2,666 research outputs found

    The CP-violating asymmetry in K_L -> pi+ pi- e+ e-

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    We update the theoretical analysis of the CP-violating asymmetry in the decay K_L -> pi+ pi- e+ e-, relying on chiral perturbation theory and on the most recent phenomenological information. With the experimentally determined magnetic amplitude and branching ratio as input, the asymmetry can be calculated with good accuracy. The theoretical interpretation of the sign of the asymmetry is discussed.Comment: 11 page

    CP Violation and Arrows of Time Evolution of a Neutral KK or BB Meson from an Incoherent to a Coherent State

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    We study the evolution of a neutral KK meson prepared as an incoherent equal mixture of K0K^0 and K0ˉ\bar{K^0}. Denoting the density matrix by \rho(t) = {1/2} N(t) [\1 + \vec{\zeta}(t) \cdot \vec{\sigma} ] , the norm of the state N(t)N(t) is found to decrease monotonically from one to zero, while the magnitude of the Stokes vector ζ(t)|\vec{\zeta}(t)| increases monotonically from zero to one. This property qualifies these observables as arrows of time. Requiring monotonic behaviour of N(t)N(t) for arbitrary values of γL,γS\gamma_L, \gamma_S and Δm\Delta m yields a bound on the CP-violating overlap δ=KLKS\delta = \braket{K_L}{K_S}, which is similar to, but weaker than, the known unitarity bound. A similar requirement on ζ(t)|\vec{\zeta}(t)| yields a new bound, δ2<1/2(ΔγΔm)sinh(3π4ΔγΔm)\delta^2 < {1/2} (\frac{\Delta \gamma}{\Delta m}) \sinh (\frac{3\pi}{4} \frac{\Delta \gamma}{\Delta m}) which is particularly effective in limiting the CP-violating overlap in the B0B^0-B0ˉ\bar{B^0} system. We obtain the Stokes parameter ζ3(t)\zeta_3(t) which shows how the average strangeness of the beam evolves from zero to δ\delta. The evolution of the Stokes vector from ζ=0|\vec{\zeta}| = 0 to ζ=1|\vec{\zeta}| = 1 has a resemblance to an order parameter of a system undergoing spontaneous symmetry breaking.Comment: 13 pages, 6 figures. Inserted conon "." in title; minor change in text. To appear in Physical review

    Understanding the Forward Muon Deficit in Coherent Pion Production

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    For any inelastic process v+I+Fv_{\ell} + I \to \ell^- + F with m=0m_{\ell} = 0, the cross section at θ=0\theta_{\ell} = 0 is given by Adler's PCAC theorem. Inclusion of the lepton mass has a dynamical effect (``PCAC-screening'') caused by interference of spin-zero (π+\pi^+) and spin-one exchanges. This effect may be relevant to the forward suppression reported in recent experiments.Comment: 3 pages, 2 figures, presented at NuInt07, Fermilab, may 31 - june 3 200

    CMB Lensing Power Spectrum Biases from Galaxies and Clusters using High-angular Resolution Temperature Maps

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    The lensing power spectrum from cosmic microwave background (CMB) temperature maps will be measured with unprecedented precision with upcoming experiments, including upgrades to ACT and SPT. Achieving significant improvements in cosmological parameter constraints, such as percent level errors on sigma_8 and an uncertainty on the total neutrino mass of approximately 50 meV, requires percent level measurements of the CMB lensing power. This necessitates tight control of systematic biases. We study several types of biases to the temperature-based lensing reconstruction signal from foreground sources such as radio and infrared galaxies and the thermal Sunyaev-Zel'dovich effect from galaxy clusters. These foregrounds bias the CMB lensing signal due to their non-Gaussian nature. Using simulations as well as some analytical models we find that these sources can substantially impact the measured signal if left untreated. However, these biases can be brought to the percent level if one masks galaxies with fluxes at 150 GHz above 1 mJy and galaxy clusters with masses above M_vir = 10^14 M_sun. To achieve such percent level bias, we find that only modes up to a maximum multipole of l_max ~ 2500 should be included in the lensing reconstruction. We also discuss ways to minimize additional bias induced by such aggressive foreground masking by, for example, exploring a two-step masking and in-painting algorithm.Comment: 14 pages, 14 figures, to be submitted to Ap

