arXiv subjects

B. Bhuyan

Publications and source records attributed to B. Bhuyan.

At least 397 records · Page 22Linked to original sources

arXiv2014

Measurement of the branching fraction of $B^+ \to τ^+ ν_τ$ decays with the semileptonic tagging method and the full Belle data sample

We report a measurement of the branching fraction of $B^+ \to τ^+ ν_τ$ decays using a data sample of $772 \times 10^6 B \bar{B}$ pairs, collected at the $Υ(4S)$ resonance with the Belle detector at the KEKB asymmetric-energy $e^+e^-$ collider. We reconstruct the accompanying $B$ meson in a semileptonic decay and detect the $B^+ \to τ^+ ν_τ$ candidate in the recoiling event. We obtain a branching fraction of ${\cal B}(B^+ \to τ^+ ν_τ) = [1.25 \pm 0.28 ({\rm stat.}) \pm 0.27({\rm syst.})] \times 10^{-4}$. This result is in good agreement with previous measurements and the expectation from calculations based on the Standard Model.

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arXiv2014

Observation of $e^+e^- \to π^+ π^- π^0 χ_{bJ}$ and search for $X_b \to ωΥ(1S)$ at $\sqrt{s}\sim 10.867$ GeV

The $e^+e^- \to π^+ π^- π^0 χ_{bJ}$ ($J=0,~1,~2$) processes are studied using a 118~fb$^{-1}$ data sample collected at a center-of-mass energy of 10.867 GeV, in the $Υ(10860)$ energy range, with the Belle detector. The $π^+ π^- π^0 χ_{b1}$, $π^+π^-π^0χ_{b2}$, $ωχ_{b1}$ signals and the evidence of $ωχ_{b2}$ are observed for the first time and the cross sections are measured. No significant $π^+π^-π^0χ_{b0}$ or $ωχ_{b0}$ signal is observed and 90\% confidence level upper limits on the cross sections for these two processes are obtained. In the $π^+π^-π^0$ invariant mass spectrum, significant non-$ω$ signals are also observed. We search for the $X(3872)$-like state with a hidden $b\bar{b}$ component (named $X_b$) decaying into $ωΥ(1S)$; no significant signal is observed with a mass between $10.55$ and $10.65$ GeV/$c^2$.

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arXiv2014

Observation of the decay $B^0 \to η' K^*(892)^0$

We report a search for charmless hadronic decays of neutral $B$ mesons to $η' K^{*}(892)^{0}$. The results are based on a 711fb$^{-1}$ data sample that contains $772\times 10^6 B\overline{B}$ pairs, collected at the $Υ(4S)$ resonance with the Belle detector at the KEKB asymmetric energy $e^+e^-$ collider. We observe the decay for the first time with a significance of 5.0 standard deviations and obtain its branching fraction ${\cal B}[B^0\toη' K^{*}(892)^{0}]=[2.6\pm0.7{\rm (stat)}\pm0.2{\rm (syst)}]\times 10^{-6}$. We also measure the $CP$ violating asymmetry as ${\cal A}_{CP}[B^0\toη' K^{*}(892)^{0}]=-0.22\pm0.29{\rm (stat)}\pm0.07{\rm syst}$.

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arXiv2014

Measurement of the Branching Fraction Br(Lambda_c+ -> p K- pi+)

We present the first model-independent measurement of the absolute branching fraction of the Lambda_c+ -> p K- pi+ decay using a data sample of 978 fb^-1 collected with the Belle detector at the KEKB asymmetric-energy e+e- collider. The number of Lambda_c+ baryons is determined by reconstructing the recoiling D(*)- anti-p pi+ system in events of the type e+e- -> D(*)- anti-p pi+ Lambda_c+. The branching fraction is measured to be Br(Lambda_c+ -> p K- pi+) = (6.84 +- 0.24^{+0.21}_{-0.27})%, where the first and second uncertainties are statistical and systematic, respectively.

