C. A. Davis

Bio: C. A. Davis is an academic researcher from University of Manitoba. The author has contributed to research in topics: Elastic scattering & Neutron. The author has an hindex of 16, co-authored 60 publications receiving 1074 citations. Previous affiliations of C. A. Davis include TRIUMF.

Evidence of Xi hypernuclear production in the C-12(K-,K+)(Xi)Be-12 reaction

Abstract: The E885 Collaboration utilized the $1.8 \mathrm{GeV}{/cK}^{\ensuremath{-}}$ beam line at the Alternating Gradient Synchrotron (AGS) to accumulate greater than 10 times the world's existing data sample of ${(K}^{\ensuremath{-}}{,K}^{+})$ events on carbon. A total of about $3\ifmmode\times\else\texttimes\fi{}{10}^{5} {(K}^{\ensuremath{-}}{,K}^{+})$ events were collected and analyzed. $\ensuremath{\Xi}$ hypernuclear states are expected to be produced through the reaction ${K}^{\ensuremath{-}}{+}^{12}\stackrel{\ensuremath{\rightarrow}}{C}{K}^{+}{+}_{\ensuremath{\Xi}}^{12}\mathrm{Be}.$ A signal could also result from direct production of ${}_{\ensuremath{\Lambda}}^{11}\mathrm{Be}+\ensuremath{\Lambda}$ without a distinct $\ensuremath{\Xi}$ intermediate state. The measured missing-mass spectrum indicates the existence of a signal below the threshold for free ${\ensuremath{\Xi}}^{\ensuremath{-}}$ production that cannot be explained by background or effects of limited resolution. Although the resolution was not sufficient to resolve discrete hypernuclear states, the excess of events in the region of missing mass, kinematically inaccessible in free ${\ensuremath{\Xi}}^{\ensuremath{-}}$ production, can be compared with theoretical predictions for ${}_{\ensuremath{\Xi}}^{12}\mathrm{Be}$ production. Reasonable agreement between the data and theory is achieved by assuming a $\ensuremath{\Xi}$-nucleus potential well depth ${\mathrm{V}}_{0\ensuremath{\Xi}}$ of about 14 MeV within the Woods-Saxon prescription.

First Determination of the Weak Charge of the Proton

Abstract: The Qweak experiment has measured the parity-violating asymmetry in polarized e-p elastic scattering at Q2 = 0.025(GeV/c)2, employing 145 microamps of 89% longitudinally polarized electrons on a 34.4cm long liquid hydrogen target at Jefferson Lab. The results of the experiment's commissioning run are reported here, constituting approximately 4% of the data collected in the experiment. From these initial results the measured asymmetry is Aep = -279 +- 35 (statistics) +- 31 (systematics) ppb, which is the smallest and most precise asymmetry ever measured in polarized e-p scattering. The small Q2 of this experiment has made possible the first determination of the weak charge of the proton, QpW, by incorporating earlier parity-violating electron scattering (PVES) data at higher Q2 to constrain hadronic corrections. The value of QpW obtained in this way is QnW(PVES) = 0.064 +- 0.012, in good agreement with the Standard Model prediction of QpW(SM) = 0.0710 +- 0.0007. When this result is further combined with the Cs atomic parity violation (APV) measurement, significant constraints on the weak charges of the up and down quarks can also be extracted. That PVES+APV analysis reveals the neutron's weak charge to be QnW(PVES+APV) = -0.975 +- 0.010.

Precision Measurement of the Weak Charge of the Proton

Abstract: The fields of particle and nuclear physics have undertaken extensive programs to search for evidence of physics beyond that explained by current theories. The observation of the Higgs boson at the Large Hadron Collider completed the set of particles predicted by the Standard Model (SM), currently the best description of fundamental particles and forces. However, the theory's limitations include a failure to predict fundamental parameters and the inability to account for dark matter/energy, gravity, and the matter-antimater asymmetry in the universe, among other phenomena. Given the lack of additional particles found so far through direct searches in the post-Higgs era, indirect searches utilizing precise measurements of well predicted SM observables allow highly targeted alternative tests for physics beyond the SM. Indirect searches have the potential to reach mass/energy scales beyond those directly accessible by today's high-energy accelerators. The value of the weak charge of the proton Q_W^p is an example of such an indirect search, as it sets the strength of the proton's interaction with particles via the well-predicted neutral electroweak force. Parity violation (invariance under spatial inversion (x,y,z) -> (-x,-y,-z)) is violated only in the weak interaction, thus providing a unique tool to isolate the weak interaction in order to measure the proton's weak charge. Here we report Q_W^p=0.0719+-0.0045, as extracted from our measured parity-violating (PV) polarized electron-proton scattering asymmetry, A_ep=-226.5+-9.3 ppb. Our value of Q_W^p is in excellent agreement with the SM, and sets multi-TeV-scale constraints on any semi-leptonic PV physics not described within the SM.

Production of (4)(double Lambda)H hypernuclei.

