Charmed-strange Baryon Research Articles

Observation of New States Decaying intoΛc+K−π+andΛc+KS0π−

We report the first observation of two charmed strange baryons that decay into Lambda(c)(+)Kappa(-)pi(+). The broader of the two states is measured to have a mass of 2978.5+/-2.1+/-2.0 MeV/c2 and a width of 43.5+/-7.5+/-7.0 MeV/c2. The mass and width of the narrow state are measured to be 3076.7+/-0.9+/-0.5 MeV/c;{2} and 6.2+/-1.2+/-0.8 MeV/c2, respectively. We also perform a search for the isospin partner states that decay into Lambda(c)(+)Kappa(0)/(s)pi(-) and observe a significant signal at the mass of 3082.8+/-1.8+/-1.5 MeV/c2. The data used for this analysis were accumulated at or near the Upsilon(4S) resonance, using the Belle detector at the e+ e- asymmetric-energy collider KEKB. The integrated luminosity of the data sample used is 461.5 fb(-1).

Production of $\Xi{_c^0}$ and $\Xi{_b}$ in Z decays and lifetime measurement of $\Xi{_b}$

The charmed strange baryon Ξ0c was searched for in the decay channel Ξ0c → Ξ−π+, and the beauty strange baryon Ξb in the inclusive channel Ξb → Ξ−−¯νX, using the 3.5 million hadronic Z events collected by the DELPHI experiment in the years 1992–1995. The Ξ− was reconstructed through the decay Ξ− → Λπ−, using a constrained fit method for cascade decays. An iterative discriminant analysis was used for the Ξ0c and Ξb selection. The production rates were measured to be fΞ0c ×BR(Ξ0c → Ξ−π+) = (4.7 ± 1.4(stat.) ± 1.1(syst.)) × 10−4 per hadronic Z decay, and BR(b → Ξb)×BR(Ξb → Ξ−−X) = (3.0 ± 1.0(stat.) ± 0.3(syst.)) × 10−4 for each lepton species (electron or muon). The lifetime of the Ξb baryon was measured to be τΞb = 1.45+0.55 −0.43(stat.) ± 0.13(syst.) ps. A combination with the previous DELPHI lifetime measurement gives τΞb = 1.48+0.40 −0.31(stat.) ± 0.12(syst.) ps.

A new measurement of the Ξ+ lifetime

A precise determination of the charm-strange baryon Ξ c + lifetime is presented. The data were accumulated by the Fermilab high-energy photoproduction experiment FOCUS. The measurement is made with 300 Ξ c + → Ξ − π + π + decays, 130 Ξ c + → Σ + K − π + decays, 45 Ξ c + → pK − π + decays and 58 Ξ c + → Λ 0 K − π + π + decays. The Ξ c + lifetime is measured to be 0.439 ± 0.022 ± 0.009 ps.

A HIGH STATISTICS MEASUREMENT OF Ξc LIFETIMES

Preliminary results of the charm-strange baryon lifetimes from the FOCUS experiment at Fermilab are presented. The [Formula: see text] lifetime is determined to be 0.440±0.031 ps and the [Formula: see text] lifetime to be 0.124±0.013 ps. The systematic errors are still under review.

Determination of the total $c\bar c$ production cross section in 340 GeV/c $\Sigma^-$ -nucleus interactions

The production of charmed particles by 340 GeV/c momentum $\Sigma^-$ was studied in the hyperon beam experiment WA89 at the CERN-SPS, using the $\Omega$ -spectrometer. In two data-taking periods in 1993 and 1994 an integrated luminosity of $1600\,\mu\mbox{b}^{-1}$ on copper and carbon targets was recorded. From the reconstruction of $ 930 \pm 90$ charm particle decays in 10 decay channels production cross sections for D, ${\mathrm{\overline D}}$ , $\mathrm{D_{s}^-}$ and $\mathrm{\Lambda_c^+}$ were determined in the region $x_F>0$ . Assuming an $A^1$ dependence of the cross section on the nucleon number, we calculate a total $c\bar c$ production cross section of $\sigma_{\mathrm c\mathrm{\overline c}}(x_F > 0) = 5.3\, \pm\, 0.4\,\, (stat)\,\, \pm\, 1.0\,\, (syst)\,\,+1.0\,\,(\mathrm{\Xi_c})\, \mu\mbox{b}$ per nucleon. The last term is an upper limit on the unknown contribution from charmed-strange baryon production.

Determination of the total

The production of charmed particles by 340 GeV/c momentum $\Sigma^-$ was studied in the hyperon beam experiment WA89 at the CERN-SPS, using the $\Omega$ -spectrometer. In two data-taking periods in 1993 and 1994 an integrated luminosity of $1600\,\mu\mbox{b}^{-1}$ on copper and carbon targets was recorded. From the reconstruction of $ 930 \pm 90$ charm particle decays in 10 decay channels production cross sections for D, ${\mathrm{\overline D}}$ , $\mathrm{D_{s}^-}$ and $\mathrm{\Lambda_c^+}$ were determined in the region $x_F>0$ . Assuming an $A^1$ dependence of the cross section on the nucleon number, we calculate a total $c\bar c$ production cross section of $\sigma_{\mathrm c\mathrm{\overline c}}(x_F > 0) = 5.3\, \pm\, 0.4\,\, (stat)\,\, \pm\, 1.0\,\, (syst)\,\,+1.0\,\,(\mathrm{\Xi_c})\, \mu\mbox{b}$ per nucleon. The last term is an upper limit on the unknown contribution from charmed-strange baryon production.

