arXiv subjects

L. E. Piilonen

Publications and source records attributed to L. E. Piilonen.

At least 37 records · Page 2Linked to original sources

arXiv2013

Search for the process $e^+e^-\to J/ψ+ X(1835)$ at $\sqrt{s}\approx10.6$GeV

We report the results of a search for the $X(1835)$ state in the process $e^+e^-\to J/ψ+X(1835)$ using a data sample of 672 fb$^{-1}$ collected with the Belle detector at and near the $Υ(4S)$ resonance at the KEKB asymmetric-energy $e^+e^-$ collider. No significant evidence is found for this process, and an upper limit is set on its cross section times the branching fraction: $σ_{\rm Born}(e^+e^- \to J/ψX(1835)) \cdot$ {${\cal B}(X(1835)\to \ge 3$ charged tracks)} $< 1.3 \ {\rm fb}$ at 90% confidence level.

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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

Precise measurement of the branching fractions for Bs->Ds()+ Ds()- and first measurement of the Ds+ Ds- polarization using e+e- collisions

We have made a precise measurement of the absolute branching fractions of Bs->Ds(*)+ Ds(*)- decays using 121.4 fb-1 of data recorded by the Belle experiment running on the Upsilon(5S) resonance. The results are B(Bs0->Ds+ Ds-) = (0.58 +0.11 -0.09 +-0.13)%, B(Bs0->Ds*+- Ds-+) = (1.8 +-0.2 +-0.4)%, and B(Bs0->Ds*+ Ds*-) = (2.0 +-0.3 +-0.5)%; the sum is B(Bs0->Ds(*)+ Ds(*)- = (4.3 +-0.4 +-1.0)%. Assuming Bs->Ds(*)+ Ds(*)- saturates decays to CP-even final states, the branching fraction constrains the ratio Delta(Gamma_s)/cos(phi_s), where Delta(Gamma_s) is the difference in widths between the two Bs0-Bs0bar mass eigenstates, and phi_s is the CP-violating phase in Bs0-Bs0bar mixing. For phi_s=0 we obtain Delta(Gamma_s)/Gamma_s = 0.090 +-0.009 (stat.) +-0.023 (syst.), where Gamma_s is the mean decay width. We also measure for the first time the longitudinal polarization fraction of Bs->Ds*+ Ds*-; the result is 0.12 +0.30 -0.28 +0.04 -0.05.

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arXiv2013

Measurements of Branching Fractions and Direct CP Asymmetries for B -> K pi, B->pi pi and B->to KK Decays

We report measurements of the branching fractions and direct CP asymmetries (A_{CP}) for B->K pi, pi pi and KK decays (but not pi^0 pi^0) based on the final data sample of 772x10^6 B B-bar pairs collected at the Upsilon(4S) resonance with the Belle detector at the KEKB asymmetric-energy e^+ e^- collider. We set a 90% confidence-level upper limit for K^+- K^-+ at 2.0x10^{-7}; all other decays are observed with branching fractions ranging from 10^{-6} to 10^{-5}. In the $B^0/B^0-bar -> K^+-π^-+ mode, we confirm Belle's previously reported large A_{CP} with a value of -0.069 +- 0.014 +- 0.007 and a significance of 4.4 sigma. For all other flavor-specific modes, we find A_{CP} values consistent with zero, including A_{CP}(K^+- π^0) = +0.043 +- 0.024 +- 0.007 with 1.8 sigma significance. The difference of CP asymmetry between B^+- -> K^+- pi^0 and B^0/B^0-bar -> K^+-π^-+ is found to be Delta A_{K pi} equiv A_{CP} (K^+ pi^0) - A_{CP}(K^+ pi^-) = +0.112 +- 0.027 +- 0.007 with 4.0 sigma significance. We also calculate the ratios of partial widths for the B-> K pi decays. Using our results, we test the validity of the sum rule A_{CP}(K^+ pi^-) + A_{CP}(K^0π^+) x Gamma(K^0π^+)/Gamma(K^+ pi^-)} - A_{CP}(K^+ pi^0)x 2Gamma(K^+ pi^0)/Gamma(K^+ pi^-) - A_{CP}(K^0 pi^0)x 2Gamma(K^0 pi^0)/Gamma(K^+ pi^-) = 0 and obtain a sum of -0.270 +- 0.132 +- 0.060 with 1.9 sigma significance.

