3,673 research outputs found
Double Bragg diffraction: A tool for atom optics
The use of retro-reflection in light-pulse atom interferometry under
microgravity conditions naturally leads to a double-diffraction scheme. The two
pairs of counterpropagating beams induce simultaneously transitions with
opposite momentum transfer that, when acting on atoms initially at rest, give
rise to symmetric interferometer configurations where the total momentum
transfer is automatically doubled and where a number of noise sources and
systematic effects cancel out. Here we extend earlier implementations for Raman
transitions to the case of Bragg diffraction. In contrast with the
single-diffraction case, the existence of additional off-resonant transitions
between resonantly connected states precludes the use of the adiabatic
elimination technique. Nevertheless, we have been able to obtain analytic
results even beyond the deep Bragg regime by employing the so-called "method of
averaging," which can be applied to more general situations of this kind. Our
results have been validated by comparison to numerical solutions of the basic
equations describing the double-diffraction process.Comment: 26 pages, 20 figures; minor changes to match the published versio
Self-alignment of a compact large-area atomic Sagnac interferometer
We report on the realization of a compact atomic Mach-Zehndertype Sagnac interferometer of 13.7 cm length, which covers an area of 19 mm(2) previously reported only for large thermal beam interferometers. According to Sagnac's formula, which holds for both light and atoms, the sensitivity for rotation rates increases linearly with the area enclosed by the interferometer. The use of cold atoms instead of thermal atoms enables miniaturization of Sagnac interferometers without sacrificing large areas. In comparison with thermal beams, slow atoms offer better matching of the initial beam velocity and the velocity with which the matter waves separate. In our case, the area is spanned by a cold atomic beam of 2.79m s(-1), which is split, deflected and combined by driving a Raman transition between the two hyperfine ground states of Rb-87 in three spatially separated light zones. The use of cold atoms requires a precise angular alignment and high wave front quality of the three independent light zones over the cloud envelope. We present a procedure for mutually aligning the beam splitters at the microradian level by making use of the atom interferometer itself in different configurations. With this method, we currently achieve a sensitivity of 6.1 x 10(-7) rad s(-1) Hz(-1/2).DFG/SFB/407EU/NESTEU/FINAQSEU/EuroquasarEU/IQSQUESTMax-Planck-GesellschaftINTERCAN networkUFA-DF
Phase-locking of two self-seeded tapered amplifier lasers
We report on the phase-locking of two diode lasers based on self-seeded
tapered amplifiers. In these lasers, a reduction of linewidth is achieved using
narrow-band high-transmission interference filters for frequency selection. The
lasers combine a compact design with a Lorentzian linewidth below 200 kHz at an
output power of 300 mW. We characterize the phase noise of the phase-locked
laser system and study its potential for coherent beam-splitting in atom
interferometers.Comment: 7 pages, 4 figure
Les Houches 2015: Physics at TeV Colliders Standard Model Working Group Report
This Report summarizes the proceedings of the 2015 Les Houches workshop on
Physics at TeV Colliders. Session 1 dealt with (I) new developments relevant
for high precision Standard Model calculations, (II) the new PDF4LHC parton
distributions, (III) issues in the theoretical description of the production of
Standard Model Higgs bosons and how to relate experimental measurements, (IV) a
host of phenomenological studies essential for comparing LHC data from Run I
with theoretical predictions and projections for future measurements in Run II,
and (V) new developments in Monte Carlo event generators.Comment: Proceedings of the Standard Model Working Group of the 2015 Les
Houches Workshop, Physics at TeV Colliders, Les Houches 1-19 June 2015. 227
page
The Quark Beam Function at NNLL
In hard collisions at a hadron collider the most appropriate description of
the initial state depends on what is measured in the final state. Parton
distribution functions (PDFs) evolved to the hard collision scale Q are
appropriate for inclusive observables, but not for measurements with a specific
number of hard jets, leptons, and photons. Here the incoming protons are probed
and lose their identity to an incoming jet at a scale \mu_B << Q, and the
initial state is described by universal beam functions. We discuss the
field-theoretic treatment of beam functions, and show that the beam function
has the same RG evolution as the jet function to all orders in perturbation
theory. In contrast to PDF evolution, the beam function evolution does not mix
quarks and gluons and changes the virtuality of the colliding parton at fixed
momentum fraction. At \mu_B, the incoming jet can be described perturbatively,
and we give a detailed derivation of the one-loop matching of the quark beam
function onto quark and gluon PDFs. We compute the associated NLO Wilson
coefficients and explicitly verify the cancellation of IR singularities. As an
application, we give an expression for the next-to-next-to-leading logarithmic
order (NNLL) resummed Drell-Yan beam thrust cross section.Comment: 54 pages, 9 figures; v2: notation simplified in a few places, typos
fixed; v3: journal versio
Shape-Function Effects and Split Matching in B-> Xs l+ l-
We derive the triply differential spectrum for the inclusive rare decay B ->
Xs l+ l- in the shape function region, in which Xs is jet-like with . Experimental cuts make this a relevant region. The
perturbative and non-perturbative parts of the matrix elements can be defined
with the Soft-Collinear Effective Theory, which is used to incorporate alphas
corrections consistently. We show that, with a suitable power counting for the
dilepton invariant mass, the same universal jet and shape functions appear as
in B-> Xs gamma and B-> Xu l nu decays. Parts of the usual alphas(m_b)
corrections go into the jet function at a lower scale, and parts go into the
non-perturbative shape function. For B -> Xs l+ l-, the perturbative series in
alphas are of a different character above and below mu=mb. We introduce a
``split matching'' method that allows the series in these regions to be treated
independently.Comment: 33 pages; journal versio
Jet Substructure at the Tevatron and LHC: New results, new tools, new benchmarks
In this report we review recent theoretical progress and the latest
experimental results in jet substructure from the Tevatron and the LHC. We
review the status of and outlook for calculation and simulation tools for
studying jet substructure. Following up on the report of the Boost 2010
workshop, we present a new set of benchmark comparisons of substructure
techniques, focusing on the set of variables and grooming methods that are
collectively known as "top taggers". To facilitate further exploration, we have
attempted to collect, harmonise, and publish software implementations of these
techniques.Comment: 53 pages, 17 figures. L. Asquith, S. Rappoccio, C. K. Vermilion,
editors; v2: minor edits from journal revision
Evidence for the η_b(1S) Meson in Radiative Υ(2S) Decay
We have performed a search for the η_b(1S) meson in the radiative decay of the Υ(2S) resonance using a sample of 91.6 × 10^6 Υ(2S) events recorded with the BABAR detector at the PEP-II B factory at the SLAC National Accelerator Laboratory. We observe a peak in the photon energy spectrum at E_γ = 609.3^(+4.6)_(-4.5)(stat)±1.9(syst) MeV, corresponding to an η_b(1S) mass of 9394.2^(+4.8)_(-4.9)(stat) ± 2.0(syst) MeV/c^2. The branching fraction for the decay Υ(2S) → γη_b(1S) is determined to be [3.9 ± 1.1(stat)^(+1.1)_(-0.9)(syst)] × 10^(-4). We find the ratio of branching fractions B[Υ(2S) → γη_b(1S)]/B[Υ(3S) → γη_b(1S)]= 0.82 ± 0.24(stat)^(+0.20)_(-0.19)(syst)
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