arXiv subjects

C. P. Shen

Publications and source records attributed to C. P. Shen.

66 records · Page 4Linked to original sources

arXiv2012

Observation of new resonant structures in $γγ\to ωϕ$, $ϕϕ$ and $ωω$

The processes $γγ\to ωϕ$, $ϕϕ$, and $ωω$ are measured using an 870 fb$^{-1}$ data sample collected with the Belle detector at the KEKB asymmetric-energy $e^+e^-$ collider. Production of vector meson pairs is clearly observed and their cross sections are measured for masses that range from threshold to 4.0 GeV. In addition to signals from well established spin zero and spin two charmonium states, there are clear resonant structures below charmonium threshold, which have not been previously observed. We report a spin-parity analysis for the new structures and determine the products of the $\etac$, $χ_{c0}$, and $χ_{c2}$ two-photon decay widths and branching fractions.

hep-ex↗

arXiv2012

Search for the exotic states at Belle

We review recent results on charmonium-like exotic states from the Belle experiment. The two-photon process $γγ\to ϕ\jpsi$ is measured to search for Y(4140). No signal for the $Y(4140) \to ϕ\jpsi$ is observed. But a narrow peak with a significance of 3.2$σ$ deviations including systematic uncertainty is observed at 4350.6 MeV/$c^2$ that we named X(4350). We also search for charmonium-like states, including X(3872), Y(4140), X(3915) and X(4350), in $Υ(1S)$ and $Υ(2S)$ radiative decays. No significant signal of any charmonium-like state is observed. The processes $γγ\to VV$ ($V=ω$ or $ϕ$) are also measured to search for the possible exotic states in low mass region. There are clear resonant structures in all the decay modes.

hep-ex↗

arXiv2011

Search for CP Violation in D Meson Decays to phi pi+

We search for CP violation in Cabibbo-suppressed charged D meson decays by measuring the difference between the CP violating asymmetries for the Cabibbo-suppressed decays D+ -> K+K-pi+ and the Cabibbo-favored decays Ds -> K+K-pi+ in the K+K- mass region of the phi resonance. Using 955/fb of data collected with the Belle detector we obtain A_CP(D+ -> phi pi+) = (+0.51 +- 0.28 +- 0.05)%. The measurement improves the sensitivity of previous searches by more than a factor of five. We find no evidence for direct CP violation.

hep-ex↗

arXiv2011

The beam energy measurement system for the Beijing electron-positron collider

The beam energy measurement system (BEMS) for the upgraded Beijing electron-positron collider BEPC-II is described. The system is based on measuring the energies of Compton back-scattered photons. The relative systematic uncertainty of the electron and positron beam energy determination is estimated as 2 \cdot 10^{-5}. The relative uncertainty of the beam's energy spread is about 6 %.

physics.acc-ph↗

arXiv2011

Search for charmonium and charmonium-like states in Υ(2S) radiative decays

Using a sample of 158 million Υ(2S) events collected with the Belle detector, charmonium and charmonium-like states with even charge parity are searched for in Υ(2S) radiative decays. No significant χ_{cJ} or η_c signal is observed and the following upper limits at 90% confidence level (C.L.) are obtained: BR(Υ(2S)\to γχ_{c0})< 1.0 \times 10^{-4}, BR(Υ(2S) \to γχ_{c1})<3.6 \times 10^{-6}, BR(Υ(2S) \to γχ_{c2})<1.5 \times 10^{-5}, and BR(Υ(2S) \to γη_c)< 2.7 \times 10^{-5}. No significant signal of any charmonium-like state is observed, and we obtain the limits \BR(Υ(2S)\to γX(3872))\times\BR(X(3872)\toπ^+π^-J/ψ)< 0.8 \times 10^{-6}, BR(Υ(2S) \to γX(3872))\times BR(X(3872)\toπ^+π^-π^0 J/ψ)< 2.4\times 10^{-6}, BR(Υ(2S) \to γX(3915))\times BR(X(3915)\toωJ/ψ)< 2.8\times 10^{-6}, BR(Υ(2S) \to γY(4140))\times BR(Y(4140)\toϕJ/ψ)) < 1.2\times 10^{-6}, and BR(Υ(2S) \to γX(4350))\times BR(X(4350)\toϕJ/ψ))< 1.3\times 10^{-6} at 90% C.L.

