143,491 research outputs found
Collider phenomenology of the 4D composite Higgs model
No full textThis thesis is devoted to the phenomenological analysis at the large hadron collider (LHC), as well at a future electron positron collider, of the 4 dimensional (4D) composite Higgs model (4DCHM), a compelling beyond the standard model scenario where the Higgs state arises as a pseudo Nambu Goldstone boson. The motivations and the main characteristics of the model are summarised and then an analysis of the gauge and Higgs sectors of the 4DCHM is performed. Finally we propose a general framework for the analysis of models with an extended quark sector that we have applied to a simplified composite Higgs scenario
The Higgs sector of the complex minimal supersymmetric standard model
No full textComplete one-loop results for the decay widths of neutral Higgs bosons ( h(_a)) into lighter neutral Higgs bosons ( h(_b), h(_c). ) arc presented for the MSSM with complex parameters. The results are obtained in the Feynman-diagrammatic approach, taking into account the full dependence on the spectrum of supersymmetric particles and all complex phases of the supersymmetric parameters. The genuine triple-Higgs vertex contributions are supplemented with two-loop propagator-type corrections, yielding the currently most precise prediction for this class of processes. The genuine vertex corrections turn out to be very important, yielding a large increase of the decay width compared to a prediction based on the tree-level vertex. One-loop propagator-type mixing between neutral Higgs bosons and Goldstone and Z bosons is also consistently taken into account. Complete one-loop results for the decay of a neutral Higgs boson into fermions are also presented, which include the full dependence on complex phases. The new results are used to analyse the impact of the experimental limits from the LEP Higgs searches on the parameter space with a very light MSSM Higgs boson. It is found that a significant part of the parameter space of the CPX benchmark scenario exists where channels involving the decay h(_2)→ h(_1) h(_1) have the highest search sensitivity, and the existence of an unexcluded region with M(_h1) ~ 45 GeV is confirmed. The public code Higgs Bounds is also presented, which can be used in conjunction with models with an arbitrary number of neutral Higgs bosons to determine whether parameter points have been excluded at the 95% CL by the LEP and Tevatron Higgs searches
Higgs Boson Studies at the Tevatron
No full textWe combine searches by the CDF and D0 Collaborations for the standard model Higgs boson with mass in the range 90--200 GeV produced in the gluon-gluon fusion, , , , and vector boson fusion processes, and decaying in the , , , , and modes. The data correspond to integrated luminosities of up to 10 fb and were collected at the Fermilab Tevatron in collisions at TeV. The searches are also interpreted in the context of fermiophobic and fourth generation models. We observe a significant excess of events in the mass range between 115 and 140 GeV/. The local significance corresponds to 3.0 standard deviations at GeV/, consistent with the mass of the Higgs boson observed at the LHC, and we expect a local significance of 1.9 standard deviations. We separately combine searches for , , , and . The observed signal strengths in all channels are consistent with the presence of a standard model Higgs boson with a mass of 125 GeV/
Evidence for the 125 GeV Higgs boson decaying to a pair of τ leptons
No full textOpen Access. This article is distributed under the terms of the Creative Commons Attribution License (CC-BY 4.0), which permits any use, distribution and reproduction in any medium, provided the original author(s) and source are credited.A search for a standard model Higgs boson decaying into a pair of τ leptons is performed using events recorded by the CMS experiment at the LHC in 2011 and 2012. The dataset corresponds to an integrated luminosity of 4.9 fb−1 at a centre-of-mass energy of 7 TeV and 19.7 fb−1 at 8 TeV. Each τ lepton decays hadronically or leptonically to an electron or a muon, leading to six different final states for the τ -lepton pair, all considered in this analysis. An excess of events is observed over the expected background contributions, with a local significance larger than 3 standard deviations for m H values between 115 and 130 GeV. The best fit of the observed H → τ τ signal cross section times branching fraction for m H = 125 GeV is 0.78 ± 0.27 times the standard model expectation. These observations constitute evidence for the 125 GeV Higgs boson decaying to a pair of τ leptons
Combined search for the Higgs boson with the D0 experiment
No full textWe perform a combination of searches for standard model Higgs boson production in collisions recorded by the D0 detector at the Fermilab Tevatron Collider at a center of mass energy of TeV. The different production and decay channels have been analyzed separately, with integrated luminosities of up to 9.7 fb and for Higgs boson masses GeV. We combine these final states to achieve optimal sensitivity to the production of the Higgs boson. We also interpret the combination in terms of models with a fourth generation of fermions, and models with suppressed Higgs boson couplings to fermions. The result excludes a standard model Higgs boson at 95% C.L. in the ranges $90 M_HM_
Measurement of Higgs boson production and properties in the WW decay channel with leptonic final states
No full textA search for the standard model Higgs boson decaying to a W-boson pair at the LHC is reported. The event sample corresponds to an integrated luminosity of 4.9 fb−1 and 19.4 fb−1 collected with the CMS detector in pp collisions at s√ = 7 and 8 TeV, respectively. The Higgs boson candidates are selected in events with two or three charged leptons. An excess of events above background is observed, consistent with the expectation from the standard model Higgs boson with a mass of around 125 GeV. The probability to observe an excess equal or larger than the one seen, under the background-only hypothesis, corresponds to a significance of 4.3 standard deviations for m H = 125.6 GeV. The observed signal cross section times the branching fraction to WW for m H = 125.6 GeV is 0.72+0.20−0.18 times the standard model expectation. The spin-parity J P = 0+ hypothesis is favored against a narrow resonance with J P = 2+ or J P = 0− that decays to a W-boson pair. This result provides strong evidence for a Higgs-like boson decaying to a W-boson pair
Search for invisible decays of Higgs bosons in the vector boson fusion and associated ZH production modes
