5,821 research outputs found
Searching for Higgs Bosons in Association with Top Quark Pairs in the H -> bb Decay Mode
Search for the Higgs Boson is one of the prime goals of the LHC. Higgs bosons
lighter than 130 GeV decay mainly to a b-quark pair. While the detection of a
directly produced Higgs boson in the bb channel is impossible because of the
huge QCD background, the channel ttH -> lnqqbbbb is very promising in the
Standard Model and the MSSM.
We discuss an event reconstruction and selection method based on likelihood
functions. The CMS detector response is performed with parametrisations
obtained from detailed simulations. Various physics and detector performance
scenarios are investigated and the results are presented. It turns out that
excellent b-tagging performance and good mass resolution are essential for this
channel.Comment: 10 pages, 6 figure
Prospects for Higgs Boson Searches in the Channel WH -> lnbb
We present a method how to detect the WH -> lnbb in the high luminosity LHC
environment with the CMS detector. This study is performed with fast detector
response simulation including high luminosity event pile up. The main aspects
of reconstruction are pile up jet rejection, identification of b-jets and
improvement of Higgs mass resolution.
The detection potential in the SM for m(H) < 130 GeV and in the MSSM is only
encouraging for high integrated luminosity. Nevertheless it is possible to
extract important Higgs parameters which are useful to elucidate the nature of
the Higgs sector. In combination with other channels, this channel provides
valuable information on Higgs boson couplings.Comment: 8 pages, 8 figure
New angles on top quark decay to a charged Higgs
To properly discover a charged Higgs Boson () requires its spin and
couplings to be determined. We investigate how to utilize \ttbar spin
correlations to analyze the couplings in the decay . Within the framework of a general Two-Higgs-Doublet Model, we
obtain results on the spin analyzing coefficients for this decay and study in
detail its spin phenomenology, focusing on the limits of large and small values
for . Using a Monte Carlo approach to simulate full hadron-level
events, we evaluate systematically how the decay
mode can be used for spin analysis. The most promising observables are obtained
from azimuthal angle correlations in the transverse rest frames of
. This method is particularly useful for determining the coupling
structure of in the large limit, where differences from the
SM are most significant.Comment: 28 pages, 13 figures. Uses JHEP forma
Phases in the gaugino sector: direct reconstruction of the basic parameters and impact on the neutralino pair production
We consider recovering analytically the (generally complex) parameters ,
and of the gaugino and Higgsino Lagrangian, from appropriate
physical input in the chargino and neutralino sectors. For given ,
we obtain very simple analytic solutions for , , in the
chargino sector and a twofold , analytic solution in the
neutralino sector, assuming two chargino, two neutralino masses, and one of the
chargino mixing angles as physical input. The twofold ambiguity in the
neutralino parameters reconstruction may be essentially resolved by measuring
the production cross-section at future linear
collider energies, which we study explicitly with the phase dependences. Some
salient features and specific properties of this complex case gaugino "spectrum
inversion" are illustrated and compared with the similar inversion in the real
case. In particular, our algorithms exhibit in a direct and transparent way the
non-trivial theoretical correlation among the chargino and neutralino
parameters, and the resulting allowed domains when only a subset of the
required physical input masses and production cross-sections is known.Comment: Latex, 28 pages, 10 figure
Digital play and the actualisation of the consumer imagination
In this article, the authors consider emerging consumer practices in digital virtual spaces. Building on constructions of consumer behavior as both a sense-making activity and a resource for the construction of daydreams, as well as anthropological readings of performance, the authors speculate that many performances during digital play are products of consumer fantasy. The authors develop an interpretation of the relationship between the real and the virtual that is better equipped to understand the movement between consumer daydreams and those practices actualized in the material and now also in digital virtual reality. The authors argue that digital virtual performances present opportunities for liminoid transformations through inversions, speculations, and playfulness acted out in aesthetic dramas. To illustrate, the authors consider specific examples of the theatrical productions available to consumers in digital spaces, highlighting the consumer imagination that feeds them, the performances they produce, and the potential for transformation in consumer-players
Determining with Neutral and Charged Higgs Bosons at a Future Linear Collider
The ratio of neutral Higgs field vacuum expectation values, tan(beta), is one
of the most important parameters to determine in either the Minimal
Supersymmetric Standard Model (MSSM) or a general type-II Two-Higgs Doublet
Model (2HDM). Assuming an energy and integrated luminosity of sqrts=500 GeV and
L=2000 fb-1 at a future linear collider (LC), we show that a very accurate
determination of tan(beta) will be possible for low and high tan(beta) values
