arXiv subjects

M. N. Achasov

Publications and source records attributed to M. N. Achasov.

At least 865 records · Page 48Linked to original sources

arXiv2013

A system of beam energy measurement based on the Compton backscattered laser photons for the VEPP-2000 electron-positron collider

The beam energy measurement system for the VEPP-2000 electron-positron collider is described. The method of Compton backscattering of $CO$ laser photons on the electron beam is used. The relative systematic uncertainty of the beam energy determination is estimated as 6\cdot10^{-5}. It was obtained through comparison of the results of the beam energy measurements using the Compton backscattering and resonance depolarization methods.

physics.acc-ph↗

arXiv2013

Observation of the decay $ψ(3686)$ $\rightarrow$ $Λ\barΣ^{\pm}π^{\mp}+c.c.$

Using a sample of $1.06\times10^{8}$ $ψ(3686)$ events collected with the BESIII detector, we present the first observation of the decays of $ψ(3686)$ $\rightarrow$ $Λ\barΣ^{+}π^{-}+c.c.$ and $ψ(3686)$ $\rightarrow$ $Λ\barΣ^{-}π^{+}+c.c.$. The branching fractions are measured to be $\mathcal{B}(ψ(3686) \rightarrow Λ\barΣ^{+}π^{-} + c.c.)=(1.40\pm 0.03 \pm 0.13)\times10^{-4}$ and $\mathcal{B}(ψ(3686) \rightarrow Λ\barΣ^{-}π^{+}+c.c.)=(1.54\pm 0.04 \pm 0.13)\times10^{-4}$, where the first errors are statistical and the second ones systematic.

hep-ex↗

arXiv2013

Observation of a charged (DDbar)- mass peak in e+e- --> pi+ (DDbar)- at Ecm=4.26 GeV

We report on a study of the process e+e- --> pi+(D D*bar)- at Ecm=4.26 GeV using a 525 /pb data sample collected with the BESIII detector at the BEPCII storage ring. A distinct charged structure is observed in the (DD*bar)- invariant mass distribution. When fitted to a mass-dependent-width Breit-Wigner lineshape, the pole mass and width are determined to be M_pole=(3883.9 +- 1.5 +- 4.2) MeV and Gamma_pole=(24.8 +- 3.3 +- 11.0) MeV. The mass and width of the structure, which we refer to as Z_c(3885), are 2sigma and 1sigma, respectively, below those of the Z_c(3900) --> pi+J/psi peak observed by BESIII and Belle in pi+pi-J/psi final states produced at the same center-of-mass energy. The angular distribution of the pi Z_c(3885) system favors a JP=1+ quantum number assignment for the structure and disfavors 1- or 0-. The Born cross section times the DD*bar branching fraction of the Z_(3885) is measured to be sigma(e+e- --> pi+ Z_c(3885)-) x Bf(Z_c(3885)-->DD*bar)=(83.5 +-6.6 +- 22.0) pb. Assuming the Z_c(3885) --> DD*bar signal reported here and the Z_c(3900) --> pi J/psi signal are from the same source, the partial width ratio Gamma(Z_c(3885) --> DD*bar)/Gamma(Z_c(3900) -->pi J/psi)=6.2 +- 1.1 +- 2.7 is determined.

hep-ex↗

arXiv2013

Study of e+e- --> omega pi0 --> pi0 pi0 gamma in the energy range 1.05--2.00 GeV with SND

The cross section for the process e+e- --> omega pi0 --> pi0 pi0 gamma has been measured in the energy range 1.05--2.00 GeV. The experiment has been performed at the e+e- collider VEPP-2000 with the SND detector. The measured e+e- --> omega pi0 cross section above 1.4 GeV is the most accurate to date. Below 1.4 GeV our data are in good agreement with the previous SND and CMD-2 measurements. Data on the e+e- --> omega pi0 cross section are well described by the VMD model with two excited rho-like states. From the measured cross section we have extracted the gamma^* --> omega pi0 transition form factor. It has been found that the VDM model cannot describe simultaneously our data and data obtained from the omega --> pi0 mu+ mu- decay. We have also tested CVC hypothesis comparing our results on the e+e- --> omega pi0 cross section with data on the tau- --> omega pi- nu_{tau} decay.

