Blogging ICHEP 2010

A collective forum about the 35th edition of
the International Conference on High Energy Physics (Paris, July 2010)

Thursday, July 22, 2010

Day one, session two -- Heavy Quarks

The first talk of this session was given by Matthias Steinhauser, who spoke about the three-loop heavy quark potential. The heavy quark potential, which describes the forces acting between two quarks in the limit in which those quarks are taken to be infinitely heavy, is an important quantity in QCD -- its non-perturbative linear rise at large distances encodes confinement, and its perturbative short-distance behaviour gives a way to define the strong coupling αs. It also plays a role in theoretical descriptions of quarkonium physics. The three-loop calculation presented is the result of long and very hard work by theorists.

This was followed by experimental results for radiative transitions between charmonium states, presented by Gang Li, and radiative decays of charmonia, presented by Rong-Gang Ping, both from BESIII, and on the properties of ψ resonances by Korneliy Todyshev from the KEDR expriment at the Russian VEPP-4M collider.

Moving from Charmonium to Bottomonium, but staying with experimental, Bryan Fulsom presented BaBar results for Υ(1DJ) states, finding the Υ(1D2) at 10164.5(8)(6) MeV, for the ηb, where the Υ(1S)-ηb(1S) hyperfine splitting is about 70 MeV, a fair bit larger than theoretical predictions. It should be noted, however, that those theoretical predictions rely on effective field theories for heavy quarks, and that the next order in 1/M may account for the difference. Some indications for the hb were presented, but the significance was below 3σ.

1 comment:

  1. In lattice NRQCD, the next order relativistic corrections to the Bottomonium hyperfine splitting, which are order v^6, actually reduce the hyperfine splitting by about 20%, moving it away from experiment. However, the discrepancy may be due to missing radiative corrections to the coefficient of the sigma.B operator in the NRQCD action.
    These unknown radiative corrections cancel in suitable ratios of spin splittings. Using the ratio of the 1S hyperfine and 1P tensor splitting from lattice QCD, and the P-wave tensor splitting from experiment, a new precise result for the 1S hyperfine splitting has been obtained in
    arXiv:1007.3966 :
    60 +- 7 MeV, where the error includes all systematics.
    In this paper, the ratio of the 2S and 1S hyperfine splittings is also predicted: 0.40 +- 0.06.


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