Author
Zhen Liu
Other affiliations: University of Pittsburgh, University of Wisconsin-Madison, University of Minnesota ...read more
Bio: Zhen Liu is an academic researcher from University of Maryland, College Park. The author has contributed to research in topics: Higgs boson & Large Hadron Collider. The author has an hindex of 39, co-authored 101 publications receiving 5134 citations. Previous affiliations of Zhen Liu include University of Pittsburgh & University of Wisconsin-Madison.
Papers
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Stanford University1, Rutgers University2, Johns Hopkins University3, Cornell University4, Fermilab5, University of California, Davis6, University of Oregon7, University of California, Berkeley8, Michigan State University9, University of Tokyo10, University of California, Santa Barbara11, Stony Brook University12, Boston University13, École Polytechnique Fédérale de Lausanne14, University of Pittsburgh15, Argonne National Laboratory16, Northwestern University17, Carleton University18, CERN19, University of Wisconsin-Madison20, Syracuse University21, Seoul National University22, Tohoku University23, Korea Institute for Advanced Study24, Harvard University25, University of Michigan26, Princeton University27, TRIUMF28, Florida State University29, University of California, San Diego30, Lawrence Berkeley National Laboratory31, University of Florida32, Massachusetts Institute of Technology33, University of California, Irvine34, University of Arizona35, University of Washington36, York University37, Perimeter Institute for Theoretical Physics38, University of Illinois at Chicago39, University of Zurich40, Yale University41, University of Hawaii at Manoa42, Austrian Academy of Sciences43, New York University44
TL;DR: A collection of simplified models relevant to the design of new-physics searches at the Large Hadron Collider (LHC) and the characterization of their results is presented in this paper.
Abstract: This document proposes a collection of simplified models relevant to the design of new-physics searches at the Large Hadron Collider (LHC) and the characterization of their results. Both ATLAS and CMS have already presented some results in terms of simplified models, and we encourage them to continue and expand this effort, which supplements both signature-based results and benchmark model interpretations. A simplified model is defined by an effective Lagrangian describing the interactions of a small number of new particles. Simplified models can equally well be described by a small number of masses and cross-sections. These parameters are directly related to collider physics observables, making simplified models a particularly effective framework for evaluating searches and a useful starting point for characterizing positive signals of new physics. This document serves as an official summary of the results from the 'Topologies for Early LHC Searches' workshop, held at SLAC in September of 2010, the purpose of which was to develop a set of representative models that can be used to cover all relevant phase space in experimental searches. Particular emphasis is placed on searches relevant for the first similar to 50-500 pb(-1) of data and those motivated by supersymmetric models. This note largely summarizes material posted at http://lhcnewphysics.org/, which includes simplified model definitions, Monte Carlo material, and supporting contacts within the theory community. We also comment on future developments that may be useful as more data is gathered and analyzed by the experiments.
491 citations
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C. N. Yang Institute for Theoretical Physics1, Argonne National Laboratory2, Perimeter Institute for Theoretical Physics3, University of Chicago4, Florida State University5, Harvard University6, Hong Kong University of Science and Technology7, University of Pittsburgh8, University of Washington9, University of Victoria10, Boston University11
TL;DR: A survey of nonstandard Higgs decays that are consistent with the 125-GeV Higgs-like resonance can be found in this paper, where a large set of new experimental analyses on the existing and forthcoming data from the Large Hadron Collider (LHC) are presented.
Abstract: We perform an extensive survey of nonstandard Higgs decays that are consistent with the 125 GeV Higgs-like resonance. Our aim is to motivate a large set of new experimental analyses on the existing and forthcoming data from the Large Hadron Collider (LHC). The explicit search for exotic Higgs decays presents a largely untapped discovery opportunity for the LHC collaborations, as such decays may be easily missed by other searches. We emphasize that the Higgs is uniquely sensitive to the potential existence of new weakly coupled particles and provide a unified discussion of a large class of both simplified and complete models that give rise to characteristic patterns of exotic Higgs decays. We assess the status of exotic Higgs decays after LHC run I. In many cases we are able to set new nontrivial constraints by reinterpreting existing experimental analyses. We point out that improvements are possible with dedicated analyses and perform some preliminary collider studies. We prioritize the analyses according to their theoretical motivation and their experimental feasibility. This document is accompanied by a Web site that will be continuously updated with further information [ http://exotichiggs.physics.sunysb.edu ].
363 citations
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19 Feb 2019
TL;DR: The potential reach and opportunities in Higgs physics during the High Luminosity phase of the LHC were summarized in this paper, with an expected dataset of pp collisions at 14 TeV, corresponding to an integrated luminosity of 3~ab$^{-1}$.
Abstract: The discovery of the Higgs boson in 2012, by the ATLAS and CMS experiments, was a success achieved with only a percent of the entire dataset foreseen for the LHC. It opened a landscape of possibilities in the study of Higgs boson properties, Electroweak Symmetry breaking and the Standard Model in general, as well as new avenues in probing new physics beyond the Standard Model. Six years after the discovery, with a conspicuously larger dataset collected during LHC Run 2 at a 13 TeV centre-of-mass energy, the theory and experimental particle physics communities have started a meticulous exploration of the potential for precision measurements of its properties. This includes studies of Higgs boson production and decays processes, the search for rare decays and production modes, high energy observables, and searches for an extended electroweak symmetry breaking sector. This report summarises the potential reach and opportunities in Higgs physics during the High Luminosity phase of the LHC, with an expected dataset of pp collisions at 14 TeV, corresponding to an integrated luminosity of 3~ab$^{-1}$. These studies are performed in light of the most recent analyses from LHC collaborations and the latest theoretical developments. The potential of an LHC upgrade, colliding protons at a centre-of-mass energy of 27 TeV and producing a dataset corresponding to an integrated luminosity of 15~ab$^{-1}$, is also discussed.