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arXiv2014

Measurement of Branching Fractions and CP Asymmetries in B -> wK Decays and First Evidence of CP Violation in B0 -> wKS0

We present a measurement of the branching fractions and charge-parity-(CP-) violating parameters in B -> omega K decays. The results are obtained from the final data sample containing 772 x 10^(6) BBbar pairs collected at the Y(4S) resonance with the Belle detector at the KEKB asymmetric-energy e+e- collider. We obtain the branching fractions B(B0 -> omega K0) = (4.5 +/- 0.4 (stat) +/- 0.3 (syst)) x 10^(-6), B(B- -> omega K-) = (6.8 +/- 0.4 (stat) +/- 0.4 (syst)) x 10^(-6), which are in agreement with their respective current world averages. For the CP violating parameters, we obtain A(B0 -> omega KS) = -0.36 +/- 0.19 (stat) +/- 0.05 (syst), S(B0 -> omega KS) = +0.91 +/- 0.32 (stat) +/- 0.05 (syst), A(B- -> omega K-) = -0.03 +/- 0.04 (stat) +/- 0.01 syst), where A and S represent the direct and mixing-induced CP asymmetry, respectively. We find no evidence of CP violation in the decay channel B-->omega K-; however, we obtain the first evidence of CP violation in the B0 -> omega KS decay channel at the level of 3.1 standard deviations.

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arXiv2014

Measurements of the masses and widths of the $Σ_{c}(2455)^{0/++}$ and $Σ_{c}(2520)^{0/++}$ baryons

We present measurements of the masses and decay widths of the baryonic states $Σ_{c}(2455)^{0/++}$ and $Σ_{c}(2520)^{0/++}$ using a data sample corresponding to an integrated luminosity of 711 fb$^{-1}$ collected with the Belle detector at the KEKB $e^{+}e^{-}$ asymmetric-energy collider operating at the $Υ(4S)$ resonance. We report the mass differences with respect to the $Λ_{c}^{+}$ baryon $M(Σ_{c}(2455)^{0})-M(Λ_{c}^{+}) = 167.29\pm0.01\pm0.02$ MeV/$c^{2}$, $M(Σ_{c}(2455)^{++})-M(Λ_{c}^{+}) = 167.51\pm0.01\pm0.02$ MeV/$c^{2}$, $M(Σ_{c}(2520)^{0})-M(Λ_{c}^{+}) = 231.98\pm0.11\pm0.04$ MeV/$c^{2}$, $M(Σ_{c}(2520)^{++})-M(Λ_{c}^{+}) = 231.99\pm0.10\pm0.02$ MeV/$c^{2}$, and the decay widths $Γ(Σ_{c}(2455)^{0}) = 1.76\pm0.04^{+0.09}_{-0.21}$ MeV/$c^{2}$, $Γ(Σ_{c}(2455)^{++}) = 1.84\pm0.04^{+0.07}_{-0.20}$ MeV/$c^{2}$, $Γ(Σ_{c}(2520)^{0}) = 15.41\pm0.41^{+0.20}_{-0.32}$ MeV/$c^{2}$, $Γ(Σ_{c}(2520)^{++}) = 14.77\pm0.25^{+0.18}_{-0.30}$ MeV/$c^{2}$, where the first uncertainties are statistical and the second are systematic. The isospin mass splittings are measured to be $M(Σ_{c}(2455)^{++})-M(Σ_{c}(2455)^{0})=0.22\pm0.01\pm0.01$ MeV/$c^{2}$ and $M(Σ_{c}(2520)^{++})-M(Σ_{c}(2520)^{0})=0.01\pm0.15\pm0.03$ MeV/$c^{2}$. These results are the most precise to date.

