)xU(1)) under which matter contents transform. This symmetry tells us how particles interact — and in fact, that makes Standard Model quite a constrained system. So the introduction of this symmetry is very important. However, this symmetry also tells us that all particles that are described there should be massless! What should one do? The idea is to break that symmetry, of course. The problem is how to break that symmetry. One cannot simply add symmetry-breaking terms (that would wreck the whole original setup), one has to do it indirectly. So the idea was proposed to introduce a field that interacts with all fields that are present in the Standard Model. That field also interacts with itself and forms a condensate (i.e. provides non-zero value for energy density of the vacuum) once, roughly speaking, the temperature of the Universe after the Big Bang drops below certain value. This mechanism gives mass to both electroweak gauge bosons (particles that represent weak force) and quark and leptons. The mechanism itself was first proposed in 1962 by Philip Warren Anderson. The model of spontaneous symmetry breaking was independently developed in 1964 by three groups, Robert Brout and Francois Englert; Peter Higgs; and Gerald Guralnik, C. R. Hagen, and Tom Kibble. The particle that manifests this effect is the famous Higgs boson. Read more about it here. I’ll talk more about it in my later posts.
CMS went first (which is a bit unusual, as Atlas, for some alphabetical reason, would always be first to deliver their talk). The talk was delivered by Joe Incandela, a CMS spokesperson. A gist of their talk is that they looked at several possible decay channels of the Higgs boson. First, Higgs can decay to two photons (H → γγ). They see a significant bump at mH = 125 GeV, but only in the combination if different reconstruction techniques. The overall significance is over 4 sigma. Next, they talked about H → ZZ channel. This channel is tougher, as they need to reconstruct Z’s that decay in different decay channels. Now, if they combine their data in H → γγ and in H → ZZ they find that statistical significance for signal that the Higgs is there at 5 sigma. However, once they combine all data, especially the H → ττ channel, their combined statistical significance goes slightly down to 4.9 sigma. This is just below discovery by the standards of Physical Review Letters, a very influential physics journal. But this is in very significant.
The next talk was by ATLAS. Fabiolla Gianotti, ATLAS spokesperson, gave that talk. They also see excess in H → γγ channel, but their statistical significance in that channel is lower, 4.5 sigma. Also, they include the so-called look-elsewhere effect — and then their statistical significance goes down to 3.5 sigma. Then, she discussed the H → ZZ channel. They see the excess with 3.4 sigma significance at mH about 125 GeV. Now, the combined results have excess at mH = 126.5 GeV with (local) statistical significance of 5.0 sigma. This is a discovery.
In passing, ATLAS also see a bump in their 4-lepton channel at approximately 90 GeV. Still not clear what it is….
This discovery is very significant. It tells us that our ideas on how electroweak symmetry is broken are at least partially correct. This is also the first truly elementary particle discovered since the Z-boson. There are still many questions, both experimental and theoretical, about the analyses presented today at CERN. What is going on with the H → ττ channel? Is it really a Standard Model Higgs boson? Or some other scalar particle. We’ll sure to study those things indeed.
P.S. The theorists who described the effects were there and not only were acknowledged by the experimental speakers, but also got to say a couple of words at the end.
Why advertisers should know physics June 12, 2012Posted by apetrov in Uncategorized.
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Some years ago, when I decided to start blogging, I wrote about an interesting advertisement that Ford Motor Company put up in all major magazines (it was even placed on the side of their headquarters in Dearborn, MI):
Here is what I said in that post of mine from several years ago: “What is interesting about this ad is the equations that this lady is writing — they look like the equations from the famous Peskin and Schroeder’s book on Quantum Field Theory (QFT), equations describing renormalization of phi^4 theory! How did Ford get a hold of them?
As it turns out, I happen know the answer. This ad was made by a company that is headquartered in Detroit — I have a business card of one of the authors of this ad!
What happened is that a couple of months ago I was sitting in my office at Wayne State University, looking over my QFT notes that I’m supposed to teach next Fall. A guy showed up at my door and asked to “write down a complicated-looking equation.” Now, that’s not a usual question that I get when I sit in my office during the lunchtime! He quickly explained that he works for this advertisement company (called JWT) and they were contracted by Ford to produce a series of ads that should highlight the talent of Ford engineers and at the same time appeal to young people. (He showed me a prototype of an ad with that girl sitting next to the blackboard.) So his boss sent him to the closest university (which happen to be WSU, we are located 5 min down Woodward Avenue from their office) to fish out a “complicated equation.” The rest is simple — I use Peskin and Schroeder as a main text for my graduate QFT course, so that list of equations was indeed about renormalization of phi^4 theory… I must add that I received no monetary (or any other) compensation…
Amazing, isn’t it?”
