Symmetry factor

I got back from Fermilab, where I stayed for a day of a Project X workshop. This workshop is the second in a series of trying to chart the intermediate future of Fermilab — in other words, in between 2009 when we loose Tevatron until 202X when the International Linear Collider (ILC) will be operational at FNAL (ok, I’m an optimist here). The first workshop was about accelerator issues, i.e. technical aspects of high intensity source at FNAL. So this one was regarding building the “physics case”, i.e. what physics one can do at the “intensity frontier” with that machine. I was curious what would be the outcome of that workshop - you see, there originally was an “intermediate project” - it was called BTeV and it was supposed to study flavor physics. So to make the long story short, I actually was in “physical” attendance for the first day of the conference and was asked to connect “virtually” for the second day (I participated in the “antiprotons” working group).

Instead of reporting about the workshop (you can actually look at the transparences of the talks here), I want to convey the atmosphere of what was happening there, in particular concentrating on the talk by Jon Bagger (which had the gist of what other theorists, Joe Lykken and Hitoshi Murayama also said). It was a bit surprizing to me to see Jon give a Project-X talk, since, as far as I know, he was the one of the biggest proponents to streamline the the high energy physics program by consolidating the efforts of most of the US physicists around ILC (which practically resulted in the cancelation of BTeV and a number of other flavor physics experiments with great physics programs such as RSVP or CKM). He concentrated on three physics topics that one can do with this device: quark flavor physics (kaon rare decays), charged lepton flavor physics (muon transitions via flavor-changing neutral currents (FCNC)) and neutrino physics. Indeed those are the things one can do with 8 GeV super-intense proton beams.

The point is that LHC might not be sensitive to flavor physics of the first two generations, i.e. how new physics at the TeV-scale couples to them. That used to be the reason to do flavor experiments — and continues to be in Japan and at CERN. The only thing that we know now that we didn’t know when the plug was pulled on experimental flavor physics effort in the US is that the Nature happened to be following the concept of “Minimal Flavor Violation” (or MFV) - or very close to it. Which means that whatever new physics awaits us at a TeV-scale, for some reason it chose to communicate itself to low energy scales by the Standard Model-like operators. We were hoping for spectacular results in B (or charm) physics, but it didn’t happen… and we don’t know why.

What was interesting in his talk are the messages that he decided to draw — and which gave him a very hostile reception. First, he asked if “some experiments could be done cheaper elsewhere” (yes, indeed - as someone in the audience noted, the US can simply NOT do any HEP experiments and wait for the Europeans/Chineese/Japaneese physicists to do them — but is this a good approach?). Second, Jon said that “detailed calculations needed to convince everybody of the importance of Project X in the world flavor program” (that drew lots of emotions from people who were on the cancelled Fermilab kaon experiments, which passed the physics studies with flying colors). I actually think that one does need to go back to the drawing board here. First of all, feasibility of new kaon experiments was not demonstrated for the high-intensity setup project X is going to be. Second, one needs to see if the expected results will improve on the approved CERN and KEK experiments. Of course, having an estimated statistics of 800-1000 events for a kaon experiment in Project-X in the FCNC channel K+ -> pi+ nu nu-bar is great! Finally, Jon said the following: “If Project-X positions Fermilab as a credible host [for ILC], it might be well worth the effort. If not — it will be a mistake”… It’s an interesting statement that reflects the ILC-centric views of many in US high energy physics (BTW, the preceeding talk by David McGinnis actually stated that accelerator issues in Project X are very much alligned to what one expects to have at the ILC). But, as many people later complained in private conversations, it significantly narrows the scope of US particle physics program. In particular, it implies that studying QCD is not worth the effort. So here is the gist of it — we report, you decide :-).

One of the impressions that I got at this conference is that how difficult it would be so see if Project X has an easy place to be in the world-wide flavor-physics effort. Many similar studies of kaon decays are done at CERN and KEK; experiments with charged leptons are being performed at PSI in Switzerland, neutrinos are being studied at CERN and KEK, and antiproton experiments will be done at GSI in Germany (PANDA) - their FAIR facility just got government approval. Of course, independent checks of the results are needed… at any rate, it’s the huge intensity of the proposed proton source that can give us an edge…

P.S. For a general discussion of the Project-X workshop (including Gene Golowich’s quote from the CHARM-2007 conference — which really has nothing to do with that particular Project-X workshop, but tells you something about the status of flavor physics in the US) see here.

