Nematic pairing from orbital-selective spin fluctuations in FeSe

FeSe is an intriguing iron-based superconductor. It presents an unusual nematic state without magnetism and can be tuned to increase the critical superconducting temperature. Recently it has been observed a noteworthy anisotropy of the superconducting gaps. Its explanation is intimately related to the understanding of the nematic transition itself. Here, we show that the spin-nematic scenario driven by orbital-selective spin fluctuations provides a simple scheme to understand both phenomena. The pairing mediated by anisotropic spin modes is not only orbital selective but also nematic, leading to stronger pair scattering across the hole and X electron pocket. The delicate balance between orbital ordering and nematic pairing points also to a marked k z dependence of the hole\u2013gap anisotropy

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

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

Radiative decay width of the a(2)(1320)(-) meson

Coherent pi (+)pi (-)pi (-) production in the interactions of a beam of 600GeV pi (-) mesons with C, Cu and Pb nuclei has been studied with the SELEX facility (Experiment E781 at Fermilab). The a(2)(1320) meson signal has been detected in the Coulomb (low q(2)) region. The Primakoff formalism used to extract radiative decay width of this meson yields Gamma = 284 +/- 25 +/- 25 keV, which is the most precise measurement to date. (C) 2001 Elsevier Science 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

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

Charm hadroproduction results from Selex

The SELEX experiment (E781) is 5-stage magnetic spectrometer for a high statistics study of hadroproduction of charm baryons out to large x(F) using 650 Gev Sigma (-), pi (-) and p beams. The main features of the spectrometer are: a high precision silicon vertex system, powerful particle identification provided by TRD and RICH, forward Lambda (s) decay spectrometer and 3-stage lead glass photon detector. An experiment overview and spectrometer features are shown. Reconstructed charm states and results on Lambda (c), D+ particles and antiparticles produced by Sigma (-), pi (-) and p beams at x(F) > 0.3 and asymmetry for Lambda (c) are presented