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論文

Charmed baryon spectrum from lattice QCD near the physical point

Bahtiyar, H.*; Can, K. U.*; Erkol, G.*; Gubler, P.; 岡 眞; 高橋 徹*

Physical Review D, 102(5), p.054513_1 - 054513_18, 2020/09

格子QCDによる第一原理計算を用いて、正負パリティのチャームバリオンの基底および励起状態のスペクトルを求めた。チャームクォークを1個, 2個あるいは3個含むバリオンの正および負パリティ状態の質量を、第一原理計算から求めることで、これまでの実験データや模型計算結果との比較を行い、その物理的な意味を解析することが可能となる。今回の計算では、パイオンの質量が観測値に十分近い物理点に近い領域で、2+1フレーバーのゲージ配位を用いた解析を行った。ディラック行列などの配置の異なる複数の演算子を用意し、その交差相関関数を計算し、固有値を求める方法により、基底状態と励起状態のスペクトルを計算した。

論文

Spectrum of singly heavy baryons from a chiral effective theory of diquarks

Kim, Y.*; 肥山 詠美子*; 岡 眞; 鈴木 渓

Physical Review D, 102(1), p.014004_1 - 014004_9, 2020/07

 被引用回数:1 パーセンタイル:100(Astronomy & Astrophysics)

カイラル対称性に基づく有効理論を、現象論的なクォーク模型の閉じ込めポテンシャルと組み合わせることにより、ヘビークォークを1子含むバリオンの質量や構造の予言をおこなった。とりわけ、ダイクォーク質量の逆ヒエラルキー効果がチャームおよびボトムバリオンの質量準位に反映されることを予言した。

論文

Search for $$B^0$$ decays to invisible final states ($$+gamma$$) at Belle

Ku, Y.*; 谷田 聖; Belle Collaboration*; 他153名*

Physical Review D, 102(1), p.012003_1 - 012003_9, 2020/07

 被引用回数:0 パーセンタイル:100(Astronomy & Astrophysics)

We report searches for $$B^0torm{invisible}$$ and $$B^0torm{invisible}+gamma$$ decays, where the energy of the photon is required to be larger than 0.5 GeV. These results are obtained from a $$711,{rm fb}^{-1}$$ data sample that contains $$772 times 10^6 Bbar{B}$$ pairs and was collected near the $$Upsilon,(4S)$$ resonance with the Belle detector at the KEKB $$e^+ e^-$$ collider. We observe no significant signal for either decay and set upper limits on their branching fractions at $$90%$$ confidence level of $$mathcal{B},(B^0torm{invisible}) < 7.8times10^{-5}$$ and $$mathcal{B},(B^0torm{invisible}+gamma) < 1.6times10^{-5}$$.

論文

Dalitz analysis of $$D^{0}to K^{-}pi^{+}eta$$ decays at Belle

Chen, Y. Q.*; 谷田 聖; Belle Collaboration*; 他181名*

Physical Review D, 102(1), p.012002_1 - 012002_12, 2020/07

 被引用回数:0 パーセンタイル:100(Astronomy & Astrophysics)

