303 research outputs found
Doublet-Triplet Splitting and Fermion Masses with Extra Dimensions
The pseudo-Goldstone boson mechanism for the ``doublet-triplet splitting''
problem of the grand unified theory can be naturally implemented in the
scenario with extra dimensions and branes. The two SU(6) global symmetries of
the Higgs sector are located on two separate branes while the SU(6) gauge
symmetry is in the bulk. After including several vector-like fields in the
bulk, and allowing the most general interactions with their natural strength
(including the higher dimensional ones which may be generated by gravity) which
are consistent with the geometry, a realistic pattern of the Standard Model
fermion masses and mixings can be naturally obtained without any flavor
symmetry. Neutrino masses and mixings required for the solar and atmospheric
neutrino problems can also be accommodated. The geometry of extra dimensions
and branes provides another way to realize the absence of certain interactions
(as required in the pseudo-Goldstone boson mechanism) or the smallness of some
couplings (e.g., the Yukawa couplings between the fermions and the Higgs
bosons), in addition to the usual symmetry arguments.Comment: 16 pages, 4 figures, LaTeX, references and some clarifying remarks
added, to be published in Phys. Rev.
The Clinical Utility of the Adolescent and Young Adult Psycho-Oncology Screening Tool (AYA-POST): Perspectives of AYA Cancer Patients and Healthcare Professionals
Objective: Routine psychosocial screening and assessment of people diagnosed with cancer are crucial to the timely detection of distress and provision of tailored supportive care; however, appropriate screening tools have been lacking for adolescents and young adults (AYAs), who have unique needs and experiences. One exception is the recently validated AYA Psycho-Oncology Screening Tool (AYA-POST) for use with young people aged 15–29 years, which comprises a distress thermometer and age-specific needs assessment. This study investigates the clinical utility of this measure, as well as the subsequent service responsiveness within the Australian Youth Cancer Services. Method: In total, 118 AYAs and 29 healthcare professionals: (HCPs) completed surveys about the clinical utility of the AYA-POST; a subset of 30 AYAs completed a 3-month follow-up survey assessing service responsiveness. Descriptive statistics (frequencies/means) were computed for all items, with chi-square analyses used to explore whether perceived clinical utility varied with AYA age, AYA sex, HCP discipline or HCP length of time using the AYA-POST. Results: Participants’ responses demonstrate high levels of satisfaction with the tool, evidencing its appropriateness, practicability and acceptability. Moreover, the AYA-POST was reported to facilitate communication about psychosocial needs and prompt referrals, indicating good service responsiveness. Ratings of clinical utility did not differ significantly between AYA and HCP groups.Conclusion: This study demonstrates that the AYA-POST is an appropriate tool in the psychosocial screening of AYAs with cancer, facilitating the identification of distress and unique concerns in this population and valuable in triaging and tailoring care for young cancer patients.Pandora Patterson, Fiona E. J. McDonald, Kimberley R. Allison, Helen Bibby, Michael Osborn, Karen Matthews, Ursula M. Sansom-Daly, Kate Thompson, Meg Plaster, and Antoinette Anazod
Status of four-neutrino mass schemes: a global and unified approach to current neutrino oscillation data
We present a unified global analysis of neutrino oscillation data within the
framework of the four-neutrino mass schemes (3+1) and (2+2). We include all
data from solar and atmospheric neutrino experiments, as well as information
from short-baseline experiments including LSND. If we combine only solar and
atmospheric neutrino data, (3+1) schemes are clearly preferred, whereas
short-baseline data in combination with atmospheric data prefers (2+2) models.
When combining all data in a global analysis the (3+1) mass scheme gives a
slightly better fit than the (2+2) case, though all four-neutrino schemes are
presently acceptable. The LSND result disfavors the three-active neutrino
scenario with only and at 99.9% CL with
respect to the four-neutrino best fit model. We perform a detailed analysis of
the goodness of fit to identify which sub-set of the data is in disagreement
with the best fit solution in a given mass scheme.Comment: 32 pages, 8 Figures included, REVTeX4.Improved discussion in sec. XI,
references added, version accepted by Phys. Rev.
A measurement of the tau mass and the first CPT test with tau leptons
We measure the mass of the tau lepton to be 1775.1+-1.6(stat)+-1.0(syst.) MeV
using tau pairs from Z0 decays. To test CPT invariance we compare the masses of
the positively and negatively charged tau leptons. The relative mass difference
is found to be smaller than 3.0 10^-3 at the 90% confidence level.Comment: 10 pages, 4 figures, Submitted to Phys. Letts.
