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Stephen Lars Olsen

Publications and source records attributed to Stephen Lars Olsen.

At least 19 recordsLinked to original sources

You never have enough J/$ψ$ events: the case for a J/$ψ$ factory

In a talk at an IHEP-Beijing symposium celebrating the 50th anniversary of the discovery of the J/$ψ$, I reminisced about some of the interesting phenomena that were observed in J/$ψ$ decays in the BES, BESII, and BESIII detectors during the 35 year long BES experimental program. The three order of magnitude increase in the J/$ψ$ event samples and the improved detector capabilities that occurred during this time led to a persistent series of interesting discoveries and new insights. As more J/$ψ$ events were collected, the scientific interest in them increased and the breadth of physics topics that are addressed by them expanded. In addition, I speculated on what might happen if, in the next few decades, the magnitude of J/$ψ$ data samples and the detector capabilities continued to increase at similar paces. In particular, I emphasize the possibilities of searches for CP violation in strange hyperon decays and testing the CPT~theorem with strangeness-tagged neutral kaon decays.

hep-ex

CP violation studies at Super Tau-Charm Facility

Charge-parity ($C\!P$) violation in the tau-charm energy region is a promising area for sensitive tests of Standard Model (SM) predictions and searches for new, beyond the SM physics. A future Tau-Charm Facility that operates at center-of-mass energies between 2.0 and 7.0 GeV, with a peak luminosity of $0.5\times10^{35}$~cm$^{-2}$s$^{-1}$, would provide huge numbers of hadrons and tau ($τ$) leptons that are produced in low-background environments and with well understood kinematic properties. In this report, prospects for unique studies of $C\!P$ violation in the decay of charmed hadrons, and in the production and decay of hyperons and $τ$ leptons at a next-generation tau-charm facility are discussed. In addition, opportunities for improved tests of $CPT$ invariance test in $K^{0}-\bar{K}^{0}$ mixing are presented.

hep-ex

The Curious Early History of CKM Matrix -- miracles happen!

The 1973 Kobayashi Maskawa paper proposed a compelling link between Cabibbo's flavor-mixing scheme and CP violation but, since it required the existence of six quarks at a time when the physics community was happy with only three, it received zero attention. However, two years after the paper appeared -- at which time it had received a grand total of two citations -- the charmed quark was discovered and it finally got some notice and acceptance. After this stumbling start, it subsequently emerged as the focal point of an enormous amount of experimental and theoretical research activity. In an invited talk at a KEK symposium to celebrate the 50th anniversary of the KM paper, I reviewed some of the less well known circumstances that occurred in the years preceding and following the paper's appearance.

hep-ph

New Window on Matter-Antimatter Differences

Recent measurements of $CP$-related comparisons of the weak-interaction parameters that describe the decays of the $Ξ^-$ and the $\barΞ^+$ doubly strange hyperon and antihyperon are reviewed and their significance is discussed.

hep-ex

New Physics Searches at the BESIII Experiment

The Standard Model (SM) of particle physics, comprised of the unified electro-weak (EW) and Quantum Chromodynamic (QCD) theories, accurately explains almost all experimental results related to the micro-world, and has made a number of predictions for previously unseen particles, most notably the Higgs scalar boson, that were subsequently discovered. As a result, the SM is currently universally accepted as the theory of the fundamental particles and their interactions. However, in spite of its numerous successes, the SM has a number of apparent shortcomings including: many free parameters that must be supplied by experimental measurements; no mechanism to produce the dominance of matter over antimatter in the universe; and no explanations for gravity, the dark matter in the universe, neutrino masses, the number of particle generations, etc. Because of these shortcomings, there is considerable incentive to search for evidence for new, non-SM physics phenomena that might provide important clues about what a new, beyond the SM theory (BSM) might look like. Although the center-of-mass energies that BESIII can access are far below the energy frontier, searches for new, BSM physics are an important component of its research program. Here we describe ways that BESIII looks for signs of BSM physics by measuring rates for processes that the SM predicts to be forbidden or very rare, searching for non-SM particles such as dark photons, making precision tests of SM predictions, and looking for violations of the discrete symmetries $C$ and $CP$ in processes for which the SM-expectations are immeasurably small.

hep-ph

The BESIII Physics Programme

The standard model of particle physics is a well-tested theoretical framework, but there are still a number of issues that deserve further experimental and theoretical investigation. For quark physics, such questions include: the nature of quark confinement, the mechanism that connects the quarks and gluons of the standard model theory to the strongly interacting particles; and the weak decays of quarks, which may provide insights into new physics mechanisms responsible for the matter-antimatter asymmetry of the Universe. These issues are addressed by the Beijing Spectrometer III (BESIII) experiment at the Beijing Electron-Positron Collider II (BEPCII) storage ring, which for the past decade has been studying particles produced in electron-positron collisions in the tau-charm energy-threshold region, and has by now accumulated the world's largest datasets that enables searches for nonstandard hadrons, weak decays of the charmed particles, and new physics phenomena beyond the standard model. Here, we review the contributions of BESIII to such studies and discuss future prospects for BESIII and other experiments.

