Hybrid Charmonium and the ρ−π\rho-\pi Puzzle

Using the method of QCD Sum Rules, we estimate the energy of the lowest hybrid Charmonium state, and find it to be at the energy of the $\Psi'(2S)$ state, about 600 Mev above the $J/\Psi(1S)$ state. Since our solution is not consistent with a pure hybrid at this energy, we conclude that the $\Psi'(2S)$ state is probably an admixed $c \bar{c}$ and hybrid $c \bar{c}g$ state. From this conjecture we find a possible explanation of the famous $\rho-\pi$ puzzle.Comment: 9 pages, 7 figure

Probing the Neutrino-Mass Scale with the KATRIN Experiment

The absolute mass scale of neutrinos is an intriguing open question in contemporary physics. The as-yet-unknown mass of the lightest and, at the same time, most abundant massive elementary particle species bears fundamental relevance to theoretical particle physics, astrophysics, and cosmology. The most model-independent experimental approach consists of precision measurements of the kinematics of weak decays, notably tritium β decay. With the KATRIN experiment, this direct neutrino-mass measurement has entered the sub-eV domain, recently pushing the upper limit on the electron-based neutrino mass down to 0.8 eV (90% CL) on the basis of first-year data out of ongoing, multiyear operations. Here, we review the experimental apparatus of KATRIN, the progress of data taking, and initial results. While KATRIN is heading toward the target sensitivity of 0.2 eV, other scientific goals are pursued. We discuss the search for light sterile neutrinos and an outlook on future keV-scale sterile-neutrino searches as well as further physics opportunities beyond the Standard Model

Report of the Topical Group on Neutrino Properties for Snowmass 2021

Neutrinos are the most elusive among the known elementary particles, because of their feeble interactions with ordinary matter. They are also the most mysterious, because of their tiny masses that suggest a novel mass generating mechanism, their unknown Dirac or Majorana nature, and their big quantum mixing leading to large-amplitude flavor oscillations. This Topical Group focuses on neutrino properties that are not directly investigated in other Topical Groups of the Neutrino Frontier: in particular, the absolute value of the neutrino masses, the Dirac or Majorana nature of neutrinos, their electromagnetic properties, their lifetime, and hypothetical exotic properties.Comment: Topical Group Report for NF05 (Neutrino Frontier Topical Group on Neutrino Properties) for Snowmass 2021. 51 pages excluding reference

Precision measurements of A1N in the deep inelastic regime

We have performed precision measurements of the double-spin virtual-photon asymmetry A1A1 on the neutron in the deep inelastic scattering regime, using an open-geometry, large-acceptance spectrometer and a longitudinally and transversely polarized 3He target. Our data cover a wide kinematic range 0.277≤x≤0.5480.277≤x≤0.548 at an average Q2Q2 value of 3.078 (GeV/c)2, doubling the available high-precision neutron data in this x range. We have combined our results with world data on proton targets to make a leading-order extraction of the ratio of polarized-to-unpolarized parton distribution functions for up quarks and for down quarks in the same kinematic range. Our data are consistent with a previous observation of anA1n zero crossing near x=0.5x=0.5. We find no evidence of a transition to a positive slope in(Δd+Δd¯)/(d+d¯) up to x=0.548x=0.548

KATRIN: Toward a High-Precision Neutrino-Mass Determination with Tritium

<p>Twenty years after the discovery of neutrino oscillations established non-zero neutrino mass, the absolute neutrino-mass scale remains unknown. The KArlsruhe TRItium Neutrino experiment (KATRIN) is designed to improve the current direct limit on this mass scale by an order of magnitude, with a projected sensitivity of 0.2 eV/c² at the 90% confidence level. To achieve this, KATRIN will perform high-precision spectroscopy of the endpoint region of the tritium beta-decay spectrum, using a high-intensity, windowless gaseous tritium source and a high-resolution electrostatic spectrometer. In this talk, I will review the theoretical basis for a tritium-based neutrino-mass measurement; explore some of the experimental challenges addressed by the KATRIN collaboration; and share early results from the commissioning of the experiment, including KATRIN's first tritium runs.</p

Probing the neutrino mass scale with the KATRIN experiment

The absolute mass scale of the neutrino is one of the most fundamental open questions in contemporary particle physics, with implications from particle theory to cosmology. Through precision measurements of beta-decay kinematics, the KATRIN experiment probes the neutrino mass with unprecedented sensitivity

Measurements of the Double-Spin Asymmetry A₁ on Helium-3: Toward a Precise Measurement of the Neutron A₁

The spin structure of protons and neutrons has been an open question for nearly twenty-five years, after surprising experimental results disproved the simple model in which valence quarks were responsible for nearly 100% of the nucleon spin. Diverse theoretical approaches have been brought to bear on the problem, but a shortage of precise data – especially on neutron spin structure – has prevented a thorough understanding. Experiment E06-014, conducted in Hall A of Jefferson Laboratory in 2009, presented an opportunity to add to the world data set for the neutron in the poorly covered valence-quark region. Jefferson Laboratory’s highly polarized electron beam, combined with Hall A’s facilities for a high-density, highly polarized 3He target, allowed a high-luminosity double-polarized experiment, while the large acceptance of the BigBite spectrometer gave coverage over a wide kinematic range: 0.15 2 2 . From these data, we extract the longitudinal asymmetry in virtual photon-nucleon scattering, A1, on the 3He nucleus. Combined with the remaining E06-014 data, this will form the basis of a measurement of the neutron asymmetry An 1 that will extend the kinematic range of the data available to test models of spin-dependent parton distributions in the nucleon.</p

Measurement of the Neutron Radius of 208Pb through Parity Violation in Electron Scattering

We report the first measurement of the parity-violating asymmetry APV in the elastic scattering of polarized electrons from Pb208. APV is sensitive to the radius of the neutron distribution (Rn). The result APV=0.656±0.060(stat)±0.014(syst)  ppm corresponds to a difference between the radii of the neutron and proton distributions Rn−Rp=0.33+0.16−0.18  fm and provides the first electroweak observation of the neutron skin which is expected in a heavy, neutron-rich nucleus.</p

New Precision Limit on the Strange Vector Form Factors of the Proton

<p>The parity-violating cross-section asymmetry in the elastic scattering of polarized electrons from unpolarized protons has been measured at a four-momentum transfer squared Q2=0.624  GeV2 and beam energy Eb=3.48  GeV to be APV=−23.80±0.78(stat)±0.36(syst) parts per million. This result is consistent with zero contribution of strange quarks to the combination of electric and magnetic form factors GsE+0.517GsM=0.003±0.010(stat)±0.004(syst)±0.009(ff), where the third error is due to the limits of precision on the electromagnetic form factors and radiative corrections. With this measurement, the world data on strange contributions to nucleon form factors are seen to be consistent with zero and not more than a few percent of the proton form factors.</p