495 research outputs found
Production and FCNC decay of supersymmetric Higgs bosons into heavy quarks in the LHC
We analyze the production and subsequent decay of the neutral MSSM Higgs
bosons (h = h^0, H^0, A^0) mediated by flavor changing neutral currents (FCNC)
in the LHC collider. We have computed the h-production cross-section times the
FCNC branching ratio, \sigma(pp -> h -> qq') = \sigma(pp -> h) B(h -> qq'), in
the LHC focusing on the strongly-interacting FCNC sector. Here qq' is an
electrically neutral pair of quarks of different flavors, the dominant modes
being those containing a heavy quark: tc or bs. We determine the maximum
production rates for each of these modes and identify the relevant regions of
the MSSM parameter space, after taking into account the severe restrictions
imposed by low energy FCNC processes. The analysis of \sigma(pp -> h -> qq')
singles out regions of the MSSM parameter space different from those obtained
by maximizing only the branching ratio, due to non-trivial correlations between
the parameters that maximize/minimize each isolated factor. The production
rates for the bs channel can be huge for a FCNC process (0.1-1 pb), but its
detection can be problematic. The production rates for the tc channel are more
modest (10^{-3}-10^{-2} pb), but its detection should be easier due to the
clear-cut top quark signature. A few thousand tc events could be collected in
the highest luminosity phase of the LHC, with no counterpart in the SM.Comment: 25 pages, 9 figures, 2 tables, LaTeX 2e. Typos corrected. Version to
appear in JHE
Characterization of the known T type dwarfs towards the Sigma Orionis cluster
(Abridged) A total of three T type candidates (SOri70, SOri73, and
SOriJ0538-0213) lying in the line of sight towards Sigma Orionis were
characterized by means of near-infrared photometric, astrometric, and
spectroscopic studies. H-band methane images were collected for all three
sources and an additional sample of 15 field T type dwarfs using LIRIS/WHT.
J-band spectra of resolution of ~500 were obtained for SOriJ0538-0213 with
ISAAC/VLT, and JH spectra of resolution of ~50 acquired with WFC3/HST were
employed for the spectroscopic classification of SOri70 and 73. Proper motions
with a typical uncertainty of +/-3 mas/yr and a time interval of ~7-9 yr were
derived. Using the LIRIS observations of the field T dwarfs, we calibrated this
imager for T spectral typing via methane photometry. The three SOri objects
were spectroscopically classified as T4.5+/-0.5 (SOri73), T5+/-0.5
(SOriJ0538-0213), and T7 (SOri70). The similarity between the
observed JH spectra and the methane colors and the data of field ultra-cool
dwarfs of related classifications suggests that SOri70, 73, and
SOriJ053804.65-021352.5 do not deviate significantly in surface gravity in
relation to the field. Additionally, the detection of KI at ~1.25 microns in
SOriJ0538-0213 points to a high-gravity atmosphere. Only the K-band reddish
nature of SOri70 may be consistent with a low gravity atmosphere. The proper
motions of SOri70 and 73 are measurable and are larger than that of the cluster
by >3.5 sigma. The proper motion of SOriJ0538-0213 is consistent with a null
displacement. These observations suggest that none of the three T dwarfs are
likely Sigma Orionis members, and that either planetary-mass objects with
masses below ~4 MJup may not exist free-floating in the cluster or they may lie
at fainter near-infrared magnitudes than those of the targets (this is H>20.6
mag), thus remaining unidentified to date.Comment: Accepted for publication in A&A (2014), corrected typo
Confirming the least massive members of the Pleiades star cluster
We present optical photometry (i- and Z-band) and low-resolution spectroscopy
(640-1015 nm) of very faint candidate members (J = 20.2-21.2 mag) of the
Pleiades star cluster (120 Myr). The main goal is to address their cluster
membership via photometric, astrometric, and spectroscopic studies, and to
determine the properties of the least massive population of the cluster through
the comparison of the data with younger and older spectral counterparts and
state-of-the art model atmospheres. We confirm three bona-fide Pleiades members
that have extremely red optical and infrared colors, effective temperatures of
~1150 K and ~1350 K, and masses in the interval 11-20 Mjup, and one additional
likely member that shares the same motion as the cluster but does not appear to
be as red as the other members with similar brightness. This latter object
