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- Hadron-Hadron scattering (experiments) (4)
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- Physik (291) (entfernen)
Lattice QCD investigation of a doubly-bottom b̄b̄ud tetraquark with quantum numbers I(JP) = 0(1⁺)
(2019)
We use lattice QCD to investigate the spectrum of the ¯𝑏¯𝑏𝑢𝑑 four-quark system with quantum numbers 𝐼(𝐽𝑃)=0(1+). We use five different gauge-link ensembles with 2+1 flavors of domain-wall fermions, including one at the physical pion mass, and treat the heavy ¯𝑏 quark within the framework of lattice nonrelativistic QCD. Our work improves upon previous similar computations by considering in addition to local four-quark interpolators also nonlocal two-meson interpolators and by performing a Lüscher analysis to extrapolate our results to infinite volume. We obtain a binding energy of (−128±24±10) MeV, corresponding to the mass (10476±24±10) MeV, which confirms the existence of a ¯𝑏¯𝑏𝑢𝑑 tetraquark that is stable with respect to the strong and electromagnetic interactions.
Measurement of branching fractions for D meson decaying into ϕ meson and a pseudoscalar meson
(2019)
The four decay modes D0 → φπ0, D0 → φη, D+ → φπ+, and D+ → φK + are studied by using a data sample taken at the centre-of-mass energy √s = 3.773 GeV with the BESIII detector, corresponding to an integrated luminosity of 2.93 fb−1. The branching fractions of the first three decay modes are measured to be B(D0 → φπ0) = (1.168 ± 0.028 ± 0.028) × 10−3, B(D0 → φη) = (1.81 ± 0.46 ± 0.06) × 10−4, and B(D+ → φπ+) = (5.70 ± 0.05 ± 0.13) × 10−3, respectively, where the first uncertainties are statistical and the second are systematic. In addition, the upper limit of the branching fraction for D+ → φK+ is given to be 2.1 × 10−5 at the 90% confidence level. The ratio of B(D0 → φπ0) to B(D+ → φπ+) is calculated to be (20.49 ± 0.50 ± 0.45)%, which is consistent with the theoretical prediction based on isospin symmetry between these two decay modes.
Using a data sample with an integrated luminosity of 2.93 fb−1 taken at the center-of-mass energy of 3.773 GeV, we search for the Majorana neutrino (𝜈𝑚) in the lepton number violating decays 𝐷→𝐾𝜋𝑒+𝑒+. No significant signal is observed, and the upper limits on the branching fraction at the 90% confidence level are set to be ℬ(𝐷0→𝐾−𝜋−𝑒+𝑒+)<2.8×10−6, ℬ(𝐷+→𝐾0𝑆𝜋−𝑒+𝑒+)<3.3×10−6 and ℬ(𝐷+→𝐾−𝜋0𝑒+𝑒+)<8.5×10−6. The Majorana neutrino is searched for with different mass assumptions ranging from 0.25 to 1.0 GeV/𝑐2 in the decays 𝐷0→𝐾−𝑒+𝜈𝑚,𝜈𝑚→𝜋−𝑒+ and 𝐷+→𝐾0𝑆𝑒+𝜈𝑚,𝜈𝑚→𝜋−𝑒+, and the upper limits on the branching fraction at the 90% confidence level are at the level of 10−7∼10−6, depending on the mass of the Majorana neutrino. The constraints on the mixing matrix element |𝑉𝑒𝜈𝑚|2 are also evaluated.
We study the electromagnetic Dalitz decay 𝐽/𝜓→𝑒+𝑒−𝜂 and search for dielectron decays of a dark gauge boson (𝛾′) in 𝐽/𝜓→𝛾′𝜂 with the two 𝜂 decay modes 𝜂→𝛾𝛾 and 𝜂→𝜋+𝜋−𝜋0 using (1310.6±7.0)×106 𝐽/𝜓 events collected with the BESIII detector. The branching fraction of 𝐽/𝜓→𝑒+𝑒−𝜂 is measured to be (1.43±0.04(stat)±0.06(syst))×10−5, with a precision that is improved by a factor of 1.5 over the previous BESIII measurement. The corresponding dielectron invariant mass dependent modulus square of the transition form factor is explored for the first time, and the pole mass is determined to be Λ=2.84±0.11(stat)±0.08(syst) GeV/𝑐2. We find no evidence of 𝛾′ production and set 90% confidence level upper limits on the product branching fraction ℬ(𝐽/𝜓→𝛾′𝜂)×ℬ(𝛾′→𝑒+𝑒−) as well as the kinetic mixing strength between the standard model photon and 𝛾′ in the mass range of 0.01≤𝑚𝛾′≤2.4 GeV/𝑐2.