The reason I re-post part of that old post is the following. I recently went to Florida to participate in CIPANP-2012 conference (I’ll post my impressions of this conference later this week). Now, Kennedy Space Center is on Cape Canaveral in Florida, so I rented a car and went to visit that marvelous place. The place is truly amazing! Lots of things to see. The place is still making history: I visited it just a couple of days after the historic launch of the Space X‘s Dragon capsule.
I also visited a gift shop and bought the following souvenir there:
See how many mistakes they got in there? And it’s not “rocket science”, it’s freshman physics! Quite embarrassing… Clearly, people from that JWT advertising agency in the example above take their job responsibilities much more seriously.
See that NASA seal in the upper left corner? Since I am sure that NASA scientists know physics, I take it as indication that they never visit their gift shop.
CHARM of Hawaii May 14, 2012Posted by apetrov in Uncategorized.
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I’m blogging from the site of CHARM-2012 conference, which has just started in Honolulu, Hawaii. This is a fantastic conference at a fantastic place! The conference will have four full-packed days filled with many aspects of physics related to charmed quark. As I reported earlier, many exciting recent results are associated with charm quark.
Why is the conference taking part in Hawaii? Besides being a nice place in general, it is almost exactly half way between Japan and the US. This meeting alternates between Asian, US and European locations, and last meeting, in 2009, was in Beijing — so it is US’ turn. There will be many talks from KEK‘s Belle collaboration (which University of Hawaii is a member of), LHC experiments, as well as from Tevatron experiments. Besides, world’s only operating charm experiment (BES 3) is located in Beijing, China. Indeed, there would be many theory talks as well. It shapes to be a very nice conference — and I’ll be reporting about exciting results to be discussed here.
Inverse superconductivity in iron telluride April 1, 2012Posted by apetrov in Funny, Near Physics, Physics, Science, Uncategorized.
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One of the most significant advances of science in the 21st century so far is the 2008 discovery of iron-based high temperature superconductors such as LaFeAsO1-xFx. Previously, all high-temperature superconducting compounds, there so-called cuprates, were based on copper and consisted of copper oxide layers sandwiched between other substances. Much of the interest in those materials has arisen because the new compounds are very different from the cuprates and may help lead to a theory that is different from the conventional BCS theory of superconductivity, where electrons pair up in such a way that so coupled they can then move without resistance through the atomic lattice.
Among those new materials is the iron telluride, FeTe. This compound has the simplest crystal structure and exhibits antiferromagnetic ordering around 70 K and does not show superconductivity. It is now known that substitution of S for Te sites suppresses the antiferromagnetic order and induces superconductivity. Quite amazingly, this is not the most surprising property of those compounds. In a quite remarkable study performed by a group of Japanese physicists, it was shown that the iron-based compound FeTe0.8S0.2 exhibit superconductivity if soaked in red wine. They also performed a study of the effect with different types of wine and other alcoholic beverages, finding that a particular type of wine, 2009 Beajoulais from the French winery of Paul Beaudet, has the most profound effect.
A recent follow-up analysis, however, showed that subsequent and repeated applications of red wine and hard alcoholic beverages, such as cognac or vodka, can induce a new state in the study samples, dubbed the inverse superconductivity. The results, reported in the recent issue of Wine Spectator, clearly show steep increase of the samples’ resistivity after only five consequent applications of the liquid substance. As explained by the lead author of the study, John Piannicca, the results follow the simple model of the electron crowd. Interestingly enough, as reported by Dr. Piannicca, this model was developed by observing the change in the mean free path of a group of students visiting bars near the campus of his University.
Moreover, as was shown in a recent work of a group of scientists at the Siberian institute of Advanced Kevlar Engineering, it is also the quantity of alcohol that was responsible for the onset of inverse superconductivity. While this is also consistent with the already mentioned model of electron crowd, the samples obtained in the Siberian lab required much larger quantities of alcohol to achieve the same effect than those obtained in the American or Japanese labs, which could probably be explained by the specifics of liquid utilization. As was shown, the best effect was achieved with a brand of vodka “Imperia” commonly “recognized for it superbly smooth spirit and pure taste,” as advocated by its producers. It would be interesting to see how other brands would fare in such a study, which is on-going.
