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Using an 𝑒+𝑒− collision data sample with a total integrated luminosity of 3.19 fb−1 collected with the BESIII detector at a center-of-mass energy of 4.178 GeV, the branching fraction of the inclusive decay of the 𝐷+𝑠 meson to final states including at least three charged pions is measured for the first time to be ℬ(𝐷+𝑠→𝜋+𝜋+𝜋−𝑋)=(32.81±0.35stat±0.63syst)%. In this measurement the charged pions from 𝐾0𝑆 meson decays are excluded. The partial branching fractions of 𝐷+𝑠→𝜋+𝜋+𝜋−𝑋 are also measured as a function of the 𝜋+𝜋+𝜋− invariant mass.
The process e+e−→Σ+Σ¯− is studied from threshold up to 3.04 GeV/c2 via the initial-state radiation technique using data with an integrated luminosity of 12.0 fb−1, collected at center-of-mass energies between 3.773 and 4.258 GeV with the BESIII detector at the BEPCII collider. The pair production cross sections and the effective form factors of Σ are measured in eleven Σ+Σ¯− invariant mass intervals from threshold to 3.04 GeV/c2. The results are consistent with the previous results from Belle and BESIII. Furthermore, the branching fractions of the decays J/ψ→Σ+Σ¯− and ψ(3686)→Σ+Σ¯− are determined and the obtained results are consistent with the previous results of BESIII.
The process 𝑒+𝑒−→Σ+¯Σ− is studied from threshold up to 3.04 GeV/𝑐2 via the initial-state radiation technique using data with an integrated luminosity of 12.0 fb−1, collected at center-of-mass energies between 3.773 and 4.258 GeV with the BESIII detector at the BEPCII collider. The pair production cross sections and the effective form factors of Σ are measured in eleven Σ+¯Σ− invariant mass intervals from threshold to 3.04 GeV/𝑐2. The results are consistent with the previous results from Belle and BESIII. Furthermore, the branching fractions of the decays 𝐽/𝜓→Σ+¯Σ− and 𝜓(3686)→Σ+¯Σ− are determined and the obtained results are consistent with the previous results of BESIII.
The main focus of this thesis is the application of the nonperturbative Functional Renormalization Group (FRG) to the study of low-energies effective models for Quantum Chromodynamics (QCD). The study of effective field theories and models is crucial for our understanding of physics, especially when we deal with fundamental interaction theories like QCD. In particular, the ultimate goal is the understanding of the critical properties of these models in such a way that we can have an insight on the actual critical phenomena of QCD, with a special focus on its chiral phase transition. The choice of the FRG method derives from the fact that it belongs to the class of functional non-perturbative methods and has also the advantage of linking physics at different energy scales. These features make FRG perfectly compatible with the task of studying non-perturbative phenomena and in particular phase transitions, like the ones expected for strongly interacting matter. However, the functional nature of the FRG approach and of the Wetterich equation has a consequence that its exact resolution is hardly possible, and an ansatz for the effective action is generally needed. In this work we choose to adopt the local-potential approximation (LPA), which prescribes to stop at zeroth order in the expansion in derivative operators of the quantum effective action, including only the quantum effective potential. In this work we exploited the key observation that the FRG flow equation can be cast, for specific models and truncation schemes, in the form of an advection-diffusion, possibly with a source term. This type of equation belongs to the class of problems faced in the context of viscous hydrodynamics. Therefore, an innovative approach to the solution of the FRG flow equation consists in the choice of a method developed specifically for the resolution of this class of hydrodynamic equations. In particular, the Kurganov-Tadmor finite-volume scheme is adopted. Throughout this work we apply this scheme to the study of different physical systems, showing the reliability and the flexibility of this approach.
