CHARM-2007: day 1 August 7, 2007Posted by apetrov in Particle Physics, Physics, Science.
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…