Rubin-LSST

Abstract:

We report a measurement of the forward-backward charge asymmetry of electrons from W boson decays in pp̄ collisions at √s=1.96 TeV using a data sample of 170 pb^-1 collected by the Collider Detector at Fermilab. The asymmetry is measured as a function of electron rapidity and transverse energy and provides new input on the momentum fraction dependence of the u and d quark parton distribution functions within the proton. © 2005 The American Physical Society.

Abstract:

Using 180 pb ^-1 of data collected with the CDF II detector at the Tevatron, we measure the first two moments of the hadronic invariant mass-squared distribution in charmed semileptonic B decays. From these we determine the nonperturbative Heavy Quark Effective Theory parameters Λ and λ 1 used to relate the B meson semileptonic branching ratio to the CKM matrix element |V cb|. For a minimum lepton momentum of 0.7 GeV/c in the B rest frame we measure the first two moments of the D** → D ^(*)π component to be 〈m D** ²〉 = (5.83 ± 0.16 stat ± 0.08 syst) GeV ²/c ⁴ and 〈(m D** ² - 〈m D** ²〉) ²〉 = (1.30 ± 0.69 stat ± 0.22 syst) GeV ⁴/c ⁸. Combining these with the discrete mass terms from the D and D* mesons, we find the total moments to be 〈M Ξc ²〉 - m̄ D ² = (0.467 ± 0.038 stat ± 0.068 syst GeV ²/c ⁴ and 〈(M Ξc ² - 〈M Ξc ²〉) ²〉 = (1.05 ± 0.26 stat ± 0.13 syst) GeV ⁴/c ⁸, where m̄ D is the spin-averaged D mass. The systematic error is dominated by the uncertainties in the world-average branching ratios used to combine the D, D*, and D** contributions. The analysis makes no assumptions about the shape or resonant structure of the D** → D (*)π invariant mass distribution. © 2005 The American Physical Society.

Abstract:

We present a measurement of the tt̄ production cross section using events with one charged lepton and jets from pp̄ collisions at a center-of-mass energy of 1.96 TeV. In these events, heavy flavor quarks from top quark decay are identified with a secondary vertex tagging algorithm. From 162 pb^-1 of data collected by the Collider Detector at Fermilab, a total of 48 candidate events are selected, where 13.5 ± 1.8 events are expected from background contributions. We measure a tt̄ production cross section of 5.6-1.1^+1.2(stat.)-0.6^+0.9(syst.) pb. © 2005 The American Physical Society.

Abstract:

Using data recorded by the CLEO III detector at the Cornell electron storage ring (CESR), we have made measurements of some properties of the ∑c^*++ and ∑c^*0 charmed baryons. In particular: Γ(∑c^*++) = 14.4-1.5^+1.6 ± 1.4 MeV, M(∑c ^*++) - M(Λc⁺) = 231.5 ± 0.4 ± 0.3 MeV, Γ(∑c^*0) = 16.6 -1.7^+1.9 ± 1.4 MeV, M(∑c ^*0) -M(Λc⁺) = 231.4 ± 0.5 ± 0.3 MeV. © 2005 The American Physical Society.

Abstract:

We present a study of the stellar populations of galaxies in the cluster RX J0 152.7-1357 at a redshift of 0.83. The study is based on new high signal-to-noise ratio spectroscopy of 29 cluster members covering the wavelength range 5000-10000 Å, as well as r′i′z′ photometry of the cluster. We use scaling relations between the central velocity dispersions of the galaxies and their luminosities, Balmer line strengths, and various metal line strengths to parameterize the differences between the members of RX J0152.7-1357 and our low-redshift comparison sample. The luminosities of the RX J0152.7-1357 galaxies and the strengths of the higher order Balmer lines H γ and Rδ (for non-emission-line galaxies) appear to be in agreement with pure passive evolution of the stellar populations with a formation redshift Z form ≈ 4. However, the strengths of the D4000 indices and the metal indices do not support this interpretation. Compared with our low-redshift comparison sample, the metal indices (C4668, Fe4383, CN3883, G4300, and CN 2) show that at least half of the non-emission-line galaxies in RX J0152.7-1357 have an Q-element abundance ratio [a/Fe] of 0.2 dex higher, and about half of the galaxies have significantly lower metal content. X-ray data have previously shown that RX J0152.7-1357 is in the process of merging from two sub-clumps. We find that differences in stellar populations of the galaxies are associated with the location of the galaxies relative to the X-ray emission. The galaxies with weak C4668 and G4300, as well as galaxies for which weak [0 II] emission indicates a very recent star formation episode involving about 1% of the mass, are located in areas of low X-ray luminosity, on the outskirts of the two subclumps. It is possible that these galaxies are experiencing the effect of the cluster merger as (short) episodes of star formation, while the galaxies in the cores of the subclumps are unaffected by the merger. The spectroscopy of the RX JO 152.7-1357 galaxies shows for the first time galaxies in a rich cluster at intermediate redshift that cannot evolve passively into the present-day galaxy population in rich clusters. Additional physical processes may be at work, and we speculate that merging with infalling (disk) galaxies in which stars have formed over an extended period might produce the required reduction in [a/Fe]. However, the merging could not be accompanied by star formation involving a substantial mass fraction. We note that our conclusions, in part, rely on stellar population models for which the predictions of the indices in the rest-frame blue have not yet been tested extensively. © 2005. The American Astronomical Society. All rights reserved.