hep-ex

Nucleon/Hyperon Physics at BES

The year 2019 marks the 30th anniversary of BES and the 100th anniversary of Rutherford's discovery of the proton. In spite of the fact that when BES operations started the proton was already 70 years old and the strange hyperons were all over 25, BES continues to make important and unique measurements of nucleon and hyperon properties, including some interesting discoveries.

hep-ex

Comment on the X(3915) nonstandard hadron candidate

I review the experimental evidence for the $X(3915)$, the candidate nonstandard meson associated with $ωJψ$ resonance-like peaks in $B\rightarrow KωJψ$ and $γγ\rightarrowωJψ$ near $M(ωJψ)=3920$~MeV, and address the conjecture that it can be identified as the $χ_{c2}^\prime$, the radial excitation of the $χ_{c2}$ charmonium state. Since the partial decay width for $B\rightarrow K X(3915)$ is at least an order-of-magnitude larger than that for $B\rightarrow Kχ_{c2}$, its assignment as the $χ_{c2}^\prime$ is dubious.

hep-ex

The XYZ mesons: what they aren't

I discuss the properties of some representative $XYZ$ mesons in the context of the most commonly proposed models for their underlying nature.

hep-ph

Non-Standard Heavy Mesons and Baryons, an Experimental Review

Quantum Chromodynamics (QCD), the generally accepted theory for the strong interactions, describes the interactions between quarks and gluons. The strongly interacting particles that are seen in nature are hadrons, which are composites of quarks and gluons. Since QCD is a strongly coupled theory at distance scales that are characteristic of observable hadrons, there are no rigorous, first-principle methods to derive the spectrum and properties of the hadrons from the QCD Lagrangian, except for Lattice QCD simulations that are not yet able to cope with all aspects of complex and short-lived states. Instead, a variety of "QCD inspired" phenomenological models have been proposed. Common features of these models are predictions for the existence of hadrons with substructures that are more complex than the standard quark-antiquark mesons and the three quark baryons of the original quark model that provides a concise description of most of the low-mass hadrons. Recently, an assortment of candidates for non-standard multi-quark mesons, meson-gluon hybrids and pentaquark baryons that contain heavy (charm or bottom) quarks have been discovered. Here we review the experimental evidence for these states and make some general comparisons of their measured properties with standard quark-model expectations and predictions of various models for non-standard hadrons. We conclude that the spectroscopy of all but simplest hadrons is not yet understood.

hep-ph

Multiquark Hadrons

A number of candidate multiquark hadrons, i.e., particle resonances with substructures that are more complex than the quark-antiquark mesons and three-quark baryons that are prescribed in the textbooks, have recently been observed. In this talk I present: some recent preliminary BESIII results on the near-threshold behavior of sigma(e+e- --> Lambda Lambda-bar) that may or may not be related to multiquark mesons in the light- and strange-quark sectors; results from Belle and LHCb on the electrically charged, charmoniumlike Z(4430)^+ --> pi^+ psi ' resonance that necessarily has a four-quark substructure; and the recent LHCb discovery of the P_c(4380) and P_c(4450) hidden-charm resonances seen as a complex structure in the J/psi p invariant mass distribution for Lambda_b --> K^-J/psi p decays and necessarily have a five-quark substructure and are, therefore, prominent candidates for pentaquark baryons.

hep-ex

History of Belle and some of its lesser known highlights

I report on the early history of Belle, which was almost entirely focused on testing the Kobayashi Maskawa mechanism for $CP$ violation that predicted large matter-antimatter asymmetries in certain $B$ meson decay modes. Results reported by both BaBar and Belle in the summer of 2001 verified the Kobayashi Maskawa idea and led to their Nobel prizes in 2008. In addition to studies of CP violation, Belle (and BaBar) reported a large number of important results on a wide variety of other subjects, many of which that had nothing to do with B mesons. In this talk I cover three (of many) subjects where Belle measurements have had a significant impact on specific sub-fields of hadron physics but are not generally well know. These include: the discovery of an anomalously large cross sections for double charmonium production in continuum e+e- annihilation; sensitive probes of the structure of the low-mass scalar mesons; and first measurements of the Collins spin fragmentation function.

hep-ex

XYZ Meson Spectroscopy

Many candidate multiquark mesons, i.e., mesons with substructures that are more complex than the quark-antiquark prescription that is in the textbooks, have recently been observed. Many of the most recently observed candidate states are electrically charged and have the same spin and parity, namely JP=1+. In this talk I give an overview of the current experimental situation and identify patterns among the recently discovered JP=1+ states, compare these patterns with expectations from proposed theoretical models, and the existence of additional, related states that might be accessible at current and future experiments. In addition, models that attribute the observed states to kinematically induced cusps are discussed.