In the first part of the thesis, we discuss the well-known O(N) model, using the hydrodynamic formulation to solve the FRG flow equation in the LPA truncation. We focus on the study of the critical behaviour of the system and calculate the corresponding critical exponents. Particular attention is given to the error estimation in the extraction of critical exponents, which is a needed and not widely explored aspect. The results are well compatible with others in the literature, obtained with different perturbative and nonperturbative methods, which validates the procedure. In the second part of the thesis, we introduce the quark-meson model as a low-energy effective model for QCD, with a specific focus on its chiral symmetry-breaking pattern and the subsequent dynamical quark-mass generation. The LPA flow equation is of the advection-diffusion type, with an extra source contribution which is due to the inclusion of fermionic degrees of freedom. We thus adopt the developed numerical techniques to derive the phase diagram of the model, which is in agreement with the one obtained with other techniques in the literature.
We also follow another possible way for the study of the critical properties of the quark-meson model: the so-called thermodynamic geometry. This approach is based on the interpretation of the parameter space of the system as a differential manifold. One can then obtain relevant information about the phase transitions from the Ricci scalar. We studied the chiral crossover investigating the behavior of the Ricci scalar up to the critical point, featuring a peaking behavior in the presence of the crossover. We then repeated this analysis in the chiral limit, where the phase transition is expected to be of second order. Via this geometric technique it is possible to have a different view on the chiral phase transition of QCD. This is the case since this approach is based on the calculation of quantities which are influenced by higher-order momenta of the thermodynamic potential, thus allowing for a more comprehensive analysis of the phase transition.
Finally, we exploit the numerical advancement to face the issue of the regulator choice in the FRG calculations. This is one of the most delicate issues which arise when using approximations to solve the FRG flow equation and deserves extensive investigation. In particular, we performed a vacuum parameter study and used the RG consistency requirement to determine the impact of the choice of the regulator on the physical observables and on the phase diagram of the model. Via this study we develop a systematic method to comparison the results obtained via different regulators. We show the importance of the choice of an appropriate UV cutoff in the determination of UV-independent IR observables and, consequently, the impact on the latter that the truncation of the effective average action and the choice of the regulator have.
In response to pathogen infection, gasdermin (GSDM) proteins form membrane pores that induce a host cell death process called pyroptosis1–3. Studies of human and mouse GSDM pores reveal the functions and architectures of 24–33 protomers assemblies4–9, but the mechanism and evolutionary origin of membrane targeting and GSDM pore formation remain unknown. Here we determine a structure of a bacterial GSDM (bGSDM) pore and define a conserved mechanism of pore assembly. Engineering a panel of bGSDMs for site-specific proteolytic activation, we demonstrate that diverse bGSDMs form distinct pore sizes that range from smaller mammalian-like assemblies to exceptionally large pores containing >50 protomers. We determine a 3.3 Å cryo-EM structure of a Vitiosangium bGSDM in an active slinky-like oligomeric conformation and analyze bGSDM pores in a native lipid environment to create an atomic-level model of a full 52-mer bGSDM pore. Combining our structural analysis with molecular dynamics simulations and cellular assays, we define a stepwise model of GSDM pore assembly and demonstrate that pore formation is driven by local unfolding of membrane-spanning β-strand regions and pre-insertion of a covalently bound palmitoyl into the target membrane. These results yield insights into the diversity of GSDM pores found in nature and the function of an ancient post-translational modification in enabling a programmed host cell death process.
In response to pathogen infection, gasdermin (GSDM) proteins form membrane pores that induce a host cell death process called pyroptosis1–3. Studies of human and mouse GSDM pores reveal the functions and architectures of 24–33 protomers assemblies4–9, but the mechanism and evolutionary origin of membrane targeting and GSDM pore formation remain unknown. Here we determine a structure of a bacterial GSDM (bGSDM) pore and define a conserved mechanism of pore assembly. Engineering a panel of bGSDMs for site-specific proteolytic activation, we demonstrate that diverse bGSDMs form distinct pore sizes that range from smaller mammalian-like assemblies to exceptionally large pores containing >50 protomers. We determine a 3.3 Å cryo-EM structure of a Vitiosangium bGSDM in an active slinky-like oligomeric conformation and analyze bGSDM pores in a native lipid environment to create an atomic-level model of a full 52-mer bGSDM pore. Combining our structural analysis with molecular dynamics simulations and cellular assays, our results support a stepwise model of GSDM pore assembly and suggest that a covalently bound palmitoyl can leave a hydrophobic sheath and insert into the membrane before formation of the membrane-spanning β-strand regions. These results reveal the diversity of GSDM pores found in nature and explain the function of an ancient post-translational modification in enabling programmed host cell death.