hep-ex↗

arXiv2010

Observation of Bs->Ds()+Ds()- using e+e- collisions and a determination of the Bs-Bsbar width difference ΔΓ_s

We have made the first observation of Bs->Ds(*)+Ds(*)- decays using 23.6 fb-1 of data recorded by the Belle experiment running on the Upsilon(5S) resonance. The branching fractions are measured to be B(B^0_s\ra D^+_s D^-_s) = (1.0\,^{+0.4}_{-0.3}\,^{+0.3}_{-0.2})%, B(B^0_s\ra D^{*\pm}_s D^{\mp}_s) = (2.8\,^{+0.8}_{-0.7}\,\pm 0.7)%, and B(B^0_s\ra D^{*+}_s D^{*-}_s) = (3.1\,^{+1.2}_{-1.0}\,\pm 0.8)%; the sum is B(B^0_s\ra D^{(*)+}_s D^{(*)-}_s) = (6.9\,^{+1.5}_{-1.3}\,\pm 1.9)%. Assuming Bs->Ds(*)+Ds(*)- saturates decays to CP-even final states, the branching fraction determines the ratio ΔΓ_s/cos(ϕ), where ΔΓ_s is the difference in widths between the two Bs-Bsbar mass eigenstates, and ϕis a CP-violating weak phase. Taking CP violation to be negligibly small, we obtain ΔΓ_s/Γ_s = 0.147^{+0.036}_{-0.030}(stat.)^{+0.044}_{-0.042}(syst.), where Γ_s is the mean decay width.

hep-ex↗

arXiv2010

Search for charmonium and charmonium-like states in $Υ(1S)$ radiative decays

Using a sample of 102 million $Υ(1S)$ events collected with the Belle detector, we report on the first search for charge-parity-even charmonium and charmonium-like states in $Υ(1S)$ radiative decays. No significant $χ_{cJ}$ or $η_c$ signal is observed and 90% C.L. limits on $\BR(Υ(1S)\to γχ_{c0})<6.5 \times 10^{-4}$, $\BR(Υ(1S)\to γχ_{c1})<2.3\times 10^{-5}$, $\BR(Υ(1S)\to γχ_{c2})<7.6 \times 10^{-6}$, and $\BR(Υ(1S)\to γη_c)<5.7\times 10^{-5}$ are obtained. The product branching fraction limits $\BR(Υ(1S)\to γX(3872)) \BR(X(3872)\toπ^+π^-\jpsi)< 1.6 \times 10^{-6}$, $\BR(Υ(1S)\to γX(3872)) \BR(X(3872)\toπ^+π^-π^0 \jpsi)< 2.8\times 10^{-6}$, $\BR(Υ(1S)\to γX(3915)) \BR(X(3915)\toω\jpsi)< 3.0\times 10^{-6}$, and $\BR(Υ(1S)\to γY(4140)) \BR(Y(4140)\to ϕ\jpsi)<2.2\times 10^{-6}$ are obtained at the 90% C.L. Furthermore, no evidence is found for excited charmonium states below 4.8 GeV/$c^2$.