I am at Fermilab today. Yesterday I gave a seminar in the Theoretical Physics Department there, but today I decided to stay for the Project X Workshop. Basically, the idea is to toss around ideas for the physics case for the Fermlab’s intermediate future project — the high intensity proton source. Indeed, he most obvious physics application of this is a some sort of neutrino experiment. But people talk about new experiments with muons, kaons (some sort of revival of the RSVP experiment idea — but at FNAL — and with a possibility of 800-1000 events of the type K -> pi nu anti-nu), and even antiprotons (low energy, only 8 GeV). Let’s see what hapends…

The 2009 meeting of the Division of Particles and Fields (DPF) of American Physical Society (APS) will be held on campus of Wayne State University in Detroit. How do I know that? Well, I am a Chair of the Local Organizing Committee. And Executive Committee of DPF has just accepted our proposal to host this meeting.

So, what kind of meeting is that? Well, this is the main event for the DPF, usually attended by about 500 physicists working in, well, field of particles and fields (and also strings). We are looking forward to hosting this meeting. Here is the Local Organizing Committee:

Alexey Petrov (WSU, co-Chair), Claude Pruneau (WSU), David Cinabro (WSU), Eizabeth H. Simmons (MSU), Gordon Kane (Michigan), Paul Karchin (WSU, co-Chair), Rene Bellwied (WSU), Robert Harr (WSU), R. Sekhar Chivukula (MSU), Sean Gavin (WSU), Sergei Voloshin (WSU)

Please consider attending this conference to hear first results from the LHC, new results from Fermilab and B-factories and recent advances in theory. If you want to dispel some of your stereotypes about Detroit, this would be great time to do so.

I’ve been neglecting my blog for a while. Of course, I have good reasons: our Fall semester has started, I’m teaching a course that noone in our Department has taught before (including me — it’s good that I only have 12 students, it’s an advanced undergraduate class), my Mom is visiting, … Anyways, here are a couple of things that caught my attention recently.

1. DOE and NSF lauched a new website “…to tell the story of the U.S. role in the Large Hadron Collider (LHC)”. Here it is: http://www.uslhc.us. It has lots of info written for non-physicists: stuff about experiments, links to “LHC blogs” (hmm…), images from all LHC detectors: ALICE, ATLAS, CMS, LHCb, LHCf… Now, I must admit that I didn’t know anything about the LHCf experiment (shame on me), so I googled “LHCf”. To my further embarassment, it comes up almost on the top of Google search page, second only to this LHCF… Certainly worth looking at. I mean, the USLHC website…

2. SLAC appointed Persis Drell as Acting Director (here is the press-release) while they continue to search for the permanent Director. My guess is that she will be the next SLAC Director. She is a great physicist.

3. I’m on sabbatical leave next semeter — will spend most of it at the University of Michigan. So I started preparing by going there once a week. They gave me Finn Larsen’s office for the next year (who is also on sabbatical) — Finn, I promise to return it to you in the same shape and form I got it two weeks ago…

Just wanted to share some phrases by physicists that caught my attention during a recent conference I went to (CHARM-2007):

“The errors are consistent within the error” (comparing recent experimental measurement with the older one).

“I cannot measure [...], I don’t have my own accelerator. But you do!” (theorist replying to a question from an experimentalist).

“Don’t listen to what I say, listen to what I think!” (from an experimentalist who misspoke about a result, but caught himself while doing it)

“I’m not sure how to get to my conclusions now” (from a speaker having technical difficulties with a remote that advances slides)

Also, this phrase was repeated to me — it is from another meeting. That meeting wasn’t even a conference, it was a meeting on super-B factory. One of the proposals call for essentially moving SLAC’s experiment (BaBar) to Europe, reassembling it there in the new, undevelloped site and finally upgrading it to high luminocity. So a question was posed: why bother digging a new tunnel in Europe, de-assembling an experiment in the US and reassembling it back when you can just upgrade it at SLAC, one well-known physicist said: “We don’t do this anymore” [in the US]. Sadly he was referring to (almost) an executive decision to stop flavor physics programs in the US…

My colleagues tell me that CDF has become the third collaboration to observe D0-anti-D0 mixing, i.e. flavor oscillations in the charm sector. Their results were reported at the Fermilab seminar today (see website here) as part of CDF results to be presented at the Lepton-Photon conference in Korea next week. They are consistent with earlier observations — BaBar and Belle saw those oscillations a couple of months ago. And I cannot pass mentioning it again: their results are also consistent with our theoretical predictions reported here.

Day 4 was the last day of the conference. And really was even shorter than the previous day. But they finally put all the talk on the web — please see them here.