    Magnetic and axial vector form factors as probes of orbital angular momentum in the proton

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    We have recently examined the static properties of the baryon octet (magnetic moments and axial vector coupling constants) in a generalized quark model in which the angular momentum of a polarized nucleon is partly spin Sz\langle S_z \rangle and partly orbital Lz\langle L_z \rangle. The orbital momentum was represented by the rotation of a flux-tube connecting the three constituent quarks. The best fit is obtained with Sz=0.08±0.15\langle S_z \rangle = 0.08\pm 0.15, Lz=0.42±0.14\langle L_z \rangle = 0.42\pm 0.14. We now consider the consequences of this idea for the q2q^2-dependence of the magnetic and axial vector form factors. It is found that the isovector magnetic form factor GMisovec(q2)G_M^{\mathrm{isovec}}(q^2) differs in shape from the axial form factor FA(q2)F_A(q^2) by an amount that depends on the spatial distribution of orbital angular momentum. The model of a rigidly rotating flux-tube leads to a relation between the magnetic, axial vector and matter radii, r2mag=fspinr2axial+52forbr2matt\langle r^2 \rangle_{\mathrm{mag}} = f_{\mathrm{spin}} \langle r^2 \rangle_{\mathrm{axial}} + \frac{5}{2} f_{\mathrm{orb}} \langle r^2 \rangle_{\mathrm{matt}}, where forb/fspin=13Lz/GAf_{\mathrm{orb}}/ f_{\mathrm{spin}} = \frac{1}{3}\langle L_z \rangle / G_A, fspin+forb=1f_{\mathrm{spin}} + f_{\mathrm{orb}} = 1. The shape of FA(q2)F_A(q^2) is found to be close to a dipole with MA=0.92±0.06M_A = 0.92\pm 0.06 GeV.Comment: 18 pages, 5 ps-figures, uses RevTe

    Baryon Magnetic Moments and Proton Spin: A Model with Collective Quark Rotation

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    We analyse the baryon magnetic moments in a model that relates them to the parton spins Δu\Delta u, Δd\Delta d, Δs\Delta s, and includes a contribution from orbital angular momentum. The specific assumption is the existence of a 3-quark correlation (such as a flux string) that rotates with angular momentum Lz\langle L_z \rangle around the proton spin axis. A fit to the baryon magnetic moments, constrained by the measured values of the axial vector coupling constants a(3)=F+Da^{(3)}=F+D, a(8)=3FDa^{(8)}=3F-D, yields Sz=0.08±0.13\langle S_z \rangle = 0.08 \pm 0.13, Lz=0.39±0.09\langle L_z \rangle = 0.39 \pm 0.09, where the error is a theoretical estimate. A second fit, under slightly different assumptions, gives Lz=0.37±0.09\langle L_z \rangle = 0.37 \pm 0.09, with no constraint on Sz\langle S_z \rangle. The model provides a consistent description of axial vector couplings, magnetic moments and the quark polarization Sz\langle S_z \rangle measured in deep inelastic scattering. The fits suggest that a significant part of the angular momentum of the proton may reside in a collective rotation of the constituent quarks.Comment: 16 pages, 3 ps-figures, uses RevTeX. Abstract, Sec. II, III and IV have been expande

