Particle Data Tables Research Articles

Regge trajectories of excited baryons, quark-diquark models, and quark-hadron duality

The parton model relations in conjunction with quark-hadron duality in deep inelastic scattering suggests an asymptotic dominance of quark-diquark type of baryonic excited states with a radial Regge uniformly distributed mass squared spectrum $M_{n}^2 = \mu^2 n + M_0^2$. We argue that this points to a lineary quark-diquark confining potential. We analyze the radial ($n$) and angular-momentum ($J$) Regge trajectories for all light-quark states with baryon number one listed in the 2016 edition of the Particle Data Tables. The parameters of the mass squared trajectories are obtained by linear regression assuming $\Delta M_n^2 \sim M_n \Gamma_n $ weighted with the width $\Gamma_n$ of the resonance and the error analysis is carried out accordingly.

Present status of light scalars

I will briefly review in this talk the most significant developments in light scalars spectroscopy that have occurred since the last edition of this Conference, although I will comment on the updates of the mass and width of different light scalar mesons in the latest edition of the Particle Data Tables, I will be mostly focusing on the major revision of the f0(500) meson, also known as σ meson. I will explain how this major update has been driven both by new data and rigorous dispersive analysis.

Systematics of radial and angular-momentum Regge trajectories of light nonstrangeqq¯-states

We reanalyze the radial (n) and angular-momentum (J) Regge trajectories for all light-quark states with baryon number zero listed in the 2011 edition of the Particle Data Tables. The parameters of the trajectories are obtained with linear regression, with weight of each resonance inversely proportional to its half-width squared, $(\Gamma/2)^2$. That way we are side-stepping possible channel-dependent and model-dependent extractions of the resonance parameters and are able to undertake an error analysis. The method complies to the fact that the pole position of the resonance is typically shifted from channel-dependent extractions by $\sim\Gamma/2$. This is also a feature of the large-$N_c$ limit of QCD, where the masses change by $ \Gamma/2$ when evolving from $N_c=3$ to $N_c=\infty$. Our value for the slope of the radial Regge trajectories is $a=1.35(4) GeV^2$. We discuss the fundamental issue whether the masses of the light-quark non-strange states fit into a universal pattern $M_{nJ}^2 = a(n+J) +b$, as suggested by Afonin, and also predicted by some holographic models. Our joint linear-regression analysis in the $(n,J,M^2)$ Regge planes indicates, at a statistically significant level of 4.5 standard deviations, that the slopes of the radial Regge trajectories are larger from the angular-momentum slopes. Thus no strict universality of slopes occurs in the light non-strange meson spectra.

Radial and angular-momentum Regge trajectories: a systematic approach

We present the analysis of Ref.[1] of the radial (n) and angular-momentum (J) Regge trajectories for all light-quark meson states listed in the Particle Data Tables. The parameters of the trajectories are obtained with linear regression, with weight of each resonance inversely proportional to its half-width squared, (\Gamma/2)^2. The joint analysis in the (n,J,M^2) Regge plane indicates, at the 4.5 standard deviation level, that the slopes in n are larger from the slopes in J. Thus no strict universality of slopes occurs in the light non-strange meson sector. We also extend our analysis to the kaon sector.

THERMINATOR: THERMal heavy-IoN generATOR

THERMINATOR: THERMal heavy-IoN generATOR

SHARE: Statistical hadronization with resonances

SHARE: Statistical hadronization with resonances

On the mass and width of the -boson and other relativistic quasistable particles

Abstract The ambiguity in the definition for the mass and width of relativistic resonances is discussed, in particular for the case of the Z -boson. This ambiguity can be removed by requiring that a resonance's width Γ (defined by a Breit–Wigner lineshape) and lifetime τ (defined by the exponential law) always and exactly fulfill the relation Γ=ℏ/τ . To justify this, one needs relativistic Gamow vectors which in turn define the resonance's mass M R as the real part of the square root Re s R of the S -matrix pole position s R . For the Z -boson this means that M R ≈M Z −26 MeV and Γ R ≈Γ Z −1.2 MeV where M Z and Γ Z are the values reported in the particle data tables.

Constraining N ∗(1535) parameters from the eta photoproduction

Current broad uncertainties on the position, total width and eta branching ratio for N ∗ (1535), reported in the 1996 Particle Data Tables, can be narrowed down considerably utilizing the precise Mainz and Bonn data on eta photoproduction. We obtain here a precise determination of the total width from such a study, fixing other parameters. We find the set of N ∗(1535) parameters, suggested by the Particle Data Group (PDG), to be inconsistent with the experimental results from η-photoproduction. In particular, values for the photon helicity coupling and/or the eta branching ratio of the resonance, required in order to fit the data, are larger than the PDG values. This result has important consequences for the interpretation of the resonance in the framework of different models, including some exotic possibilities.

Decaysηc→γγ andηb→γγ: A test for potential models

We use a simple perturbation theory argument and measurements of charmonium leptonic widths $\Gamma (\psi_{NS} \rightarrow e^+e^-)$ to estimate the ratio \mbox{$R_\circ \equiv {\vert \Psi _{\eta_{c1S}}(0) \vert}^2 /{\vert\Psi_{\psi_{1 S}}(0)\vert}^2$} in the general context of non- relativistic potential models. We obtain $R_\circ = 1.4 \pm 0.1$. We then apply well known potential model formulas, which include lowest order QCD corrections, to find $\Gamma (\eta_c \rightarrow \gamma \gamma )/\Gamma (\psi_{1S} \rightarrow e^+e^-) \approx 2.2\pm 0.2$. The central value for $\Gamma (\psi_{1S} \rightarrow e^+ e^-)$in the 1992 Particle Data Tables then leads to a (non relativistic) prediction $\Gamma (\eta_c \rightarrow \gamma \gamma )\approx 11.8\pm 0.8 $ keV. This prediction is in good agreement with a recent measurement by the ARGUS collaboration, is consistent with a recent measurement by the L3 collaboration but is significantly higher than several earlier measurements and than previous theoretical estimates, which usually assume $R_\circ =1$. The correction to $R_\circ =1$ is estimated to be smaller but nonnegligible for the $b\bar b$ system. Using the current central measurement for $\Gamma (\Upsilon_{1S}\rightarrow e^+e^-)$ we find $\Gamma (\eta_b\rightarrow \gamma \gamma )\approx 0.58\pm 0.03$ keV. A rough estimate of relativistic corrections reduces the expected two photon rates to about 8.8 keV and 0.52 keV for the $\eta_c$ and $\eta_b$ mesons respectively. Such corrections