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.
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…
Congratulations Dr. Yeghiyan! July 26, 2011Posted by apetrov in Near Physics, Particle Physics, Physics, Science, Uncategorized.
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Today my third graduate student at WSU, Gagik Yeghiyan, defended his Ph.D. thesis. Congratulations Dr. Yeghiyan! Good luck to you in your new life as an Assistant Professor at Grand Valley State University!
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As I blogged some time ago, Italian government decided to fund a new accelerator for precision studies of New Physics in decays of heavy-flavored mesons, the so-called SuperB factory, a high-intensity B-factory, which is designed to look for glimpses of New Physics in rare decays of B- and D-mesons (for professional description of the physics case, see here; for Conceptual design Report (CDR) see here).
Last week a decision was made for a location of the site of the new machine. It will be built on campus of the University of Rome ‘Tor Vergata’. Here is the picture of the proposed site (shamelessly taken from the talk of Roberto Petronzio, President of the Italian National Institute for Nuclear Physics at XVII SuperB Workshop and Kick Off Meeting – La Biodola (Isola d’Elba) Italy):
The (“green”) site is located reasonably close (4.5 km) to another well-known Italian National Lab in Frascati, Laboratori Nazionali di Frascati (LNF). The new lab will be a CERN-like consortium. The name for the lab was proposed: Cabibbo Lab, after the great Italian physicist Nicola Cabibbo whose name is associated with some of the most important objects in flavor physics.
The new lab will bring lots of talent from all over the world and, besides experiments in high energy physics, will be used as a light source for other physics experiments. It is great that even at the time when finances are tight, European governments realize that fundamental physics is important for the future of their countries. These are exciting times for the European physics!
I usually don’t comment about politics in this blog. But today I’ll make an exception. Maybe someone from Michigan Congressional delegation will read it. I’ll be happy to answer any questions regarding this situation.
Each developed country in the world has a stake in an interdependent triad that builds up its wealth and independence: fundamental research, applied research and industry. It is only the combination of excellence in those three fields that has kept the United States at the forefront of technological revolutions of the past 50 years. Elimination of one of those components will spell trouble for the remaining two: for example, defunding fundamental and applied science in the Russian Federation in the early 1990’s led to a quick demise of that country’s high tech industry.
The new Continuing Resolution (CR) bill announced on 02/08/2011 by House Appropriations Chairman Hal Rogers  imposes deep cuts on Department of Energy’s Office of Science (DOE OS), National Science Foundation (NSF), NASA and National Institutes of Health (NIH) that simply threaten US fundamental research. The cut to DOE OS’ budget of $5.12B is $1.1B. It is proposed to happen half way through the current budget year. To keep things in perspective, the amount needed to implement this cut would be equivalent to closing down all US National Laboratories for a continuous period of time this year.
Among other things, DOE’s Office of Science supports fundamental and applied research done by the University groups all over the country. In the state of Michigan that includes University of Michigan, Michigan State University, Michigan Tech and Wayne State University. This funding is neither redundant nor wasteful: each grant issued by DOE’s Office of Science, NSF or NIH is reviewed by several independent experts and expert panels. It is this funding that helps us train the next generation of scientists and engineers that will keep America prosperous in coming years. It is this funding that the new CR proposal would severely cut.
To compare, Chinese government’s spending on science and technology was slated to rise 8% to $24 billion in 2010, of which $4 billion is basic R&D . By contrast, the cuts included in the proposed Continuing Resolution bill reduce funding to basic and applied research made by DOE’s Office of Science by 18%. Liberal and conservatives commentators alike voiced concerns about how the US is losing its edge in math and sciences. This budget cut signals that there is no reason for young Americans to pursue careers in science.
The fundamental research done by particle scientists might not have immediate applications to industry. But not all basic research projects are “long shots.” The first Internet browser developed by high energy physicists at CERN (the site of currently running Large Hadron Collider) for the needs of the experiment designed to understand the basic building blocks of Nature in 1991 made possible creation of the World Wide Web and revolutionized the US and world’s commerce.
Balancing our country’s budget is an important and noble goal, but it should not be done at the expense of the future.
 House appropriation committee website http://republicans.appropriations.house.gov/index.cfm?FuseAction=PressReleases.Detail&PressRelease_id=259
A picture on a wall? February 12, 2011Posted by apetrov in Funny, Particle Physics, Physics, Science.
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I was moving old pictures from my camera to my computer today and found this image. Here is a funny picture of a reflection on my neighbor’s wall. What does it look like?