    Pitting in Aluminum Thin Films Supersaturation and Effects of Dichromate Ions

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    The growth of pits in 209 nm thick Al films in chloride solutions with and without dichromate ions was examined using image analysis of the growing pits to determine pit current density. In pure chloride solutions, the pit current density decreased at high potentials after reaching a maximum value, and then was almost independent of applied potential. A hysteresis in the pit current density-potential behavior was observed during downward stepping of the potential from high values. This is a result of a combination of supersaturation of the pit electrolyte followed by salt film formation, and changes in mass transport from hydrogen bubbles that increase convection and lift the remnant passive film away from the dissolving surface. In solutions containing dichromate ions, the corrosion and repassivation potentials shifted in the noble direction, and rather large metastable pits formed at the open circuit. A large concentration of dichromate ions was needed to inhibit pit growth. In dichromate solutions, subsequent pit growth at higher potentials often initiated at the edge of the open-circuit pits. The rate of pit growth was lower for these pits because the remnant passive film layer was not easily lifted up at these sites, and thus created a barrier for mass transport away from the dissolving pit edge.This work was supported by Major H. DeLong at the United States Air Force Office of Scientific Research under contract F49620-96-0042

    T-odd correlations in charged Kl4 decays

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    We analyse the sensitivity to physics beyond the SM of T-odd correlations in K4K_{\ell 4} decays, which do not involve the lepton polarization. We show that a combined analysis of Kμ4+K^+_{\mu 4} and Kμ4K^-_{\mu 4} decays can lead to new constraints about CP violation in ΔS=1\Delta S=1 charged-current interactions, complementary to those obtained from the transverse muon polarization in Kμ3K_{\mu 3} and of comparable accuracy.Comment: 6 pages (LaTeX

    Oxidation of Zr-2.5 Nb Nuclear Reactor Pressure Tubes A New Model

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    The corrosion and associated deuterium (D) uptake of Zr alloy nuclear reactor pressure tubes have been studied for over 40 years. Zircaloy tubes exhibit rapid D ingress after a period of in-reactor exposure, and have been replaced with tubes fabricated from the more resistant Zr-2.5 wt % Nb alloy. Recently, however, a small percentage of Zr-2.5 Nb tubes have been found to contain high D contents. There is currently no clear understanding of the mechanism for this increased D uptake, and concern exists that an increasing number of high-D tubes will develop with time. A new model for Zr-2.5 Nb corrosion is presented in this paper. The rate of corrosion is shown to be dependent on the rate of transformation of the protective inner oxide layer (closer to the metal) to a porous outer layer. The mechanism of this transformation is not known and should be the subject of future investigations. It is assumed in the model that zirconia chemically dissolves into the solution at the pore bottom. The rate of this dissolution reaction depends on the local pH, which increases if there is a buildup of deuteroxyl ions generated in the cathodic part of the Zr corrosion reaction. A mathematical description of this model, containing several parameters with unknown values, is presented. Assigning certain values to these parameters results in predictions of oxide formation (and thus D buildup) that correspond well with observations.Support of this work by the Atomic Energy Control Board under AECB project no. 2.349.1 is gratefully acknowledged

    Monitoring the premalignant potential of Barrett's oesophagus'.

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    The landscape for patients with Barrett's oesophagus (BE) has changed significantly in the last decade. Research and new guidelines have helped gastroenterologists to better identify those patients with BE who are particularly at risk of developing oesophageal adenocarcinoma. In parallel, developments in endoscopic image enhancement technology and optical biopsy techniques have improved our ability to detect high-risk lesions. Once these lesions have been identified, the improvements in minimally invasive endoscopic therapies has meant that these patients can potentially be cured of early cancer and high-risk dysplastic lesions without the need for surgery, which still has a significant morbidity and mortality. The importance of reaching an accurate diagnosis of BE remains of paramount importance. More work is needed, however. The vast majority of those undergoing surveillance for their BE do not progress towards cancer and thus undergo a regular invasive procedure, which may impact on their psychological and physical well-being while incurring significant cost to the health service. New work that explores cheaper endoscopic or non-invasive ways to identify the at-risk individual provides exciting avenues for research. In future, the diagnosis and monitoring of patients with BE could move away from hospitals and into primary care
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