hep-ex↗

arXiv2013

Precision Measurements of ${\cal B}[ψ(3686) \to π^+π^- J/ψ]$ and ${\cal B}[J/ψ\to l^+l^-]$

Based on $(106.41 \pm 0.86)\times 10^{6}$ $ψ(3686)$ events collected with the BESIII detector at the BEPCII collider, the branching fractions of $ψ(3686) \to π^+π^- J/ψ$, $J/ψ\to e^+e^- $, and $J/ψ\to μ^+μ^-$ are measured. We obtain ${\cal B}[ψ(3686) \to π^+π^-J/ψ]=(34.98\pm 0.02\pm 0.45)%$, ${\cal B}[J/ψ\to e^+e^-] = (5.983 \pm 0.007 \pm 0.037)%$ and ${\cal B}[J/ψ\to μ^+μ^-] = (5.973 \pm 0.007 \pm 0.038)%$. The measurement of ${\cal B}[ψ(3686) \to π^{+}π^{-}J/ψ]$ confirms the CLEO-c measurement, and is apparently larger than the others. The measured $J/ψ$ leptonic decay branching fractions agree with previous experiments within one standard deviation. These results lead to ${\cal B}[J/ψ\to l^+l^-] = (5.978 \pm 0.005 \pm 0.040)%$ by averaging over the $e^{+}e^{-}$ and $μ^{+}μ^{-}$ channels and a ratio of ${\cal B}[J/ψ\to e^+e^-] / {\cal B}[J/ψ\to μ^+μ^-] = 1.0017 \pm 0.0017 \pm 0.0033$, which tests $e$-$μ$ universality at the four tenths of a percent level. All the measurements presented in this paper are the most precise in the world to date.

hep-ex↗

arXiv2013

Study of $J/ψ\rightarrow ωp \bar{p}$ at BESIII

The decay $J/ψ\rightarrow ωp \bar{p}$ has been studied, using $225.3\times 10^{6}$ $J/ψ$ events accumulated at BESIII. No significant enhancement near the $p\bar{p}$ invariant-mass threshold (denoted as $X(p\bar{p})$) is observed. The upper limit of the branching fraction $\mathcal{B}(J/ψ\rightarrow ωX(p\bar{p}) \rightarrow ωp \bar{p})$ is determined to be $3.9\times10^{-6}$ at the 95% confidence level. The branching fraction of $J/ψ\rightarrow ωp \bar{p}$ is measured to be $\mathcal{B}(J/ψ\rightarrow ωp \bar{p}) =(9.0 \pm 0.2\ (\text{stat.})\pm 0.9\ (\text{syst.})) \times 10^{-4}$.

hep-ex↗

arXiv2013

Search for Baryonic Decays of ψ(3770) and ψ(4040)

By analyzing data samples of 2.9 fb^{-1} collected at \sqrt s=3.773 GeV, 482 pb^{-1} collected at \sqrt s=4.009 GeV and 67 pb^{-1} collected at \sqrt s=3.542, 3.554, 3.561, 3.600 and 3.650 GeV with the BESIII detector at the BEPCII storage ring, we search for ψ(3770) and ψ(4040) decay to baryonic final states, including Λ\barΛπ^+π^-, Λ\barΛπ^0, Λ\barΛη, Σ^+ \barΣ^-, Σ^0 \barΣ^0, Ξ^-\barΞ^+ and Ξ^0\barΞ^0 decays. None are observed, and upper limits are set at the 90% confidence level.

hep-ex↗

arXiv2013

Observation of a charged charmoniumlike structure in e+e- to pi+pi-J/psi at \sqrt{s}=4.26 GeV

