Observation of the Heavy Baryons Sigma b and Sigma b*

70 years of hyperon spectroscopy: a review of strange Ξ, Ω baryons, and the spectrum of charmed and bottom baryons

The first hyperon was discovered about 70 years ago, but the nature of these particles, particularly with regard to multistrange hyperons, and many of their properties can still be considered to be literally strange. A dedicated and successful global spectroscopy program in the 1960s and 1970s usingK-beams revealed many multistrange candidates, but the available evidence of their existence is statistically limited. For this reason, there is still much to learn about the systematics of the spectrum of excited hyperon states and what they have in common with their non-strange companions, or how they differ from the nucleon and Δ resonances. Results from photo- and electroproduction experiments off the proton and neutron using polarized beams and targets have provided intriguing evidence for new nucleon excitations and shed light on the structure of some of the known nucleon and Δ states. Recent years have also seen a great deal of progress in the field of charmed and bottom baryon spectroscopy. Unprecedented data from the Large Hadron Collider in particular indicate continued rapid progress in the field of bottom baryons. On the theoretical side, baryons with one heavy quarkQand a lightqqsystem serve as an ideal laboratory for studying lightqq(diquark) correlations and the dynamics of the light quarks in the colour environment of a heavy quark. In this review, we discuss the status of doubly and triply strange Ξ as well as Ω baryons, and the properties of all the known charmed and bottom states. The comparison of the two heavy sectors reveals many similarities as predicted by heavy-quark symmetries, together with differences in mass splittings easily understood by potential models. The multi-strange hyperons bridge the under-explored gap between the light- and the heavy-flavour baryons. How do the properties of a singly charmedQ-qqsystem change with decreasing mass of the heavy quark in the transition to a doubly strangeq-QQsystem with a heavier quark-quark system relative to one light quark? Significant progress towards understanding hyperon resonances is expected in coming years from the ongoing experiments at the high-energy collider facilities and planned experiments usingKbeams at Jefferson Laboratory and J-PARC.

Tevatron greatest hits

The Tevatron collider led the World energy frontier program in particle physics during the late 20th and early 21st centuries. During this exciting period the standard model of particle physics was in its final stages of development and the search for physics beyond the standard model became one of the main research topics. In this review article we summarize the design and performance of the Tevatron collider and its two detectors, CDF and D0, as well as their evolution. Highlights of the Tevatron scientific results are provided, including the discovery of the top quark and measurements of its properties, studies and discoveries of the particles containing heavy quarks, precision studies of the strong and electroweak forces, searches for beyond the standard model particles and interactions, as well as the hunt for the Higgs boson.

Observation of Two Resonances in the Λ_{b}^{0}π^{±} Systems and Precise Measurement of Σ_{b}^{±} and Σ_{b}^{*±} Properties

The first observation of two structures consistent with resonances in the final states Λ_{b}^{0}π^{-} and Λ_{b}^{0}π^{+} is reported using samples of pp collision data collected by the LHCb experiment at sqrt[s]=7 and 8 TeV, corresponding to an integrated luminosity of 3  fb^{-1}. The ground states Σ_{b}^{±} and Σ_{b}^{*±} are also confirmed and their masses and widths are precisely measured.

A review of the open charm and open bottom systems

Since the discovery of the first charmed meson in 1976, many open-charm and open-bottom hadrons were observed. In 2003 two narrow charm-strange states [Formula: see text] and D _s1(2460) were discovered by the BaBar and CLEO Collaborations, respectively. After that, more excited heavy hadrons were reported. In this work, we review the experimental and theoretical progress in this field.

Progress towards understanding baryon resonances

The composite nature of baryons manifests itself in the existence of a rich spectrum of excited states, in particular in the important mass region 1-2 GeV for the light-flavoured baryons. The properties of these resonances can be identified by systematic investigations using electromagnetic and strong probes, primarily with beams of electrons, photons, and pions. After decades of research, the fundamental degrees of freedom underlying the baryon excitation spectrum are still poorly understood. The search for hitherto undiscovered but predicted resonances continues at many laboratories around the world. Recent results from photo- and electroproduction experiments provide intriguing indications for new states and shed light on the structure of some of the known nucleon excitations. The continuing study of available data sets with consideration of new observables and improved analysis tools have also called into question some of the earlier findings in baryon spectroscopy. Other breakthrough measurements have been performed in the heavy-baryon sector, which has seen a fruitful period in recent years, in particular at the B factories and the Tevatron. First results from the large hadron collider indicate rapid progress in the field of bottom baryons. In this review, we discuss the recent experimental progress and give an overview of theoretical approaches.