Observation of Two Narrow States Decaying intoΞc+γandΞc0γ

We report the first observation of two narrow charmed strange baryons decaying to $\Xi_c^+\gamma$ and $\Xi_c^0\gamma$, respectively, using data from the CLEO II detector at CESR. We interpret the observed signals as the $\Xi_c^{+\prime}(c{su})$ and $\Xi_c^{0\prime}(c{sd})$, the symmetric partners of the well-established antisymmetric $\Xi_c^+(c[su])$ and $\Xi_c^0(c[sd])$. The mass differences $M(\Xi_c^{+\prime})-M(\Xi_c^+)$ and $M(\Xi_c^{0\prime})-M(\Xi_c^0)$ are measured to be $107.8\pm 1.7\pm 2.5$ and $107.0\pm 1.4\pm 2.5 MeV/c^2$, respectively.

First Observation of InclusiveBDecays to the Charmed Strange BaryonsΞc0andΞc+

Using data collected in the region of the Upsilon(4S) resonance with the CLEO II detector operating at the Cornell Electron Storage Ring CESR, we present the first observation of B mesons decaying into the charmed strange baryons Xi_c0 and Xi_c+. We find 79 +/- 27 Xi_c0 and 125 +/- 28 Xi_c+ candidates from B decays, leading to product branching fractions of BR(Bbar -> Xi_c0 X)BR(Xi_c0 -> Xi- pi+) = (0.144 +/- 0.048 +/- 0.021) x 10^-3 and BR(Bbar -> Xi_c+ X)BR(Xi_c+ -> Xi- pi+ pi+) = (0.453 +/- 0.096 +0.085-0.065) x 10^-3.

Charm counting in b decays

The inclusive production of charmed particles in Z → b b decays has been measured from the yield of D 0, D +, D s + and Λ c + decays in a sample of q q events with high b purity collected with the ALEPH detector from 1992 to 1995. From these measurements, adding the charmonia production rate and an estimate of the charmed strange baryon contribution, the average number of charm quarks per b decay is determined to be n c = 1.230 ± 0.036 ± 0.038 ± 0.053, where the uncertainties are due to statistics, systematic effects and branching ratios, respectively.

Search for charmed-strange baryons in experiment WA89

Abstract Experiment WA89 studies charmed-strange baryons produced by a 340 GeV/c hyperon beam. The Omega RICH detector is used for identification of daughter particles, especially of charged kaons, over a wide momentum range. Results on several decay modes of the charged baryons Ξc and Ω c are presented.

Charmed baryons with J=3/2.

The width of a recently discovered excited charmed-strange baryon, a candidate for a state $\Xi_c^*$ with spin 3/2, is calculated. In the absence of configuration mixing between the ground-state (spin-1/2) charmed-strange baryon $\Xi_c^{(a)}$ and the spin-1/2 state $\Xi_c^{(s)}$ lying about 95 MeV above it, one finds $\tilde \Gamma(\Xi^*_c \to \Xi_c^{(a)} \pi) = (3/4) \tilde \Gamma(\Xi^* \to \Xi \pi)$ and $\tilde \Gamma(\Xi^*_c \to \Xi_c^{(s)} \pi) = (1/4) \tilde \Gamma(\Xi^* \to \Xi \pi)$, where the tilde denotes the partial width with kinematic factors removed. Assuming a kinematic factor for P-wave decay of $p_{\rm cm}^3$, one predicts $\Gamma(\Xi^*_c \to \Xi_c^{(a)} \pi) = 2.3$ MeV, while the $\Xi^*_c \to \Xi_c^{(s)} \pi$ channel is closed. Some suggestions are given for detecting the $\Sigma_c^*$, the spin-3/2 charmed nonstrange baryon, and the $\Omega_c^*$, the spin-3/2 charmed doubly-strange baryon.

Measurement of the lifetime of the Xi c0.

A measurement of the lifetime of the charmed strange baryon Ξc0 is presented. The data were accumulated by the Fermilab high energy photoproduction experiment E687. The measurement has been made using 42±10 Ξc0→Ξ−π+ decays. The lifetime of the Ξc0 is measured to be 0.101−0.017+0.025±0.005 ps and its mass is measured to be 2462.1±3.1±1.4 MeV/c2.Received 28 December 1992DOI:https://doi.org/10.1103/PhysRevLett.70.2058©1993 American Physical Society

Search for the charmed strange baryon Ξ c + in neutron-proton interactions at √S ≈ 10 GeV

In this paper we present the results of a search for the charmed strange baryon Ξc+ in the final states Λ0π+π+K− and Ξ−π+π+. The experiment was performed using the magnetic spectrometer BIS-2 with a hydrogen target located in the neutron beam of the Serpukhov accelerator. A narrow peak in the Λ0π+π+K− state is observed at a mass of ≈2440 and possibly also of ≈2310 MeV/c2, corresponding to signals for the Ξc+ → Λ0π+π+K− and Ξc+ → Σ0π+π+K− (Σ0 → Λ0γ) decays respectively. The statistics obtained for the Ξ−π+π+ state is too low to make any conclusion.