b̄b̄ud tetraquark resonances in the Born-Oppenheimer approximation using lattice QCD potentials
(2019)
We study tetraquark resonances for a pair of static antiquarks b¯b¯ in presence of two light quarks ud based on lattice QCD potentials. The system is treated in the Born-Oppenheimer approximation and we use the emergent wave method. We focus on the isospin I = 0 channel but take different angular momenta l of the heavy antiquarks b¯b¯ into account. Further calculations have already predicted a bound state for the l = 0 case with quantum numbers I(JP) = 0(1+). Performing computations for several angular momenta, we extract the phase shifts and search for T and S matrix poles in the second Riemann sheet. For angular momentum l = 1, we predict a tetraquark resonance with quantum numbers I(JP) = 0(1−), resonance mass m = 10576+4−4 MeV and decay width Γ = 112+90−103 MeV, which decays into two B mesons.
Using 𝑒+𝑒−→Λ+𝑐¯Λ−𝑐 production from a 567 pb−1 data sample collected by BESIII at 4.6 GeV, a full angular analysis is carried out simultaneously on the four decay modes of Λ+𝑐→𝑝𝐾0𝑆, Λ𝜋+, Σ+𝜋0, and Σ0𝜋+. For the first time, the Λ+𝑐 transverse polarization is studied in unpolarized 𝑒+𝑒− collisions, where a nonzero effect is observed with a statistical significance of 2.1𝜎. The decay asymmetry parameters of the Λ+𝑐 weak hadronic decays into 𝑝𝐾0𝑆, Λ𝜋+, Σ+𝜋0 and Σ0𝜋+ are measured to be 0.18±0.43(stat)±0.14(syst), −0.80±0.11(stat)±0.02(syst), −0.57±0.10(stat)±0.07(syst), and −0.73±0.17(stat)±0.07(syst), respectively. In comparison with previous results, the measurements for the Λ𝜋+ and Σ+𝜋0 modes are consistent but with improved precision, while the parameters for the 𝑝𝐾0𝑆 and Σ0𝜋+ modes are measured for the first time.
We measure the Born cross sections of the process 𝑒+𝑒−→𝐾+𝐾−𝐾+𝐾− at center-of-mass (c.m.) energies, √𝑠, between 2.100 and 3.080 GeV. The data were collected using the BESIII detector at the BEPCII collider. An enhancement at √𝑠=2.232 GeV is observed, very close to the 𝑒+𝑒−→Λ¯Λ production threshold. A similar enhancement at the same c.m. energy is observed in the 𝑒+𝑒−→𝜙𝐾+𝐾− cross section. The energy dependence of the 𝐾+𝐾−𝐾+𝐾− and 𝜙𝐾+𝐾− cross sections differs significantly from that of 𝑒+𝑒−→𝜙𝜋+𝜋−.
The time-dependent Schrödinger equation for quadratic Hamiltonians has Gaussian wave packets as exact solutions. For the parametric oscillator with frequency ω(t), the width of these wave packets must be time-dependent. This time-dependence can be determined by solving a complex nonlinear Riccati equation or an equivalent real nonlinear Ermakov equation. All quantum dynamical properties of the system can easily be constructed from these solutions, e.g., uncertainties of position and momentum, their correlations, ground state energies, etc. In addition, the link to the corresponding classical dynamics is supplied by linearizing the Riccati equation to a complex Newtonian equation, actually representing two equations of the same kind: one for the real and one for the imaginary part. If the solution of one part is known, the missing (linear independent) solution of the other can be obtained via a conservation law for the motion in the complex plane. Knowing these two solutions, the solution of the Ermakov equation can be determined immediately plus the explicit expressions for all the quantum dynamical properties mentioned above. The effect of a dissipative, linear velocity dependent friction force on these systems is discussed.
We investigate the role of the Pauli Exclusion Principle (PEP) for light nuclei, at the examples of 12C and 16O. We show that ignoring the PEP does lead not only to a too dense spectrum at low energy but also to a wrong grouping into bands. Using a geometrical mapping, a triangular structure for 12C and a tetrahedral structure in 16O in the ground state is obtained by using the indistinguishably of the α-particles.
Based on the positive results of the 0.63 m unmodulated 325 MHz Ladder-RFQ prototype from 2013 to 2016 [1, 2], a modulated 3.3m Ladder-RFQ (s. Fig. 1) has been designed and built for the acceleration of up to 100 mA protons from 95 keV to 3.0 MeV at the FAIR p-Linac [3, 4]. In this paper, we will show the results of manufacturing as well as low level RF measurements of the Ladder-RFQ including flatness and frequency tuning.