We study the process e+e- to pi+pi-J/psi at a center-of-mass energy of 4.260 GeV using a 525 pb^{-1} data sample collected with the BESIII detector operating at the Beijing Electron Positron Collider. The Born cross section is measured to be (62.9\pm 1.9\pm 3.7) pb, consistent with the production of the Y(4260). We observe a structure at around 3.9 GeV/c^2 in the π^\pm J/psi mass spectrum, which we refer to as the Z_c(3900). If interpreted as a new particle, it is unusual in that it carries an electric charge and couples to charmonium. A fit to the π^\pm J/psi invariant mass spectrum, neglecting interference, results in a mass of (3899.0\pm 3.6\pm 4.9) MeV/c^2 and a width of (46\pm 10\pm 20) MeV. Its production ratio is measured to be R=\frac{σ(e+e- to π^\pm Z_c(3900)^\mp to pi+pi-J/psi))} {σ(e+e- to pi+pi-J/psi)}=(21.5\pm 3.3\pm 7.5)%. In all measurements the first errors are statistical and the second are systematic.

hep-ex↗

arXiv2013

Search for the Lepton Flavor Violation Process $J/ψ\to eμ$ at BESIII

We search for the lepton-flavor-violating decay of the $J/ψ$ into an electron and a muon using $(225.3\pm2.8)\times 10^{6}$ $J/ψ$ events collected with the BESIII detector at the BEPCII collider. Four candidate events are found in the signal region, consistent with background expectations. An upper limit on the branching fraction of $\mathcal{B}(J/ψ\to eμ)< 1.5 \times 10^{-7}$ (90% C.L.) is obtained.

hep-ex↗

arXiv2013

Partial wave analysis of $ψ(2S) \to p \bar{p}η$

Using a sample of $1.06 \times 10^{8}$ $ψ(2S)$ events collected with the BESIII detector at BEPCII, the decay $ψ(2S) \to p \bar{p}η$ is studied. A partial wave analysis determines that the intermediate state N(1535) with a mass of $1524\pm5^{+10}_{-4}$ MeV/$c^2$ and a width of $130^{+27+57}_{-24-10}$ MeV/$c^2$ is dominant in the decay; the product branching fraction is determined to be $B(ψ(2S) \to N(1535)\bar{p})\times B(N(1535)\to pη)+c.c. = (5.2\pm0.3^{+3.2}_{-1.2})\times 10^{-5}$. Furthermore, the branching fraction of $ψ(2S) \to ηp \bar{p}$ is measured to be $(6.4\pm0.2\pm0.6)\times 10^{-5}$.

hep-ex↗

arXiv2013

Measurement of $η^\prime\rightarrow π^+π^- e^+e^-$ and $η^\prime\rightarrow π^+π^-μ^+μ^-$

Based on a sample of 225.3 million J/ψevents accumulated with the BESIII detector at the BEPCII, the decays of η' to pi+pi-l+l- are studied via J/ψto γη'. A clear η' signal is observed in the pi+pi-e+e- mass spectrum, and the branching fraction is measured to be \BR(η' to pi+pi-e+e-) = (2.11\pm0.12 (stat.)\pm0.15 (syst.))\times10^{-3}, which is in good agreement with theoretical predictions and the previous measurement, but is determined with much higher precision. No η' signal is found in the pi+ pi- mu+ mu- mass spectrum, and the upper limit is determined to be \BR(η' to pi+ pi- mu+ mu-)<2.9\times10^{-5} at the 90% confidence level.

