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Resonance Continuum Interference In The Di Photon Higgs Signal At The Lhc
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Book Synopsis Resonance-continuum Interference in the Di-photon Higgs Signal at the LHC. by :
Download or read book Resonance-continuum Interference in the Di-photon Higgs Signal at the LHC. written by and published by . This book was released on 2003 with total page 10 pages. Available in PDF, EPUB and Kindle. Book excerpt: A low mass Standard Model Higgs boson should be visible at the Large Hadron Collider through its production via gluon-gluon fusion and its decay to two photons. We compute the interference of this resonant process, gg → H → [gamma][gamma], with the continuum QCD background, gg → [gamma][gamma] induced by quark loops. Helicity selection rules suppress the effect, which is dominantly due to the imaginary part of the two-loop gg → [gamma][gamma] scattering amplitude. The interference is destructive, but only of order 5% in the Standard Model, which is still below the 10-20% present accuracy of the total cross section prediction. We comment on the potential size of such effects in other Higgs models.
Book Synopsis How Resonance-continuum Interference Changes 750 GeV Diphoton Excess by :
Download or read book How Resonance-continuum Interference Changes 750 GeV Diphoton Excess written by and published by . This book was released on 2016 with total page 23 pages. Available in PDF, EPUB and Kindle. Book excerpt: A hypothetical new scalar resonance, a candidate explanation for the recently observed 750 GeV diphoton excess at the LHC 13 TeV, necessarily interferes with the continuum background gg → [gamma][gamma]. The interference has two considerable effects: (1) enhancing or suppressing diphoton signal rate due to the imaginary-part interference and (2) distorting resonance shape due to the real-part interference. We study them based on the best-fit analysis of two benchmark models: two Higgs doublets with ~50 GeV width (exhibiting the imaginary-part interference effect) and a singlet scalar with 5 GeV width (exhibiting the real-part one), both extended with vector-like fermions. Furthermore, we find that the resonance contribution can be enhanced by a factor of 2 (1.6) for 3 (6) fb signal rate, or the 68% CL allowed mass region is shifted by O (1) GeV. If the best-fit excess rate decreases in the future data, the interference effects will become more significant.
Book Synopsis Resonance--Continuum Interference in Light Higgs Boson Production at a Photon Collider by :
Download or read book Resonance--Continuum Interference in Light Higgs Boson Production at a Photon Collider written by and published by . This book was released on 2009 with total page 14 pages. Available in PDF, EPUB and Kindle. Book excerpt: We study the effect of interference between the Standard Model Higgs boson resonance and the continuum background in the process [gamma][gamma] 2!H 2!b{bar b} at a photon collider. Taking into account virtual gluon exchange between the final-state quarks, we calculate the leading corrections to the height of the resonance for the case of a light (m{sub H}
Book Synopsis Discovery Of The Higgs Boson by : Aleandro Nisati
Download or read book Discovery Of The Higgs Boson written by Aleandro Nisati and published by World Scientific. This book was released on 2016-08-26 with total page 470 pages. Available in PDF, EPUB and Kindle. Book excerpt: The recent observation of the Higgs boson has been hailed as the scientific discovery of the century and led to the 2013 Nobel Prize in physics. This book describes the detailed science behind the decades-long search for this elusive particle at the Large Electron Positron Collider at CERN and at the Tevatron at Fermilab and its subsequent discovery and characterization at the Large Hadron Collider at CERN. Written by physicists who played leading roles in this epic search and discovery, this book is an authoritative and pedagogical exposition of the portrait of the Higgs boson that has emerged from a large number of experimental measurements. As the first of its kind, this book should be of interest to graduate students and researchers in particle physics.
Book Synopsis Shift in the LHC Higgs Diphoton Mass Peak from Interference with Background by :
Download or read book Shift in the LHC Higgs Diphoton Mass Peak from Interference with Background written by and published by . This book was released on 2012 with total page 10 pages. Available in PDF, EPUB and Kindle. Book excerpt: The Higgs diphoton amplitude from gluon fusion at the LHC interferes with the continuum background induced by quark loops. I investigate the effect of this interference on the position of the diphoton invariant mass peak used to help determine the Higgs mass. At leading order, the interference shifts the peak towards lower mass by an amount of order 150 MeV or more, with the precise value dependent on the methods used to analyze and fit the data.