Last chance for a Higgs prediction December 13, 2011Posted by apetrov in Uncategorized.
Tags: cern experiments, fundamental particle, higgs boson, precision measurements
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In a couple of Hours we shall know more than we did before — the CERN experiments, ATLAS and CMS are about to announce their findings about the Higgs boson. In particular, its mass. Why is it interesting? The mass of Higgs, a fundamental particle in the Standard Model (SM) and a manifestation of a Higgs mechanism (discovered by at least five people besides Dr. Peter Higgs), cannot be predicted within the Standard Model. Similarly to masses of quarks and leptons, it comes out from the combination of unknown parameters of the SM.
Yet, Higgs boson would affect precision measurements — its effects could be seen via its quantum effects. So physicists would come out with pictures like the one that accompany this post (from which, incidentally, one can learn that the most likely value of the the Higgs mass given by the minimum of that plot, is already excluded by the direct measurements; what can one say — it’s a tough game).
In principle, Higgs boson mass (or mass of a Higgs-like particle) can be predicted in some models beyond the Standard Model. So, if you have any last-minute predictions, please through your hat in the ring! There are still about two hours before it becomes a “postdiction.” My long-time prediction (as of two years ago) was m_H = 125 +- 5 GeV. What is it based on? A principle that life is tough — the Nature is not always kind to us and we have to work hard to measure what we want to measure. It is true for most measurements/parameters that were studied before, including the most recent study of CP-violation in charm. How scientific is this prediction? I’d say almost as scientific as those based on anthropic principle. 🙂
Meanwhile, let’s see what CERN physicists have to say. Tune in here and let’s hope that we don’t overwhelm CERN’s servers.
One of CERN collaborations, the LHCb, has reported observation of direct CP-violation in the decays of charmed mesons at the Hadronic Collider Physics Symposium 2011 (HCP 2011) in Paris today. This is a fantastic news! While I am not at HCP 2011, kind folks at LHCb let me know about this fantastic measurement — since charm physics is my specialty.
So, what are we talking about here?
First things first. CP (or Charge Parity) is a set of (discrete) transformations performed on a theory’s Lagrangian — a function that describes what particles we have in a theory and how they interact. If your Lagrangian is symmetric under this transformation, then particles and antiparticles — matter and antimatter — have the same properties. If not — interactions of matter particles are different from interactions of antimatter particles. This possible difference is a crucial property of a theory because, according to three Sakharov criteria, the Universe could evolve in what we see around us only if matter and antimatter have different interaction properties. Otherwise, at best, we’d have big chanks of antimatter floating around — or at worst would not not exist at all.
This is why many huge experiments built to study CP violation. Big national labs’ flagship experiments were designed to search and study CP-violation (BaBar at SLAC, Belle at KEK, LHCb at CERN), with hopes to see glimpses of New Physics that could explain matter-antimatter asymmetry in the Universe. This new result from LHCb can in principle provide one.
So, what did LHCb see? The reported analysis looks at the difference of a difference — i.e. a difference of CP-violating asymmetries in kaons and pions. The CP-violating asymmetry is defined as the difference between decay widths (roughly speaking, decay probabilities) of a neutral D-meson to decay into a final state, say positive K-meson and a negative K-meson and the same quantity for the D-anti-particle to decay to the same final state. This quantity is also defined for the final state of two pions — and it is CP-violating!
The structure of this CP-violating asymmetry, aCP, is not that simple. Because D0 is a neutral particle it can, in principle, mix with its antiparticle (see here) — and this antiparticle can also decay into the same final state! This process can be also CP-violating (this type of CP-violation is called indirect CP-violation). So the result would depend on both types of CP-violation!
Moreover, experimentally, the asymmetries like this are not easy to measure — there are experimental systematics associated with D-production asymmetries, difference of interactions of positive and negative kaons with matter, etc. For this reason, experimentalists at LHCb decided to report the difference of CP-violating asymmetries, in which many of those effects, like productions asymmetries, would cancel. So, here is the result:
ΔaCP = -0.82 ± 0.21 (stat) ±0.11 (syst) %
In other words, this quantity is 3.5 sigmas away from being zero. The first question that one should ask is whether this quantity is consistent with previous measurements. The biggest question, however, is whether this quantity is consistent with Standard Model expectations.
