10 research outputs found
Hybrid Charmonium and the Puzzle
Using the method of QCD Sum Rules, we estimate the energy of the lowest
hybrid Charmonium state, and find it to be at the energy of the
state, about 600 Mev above the state. Since our solution is not
consistent with a pure hybrid at this energy, we conclude that the
state is probably an admixed and hybrid state. From
this conjecture we find a possible explanation of the famous puzzle.Comment: 9 pages, 7 figure
Precision measurements of A1N in the deep inelastic regime
We have performed precision measurements of the double-spin virtual-photon asymmetry A1A1 on the neutron in the deep inelastic scattering regime, using an open-geometry, large-acceptance spectrometer and a longitudinally and transversely polarized 3He target. Our data cover a wide kinematic range 0.277≤x≤0.5480.277≤x≤0.548 at an average Q2Q2 value of 3.078 (GeV/c)2, doubling the available high-precision neutron data in this x range. We have combined our results with world data on proton targets to make a leading-order extraction of the ratio of polarized-to-unpolarized parton distribution functions for up quarks and for down quarks in the same kinematic range. Our data are consistent with a previous observation of anA1n zero crossing near x=0.5x=0.5. We find no evidence of a transition to a positive slope in(Δd+Δd¯)/(d+d¯) up to x=0.548x=0.548
The P2 experiment
This article describes the future P2 parity-violating electron scattering
facility at the upcoming MESA accelerator in Mainz. The physics program of the
facility comprises indirect, high precision search for physics beyond the
Standard Model, measurement of the neutron distribution in nuclear physics,
single-spin asymmetries stemming from two-photon exchange and a possible future
extension to the measurement of hadronic parity violation. The first
measurement of the P2 experiment aims for a high precision determination of the
weak mixing angle to a precision of 0.14% at a four-momentum transfer of Q^2 =
4.5 10^{-3} GeV^2. The accuracy is comparable to existing measurements at the Z
pole. It comprises a sensitive test of the standard model up to a mass scale of
50 TeV, extendable to 70 TeV. This requires a measurement of the parity
violating cross section asymmetry -39.94 10^{-9} in the elastic electron-proton
scattering with a total accuracy of 0.56 10^-9 (1.4 %) in 10,000 h of 150
\micro A polarized electron beam impinging on a 60 cm liquid H_2 target
allowing for an extraction of the weak charge of the proton which is directly
connected to the weak mixing angle. Contributions from gamma Z-box graphs
become small at the small beam energy of 155 MeV. The size of the asymmetry is
the smallest asymmetry ever measured in electron scattering with an
unprecedented goal for the accuracy. We report here on the conceptual design of
the P2 spectrometer, its Cherenkov detectors, the integrating read-out
electronics as well as the ultra-thin, fast tracking detectors. There has been
substantial theory work done in preparation of the determination of the weak
mixing angle. The further physics program in particle and nuclear physics is
described as well.Comment: Invited EPJ A Manuscript, many figures, large file siz