We present the results of the first Dalitz plot analysis of the decay $$D^{0}to K^{-}pi^{+}eta$$. The analysis is performed on a data set corresponding to an integrated luminosity of 953 $$rm{fb}^{-1}$$ collected by the Belle detector at the asymmetric-energy $$e^{+}e^{-}$$ KEKB collider. The Dalitz plot is well described by a combination of the six resonant decay channels $$bar{K}^{*}(892)^0eta$$, $$K^{-}a_0(980)^+$$, $$K^{-}a_2(1320)^+$$, $$bar{K}^{*}(1410)^0eta$$, $$K^{*}(1680)^-pi^{+}$$ and $$K_2^{*}(1980)^-pi^{+}$$, together with $$Kpi$$ and $$Keta$$ S-wave components. The decays $$K^{*}(1680)^{-}to K^{-}eta$$ and $$K_{2}^{*}(1980)^{-}to K^{-}eta$$ are observed for the first time. We measure ratio of the branching fractions, $$frac{mathcal{B}(D^{0}to K^{-}pi^{+}eta)}{mathcal{B}(D^{0}to K^{-}pi^{+})}=0.500 pm 0.002 {rm(stat)} pm0.020 {rm(syst)}pm 0.003 {rm (mathcal{B}_{PDG})}$$. Using the Dalitz fit result, the ratio $$frac{mathcal{B}(K^{*}(1680) to K eta)}{mathcal{B}(K^{*}(1680)to Kpi)}$$ is measured to be $$0.11 pm 0.02 {rm(stat)}^{+0.06}_{-0.04}{rm(syst)} pm 0.04{rm(mathcal{B}_{{PDG}})}$$; this is much lower than the theoretical expectations ($$approx 1$$) made under the assumption that $$K^{*}(1680)$$ is a pure $$1^{3}D_1$$ state. The product branching fraction $$mathcal{B}(D^0 to [K_2^{*}(1980)^- to K^{-} eta] pi^{+}) = (2.2^{+1.7}_{-1.9})times10^{-4}$$ is determined. In addition, the $$pieta^{prime}$$ contribution to the $$a_0(980)^{pm}$$ resonance shape is confirmed with 10.1$$sigma$$ statistical significance using the three-channel Flatte model. We also measure $$mathcal{B}(D^0tobar{K}^{*}(892)^0eta)=(1.41^{+0.13}_{-0.12})%$$. This is consistent with, and more precise than, the current world average $$(1.02pm0.30)%$$, deviates with a significance of more than $$3sigma$$ from the theoretical predictions of (0.51-0.92)%.

論文

Two-parameter model for optimizing target beam distribution with an octupole magnet

明午 伸一郎; 大井 元貴; 藤森 寛*

Physical Review Accelerators and Beams (Internet), 23(6), p.062802_1 - 062802_24, 2020/06

 被引用回数:0 パーセンタイル:100(Physics, Nuclear)

加速器駆動の核変換システム(ADS)や核破砕中性子源に用いられる陽子加速器のビーム出力増強につれ、ビーム窓や標的の損傷は深刻な問題となり、損傷緩和のためにビーム電流密度の均一化が重要となる。密度均一化のため比較的よく用いられるラスター磁石には、故障時のビーム集束の重大な問題がある。一方、非線形光学を用いたビーム平坦化にははビーム拡大の問題があることが指摘され、これまで非線形効果導入の八極磁石におけるビームの角度の広がりを無視したフィラメント近似模型による検討が行われた。フィラメント近似模型では、非線形収斂作用を適切に評価できないため、本研究では一般化した非線形モデルの適用により非線形ビーム光学における収斂および発散作用を詳細に検討した。正規化した八極強度$$ K^{*}_8 $$と位相進行$$phi$$における$$cotphi$$の2つのパラメータ導入により、非線形効果を特定な条件によらず一般化できることを明確にした。ビームのピーク密度低減と損失最小化という拮抗する問題の解決には、$$K^{*}_8 sim $$ 1および$$ cotphisim$$ 3とすることにより解決できることが判明した。J-PARCの陽子ビーム輸送系(3NBT)に本検討結果を適用し、核破砕中性子源の水銀標的入口のビーム形状の比較検討した結果、モデル計算によるビーム分布は実験データとよい一致を示し、線形光学においてピーク電流密度を約50%にできることを示した。

論文

$$D$$ meson mass and heavy quark potential at finite temperature

Gubler, P.; Song, T.*; Lee, S. H.*

Physical Review D, 101(11), p.114029_1 - 114029_10, 2020/06

 被引用回数:0 パーセンタイル:100(Astronomy & Astrophysics)

Based on the observation that the heavy quark-antiquark potential value at infinity corresponds to twice the $$D$$ meson mass, we constrain the asymptotic value of the heavy quark potential in a hot medium through a QCD sum rule calculation of the $$D$$ meson at finite temperature. We find that to correctly reproduce the QCD sum rule results as well as a recent model calculation for the $$D$$ meson mass near the critical temperature, the heavy quark potential should be composed mostly of the free energy with an addition of a small but non-trivial fraction of the internal energy. Combined with a previous study comparing potential model results for the J/$$psi$$ to a QCD sum rule calculation, we conclude that the composition of the effective heavy quark potential should depend on the inter-quark distance. Namely, the potential is dominated by the free energy at short distance, while at larger separation, it has a fraction of about 20% of internal energy.