hep-ex↗

arXiv2010

Evidence for a new resonance and search for the Y(4140) in $γγ\to ϕJ/ψ$

The process $γγ\to ϕ\jpsi$ is measured for $ϕ\jpsi$ masses between threshold and 5 GeV/${\it c}^2$, using a data sample of 825 fb$^{-1}$ collected with the Belle detector. A narrow peak of $8.8^{+4.2}_{-3.2}$ events, with a significance of 3.2 standard deviations including systematic uncertainty, is observed. The mass and natural width of the structure (named X(4350)) are measured to be $(4350.6^{+4.6}_{-5.1}(\rm{stat})\pm 0.7(\rm{syst})) \hbox{MeV}/{\it c}^2$ and $(13^{+18}_{-9}(\rm{stat})\pm 4(\rm{syst})) \hbox{MeV}$, respectively. The product of its two-photon decay width and branching fraction to $ϕ\jpsi$ is $(6.7^{+3.2}_{-2.4}(\rm{stat}) \pm 1.1(\rm{syst})) \hbox{eV}$ for $J^P=0^+$, or $(1.5^{+0.7}_{-0.6}(\rm{stat}) \pm 0.3(\rm{syst})) \hbox{eV}$ for $J^P=2^+$. No signal for the $Y(4140)\to ϕ\jpsi$ structure reported by the CDF Collaboration in $B\to K^+ ϕ\jpsi$ decays is observed, and limits of $Γ_{γγ}(Y(4140)) \BR(Y(4140)\toϕ\jpsi)<41 \hbox{eV}$ for $J^P=0^+$ or $<6.0 \hbox{eV}$ for $J^P=2^+$ are determined at the 90% C.L. This disfavors the scenario in which the Y(4140) is a $D_{s}^{\ast+} {D}_{s}^{\ast-}$ molecule.

hep-ex↗

arXiv2009

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

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.

hep-ph↗

arXiv2009

Combined fit to BaBar and Belle Data on e+e- to phi pi+ pi- and phi f0(980)

A combined fit is performed to the BaBar and Belle measurements of the $\EE \to ϕπ^+ π^-$ and $ϕ\fzero$ cross sections for center-of-mass energy between threshold and 3.0 GeV. The resonance parameters of the $ϕ(1680)$ and Y(2175) are determined. The mass is $(1681^{+10}_{-12})$ MeV/$c^2$ and the width is $(221^{+34}_{-24})$ MeV/$c^2$ for the $ϕ(1680)$, and the mass is $(2117^{+59}_{-49})$ MeV/$c^2$ and the width is $(164^{+69}_{-80})$ MeV/$c^2$ for the Y(2175). These information will shed light on the understanding of the nature of the excited $ϕ$ and $Y$ states observed in $\EE$ annihilation.

hep-ex↗

arXiv2009

Observation of the $ϕ(1680)$ and the Y(2175) in $e^+ e^- \to ϕπ^+π^-$

The cross sections for $e^+ e^- \to ϕπ^+π^-$ and $e^+ e^- \to ϕ\fzero$ are measured from threshold to $\sqrt{s}=3.0$ $\hbox{GeV}$ using initial state radiation. The analysis is based on a data sample of 673 fb$^{-1}$ collected on and below the $Υ(4S)$ resonance with the Belle detector at the KEKB asymmetric-energy $e^+e^-$ collider. First measurements are reported for the resonance parameters of the $ϕ(1680)$ in the $ϕπ^+π^-$ mode: $m=(1689\pm 7\pm 10)$ MeV/$c^2$ and $Γ=(211\pm 14\pm 19)$ MeV/$c^2$. A structure at $\sqrt{s}=2.1 \hbox{GeV}/c^2$, corresponding to the so called Y(2175), is observed; its mass and width are determined to be $2079\pm13^{+79}_{-28}$ MeV/$c^2$ and $192\pm23^{+25}_{-61} \hbox{MeV}/c^2$, respectively.

hep-ex↗

arXiv2008

BES3 time of flight monitoring system

A Time of Flight monitoring system has been developed for BES3. The light source is a 442-443 nm laser diode, which is stable and provides a pulse width as narrow as 50 ps and a peak power as large as 2.6 W. Two optical-fiber bundles with a total of 512 optical fibers, including spares, are used to distribute the light pulses to the Time of Flight counters. The design, operation, and performance of the system are described.

physics.ins-det↗