arXiv subjects

W. M. Sun

Publications and source records attributed to W. M. Sun.

29 records · Page 2Linked to original sources

arXiv2010

Search for rare and forbidden decays of charm and charmed-strange mesons to final states h^+- e^-+ e^+

We have searched for flavor-changing neutral current decays and lepton-number-violating decays of D^+ and D^+_s mesons to final states of the form h^+- e^-+ e^+, where h is either πor K. We use the complete samples of CLEO-c open-charm data, corresponding to integrated luminosities of 818 pb^-1 at the center-of-mass energy E_CM = 3.774 GeV containing 2.4 x 10^6 D^+D^- pairs and 602 pb^-1 at E_CM = 4.170 GeV containing 0.6 x 10^6 D^*+-_s D^-+_s pairs. No signal is observed in any channel, and we obtain 90% confidence level upper limits on branching fractions B(D^+ --> π^+ e^+ e^-) < 5.9 x 10^-6, B(D^+ --> π^- e^+ e^+) < 1.1 x 10^-6, B(D^+ --> K^+ e^+ e^-) < 3.0 x 10^-6, B(D^+ --> K^- e^+ e^+) < 3.5 x 10^-6, B(D^+_s --> π^+ e^+ e^-) < 2.2 x 10^-5, B(D^+_s --> π^- e^+ e^+) < 1.8 x 10^-5, B(D^+_s --> K^+ e^+ e^-) < 5.2 x 10^-5, and B(D^+_s --> K^- e^+ e^+) < 1.7 x 10^-5.

hep-ex↗

arXiv2010

Gauge-invariant momentum and angular momentum operators in quantum electrodynamics and chromodynamics

Differences between vector potentials in different gauges contain no dynamics in both classical and quantum electrodynamics and chromodynamics. Consequently, once gauge invariance is established, results calculated in non-covariant gauges can be expected to agree with results obtained in covariant gauges in all Lorentz frames. We show in particular that canonical quantization in the Coulomb gauge can be used without giving up explicit gauge invariance. Quantization in the Coulomb gauge is particularly simple because it involves only the two transverse photons/gluons present in all gauges. These transverse photons/gluons reside on a 2-dimensional physical plane in momentum space perpendicular to the photon/gluon momentum {\bf k}. Explicit expressions are given for the basic momentum, spin and orbital angular momentum field operators of photons/gluons in the Coulomb gauge. Their properties are discussed in some detail. In particular, these field operators are shown to be more complicated than the corresponding operators in quantum mechanics which they also contain.

hep-ph↗

arXiv2010

Study of psi(2S) Decays to gamma p bar{p}, pi^0 p bar{p} and eta p bar{p} and Search for p bar{p} Threshold Enhancements

The decays of psi(2S) into gamma p bar{p}, pi^0 p bar{p} and eta p bar{p} have been studied with the CLEO-c detector using a sample of 24.5 million psi(2S) events obtained from e^+e^- annihilations at sqrt{s} = 3686 MeV. The data show evidence for the excitation of several N^* resonances in p pi^0 and p eta channels in pi^0 p bar{p} and eta p bar{p} decays, and f_2 states in gamma p bar{p} decay. Branching fractions for decays of psi(2S) to gamma p bar{p}, pi^0 p bar{p} and eta p bar{p} have been determined. No evidence for p bar{p} threshold enhancements was found in the reactions psi(2S)-> X p bar{p}, where X = gamma, pi^0, eta. We do, however, find confirming evidence for a p bar{p} threshold enhancement in J/psi-> gamma p bar{p} as previously reported by BES.

hep-ex↗

arXiv2010

Branching fractions for chi_cJ -> p p-bar pi^0, p p-bar eta, and p p-bar omega

Using a sample of 25.9 million psi(2S) decays acquired with the CLEO-c detector at the CESR e^+e^- collider, we report branching fractions for the decays chi_cJ -> p p-bar pi^0, p p-bar eta, and p p-bar omega, with J=0,1,2. Our results for B(chi_cJ-> p p-bar pi^0) and B(chi_cJ-> p p-bar eta) are consistent with, but more precise than, previous measurements. Furthermore, we include the first measurement of B(chi_cJ-> p p-bar omega).

hep-ex↗

arXiv2010

Analysis of D+ to K- pi+ e+ nu_e and D+ to K- pi+ mu+ nu_mu Semileptonic Decays

Using a large sample (~11800 events) of D^+ into K^- pi^+ e^+ nu_e and D^+ into K^- pi^+ mu^+ nu_mu decays collected by the CLEO-c detector running at the psi(3770), we measure the helicity basis form factors free from the assumptions of spectroscopic pole dominance and provide new, accurate measurements of the absolute branching fractions for D^+ into K^- pi^+ e^+ nu_e and D^+ into K^- pi^+ mu^+ nu_mu decays. We find branching fractions which are consistent with previous world averages. Our measured helicity basis form factors are consistent with the spectroscopic pole dominance predictions for the three main helicity basis form factors describing D^+ into anti-K*0 ell^+ nu_mu decay. The ability to analyze D^+ into K^- pi^+ mu^+ nu_mu allows us to make the first non-parametric measurements of the mass-suppressed form factor. Our result is inconsistent with existing Lattice QCD calculations. Finally, we measure the form factor that controls non-resonant s-wave interference with the D^+ into anti-K*0 ell^+ nu_mu amplitude and search for evidence of possible additional non-resonant d-wave or f-wave interference with the anti-K*0.

