Production asymmetry of D-s from 600 GeV/c Sigma(-) and pi(-) beam

The production of D-S(-) relative to D-S(+) as a function of x(F) with 600 GeV/c Sigma(-) beam is measured in the interval 0.15 < x(F) < 0.7 by the SELEX (E781) experiment at Fermilab. The integrated charge asymmetries with 600 GeV/c Sigma(-) beam (0.53 +/- 0.06) and pi(-) beam (0.06 +/- 0.11) are also compared. The results show the Sigma(-) beam fragments play a role in the production of D-S(-), as suggested by the leading quark model. (C) 2003 Elsevier Science B.V. All rights reserved

Measurement of the D-s(+/-) lifetime

We report a precise measurement of the D-s(+/-) meson lifetime. The data were taken by the SELEX experiment (E781) spectrometer using 600 GeV/c Sigma (-), pi (-) and p beams. The measurement has been done using 918 reconstructed D-s(+/-). The lifetime of the D-s(+/-) s is measured to be 472.5 +/- 17.2 +/- 6.6 fs, using K*(892)K-0(+/-) and phi pi (+/-) decay modes. The lifetime ratio of D-s(+/-) to D-0 is 1.145 +/- 0.049. (C) 2001 Elsevier Science B.V. All rights reserved

First observation of the doubly charmed baryon Xi(+)(cc)

We observe a signal for the doubly charmed baryon Xi(cc)(+) in the charged decay mode Xi(cc)(+)-->Lambda(c)(+)K(-)pi(+) in data from SELEX, the charm hadroproduction experiment at Fermilab. We observe an excess of 15.9 events over an expected background of 6.1+/-0.5 events, a statistical significance of 6.3sigma. The observed mass of this state is 3519+/-1 MeV/c(2). The Gaussian mass width of this state is 3 MeV/c(2), consistent with resolution; its lifetime is less than 33 fs at 90% confidence

First measurement of pi(-)e ->pi(-)e gamma pion virtual compton scattering

Pion virtual compton scattering (VCS) via the reaction pi(-)e-->pi(-)egamma was observed in the Fermilab E781 SELEX experiment. SELEX used a 600 GeV/c pi(-) beam incident on target atomic electrons, detecting the incident pi(-) and the final state pi(-), electron and gamma. Theoretical predictions based on chiral perturbation theory are incorporated into a Monte Carlo simulation of the experiment and are compared to the data. The number of reconstructed events (=9) and their distribution with respect to the kinematic variables (for the kinematic region studied) are in reasonable accord with the predictions. The corresponding pi(-) VCS experimental cross section is sigma=38.8+/-13 nb, in agreement with the theoretical expectation of sigma=34.7 nb

Hadronic production of Lambda c from 600 GeV/c pi(-), Sigma(-) and p beams

We present data from Fermilab experiment E781 (SELEX) on the hadroproduction asymmetry for (Lambda) over bar((c)) over bar compared to Lambda(c)(+) as a function of x(F), and on p(t)(2) distributions for Lambda(c)(+). These data were measured in the same apparatus using incident pi(-),Sigma(-) beams at 600 GeV/c and proton beam at 540 GeV/c. The asymmetry is studied as a function of x(F). In the forward hemisphere with x(F) greater than or equal to 0.2 both baryon beams exhibit very strong preference for producing charm baryons rather than charm antibaryons, while the pion beam asymmetry is much smaller. In this energy regime the results show that beam fragments play a major role in the kinematics of Lambda(c) formation, as suggested by the leading quark picture. (C) 2002 Published by Elsevier Science B.V

Upper limit on the decay Sigma(1385)(-) -> Sigma(-)gamma and cross section for gamma Sigma(-) -> Lambda pi(-)

Coherent Lambdapi(-) production on Pb of 600 GeV Sigma(-) hyperons has been studied with the SELEX facility at Fermilab. Using the Primakoff formalism, we set a 90% CL upper limit on the radiative decay width Gamma[Sigma(1385)(-) --> Sigma(-) gamma] Lambdapi(-) at roots approximate to 1.385 GeV to be 56 +/- 16 mub. Crown Copyright (C) 2004 Published by Elsevier B.V. All rights reserved

Observation of a narrow charm-strange meson D-sJ(+)(2632)-> D-s(+)eta and (DK+)-K-0

We report the first observation of a charm-strange meson D-sJ(+)(2632) at a mass of 2632.5+/-1.7 MeV/c(2) in data from SELEX, the charm hadro-production experiment E781 at Fermilab. This state is seen in two decay modes, D(s)(+)eta and (DK+)-K-0. In the D(s)(+)eta decay mode we observe a peak with 101 events over a combinatoric background of 54.9 events at a mass of 2635.4+/-3.3 MeV/c(2). There is a corresponding peak of 21 events over a background of 6.9 at 2631.5+/-2.0 MeV/c(2) in the decay mode (DK+)-K-0. The decay width of this state is <17 MeV/c(2) at 90% confidence level. The relative branching ratio Gamma((DK+)-K-0)/Gamma(D(s)(+)eta) is 0.14+/-0.06. The mechanism that keeps this state narrow is unclear. Its decay pattern is also unusual, being dominated by the D(s)(+)eta decay mode

Confirmation of the doubly charmed baryon Epsilon(+)(cc)(3520) via its decay to pD(+)K(-)

We observe a signal for the doubly charmed baryon Xi(cc)(+) in the decay mode Xi(cc)(+) -> pD(+)K(-) to complement the previous cc reported decay Xi(cc)(+) -> Lambda(c)(+)K(-)pi(+) in data from SELEX, the charm hadroproduction experiment at Fermilab. In this new decay mode we observe an excess of 5.62 events over a combinatoric background estimated by event mixing to be 1.38 +/- 0.13 events. The mixed background has Gaussian statistics, giving a signal significance of 4.8 sigma. The Poisson probability that a background fluctuation can produce the apparent signal is less than 6.4 x 10(-4). The observed mass of this state is 3518 +/- 3 MeV/c(2), consistent with the published result. Averaging the two results gives a mass of 3518.7 +/- 1.7 MeV/c(2). The observation of this new weak decay mode confirms the previous SELEX suggestion that this state is a double charm baryon. The relative branching ratio for these two modes is 0.36 +/- 0.21. (c) 2005 Elsevier B.V. All rights reserved

Measurement of the Sigma(-) charge radius by Sigma(-)-electron elastic scattering

The Sigma (-) mean squared charge radius has been measured in the space-like Q(2) range 0.035--0.105 GeV2/c(2) by elastic scattering of a Sigma (-) beam off atomic electrons. The measurement was per-formed with the SELEX (E781) spectrometer using the Fermilab hyperon beam at a mean energy of 610 GeV/c We obtain Sigma (-) =(0.61 +/- 0.12(stat.) +/- 0.09(syst.)) fm(2). The proton and pi (-) charge radii were measured as well and are consistent with results of other experiments. Our result agrees with the recently measured strong interaction radius of the Sigma (-). (C) 2001 Elsevier Science B.V. All rights reserved