hep-ex

A New Hadron Spectroscopy

QCD-motivated models for hadrons predict an assortment of "exotic" hadrons that have structures that are more complex than the quark-antiquark mesons and three-quark baryons of the original quark-parton model. These include pentaquark baryons, the six-quark H-dibaryon, and tetraquark, hybrid and glueball mesons. Despite extensive experimental searches, no unambiguous candidates for any of these exotic configurations have been identified. On the other hand, a number of meson states, one that seems to be a proton-antiproton bound state, and others that contain either charmed-anticharmed quark pairs or bottom-antibottom quark pairs, have been recently discovered that neither fit into the quark-antiquark meson picture nor match the expected properties of the QCD-inspired exotics. Here I briefly review results from a recent search for the H-dibaryon, and discuss some properties of the newly discovered states --the proton-antiproton state and the so-called XYZ mesons-- and compare them with expectations for conventional quark-antiquark mesons and the predicted QCD-exotic states.

hep-ex

Is the X(3915) the chi_{c0}(2P)?

The Particle Data Group has assigned the X(3915) meson, an omega J/psi mass peak seen in B-> omega J/psi decays and in two-photon fusion reactions gamma-gamma->omega J/psi, as the chi_{c0}(2P), the 2^3P_0 charmonium state. Here it is shown that if the X(3915) is the chi_{c0}(2P), the measured strength of the gamma-gamma->X(3915) signal implies an upper limit on the branching fraction Bf(chi_{c0}(2P)->omega J/psi)<7.8% that conflicts with a >14.3% lower limit derived for the same quantity from the B-> K X(3915) decay rate. Also, the absence any signal for X(3915)-> D0 D0-bar in B+ -> K+ D0 D0-bar decays is used to establish the limit Bf(X(3915)->D0 D0-bar) < 1.2xBf(X(3915)->omega J/psi). This contradicts expectations that chi_{c0}(2P) decays to D0 D0-bar would be a dominant process, while decays to omega J/psi, which are Okubo-Zweig-Iizuka suppressed, would be relatively rare. These, plus reasons given earlier by Guo and Meissner, raise serious doubts about the X(3915)=chi_{c0}(2P) assignment.

hep-ex

The Role of Flavor Physics in the LHC Era

Although searches for new physics at the CERN Large Hadron Collider will probably dominate the the agenda of the experimental high energy physics community during the next decade or more, high-intensity experiments at the tau-charm and beauty thresholds will continue to play important complementary roles. These include the establishment of stringent constraints on proposed theories for beyond-the-Standard-Model physics and unique opportunities to address some new physics scenarios that are inaccessible at the LHC. In addition, in the event that the LHC does discover some new phenomena, high sensitivity flavor physics measurements could provide diagnostic clues as to the physics processes responsible for the observed effects. In this talk I present a few examples that illustrate the close inter-relation of new physics searches at the high-energy frontier and high-sensitivity measurements at the intensity frontier.

hep-ex

QCD Exotics

QCD-motivated models for hadrons predict an assortment of "exotic" hadrons that have structures that are more complex then the quark-antiquark mesons and three-quark baryons of the original quark-parton model. These include pentaquark baryons, the six-quark H-dibaryon, and tetra-quark, hybrid, and glueball mesons. Despite extensive experimental searches, no unambiguous candidates for any of these exotic configurations have yet to be identified. On the other hand, a number of meson states, one that seems to be a proton-antiproton bound state, and others that contain either charmed-anticharmed quark pairs or bottom-antibottom quark pairs, have been recently discovered that neither fit into the quark-antiquark meson picture nor match the expected properties of the QCD-inspired exotics. Here I briefly review results from a recent search for the H-dibaryon, and discuss some properties of the newly discovered states --the so-called XYZ mesons-- and compare them with expectations for conventional quark-antiquark mesons and the predicted QCD-exotic states.

hep-ex

Quarkonium at the Frontiers of High Energy Physics: A Snowmass White Paper

In this Snowmass White Paper, we discuss physics opportunities involving heavy quarkonia at the intensity and energy frontiers of high energy physics. We focus primarily on two specific aspects of quarkonium physics for which significant advances can be expected from experiments at both frontiers. The first aspect is the spectroscopy of charmonium and bottomonium states above the open-heavy-flavor thresholds. Experiments at e^+ e^- colliders and at hadron colliders have discovered many new, unexpected quarkonium states in the last 10 years. Many of these states are surprisingly narrow, and some have electric charge. The observations of these charged quarkonium states are the first definitive discoveries of manifestly exotic hadrons. These results challenge our understanding of the QCD spectrum. The second aspect is the production of heavy quarkonium states with large transverse momentum. Experiments at the LHC are measuring quarkonium production with high statistics at unprecedented values of p_T. Recent theoretical developments may provide a rigorous theoretical framework for inclusive production of quarkonia at large p_T. Experiments at the energy frontier will provide definitive tests of this framework. Experiments at the intensity frontier also provide an opportunity to understand the exclusive production of quarkonium states.

hep-ph