by measuring the production rates of Higgs bosons and reconstructing Higgs
boson decays. In particular, based on a TESLA simulation, and assuming no other
light Higgs bosons and 100<=mA<=200 GeV, we find that the rate for the process
e+e- --> bbA --> bbbb provides a good determination of tan(beta) at high
tan(beta). In the MSSM Higgs sector, in the sample case of mA = 200 GeV, we
find that the rates for e+e- --> bbA+bbH --> bbbb and for e+e- --> HA --> bbbb
provide a good determination of tan(beta) at high and low tan(beta),
respectively. We also show that the direct measurement of the average total
widths of the H and A in e+e- --> HA --> bbbb events provides an excellent
determination of tan(beta) at large values. In addition, the charged Higgs
boson process e+e- --> H+H- --> tbtb has been studied. The sensitivity to
tan(beta) at the LHC obtained directly from heavy Higgs boson production is
briefly compared to the LC results.Comment: 25 pages, 8 figures, revtex
A Study And Application of Face Recognition System
人脸识别是近几年来非常受关注的研究课题之一。这一研究领域综合了多个学科:图像处理、模式识别、计算机视觉、神经网络,心理学等等。人脸识别所要解决的问题可以概述如下:给定场景下的静态图像或动态图像序列,应用已知人脸库,从场景里识别一个或多个人。本文研究静态人脸图像识别,这个问题的解决包括:从场景中分割人脸(人脸检测),人脸区域的特征提取、识别或验证。在识别问题中,输入系统人脸图像是未知的人脸,系统将从人脸数据库中找出与输入一致的人脸。本文的主要研究工作:1.本文第一章主要研究与人脸识别相关的神经科学和计算机人脸识别的各种方法,探讨生物识别和计算机识别的相互联系,以及生物识别方法,特别是人脸识别技术...Machine recognition of human face still and video images is one of the active research areas including several disciplines such as image processing, pattern recognition, computer vision and neural networks, psychology and so forth. A general statement of the problem can be formulated as follows: Given still or video images of a scene, identify or verify one or more persons in the scene using a sto...学位:工学硕士院系专业:物理与机电工程学院机电工程系_测试计量技术及仪器学号:20032901
Constraining the minimal supergravity model parameter tan(beta) by measuring the dilepton mass distribution at LHC
We study the dependence on of the event kinematics of final
states with , as
expected in collisions at CERN LHC, within the framework of the minimal
supergravity model. With increase of , the third generation
sparticle masses and decrease due to the
increase of the tau and bottom Yukawa couplings. As a result, gluino, stop,
sbottom, chargino and neutralino decays to third generation particles and
sparticles are enhanced. With rising, we observe a characteristic
change in the shape of the dilepton mass spectra in versus final
states, reflecting the presence of the decays and ,
, respectively. We exploit
this effect for constraining the value of .Comment: 16 page latex file including 5 eps figure
Combination of electroweak and QCD corrections to single W production at the Fermilab Tevatron and the CERN LHC
Precision studies of the production of a high-transverse momentum lepton in
association with missing energy at hadron colliders require that electroweak
and QCD higher-order contributions are simultaneously taken into account in
theoretical predictions and data analysis. Here we present a detailed
phenomenological study of the impact of electroweak and strong contributions,
as well as of their combination, to all the observables relevant for the
various facets of the p\smartpap \to {\rm lepton} + X physics programme at
hadron colliders, including luminosity monitoring and Parton Distribution
Functions constraint, precision physics and search for new physics signals.
We provide a theoretical recipe to carefully combine electroweak and strong
corrections, that are mandatory in view of the challenging experimental
accuracy already reached at the Fermilab Tevatron and aimed at the CERN LHC,
and discuss the uncertainty inherent the combination. We conclude that the
theoretical accuracy of our calculation can be conservatively estimated to be
about 2% for standard event selections at the Tevatron and the LHC, and about
5% in the very high transverse mass/lepton transverse momentum tails. We
also provide arguments for a more aggressive error estimate (about 1% and 3%,
respectively) and conclude that in order to attain a one per cent accuracy: 1)
exact mixed corrections should be computed in
addition to the already available NNLO QCD contributions and two-loop
electroweak Sudakov logarithms; 2) QCD and electroweak corrections should be
coherently included into a single event generator.Comment: One reference added. Final version to appear in JHE
Theoretical uncertainties in sparticle mass predictions from computational tools
We estimate the current theoretical uncertainty in sparticle mass predictions
by comparing several state-of-the-art computations within the minimal
supersymmetric standard model (MSSM). We find that the theoretical uncertainty
is comparable to the expected statistical errors from the Large Hadron Collider
(LHC), and significantly larger than those expected from a future e+e- Linear
Collider (LC). We quantify the theoretical uncertainty on relevant sparticle
observables for both LHC and LC, and show that the value of the error is
significantly dependent upon the supersymmetry (SUSY) breaking parameters. We
also present the theoretical uncertainty induced in fundamental-scale SUSY
breaking parameters when they are fitted from LHC measurements. Two regions of
the SUSY parameter space where accurate predictions are particularly difficult
are examined in detail: the large tan(beta) and focus point regimes.Comment: 22 pages, 6 figures; comment added pointing out that 2-loop QCD
corrections to mt are incorrect in some of the programs investigated. We give
the correct formul
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