requires further near-infrared spectroscopy to fully address its membership in
the Pleiades. The optical spectra of two bona-fide members were classified as
L6-L7 and show features of KI, a tentative detection of CsI, hydrides and water
vapor with an intensity similar to high-gravity dwarfs of related
classification despite their young age. The properties of the Pleiades L6-L7
members clearly indicate that very red colors of L dwarfs are not a direct
evidence of ages younger than ~100 Myr. We also report on the determination of
the bolometric corrections for the coolest Pleiades members. These data can be
used to interpret the observations of the atmospheres of exoplanets orbiting
stars.Comment: Accepted for publication in MNRAS (17 pages
ST Quality Working Group
When CERN engages contractors or outside enterprises for supply and service contracts, a Quality certification is requested. CERN itself has no global certification. Nor are quality assurance systems well understood by the majority of CERN staff. This has not precluded successful activity but it is felt that a structured approach would have some benefits: elimination of occasional accelerator perturbations, improved documentation, efficient use of existing resources, enhanced sharing of experience and knowledge, avoidance of improper handover periods when staff leave CERN. In some cases talented staff spend too much time doing remedial jobs when they are capable of achieving much more. The ST quality working group was formed to address these problems. The goal of this quality working group is to help ST division maintain and continuously improve the quality of its services and operations, and give confidence to ST staff and clients that the requirements for quality are being fulfilled, maintained and improved. Since the working group was formed, the needs of the ST division have changed, thus necessitating a new Quality structure as described in this document
Search and characterization of T-type planetary mass candidates in the sigma Orionis cluster
(Abridged) We aim to: i) confirm the presence of methane absorption in S Ori
73 (a T-type member candidate of the sig Orionis cluster, 3 Myr, 352 pc)
through methane imaging; ii) study S Ori 70 and 73 cluster membership via
photometric colors and accurate proper motion analysis; iii) perform a new
search to identify additional T-type sig Orionis member candidates with likely
masses below 7 Mjup. We obtained HAWK-I (VLT) J, H, and CH4off photometry of an
area of 119.15 sq. arcmin in sig Orionis down to Jcomp = 21.7 and Hcomp = 21
mag. Near-infrared data were complemented with optical photometry using images
acquired with OSIRIS (GTC) and VISTA as part of the VISTA Orion survey. We
derived proper motions by comparison of the new HAWK-I and VISTA images with
published near-infrared data taken 3.4 - 7.9 yr ago. S Ori 73 has a red
H-CH4off color indicating methane absorption in the H-band and a spectral type
of T4 +/- 1. S Ori 70 displays a redder methane color than S Ori 73 in
agreement with its latter spectral classification. Our proper motion
measurements are larger than the motion of sig Orionis, rendering S Ori 70 and
73 cluster membership uncertain. We identified one new photometric candidate
with J = 21.69 +/- 0.12 mag and methane color consistent with spectral type
greater than T8. S Ori 73 has colors similar to those of T3-T5 field dwarfs,
which in addition to its high proper motion suggests that it is probably a
field dwarf located at 170-200 pc. The origin of S Ori 70 remains unclear: it
can be a field, foreground mid- to late-T free-floating dwarf with peculiar
colors, or an orphan planet ejected through strong dynamical interactions from
sig Orionis or from a nearby star-forming region in Orion.Comment: Accepted for publication in A&
Trigonometric parallaxes of young field L dwarfs
(Abridged) We aim to determine the trigonometric parallaxes and proper
motions of a sample of ten field L0-L5 dwarfs with spectroscopic evidence for
low-gravity atmospheres. We obtained J and Ks imaging data using 2-4-m class
telescopes with a typical cadence of one image per month between 2010 January
and 2012 December. We also obtained low resolution optical spectra (R~300,
500-1100 nm) using the 10-m GTCs to assess the presence of lithium absorption
in four targets and confirm their young age. Trigonometric parallaxes and
proper motions were derived to typical accuracies of 1 mas and +/-10 mas/yr.