There is a bunch of previous measurements available for aCP (KK) and aCP (ππ) separately. The thing is that
aCP (KK) = – aCP (ππ)
or approximately so. So by subtracting those quantities we not only subtract the experimental uncertainties, but also enhance the signal! However, looking at the table on page 6 of the talk, one can immediately realize that this measurement is at least consistent with the previous ones.
Is it a sign of something beyond the Standard Model? This one is hard to answer. I usually put an upper bound on the SM value (that is, absolute value) of asymmetries like aCP (KK) at 0.1% — which would make ΔaCP to be about 0.2%. Is it consistent with LHCb findings? Maybe. The size of this asymmetry is notoriously difficult to estimate due to hadronic effects. Maybe it is a sign of New Physics — this could be an exciting conclusion, as we have never seen CP-violation in up-quark sector.
It is interesting that the first “big” result from LHC comes in the realm of charm physics, not Higgs searches. Moreover, all “big” results in the last decade were from the experiments searching for New Physics indirectly, in the “intensity frontier” (this is lingo of US Department of Energy) — with most of them coming from charm physics. Maybe at the very least LHC-b should be renamed as LHC-c?
We have a job… or two! October 21, 2011Posted by apetrov in Particle Physics, Physics, Science.
Depending on how the budget for the new year looks like, we (the high energy particle theory group at WSU) will have two new postdoc positions. Please apply, if you are interested! Here is the ad.
The high energy theory group at Wayne State University ( http://www.physics.wayne.edu/heptheory ) anticipates making TWO postdoctoral research appointments to start September 1, 2012, subject to budgetary approval. The initial appointments will be for one year, and may be extended for one or more years depending on the performance and availability of funding.
The group consists of faculty Gil Paz and Alexy A. Petrov, as well as a postdoc and several students. Research interests of the group include particle phenomenology, physics beyond the Standard Model, effective field theori es, heavy quark physics, CP violation, Dark Matter phenomenology and particle astrophysics. The group has close ties to the nuclear theory group of Sean Gavin and Abhijit Majumder. The WSU Department of Physics and Astronomy offers a unique opportunity of close interaction with experimental high energy particle and nuclear physics groups.
Applications including CV, a list of publications, a brief statement of research interests and three letters of recommendation should be submitted to Academic Jobs Online at http://academicjobsonline.org/ajo/jobs/1128
or by mail to
Prof. Gil Paz
Department of Physics and Astronomy
Wayne State University
Detroit, Michigan, 48201
Prof. Alexey A. Petrov
Department of Physics and Astronomy
Wayne State University
Detroit, Michigan, 48201
or electronically to firstname.lastname@example.org or email@example.com. The deadline for application is January 15, 2012. Later applications will be considered until the positions are filled. Informal inquiries are welcomed.
Wayne State University is an affirmative action/equal opportunity employer. Women and members of minority groups are encouraged to apply.
2011 Physics Nobel Prize and related matters October 4, 2011Posted by apetrov in Uncategorized.
4 October 2011 is a day to remember. And I’m not talking about unveiling of the new iPhone, although it is also quite a remarkable event. Today, a 2011 Nobel Prize in Physics was awarded. As expected, in its annual failure, Thompson Reuters got it wrong in predicting 2011 Nobel Prize in Physics (to give them credit, they do put up the names of the right people, but always in the wrong year; this year they were predicting people from quantum entaglement). Anyways, this year’s Nobel Prize is totally deserving. The Nobel Prize in Physics 2011 was awarded jointly to Saul Perlmutter, Brian P. Schmidt, and Adam G. Riess “for the discovery of the accelerating expansion of the Universe through observations of distant supernovae.”
This Nobel Prize is for the 1998 analysis of data from two collaborations, Supernova Cosmology Project (SCP), headed by Perlmutter, and High-z Supernova Search Team, headed by Schmidt and Reiss. The analyses centered on the the so-called Ia-type supernovae that have consistent peak brightness, which makes them “standard candles” of the Universe. This is an important property, which allows unambiguous measurement of distances (via the Hubble relation between the distance and the redshift) to the galaxy hosts of those supernovae. Using this data, they concluded that the Universe is going through the stage of accelerated expansion! This is a very interesting fact, especially taking into account the fact that the gravitational interaction is attractive!