No full textA search for invisible decays of Higgs bosons is performed using the vector boson fusion and associated ZH production modes. In the ZH mode, the Z boson is required to decay to a pair of charged leptons or a bb quark pair. The searches use the 8  TeV pp collision dataset collected by the CMS detector at the LHC, corresponding to an integrated luminosity of up to 19.7  fb-1. Certain channels include data from 7  TeV collisions corresponding to an integrated luminosity of 4.9  fb-1. The searches are sensitive to non-standard-model invisible decays of the recently observed Higgs boson, as well as additional Higgs bosons with similar production modes and large invisible branching fractions. In all channels, the observed data are consistent with the expected standard model backgrounds. Limits are set on the production cross section times invisible branching fraction, as a function of the Higgs boson mass, for the vector boson fusion and ZH production modes. By combining all channels, and assuming standard model Higgs boson cross sections and acceptances, the observed (expected) upper limit on the invisible branching fraction at mH = 125   GeV is found to be 0.58 (0.44) at 95 % confidence level. We interpret this limit in terms of a Higgs-portal model of dark matter interactions
Higher order and CP-violating effects in the neutralino and Higgs boson sectors of the MSSM
No full textComplete one-loop results are presented for neutralino and Higgs decay processes of the form chi^0_i->chi^0_j h_a and h_a->chi^0_i chi^0_j in the MSSM with CP-violating parameters. An on-shell renormalisation scheme is developed for the chargino–neutralino sector that consistently takes into account imaginary parts arising from complex parameters and absorptive parts of loop integrals. The genuine vertex contributions are combined with two-loop Higgs propagator-type corrections to obtain the most precise
prediction currently available for this class of processes. In the CP-violating CPX benchmark scenario, the corrections to the neutralino decay width are found to be particularly large – of order 45% for a Higgs mass of 40GeV. We find that in this unexcluded parameter region, which will be difficult to cover by standard Higgs search channels
at the LHC, the branching ratio for the decay chi^0_2->chi^0_1 h_1 is large. This may offer good prospects of detecting such a light Higgs boson in cascade decays of supersymmetric particles. We also study the full Higgs production and decay processes in scenarios where the intermediate Higgs bosons are nearly mass degenerate and interference effects can have a significant impact. We find that an on-shell approximation gives results in good numerical agreement with the full momentum-dependent Higgs propagator matrix calculation and we develop a generalised
narrow width approximation to be used in such a situation. We use these methods to study the asymmetry between the production of left-handed and right-handed neutralinos in Higgs decays at the LHC in the presence of CP-violating phases. Large asymmetries are found to be possible for large M_H^± > 500GeV and tan beta < 10, where the decay
into neutralinos may be the only possibility to detect the heavy Higgs bosons
Is there a relationship between the leadership of change and emotional intelligence?
No full textOver the last few years there has been a significant and sustained growth in interest in the area of leadership (Chaudry, 2000; Bagshaw & Bagshaw, 1999; Goffee & Jones, 2000). This paper reviews the development in thinking and research in relation to leadership. The limitations of progress in our understanding of the phenomenon are discussed (eg. Kets De Vries, 1993). Building from this review, the potential for a view of leadership relating to its role in the context of change (eg Conner, 1999; Kotter, 1998) and its relationship to Emotional Intelligence (eg Higgs & Dulewicz, 1999) is explored. The relationship between the Competencies associated with change leadership and Emotional Intelligence is examined by means of a quantitative study involving a sample of 70 managers. Change Leadership Competencies are operationalised using an instrument reported by Higgs and Rowland (2000). Further support is offered for the reliability of this instrument based on a separate sample of 84 change leaders. Emotional Intelligence is operationalised using the EIQ developed by Dulewicz and Higgs (1999).The study demonstrates strong correlations between six of the seven elements of Emotional Intelligence and all five factors in the Change Leadership Competency model. In addition, the overall EI score correlates significantly with the overall CLC score.The authors conclude that Emotional Intelligence plays a significant part in the effectiveness of Change Leadership and propose a model which can be employed in the identification of the development needs of Change Leaders. In addition they discuss the limitations of the current study and identify areas for further research.<br/
Change and culture: an examination of the relationship between organisation culture and approaches to change
No full textIt is widely asserted that a high proportion of change initiatives fail (e.g. Kotter, 1996; Higgs & Rowland, 2000). Furthermore the success of initiatives involving cultural change is significantly lower (Smith, 2003). However, there is some debate around whether or not change can only be effected if organisational culture is also changed or that, for change to be successful it has to be positioned within the dominant organisational culture paradigm (e.g. Trompenaars & Wooliams, 2004).In a study by Higgs and Rowland (2003) it was suggested that approaches to change based on an understanding of complexity, rather than an assumption of linearity, were more likely to be successful. Furthermore they identified the significance of leader behaviours in impacting on change success. In particular they indicated that leader-centric behaviours (Shaping) were negatively related to success. Behaviours focusing on creating a change framework and building capability (Framing) were positively related to success. In discussing these findings they indicated a need for further research to explore their results in differing organisational contexts. They also identified a need to explore the impact of differing organisational cultures on the findings. These two needs for research are the focus of this paper.The study reported involved collecting stories from change leaders in nine organisations. Whilst the Higgs and Rowland (2003) framework was used to explore change approaches and leader behaviours, the construct of culture was operationalised using the Goffee and Jones 91998) model. The findings presented offer some support for the proposition that there is a relationship between culture, change approach, leadership behaviours and change success. However, the sample size does provide a limitation of the research and further exploration in future research is called for
- …