hep-ex↗

arXiv2013

Measurements of Baryon Pair Decays of $χ_{cJ}$ Mesons

Using 106 $\times 10^{6}$ $ψ^{\prime}$ decays collected with the BESIII detector at the BEPCII, three decays of $χ_{cJ}$ ($J=0,1,2$) with baryon pairs ($\llb$, $\ssb$, $\SSB$) in the final state have been studied. The branching fractions are measured to be $\cal{B}$$(χ_{c0,1,2}\rightarrowΛ\barΛ) =(33.3 \pm 2.0 \pm 2.6)\times 10^{-5}$, $(12.2 \pm 1.1 \pm 1.1)\times 10^{-5}$, $(20.8 \pm 1.6 \pm 2.3)\times 10^{-5}$; $\cal{B}$$(χ_{c0,1,2}\rightarrowΣ^{0}\barΣ^{0})$ = $(47.8 \pm 3.4 \pm 3.9)\times 10^{-5}$, $(3.8 \pm 1.0 \pm 0.5)\times 10^{-5}$, $(4.0 \pm 1.1 \pm 0.5) \times 10^{-5}$; and $\cal{B}$$(χ_{c0,1,2}\rightarrowΣ^{+}\barΣ^{-})$ = $(45.4 \pm 4.2 \pm 3.0)\times 10^{-5}$, $(5.4 \pm 1.5 \pm 0.5)\times 10^{-5}$, $(4.9 \pm 1.9 \pm 0.7)\times 10^{-5}$, where the first error is statistical and the second is systematic. Upper limits on the branching fractions for the decays of $χ_{c1,2}\rightarrowΣ^{0}\barΣ^{0}$, $Σ^{+}\barΣ^{-}$, are estimated to be $\cal{B}$$(χ_{c1}\rightarrowΣ^{0}\barΣ^{0}) < 6.2\times 10^{-5}$, $\cal{B}$$(χ_{c2}\rightarrowΣ^{0}\barΣ^{0}) < 6.5\times 10^{-5}$, $\cal{B}$$(χ_{c1}\rightarrowΣ^{+}\barΣ^{-}) < 8.7\times 10^{-5}$ and $\cal{B}$$(χ_{c2}\rightarrowΣ^{+}\barΣ^{-}) < 8.8\times 10^{-5}$ at the 90% confidence level.

hep-ex↗

arXiv2013

Evidence for $η_{c} \rightarrow γγ$ and Measurement of $J/ψ\rightarrow 3γ$

The decay of $J/ψ$ to three photons is studied using $ψ(3686)\toπ^+π^-J/ψ$ in a sample of $1.0641\times10^8$ $ψ(3686)$ events collected with the BESIII detector. Evidence of the direct decay of $η_c$ to two photons, $η_c\toγγ$, is reported, and the product branching fraction is determined to be $\mathcal{B}(J/ψ\toγη_c,η_c\to γγ)=(4.5\pm1.2\pm0.6)\times10^{-6}$, where the first error is statistical and the second is systematic. The branching fraction for $J/ψ\to3γ$ is measured to be $(11.3\pm1.8\pm2.0)\times 10^{-6}$ with improved precision.

hep-ex↗

arXiv2013

Search for $η$ and $η^\prime\to π^+ e^- \barν_e +c.c.$ decays in $\jpsi \to ϕη$ and $ϕη^\prime$

Using a sample of 225.3 million $\jpsi$ events collected with the BESIII detector at the BEPCII $e^+e^-$ collider in 2009, searches for the decays of $η$ and $η^\prime\toπ^+ e^- \barν_e +c.c.$ in $\jpsi \to ϕη$ and $ϕη^\prime$ are performed. The $ϕ$ signals, which are reconstructed in $K^+K^-$ final states, are used to tag $η$ and $η^\prime$ semileptonic decays. No signals are observed for either $η$ or $η^\prime$, and upper limits at the 90% confidence level are determined to be $7.3\times 10^{-4}$ and $5.0\times 10^{-4}$ for the ratios $\frac{{\mathcal B}(η\to π^+ e^- \barν_e +c.c.)}{{\mathcal B}(η\to \pip\pim\piz)}$ and $\frac{{\mathcal B}(η^\prime\to π^+ e^-\barν_e +c.c.)}{{\mathcal B}(η^\prime \to \pip\pimη)}$, respectively. These are the first upper limit values determined for $η$ and $η^\prime$ semileptonic weak decays.

