1,720,987 research outputs found
Is the X(3915) the x(c0)(2P)?
No full textThe Particle Data Group Meson Summary Table lists the X(3915) meson, omega J/psi. mass peak seen in B -> K omega J/psi decays and gamma gamma -> omega J/psi two-photon fusion reactions, as the x(c0)(2P), the 2(3)P(0) charmonium state. Here, with some reasonable assumptions, it is shown that if the X(3915) is the x(c0)(2P), the measured strength of the gamma gamma -> X(3915) signal implies an upper limit on the branching fraction B(x(c0)(2P) -> omega J/psi) that is below a lower limit inferred for the same quantity from the B -> KX(3915) decay rate. Also, the absence any signal for X(3915) -> D-0(D) over bar (0) in B+ -> (K+D0)(D) over bar (0) decays is used to infer the limit B(X(3915) -> D-0(D) over bar (0)) omega J/psi). This contradicts expectations that x(c0)(2P) decays to D-0(0) should be a dominant process, while decays to omega J/psi, which are Okubo-Zweig-Iizuka suppressed, should be relatively rare. These, plus reasons given earlier by Guo and Meissner, raise concerns about the X(3915) = x(c0)(2P) assignment.273511Nsciescopu
A new hadron spectroscopy
No full textQCD-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 charmedanticharmed
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 QCDinspired
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 XY Z
mesons– and compare them with expectations for conventional quark-antiquark mesons and the
predicted QCD-exotic states.544011sciescopu
New physics searches at the BESIII experiment
No full text©TheAuthor(s) 2021. Published byOxfordUniversity Press on behalf of China Science Publishing&Media Ltd. The standard model (SM) of particle physics, comprised of the unified electroweak and quantum chromodynamic 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. This report reviews some of the highlights from BESIII's searches for signs of new, 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; performing 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.11Nsciescopu
New window on matter-antimatter differences from BESIII
No full textRecent measurements of CP-related comparisons of the weak-interaction parameters that describe the decays of the Xi(-) and the Xi(+) doubly strange hyperon and antihyperon are reviewed and their significance is discussed.11Nsciescopu
Nonstandard heavy mesons and baryons: Experimental evidence
No full textQuantum chromodynamics (QCD), the generally accepted theory for 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 nonstandard multiquark mesons, meson-gluon hybrids, and pentaquark baryons that contain heavy (charm or bottom) quarks has been discovered. Here the experimental evidence for these states is reviewed and some general comparisons of their measured properties with standard quark model expectations and predictions of various models for nonstandard hadrons are made. The conclusion is that the spectroscopy of all but the simplest hadrons is not yet understood. © 2018 American Physical Societ
Perspective study of charmonium and exotics above the DD threshold
No full textThe spectroscopy of exotic states with hidden charm is discussed. Together with charmonium, these provide a good tool for testing theories of the strong interactions including both perturbative and nonperturbative QCD, lattice QCD, potential and other phenomenological models. An elaborated analysis of exotics spectrum is given, and attempts to interpret recent experimentally observed states with masses above the D (Formula presented.) threshold region are considered. Experimental results from different collaborations (BES, BaBar, Belle, LHCb) are analyzed with special attention given to recently discovered hidden charm states. Some of these states can be interpreted as higher-lying charmonium states and others as tetraquarks with hidden charm. It has been shown that charged/neutral tetraquarks must have their neutral/charge partners with mass values differing by at most a few MeV. However, measurements of different decay modes are needed before firm conclusions can be made. These data can be derived directly from the experiments using a high quality antiproton beam with momentum up to 15 GeV/c and proton–proton collisions with momentum up to 26 GeV/c. © 2016, Pleiades Publishing, Ltd011sciescopu
Resonances in QCD