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arXiv2013

Search for CP Violation in the Decay $D^+\rightarrow K^0_S K^+$

We search for CP violation in the decay $D^+\rightarrow K^0_S K^+$ using a data sample with an integrated luminosity of 977 fb$^{-1}$ collected with the Belle detector at the KEKB $e^+e^-$ asymmetric-energy collider. No CP violation has been observed and the CP asymmetry in $D^+\rightarrow K^0_S K^+$ decay is measured to be $(-0.25\pm0.28\pm0.14)%$, which is the most sensitive measurement to date. After subtracting CP violation due to $K^0-\bar{K}^0$ mixing, the CP asymmetry in $D^+\rightarrow\bar{K}^0 K^+$ decay is found to be $(+0.08\pm0.28\pm0.14)%$.

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arXiv2013

Measurement of Branching Fraction and First Evidence of CP Violation in B0 --> a1+-(1260) pi-+ Decays

We present a measurement of the branching fraction and time-dependent CP violation parameters in B0 --> a_1^+-(1260) pi^-+ decays. The results are obtained from the final data sample containing 772x10^6 BBbar pairs collected at the Upsilon(4S) resonance with the Belle detector at the KEKB asymmetric-energy e^+e^- collider. We also measure an upper limit on the product branching fraction for a possible decay with the same final state B0 --> a_2^+-(1320) pi^-+. In a time-dependent measurement to extract CP asymmetries, we find evidence of mixing-induced CP violation in B0 --> a_1^+-(1260) pi^-+ decays with a 3.1 sigma significance and the rate where the a_1^+-(1260) does not contain the spectator quark is found to dominate the rate where it does at the 4.1 sigma level. However, there is no evidence for either time and flavor integrated direct CP violation or flavor-dependent direct CP violation.

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arXiv2013

Search for Lepton-Flavor-Violating and Lepton-Number-Violating tau to lhh' Decay Modes

We search for lepton-flavor-violating and lepton-number-violating tau decays into a lepton (l = electron or muon) and two charged mesons (h, h' = pion or Kaon) using 854 fb^{-1} of data collected with the Belle detector at the KEKB asymmetric-energy e^+e^- collider. We obtain 90% confidence level upper limits on the tau to lhh' branching fractions in the range (2.0-8.4)*10^{-8}. These results improve upon our previously published upper limits by factors of about 1.8 on average.

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arXiv2012

Observation of ψ(4040) and ψ(4160) decay into ηJ/ψ

The cross section for e^+e^- \to ηJ/ψbetween \sqrt{s}=3.8 GeV/c^2 and 5.3 GeV/c^2 is measured via initial state radiation using 980 fb^{-1} of data on and around the Υ(nS)(n=1,2,3,4,5) resonances collected with the Belle detector at KEKB. Two resonant structures at the ψ(4040) and ψ(4160) are observed in the ηJ/ψinvariant mass distribution. Fitting the mass spectrum with the coherent sum of two Breit-Wigner functions, one obtains BR(ψ(4040)\toηJ/ψ)\cdotΓ_{ee}^{ψ(4040)} = (4.8\pm0.9\pm1.4) eV and BR(ψ(4160)\toηJ/ψ)\cdotΓ_{ee}^{ψ(4160)} = (4.0\pm0.8\pm1.4) eV for one solution and BR(ψ(4040)\toηJ/ψ)\cdotΓ_{ee}^{ψ(4040)} = (11.2\pm1.3\pm1.9) eV and BR(ψ(4160)\toηJ/ψ)\cdotΓ_{ee}^{ψ(4160)} = (13.8\pm1.3\pm2.0) eV for the other solution, where the first errors are statistical and the second are systematic. This is the first measurement of this hadronic transition mode of these two states, and the partial widths to ηJ/ψare found to be about 1 MeV. There is no evidence for the Y(4260), Y(4360), ψ(4415), or Y(4660) in the ηJ/ψfinal state, and upper limits of their production rates in e^+e^- annihilation are determined.

