Observation of a Charged(DD¯*)±Mass Peak ine+e−→πDD¯*ats=4.26  GeV

We report on a study of the process e(+)e(-) -> pi(+/-) (D (D) over bar*)(-/+) at root s = 4.26 GeV using a 525 pb(-1) data sample collected with the BESIII detector at the BEPCII storage ring. A distinct charged structure is observed in the (D (D) over bar*)(-/+) invariant mass distribution. When fitted to a mass- dependent- width Breit- Wigner line shape, the pole mass and width are determined to be M-pole (3883: 9 +/- 1.5 (stat) +/- 4.2 dsyst__ MeV= c(2) and Gamma(pole) = (24: 8 +/- 3.3 (stat) +/- 11: 0 (syst)) MeV. The mass and width of the structure, which we refer to as Z(c)(3885), are 2 sigma and 1 sigma, respectively, below those of the Z(c)(3900) -> pi(+/-) J/psi peak observed by B…

Observation of e+e−→γX(3802) at BESIII

Two-photon widths of theχc0,2states and helicity analysis forχc2→γγ

Based on a data sample of 106 X 10(6) psi' events collected with the BESIII detector, the decays psi' -> gamma chi(c0,2), chi(c0,2) -> gamma gamma are studied to determine the two-photon widths of the chi(c0,2) states. The two-photon decay branching fractions are determined to be B(chi(c0) -> gamma gamma) = (2.24 +/- 0.19 +/- 0.12 +/- 0.08) X 10(-4) and B(chi(c2) -> gamma gamma) = (3.21 +/- 0.18 +/- 0.17 +/- 0.13) X 10(-4) From these, the two-photon widths are determined to be Gamma(gamma gamma)(chi(c0)) = (2.33 +/- 0.20 +/- 0.13 +/- 0.17) keV, Gamma(gamma gamma)(chi(c2)) = (0.63 +/- 0.04 +/- 0.04 +/- 0.04) keV, and R = Gamma(gamma gamma)(chi(c2))/Gamma(gamma gamma)(chi(c0)) = 0.271 +/- 0.0…

Search forηandη′invisible decays inJ/ψ→ϕηandϕη′

Using a sample of (225.3 +/- 2.8) x 10(6) J/psi decays collected with the BESIII detector at BEPCII, searches for invisible decays of eta and eta ' in J/psi -> phi eta and phi eta ' are performed. Decays of phi -> K+K- are used to tag the eta and eta ' decays. No signals above background are found for the invisible decays, and upper limits at the 90% confidence level are determined to be 2.6 x 10(-4) for the ratio B(eta -> invisible)/B(eta ->gamma gamma) and 2.4 x 10(-2) for B(eta '-> invisible)/B(eta '->gamma gamma). These limits may be used to constrain light dark matter particles or spin-1 U bosons. DOI: 10.1103/PhysRevD.87.012009

Measurement of the absolute branching fraction of D + → K̅ 0 e + ν e via K̅ 0 → π 0 π 0

By analyzing 2.93 fb(-1) data collected at the center-of-mass energy root s = 3.773 GeV with the BESIII detector, we measure the absolute branching fraction of the semileptonic decay D+ -> (K) over bar (0)e(+)nu(e) to be B(D (+) -> (K) over bar (0)e(+)nu(e)) = (8.59 +/- 0.14 +/- 0.21)% using (K) over bar (0) -> K-S(0) -> pi(0) pi(0), where the first uncertainty is statistical and the second systematic. Our result is consistent with previous measurements within uncertainties..

First observation of the isospin violating decayJ/ψ→ΛΣ¯0+c.c.