Abstract: An experiment demonstrating the production of double-Lambda hypernuclei in (K(-),K(+)) reactions on (9)Be was carried out at the D6 line in the BNL alternating-gradient synchrotron. The technique was the observation of pions produced in sequential mesonic weak decay, each pion associated with one unit of strangeness change. The results indicate the production of a significant number of the double hypernucleus (4)(double Lambda)H and the twin hypernuclei (4)(Lambda)H and (3)(Lambda)H. The relevant decay chains are discussed and a simple model of the production mechanism is presented. An implication of this experiment is that the existence of an S = -2 dibaryon more than a few MeV below the double Lambda mass is unlikely.

Precision measurement of the weak charge of the proton

Abstract: Large experimental programmes in the fields of nuclear and particle physics search for evidence of physics beyond that explained by current theories. The observation of the Higgs boson completed the set of particles predicted by the standard model, which currently provides the best description of fundamental particles and forces. However, this theory’s limitations include a failure to predict fundamental parameters, such as the mass of the Higgs boson, and the inability to account for dark matter and energy, gravity, and the matter–antimatter asymmetry in the Universe, among other phenomena. These limitations have inspired searches for physics beyond the standard model in the post-Higgs era through the direct production of additional particles at high-energy accelerators, which have so far been unsuccessful. Examples include searches for supersymmetric particles, which connect bosons (integer-spin particles) with fermions (half-integer-spin particles), and for leptoquarks, which mix the fundamental quarks with leptons. Alternatively, indirect searches using precise measurements of well predicted standard-model observables allow highly targeted alternative tests for physics beyond the standard model because they can reach mass and energy scales beyond those directly accessible by today’s high-energy accelerators. Such an indirect search aims to determine the weak charge of the proton, which defines the strength of the proton’s interaction with other particles via the well known neutral electroweak force. Because parity symmetry (invariance under the spatial inversion (x, y, z) → (−x, −y, −z)) is violated only in the weak interaction, it provides a tool with which to isolate the weak interaction and thus to measure the proton’s weak charge1. Here we report the value 0.0719 ± 0.0045, where the uncertainty is one standard deviation, derived from our measured parity-violating asymmetry in the scattering of polarized electrons on protons, which is −226.5 ± 9.3 parts per billion (the uncertainty is one standard deviation). Our value for the proton’s weak charge is in excellent agreement with the standard model2 and sets multi-teraelectronvolt-scale constraints on any semi-leptonic parity-violating physics not described within the standard model. Our results show that precision parity-violating measurements enable searches for physics beyond the standard model that can compete with direct searches at high-energy accelerators and, together with astronomical observations, can provide fertile approaches to probing higher mass scales. Measurement of the asymmetry in the parity-violating scattering of polarized electrons on protons gives the weak charge of the proton as 0.0719 ± 0.0045, in agreement with the standard model.

Modern theory of nuclear forces

Abstract: Nuclear forces can be systematically derived using effective chiral Lagrangians consistent with the symmetries of QCD. I review the status of the calculations for two- and three-nucleon forces and their applications in few-nucleon systems. I also address issues like the quark mass dependence of the nuclear forces and resonance saturation for four-nucleon operators.

Search for New Physics with Atoms and Molecules

Abstract: Advances in atomic physics, such as cooling and trapping of atoms and molecules and developments in frequency metrology, have added orders of magnitude to the precision of atom-based clocks and sensors. Applications extend beyond atomic physics and this article reviews using these new techniques to address important challenges in physics and to look for variations in the fundamental constants, search for interactions beyond the standard model of particle physics, and test the principles of general relativity.

The Meson Theory of Nuclear Forces and Nuclear Structure

Abstract: Nowadays it has become customary in nuclear physics to denote by “tradition” the approach that considers nucleons and mesons as the relevant degrees of freedom. It is the purpose of this chapter to review this “traditional” approach in the area of nuclear forces and their applications to nuclear structure.

Electron-Ion Collider: The next QCD frontier: Understanding the glue that binds us all

Abstract: This White Paper presents the science case of an Electron-Ion Collider (EIC), focused on the structure and interactions of gluon-dominated matter, with the intent to articulate it to the broader nuclear science community. It was commissioned by the managements of Brookhaven National Laboratory (BNL) and Thomas Jefferson National Accelerator Facility (JLab) with the objective of presenting a summary of scientific opportunities and goals of the EIC as a follow-up to the 2007 NSAC Long Range plan. This document is a culmination of a community-wide effort in nuclear science following a series of workshops on EIC physics over the past decades and, in particular, the focused ten-week program on “Gluons and quark sea at high energies” at the Institute for Nuclear Theory in Fall 2010. It contains a brief description of a few golden physics measurements along with accelerator and detector concepts required to achieve them. It has been benefited profoundly from inputs by the users’ communities of BNL and JLab. This White Paper offers the promise to propel the QCD science program in the US, established with the CEBAF accelerator at JLab and the RHIC collider at BNL, to the next QCD frontier.