7,958 research outputs found
The inclusive reaction pp=pX at the CERN ISR
Experiments at the CERN ISR have given evidence for proton single-dissociation processes where the missing mass of the system X, measured on the proton which is observed in the reaction p + p â p + X, presents a distribution extending up to large values , in the 10 GeV range. These processes globally account for âŒ15% of the inelastic p-p cross section. Evidence for such a distinct class of inelastic phenomena is also provided by long-range rapidity correlations and clustering. The nature of these processes appears to be predominantly diffractive. The physics which emerges from ISR observations is discussed , together with a presentation of present and planned lines of experimental investigation at the ISR
Associated central exclusive production of charged Higgs bosons
We propose central exclusive production of a charged Higgs boson in
association with a W boson as a possible signature of certain types of extended
Higgs sectors. We calculate the cross section and find that the rate at the LHC
could be large enough to allow observation in some models with two Higgs
doublets, where the charged Higgs and at least one of the neutral scalars can
be light enough. We use the two-Higgs doublet model as a prototype and consider
two distinct regions of parameter space, but we also briefly discuss the
prospects for the next-to-minimal supersymmetric standard model, where the
charged Higgs may very well be quite light.Comment: 9 pages, 5 figures. Minor changes, references added. Version to
appear in PR
Quartz Cherenkov Counters for Fast Timing: QUARTIC
We have developed particle detectors based on fused silica (quartz) Cherenkov
radiators read out with micro-channel plate photomultipliers (MCP-PMTs) or
silicon photomultipliers (SiPMs) for high precision timing (Sigma(t) about
10-15 ps). One application is to measure the times of small angle protons from
exclusive reactions, e.g. p + p - p + H + p, at the Large Hadron Collider, LHC.
They may also be used to measure directional particle fluxes close to external
or stored beams. The detectors have small areas (square cm), but need to be
active very close (a few mm) to the intense LHC beam, and so must be radiation
hard and nearly edgeless. We present results of tests of detectors with quartz
bars inclined at the Cherenkov angle, and with bars in the form of an "L" (with
a 90 degree corner). We also describe a possible design for a fast timing
hodoscope with elements of a few square mm.Comment: 24 pages, 14 figure
t' at the LHC: the physics of discovery
A search for a fourth family at the LHC is presently a low priority, but we
argue that an effective search can be conducted early with only a few inverse
femtobarns of data. We discuss a method based on invariant masses of single
jets for identifying the 's originating from heavy quark decays. This can
significantly increase signal to background in the reconstruction of the
mass. We also study the various types of physics that can impact the background
estimate, most notably higher order effects, initial state radiation, and
models of the underlying event.Comment: 16 pages, 12 figures, small improvements, version to appear in JHE
Limb-darkening measurements for a cool red giant in microlensing event OGLE 2004-BLG-482
Aims: We present a detailed analysis of OGLE 2004-BLG-482, a relatively
high-magnification single-lens microlensing event which exhibits clear
extended-source effects. These events are relatively rare, but they potentially
contain unique information on the stellar atmosphere properties of their source
star, as shown in this study. Methods: Our dense photometric coverage of the
overall light curve and a proper microlensing modelling allow us to derive
measurements of the OGLE 2004-BLG-482 source star's linear limb-darkening
coefficients in three bands, including standard Johnson-Cousins I and R, as
well as in a broad clear filter. In particular, we discuss in detail the
problems of multi-band and multi-site modelling on the expected precision of
our results. We also obtained high-resolution UVES spectra as part of a ToO
programme at ESO VLT from which we derive the source star's precise fundamental
parameters. Results: From the high-resolution UVES spectra, we find that OGLE
2004-BLG-482's source star is a red giant of MK type a bit later than M3, with
Teff = 3667 +/- 150 K, log g = 2.1 +/- 1.0 and an assumed solar metallicity.
