Symmetry factor

I am at the CHARM-2009 conference in Leiman (a suburb of Heidelberg, Germany). This is the third charm conference that I’m participating in since the rebirth of the series in 2006. That year the conference was in Beijing and it finally made it to Germany by the way of Cornell University. All of those places have rich connections to charm (BESII/III experiment in Beijing, CLEO-c at Cornell and the upcoming PANDA at GSI just a short drive from Leimen). The conference is winding down, so I wanted to update you on what happened. Please see the talks posted on the website next week.

The program of talks has three days of plenary presentations. The first day is mainly devoted to hidden charm states, both conventianl and exotic. So everything you wanted to know about states from J/psi to X, Y, and Z was discussed. The second day is all about open charm states, with strong and electroweak studies of all of those with a main concentration on mixing of DDbar mesons and CP-violation. The topic continued today (during the third day), gradually moving to “future hardware” — i.e. how upcoming data from current BESIII and upcoming PANDA, LHCb, and SuperFlavor factories will change the world.

The first day had a lot of discussions on QCD studies with charmonia. The main reason one wants to study QCD with heavy quarkonium states is the fact that this is one of the simplest QCD systems, kina like positronium in QED. But unlike QED, QCD is much more complicated, so one can study quite non-trivial systems such as molecules built of heavy mesons that behave just like hidden charm states. The cool thing is that those things are actually experimentally observed!!! In fact, most of discoveries (not “anomalies” as in cosmic ray physics) done in the past seven years were done in charm systems.Pierre Artoisenet, Antonio Vairo, Gunnar Bali, Steve Olsen, Helmut Vogel,Kay Yi, Daniel Gamermann,Ruslan Chistov, and Claudia Patrigiani talked about various experimental and theoretical issues in quarkonium states. I wanted to mention that, according to Pierre Artoisenet, there problem of chamonium polarization in ppbar collisions has been solved. The problem is (was) that in non-relativistic QCD (NRQCD), at the leading order, one predicts that a J/psi state that is transvesely polarized. This comes from the fact that the dominant mechanism is gluon fragmentation to charm-anticharm pair — so J/psi retains polarization of a gluon, which is transverse (as gluon is a massless particle). Now the problem was that experiment (CDF) saw J/psi’s being quite an opposite condition – longitudinally polarized. So he claimed that at higher orders in QCD one gets new channels (new machainisms for J/psi production) that for some reason (?) makes J/psi polarized longtudinally.  Steve Olsen reported a (yet another) new charmonium state, X(3915). It’s amazing that some years ago people talked about the fact that experimentally we see too few charmonium states. Now I think we have too many. Helmut Vogel pointed out an intersting problem in radiative decays of J/psi and psi(2s) into eta and eta’ mesons. In addition, charmonia production in heavy ion collisions was discussed by Carlos Lourenco, Hermine Woehri, and Peter Petreczky.

The second day was mainly about DDbar mixing. It is the last meson-antimeson mixing observed experimentally (in total agreement with theoretical predictions ). Tina Cartaro, Marko Staric, Paras Naik, Angelo di Canto gave talks on DDbar measurments from different experiments, AlanS chwartz gave an HFAG (Heavy Flavor Averaging Group) take on that — and provided us with most recent averages of  mixing and CP-violating parametres. Ikaros Bigi and I gave theoretical reviews on mixing and CP-violation. Then it was an area of Dalitz plot analyses… It’s interesting that there are not so many people who know how to “work” Dalitz plots…

And today we talked about open charm exotic states. An interesting discussion came after Christoph Hanhart’s claims about mlecular nature of some states and Fulvia de Fazio’s statements about their “conventioal” nature. Leptonic and semileptonic decays of charm were also discussed, with the recent controvercy about f_Ds, the observation vs. lattice computation of leptonic decay constants… And then there are “machine” talks. BESIII was just over. What I also learned from Yifang Wang’s talk, besides the current status of BESSIII (they are slowly getting to their design lumnocity of 10^33 cm^-2 s^-1, now getting a third of it), is ajoke  that they wanted to buy a beampipe in the US, but they wouldn’t sell it to them. I wonder why…