Using a sample of (225.2 +/- 2.8) x 10(6) J/psi events collected with the BESIII detector, we present results of a study of J/psi -> gamma Lambda(Lambda) over bar and report the first observation of the isospin violating decay J/psi -> Lambda(Sigma) over bar (0) + c.c., in which (Sigma) over bar (0) decays to gamma (Lambda) over bar. The measured branching fractions are B(J/psi -> (Lambda) over bar Sigma(0)) = (1.46 +/- 0.11 +/- 0.12) x 10(-5) and B(J/psi -> Lambda(Sigma) over bar (0)) = (1.37 +/- 0.12 +/- 0.11) x 10(-5). We search for Lambda(1520) -> gamma Lambda decay, and find no evident signal, and an upper limit for the product branching fraction B(J/psi -> Lambda(Lambda) over bar (152…

Observation of a Charged Charmoniumlike Structure ine+e−→π+π−J/ψats=4.26  GeV

We study the process e(+)e(-) -> 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 +/- 1.9 +/- 3.7) pb, consistent with the production of the Y(4260). We observe a structure at around 3.9 GeV/c(2) in the pi(+/-) 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 pi(+/-) J/psi invariant mass spectrum, neglecting interference, results in a mass of (3899.0 +/- 3.6 +/- 4.9) MeV/c(2) and a width…

Observation of electromagnetic Dalitz decaysJ/ψ→Pe+e−

Based on a sample of (225.3 +/- 2.8) x 10(6) J/psi events collected with the BESIII detector, the electromagnetic Dalitz decays of J/psi -> Pe(+)e(-)(P = eta'/eta/pi(0)) are studied. By reconstructing the pseudoscalar mesons in various decay modes, the decays J/psi -> eta'e(+)e(-), J/psi -> eta e(+)e(-), and J/psi -> pi(0)e(+)e(-) are observed for the first time. The branching fractions are determined to be B(J/psi -> eta'e(+)e(-)) = (5.81 +/- 0.16 +/- 0.31) x 10(-5), B(J/psi -> eta e(+)e(-)) = (1.16 +/- 0.07 +/- 0.06) x 10(-5), and B(J/psi -> pi(0)e(+)e(-)) = (7.56 +/- 1.32 +/- 0.50) x 10(-7), where the first errors are statistical and the second ones systematic.

Search forηandη′→π+e−ν¯e+c.c.decays inJ/ψ→ϕηandϕη′

Using a sample of 225.3 million J/psi events collected with the BESIII detector at the BEPCII e(+)e(-) collider in 2009, searches for the decays of eta and eta' -> pi(+)e(-)(v) over bar (e) + c.c. in J/psi -> phi eta and phi eta' are performed. The phi signals, which are reconstructed in K+K- final states, are used to tag eta and eta' semileptonic decays. No signals are observed for either eta or eta', and upper limits at the 90% confidence level are determined to be 7.3 x 10(-4) and 5.0 x 10(-4) for the ratios B(eta ->pi(+)e(-)(v) over bar (e) + c.c)/B(eta ->pi(+)pi(-)pi(0)) and B(eta'->pi(+)e(-)(v) over bar (e) + c.c)/B(eta'->pi(+)pi(-)eta) respectively. These are the first upper- limit v…

Measurements of baryon pair decays of chi(cJ) mesons

Using 106 $\times 10^{6}$ $\psi^{\prime}$ decays collected with the BESIII detector at the BEPCII, three decays of $\chi_{cJ}$ ($J=0,1,2$) with baryon pairs ($\llb$, $\ssb$, $\SSB$) in the final state have been studied. The branching fractions are measured to be $\cal{B}$$(\chi_{c0,1,2}\rightarrow\Lambda\bar\Lambda) =(33.3 \pm 2.0 \pm 2.6)\times 10^{-5}$, $(12.2 \pm 1.1 \pm 1.1)\times 10^{-5}$, $(20.8 \pm 1.6 \pm 2.3)\times 10^{-5}$; $\cal{B}$$(\chi_{c0,1,2}\rightarrow\Sigma^{0}\bar\Sigma^{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}$$(\chi_{c0,1,2}\rightarrow\Sigma^{+}\bar\Sigma^{-})$ = $(45.4 \pm…

Observation of a Charged Charmoniumlike StructureZc(4020)and Search for theZc(3900)ine+e−→π+π−hc