This led to reevaluation of what we know about the Universe. It is widely accepted now that Dark Energy (i.e. something that permeates space and tends to increase the rate of expansion of the universe) accounts for about 74% of the total mass of the universe! Recalling that Dark Matter is responsible for about 22% of total mass gives us a fact that we really know almost next to nothing about the place we live in…
What is Dark Energy? This is a very good question. The simplest possibility is that it is the old good cosmological constant introduced by Einstein in the beginning of the last century. This leads to a particularly simple model of the Universe called Lambda-CDM model. Whether or not it is true remains to be seen. At any rate, Dark Energy/Dark Matter are currently one of the most exciting avenues for research in astrophysics (which is, of course, my subjective opinion!).
Meanwhile, the annual 2011 Ig Nobel Prizes were awarded on September 29, 2011. Among the most remarkable are
“PHYSICS PRIZE: Philippe Perrin, Cyril Perrot, Dominique Deviterne and Bruno Ragaru (of FRANCE), and Herman Kingma (of THE NETHERLANDS), for determining why discus throwers become dizzy, and why hammer throwers don’t.” As expected, for a work of this magnitude, the prize-winning research was published in the widely-read physics journal Acta Oto-laryngologica.
“MATHEMATICS PRIZE: Dorothy Martin of the USA (who predicted the world would end in 1954), Pat Robertson of the USA (who predicted the world would end in 1982), Elizabeth Clare Prophet of the USA (who predicted the world would end in 1990), Lee Jang Rim of KOREA (who predicted the world would end in 1992), Credonia Mwerinde of UGANDA (who predicted the world would end in 1999), and Harold Camping of the USA (who predicted the world would end on September 6, 1994 and later predicted that the world will end on October 21, 2011), for teaching the world to be careful when making mathematical assumptions and calculations.” This prize is quite timely, as the world once again is predicted to end 21 December 2012, although, frankly, they could have waited one year for this one.
Once again, the biology prize went for sexuality-related research. This time, among certain type of beetles and certain types of beer bottles (which should make a nice commercial of the type “Fosters is Australian for beer” (C)):
“BIOLOGY PRIZE: Darryl Gwynne (of CANADA and AUSTRALIA and the UK and the USA) and David Rentz (of AUSTRALIA and the USA) for discovering that a certain kind of beetle mates with a certain kind of Australian beer bottle.”
And my personal favorite is this year’s literature prize:
“LITERATURE PRIZE: John Perry of Stanford University, USA, for his Theory of Structured Procrastination, which says: To be a high achiever, always work on something important, using it as a way to avoid doing something that’s even more important.”
I would like to remind my readers that so far, there is only one “Grand Slam winner” — a person who got both Ig Nobel and a Nobel prizes: last year’s recipient of the Physics Nobel Prize Andre Geim.
Why do physicists go to Aspen? September 1, 2011Posted by apetrov in Near Physics, Particle Physics, Physics, Science.
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While the most obvious answer to this question is “to ski”, it is, nonetheless, not the correct one. Yes, skiing is great here in the winter (and hiking is great in the summer), but most of the time physicists come here to work. The reason is Aspen Center for Physics. I write “here” because I’m currently participating in one of the programs organized by the Center (the program is called “Flavor Origins” — it brought together theorists working on the problems of neutrinos, heavy and light quarks, CP-violation, etc.). The Center, which exists here since 1961, organizes workshops and conferences. But the main reason that theorists (and occasional experimentalists) come here is to talk to other theorists. In short, it is as if you are visiting a huge theory group — you can work individually or with your colleagues, but you can always knock on an office door and bounce your ideas off someone else visiting the Center, etc. It is great to have such a concentration of theorists of different trades. And it leads to breakthroughs and simply good papers. As it is said on the Center’s website:
“Many seminal papers have been written in Aspen, which has grown to be the largest center for theoretical physics in the world during its summer sessions. Among many other subjects, the theories of superstrings, chaos, evolution of stars and galaxies, and high temperature superconductivity have all made large strides in recent Aspen seasons.”
There is almost always someone with an expertise in a subject that you have a question about. And that makes this Center great. And, of course, hiking and skiing is also good. The only “downside” (note the quotes) is that you can meet a real bear (even at the Center) or other wildlife. Today a snake came to check out a lecture on conformal field theories…
P.S. Also check out my blog on Quantum Diaries…