The first section started with the talk by Mikhail (Borisovich) Voloshin about charmed meson spectroscopy. I really enjoyed his talk. He talked about mass splittings among ground and exciting states in D-system both from quark mass difference and from electromagnetic effects. Kinda bread-and-butter physics. At the end he also talked difficulties with interpretation of Ds(2317) states as parity doublers of usual pseudoscalar D-states. In particular, he explained that the old calculation of E. Eichten et al from 2003 actually is not self-consistent and requires extra assumptions (now, of course, we explained the existence of this state via a mixture of 2-quark and 4-quark states). Then he proposed something that I didn’t quite understood: that these states are really 0- states with “charm quark dressed up by 0- glue field.” He referred to an old paper by NSVZ (Novikov, Shifman, Vainshtein and Zakharov) from the 80’s, where the idea was explained. I don’t know how this mechanism works, maybe someone can teach me… Then A. Polosa talked about modification of the 4-quark picture to explain X(3872) charmonium state. They propose 2 states around 3872 MeV instead of one — one containing c, anti-c and u and anti-u and another one containing c, anti-c and d and anti-d. So these states decay into different decay channels. The way I see it, their mechanism cannot be right, as those states must mix among themselves, so both states would decay into both channels. The session ened with two experimental talks about spectroscopy of charmed particles.

The second section contained several talks about future experimental facilities: BESIII, LHC-b, PANDA, and Super-B. Take a look at the slides yourself. The conference ended with a question-and-answer section about the future of flavor physics.

I must say that contrary to recent claims, flavor physics is not dead, it just moved to Europe and Asia with the rest of high energy experimental particle physics.

The third day of the conference was really a half-day. The reason is that the organizers scheduled a conference hike in the beautifull Treman Park with subsequent barbeque. The day stared with experimentral talks on semileptonic and leptonic charm decays — here CLEO-c has a fantastic advantage of an experiment in pristine enviroment. This, of course, is partially off-set by huge statistics of other experiments. At the end of the first section Aida El-Khadra talked about lattice approaches to formfactors and decay constants. And yes, she did show that plot of HPQCD collaboration that they show for three years already. Some of their results are quite amazing and dwarf the experimental results (and also somewhat inconsistent with them). F. Follana elaborated on HPQCD collaboration’s results. Then there were several talks on semileptonic decays, including Richard Hill’s talk on z-expansion. The point is that one has no idea what q^2-dependence semileptonic form-factors have, so meaningful comaprision of theory and experiment is a bit unclear — that is, if you want to claim model-independent theory. He puts some meaning into how to do that.

 At the end, Peter Cooper reported on the number of doubly-charmed baryon production at SELEX. Now, it is known (for once, from the calculations  of my former postdoc A. Onishchenko) that the production cross-section that they measure is _orders_ of magnitude higher than what is predicted. Jon Rosner made an intersting suggestion that those states could even be highly-excited single charm states. The rest of the session was about charmed baryons and their decays. In particular, H.-Y. Cheng gave an extensive discussion of charmed baryon spectroscopy.  

The conference hike was probably ok, I didn’t go (I did it when I lived in Ithaca) — it’s hard to go up and down with a kid’s stroller. It also started to rain midway through the hike. In taht respect, giving out a “conference umbrella” instead of usual conference bag was entirely appropriate. 

Here is the day two of the CHARM-2007 conference. The day started with Brendan Casey talking about rare D-decays. This is quite interesting, since these decays are sensitive to indirect effects of new physics. Among other things, he talked about D_s decays to fully leptonic final states. These decays are rare not because they are generated by quantum effects (so-called penguins), but simply because of the structure of weak interactions inducing the so-called helicity suppression of the decay — the decay  probability is proportional to square of the lepton mass in the final state. This means that the largest decay probability would be for tau+tau-neutrino final state. The interesting this about that transition is that it is also sensitive to effects of the charged Higgs, required in supersymmetric extensions of the Standard Model. He reported on the ratio of Ds -> tau nu/Ds -> mu nu decay probabilities corrected for the kinematical effects and took a ratio of that ratio (he-he) to the theoretical calculation. I cannot verify this at the moment (I cannot look again at his transparencies), but he says it is 0.78 +- 0.12, which is away from expected unity. This might mean that there is a charged Higgs contribution there (I’m speculating). There were also talks by H. Muramatsu and Fred Harris (for R. Ping, who didn’t get his visa) on charmonium decays. In particular, it was reported on the status of the so-called “rho-pi” (or 12%) puzzle. Then  Zaza Metreveli gave a great talk about spectroscopy and ways of using it for things like measuring strong coupling in charmonium decays.