By analyzing 𝑒+𝑒− annihilation data with an integrated luminosity of 2.93 fb−1 collected at the center-of-mass energy √𝑠=3.773 GeV with the BESIII detector, we present the first absolute measurements of the branching fractions of twenty Cabibbo-suppressed hadronic 𝐷0(+) decays involving multiple pions. The highest four branching fractions obtained are ℬ(𝐷0→𝜋+𝜋−𝜋0) = (1.343±0.013stat±0.016syst)%, ℬ(𝐷0→𝜋+𝜋−2𝜋0) = (1.002±0.019stat±0.024syst)%, ℬ(𝐷+→2𝜋+𝜋−𝜋0) = (1.165±0.021stat±0.021syst)%, and ℬ(𝐷+→2𝜋+𝜋−2𝜋0) = (1.074±0.040stat±0.030syst)%. The 𝐶𝑃 asymmetries for the six decays with highest signal yields are also determined and found to be compatible with zero.
By analyzing e+e− annihilation data with an integrated luminosity of 2.93 fb−1 collected at the center-of-mass energy s√= 3.773 GeV with the BESIII detector, we present the first absolute measurements of the branching fractions of twenty Cabibbo-suppressed hadronic D0(+) decays involving multiple pions. The largest four branching fractions obtained are B(D0→π+π−π0) = >(1.343±0.013stat±0.016syst)%, B(D0→π+π−2π0) = (0.998±0.019stat±0.024syst)%, B(D+→2π+π−π0)
(1.174±0.021stat±0.021syst)%, and B(D+→2π+π−2π0) = (1.074±0.040stat±0.030syst)%. The CP asymmetries for the six decays with highest event yields are also determined.
Using a sample of (448.1±2.9)×106 𝜓(3686) decays collected with the BESIII detector at BEPCII, we report an observation of Ξ− transverse polarization with a significance of 7.3𝜎 in the decay 𝜓(3686)→Ξ− ¯Ξ+ (Ξ−→Λ𝜋−, ¯Ξ+→¯Λ𝜋+, Λ→𝑝𝜋−, ¯Λ→¯𝑝𝜋+). The relative phase of the electric and magnetic form factors is determined to be ΔΦ=(0.667±0.111±0.058) rad. This is the first measurement of the relative phase for a 𝜓(3686) decay into a pair of Ξ−¯Ξ+ hyperons. The Ξ− decay parameters (𝛼Ξ−, 𝜙Ξ−) and their conjugates (𝛼¯Ξ+, 𝜙¯Ξ+), the angular-distribution parameter 𝛼𝜓, and the strong-phase difference 𝛿𝑝−𝛿𝑠 for Λ𝜋− scattering are measured to be consistent with previous BESIII results.
Luminosities and energies of e⁺e⁻ collision data taken between √s=4.61 GeV and 4.95 GeV at BESIII
(2022)
From December 2019 to June 2021, the BESIII experiment collected about 5.85 fb−1 of data at center-of-mass energies between 4.61 GeV and 4.95 GeV. This is the highest collision energy BEPCII has reached so far. The accumulated e+e− annihilation data samples are useful for studying charmonium(-like) states and charmed-hadron decays. By adopting a novel method of analyzing the production of Λ+cΛ¯−c pairs in e+e− annihilation, the center-of-mass energies are measured with a precision of ∼0.6 MeV. Integrated luminosities are measured with a precision of better than 1\% by analyzing the events of large-angle Bhabha scattering. These measurements provide important inputs to the analyses based on these data samples.