Precision measurement of charged pion and kaon differential cross sections in e+ e- annihilation at sqrt[s]=10.52 GeV.

Measurements of inclusive differential cross sections for charged pion and kaon production in e+ e- annihilation have been carried out at a center-of-mass energy of sqrt[s]=10.52 GeV. The measurements were performed with the Belle detector at the KEKB e+ e- collider using a data sample containing 113×10(6) e+ e- → qq events, where q={u,d,s,c}. We present charge-integrated differential cross sections dσ(h±)/dz for h±={π±,K±} as a function of the relative hadron energy z=2E(h)/sqrt[s] from 0.2 to 0.98. The combined statistical and systematic uncertainties for π± (K±) are 4% (4%) at z∼0.6 and 15% (24%) at z∼0.9. The cross sections are the first measurements of the z dependence of pion and kaon production for z>0.7 as well as the first precision cross section measurements at a center-of-mass energy far below the Z0 resonance used by the experiments at LEP and SLC.

Evidence of a new narrow resonance decaying to χ(c1)γ in B→χ(c1)γK.

We report measurements of B→χ(c1)γK and χ(c2)γK decays using 772×10(6) BB[over ¯] events collected at the Υ(4S) resonance with the Belle detector at the KEKB asymmetric-energy e(+)e(-) collider. Evidence of a new resonance in the χ(c1)γ final state is found with a statistical significance of 3.8σ. This state has a mass of 3823.1±1.8(stat)±0.7(syst) MeV/c(2), a value that is consistent with theoretical expectations for the previously unseen 1(3)D(2) cc[over ¯] meson. We find no other narrow resonance and set upper limits on the branching fractions of the X(3872)→χ(c1)γ and χ(c2)γ decays.

Study of e+ e- → π+ π- J/ψ and observation of a charged charmoniumlike state at Belle.

The cross section for ee+ e- → π+ π- J/ψ between 3.8 and 5.5 GeV is measured with a 967 fb(-1) data sample collected by the Belle detector at or near the Υ(nS) (n = 1,2,…,5) resonances. The Y(4260) state is observed, and its resonance parameters are determined. In addition, an excess of π+ π- J/ψ production around 4 GeV is observed. This feature can be described by a Breit-Wigner parametrization with properties that are consistent with the Y(4008) state that was previously reported by Belle. In a study of Y(4260) → π+ π- J/ψ decays, a structure is observed in the M(π(±)J/ψ) mass spectrum with 5.2σ significance, with mass M = (3894.5 ± 6.6 ± 4.5) MeV/c2 and width Γ = (63 ± 24 ± 26) MeV/c2, where the errors are statistical and systematic, respectively. This structure can be interpreted as a new charged charmoniumlike state.

First observation of the P-wave spin-singlet bottomonium states hb(1P) and hb(2P).

We report the first observations of the spin-singlet bottomonium states h(b)(1P) and h(b)(2P). The states are produced in the reaction e(+)e(-)→h(b)(nP)π(+)π(-) using a 121.4 fb(-1) data sample collected at energies near the Υ(5S) resonance with the Belle detector at the KEKB asymmetric-energy e(+)e(-) collider. We determine M[h(b)(1P)]=(9898.2(-1.0-1.1)(+1.1+1.0)) MeV/c(2) and M[h(b)(2P)]=(10,259.8±0.6(-1.0)(+1.4)) MeV/c(2), which correspond to P-wave hyperfine splittings ΔM(HF)=(+1.7±1.5) and (+0.5(-1.2)(+1.6)) MeV/c(2), respectively. The significances of the h(b)(1P) and h(b)(2P) are 5.5σ and 11.2σ, respectively. We find that the production of the h(b)(1P) and h(b)(2P) is not suppressed relative to the production of the Υ(1S), Υ(2S), and Υ(3S).

Evidence for the η(b)(2S) and observation of h(b)(1P)→η(b)(1S)γ and h(b)(2P)→η(b)(1S)γ.

We report the first evidence for the η(b)(2S) using the h(b)(2P)→η(b)(2S)γ transition and the first observation of the h(b)(1P)→η(b)(1S)γ and h(b)(2P)→η(b)(1S)γ transitions. The mass and width of the η(b)(1S) and η(b)(2S) are measured to be m(η(b)(1S))=(9402.4±1.5±1.8) MeV/c(2), m(η(b)(2S))=(9999.0±3.5(-1.9)(+2.8)) MeV/c(2), and Γ(η(b)(1S))=(10.8(-3.7-2.0)(+4.0+4.5)) MeV. We also update the h(b)(1P) and h(b)(2P) mass measurements. We use a 133.4 fb(-1) data sample collected at energies near the Υ(5S) resonance with the Belle detector at the KEKB asymmetric-energy e(+)e(-) collider.