論文

Roper-like resonances with various flavor contents and their two-pion emission decays

Arifi, A. J.*; 永廣 秀子*; 保坂 淳; 谷田 聖

Physical Review D, 101(11), p.111502_1 - 111502_5, 2020/06

 被引用回数:1 パーセンタイル:33.39(Astronomy & Astrophysics)

We study the three-body decay of the newly observed bottom baryon $$Lambda_b^*(6072)$$ by LHCb; $$Lambda_b^*(6072) to Lambda_b pi pi$$. Its mass about 500 MeV above the ground state $$Lambda_b$$ and a broad width imply that the state could be an analogue of the Roper resonance of the nucleon $$N(1440)$$. In terms of sequential processes going through $$Sigma_b$$ and $$Sigma_b^*$$, we find that the observed invariant mass distribution is reproduced assuming its spin and parity $$J^P = 1/2^+$$. We discuss that the ratio of the two sequential processes and angular correlation of two pions are useful for the determination of spin and parity. We suggest further studies for the Roper resonance analogue in various flavor contents, raising an interesting and important question in baryon spectroscopy.

論文

Photoneutron detection in lightning by gadolinium orthosilicate scintillators

和田 有希*; 中澤 知洋*; 榎戸 輝揚*; 古田 禄大; 湯浅 孝行*; 牧島 一夫*; 土屋 晴文

Physical Review D, 101(10), p.102007_1 - 102007_6, 2020/05

 被引用回数:0 パーセンタイル:100(Astronomy & Astrophysics)

During a winter thunderstorm on November 24, 2017, a downward terrestrial gamma-ray flash took place and triggered photonuclear reactions with atmospheric nitrogen and oxygen nuclei, coincident with a lightning discharge at the Kashiwazaki-Kariwa nuclear power station in Japan. We directly detected neutrons produced by the photonuclear reactions with gadolinium orthosilicate scintillation crystals installed at sea level. Two gadolinium isotopes included in the scintillation crystals, $$^{155}$$Gd and $$^{157}$$Gd, have large cross sections of neutron captures to thermal neutrons such as $$^{155}$$Gd(n,$$gamma$$)$$^{156}$$Gd and $$^{157}$$Gd(n,$$gamma$$)$$^{158}$$Gd. De-excitation gamma rays from $$^{156}$$Gd and $$^{158}$$Gd are self-absorbed in the scintillation crystals, and make spectral-line features which can be distinguished from other non-neutron signals. The neutron burst lasted for $$sim$$100 ms, and neutron fluences are estimated to be $$>$$ 58 and $$>$$ 31 neutrons cm$$^{-2}$$ at two observation points at the power plant. Gadolinium orthosilicate scintillators work as valid detectors for thermal neutrons in lightning.

論文

Update of inclusive cross sections of single and pairs of identified light charged hadrons

Seidl, R.*; 谷田 聖; Belle Collaboration*; 他136名*

Physical Review D, 101(9), p.092004_1 - 092004_13, 2020/05

 被引用回数:0 パーセンタイル:100(Astronomy & Astrophysics)

We report new measurements of the production cross sections of pairs of charged pions and kaons as a function of their fractional energies using various fractional-energy definitions. Two different fractional-energy definitions were used and compared to the conventional fractional-energy definition reported previously. The new variables aim at either identifying dihadron cross sections in terms of single-hadron fragmentation functions, or to provide a means of characterizing the transverse momentum created in the fragmentation process. The results were obtained applying the updated initial-state radiation correction used in other recent Belle publications on light-hadron production cross sections. In addition, production cross sections of single charged pions, kaons, and protons were also updated using this initial-state radiation correction. The cross sections are obtained from a 558 fb$$^{-1}$$ data sample collected at the $$Upsilon(4S)$$ resonance with the Belle detector at the KEKB asymmetric-energy $$e^+ e^-$$ collider.