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arXiv2014

Study of B^0 -> rho^0 rho^0 decays, implications for the CKM angle phi_2 and search for other B^0 decay modes with a four-pion final state

We present a study of the branching fraction of the decay B^0->rho0rho0 and the fraction of longitudinally polarized rho0 mesons in this decay. The results are obtained from the final data sample containing 772 million BBbar pairs collected at the Y(4S) resonance with the Belle detector at the KEKB asymmetric-energy e+e- collider. We find 166 +- 59 B^0 -> rho0 rho0 events (including systematic uncertainties), corresponding to a branching fraction of B(B^0->rho0rho0) = (1.02 +- 0.30 (stat) +- 0.15 (syst)) x 10^{-6} with a significance of 3.4 standard deviations and a longitudinal polarization fraction fL = 0.21^{+0.18}_{-0.22} (stat) +- 0.15 (syst). We use the longitudinal polarization fraction to determine the Cabibbo-Kobayashi-Maskawa matrix angle phi_2 = (84.9 +- 13.5) degrees through an isospin analysis in the B->rhorho system. We furthermore find 149 +- 49 B^0->f0rho0 events, corresponding to B(B^0->f0rho0) x B(f0->pi+pi-) = (0.78 +- 0.22 (stat) +- 0.11 (syst)) x 10^{-6}, with a significance of 3.1 standard deviations. We find no other significant contribution with the same final state, and set upper limits at 90% confidence level on the (product) branching fractions, B(B^0->pi+pi-pi+pi-)<11.2 x 10^{-6}, B(B^0->rho0pi+pi-)<12.0 x 10^{-6}, B(B^0->f0pi+pi-) x B(f0->pi+pi-) <3.0 x 10^{-6} and B(B^0->f0f0) x B(f0->pi+pi-)^{2} < 0.2 x 10^{-6}.

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arXiv2014

Measurement of ${D^{0}}$-${\overline{D}{}^{0}}$ Mixing and Search for Indirect $CP$ Violation Using ${D^0\to K_S^0π^+π^-}$ Decays

We report a measurement of ${D^{0}}$-${\overline{D}{}^{0}}$ mixing parameters and a search for indirect $CP$ violation through a time-dependent amplitude analysis of ${D^0\to K_S^0π^+π^-}$ decays. The results are based on 921~fb$^{-1}$ of data accumulated with the Belle detector at the KEKB asymmetric-energy $e^+e^-$ collider. Assuming $CP$ conservation, we measure the mixing parameters $x=(0.56\pm0.19^{+0.03}_{-0.09}{^{+0.06}_{-0.09}})\%$ and $y=(0.30\pm0.15^{+0.04}_{-0.05}{^{+0.03}_{-0.06})}\%$, where the errors are statistical, experimental systematic, and systematic due to the amplitude model, respectively. With $CP$ violation allowed, the parameters $|q/p|=0.90^{+0.16}_{-0.15}{^{+0.05}_{-0.04}}{^{+0.06}_{-0.05}}$ and $\arg(q/p)=(-6\pm11{\pm3}{^{+3}_{-4}})^{\circ}$ are found to be consistent with conservation of $CP$ symmetry in mixing and in the interference between mixing and decay, respectively.

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arXiv2014

Observation of $D^0-\bar{D}^0$ Mixing in $e^+e^-$ Collisions

We observe $D^0-\bar{D}^0$ mixing in the decay $D^0\rightarrow K^+π^-$ using a data sample of integrated luminosity 976 fb$^{-1}$ collected with the Belle detector at the KEKB $e^+e^-$ asymmetric-energy collider. We measure the mixing parameters ${x'}^2 = (0.09\pm0.22)\times 10^{-3}$ and $y' = (4.6\pm3.4)\times 10^{-3}$ and the ratio of doubly Cabibbo-suppressed to Cabibbo-favored decay rates $R_D = (3.53\pm0.13)\times 10^{-3}$, where the uncertainties are statistical and systematic combined. Our measurement excludes the no-mixing hypothesis at the 5.1 standard deviation level.