Observation of D+ → K(+)η(') and search for CP violation in D+ → π(+)η(') decays.

We report the first observation of the doubly Cabibbo-suppressed decays D(+)→K(+)η((')) using a 791 fb(-1) data sample collected with the Belle detector at the KEKB asymmetric-energy e(+)e(-) collider. The ratio of the branching fractions of doubly Cabibbo-suppressed relative to singly Cabibbo-suppressed D(+)→π(+)η((')) decays are B(D(+)→K(+)η)/B(D(+)→π(+)η)=(3.06±0.43±0.14)% and B(D(+)→K(+)η')/B(D(+)→π(+)η')=(3.77±0.39±0.10)%. From these, we find that the relative final-state phase difference between the tree and annihilation amplitudes in D(+) decays, δ(TA), is (72±9)° or (288±9)°. We also report the most precise measurements of CP asymmetries to date: A(CP)(D(+)→π(+)η)=(+1.74±1.13±0.19)% and A(CP)(D(+)→π(+)η')=(-0.12±1.12±0.17)%.

Observation of X(3872)→J/ψγ and search for X(3872)→ψ'γ in B decays.

We report a study of B→(J/ψγ)K and B→(ψ'γ)K decay modes using 772×106 B ̅B events collected at the Υ(4S) resonance with the Belle detector at the KEKB energy-asymmetric e(+)e(-) collider. We observe X(3872)→J/ψγ and report the first evidence for χ(c2)→J/ψγ in B→(X_{c ̅cγ)K decays, while in a search for X(3872)→ψ'γ no significant signal is found. We measure the branching fractions, B(B(±)→X(3872)K(±))B(X(3872)→J/ψγ)=(1.78(-0.44)(+0.48)±0.12)×10(-6), B(B(±)→χ(c2)K(±))=(1.11(-0.34)(+0.36)±0.09)×10(-5), B(B(±)→X(3872)K(±))B(X(3872)→ψ'γ)<3.45×106 (upper limit at 90% C.L.), and also provide upper limits for other searches.

Search for CP violation in the decays D(0)→K(S)(0)P(0).

We have searched for CP violation in the decays D(0)→K(S)(0)P(0) where P(0) denotes a neutral pseudoscalar meson that is either a π(0), η, or η' using KEKB asymmetric-energy e(+)e(-) collision data corresponding to an integrated luminosity of 791 fb(-1) collected with the Belle detector. No evidence of significant CP violation is observed. We report the most precise CP asymmetry measurement in the decay D(0)→K(S)(0)π(0) to date: A(CP)(D(0)→K(S)(0)π(0))=(-0.28±0.19±0.10)%. We also report the first measurements of CP asymmetries in the decays D(0)→K(S)(0)η and D(0)→K(S)(0)η': A(CP)(D(0)→K(S)(0)η)=(+0.54±0.51±0.16)% and A(CP)(D(0)→K(S)(0)η')=(+0.98±0.67±0.14)%, respectively.

Observation of the doubly cabibbo-suppressed decay D_{s};{+}-->K;{+}K;{+}pi;{-}.

We report the first observation of the doubly Cabibbo-suppressed decay D_{s};{+}-->K;{+}K;{+}pi;{-} using 605 fb;{-1} of data collected with the Belle detector at the KEKB asymmetric-energy e;{+}e;{-} collider. The branching ratio with respect to its Cabibbo-favored counterpart B(D_{s};{+}-->K;{+}K;{+}pi;{-})/B(D_{s};{+}-->K;{+}K;{-}pi;{+}) is (0.229+/-0.028+/-0.012)%, where the first uncertainty is statistical and the second is systematic. We also report a significantly improved measurement of the doubly Cabibbo-suppressed decay D;{+}-->K;{+}pi;{+}pi;{-}, with a branching ratio B(D;{+}-->K;{+}pi;{+}pi;{-})/B(D;{+}-->K;{-}pi;{+}pi;{+})=(0.569+/-0.018+/-0.014)%.

Observation of a near-threshold enhancement in the e+e- -->Lambda+_(c)Lambda-_(c) cross section using initial-state radiation.