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arXiv2012

Study of the Hadronic Transitions $Υ$(2S)$\rightarrow (η,π^0)Υ$(1S) at Belle

We study the rare hadronic transitions $Υ(2S)\rightarrow Υ(1S)η$ and $Υ(2S)\rightarrow Υ(1S)π^0$ using a sample of 158 $\times 10^6$ $Υ(2S)$ decays collected with the Belle detector at the KEKB asymmetric-energy $e^+ e^-$ collider. We observe the $η$ meson decay to $γγ$ and $π^+π^-π^0$ final states; the $Υ(1S)$ is reconstructed in the $μ^+μ^-$ and $e^+e^-$ decay modes. We measure the ratios of branching fractions (${\mathcal B}$) $\frac{{\mathcal B}(Υ(2S)\rightarrowΥ(1S)η)}{{\mathcal B}(Υ(2S)\rightarrowΥ(1S)π^+π^-)}$ = (1.99$\pm$0.14 (stat) $\pm$0.11 (syst)) $\times 10^{-3}$ and $\frac{{\mathcal B}(Υ(2S)\rightarrowΥ(1S)π^0)}{{\mathcal B}(Υ(2S)\rightarrowΥ(1S)π^+π^-)} < 2.3 \times 10^{-4}$ at the 90% confidence level (CL). Assuming the value ${\mathcal B}(Υ(2S) \rightarrow Υ(1S)π^-π^+)$ = (17.92$\pm$0.26)%, we obtain $ {\mathcal B}(Υ(2S)\rightarrowΥ(1S)η) = (3.57 \pm 0.25 ({\rm stat})\ \pm 0.21 ({\rm syst}))\times 10^{-4} $ and $ {\mathcal B}(Υ(2S)\rightarrowΥ(1S)π^0) < 4.1\times 10^{-5}\ ({\rm 90%\ CL}). $

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arXiv2012

First study of η_c, η(1760) and X(1835) production via η'π^+π^- final states in two-photon collisions

The invariant mass spectrum of the η' π^+ π^- final state produced in two-photon collisions is obtained using a 673 fb^{-1} data sample collected in the vicinity of the Υ(4S) resonance with the Belle detector at the KEKB asymmetric-energy e^+e^- collider. We observe a clear signal of the η_c and measure its mass and width to be M(η_c)=(2982.7 +- 1.8(stat) +- 2.2(syst) +- 0.3(model)) MeV/c^2 and Γ(η_c) = (37.8^{+5.8}_{-5.3}(stat) +- 2.8(syst) +- 1.4(model)) MeV/c^2. The third error is an uncertainty due to possible interference between the η_c and a non-resonant component. We also report the first evidence for η(1760) decay to η' π^+ π^-; we find two solutions for its parameters, depending on the inclusion or not of the X(1835), whose existence is of marginal significance in our data. From a fit to the mass spectrum using coherent X(1835) and η(1760) resonant amplitudes, we set a 90% confidence level upper limit on the product Γ_{γγ} \BR (η' π^+ π^-) for the X(1835).

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arXiv2012

Search for the decay $B^0\to DK^{*0}$ followed by $D\to K^-π^+$

We report a study of the decay $B^0\rightarrow D K^+π^-$ followed by $D\rightarrow K^-π^+$, where $D$ indicates $D^0$ or $\bar{D}^0$. We reconstruct the $D K^+π^-$ state in a phase space corresponding to $D K^{*}(892)^0$. The CP-violating angle $ϕ_3$ affects its decay rate via the interference between $b\rightarrow u$ and $b\rightarrow c$ transitions. The result is obtained from a 711 ${\rm fb}^{-1}$ data sample that contains 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 measure the ratio ${\cal R}_{DK^{*0}} \equiv Γ(B^0\rightarrow [K^-π^+]_DK^+π^-)/Γ(B^0\rightarrow [K^+π^-]_DK^+π^-)$ to be $(4.1 ^{+ 5.6 + 2.8}_{- 5.0 - 1.8}) \times 10^{-2}$, and set an upper limit of ${\cal R}_{DK^{*0}} < 0.16$ at the 95% confidence level.