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arXiv2014

Evidence for the decay B0 --> omega omega and search for B0 --> omega phi

We describe searches for B meson decays to the charmless vector-vector final states omega omega and omega phi with 471 x 10^6 B Bbar pairs produced in e+ e- annihilation at sqrt(s) = 10.58 GeV using the BABAR detector at the PEP-II collider at the SLAC National Accelerator Laboratory. We measure the branching fraction B(B0 --> omega omega) = (1.2 +- 0.3 +0.3-0.2) x 10^-6, where the first uncertainty is statistical and the second is systematic, corresponding to a significance of 4.4 standard deviations. We also determine the upper limit B(B0 --> omega phi) < 0.7 x 10^-6 at 90% confidence level. These measurements provide the first evidence for the decay B0 --> omega omega, and an improvement of the upper limit for the decay B0 --> omega phi.

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arXiv2014

Measurement of branching fractions for B \to J/ψηK decays and search for a narrow resonance in the J/ψηfinal state

We report an observation of the $B^{\pm} \to J/ψηK^{\pm}$ and $B^0 \to J/ψηK^0_S$ decays using 772$\times 10^{6}$ $B\bar{B}$ pairs collected at the $Υ(4S)$ resonance with the Belle detector at the KEKB asymmetric-energy $e^+e^-$ collider. We obtain the branching fractions ${\cal B}(B^{\pm}\rightarrow J/ψηK^{\pm})=(1.27\pm 0.11{\rm (stat.)\pm 0.11{\rm (syst.)})}\times10^{-4}$ and ${\cal B}(B^0\to J/ψηK^0_S)=(5.22 \pm 0.78 {\rm(stat.)} \pm 0.49{\rm(syst.)})\times10^{-5}$. We search for a new narrow charmonium(-like) state $X$ in the $J/ψη$ mass spectrum and find no significant excess. We set upper limits on the product of branching fractions, ${\cal B}(B^\pm \to XK^\pm){\cal B}(X \to J/ψη)$, at 3872 MeV$/c^2$ where a $C$-odd partner of X(3872) may exist, at $ψ(4040)$ and $ψ(4160)$ assuming their known mass and width, and over a range from 3.8 to 4.8 GeV$/c^2$. % at a 5 MeV$/c^2$ step. The obtained upper limits at 90% confidence level for $X^{C{\rm -odd}}(3872)$, $ψ(4040)$ and $ψ(4160)$ are 3.8$\times 10^{-6}$, 15.5$\times 10^{-6}$ and 7.4$\times 10^{-6}$, respectively.

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arXiv2014

Measurements of Branching Fractions of $τ$ Lepton Decays with one or more $K^{0}_{S}$

We report measurements of branching fractions of $τ$ lepton decays to final states with a $K^{0}_{S}$ meson using a 669 fb$^{-1}$ data sample accumulated with the Belle detector at the KEKB asymmetric-energy $e^{+}e^{-}$ collider. The inclusive branching fraction is measured to be $\mathcal{B}(τ^{-} \to K^{0}_{S}\ X^{-} ν_τ)=(9.15 \pm 0.01 \pm 0.15) \times 10^{-3}$, where $X^{-}$ can be anything; the exclusive branching fractions are $\mathcal{B}(τ^{-} \to π^{-} K^{0}_{S} ν_τ) = (4.16 \pm 0.01 \pm 0.08) \times 10^{-3}$, $\mathcal{B}(τ^{-} \to K^{-} K^{0}_{S} ν_τ) = (7.40 \pm 0.07 \pm 0.27) \times 10^{-4}$, $\mathcal{B}(τ^{-} \to π^{-} K^{0}_{S} π^{0} ν_τ) = (1.93 \pm 0.02 \pm 0.07) \times 10^{-3}$, $\mathcal{B}(τ^{-} \to K^{-} K^{0}_{S} π^{0} ν_τ) = (7.48 \pm 0.10 \pm 0.37)\times 10^{-4}$, $\mathcal{B}(τ^{-} \to π^{-} K^{0}_{S} K^{0}_{S} ν_τ) = (2.33 \pm 0.03 \pm 0.09) \times 10^{-4}$, $\mathcal{B}(τ^{-} \to π^{-} K^{0}_{S} K^{0}_{S} π^{0} ν_τ) = (2.00 \pm 0.22 \pm 0.20) \times 10^{-5}$, where the first uncertainty is statistical and the second is systematic. For each mode, the accuracy is improved over that of pre-$B$-factory measurements by a factor ranging from five to ten. In $τ^{-} \to π^{-} K^0_S K^0_S π^{0} ν_τ$ decays, clear signals for the intermediate states $τ^{-} \to π^- f_{1}(1285)ν_τ$ and $τ^{-} \to K^{*-}K^{0}_{S} π^{0} ν_τ$ are observed.