Observation of excited Λ(b)(0) baryons

Using pp collision data corresponding to 1.0 fb(-1) integrated luminosity collected by the LHCb detector, two narrow states are observed in the Λ(b)(0)π(+)π(-) spectrum with masses 5911.97±0.12(stat)±0.02(syst)±0.66(Λ(b)(0) mass) MeV/c(2) and 5919.77±0.08(stat)±0.02(syst)±0.66(Λ(b)(0) mass) MeV/c(2). The significances of the observations are 5.2 and 10.2 standard deviations, respectively. These states are interpreted as the orbitally excited Λ(b)(0) baryons, Λ(b)(*0)(5912) and Λ(b)(*0)(5920).

Axial couplings and strong decay widths of heavy hadrons

We calculate the axial couplings of mesons and baryons containing a heavy quark in the static limit using lattice QCD. These couplings determine the leading interactions in heavy hadron chiral perturbation theory and are central quantities in heavy quark physics, as they control strong decay widths and the light quark mass dependence of heavy hadron observables. Our analysis makes use of lattice data at six different pion masses, 227 MeV<m(π)<352 MeV, two lattice spacings, a=0.085, 0.112 fm, and a volume of (2.7 fm)(3). Our results for the axial couplings are g(1)=0.449(51), g(2)=0.84(20), and g(3)=0.71(13), where g(1) governs the interaction between heavy-light mesons and pions and g(2,3) are similar couplings between heavy-light baryons and pions. Using our lattice result for g(3), and constraining 1/m(Q) corrections in the strong decay widths with experimental data for Σ(c)(*) decays, we obtain Γ[Σ(b)(*)→Λ(b)π(±)]=4.2(1.0), 4.8(1.1), 7.3(1.6), 7.8(1.8) MeV for the Σ(b)(+), Σ(b)(-), Σ(b)(*+), Σ(b)(*-) initial states, respectively. We also derive upper bounds on the widths of the Ξ(b)(I(*)) baryons.

Observation of the Ξ(b)(0) baryon

The observation of the bottom, strange baryon Ξ(b)(0) through the decay chain Ξ(b)(0)→Ξ(c)(+)π-, where ΞΞ(c)(+)→Ξ- π+ π+, Ξ-→Λπ-, and Λ→pπ-, is reported by using data corresponding to an integrated luminosity of 4.2  fb(-1) from pp collisions at square root(s)=1.96  TeV recorded with the Collider Detector at Fermilab. A signal of 25.3(-5.4)(+5.6) candidates is observed whose probability of arising from a background fluctuation is 3.6×10(-12), corresponding to 6.8 gaussian standard deviations. The Ξ(b)(0) mass is measured to be 5787.8±5.0(stat)±1.3(syst)  MeV/c2. In addition, the Ξ(b)- baryon is observed through the process Ξ(b)-→Ξ(c)(0)π-, where Ξ(c)(0)→Ξ- π+, Ξ-→Λπ-, and Λ→pπ-.

Measurement of the Lambdab0 lifetime in Lambdab0 --> Lambdac+pi- decays in pp collisions at square root of s = 1.96 TeV

We report a measurement of the lifetime of the Lambda(b)(0) baryon in decays to the Lambda(c)(+)pi(-) final state in a sample corresponding to 1.1 fb(-1) collected in pp collisions at square root of s = 1.96 TeV by the CDF II detector at the Tevatron collider. Using a sample of about 3000 fully reconstructed Lambda(b)(0) events we measure tau(Lambda(b)(0)) = 1.401 +/- 0.046(stat) +/- 0.035(syst) ps (corresponding to ctau(Lambda(b)(0)) = 420.1 +/- 13.7(stat) +/- 10.6(syst) microm, where c is the speed of light). The ratio of this result and the world average B(0) lifetime yields tau(Lambda(b)(0))/tau(B(0)) = 0.918 +/- 0.038 (stat) and (syst), in good agreement with recent theoretical predictions.