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arXiv2011

Study of B^{+-} -> K^{+-}(K_S K pi)^0 Decay and Determination of eta_c and eta_c(2S) Parameters

We report the results of a study of $B^{\pm}\to K^{\pm}η_c$ and $B^{\pm}\to K^{\pm}η_c(2S)$ decays followed by $η_c$ and $η_c(2S)$ decays to $(K_SKπ)^0$. The results are obtained from a data sample containing 535 million $B\bar{B}$-meson pairs collected by the Belle experiment at the KEKB $e^+e^-$ collider. We measure the products of the branching fractions ${\mathcal B}(B^{\pm}\to K^{\pm}η_c){\mathcal B}(η_c\to K_S K^{\pm}π^{\mp})=(26.7\pm 1.4(stat)^{+2.9}_{-2.6}(syst)\pm 4.9(model))\times 10^{-6}$ and ${\mathcal B}(B^{\pm}\to K^{\pm}η_c(2S)){\mathcal B}(η_c(2S)\to K_S K^{\pm}π^{\mp})=(3.4^{+2.2}_{-1.5}(stat+model)^{+0.5}_{-0.4} syst))\times 10^{-6}$. Interference with the non-resonant component leads to significant model uncertainty in the measurement of these product branching fractions. Our analysis accounts for this interference and allows the model uncertainty to be reduced. We also obtain the following charmonia masses and widths: $M(η_c)=(2985.4\pm 1.5(stat)^{+0.5}_{-2.0}(syst))$ MeV/$c^2$, $Γ(η_c)=(35.1\pm 3.1(stat)^{+1.0}_{-1.6}(syst))$ MeV/$c^2$, $M(η_c(2S))=(3636.1^{+3.9}_{-4.2}(stat+model)^{+0.7}_{-2.0}(syst))$ MeV/$c^2$, $Γ(η_c(2S))=(6.6^{+8.4}_{-5.1}(stat+model)^{+2.6}_{-0.9}(syst))$ MeV/$c^2$.

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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.

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arXiv2011

Search for CP violation in tau -> K^0_S pi nu_tau decays at Belle

We report on a search for CP violation in tau -> K^0_S pi nu_tau decays using a data sample of 699 fb^{-1} collected in the Belle experiment at the KEKB electron-positron asymmetric-energy collider. The CP asymmetry is measured in four bins of the invariant mass of the K^0_S pi system and found to be compatible with zero with a precision of O(10^{-3}) in each mass bin. Limits for the CP violation parameter Im(eta_S) are given at a 90 % confidence level. These limits are |Im(eta_S)|<0.026 or better, depending on the parameterization used to describe the hadronic form factors and improve upon previous limits by one order of magnitude.

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arXiv2011

Observation of B- to pbar Lambda D0 at Belle

We study B- meson decays to pbar Lambda D(*)0 final states using a sample of 657 * 10^6 B Bbar events collected at the Upsilon(4S) resonance with the Belle detector at the KEKB asymmetric-energy e+ e- collider. The observed branching fraction for B- to pbar Lambda D0 is (1.43^ +0.28_-0.25 +- 0.18)*10^-5. with a significance of 8.1 standard deviations, where the uncertainties are statistical and systematic, respectively. Most of the signal events have the pbarLambda mass peaking near threshold. No significant signal is observed for B- to pbar Lambda D*0 and the corresponding upper limit on the branching fraction is 4.8 * 10^-5 at the 90% confidence level.

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arXiv2011

Observation of transverse polarization asymmetries of charged pion pairs in e+e- annihilation near sqrt s=10.58 GeV

The interference fragmentation function translates the fragmentation of a quark with a transverse projection of the spin into an azimuthal asymmetry of two final-state hadrons. In e+e- annihilation the product of two interference fragmentation functions is measured. We report nonzero asymmetries for pairs of charge-ordered pi+pi- pairs, which indicate a significant interference fragmentation function in this channel. The results are obtained from a 672 fb-1 data sample that contains 711 \times 106 pi+pi- pairs and was collected at and near the ?(4S) resonance, with the Belle detector at the KEKB asymmetric-energy e+e- collider.

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arXiv2011

Evidence for the Suppressed Decay B- -> DK-, D -> K+pi-

The suppressed decay chain B- -> DK-, D -> K+pi-, where D indicates a anti-D0 or D0 state, provides important information on the CP-violating angle phi_3. We measure the ratio R_{DK} of the decay rates to the favored mode B- -> DK-, D -> K-pi+ to be R_{DK} = [1.63^{+0.44}_{-0.41}(stat)^{+0.07}_{-0.13}(syst)] x 10^{-2}, which indicates the first evidence of the signal with a significance of 4.1sigma. We also measure the asymmetry A_{DK} between the charge-conjugate decays to be A_{DK} = -0.39^{+0.26}_{-0.28}(stat)^{+0.04}_{-0.03}(syst). The results are based on the full 772 x 10^6 B anti-B pair data sample collected at the Upsilon(4S) resonance with the Belle detector.

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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.

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