We study e(+)e(-) -> pi(+) pi(-)h(c) at center-of-mass energies from 3.90 to 4.42 GeV by using data samples collected with the BESIII detector operating at the Beijing Electron Positron Collider. The Born cross sections are measured at 13 energies and are found to be of the same order of magnitude as those of e(+)e(-) -> pi(+) pi(-) J/Psi but with a different line shape. In the pi(+/-)h(c) mass spectrum, a distinct structure, referred to as Z(c)(4020) is observed at 4. 02 GeV/c(2). The Z(c)(4020) carries an electric charge and couples to charmonium. A fit to the pi(+/-)h(c) invariant mass spectrum, neglecting possible interferences, results in a mass of (4022.9 +/- 0.8 +/- 2.7) MeV/c(2) and…

Study ofe+e−→pp¯π0in the vicinity of theψ(3770)

The process e(+)e(-) -> p (p) over bar pi(0) has been studied by analyzing data collected at root s = 3.773 GeV, root s = 3.650 GeV, and during a psi(3770) line shape scan with the BESIII detector at the BEPCII collider. The Born cross section of p (p) over bar pi(0) in the vicinity of the psi(3770) is measured, and the Born cross section of psi(3770) -> p (p) over bar pi(0) is extracted considering interference between resonant and continuum production amplitudes. Two solutions with the same probability and a significance of 1.5 sigma are found. The solutions for the Born cross section of psi(3770) -> p (p) over bar pi(0) are 33.8 +/- 1.8 +/- 2.1 pb and 0.06(-0.04-0.01)(+0.10+0.01) pb ( ->…

Search for baryonic decays ofψ(3770)andψ(4040)

By analyzing data samples of 2.9 fb(-1) collected at root s = 3.773 GeV, 482 pb(-1) collected at root s = 4.009 GeV and 67 pb(-1) collected at root 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 psi(3770) and psi(4040) decay to baryonic final states, including Lambda(Lambda) over bar pi(+)pi(-), Lambda(Lambda) over bar pi(0), Lambda(Lambda) over bar eta , Sigma(0)(Sigma) over bar (0) and Xi(0) (Xi) over bar (0) decays. None are observed, and upper limits are set at the 90% confidence level.

Evidence forηc(2S)inψ(3686)→γKS0K±π∓π+π−

We search for the M1 radiative transition psi(3686) -> gamma eta(c)(2S) by reconstructing the exclusive eta(c)(2S) -> (KSK +/-)-K-0 pi(-/+)pi(+)pi(-) decay using 1.06 X 10(8) psi(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 eta(c)(2S) is 3646.9 +/- 1.6(stat) +/- 3.6(syst) MeV/c(2), and the width is 9.9 +/- 4.8(stat) +/- 2.9(syst) MeV/c(2). The product branching fraction is measured to be B(psi(3686) -> gamma eta(c)(2S)) X B(eta(c)(2S) -> gamma(KSK +/-)-K-0 pi(-/+)pi(+)pi(-) = (7.03 +/- 2.10(stat) +/- 0.70(syst)) X 10(-6). This measurement complements a previous BESIII m…

Search for the radiative transitionsψ(3770)→γηcandγηc(2S)

By using a 2.92 fb-1 data sample taken at pffisffiffi 3.773 GeV with the BESIII detector operating at the BEPCII collider, we search for the radiative transitions.d3770c and cd2S through the hadronic decays cdcd2S. K0 SK p. No significant excess of signal events above background is observed. We set upper limits at a 90% confidence level for the product branching fractions to be Bdd3770cxBd.c. K0 SK k p < 1.6x10-5 and Bd.d3770cd2SxBd.cd2S. K0 SK p<5.6x10-6. Combining our result with world-average values of Bd.cd.cd2S. K0 SK p, we find the branching fractions Bd.d3770c< 6.8 x 10-4 and Bd.d3770cd2S< 2.0 x 10-3 at a 90% confidence level.