This is confirmed by an OGLE calibrated colour-magnitude diagram. We then
obtain from a detailed microlensing modelling of the light curve linear
limb-darkening coefficients that we compare to model-atmosphere predictions
available in the literature, and find a very good agreement for the I and R
bands. In addition, we perform a similar analysis using an alternative
description of limb darkening based on a principal component analysis of ATLAS
limb-darkening profiles, and also find a very good agreement between
measurements and model predictions.Comment: Accepted in A&
Probing the atmosphere of the bulge G5III star OGLE-2002-BUL-069 by analysis of microlense H alpha line
We discuss high-resolution, time-resolved spectra of the caustic exit of the
binary microlensing event OGLE 2002-BUL-69 obtained with UVES on the VLT. The
source star is a G5III giant in the Galactic Bulge. During such events, the
source star is highly magnified, and a strong differential magnification around
the caustic resolves its surface. Using an appropriate model stellar atmosphere
generated by the NextGEN code we obtained a model light curve for the caustic
exit and compared it with a dense set of photometric observations obtained by
the PLANET microlensing follow up network. We further compared predicted
variations in the H alpha equivalent width with those measured from our
spectra. While the model and observations agree in the gross features, there
are discrepancies suggesting shortcomings in the model, particularly for the H
alpha line core, where we have detected amplified emission from the stellar
chromosphere as the source star's trailing limb exited the caustic. This
achievement became possible by the provision of the OGLE-III Early Warning
System, a network of small telescopes capable of nearly-continuous
round-the-clock photometric monitoring, on-line data reduction, daily
near-real-time modelling in order to predict caustic crossing parameters, and a
fast and efficient response of a 8m-class telescope to a
``Target-Of-Opportunity'' observation request.Comment: 4 pages Latex, 3 figures, accepted for publication to astronomy and
astrophysics letter
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Environmentally stable black phosphorus saturable absorber for ultrafast laser
Abstract
Black phosphorus (BP) attracts huge interest in photonic and optoelectronic applications ranging from passive switch for ultrafast lasers to photodetectors. However, the instability of chemically unfunctionalized BP in ambient environment due to oxygen and moisture remains a critical barrier to its potential applications. Here, the parylene-C layer was used to protect inkjet-printed BP-saturable absorbers (BP-SA), and the efficacy of this passivation layer was demonstrated on the stable and continuous operation of inkjet-printed BP-SA in harsh environmental conditions. BP-SA was integrated in an erbium-doped ring laser cavity and immersed in water at ~60°C during operation for investigation. Mode-locked pulses at ~1567.3 nm with ~538 fs pulse width remained stable for >200 h. The standard deviation of spectral width, central wavelength, and pulse width were 0.0248 nm, 0.0387 nm, and 2.3 fs, respectively, in this period, underscoring the extreme stability of BP-SA against high temperature and humidity. This approach could enable the exploitation of BP-based devices for photonic applications when operating under adverse environmental conditions.This work was supported by the National Natural Science Foundation of China (grants 51778030 and 51978024, Funder Id: http:// dx.doi.org/10.13039/501100001809) and EPSRC (grant EP/L016087/1, Funder Id: http://dx.doi. org/10.13039/501100000266)
Heavy MSSM Higgs Bosons at CMS: "LHC wedge" and Higgs-Mass Precision
The search for MSSM Higgs bosons will be an important goal at the LHC. In
order to analyze the search reach of the CMS experiment for the heavy neutral
MSSM Higgs bosons, we combine the latest results for the CMS experimental
sensitivities based on full simulation studies with state-of-the-art
theoretical predictions of MSSM Higgs-boson properties. The experimental
analyses are done assuming an integrated luminosity of 30 or 60 fb^-1. The
results are interpreted as 5 \si discovery contours in MSSM M_A-tan_beta
benchmark scenarios. Special emphasis is put on the variation of the Higgs
mixing parameter mu. While the variation of mu can shift the prospective
discovery reach (and correspondingly the ``LHC wedge'' region) by about Delta
tan_beta= 10, the discovery reach is rather stable with respect to the impact
of other supersymmetric parameters. Within the discovery region we analyze the
accuracy with which the masses of the heavy neutral Higgs bosons can be
determined. An accuracy of 1-4% should be achievable, depending on M_A and
tan_beta.Comment: Talk given by G.W. at EPS07 (Manchester, July 2007) and talk given by
S.H. at SUSY07 (Karlsruhe, July 2007). 4 pages, 2 figure
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