論文

Evidence for a vector charmoniumlike state in $$e^+e^- to D^+_sD^*_{s2}(2573)^-+c.c.$$

Jia, S.*; 谷田 聖; Belle Collaboration*; 他175名*

Physical Review D, 101(9), p.091101_1 - 091101_8, 2020/05

 被引用回数:2 パーセンタイル:15.72(Astronomy & Astrophysics)

We report the measurement of $$e^+e^- to D^+_sD^*_{s2}(2573)^-+c.c.$$ via initial-state radiation using a data sample of an integrated luminosity of 921.9 fb$$^{-1}$$ collected with the Belle detector at the $$Upsilon(4S)$$ and nearby. We find evidence for an enhancement with a 3.4$$sigma$$ significance in the invariant mass of $$D^+_sD^*_{s2}(2573)^- +c.c.$$ The measured mass and width are $$(4619.8^{+8.9}_{-8.0}({rm stat.})pm2.3({rm syst.}))~{rm MeV}/c^{2}$$ and $$(47.0^{+31.3}_{-14.8}({rm stat.})pm4.6({rm syst.}))~{rm MeV}$$, respectively. The mass, width, and quantum numbers of this enhancement are consistent with the charmonium-like state at 4626 MeV/$$c^2$$ recently reported by Belle in $$e^+e^-to D^+_sD_{s1}(2536)^-+c.c.$$ The product of the $$e^+e^-to D^+_sD^*_{s2}(2573)^-+c.c.$$ cross section and the branching fraction of $$D^*_{s2}(2573)^-to{bar D}^0K^-$$ is measured from $$D^+_sD^*_{s2}(2573)^-$$ threshold to 5.6 GeV.

論文

Three-body decay of $$Lambda_c^{*} (2765)$$ and determination of its spin-parity

Arifi, A. J.*; 永廣 秀子*; 保坂 淳; 谷田 聖

Physical Review D, 101(9), p.094023_1 - 094023_17, 2020/05

 被引用回数:1 パーセンタイル:33.39(Astronomy & Astrophysics)

We study three-body decays of $$Lambda_c^{*}(2765) to Lambda_c^+pi^+pi^-$$ by using effective Lagrangians in a non-relativistic framework. We consider the sequential decays through $$Sigma_c(2455)pi$$ and $$Sigma_c^*(2520)pi$$ in intermediate states which are dominant contributions. The coupling constants in the effective Lagrangians are computed in the quark model. We demonstrate that the ratio $$R= Gamma(Lambda_c^*toSigma_c^*(2520)pi)/Gamma(Lambda_c^*to Sigma_c(2455)pi)$$ and angular correlations are sensitive to the spin and parity of $$Lambda_c^{*}(2765)$$. Thus, the measurement of these observables in experimental facilities such as Belle and LHCb can provide useful constraints to determine the spin and parity of $$Lambda_c^{*}(2765)$$.

論文

Chiral effective theory of diquarks and the $$U_A(1)$$ anomaly

原田 正康*; Liu, Y.-R.*; 岡 眞; 鈴木 渓

Physical Review D, 101(5), p.054038_1 - 054038_11, 2020/03

 被引用回数:2 パーセンタイル:15.72(Astronomy & Astrophysics)

カイラル対称性に基づく有効理論を用いて、ダイクォークおよびそれを含むヘビーバリオンの質量や構造の解析を行った。特に、有効理論における軸性$$U_A(1)$$アノーマリーの効果について新しい知見を得た。

論文

$$J/psi$$ and $$psi(2S)$$ production at forward rapidity in $$p$$+$$p$$ collisions at $$sqrt{s}=510$$ GeV

Acharya, U. A.*; 長谷川 勝一; 今井 憲一*; 永宮 正治*; 佐甲 博之; 佐藤 進; 谷田 聖; PHENIX Collaboration*; 他353名*

Physical Review D, 101(5), p.052006_1 - 052006_13, 2020/03

 被引用回数:0 パーセンタイル:100(Astronomy & Astrophysics)

