arXiv subjects

L. M. Zhang

Publications and source records attributed to L. M. Zhang.

32 records · Page 2Linked to original sources

arXiv2011

Measurements of branching fractions for electromagnetic transitions involving the $χ_{bJ}(1P)$ states

Using 9.32, 5.88 million Upsilon(2S,3S) decays taken with the CLEO-III detector, we obtain five product branching fractions for the exclusive processes Upsilon(2S) => gamma chi_{b0,1,2}(1P) => gamma gamma Upsilon(1S) and Upsilon(3S) => gamma chi_{b1,2}(1P) => gamma gamma Upsilon(1S). We observe the transition chi_{b0}(1P) => gamma Upsilon(1S) for the first time. Using the known branching fractions for B[Upsilon(2S) => gamma chi_{bJ}(1P)], we extract values for B[chi_{bJ}(1P) => gamma Upsilon(1S)] for J=0, 1, 2. In turn, these values can be used to unfold the Upsilon(3S) product branching fractions to obtain values for B[Upsilon(3S) => gamma chi_{b1,2}(1P) for the first time individually. Comparison of these with each other and with the branching fraction B[Upsilon(3S) => gamma chi_{b0}] previously measured by CLEO provides tests of relativistic corrections to electric dipole matrix elements.

hep-ex↗

arXiv2010

Upsilon(1S)->gamma+f2'(1525); f2'(1525)->K0sK0s decays

We report on a study of exclusive radiative decays of the Upsilon(1S) resonance into a final state consisting of a photon and two K0s candidates. We find evidence for a signal for Upsilon(1S)->gamma f_2'(1525); f_2'(1525)->K0sK0s, at a rate (4.0+/-1.3+/-0.6)x10^{-5}, consistent with previous observations of Upsilon(1S)->gamma f_2'(1525); f_2'(1525)->K+K-, and isospin. Combining this branching fraction with existing branching fraction measurements of Upsilon(1S)->gamma f_2'(1525) and J/psi->gamma f_2'(1525), we obtain the ratio of branching fractions: B(Upsilon(1S)->gamma f_2'(1525))/B(J/psi->gamma f_2'(1525))=0.09+/-0.02, approximately consistent with expectations based on soft collinear effective theory.

hep-ex↗

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

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

Magnetoelectric coupling, Berry phase, and Landau level dispersion in a biased bilayer graphene

We study the energy spectrum of a graphene bilayer in the presence of transverse electric and magnetic fields. We find that the resulting Landau levels exhibit a nonmonotonic dependence on the electric field, as well as numerous level crossings. This behavior is explained using quasiclassical quantization rules that properly take into account the pseudospin of the quasiparticles. The pseudospin generates the Berry phase, which leads to a shift in energy quantization and results in a pseudo-Zeeman effect. The latter depends on the electric field, alternates in sign among the two valleys, and also reduces the band gap. Analytic formulas for other pseudospin-related quantities, such as the anomalous Hall conductivity, are derived and compared with prior theoretical work.

cond-mat.mes-hall↗

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.

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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.

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arXiv2008

Determination of the electronic structure of bilayer graphene from infrared spectroscopy results

We present an experimental study of the infrared conductivity, transmission, and reflection of a gated bilayer graphene and their theoretical analysis within the Slonczewski-Weiss-McClure (SWMc) model. The infrared response is shown to be governed by the interplay of the interband and the intraband transitions among the four bands of the bilayer. The position of the main conductivity peak at the charge neutrality point is determined by the interlayer tunneling frequency. The shift of this peak as a function of the gate voltage gives information about less known parameters of the SWMc model, in particular, those responsible for the electron-hole and sublattice asymmetries. These parameter values are shown to be consistent with recent electronic structure calculations for the bilayer graphene and the SWMc parameters commonly used for the bulk graphite.

cond-mat.mes-hall↗

arXiv2007

D0 mixing at Belle

We report the recent two results of D0-D0bar mixing studies at Belle in D0->K+K-/pi+pi- and D0->K_S^0 pi+pi- decays. The former measures the relative difference of the lifetimes y_{CP}, giving the evidence of D0-D0bar mixing; the latter measures the D0 mixing parameters x and y.

hep-ex↗

arXiv2007

Nonlinear screening and ballistic transport in a graphene p-n junction

We study the charge density distribution, the electric field profile, and the resistance of an electrostatically created lateral p-n junction in graphene. We show that the electric field at the interface of the electron and hole regions is strongly enhanced due to limited screening capacity of Dirac quasiparticles. Accordingly, the junction resistance is lower than estimated in previous literature.

cond-mat.mes-hall↗

arXiv2007

Measurement of D0-D0bar mixing in D0->Ks pi+ pi- decays

We report a measurement of D0-D0bar mixing in D0->Ks pi+ pi- decays using a time-dependent Dalitz plot analysis. We first assume CP conservation and subsequently allow for CP violation. The results are based on 540 fb$^{-1}$ of data accumulated with the Belle detector at the KEKB $e^+e^-$ collider. Assuming negligible CP violation, we measure the mixing parameters $x=(0.80\pm0.29^{+0.09 +0.10}_{-0.07 -0.14})%$ and $y=(0.33\pm0.24^{+0.08 +0.06}_{-0.12 -0.08})%$, where the errors are statistical, experimental systematic, and systematic due to the Dalitz decay model, respectively. Allowing for CP violation, we obtain the $CPV$ parameters $|q/p|=0.86^{+0.30 +0.06}_{-0.29 -0.03}\pm0.08$ and $\arg(q/p)=(-14^{+16 +5 +2}_{-18 -3 -4})^\circ$.

hep-ex↗

arXiv2006

Improved Constraints on D0-D0bar Mixing in D0 -> K+ pi- Decays from the Belle Detector

We report the results of a search for D0-D0bar mixing in D0 -> K+ pi- decays based on 400 fb^{-1} of data accumulated by the Belle detector at KEKB. Both assuming CP conservation and allowing for CP violation, we fit the decay-time distribution for the mixing parameters x' and y', as well as for the parameter R_D, the ratio of doubly-Cabibbo-suppressed decays to Cabibbo-favored decays. The 95% confidence level region in the (x'^2,y') plane is obtained using a frequentist method. Assuming CP conservation, we find x'^2<0.72 x 10^{-3} and -9.9 x 10^{-3}<y'<6.8 x 10^{-3} at the 95% confidence level; these are the most stringent constraints on the mixing parameters to date. The no-mixing point (0,0) has a confidence level of 3.9%. Assuming no mixing, we measure R_D=(0.377+-0.008+-0.005)%.

hep-ex↗

arXiv2005

Search for B0 -> J/psi D0bar and B+ -> J/psi D0bar pi+ decays

We report the results of a search for the decay modes B0 -> J/psi D0bar and B+ -> J/psi D0bar pi+. The analysis is based on 140 $\rm fb^{-1}$ of data accumulated by the Belle detector at the KEKB asymmetric-energy $e^{+} e^{-}$ collider. No significant signals are observed and we determine the branching fraction upper limits B(B0 -> J/psi D0bar) < 2.0 10^{-5} and B(B+ -> J/psi D0bar pi+) < 2.5 10^{-5} at 90% confidence level. These results rule out the explanation of the excess in the low momentum region of the inclusive J/psi spectrum as intrinsic charm content in the B meson. The branching fractions of the corresponding non-resonant decay channels are also reported.

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