WW Production Cross Section and W Branching Fractions in e+e- Collisions at 189 GeV
From a data sample of 183 pb^-1 recorded at a center-of-mass energy of roots
= 189 GeV with the OPAL detector at LEP, 3068 W-pair candidate events are
selected. Assuming Standard Model W boson decay branching fractions, the W-pair
production cross section is measured to be sigmaWW = 16.30 +- 0.34(stat.) +-
0.18(syst.) pb. When combined with previous OPAL measurements, the W boson
branching fraction to hadrons is determined to be 68.32 +- 0.61(stat.) +-
0.28(syst.) % assuming lepton universality. These results are consistent with
Standard Model expectations.Comment: 22 pages, 5 figures, submitted to Phys. Lett.
Genuine Correlations of Like-Sign Particles in Hadronic Z0 Decays
Correlations among hadrons with the same electric charge produced in Z0
decays are studied using the high statistics data collected from 1991 through
1995 with the OPAL detector at LEP. Normalized factorial cumulants up to fourth
order are used to measure genuine particle correlations as a function of the
size of phase space domains in rapidity, azimuthal angle and transverse
momentum. Both all-charge and like-sign particle combinations show strong
positive genuine correlations. One-dimensional cumulants initially increase
rapidly with decreasing size of the phase space cells but saturate quickly. In
contrast, cumulants in two- and three-dimensional domains continue to increase.
The strong rise of the cumulants for all-charge multiplets is increasingly
driven by that of like-sign multiplets. This points to the likely influence of
Bose-Einstein correlations. Some of the recently proposed algorithms to
simulate Bose-Einstein effects, implemented in the Monte Carlo model PYTHIA,
are found to reproduce reasonably well the measured second- and higher-order
correlations between particles with the same charge as well as those in
all-charge particle multiplets.Comment: 26 pages, 6 figures, Submitted to Phys. Lett.
Measurement of the B0 Lifetime and Oscillation Frequency using B0->D*+l-v decays
The lifetime and oscillation frequency of the B0 meson has been measured
using B0->D*+l-v decays recorded on the Z0 peak with the OPAL detector at LEP.
The D*+ -> D0pi+ decays were reconstructed using an inclusive technique and the
production flavour of the B0 mesons was determined using a combination of tags
from the rest of the event. The results t_B0 = 1.541 +- 0.028 +- 0.023 ps, Dm_d
= 0.497 +- 0.024 +- 0.025 ps-1 were obtained, where in each case the first
error is statistical and the second systematic.Comment: 17 pages, 4 figures, submitted to Phys. Lett.
First Measurement of Z/gamma* Production in Compton Scattering of Quasi-real Photons
We report the first observation of Z/gamma* production in Compton scattering
of quasi-real photons. This is a subprocess of the reaction e+e- to
e+e-Z/gamma*, where one of the final state electrons is undetected.
Approximately 55 pb-1 of data collected in the year 1997 at an e+e-
centre-of-mass energy of 183 GeV with the OPAL detector at LEP have been
analysed. The Z/gamma* from Compton scattering has been detected in the
hadronic decay channel. Within well defined kinematic bounds, we measure the
product of cross-section and Z/gamma* branching ratio to hadrons to be
(0.9+-0.3+-0.1) pb for events with a hadronic mass larger than 60 GeV,
dominated by (e)eZ production. In the hadronic mass region between 5 GeV and 60
GeV, dominated by (e)egamma* production, this product is found to be
(4.1+-1.6+-0.6) pb. Our results agree with the predictions of two Monte Carlo
event generators, grc4f and PYTHIA.Comment: 18 pages, LaTeX, 5 eps figures included, submitted to Physics Letters
Search for Higgs Bosons in e+e- Collisions at 183 GeV
The data collected by the OPAL experiment at sqrts=183 GeV were used to
search for Higgs bosons which are predicted by the Standard Model and various
extensions, such as general models with two Higgs field doublets and the
Minimal Supersymmetric Standard Model (MSSM). The data correspond to an
integrated luminosity of approximately 54pb-1. None of the searches for neutral
and charged Higgs bosons have revealed an excess of events beyond the expected
background. This negative outcome, in combination with similar results from
searches at lower energies, leads to new limits for the Higgs boson masses and
other model parameters. In particular, the 95% confidence level lower limit for
the mass of the Standard Model Higgs boson is 88.3 GeV. Charged Higgs bosons
can be excluded for masses up to 59.5 GeV. In the MSSM, mh > 70.5 GeV and mA >
72.0 GeV are obtained for tan{beta}>1, no and maximal scalar top mixing and
soft SUSY-breaking masses of 1 TeV. The range 0.8 < tanb < 1.9 is excluded for
minimal scalar top mixing and m{top} < 175 GeV. More general scans of the MSSM
parameter space are also considered.Comment: 49 pages. LaTeX, including 33 eps figures, submitted to European
Physical Journal
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