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arXiv2014

Search for doubly charmed baryons and study of charmed strange baryons at Belle

We report results of a study of doubly charmed baryons and charmed strange baryons. The analysis is performed using a 980 fb^-1 data sample collected with the Belle detector at the KEKB asymmetric-energy e^+e^- collider. We search for doubly charmed baryons Xi_cc^+(+) with the Lambda_c^+K^-pi^+(pi^+) and Xi_c^0pi^+(pi^+) final states. No significant signal is observed. We also search for two excited charmed strange baryons, Xi_c(3055)^+ and Xi_c(3123)^+ with the Sigma_c^++(2455)K^- and Sigma_c^++(2520)K^- final states. The Xi_c(3055)^+ signal is observed with a significance of 6.6 standard deviations including systematic uncertainty, while no signature of the Xi_c(3123)^+ is seen. We also study properties of the Xi_c(2645)^+ and measure a width of 2.6 +- 0.2 (stat) +- 0.4 (syst) MeV/c^2, which is the first significant determination.

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arXiv2013

Search for B0 to p Lambdabar pi- gamma at Belle

We search for the charmless B^0 decay with final state particles p Lambdabar pi^- gamma using the full data sample that contains 772 * 10^6 B Bar pairs collected at the Upsilon(4S) resonance with the Belle detector at the KEKB asymmetric-energy e^+ e^- collider. This decay is predicted to proceed predominantly via the b to s gamma radiative penguin process with a high energy photon. No significant signal is found. We set an upper limit of 6.5 * 10^-7 for the branching fraction of B^0 to p Lambdabar pi^- gamma at the 90% confidence level.

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arXiv2013

High-statistics study of K^0_S pair production in two-photon collisions

We report a high-statistics measurement of the differential cross section of the process gamma gamma --> K^0_S K^0_S in the range 1.05 GeV <= W <= 4.00 GeV, where W is the center-of-mass energy of the colliding photons, using 972 fb^{-1} of data collected with the Belle detector at the KEKB asymmetric-energy e^+ e^- collider operated at and near the Upsilon-resonance region. The differential cross section is fitted by parameterized S-, D_0-, D_2-, G_0- and G_2-wave amplitudes. In the D_2 wave, the f_2(1270), a_2(1320) and f_2'(1525) are dominant and a resonance, the f_2(2200), is also present. The f_0(1710) and possibly the f_0(2500) are seen in the S wave. The mass, total width and product of the two-photon partial decay width and decay branching fraction to the K bar{K} state Gamma_{gamma gamma}B(K bar{K}) are extracted for the f_2'(1525), f_0(1710), f_2(2200) and f_0(2500). The destructive interference between the f_2(1270) and a_2(1320) is confirmed by measuring their relative phase. The parameters of the charmonium states chi_{c0} and chi_{c2} are updated. Possible contributions from the chi_{c0}(2P) and chi_{c2}(2P) states are discussed. A new upper limit for the branching fraction of the P- and CP-violating decay channel eta_c --> K^0_S K^0_S is reported. The detailed behavior of the cross section is updated and compared with QCD-based calculations.