Measurement of Ξ c production in e +e − annihilation at 10.5 GeV center-of-mass energy

Using the ARGUS detector at the e +e − storage ring DORIS II at DESY, we have observed production of the charmed-strange baryon Ξ c + and its neutral isospin partner, the Ξ c 0. The Ξ c + was reconstructed in the final state Ξ −π +π +, while the Ξ c 0 was seen in decay to Ξ −π + and Ξ −π +π +π −. The average Ξ c fragmentation spectrum has been determined, as well as the production cross section times branching ratio for each decay mode. The charged and neutral masses were measured to be 2465.1 ± 3.6 ± 1.9 MeV/ c 2 and 2472.1 ± 2.7 ± 1.6 MeV/ c 2 respectively, corresponding to a mass-splitting, M( Ξ c +) − M( Ξ c 0), of −7.0±4.5±2.2 MeV/ c 2.

First measurement of the lifetime of the charmed strange baryon Ξc0

We have observed four unambiguous decays of the charmed strange baryon Ξ c o in the NA32 experiment at CERN. Charge- coupled devices and silicon microstrip detectors were used to reconstruct the decay mode Ξ c o → pK − K∗ (892) o seen in events produced by the interaction of 230 GeV/ c negative poins and kaons on a copper target. We present the first measurement of the lifetime of the Ξ c o , together with a determination of its mass and production cross section. The resonant components of the Ξ c o decay are studied. We use our earlier measurement of the mass of the Ξ c + in the determination of the isospin mass splitting of the Ξ c states.

Measurement of the mass and lifetime of the charmed strange baryon Ξ+c

We have observed six unambiguous decays of the charmed strange baryon Ξ c + (or charge conjugate Ξ c −) in the 230 GeV/c negative pions or kaons on a copper target at the CERN SPS using silicon microstrip detectors and charge-coupled devices for vertex reconstruction. Three of them have been reconstructed through the decay chain Ξ c + → Ξ − π + π +, Ξ − → Λ 0 π −, Λ 0 → pπ − and the other three through the decay chain Ξ c + → Σ + K − π + → pπ 0. We present our measurements of the mass, lifetime and production cross-section of the Ξ c +, as well as of the branching ration for the two decay modes.

Observation of the charmed strange baryon Xi c0.

We present evidence from the CLEO detector for the charmed strange baryon ..gamma../sub c//sup 0/. It is seen in nonresonant e/sup +/e/sup -/ annihilations at ..sqrt..s of 10.5 GeV through its decay to ..gamma../sup -/..pi../sup +/. The measured ..gamma../sub c//sup 0/ mass is 2471 +- 3 +- 4 MeV/c/sup 2/.

Charm hadroproduction results from Fermilab E-400

Results are presented from Fermilab E-400 on the production of charmed baryons and mesons at a mean energy of 640 GeV. We show evidence for the charm-strange baryon, Ξ c +, and present our measurements of its mass, width, lifetime, cross section and relative branching fractions, and the A, ξ f , p t , and particle/antiparticle dependence of the state. We show evidence for both the Σ c ++ and Σ c 0, and present measurements of three mass differences, Σ c ++ − Σ c 0, Σ c 0 − Λ c +, and Σ c ++ − Λ c +. Measurements of the A dependence and particle/antiparticle ratios for Σ c production are also presented. We show preliminary results on the ratio of two decay modes of the D 0, D 0 → K +K − and D 0 → K 0 K 0 . The latter mode has not been previously observed.

Measurement of the lifetime of the charmed strange baryon A +

The lifetime of the charmed strange baryon A + has been determined in an experiment at the CERN SPS hyperon beam from the distribution of distances between production and decay of A + candidates of known momentum. The result is: τ = (4.8 −1.8 +2.9) × 10 −13 s .

Observation of a narrow state at 2.46 GeV/ c2 — a candidate for the charmed strange Baryon A +

A narrow state has been observed in the reaction Σ − + Be → ( ΛK − π + π +) + X in an experiment at the CERN SPS hyperon beam. At 2.46 GeV/ c 2 the effective ( ΛK − π + π +) mass distribution shows an excess of 82 events above a background estimated to be 147, corresponding to a statistical significance of more than 6 standard deviations. The positive charge of the observed final state, which has strangeness −2, suggests the interpretation as a Cabibbo favoured decay of the charmed strange baryon, A + [quark content (csu)]. The cross section times branching ratio is measured to be σ · B = (5.3 ± 2.0) μb/ (Be nucleus) for x > 0.6. The invariant production cross section is described by E d 3 σ/d p 3 ∞ (1 - x) (1.7±0.7) exp[−(1.1 −0.4 +0.7) p T 2].