The PHENIX experiment at the Relativistic Heavy Ion Collider has measured the differential cross section, mean transverse momentum, mean transverse momentum squared of inclusive $$J/psi$$ and cross-section ratio of $$psi(2S)$$ to $$J/psi$$ at forward rapidity in $$pp$$ collisions at $$sqrt{s} = 510$$ GeV via the dimuon decay channel. Comparison is made to inclusive $$J/psi$$ cross sections measured at $$sqrt{s} = 200$$ GeV and 2.76 - 13 TeV. The result is also compared to leading-order nonrelativistic QCD calculations coupled to a color-glass-condensate description of the low-$$x$$ gluons in the proton at low transverse momentum ($$p_T$$) and to next-to-leading order nonrelativistic QCD calculations for the rest of the $$p_T$$ range. These calculations overestimate the data at low $$p_T$$. While consistent with the data within uncertainties above $$approx 3$$ GeV/$$c$$, the calculations are systematically below the data. The total cross section times the branching ratio is BR $$dsigma^{J/psi}_{pp}/dy (1.2 < |y| < 2.2, 0 < p_T < 10$$ GeV/$$c$$) = 54.3 $$pm$$ 0.5 (stat) $$pm$$ 5.5 (syst) nb.

論文

Study of $$B to p {bar p} pi pi$$

Chu, K.*; 谷田 聖; Belle Collaboration*; 他176名*

Physical Review D, 101(5), p.052012_1 - 052012_8, 2020/03

 被引用回数:0 パーセンタイル:100(Astronomy & Astrophysics)

Using a data sample of $$772 times 10^6$$ BB pairs collected on the $${Upsilon}(4S)$$ resonance with the Belle detector at the KEKB asymmetric-energy $$e^+e^-$$ collider, we report the observations of $$B^0to p{bar p}pi^+pi^-$$ and $$B^+ to p{bar p}pi^+pi^0$$. We measure a decay branching fraction of $$(0.83 pm 0.17 pm 0.17) times 10^-6$$ in $$B^0to p{bar{p}}pi^+pi^-$$ for $$M_{pi^+pi^-} < 1.22 GeV/c^2$$ with a significance of 5.5 standard deviations. The contribution from $$B0 to p{bar p}K^0$$ is excluded. We measure a decay branching fraction of $$(4.58 pm 1.17 pm 0.67) times 10^-6$$ for $$B^+ to p{bar p}pi^+pi^0$$ with $$M_{pi^+pi^0} < 1.3 GeV/c^2$$ with a significance of 5.4 standard deviations. We study the difference of the $$M_{p{bar p}}$$ distributions in $$B^0to p{bar p}pi^+pi^-$$ and $$B^+ to p{bar p}pi^+pi^0$$.

論文

Development of a radio frequency quadrupole linac implemented with the equipartitioning beam dynamics scheme

近藤 恭弘; 森下 卓俊; Jameson, R. A.*

Physical Review Accelerators and Beams (Internet), 22(12), p.120101_1 - 120101_8, 2019/12

 被引用回数:0 パーセンタイル:100(Physics, Nuclear)

RFQは現代の大電流リニアックの実現のための鍵となる加速器であるが、これまで多くのRFQが非常に保守的な設計思想で設計されてきた。我々は空間電荷の物理に基づいて、3MeV、50mAの負イオンRFQを開発した。大電流リニアックで広く用いられている等分配測をRFQ設計に実装し、ヴェーン長3mの3MeV RFQで、設計ビーム透過率99.1%、ビーム垂直方向エミッタンス0.24$$pi$$ mm mrad、ビーム方向エミッタンス0.11$$pi$$ MeV degを得た。このRFQを実際に製作し、ビーム運転を行い設計性能を実証した。この論文ではこの等分配RFQの設計の詳細とビーム運転結果を述べる。

論文

Measurements of the branching fractions $${cal B}(B^{-} to bar{Lambda}_{c}^{-} Xi_{c}^{'0})$$, $${cal B}(B^{-} to bar{Lambda}_{c}^{-} Xi_{c}(2645)^{0})$$ and $${cal B}(B^{-} to bar{Lambda}_{c}^{-} Xi_{c}(2790)^{0})$$