The second installment was more theoretical. It started with Estia Eichten’s talk on charmonium states above threshold — he talked about the weird X(3872) state and various ways of explaining it. He didn’t like our cool paper on the subject. Bob McErlath talked about new physics in heavy quarkonium decays. I was surprised to learn that there are essentially no model-independent constraints on the neutralino mass, one of the primary candidates for the Dark Matter particles in SUSY (it has to be heavier than 2 eV to insure that dark matter is dominated by its cold component). In fact, he claims that it can be so light that heavy quarkonium can decay into it. Who knew… Nora Brambilla talked about theory of extraction of mass and strong coupling in heavy quarkonium decay in non-relativistic QCD. It’s been kown for years that the definition of quark mass in QCD is not trivial, as quarks never appear as free states due to confinement. So one needs a convenient definition — and there are several. Jo Dudek gave a nice talk on radiative charmonium decays in lattice QCD.

After lunch there were many talks on hadronic decays of charmed mesons. Jon Rosner talked about extraction of strong phases with U-spin triangles (U-spin is a subgroup of flavor SU(3)). Alex Bondar gave a telephone talk about his elegant method of extraction of phase gamma (or phi_3 in Japan) in B decays to charmed meson with D-meson Dalitz plot analysis. We also had talks on various ways of doing Dalitz plot analysis. The problem there is more of the “memory” than physics — Dalitz plot analyses were popular in the sixties, so not so many people are fully versed in those analyses nowdays. In particular, the simplest analysis that is done by many people nowdays (using the so-called isobar method) violates unitarity.

Stay tuned for day 3 and final day of the conference. 

I’ve been slow in posting this conference report — mainly because I’ve been writing my talk… Ayways, it’s a great time to be at a charm conference — several collaborations recently announced evidence for observations of charm mixing, a bunch of new (and weird) hadrons have been recently discovered, which happened to contain charm quark, etc. So it is a good time for such a conference.

This particular workshop, CHARM-2007, has only plenary talks, so I’ll only report about things that I find interesting (hm…). The first section of the Day 1 contained three talks from Brian Lang, H.Hu and Bruce Yabsley and dealt with charmonum production at ~ 4 GeV and at higher energies at KEK. In particular, Bruce was talking about a problem that was hanging over theorists for quite some time now — production of J/psi  plus two charmed quarks at Belle energies. The problem there is that NRQCD, an approximation to QCD for non-relativistic quarks, underestimates the observation, even taking into account more exotic mechanisms such as gamma-gamma processes. Bruce claims that with the refined experimental analysis Belle sees two newish charmonium resonaces recoiling against the J/psi: X(3940) and X(4160) — not very well established resonances.

In the next section, Eric Swanson talked about some theoretical (quark model-motivated) approaches to charmonium production, including the X-states, some of which are believed to be the molecular states of two D-mesons and their excitations. J Radenmacker gave a nice report on charmonium production at the Tevatron, inlcuding polarization of J/psi and its excitation, psi’. There is a funny problem there — NRQCD prdicts that at high p_T (transverse momentum), all heavy quarkonia, i.e. both charmonia and bottomonia would have to be produced transversely polarized. This is easy to explain — at high p_T the dominant mechanism for heavy quarkonia production is gluon fragmentation, so produced quarkonium should retain polarizatin of that gluon. Since gluon is massless, it only has transverse polarization, so the resulting quarkonium should be transversely polarized. Now, what’s interesting is that this prediction fails miserably at the Tevatron. In fact, the produced psi’s show the opposite trend: more longitudinal polarization! And he showed new data that confirms that… so it is a problem — maybe charm quark is not heavy enough for NRQCD to work at leading or next-to-leading order in velocity expansion… also p_T maybe not high enough… It sort of works for bottomonium, but the statistics is not that great there. The last talk of that section was by A. Knospe, who gave a crush course in heavy ion collisions and charm production at RHIC.

The rest of the first day was about charm mixing and CP-violation. Personally, I think that’s the hottest topic of this conference, but I might be biased. :-)  Abe Seiden talked about mixing at BaBar, Werner Sun talked about TQCA analysis of mixing at CLEO-c (they don’t see mixing — not enough statistics, but the “tendency” is towards negative values of th elifetime difference, which is just the opposite of what other collaboratons see) and Brian Petersen talked about Heavy Flavor Averaging Group (HFAG) averages of charm mixing parameters. Them there was a talk of my long-time collaborator Gene Golowich about theory of charm mixing, reporting, among other things, on posiible New Physics in charm mixing. I talked about CP-violation in charmed particle decays amd G. Mancinelli talked about experimental prospects for measuring CP-violation in charm.    

All in all, it is great workshop. One problem (that I thought was resolved some time ago) was that several physicists from China and Russia did not get their visas on time, so could not actually come to Cornell. Their talks were given by their collaborators. This is very frustarting! The thing about it is that those people are well-known experts in their fields and have absolutely no desire to stay in the US illigally. So I don’t see why there were not issued visas on time. What will happen is that at some point well-known physicists would stop holding high-profile conferences inthe US, which would be a shame…