hep-ex↗

arXiv2013

Search for $η$ and $η'$ Invisible Decays in $J/ψ\toϕη$ and $ϕη'$

Using a sample of $(225.3\pm 2.8)\times 10^{6}$ $J/ψ$ decays collected with the BESIII detector at BEPCII, searches for invisible decays of $η$ and $η^\prime$ in $J/ψ\toϕη$ and $ϕη^\prime$ are performed. Decays of $ϕ\to K^{+}K^{-}$ are used to tag the $η$ and $η^\prime$ decays. No signals above background are found for the invisible decays, and upper limits at the 90% confidence level are determined to be $2.58\times10^{-4}$ for the ratio $\frac{\mathcal{B}(η\to\rm{invisible})}{\mathcal{B}(η\toγγ)}$ and $2.39\times10^{-2}$ for $\frac{\mathcal{B}(η^\prime\to\rm{invisible})}{\mathcal{B}(η^\prime \toγγ)}$.

hep-ex↗

arXiv2013

Evidence for η_{c}(2S) in ψ(3686) \to γK_{S}^{0}K^{\pm}π^{\mp}π^{+}π^{-}

We search for the M1 radiative transition ψ(3686) \to γη_{c}(2S) by reconstructing the exclusive η_{c}(2S) \to K_{S}^{0}K^{\pm}π^{\mp}π^{+}π^{-} decay using 1.06 \times 10^8 ψ(3686) events collected with the BESIII detector. The signal is observed with a statistical significance of greater than 4 standard deviations. The measured mass of the η_{c}(2S) is 3646.9 \pm 1.6(stat) \pm 3.6(syst) MeV/c^2, and the width is 9.9 \pm 4.8(stat) \pm 2.9(syst) MeV/c^2. The product branching fraction is measured to be B(ψ(3686) \to γη_{c}(2S)) \times B(η_{c}(2S) \to K_{S}^{0}K^{\pm}π^{\mp}π^{+}π^{-}) = (7.03 \pm 2.10(stat) \pm 0.70(syst)) \times 10^{-6}. This measurement complements a previous BESIII measurement of ψ(3686) \to γη_{c}(2S) with η_{c}(2S) \to K_{S}^{0} K^{\pm}π^{\mp} and K^{+}K^{-}π^{0}.

hep-ex↗

arXiv2013

Partial wave analysis of $J/ψ\to γηη$

Based on a sample of $2.25\times 10^{8}$ $J/ψ$ events collected with the BESIII detector at BEPCII, a full partial wave analysis on $J/ψ\toγηη$ was performed using the relativistic covariant tensor amplitude method. The results show that the dominant $0^{++}$ and $2^{++}$ components are from the $f_0(1710)$, $f_0(2100)$, $f_0(1500)$, $f_2'(1525)$, $f_2(1810)$ and $f_2(2340)$. The resonance parameters and branching fractions are also presented.

hep-ex↗

arXiv2012

Observation of $η_{c}$ decay into $Σ^{+}\barΣ^{-}$ and $Ξ^{-}\barΞ^{+}$ final states

Using a data sample of $2.25\times10^{8}$ $J/ψ$ events collected with the BESIII detector, we present the first observation of the decays of $η_{c}$ mesons to $Σ^{+}\barΣ^{-}$ and $Ξ^{-}\barΞ^{+}$. The branching fractions are measured to be $(2.11\pm0.28_{\rm stat.}\pm0.18_{\rm syst.}\pm0.50_{\rm PDG})\times10^{-3}$ and $(0.89\pm0.16_{\rm stat.}\pm0.08_{\rm syst.}\pm0.21_{\rm PDG})\times10^{-3}$ for $η_{c} \to Σ^{+}\barΣ^{-}$ and $Ξ^{-}\barΞ^{+}$, respectively. These branching fractions provide important information on the helicity selection rule in charmonium-decay processes.

hep-ex↗