Li, Y.*; 谷田 聖; Belle Collaboration*; 他175名*

Physical Review D, 100(11), p.112010_1 - 112010_8, 2019/12

Using the data sample of 711 fb$$^{-1}$$ of $$Upsilon(4S)$$ on-resonance data taken by the Belle detector at the KEKB asymmetric-energy electron-positron collider, we present the first measurements of branching fractions of the decays $$B^{-} to bar{Lambda}_{c}^{-} Xi_{c}^{'0}$$, $$B^{-} to bar{Lambda}_{c}^{-} Xi_{c}(2645)^{0}$$, and $$B^{-} to bar{Lambda}_{c}^{-} Xi_{c}(2790)^{0}$$. The signal yields for these decays are extracted from the recoil mass spectrum of the system recoiling against $$bar{Lambda}_{c}^{-}$$ baryons in selected $$B^-$$ candidates. The branching fraction of $$B^{-} to bar{Lambda}_{c}^{-} Xi_{c}(2790)^{0}$$ is measured to be $$(1.1 pm 0.4 pm 0.2)times 10^{-3}$$, where the first uncertainty is statistical and the second is systematic. The 90% credibility level upper limits on $${cal B}(B^{-} to bar{Lambda}_{c}^{-} Xi_{c}^{'0})$$ and $${cal B}(B^{-} to bar{Lambda}_{c}^{-} Xi_{c}(2645)^{0})$$ are determined to be $$6.5times 10^{-4}$$ and $$7.9times 10^{-4}$$, respectively.

論文

Observation of a vector charmoniumlike state in $$e^+e^- to D^+_sD_{s1}(2536)^-+c.c.$$

Jia, S.*; 谷田 聖; Belle Collaboration*; 他172名*

Physical Review D, 100(11), p.111103_1 - 111103_8, 2019/12

 被引用回数:10 パーセンタイル:12.8(Astronomy & Astrophysics)

Using a data sample of 921.9 fb$$^{-1}$$ collected with the Belle detector, we study the process of $$e^+e^-to D^+_sD_{s1}(2536)^-+c.c.$$ via initial-state radiation. We report the first observation of a vector charmoniumlike state decaying to $$D^+_sD_{s1}(2536)^-+c.c.$$ with a significance of 5.9$$sigma$$, including the systematic uncertainties. The measured mass and width are $$(4625.9^{+6.2}_{-6.0}({rm stat.})pm0.4({rm syst.}))~{rm MeV}/c^{2}$$ and $$(49.8^{+13.9}_{-11.5}({rm stat.})pm4.0({rm syst.}))~{rm MeV}$$, respectively. The product of the $$e^+e^-to D^+_sD_{s1}(2536)^-+c.c.$$ cross section and the branching fraction of $$D_{s1}(2536)^-to{bar D}^{*0}K^-$$ is measured from the $$D_s bar{D}_{s1}(2536)$$ threshold to 5.59 GeV.

論文

Azimuthal asymmetries of back-to-back $$pi^pm-(pi^0,eta,pi^pm)$$ pairs in $$e^+e^-$$ annihilation

Li, H.*; 谷田 聖; Belle Collaboration*; 他131名*

Physical Review D, 100(9), p.092008_1 - 092008_26, 2019/11

 被引用回数:1 パーセンタイル:100(Astronomy & Astrophysics)

This work reports the first observation of azimuthal asymmetries around the thrust axis in $$e^+e^-$$ annihilation of pairs of back-to-back charged pions in one hemisphere, and $$pi^0$$ and $$eta$$ mesons in the opposite hemisphere. These results are complemented by a new analysis of pairs of back-to-back charged pions. The $$pi^0$$ and $$eta$$ asymmetries rise with the relative momentum $$z$$ of the detected hadrons as well as with the transverse momentum with respect to the thrust axis. These asymmetries are sensitive to the Collins fragmentation function $$H_1^{perp}$$ and provide complementary information to previous measurements with charged pions and kaons in the final state. In particular, the $$eta$$ final states will provide additional information on the flavor structure of $$H_1^{perp}$$. This is the first measurement of the explicit transverse-momentum dependence of the Collins fragmentation function from Belle data. It uses a dataset of 980.4 fb$$^{-1}$$ collected by the Belle experiment at or near a center-of-mass energy of 10.58 GeV.