We report a measurement of the exclusive e+ e- -->Lambda+_(c)Lambda-_(c) cross section as a function of center-of-mass energy near the Lambda+_(c)Lambda-_(c) threshold. A clear peak with a significance of 8.2sigma is observed in the Lambda+_(c)Lambda-_(c) invariant mass distribution just above threshold. With an assumption of a resonance origin for the observed peak, a mass and width of M=[4634 (+8)_(-7)(stat)(+5)_(-8)(syst)] MeV/c(2) and Gamma_(tot)=[92 (+40)_(-24)(stat)(+10)_(-21)(syst)] MeV are determined. The analysis is based on a study of events with initial-state-radiation photons in a data sample collected with the Belle detector at the Upsilon(4S) resonance and nearby continuum with an integrated luminosity of 695 fb(-1) at the KEKB asymmetric-energy e+ e- collider.

Measurement of B(Ds{+}-->mu+nu(mu)).

We present a measurement of the branching fraction B(D{s}{+}-->mu{+}nu{mu}) using a 548 fb{-1} data sample collected by the Belle experiment at the KEKB e{+}e{-} collider. The D{s} momentum is determined by reconstruction of the system recoiling against DKgammaX in events of the type e{+}e{-}-->D{s}{*}DKX, D{s}{*}-->D{s}gamma, where X represents additional pions or photons from fragmentation. This full-reconstruction method provides high resolution in the neutrino momentum and thus good background separation, equivalent to that achieved by experiments at the tau-charm factories. We obtain the branching fraction B(D{s}{+}-->mu{+}nu{mu})=[6.44+/-0.76(stat)+/-0.57(syst)]x10{-3}, implying a D{s} decay constant of f{D{s}}=[275+/-16(stat)+/-12(syst)] MeV.

Observation of anomalous upsilon(1S)pi+pi(-) and upsilon(2S)pi+pi(-) production near the upsilon(5S) resonance.

We report the first observation of e;{+}e;{-}-->Upsilon(1S)pi;{+}pi;{-}, Upsilon(2S)pi;{+}pi;{-}, and first evidence for e;{+}e;{-}-->Upsilon(3S)pi;{+}pi;{-}, Upsilon(1S)K+K-, near the peak of the Upsilon(5S) resonance at sqrt[s] approximately 10.87 GeV. The results are based on a data sample of 21.7 fb;{-1} collected with the Belle detector at the KEKB e;{+}e;{-} collider. Attributing the signals to the Upsilon(5S) resonance, the partial widths Gamma(Upsilon(5S)-->Upsilon(1S)pi;{+}pi;{-})=0.59+/-0.04(stat)+/-0.09(syst) MeV and Gamma(Upsilon(5S)-->Upsilon(2S)pi;{+}pi;{-})=0.85+/-0.07(stat)+/-0.16(syst) MeV are obtained from the observed cross sections. These values exceed by more than 2 orders of magnitude the previously measured partial widths for dipion transitions between lower Upsilon resonances.

Observation of a resonancelike structure in the pi +- psi' mass distribution in exclusive B-->Kpi +- psi' decays.

A distinct peak is observed in the pi +/- psi' invariant mass distribution near 4.43 GeV in B-->K pi +/- psi' decays. A fit using a Breit-Wigner resonance shape yields a peak mass and width of M=4433+/-4(stat)+/-2(syst) MeV and Gamma=45-13+18(stat)-13+30(syst) MeV. The product branching fraction is determined to be B(B 0-->K -/+Z+/-(4430)) x B(Z+/-(4430)-->pi+/-psi')=(4.1+/-1.0(stat)+/-1.4(syst)) x 10(-5), where Z+/-(4430) is used to denote the observed structure. The statistical significance of the observed peak is 6.5 sigma. These results are obtained from a 605 fb(-1) data sample that contains 657 x 10(6) BB pairs collected near the Upsilon(4S) resonance with the Belle detector at the KEKB asymmetric energy e+ e- collider.

Observation of the psi(4415)-->DD2*(2460) decay using initial-state radiation.

We report measurements of the exclusive cross section for e(+)e(-)-->D(0)D(-)pi(+) over the center-of-mass energy range 4.0 GeV to 5.0 GeV with initial-state radiation and the first observation of the decay psi(4415)-->D(0)D(-)pi(+). From a study of the resonant substructure in psi(4415) decay we conclude that the psi(4415)-->D(0)D(-)pi(+) decay is dominated by psi(4415)-->DD(2)(*)(2460). We obtain B(psi(4415)-->D(0)D(-)pi(nonresonant)(+))/B(psi(4415)-->DD(2)(*)(2460)-->D(0)D(-)pi(+))<0.22 at 90% C.L. The analysis is based on a data sample collected with the Belle detector with an integrated luminosity of 673 fb(-1).