All ten L dwarfs have large motions, and are located at distances between 9 and
47 pc. They lie above and on the sequence of field dwarfs in the absolute J and
K_s magnitude versus spectral type and luminosity versus Teff diagrams,
implying ages similar to or smaller than those typical of the field. The
detection of atomic lithium in the atmosphere of 2MASS J00452143+1634446 is
reported for the first time. Three dwarfs have locations in the HR diagram
indicative of old ages and high masses consistent with the observed lithium
depletion previously published. We did not find evidence for the presence of
astrometric companions with minimum detectable masses typically >=25 Mjup and
face-on, circular orbits with periods between 60-90 d and 3 yr around eight
targets. The astrometric and spectroscopic data indicate that about 60-70% of
the field L-type dwarfs in our sample with evidence for low-gravity atmospheres
are indeed young-to-intermediate-age brown dwarfs of the solar neighborhood
with expected ages and masses in the intervals 10-500 Myr and 11-45 Mjup. The
peaked-shape of the H-band spectra of L dwarfs, a signpost of youth, appears to
be present up to ages of 120-500 Myr and intermediate-to-high gravities.Comment: Accepted for publication in A&
Using binary statistics in Taurus-Auriga to distinguish between brown dwarf formation processes
Whether BDs form as stars through gravitational collapse ("star-like") or BDs
and some very low-mass stars constitute a separate population which form
alongside stars comparable to the population of planets, e.g. through
circumstellar disk ("peripheral") fragmentation, is one of the key questions of
the star-formation problem. For young stars in Taurus-Auriga the binary
fraction is large with little dependence on primary mass above ~0.2Msun, while
for BDs it is <10%. We investigate a case in which BDs in Taurus formed
dominantly through peripheral fragmentation. The decline of the binary
frequency in the transition region between star-like and peripheral formation
is modelled. A dynamical population synthesis model is employed in which
stellar binary formation is universal. Peripheral objects form separately in
circumstellar disks with a distinctive initial mass function (IMF), own orbital
parameter distributions for binaries and a low binary fraction. A small amount
of dynamical processing of the stellar component is accounted for as
appropriate for the low-density Taurus-Auriga embedded clusters. The binary
fraction declines strongly between the mass-limits for star-like and peripheral
formation. The location of characteristic features and the steepness depend on
these mass-limits. Such a trend might be unique to low density regions hosting
dynamically unprocessed binary populations. The existence of a strong decline
in the binary fraction -- primary mass diagram will become verifiable in future
surveys on BD and VLMS binarity in the Taurus-Auriga star forming region. It is
a test of the (non-)continuity of star formation along the mass-scale, the
separateness of the stellar and BD populations and the dominant formation
channel for BDs and BD binaries in regions of low stellar density hosting
dynamically unprocessed populations.Comment: accepted for publication in A&A, 11 pages, 4 figures, 1 tabl
Keck NIRC Observations of Planetary-mass Candidate Members in the sigma Orionis Open Cluster
We present K-band photometry and low-resolution near-infrared spectroscopy
from 1.44 to 2.45 micron of isolated planetary-mass candidate members in the
sigma Orionis cluster found by Zapatero Osorio et al. The new data have been
obtained with NIRC at the Keck I telescope. All of our targets, except for one,
are confirmed as likely cluster members. Hence, we also confirm that the
planetary-mass domain in the cluster is well populated. Using our deep K-band
images we searched for companions to the targets in the separation range 0.3"
to 10" up to a maximum faint limit of K=19.5 mag. One suspected companion seems
to be an extremely red galaxy. The near-infrared colors of the sigma Orionis
substellar members indicate that dust grains condense and settle in their
atmospheres. We estimate that the surface temperatures range from 2500 K down
to 1500 K. The spectroscopic sequence covers the full range of L subclasses,
and the faintest object is tentatively classified as T0. These targets provide
a sequence of substellar objects of known age, distance and metallicity, which
can be used as benchmark for understanding the spectral properties of ultracool
dwarfs.Comment: Accepted for publication in ApJ Letters. 9 pages, 4 figures include
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