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Measurements of the branching fractions for D⁺ → Kₛ⁰Kₛ⁰K⁺, Kₛ⁰Kₛ⁰π⁺ and D⁰ → Kₛ⁰Kₛ⁰, Kₛ⁰Kₛ⁰Kₛ⁰
(2016)
By analyzing 2.93 fb−1 of data taken at the ψ(3770) resonance peak with the BESIII detector, we measure the branching fractions for the hadronic decays D+ → K0S K0S K +, D+ → K0S K0Sπ+, D0 → K0S K0S and D0 → K0S K0S K0S . They are determined to be B(D+ → K0S K0S K +) = (2.54 ± 0.05stat. ± 0.12sys.) × 10−3, B(D+ → K0S K0Sπ+) = (2.70 ± 0.05stat. ± 0.12sys.) × 10−3, B(D0 → K0S K0S ) = (1.67 ± 0.11stat. ± 0.11sys.) × 10−4 and B(D0 → K0S K0S K0S ) = (7.21 ± 0.33stat. ± 0.44sys.) × 10−4, where the second one is measured for the first time and the others are measured with significantly improved precision over the previous measurements.
To study the nature of the state Y (2175), a dedicated data set of e+e− collision data was collected at the center-of-mass energy of 2.125 GeV with the BESIII detector at the BEPCII collider. By analyzing large-angle Bhabha scattering events, the integrated luminosity of this data set is determined to be 108.49±0.02±0.85 pb−1, where the first uncertainty is statistical and the second one is systematic. In addition, the center-of-mass energy of the data set is determined with radiative dimuon events to be 2126.55±0.03±0.85 MeV, where the first uncertainty is statistical and the second one is systematic.
We report on an analysis of the decay J/ψ→γπ0η′ using a sample of (1310.6±7.0)× 106 J/ψ events collected with the BESIII detector. We search for the CP-violating process ηc→π0η′ and a dark gauge boson U′ in J/ψ→U′η′, U′→γπ0, π0→γγ. No evidence of an ηc signal is observed in the π0η′ invariant-mass spectrum and the upper limit of the branching fraction is determined to be 7.2× 10−5 at the 90\% confidence level. We also find no evidence of U′ production and set upper limits at the 90\% confidence level on the product branching fraction B(J/ψ→U′η′)×B(U′→π0γ) in the range between (0.8−6.5)×10−7 for 0.2 ≤mU′≤2.1GeV/c2. In addition, we study the process J/ψ→ωη′ with ω→γπ0. The branching fraction of J/ψ→ωη′ is found to be (1.87±0.09±0.12)×10−4, where the first uncertainty is statistical and the second is systematic, with a precision that is improved by a factor of 1.4 over the previously published BESIII measurement.
Using a 2.93 fb−1 data sample of electron-positron collisions taken with the BESIII detector at a center-of-mass energy of 3.773 GeV, which corresponds to (8296±31±64)×103D+D− pairs, we search for the baryon and lepton number violating decays D+→Λ¯(Σ¯0)e+ and D+→Λ(Σ0)e+. No obvious signals are found with the current statistics and upper limits on the branching fractions of these four decays are set at the level of 10−6 at 90% confidence level.
By analyzing a 2.93~fb−1 data sample of e+e− collisions, recorded at a center-of-mass energy of 3.773 GeV with the BESIII detector operated at the BEPCII collider, we have searched for the semileptonic D+ transition into the axial-vector meson K¯1(1270)0. The D+→K¯1(1270)0e+νe decay is observed for the first time with a statistical significance greater than 10σ. Its decay branching fraction is determined to be B[D+→K¯1(1270)0e+νe]=(2.30±0.26±0.18±0.25)×10−3, where the first and second uncertainties are statistical and systematic, respectively, and the third originates from the input branching fraction of K¯1(1270)0→K−π+π0.
Using an e+e− annihilation data sample corresponding to an integrated luminosity of 2.93fb−1 collected at the center-of-mass energy of 3.773\,GeV with the BESIII detector, we measure the absolute branching fractions of D+→ηηπ+, D+→ηπ+π0, and D0→ηπ+π− to be (2.96±0.24±0.13)×10−3, (2.23±0.15±0.11)×10−3, and (1.20±0.07±0.04)×10−3, respectively, where the first uncertainties are statistical and the second ones systematic. The D+→ηηπ+ decay is observed for the first time and the branching fractions of D+(0)→ηπ+π0(−) are measured with much improved precision. In addition we test for CP asymmetries in the separated charge-conjugate branching fractions; no evidence of CP violation is found.
Using a data sample of (448.1±2.9)×106 ψ(3686) decays collected by the BESIII detector at the Beijing Electron Positron Collider (BEPCII), we observe the decays χcJ→ϕϕη (J=0, 1, 2), where the χcJ are produced via the radiative processes ψ(3686)→γχcJ. The branching fractions are measured to be B(χc0→ϕϕη)=(8.41±0.74±0.62)×10−4, B(χc1→ϕϕη)=(2.96±0.43±0.22)×10−4, and B(χc2→ϕϕη)=(5.33±0.52±0.39)×10−4, where the first uncertainties are statistical and the second are systematic. We also search for intermediate states in the ϕϕ or ηϕ combinations, but no significant structure is seen due to the limited statistics.
We report the first observation of D+→τ+ντ with a significance of 5.1σ. We measure B(D+→τ+ντ)=(1.20±0.24stat.±0.12syst.)×10−3. Taking the world average B(D+→μ+νμ)=(3.74±0.17)×10−4, we obtain Rτ/μ=Γ(D+→τ+ντ)/Γ(D+→μ+νμ)=3.21±0.64stat.±0.43syst., which is consistent with the Standard Model expectation of lepton flavor universality. Using external inputs, our results give values for the D+ decay constant fD+ and the CKM matrix element |Vcd| that are consistent with, but less precise than, other determinations.
The ALICE experiment was proposed in 1993, to study strongly interacting matter at extreme energy densities via a comprehensive investigation of nuclear collisions at the LHC. Its physics programme initially focused on the determination of the properties of the Quark-Gluon Plasma (QGP), a deconfined state of quarks and gluons and was extended along the years, covering a diverse ensemble of observables related to Quantum Chromodynamics (QCD), the theory of strong interactions. The experiment has studied Pb-Pb, Xe-Xe, p-Pb and pp collisions in the multi-TeV energy range, during the Run 1 and Run 2 data taking periods at the LHC (2009-2018). The aim of this review article is to gather and summarise a selection of ALICE physics results and to discuss their implications on the current understanding of the macroscopic and microscopic properties of strongly interacting matter at the highest temperature reached in the laboratory. It will be shown that it is possible to have a quantitative description of the properties of the QGP produced in Pb--Pb collisions. We also show that various features, commonly ascribed to QGP formation, are detected for a wide range of interacting system sizes. Precision measurements of QCD-related observables not directly connected to the study of the QGP will also be discussed. Prospects for future measurements with the ALICE detector and its foreseen upgrades will also be briefly described.