Observation of a new DsJ meson in B+-->D0D0K+ decays.

We report the observation of a new DsJ meson produced in B+-->D0DsJ-->D0D0K+. This state has a mass of M=2708+/-9(-10)(+11) MeV/c2, a width Gamma=108+/-23(-31)(+36) MeV/c2 and a 1- spin-parity. The statistical significance of this observation is 8.4 sigma. The results are based on an analysis of 449 x 10(6) BB events collected at the Upsilon(4S) resonance with the Belle detector at the KEKB asymmetric-energy e+e- collider.

Measurement of the e+e- -->pi+pi- J/psi cross section via initial-state radiation at Belle.

The cross section for e(+)e(-)-->pi(+)pi(-)J/psi between 3.8 and 5.5 GeV/c(2) is measured using a 548 fb(-1) data sample collected on or near the Upsilon(4S) resonance with the Belle detector at KEKB. A peak near 4.25 GeV/c(2), corresponding to the so called Y(4260), is observed. In addition, there is another cluster of events at around 4.05 GeV/c(2). A fit using two interfering Breit-Wigner shapes describes the data better than one that uses only the Y(4260), especially for the lower-mass side of the 4.25 GeV enhancement.

Measurement of D0-D0 mixing parameters in D0 --> Ks pi+ pi- decays.

We report a measurement of D0-D(0) mixing parameters in D(0) --> K(s)(0) 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 +/- 0.29(-0.07-0.14)(+0.09+0.10))% and y = (0.33+/-0.24(-0.12-0.08)(+0.08+0.06))%, where the errors are statistical, experimental systematic, and systematic due to the Dalitz decay model, respectively. Allowing for CP violation, we obtain the CP-violating parameters |q / p| = 0.86(-0.29-0.03)(+0.30+0.06) +/- 0.08 and arg(q/p) = (-14(-18-3-4)(+16+5+2)) degrees .

Observation of two resonant structures in e+ e- -->pi+ pi- psi(2S) via initial-state radiation at Belle.

The cross section for e+ e- --> pi+ pi- psi(2S) between threshold and sqrt[s]=5.5 GeV is measured using 673 fb(-1) of data on and off the Upsilon(4S) resonance collected with the Belle detector at KEKB. Two resonant structures are observed in the pi+ pi- psi(2S) invariant-mass distribution, one at 4361 +/- 9 +/- 9 MeV/c2 with a width of 74 +/- 15 +/- 10 MeV/c2, and another at 4664 +/- 11 +/- 5 MeV/c2 with a width of 48 +/- 15 +/- 3 MeV/c2, if the mass spectrum is parametrized with the coherent sum of two Breit-Wigner functions. These values do not match those of any of the known charmonium states.

Evidence for D0-D0 mixing.

We observe evidence for D(0)-D(0) mixing by measuring the difference in the apparent lifetime when a D(0) meson decays to the CP eigenstates K(+)K(-) and pi(+)pi(-) and when it decays to the final state K(-)pi(+). We find the relative difference of the lifetimes y(CP) to be [1.31+/-0.32(stat)+/-0.25(syst)]%, 3.2 standard deviations from zero. We also search for a CP asymmetry between D(0) and D(0) decays; no evidence for CP violation is found. These results are based on 540 fb(-1) of data recorded by the Belle detector at the KEKB e(+)e(-) collider.

Evidence for CP violation in B0-->D+D- decays.

We report measurements of the branching fraction and CP violation parameters in B(0)-->D+ D- decays. The results are based on a data sample that contains 535 x 10(6) BB pairs collected at the Upsilon(4S) resonance, with the Belle detector at the KEKB asymmetric-energy e+e- collider. We obtain [1.97+/-0.20(stat) +/- 0.20(syst)] x 10(-4) for the branching fraction of B0-->D+D-. The measured values of the CP violation parameters are S=-1.13+/-0.37+/-0.09, A=0.91+/-0.23+/-0.06, where the first error is statistical and the second is systematic. We find evidence of CP violation in B0-->D+D- at the 4.1sigma confidence level. While the value of S is consistent with expectations from other measurements, the value of the parameter A favors large direct CP violation at the 3.2sigma confidence level, in contradiction to standard model expectations.