論文

Observation of $$tau^- rightarrow pi^- nu_{tau} e^+ e^- $$ and search for $$tau^- rightarrow pi^- nu_{tau} mu^+ mu^-$$

Jin, Y.*; 谷田 聖; Belle Collaboration*; 他198名*

Physical Review D, 100(7), p.071101_1 - 071101_9, 2019/10

 被引用回数:0 パーセンタイル:100(Astronomy & Astrophysics)

We present the first measurements of branching fractions of rare tau-lepton decays, $$tau^- rightarrow pi^- nu_{tau} ell^+ ell^-$$ ($$ell = e$$ or $$mu$$), using a data sample corresponding to 562 fb$$^{-1}$$ collected at a center-of-mass energy of 10.58 GeV with the Belle detector at the KEKB asymmetric-energy $$e^+ e^-$$ collider. The $$tau^- rightarrow pi^- nu_tau e^+ e^-$$ decay is observed for the first time with 7.0$$sigma$$ significance. The partial branching fraction determined by the structure-dependent mechanisms mediated by either a vector or an axial-vector current for the mass region $$M_{pi e e} > 1.05$$ GeV/$$c^2$$ is measured to be $$mathcal{B}(tau^-rightarrow pi^- nu_tau e^+ e^-)[M_{pi^- e^+ e^-} > 1.05~{rm GeV}/c^2] = (5.90 pm 0.53 pm 0.85 pm 0.11) times 10^{-6}$$, where the first uncertainty is statistical, the second is systematic, and the third is due to the model dependence. In the full phase space, due to the different detection efficiencies for the structure-dependent mechanisms mediated by axial-vector and vector currents, the branching fraction varies from $$mathcal{B}_{A}(tau^-rightarrow pi^- nu_tau e^+ e^-) = (1.46 pm 0.13 pm 0.21) times 10^{-5}$$ to $$mathcal{B}_{V}(tau^-rightarrow pi^- nu_tau e^+ e^-) = (3.01 pm 0.27 pm 0.43) times 10^{-5}$$, respectively. An upper limit is set on the branching fraction of the $$tau^- rightarrow pi^- nu_tau mu^+ mu^-$$ decay, $$mathcal{B}(tau^-rightarrow pi^- nu_tau mu^+ mu^-) < 1.14 times 10^{-5}$$, at the 90% confidence level.

論文

Multiharmonic vector rf voltage control for wideband cavities driven by vacuum tube amplifiers in a rapid cycling synchrotron

田村 文彦; 杉山 泰之*; 吉井 正人*; 山本 昌亘; 大森 千広*; 野村 昌弘; 島田 太平; 長谷川 豪志*; 原 圭吾*; 古澤 将司*

Physical Review Accelerators and Beams (Internet), 22(9), p.092001_1 - 092001_22, 2019/09

 被引用回数:0 パーセンタイル:100(Physics, Nuclear)

ビーム誘起電流による影響の低減(ビームローディング補償)はJ-PARC 3GeVシンクロトロン(RCS)における大強度ビーム加速に最も重要な課題の一つである。RCSでは広帯域金属磁性体空胴が用いられており、ビームの誘起する電圧は周回周波数の整数倍の成分を含むことから、それら複数の周波数成分(マルチハーモニック)の誘起電圧を抑制するビームローディング補償が必要である。これまではビーム電流の測定から補償信号を生成するRFフィードフォワード法による補償が行われており、マルチハーモニックフィードフォワードシステムは1MWまでのビーム試験においてその役割を果たしてきた。しかしながら、大強度になるにつれて補償性能の低下が確認されていた。そこで、低電力高周波(LLRF)制御システムの更新にあたり、マルチハーモニックベクトル電圧制御によるフィードバック制御を採用することとした。フィードバック制御はゲインの変動についても安定性の範囲内で性能を発揮することが期待される。本論文では、システムの構成、調整方法、大強度ビーム試験の結果について報告する。設計パワーである1MW相当のビーム加速において、ビームローディングはよく補償されている。

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