To a particle physicist, this is just a pair of Feynman graphs for 2 -> 2 scattering amplitudes… with the left one in an external field . Enjoy.
Bye-bye, Tevatron! January 10, 2011Posted by apetrov in Particle Physics, Physics, Science.
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Well, it is now official: DOE has decided not to pursue the extension of the Tevatron running until the year 2013. The operations of the Tevatron, the largest US hadron accelerator, will end at the end of this year, 2011. The details of the DOE decision can be found here.
To remind you, the original idea to extend the Tevatron running until 2013 came out because of the LHC shutdown schedule (and physics, of course), Tevatron might have been competitive with the LHC in the search for light (~ 120 GeV) Higgs. Now we have to rely solely on the LHC.
Now it’s official: Italian Government Funds the Super-B December 23, 2010Posted by apetrov in Particle Physics, Physics, Science.
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So it is official. According to Roberto Petronzio (INFN President), “The Ministry for Education, University and Research [of Italy] has decided to select the SuperB project conducted by the Italian National Institute of Nuclear Physics (INFN) as one of its “flagship projects” in Italy over the next few years and has delivered an initial funding for 2010 as a part of a multiannual funding program” (see here from interaction.org site).
This was first announced by Marcelo Giorgi (Super-B spokesperson) on December 18 at the closing of the XV SuperB General Meeting in Caltech (“SuperB has been approved and funded by the Italian government. Approval has been announced in a closed session of the CERN council. We should expect press releases with announcements from INFN and the Italian minister of science and education within the next few days,” see here). The announcement was a bit unexpected — many of my colleagues even believed that the project would never be funded, especially in such difficult times. But it happened!
This is s very good news for flavor physics. The Super-B experiment is a high-intensity B-factory, which is designed to look for glimpses of New Physics in rare decays of B- and D-mesons (for professional description of the physics case, see here; for Conceptual design Report (CDR) see here). It is a descendant of the SLAC B-factory experiment BaBar — almost literally, as parts of the accelerator and BaBar detector will be disassembled at SLAC and delivered to Italy and reassembled there. This is done as part of the US strategy of moving scientific expertise in high energy physics from the US to Europe and Asia (which started with plowing most other high energy physics programs in favor of the linear collider program that was never funded in full… actually, it is not even mentioned that often nowdays — partially because of the excitement over LHC) along with scientific leadership in that area .
So these are the exciting times for the SuperB collaboration! One important thing is that the site for the experiment is not yet chosen. Currently the possibilities include a green site at Tor Vergata or exciting site of the Frascati Lab of INFN near Rome. So hey have their work cut out for them.
Update on our faculty search in particle theory December 10, 2010Posted by apetrov in Particle Physics, Physics, Science.
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The deadline for applications for an Assistant Professorship in theoretical particle physics at WSU is December 15, five days from today. So far we received 44 applications.
Is that a lot? Well, it depends. According to some of my friends at SLAC, they receive upwards of 400 applications for their postdoctoral positions. I regularly receive about 50-60 applications for postdoctoral position — when I have one. While the numbers are not important (as long as the applicants are great — and they are!), we were planning for about 100 applications for our faculty position. Of course, WSU is not Harvard or Stanford. Also, Detroit is not Boston or Palo Alto. And, the future assistant professor would have to work more to get recognized in the field — the name of the institution will not be of much help. But this position will give that person a chance to define the program. And this person will not be alone. There is Sean Gavin (nuclear theorist), there would be another nuclear theorist next year (we also have a search for an Assistant Professor in theoretical nuclear physics) — and then, according to the Strategic Plan adopted by our Department, a theoretical cosmologist will be hired in a couple of years.All of that makes our position quite attractive.
So, what’s going to happen next? The Search Committee will meet shortly after December 15 to take initial look at the application pool. We will select a “long short lost” of 20 applicants and ask them to submit their application materials to the University’s job management system (a new requirement). Then we’ll select top five from the list of that twenty and invite them for interviews on campus.
This is an interesting year for physics at WSU. There are four (4!!!) searches going on in the physics department — particle theory, nuclear theory, nuclear experiment (heavy ion collisions — WSU has one of the largest groups in relativistic heavy ions in the US), and observational astronomy. Hopefully, we will get good people. I’ll keep you updated.
Update: we have 61 applications in our pool as of Dec 15 that we started to look at. The first serious meeting of the search committee will be in the first week of the new year.