Observation ofe+e−→ηJ/ψat center-of-mass energys=4.009  GeV

Using a 478 pb(-1) data sample collected with the BESIII detector operating at the Beijing Electron Positron Collider storage ring at a center-of-mass energy of root s = 4.009 GeV, the production of e(+)e(-) -> eta J/psi is observed for the first time with a statistical significance of greater than 10 sigma. The Born cross section is measured to be (32.1 +/- 2.8 +/- 1.3) pb, where the first error is statistical and the second systematic. Assuming the eta J/psi signal is from a hadronic transition of the psi(4040), the fractional transition rate is determined to be B(psi(4040) -> eta J/psi) = (5.2 +/- 0.5 +/- 0.2 +/- 0.5) x 10(-3), where the first, second, and third errors are statistical, s…

Observation of a Charged Charmoniumlike Structure Zc(4020) and Search for the Zc(3900) in e+e−→π+π−hc

Partial wave analysis ofJ/ψ→γηη

Based on a sample of 2.25 x 10(8) J/psi events collected with the BESIII detector at BEPCII, a full partial wave analysis on J/psi -> gamma eta eta 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.

Partial wave analysis of ψ(2S)→ppˉη

Using a sample of 1.06 x 10(8) psi(2) events collected with the BESIII detector at BEPCII, the decay psi(2S) -> p (p) over bar eta is studied. A partial wave analysis determines that the intermediate state N(1535) with a mass of 1524 +/- 5(-4)(+10) MeV/c(2) and a width of 130(-24-10)(+27+57) MeV/c(2) is dominant in the decay; the product branching fraction is determined to be B(psi(2S) -> N(1535)(p) over bar x B(N(1535) -> p eta + c.c. = 5.2 +/- 0.3(-1.2)(+3.2)) x 10(-5). Furthermore, the branching fraction of psi(2S) -> p (p) over bar eta is measured to be (6.4 +/- 0.2 +/- 0.6) x 10(-5). Here, the first error is statistical and the second is systematic.

Search for hadronic transitionχcJ→ηcπ+π−and observation ofχcJ→KK¯πππ

Hadronic transitions of chi(cJ) -> eta(c)pi(+)pi(-) (J = 0, 1, 2) are searched for using a sample of 1.06 x 10(8) psi(3686) events collected with the BESIII detector at the BEPCII storage ring. The eta(c) is reconstructed with (KSK +/-)-K-0 pi(-/+) and K+K-pi(0) final states. No signals are observed in any of the three chi(cJ) states in either eta(c) decay mode. At the 90% confidence level, the upper limits are determined to be B(chi(c0) -> eta(c)pi(+)pi(-)) eta(c)pi(+)pi(-)) eta(c)pi(+)pi(-)) eta(c)pi(+)pi(-)) is lower than the existing theoretical prediction by almost an order of magnitude. The branching fractions of chi(cJ) -> (KSK +/-)-K-0 pi(-/+)pi(+)pi(-), K+K-pi(+)pi(-)pi(0), omega K…

Experimental study ofψ′decays toK+K−π0andK+K−η

Using (106 +/- 4) x 10(6) psi ' events accumulated with the BESIII detector at the BEPCII e(+)e(-) collider, we present measurements of the branching fractions for psi' decays to K+K- pi(0) and K+K- eta. In these final states, the decay psi' -> K-2(*) (1430)(+) K- + 10(-5), is observed for the first time, and its branching fraction is measured to be (7.12 +/- 0: 62(stat)(-0.61)(+1.13) (syst)) x 10(-5), which indicates a violation of the helicity selection rule in psi' decays. The branching fractions of psi' -> K* (892)(+) K- + c.c., phi eta, and phi pi(0) are also measured. The measurements are used to test the QCD predictions on charmonium decays.

