The hidden-charm pentaquark and tetraquark states

Echoes of a hidden valley at hadron colliders

The new experiment planned at Brookhaven to measure the anomalous magnetic moment of the muonaμ≡(gμ−2)/2 will improve the present accuracy of 7 ppm by about a factor of 20. This requires a careful reconsideration of the theoretical uncertainties of theg−2 predictions, which are dominated by the error of the contribution from the light quarks to the photon vacuum polarization. This issue is cruicial also for the precise determination of the running fine structure constant at theZ-peak as LEP/SLC experiments continue to increase their precision. In this paper we present an updated analysis of the hadronic vacuum polarization using all presently availablee+e− data. This seems to be justified because previous work on the subject was based to some extent on preliminary or incomplete experimental data. Contributions from different energy ranges are presented separately forg−2 of the muon and the τ-lepton and for α(MZ2). We obtain the resultsaμhad*=(725±16)×10−10 andaτhad*=(351±10)×10−8, where the asterisk indicates the dressed (renormalization group improved) value. For the effective fine structure constant atMZ=91.1888 GeV we obtainΔαhad(5)=0.0280±0.0007 and α(MZ2)−1=128.896±0.090. Further improvement in the accuracy of theoretical predictions which depend on the hadronic vacuum polarization requires more precise measurements ofe+e− cross-sections at energies below about 12 GeV in future experiments.

Hadronic contributions to ( g-2) of the leptons and to the effective fine structure constant α( M { Z / 2 })

We present the achievements of the last years of the experimental and theoretical groups working on hadronic cross section measurements at the low energy e+e- colliders in Beijing, Frascati, Ithaca, Novosibirsk, Stanford and Tsukuba and on tau decays. We sketch the prospects in these fields for the years to come. We emphasise the status and the precision of the Monte Carlo generators used to analyse the hadronic cross section measurements obtained as well with energy scans as with radiative return, to determine luminosities and tau decays. The radiative corrections fully or approximately implemented in the various codes and the contribution of the vacuum polarisation are discussed.

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Quest for precision in hadronic cross sections at low energy: Monte Carlo tools vs. experimental data

https://cds.cern.ch/record/284573/files/SCAN-9507094.pdf

Update of the hadronic contribution to the QED vaccum polarization

Measurements of multihadron production in e+e− annihilation at center-of-mass energies between 2.6 and 7.8 GeV are presented. Aside from the narrow resonances ψ(3095) and ψ(3684), the total hadronic cross section is found to be approximately 2.7 times the cross section for the production of muon pairs at c.m. energies below 3.7 GeV and 4.3 times the muon-pair cross section at c.m. energies above 5.5 GeV. Complicated structure is found at intermediate energies. Charged-particle multiplicities and inclusive momentum distributions are presented.

/pdf/hadron-production-by-e-e-annihilation-at-center-of-mass-5g05u9df5m.pdf

Hadron production by e+e- annihilation at center-of-mass energies between 2.6 and 7.8 GeV. I. Total cross section, multiplicities, and inclusive momentum distributions

James L. Siegrist

Papers

Hadron production by e+e- annihilation at center-of-mass energies between 2.6 and 7.8 GeV. I. Total cross section, multiplicities, and inclusive momentum distributions