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We describe in this paper two approved experiments in Hall A and Hall C at Jefferson Lab that will investigate the pure gluonic component of the strong interaction of Quantum Chromodynamics by measuring the elastic J / ψ electro and photo-production cross section in the threshold region as well as explore the nature of the recently discovered LHCb charmed pentaquarks.

The atomic nucleus is made of protons and neutrons (nucleons), which are themselves composed of quarks and gluons. Understanding how the quark–gluon structure of a nucleon bound in an atomic nucleus is modified by the surrounding nucleons is an outstanding challenge. Although evidence for such modification—known as the EMC effect—was first observed over 35 years ago, there is still no generally accepted explanation for its cause 1 – 3 . Recent observations suggest that the EMC effect is related to close-proximity short-range correlated (SRC) nucleon pairs in nuclei 4 , 5 . Here we report simultaneous, high-precision measurements of the EMC effect and SRC abundances. We show that EMC data can be explained by a universal modification of the structure of nucleons in neutron–proton SRC pairs and present a data-driven extraction of the corresponding universal modification function. This implies that in heavier nuclei with many more neutrons than protons, each proton is more likely than each neutron to belong to an SRC pair and hence to have distorted quark structure. This universal modification function will be useful for determining the structure of the free neutron and thereby testing quantum chromodynamics symmetry-breaking mechanisms and may help to discriminate between nuclear physics effects and beyond-the-standard-model effects in neutrino experiments. Simultaneous high-precision measurements of the EMC effect and short-range correlated abundances for several nuclei reveal a universal modification of the structure of nucleons in short-range correlated neutron–proton pairs.

A high-precision parity-violating electron–quark scattering experiment provides measurements of a combination of electron–quark weak couplings with a precision five times higher than the single previous direct study, confirming the predictions of the electroweak particle-physics theory and providing constraints on parity-violating interactions beyond the standard model. Parity-violating asymmetry revisited Parity symmetry — or mirror-image symmetry — implies that flipping left and right does not change the laws of physics. Violation of parity symmetry in the weak nuclear force was discovered in the mid-1950s and parity violation in electron scattering was important in establishing, and is now used to test, the standard model of particle physics. This study reports a high-precision electron–quark scattering experiment that provides a measurement of the parity-violating asymmetry with a precision of five times higher than the single previous direct study via this scattering process. The results confirm the predictions of electroweak particle-physics theory, while providing constraints on parity-violating interactions beyond the standard model. Symmetry permeates nature and is fundamental to all laws of physics. One example is parity (mirror) symmetry, which implies that flipping left and right does not change the laws of physics. Laws for electromagnetism, gravity and the subatomic strong force respect parity symmetry, but the subatomic weak force does not 1 , 2 . Historically, parity violation in electron scattering has been important in establishing (and now testing) the standard model of particle physics. One particular set of quantities accessible through measurements of parity-violating electron scattering are the effective weak couplings C 2 q , sensitive to the quarks’ chirality preference when participating in the weak force, which have been measured directly 3 , 4 only once in the past 40 years. Here we report a measurement of the parity-violating asymmetry in electron–quark scattering, which yields a determination of 2 C 2 u  −  C 2 d (where u and d denote up and down quarks, respectively) with a precision increased by a factor of five relative to the earlier result. These results provide evidence with greater than 95 per cent confidence that the C 2 q couplings are non-zero, as predicted by the electroweak theory. They lead to constraints on new parity-violating interactions beyond the standard model, particularly those due to quark chirality. Whereas contemporary particle physics research is focused on high-energy colliders such as the Large Hadron Collider, our results provide specific chirality information on electroweak theory that is difficult to obtain at high energies. Our measurement is relatively free of ambiguity in its interpretation, and opens the door to even more precise measurements in the future.

We present evidence of non-excimer-based secondary scintillation in gaseous xenon, obtained using both the NEXT-White time projection chamber (TPC) and a dedicated setup. Detailed comparison with first-principle calculations allows us to assign this scintillation mechanism to neutral bremsstrahlung (NBrS), a process that is postulated to exist in xenon that has been largely overlooked. For photon emission below 1000 nm, the NBrS yield increases from about10−2photon/e−cm−1bar−1at pressure-reduced electric field values of50Vcm−1bar−1to above3×10−1photon/e−cm−1bar−1at500Vcm−1bar−1. Above1.5kVcm−1bar−1, values that are typically employed for electroluminescence, it is estimated that NBrS is present with an intensity around1photon/e−cm−1bar−1, which is about 2 orders of magnitude lower than conventional, excimer-based electroluminescence. Despite being fainter than its excimeric counterpart, our calculations reveal that NBrS causes luminous backgrounds that can interfere, in either gas or liquid phase, with the ability to distinguish and/or to precisely measure low primary-scintillation signals (S1). In particular, we show this to be the case in the “buffer” region, where keeping the electric field below the electroluminescence threshold does not suffice to extinguish secondary scintillation. The electric field leakage in this region should be mitigated to avoid intolerable levels of NBrS emission. Furthermore, we show that this new source of light emission opens up a viable path toward obtaining S2 signals for discrimination purposes in future single-phase liquid TPCs for neutrino and dark matter physics, with estimated yields up to20–50photons/e−cm−1.