Amplitude analysis of theD+→KS0π+π0Dalitz plot

We perform an analysis of the D+ -> K-S(0)pi + (0)(pi) Dalitz plot using a data set of 2.92 fb(-1) of e(+) e(-) collisions at the (3770) mass accumulated by the BESIII experiment, in which 166694 candidate events are selected with a background of 15.1%. The Dalitz plot is found to be well represented by a combination of six quasitwo- body decay channels [k(SP)(0)(+) (1450)(+,) ] plus a small nonresonant component. Using the fit fractions from this analysis, partial branching ratios are updated with higher precision than previous measurements.

Observation of a Charged Charmoniumlike Structure in e+e−→π+π−J/ψ at s=4.26 GeV

Measurement ofη′→π+π−e+e−andη′→π+π−μ+μ−

Based on a sample of 225.3 million $J/\ensuremath{\psi}$ events accumulated with the BESIII detector at the BEPCII, the decays of ${\ensuremath{\eta}}^{\ensuremath{'}}\ensuremath{\rightarrow}{\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}{l}^{+}{l}^{\ensuremath{-}}$ are studied via $J/\ensuremath{\psi}\ensuremath{\rightarrow}\ensuremath{\gamma}{\ensuremath{\eta}}^{\ensuremath{'}}$. A clear ${\ensuremath{\eta}}^{\ensuremath{'}}$ signal is observed in the ${\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}{e}^{+}{e}^{\ensuremath{-}}$ mass spectrum, and the branching fraction is measured to be $\mathcal{B}({\ensuremath{\eta}}^{\ensuremath{'}}\ensuremath{\rightarrow}{\ensuremat…

Search for the rare decaysJ/ψ→Ds−ρ+andJ/ψ→D¯0K¯*0

A search for the rare decays of J/psi -> D-S(-) rho(+) + c.c. and J/psi -> D-S(-)rho(+) + c.c.) <(D)over bar(0)<(K)over bar*(0) + c.c.) < 2.5 x 10(-6) at the 90% confidence level.

Evidence forηc→γγand measurement ofJ/ψ→3γ

The decay of J/psi to three photons is studied using psi (3686) -> pi(+) pi(-) J/psi in a sample of 1.0641 X 10(8) psi (3686) events collected with the BESIII detector. Evidence of the direct decay of eta(c) to two photons, eta(c) -> gamma gamma, is reported, and the product branching fraction is determined to be B(J/psi -> gamma eta(c,) eta(c) -> gamma gamma = (4.5 +/- 1.2 +/- 0.6) X 10(-6), where the first error is statistical and the second is systematic. The branching fraction for J/psi -> 3 gamma is measured to be (11.3 +/- 1.8 +/- 2.0) X 10(-6) with improved precision. DOI: 10.1103/PhysRevD.87.032003

Observation of a Charged Charmoniumlike Structure ine+e−→(D*D¯*)±π∓ats=4.26  GeV

We study the process e(+)e(-) -> (D* (D) over bar*)(+/-)pi(-/+) at a center-of-mass energy of 4.26 GeV using a 827 pb(-1) data sample obtained with the BESIII detector at the Beijing Electron Positron Collider. Based on a partial reconstruction technique, the Born cross section is measured to be (137 +/- 9 +/- 15) pb. We observe a structure near the (D* (D) over bar*)(+/-) threshold in the pi(-/+) recoil mass spectrum, which we denote as the Z(c)(+/-) (4025). The measured mass and width of the structure are (4026.3 +/- 2.6 +/- 3.7) MeV/c(2) and (24.8 +/- 5.6 +/- 7.7) MeV, respectively. Its production ratio sigma(e(+)e(-) -> Z(c)(+/-)(4025)pi(-/+)-> (D* (D) over bar*)(+/-)pi(-/+)/sigma(e(+)e…

Precision measurements ofB[ψ(3686)→π+π−J/ψ]andB[J/ψ→l+l−]