Book Synopsis Interference Effects in the H($\to \gamma\gamma$) 2 Jets Channel at the LHC. by :
Download or read book Interference Effects in the H($\to \gamma\gamma$) 2 Jets Channel at the LHC. written by and published by . This book was released on 2015 with total page 7 pages. Available in PDF, EPUB and Kindle. Book excerpt: We compute the interference between the resonant process pp → H(→[gamma][gamma])+2 jets and the corresponding continuum background at leading order in QCD. For the Higgs signal, we include gluon fusion (GF) and vector boson fusion (VBF) production channels, while for the background we consider all tree-level contributions, including pure EW effects (O([alpha]4QED)) and QCD contributions (O([alpha]2QED[alpha]2s)), plus the loop-induced gluon-initiated process. After convolution with the experimental mass resolution, the main effect of the interference is to shift the position of the mass peak, as in the inclusive GF case studied previously. The apparent mass shift is small in magnitude but strongly dependent on the Higgs width, potentially allowing for a measurement of, or bound on, the width itself. In the H(→[gamma][gamma])+2 jets channel, the VBF and GF contributions generate shifts of opposite signs which largely cancel, depending on the sets of cuts used, to as little as 5 MeV (toward a lower Higgs mass). As a result, the small magnitude of the shift makes this channel a good reference mass for measuring the inclusive mass shift of around 60 MeV in the Standard Model.
Book Synopsis Observation and Measurement of a Standard Model Higgs Boson-like Diphoton Resonance with the CMS Detector by : Mingming Yang (Ph. D.)
Download or read book Observation and Measurement of a Standard Model Higgs Boson-like Diphoton Resonance with the CMS Detector written by Mingming Yang (Ph. D.) and published by . This book was released on 2015 with total page 201 pages. Available in PDF, EPUB and Kindle. Book excerpt: This thesis concerns the observation of a new particle and the measurements of its properties, from the search of the Higgs boson through its decay into two photons at the CMS experiment at CERN's Large Hadron Collider (LHC), on the full LHC "Run I" data collected by the CMS detector during 2011 and 2012, consisting of proton-proton collision events at [square root of] s = 7 TeV with L = 5.1 fb-1 and at [square root of] s = 8 TeV with L = 19.7 fb-1, with the final calibration. In particular, an excess of events above the background expectation is observed, with a local significance of 5.7 standard deviations at a mass of 124.7 GeV, which constitutes the observation of a new particle through the two photon decay channel. A further measurement provides the precise mass of this new particle as 124.72+0.35 -0.36 GeV = 124.72+0.31 -0.32(stat)+0.16 -0.16(syst) GeV. Its total production cross section times two photon decay branching ratio relative to that of the Standard Model Higgs boson is determined as 1.12+0.26 -0.23 = 1.12+0.21 -0.21(stat)+0.15 -0.09(syst), compatible with the Higgs boson expectation. Further extractions of its properties relative to the Higgs boson, including the production cross section times decay branching ratios for separate Higgs production processes, couplings to bosons and to fermions, and effective couplings to the photon and to the gluon, are all compatible with the expectations for the Standard Model Higgs boson.
Book Synopsis Evidence for a Narrow Higgs-like Diphoton Resonance with a Mass of 125 GeV in Pp Collisions at [square Root Of]s by : Joshua Lorne Bendavid
Download or read book Evidence for a Narrow Higgs-like Diphoton Resonance with a Mass of 125 GeV in Pp Collisions at [square Root Of]s written by Joshua Lorne Bendavid and published by . This book was released on 2013 with total page 158 pages. Available in PDF, EPUB and Kindle. Book excerpt: We have performed a search for the production of the standard model Higgs boson decaying to diphotons in pp collisions at the LHC at [square root of]s = 7-8 TeV with the CMS detector. Having analyzed data corresponding to 5.1 fb-1 at [square root of]s = 7 TeV (2011) and 5.3 fb-1 at [square root of]s = 8 TeV (2012), a statistically significant excess of events is observed with respect to the background prediction. Interpreted as a standard model Higgs, this excess has a local significance of 4.1 standard deviations, with the maximum significance occurring for a Higgs mass of 125 GeV. Taking into account the trials factor given the search range of 110 GeV to 150 GeV in Higgs mass, this excess has a global significance of 3.2 standard deviations. This constitutes evidence for a new particle decaying to diphotons with a mass of around 125 GeV. The rate of observed events is consistent with predictions for the standard model Higgs boson.