The atomic nucleus is made of protons and neutrons (nucleons), which are themselves composed of quarks and gluons. Understanding how the quark-gluon structure of a nucleon bound in an atomic nucleus is modified by the surrounding nucleons is an outstanding challenge. Although evidence for such modification--known as the EMC effect--was first observed over 35 years ago, there is still no generally accepted explanation for its cause.sup.1-3. Recent observations suggest that the EMC effect is related to close-proximity short-range correlated (SRC) nucleon pairs in nuclei.sup.4,5. Here we report simultaneous, high-precision measurements of the EMC effect and SRC abundances. We show that EMC data can be explained by a universal modification of the structure of nucleons in neutron-proton SRC pairs and present a data-driven extraction of the corresponding universal modification function. This implies that in heavier nuclei with many more neutrons than protons, each proton is more likely than each neutron to belong to an SRC pair and hence to have distorted quark structure. This universal modification function will be useful for determining the structure of the free neutron and thereby testing quantum chromodynamics symmetry-breaking mechanisms and may help to discriminate between nuclear physics effects and beyond-the-standard-model effects in neutrino experiments.

A bstract Double electron capture by proton-rich nuclei is a second-order nuclear process analogous to double beta decay. Despite their similarities, the decay signature is quite different, potentially providing a new channel to measure the hypothesized neutrinoless mode of these decays. The Standard-Model-allowed two-neutrino double electron capture (2 νEC EC ) has been predicted for a number of isotopes, but only observed in 78 Kr, 130 Ba and, recently, 124 Xe. The sensitivity to this decay establishes a benchmark for the ultimate experimental goal, namely the potential to discover also the lepton-number-violating neutrinoless version of this process, 0 νEC EC . Here we report on the current sensitivity of the NEXT-White detector to 124 Xe 2 νEC EC and on the extrapolation to NEXT-100. Using simulated data for the 2 νEC EC signal and real data from NEXT-White operated with 124 Xe-depleted gas as background, we define an optimal event selection that maximizes the NEXT-White sensitivity. We estimate that, for NEXT-100 operated with xenon gas isotopically enriched with 1 kg of 124 Xe and for a 5-year run, a sensitivity to the 2 νEC EC half-life of 6 × 10 22 y (at 90% confidence level) or better can be reached.

The double-spin-polarization observable$${\\mathbb {E}}$$E for$$\\vec {\\gamma }\\vec {p}\\rightarrow p\\pi ^0$$γ → p → → p π 0 has been measured with the CEBAF Large Acceptance Spectrometer (CLAS) at photon beam energies$$E_\\gamma $$E γ from 0.367 to$$2.173~\\textrm{GeV}$$2.173 GeV (corresponding to center-of-mass energies from 1.240 to$$2.200~\\textrm{GeV}$$2.200 GeV ) for pion center-of-mass angles,$$\\cos \\theta _{\\pi ^0}^{c.m.}$$cos θ π 0 c . m . , between$$-$$- 0.86 and 0.82. These new CLAS measurements cover a broader energy range and have smaller uncertainties compared to previous CBELSA data and provide an important independent check on systematics. These measurements are compared to predictions as well as new global fits from The George Washington University, Mainz, and Bonn-Gatchina groups. Their inclusion in multipole analyses will allow us to refine our understanding of the single-pion production contribution to the Gerasimov-Drell-Hearn sum rule and improve the determination of resonance properties, which will be presented in a future publication.

The double-spin-polarization observable ${\\mathbb {E}}$ for $\\vec {\\gamma }\\vec {p} \\rightarrow p \\pi ^0$ has been measured with the CEBAF Large Acceptance Spectrometer (CLAS) at photon beam energies $E_γ$ from 0.367 to $\\mathrm{2.173}$ $\\mathrm{GeV}$ (corresponding to center-of-mass energies from 1.240 to $\\mathrm{2.200}$ $\\mathrm{GeV}$) for pion center-of-mass angles, $\\mathrm{cosθ}_{π^0}^{c.m.}$, between — 0.86 and 0.82. These new CLAS measurements cover a broader energy range and have smaller uncertainties compared to previous CBELSA data and provide an important independent check on systematics. These measurements are compared to predictions as well as new global fits from The George Washington University, Mainz, and Bonn-Gatchina groups. Their inclusion in multipole analyses will allow us to refine our understanding of the single-pion production contribution to the Gerasimov-Drell-Hearn sum rule and improve the determination of resonance properties, which will be presented in a future publication.

The Neutrino Experiment with a Xenon TPC (NEXT) searches for the neutrinoless double-beta (0νββ) decay of 136Xe using high-pressure xenon gas TPCs with electroluminescent amplification. A scaled-up version of this technology with about 1 tonne of enriched xenon could reach in less than 5 years of operation a sensitivity to the half-life of 0νββ decay better than 1027 years, improving the current limits by at least one order of magnitude. This prediction is based on a well-understood background model dominated by radiogenic sources. The detector concept presented here represents a first step on a compelling path towards sensitivity to the parameter space defined by the inverted ordering of neutrino masses, and beyond.

The double-spin-polarization observable $\\mathbb{E}$ for $\\vec{\\gamma}\\vec{p}\\to p\\pi^0$ has been measured with the CEBAF Large Acceptance Spectrometer (CLAS) at photon beam energies $E_\\gamma$ from 0.367 to $2.173~\\mathrm{GeV}$ (corresponding to center-of-mass energies from 1.240 to $2.200~\\mathrm{GeV}$) for pion center-of-mass angles, $\\cos\\theta_{\\pi^0}^{c.m.}$, between -0.86 and 0.82. These new CLAS measurements cover a broader energy range and have smaller uncertainties compared to previous CBELSA data and provide an important independent check on systematics. These measurements are compared to predictions as well as new global fits from The George Washington University, Mainz, and Bonn-Gatchina groups. Their inclusion in multipole analyses will refine our understanding of the single-pion production contribution to the Gerasimov-Drell-Hearn sum rule and improve the determination of resonance properties.