Based on (106.41 +/- 0.86) x 10(6) psi(3686) events collected with the BESIII detector at the BEPCII collider, the branching fractions of psi(3686) -> pi(+)pi(-)J/psi, J/psi -> e(+)e(-), and J/psi -> mu(+)mu(-) are measured. We obtain B[psi(3686) -> pi(+)pi(-)J/psi] = (34.98 +/- 0.02 +/- 0.45)%, B[J/psi -> e(+)e(-)] = (5.983 +/- 0.007 +/- 0.037)%, and B[J/psi -> mu(+)mu(-)] = (5.973 +/- 0.0007 +/- 0.038)%. The measurement of B[psi(3686) -> pi(+)pi(-)J/psi] confirms the CLEO-c measurement, and is apparently larger than the others. The measured J/psi leptonic decay branching fractions agree with previous experiments within one standard deviation. These results lead to B[J/psi -> l(+)l(-)] = (…

Precision measurements of branching fractions forψ′→π0J/ψandηJ/ψ

We present a precision study of the psi' -> pi(0)J/Psi and eta J/Psi decay modes. The measurements are obtained using 106 x 10(6) psi' events accumulated with the BESIII detector at the BEPCII e(+)e(-) collider operating at a center-of-mass energy corresponding to the psi' mass. We obtain B(psi' -> pi(0)J/Psi) = (1.26 +/- 0.02(stat) +/- 0.03(syst)) x 10(-3) and B(psi' -> eta J/Psi) = (33.75 +/- 0.17(stat) +/- 0.86(syst)) x 10(-3). The branching fraction ratio R = B(psi'->pi(0)J/psi)/B(psi'->eta J/psi) is determined to be (3.74 +/- 0.06(stat) +/- 0.04(syst)) x 10(-2). The precision of these measurements of B(Psi' -> pi(0)J/Psi) and R represent a significant improvement over previously publis…

Search for the Lepton Flavor Violation Process J/ψ→eμ at BESIII

We search for the lepton-flavor-violating decay of the $J/\psi$ into an electron and a muon using $(225.3\pm2.8)\times 10^{6}$ $J/\psi$ 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 $\mathcal{B}(J/\psi \to e\mu)< 1.5 \times 10^{-7}$ (90% C.L.) is obtained.

Search forηc(2S)hc→pp¯decays and measurements of theχcJ→pp¯branching fractions

Using a sample of 1.06 x 10(8)psi(3686) events collected with the BESIII detector at BEPCII, the decays eta(c)(2S) -> p (p) over bar and h(c) -> p (p) over bar are searched for, where eta(c)(2S) and h(c) are reconstructed in the decay chains psi(3686) -> gamma eta(c)(2S), eta(c)(2S) -> p (p) over bar and psi(3686) -> pi(0)h(c), h(c) -> p (p) over bar, respectively. No significant signals are observed. The upper limits of the product branching fractions are determined to be B(psi(3686) -> gamma eta(c)(2S)) x B(eta(c)(2S) -> p (p) over bar) pi(0)h(c)) x B(h(c) -> p ) p (J = 0, 1, 2) are also measured to be (24.5 +/- 0.8 +/- 1.3, 8.6 +/- 0.5 +/- 0.5, 8.4 +/- 0.5 +/- 0.5) x 10(-5), which are th…

Precision measurements of B(D+→μ+νμ), the pseudoscalar decay constant fD+, and the quark mixing matrix element |Vcd|

We report a measurement of the branching fraction B(D+ -> mu(+)nu(mu)) = [3.71 +/- 0.19(stat) +/- 0.06(sys)] x 10(-4) based on 2.92 fb(-1) of data accumulated at root s = 3.773 GeV with the BESIII detector at the BEPCII collider. This measurement, in conjunction with the Cabibbo-Kobayashi-Maskawa matrix element vertical bar V-cd vertical bar determined from a global Standard Model fit, implies a value for the weak decay constant f(D+) = (203.2 +/- 5.3 +/- 1.8) MeV. Additionally, using this branching fraction measurement together with a lattice QCD prediction for f(D+), we find vertical bar V-cd vertical bar 0.2210 +/- 0.0058 +/- 0.0047. In either case, these are the most precise results for…