No full textWe report on the EMMI Rapid Reaction Task Force meeting 'Resonances in QCD', which took place at GSI October 12-14, 2015. A group of 26 people met to discuss the physics of resonances in QCD. The aim of the meeting was defined by the following three key questions:. •What is needed to understand the physics of resonances in QCD?•Where does QCD lead us to expect resonances with exotic quantum numbers?•What experimental efforts are required to arrive at a coherent picture? For light mesons and baryons only those with up, down and strange quark content were considered. For heavy-light and heavy-heavy meson systems, those with charm quarks were the focus.This document summarizes the discussions by the participants, which in turn led to the coherent conclusions we present here. © 2016 Elsevier B.V1781sciescopu
Improving the light collection using a new NaI(Tl) crystal encapsulation
No full text© 2020 Elsevier B.V. NaI(Tl) crystals are used as particle detectors in a variety of rare-event search experiments because of their superb light-emission quality. The crystal light yield is generally high, above 10 photoelectrons per keV, and its emission spectrum is peaked around 400 nm, which matches well to the sensitive region of bialkali photocathode photomultiplier tubes. However, since NaI(Tl) crystals are hygroscopic, a sophisticated method of encapsulation has to be applied that prevents moisture from chemically attacking the crystal and thereby degrading the emission. In addition, operation with low energy thresholds, which is essential for a number of new phenomenon searches, is usually limited by the crystal light yield; in these cases higher light yields can translate into lower thresholds that improve the experimental sensitivity. Here we describe the development of an encapsulation technique that simplifies the overall design by attaching the photo sensors directly to the crystal so that light losses are minimized. The light yield of a NaI(Tl) crystal encapsulated with this technique was improved by more than 30%, and as many as 22 photoelectrons per keV have been measured. Consequently, the energy threshold can be lowered and the energy resolution improved. Detectors with this higher light yield are sensitive to events with sub-keV energies and well suited for low-mass dark matter particle searches and measurements of neutrino-nucleus coherent scattering11Nsciescopu
Measurements of B -> (D)over-barDs0*(+)(2317) decay rates and a search for isospin partners of the Ds0*(+)(2317)
No full textWe report improved measurements of the product branching fractions B(B+ --> (D) over bar D-0(s0)*(+)(2317)) x B(D-s0*(+)(2317) --> D-s(+) pi(0)) (8.0(-1.2)(+1.3) +/- 1.1 +/- 0.4) x 10(-4) and B(B-0 --> D-Ds0*(+)(2317)) x B(D-s0*(+)(2317)) --> D-s(+) pi(0)) = (10.2(-1.2)(+1.3) +/- 1.0 +/- 0.4) x 10(-4) where the first errors are statistical, the second are systematic and the third are from D and D-s(+) branching fractions. In addition, we report negative results from a search for hypothesized neutral (z(0)) and doubly charged (z(++)) isospin partners of the D-s0*(+)(2317) and provide upper limits on the product branching fractions B(B-0 --> D(0)z(0)) x B(z(0) --> D-s(+)pi(-)) and B(B+ --> D(0)z(++) ) x B(z(++) --> D-s(+)pi(+)) that are more than an order of magnitude smaller than theoretical expectations for the hypotheses that the D-s0(*+)(2317) is a member of an isospin triplet. The analysis uses a 711 fb(-1) data sample containing 772 million B (B) over bar -meson pairs collected at the Upsilon(4S) resonance in the Belle detector at the KEKB collider.9711Nsciescopu
Observation of an alternative χc0 (2P) candidate in e+e- →j /ψD D OBSERVATION of AN ALTERNATIVE χc0 (2P) ... K. CHILIKIN et al.
No full textWe perform a full amplitude analysis of the process e+e-→J/ψDD, where D refers to either D0 or D+. A new charmoniumlike state X∗(3860) that decays to DD is observed with a significance of 6.5σ. Its mass is (3862-32+26 -13+40) MeV/c2, and its width is (201-67+154 -82+88) MeV. The JPC=0++ hypothesis is favored over the 2++ hypothesis at the level of 2.5σ. The analysis is based on the 980 fb-1 data sample collected by the Belle detector at the asymmetric-energy e+e- collider KEKB. © 2017 American Physical Society81411Nsciescopu
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