340 citations
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TL;DR: The work of the Energy Frontier Higgs Boson working group of the 2013 Community Summer Study (Snowmass) as mentioned in this paper summarizes the key elements of a precision Higgs physics program and document the physics potential of future experimental facilities as elucidated during the Snowmass study.
Abstract: This report summarizes the work of the Energy Frontier Higgs Boson working group of the 2013 Community Summer Study (Snowmass). We identify the key elements of a precision Higgs physics program and document the physics potential of future experimental facilities as elucidated during the Snowmass study. We study Higgs couplings to gauge boson and fermion pairs, double Higgs production for the Higgs self-coupling, its quantum numbers and $C\!P$-mixing in Higgs couplings, the Higgs mass and total width, and prospects for direct searches for additional Higgs bosons in extensions of the Standard Model. Our report includes projections of measurement capabilities from detailed studies of the Compact Linear Collider (CLIC), a Gamma-Gamma Collider, the International Linear Collider (ILC), the Large Hadron Collider High-Luminosity Upgrade (HL-LHC), Very Large Hadron Colliders up to 100 TeV (VLHC), a Muon Collider, and a Triple-Large Electron Positron Collider (TLEP).
219 citations
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Juliette Alimena1, James Baker Beacham2, Martino Borsato3, Yangyang Cheng4 +213 more•Institutions (105)
TL;DR: In this paper, the authors present a survey of the current state of LLP searches at the Large Hadron Collider (LHC) and chart a path for the development of LLP searches into the future, both in the upcoming Run 3 and at the high-luminosity LHC.
Abstract: Particles beyond the Standard Model (SM) can generically have lifetimes that are long compared to SM particles at the weak scale. When produced at experiments such as the Large Hadron Collider (LHC) at CERN, these long-lived particles (LLPs) can decay far from the interaction vertex of the primary proton–proton collision. Such LLP signatures are distinct from those of promptly decaying particles that are targeted by the majority of searches for new physics at the LHC, often requiring customized techniques to identify, for example, significantly displaced decay vertices, tracks with atypical properties, and short track segments. Given their non-standard nature, a comprehensive overview of LLP signatures at the LHC is beneficial to ensure that possible avenues of the discovery of new physics are not overlooked. Here we report on the joint work of a community of theorists and experimentalists with the ATLAS, CMS, and LHCb experiments—as well as those working on dedicated experiments such as MoEDAL, milliQan, MATHUSLA, CODEX-b, and FASER—to survey the current state of LLP searches at the LHC, and to chart a path for the development of LLP searches into the future, both in the upcoming Run 3 and at the high-luminosity LHC. The work is organized around the current and future potential capabilities of LHC experiments to generally discover new LLPs, and takes a signature-based approach to surveying classes of models that give rise to LLPs rather than emphasizing any particular theory motivation. We develop a set of simplified models; assess the coverage of current searches; document known, often unexpected backgrounds; explore the capabilities of proposed detector upgrades; provide recommendations for the presentation of search results; and look towards the newest frontiers, namely high-multiplicity 'dark showers', highlighting opportunities for expanding the LHC reach for these signals.
218 citations
Cited by
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TL;DR: In this paper, the ATLAS experiment is described as installed in i ts experimental cavern at point 1 at CERN and a brief overview of the expec ted performance of the detector is given.
Abstract: This paper describes the ATLAS experiment as installed in i ts experimental cavern at point 1 at CERN. It also presents a brief overview of the expec ted performance of the detector.
2,798 citations
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TL;DR: In this paper, the authors report world averages of measurements of b-hadron, c-, c-, and tau-lepton properties obtained by the Heavy Flavor Averaging Group (HFAG) using results available through the end of 2011.
Abstract: This article reports world averages of measurements of b-hadron, c-hadron, and tau-lepton properties obtained by the Heavy Flavor Averaging Group (HFAG) using results available through the end of 2011. In some cases results available in the early part of 2012 are included. For the averaging, common input parameters used in the various analyses are adjusted (rescaled) to common values, and known correlations are taken into account. The averages include branching fractions, lifetimes, neutral meson mixing parameters, CP violation parameters, parameters of semileptonic decays and CKM matrix elements.
2,151 citations
01 Apr 2003
TL;DR: In this paper, the authors measured the flux of neutrino from distant nuclear reactors and found fewer nu;(e) events than expected from standard assumptions about nu; (e) propagation at the 99.95% C.L.yr exposure.
Abstract: KamLAND has measured the flux of nu;(e)'s from distant nuclear reactors. We find fewer nu;(e) events than expected from standard assumptions about nu;(e) propagation at the 99.95% C.L. In a 162 ton.yr exposure the ratio of the observed inverse beta-decay events to the expected number without nu;(e) disappearance is 0.611+/-0.085(stat)+/-0.041(syst) for nu;(e) energies >3.4 MeV. In the context of two-flavor neutrino oscillations with CPT invariance, all solutions to the solar neutrino problem except for the "large mixing angle" region are excluded.
1,659 citations
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01 Jan 2007
TL;DR: In this paper, a preliminary set of updated NLO parton distributions and their uncertainties determined from CCFR and NuTeV dimuon cross sections are presented, along with additional jet data from HERA and the Tevatron.
Abstract: We present a preliminary set of updated NLO parton distributions. For the first time we have a quantitative extraction of the strange quark and antiquark distributions and their uncertainties determined from CCFR and NuTeV dimuon cross sections. Additional jet data from HERA and the Tevatron improve our gluon extraction. Lepton asymmetry data and neutrino structure functions improve the flavour separation, particularly constraining the down quark valence distribution.
1,288 citations