hep-ex↗

arXiv2010

Measurement of the eta_b(1S) mass and the branching fraction for Upsilon(3S) --> gamma eta_b(1S)

We report evidence for the ground state of bottomonium, eta_b(1S), in the radiative decay Upsilon(3S) --> gamma eta_b in e^+e^- annihilation data taken with the CLEO III detector. Using 6 million Upsilon(3S) decays, and assuming Gamma(eta_b) = 10 MeV/c^2, we obtain B(Upsilon(3S) --> gamma eta_b) = (7.1 +- 1.8 +- 1.1) X 10^{-4}, where the first error is statistical and the second is systematic. The statistical significance is about 4 sigma. The mass is determined to be M(eta_b) = 9391.8 +- 6.6 +- 2.0 MeV/c^2, which corresponds to the hyperfine splitting Delta M_{hf}(1S)_b = 68.5 +- 6.6 +- 2.0 MeV/c^2. Using 9 million Upsilon(2S) decays, we place an upper limit on the corresponding Y(2S) decay, B(Y(2S) --> gamma eta_b) < 8.4 X 10^{-4} at 90 % confidence level.

hep-ex↗

arXiv2009

The application of gauge invariance and canonical quantization to the internal structure of gauge field systems

It is unavoidable to deal with the quark and gluon momentum and angular momentum contributions to the nucleon momentum and spin in the study of nucleon internal structure. However, we never have the quark and gluon momentum, orbital angular momentum and gluon spin operators which satisfy both the gauge invariance and the canonical momentum and angular momentum commutation relation. The conflicts between the gauge invariance and canonical quantization requirement of these operators are discussed. A new set of quark and gluon momentum, orbital angular momentum and spin operators, which satisfy both the gauge invariance and canonical momentum and angular momentum commutation relation, are proposed. The key point to achieve such a proper decomposition is to separate the gauge field into the pure gauge and the gauge covariant parts. The same conflicts also exist in QED and quantum mechanics and have been solved in the same manner. The impacts of this new decomposition to the nucleon internal structure are discussed.

hep-ph↗

arXiv2007

Time-Independent Measurements of D0-D0bar Mixing and Relative Strong Phases Using Quantum Correlations

Due to quantum correlations in the C=-1 and C=+1 D0 D0bar pairs produced in the reactions e+ e- --> D0 D0bar (n pi0) and e+ e- --> D0 D0bar gamma (n pi0), respectively, the time-integrated D0 D0bar decay rates are sensitive to interference between amplitudes for indistinguishable final states. The size of this interference is governed by the relevant amplitude ratios and can include contributions from D0-D0bar mixing. We present a method for simultaneously measuring the magnitudes and phases of these amplitude ratios and searching for D0-D0bar mixing. We make use of fully- and partially-reconstructed D0 D0bar pairs in both C eigenstates. Our method is insensitive to CP violation, and we estimate experimental sensitivities based on a plausible charm factory dataset. Similar analyses can be applied to coherent K0 K0bar, B0 B0bar, or Bs Bsbar pairs.

hep-ph↗

arXiv2007

Measurement of the Strong Phase in D0 -> K+pi- Using Quantum Correlations

We exploit the quantum coherence between pair-produced D0 and D0bar in psi(3770) decays to study charm mixing and to make a first measurement of the relative strong phase δbetween D0 -> K+pi- and D0bar -> K+pi-. Using 281 pb^-1 of e+e- collision data collected with the CLEO-c detector at E_cm=3.77 GeV, as well as branching fraction input from other experiments, we make a preliminary determination of \cosδ= 1.03 +- 0.19 +- 0.08, where the uncertainties are statistical and systematic, respectively. By further including other external mixing parameter measurements, we obtain an alternate measurement of \cosδ= 0.93 +- 0.32 +- 0.04, where the systematic uncertainty from assuming x\sinδ=0 has not been included.

hep-ex↗

arXiv2007

Spin and orbital angular momentum in gauge theories (I): QED and determination of the angular momentum density

This two-paper series addresses and fixes the long-standing gauge invariance problem of angular momentum in gauge theories. This QED part reveals: 1) The spin and orbital angular momenta of electrons and photons can all be consistently defined gauge invariantly. 2) These gauge-invariant quantities can be conveniently computed via the canonical, gauge-dependent operators (e.g, $ψ^\dagger \vec x \times\frac 1i \vec \nabla ψ$) in the Coulomb gauge, which is in fact what people (unconsciously) do in atomic physics. 3) The renowned formula $\vec x\times(\vec E\times\vec B)$ is a wrong density for the electromagnetic angular momentum. The angular distribution of angular-momentum flow in polarized atomic radiation is properly described not by this formula, but by the gauge invariant quantities defined here. The QCD paper [arXiv:0907.1284] will give a non-trivial generalization to non-Abelian gauge theories, and discuss the connection to nucleon spin structure.

hep-ph↗

arXiv2007

Spin and orbital angular momentum in gauge theories (II): QCD and nucleon spin structure

Parallel to the construction of gauge invariant spin and orbital angular momentum for QED in paper (I) of this series, we present here an analogous but non-trivial solution for QCD. Explicitly gauge invariant spin and orbital angular momentum operators of quarks and gluons are obtained. This was previously thought to be an impossible task, and opens a more promising avenue towards the understanding of the nucleon spin structure.

hep-ph↗