Book Synopsis Bounding the Higgs Width at the LHC Using Full Analytic Results for $gg 2!e^- E^+ \mu^- \mu^+$ by :
Download or read book Bounding the Higgs Width at the LHC Using Full Analytic Results for $gg 2!e^- E^+ \mu^- \mu^+$ written by and published by . This book was released on 2014 with total page 45 pages. Available in PDF, EPUB and Kindle. Book excerpt: We revisit the hadronic production of the four-lepton final state, e- e+ [mu]- [mu]+, through the fusion of initial state gluons. This process is mediated by loops of quarks and we provide first full analytic results for helicity amplitudes that account for both the effects of the quark mass in the loop and off-shell vector bosons. The analytic results have been implemented in the Monte Carlo program MCFM and are both fast, and numerically stable in the region of low Z transverse momentum. We use our results to study the interference between Higgs-mediated and continuum production of four-lepton final states, which is necessary in order to obtain accurate theoretical predictions outside the Higgs resonance region. We have confirmed and extended a recent analysis of Caola and Melnikov that proposes to use a measurement of the off-shell region to constrain the total width of the Higgs boson. Using a simple cut-and-count method, existing LHC data should bound the width at the level of 25-45 times the Standard Model expectation. We investigate the power of using a matrix element method to construct a kinematic discriminant to sharpen the constraint. Furthermore, in our analysis the bound on the Higgs width is improved by a factor of about 1.6 using a simple cut on the MEM discriminant, compared to an invariant mass cut [mu]4l> 300 GeV.
Book Synopsis Search and Discovery with the Resonant [diphoton] Final State at ATLAS by : Andrew Straiton Hard
Download or read book Search and Discovery with the Resonant [diphoton] Final State at ATLAS written by Andrew Straiton Hard and published by . This book was released on 2016 with total page 159 pages. Available in PDF, EPUB and Kindle. Book excerpt: A search for the Standard Model Higgs boson was conducted with the ATLAS Experiment at the LHC using the two-photon decay channel. Datasets with integrated luminosities of 4.8 inverse femtobarns and 5.9 inverse femtobarns were collected in 2011 and 2012 for proton-proton collisions with center-of-mass energies of 7 TeV and 8 TeV, respectively. A statistically significant excess of events above the background-only expectation in the [diphoton] decay channel of 4.5 standard deviations was observed. Combined with excesses in the WW and ZZ decays, this observation led to the discovery of a Higgs boson with a significance of 5.9 standard deviations at a mass of 126.0 +/- 0.4 (stat) +/- 0.4 (sys) GeV. Searches for diphoton resonances during 2015 and 2016 with LHC data were motivated by extensions to the Standard Model that predict additional scalar particles. Data were analyzed from 13 TeV proton-proton collisions, corresponding to an integrated luminosity of 15.4 inverse femtobarns, and no significant deviations from the Standard Model hypothesis were observed. 95% CL limits on the production cross-section times branching ratio to [diphotons] were calculated for scalar models with masses between 200 GeV and 2.4 TeV and widths ranging from 4 MeV to 10% of the scalar mass.
Book Synopsis Di-photon Production at the LHC. by :
Download or read book Di-photon Production at the LHC. written by and published by . This book was released on 2003 with total page 4 pages. Available in PDF, EPUB and Kindle. Book excerpt: The standard model production of two photons is one of the most important backgrounds to light Higgs boson production at the LHC. In this talk we discuss the di-photon background, with emphasis on the effects of the recently calculated next-to-leading-order (NLO) corrections to the gluon-gluon-initiated component. We find that the K-factor for this component is smaller than that for the analogous gg → H process, and that the correction to the total irreducible di-photon production is modest. We also investigate ways to enhance the statistical significance of the Higgs signal in the [gamma][gamma] channel.
Book Synopsis A Pseudoscalar Decaying to Photon Pairs in the Early LHC Run 2 Data by :
Download or read book A Pseudoscalar Decaying to Photon Pairs in the Early LHC Run 2 Data written by and published by . This book was released on 2016 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: In this paper we explore the possibility of a pseudoscalar resonance to account for the 750 GeV diphoton excess observed both at ATLAS and at CMS. We analyze the ingredients needed from the low energy perspective to obtain a sufficiently large diphoton rate to explain the signal while avoiding constraints from other channels. Additionally, we point out composite Higgs models in which one can naturally obtain a pseudoscalar at the 750 GeV mass scale and we estimate the pseudoscalar couplings to standard model particles that one would have in such models. A generic feature of models that can explain the excess is the presence of new particles in addition to the 750 GeV state. In conclusion, we note that due to the origin of the coupling of the resonance to photons, one expects to see comparable signals in the Z[gamma], ZZ, and W W channels.
Book Synopsis Implications of the LHC Two-photon Signal for Two-Higgs-doublet Models by :
Download or read book Implications of the LHC Two-photon Signal for Two-Higgs-doublet Models written by and published by . This book was released on 2012 with total page 4 pages. Available in PDF, EPUB and Kindle. Book excerpt: We study the implications for Two Higgs Doublet Models of the recent announcement at the LHC giving a tantalizing hint for a Higgs boson of mass 125 GeV decaying into two photons. We require that the experimental result be within a factor of two of the theoretical Standard Model prediction, and analyze the type I and type II models as well as the lepton-specific and flipped models, subject to this requirement. It is assumed that there is no new physics other than two Higgs doublets. In all of the models, we display the allowed region of parameter space taking the recent LHC announcement at face value, and we analyze the WW−, ZZ, {bar b}b and?+?− expectations in these allowed regions. Throughout the entire range of parameter space allowed by the?? constraint, the number of events for Higgs decays into WW, ZZ and b{bar b} are not changed from the Standard Model by more than a factor of two. In contrast, in the Lepton Specific model, decays to?+?− are very sensitive across the entire??-allowed region.