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arXiv2013

Measurement of the CP Violation Parameters in B0 -> pi+ pi- Decays

We present a measurement of the time-dependent charge-parity (CP) violation parameters in B0 -> pi+ pi- decays. The results are obtained from the final data sample containing 772 million BBbar pairs collected at the Upsilon(4S) resonance with the Belle detector at the KEKB asymmetric-energy e+e- collider. We obtain the CP violation parameters Acp = +0.33 +/- 0.06 (stat) +/- 0.03 (syst) and Scp = -0.64 +/- 0.08 (stat) +/- 0.03 (syst), where Acp and Scp represent the direct and mixing-induced CP asymmetry, respectively. Using an isospin analysis including results from other Belle measurements, we find 23.8 < phi2 < 66.8 degrees is disfavored at the 1 sigma level, where phi2 is one of the three interior angles of the CKM unitarity triangle related to B_{u,d} decays.

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arXiv2013

Measurement of the Decays $B^0_s\to J/ψ\,ϕ(1020)$, $B^0_{s}\to J/ψ\,f'_2(1525)$ and $B^0_s\to J/ψ\,K^+K^-$ at Belle

We report a measurement of the branching fraction of the decay $B^0_s\to J/ψ\,ϕ(1020)$, evidence and a branching fraction measurement for $B^0_s\to J/ψ\,f'_2(1525)$, and the determination of the total $B^0_s\to J/ψ\,K^+K^-$ branching fraction, including the resonant and non-resonant contributions to the $K^+K^-$ channel. We also determine the $S$-wave contribution within the $ϕ(1020)$ mass region. The absolute branching fractions are $\mathcal{B}[B^0_s\to J/ψ\,ϕ(1020)]=(1.25 \pm 0.07\left(\mathrm{stat}\right)\pm 0.08\left(\mathrm{syst}\right)\pm 0.22\left(f_s\right))\times 10^{-3}$, $\mathcal{B}[B^0_s\to J/ψ\,f'_2(1525)]=(0.26\pm 0.06\left(\mathrm{stat}\right)\pm 0.02\left(\mathrm{syst}\right) \pm 0.05\left(f_s\right))\times 10^{-3}$ and $\mathcal{B}[B^0_s\to J/ψ\,K^+K^-] = (1.01\pm 0.09\left(\mathrm{stat}\right) \pm 0.10\left(\mathrm{syst}\right)\pm 0.18\left(f_s\right))\times 10^{-3}$, where the last systematic error is due to the branching fraction of $b\bar{b}\to B^{(*)}_s B^{(*)}_s$. The branching fraction ratio is found to be $\mathcal{B}[B^0_s\to J/ψ\,f'_2(1525)]/\mathcal{B}[B^0_s\to J/ψ\,ϕ(1020)]=(21.5\pm 4.9\left(\mathrm{stat}\right) \pm2.6\left(\mathrm{syst}\right))%$. All results are based on a 121.4 fb$^{-1}$ data sample collected at the $Υ(5S)$ resonance by the Belle experiment at the KEKB asymmetric-energy $e^+e^-$ collider.

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arXiv2013

Measurement of the $τ$-lepton lifetime at Belle

The lifetime of the $τ$-lepton is measured using the process $e^+e^-\rightarrowτ^+τ^-$, where both $τ$-leptons decay to $3πν_τ$. The result for the mean lifetime, based on $711\,\mathrm{fb}^{-1}$ of data collected with the Belle detector at the $Υ(4S)$ resonance and $60\,\mathrm{MeV}$ below, is $τ= (290.17 \pm 0.53(\mathrm{stat.}) \pm 0.33(\mathrm{syst.}))\cdot10^{-15}\,\mathrm{s}$. The first measurement of the lifetime difference between $τ^+$ and $τ^-$ is performed. The upper limit on the relative lifetime difference between positive and negative $τ$-leptons is $|Δτ| / τ< 7.0 \times 10^{-3}$ at 90% CL.

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