Book Synopsis LHC Search for Di-Higgs Decays of Stoponium and Other Scalars in Events with Two Photons and Two Bottom Jets by :
Download or read book LHC Search for Di-Higgs Decays of Stoponium and Other Scalars in Events with Two Photons and Two Bottom Jets written by and published by . This book was released on 2014 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: We study the prospects for LHC discovery of a narrow resonance that decays to two Higgs bosons, using the final state of two photons and two bottom jets. Our work is motivated in part by a scenario in which two-body flavor-preserving decays of the top squark are kinematically forbidden. Stoponium, a hadronic bound state of the top squark and its anti-particle, will then form, and may have a large branching fraction into the two Higgs boson final state. We estimate the cross-section needed for a 5-sigma discovery at the 14 TeV LHC for such a narrow di-Higgs resonance, using the invariant mass distributions of the final state bottom jets and photons, as a function of the integrated luminosity. The results are also applicable to any other di-Higgs resonance produced by gluon fusion.
Book Synopsis Observation of a Higgs Boson and Measurement of Its Mass in the Diphoton Decay Channel with the ATLAS Detector at the LHC by : Narei Lorenzo Martinez
Download or read book Observation of a Higgs Boson and Measurement of Its Mass in the Diphoton Decay Channel with the ATLAS Detector at the LHC written by Narei Lorenzo Martinez and published by . This book was released on 2013 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: The Standard Model of the particle physics predicts the existence of a massive scalar boson, usually referred to as Higgs boson in the literature, as resulting from the Spontaneous Symmetry Breaking mechanism, needed to generate the mass of the particles. The Higgs boson whose mass is theoretically undetermined, is experimentally looked for since half a century by various experiments. This is the case of the ATLAS experiment at LHC which started taking data from high energy collisions in 2010. One of the most important decay channel in the LHC environment is the diphoton channel, because the final state can be completely reconstructed with high precision. The photon energy response is a key point in this analysis, as the signal would appear as a narrow resonance over a large background. In this thesis, a detailed study of the photon energy response, using the ATLAS electromagnetic calorimeter has been performed. This study has provided a better understanding of the photon energy resolution and scale, thus enabling an improvement of the sensitivity of the diphoton analysis as well as a precise determination of the systematic uncertainties on the peak position. The diphoton decay channel had a prominent role in the discovery of a new particle compatible with the Standard Model Higgs boson by the ATLAS and CMS experiments, that occurred in July 2012. Using this channel as well as the better understanding of the photon energy response, a measurement of the mass of this particle is proposed in this thesis, with the data collected in 2011 and 2012 at a center-of-mass energy of 7 TeV and 8 TeV. A mass of 126.8 +/- 0.2 (stat) +\- 0.7 (syst) GeV/c2 is found. The calibration of the photon energy measurement with the calorimeter is the source of the largest systematic uncertainty on this measurement. Strategies to reduce this systematic error are discussed.
Book Synopsis Search for Resonances in Diphoton Events at $\sqrt{s} by :
Download or read book Search for Resonances in Diphoton Events at $\sqrt{s} written by and published by . This book was released on 2016 with total page 50 pages. Available in PDF, EPUB and Kindle. Book excerpt: Searches for new resonances decaying into two photons in the ATLAS experiment at the CERN Large Hadron Collider are described. The analysis is based on proton-proton collision data corresponding to an integrated luminosity of 3.2 fb-1 at √s = 13 TeV recorded in 2015. Two searches are performed, one targeted at a spin-2 particle of mass larger than 500 GeV, using Randall-Sundrum graviton states as a benchmark model, and one optimized for a spin-0 particle of mass larger than 200 GeV. Varying both the mass and the decay width, the most significant deviation from the background-only hypothesis is observed at a diphoton invariant mass around 750 GeV with local significances of 3.8 and 3.9 standard deviations in the searches optimized for a spin-2 and spin-0 particle, respectively. The global significances are estimated to be 2.1 standard deviations for both analyses. As a result, the consistency between the data collected at 13 TeV and 8 TeV is also evaluated. Limits on the production cross section times branching ratio to two photons for the two resonance types are reported.
Book Synopsis Interference Effect on Heavy Higgs Resonance Signal in \gamma\gamma and ZZ Channels by :
Download or read book Interference Effect on Heavy Higgs Resonance Signal in \gamma\gamma and ZZ Channels written by and published by . This book was released on 2016 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:
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