Search

The strong CP violation problem has a long history emanating from its discovery 60 years ago in the decay of neutral kaons and subsequent experimental and theoretical studies over several decades. We review herein experimental data that observe indirect CP violation of the order of $\sim10^{-3}$, as well as the discovery of direct CP violation of the order of $\sim10^{-6}$. Despite improved experimental methods over the past half a century, the original CP violation numbers have remained the same. Verification of the CP violation in the decay of charged kaons was also observed. Data reflecting CP violation in the decays of $B$ and $D$ mesons have become very important and are also discussed in this review. The question of CP violation only with the participation of $s\bar{s}$, $c\bar{c}$, and $b\bar{b}$ quarks in the framework of the Standard Model or beyond it and its small magnitude remains open., Comment: 25 pages, 5 figures; we have revised the paper accordingly: 35 pages and 8 figures now

During the past several decades a large quantity of high-quality mesonic photo- and electro- production data have been measured at electromagnetic facilities worldwide. By contrast, meson-beam data for these same final states are mostly outdated, largely of poorer quality, or even non-existent, especially those involving spin asymmetries and polarizations. Thus existing meson beam results provide inadequate input to interpret, analyze, and exploit the potential of the new electromagnetic data. To achieve full benefit of these high-precision electromagnetic data, new high-statistics data from measurements with meson beams, with good angle and energy coverage for a wide range of reactions, are critically needed to advance our knowledge in baryon and meson spectroscopy and other related areas of hadron physics. To address this situation, new, state-of-the-art meson-beam facilities are needed. This presentation summarizes unresolved issues in hadron physics and outlines the opportunities and advances that are possible with such facilities., Comment: 8 pages, 8 figures, Submitted to Proceedings of the 25th International Symposium on Spin Physics

A unified Chew-Mandelstam description of single-pion photoproduction data, together with pion- and eta-hadroproduction data, has been extended to include measurements carried out over the last decade. We consider photo-decay amplitudes evaluated at the pole with particular emphasis on ng couplings and the influence of weighting on our fits. Both energy-dependent and single-energy analysis (energy-binned data) are considered., Comment: 30 pages, 18 figures, and 14 tables

New high-statistics total cross section data for $\gamma p\to J/\psi p$ from the GLUonic EXcitation (GlueX) experiment are fitted in a search for the exotic $P_c(4312)^+$ state observed by the Large Hadron Collider beauty (LHCb) collaboration. The integrated luminosity of this GlueX experiment was about $320~\mathrm{pb^{-1}}$. The fits show that destructive interference involving an $S$-wave resonance and associated non-resonance background produces a sharp dip structure about $75~\mathrm{MeV}$ below the LHCb mass, in the same location as a similar structure is seen in the data. Limitations of the employed model and the need for improved statistics are discussed., Comment: 4 pages, 3 figures, 2 tables

We have evaluated pseudoscalar and scalar neutral pion photoproduction in $\vec{\gamma}p\to\pi^0p$ and $\vec{\gamma}p\to a_0^0p$ above the resonance region and within Regge phenomenology. Our fit, including GlueX $\Sigma$ pseudoscalar photoproduction data, shows that previous SLAC $\Sigma$ measurements for $\vec{\gamma}p \to \pi^0p$ above $E_\gamma = 4~\mathrm{GeV}$ are at variance with SLAC data with more recent measurements made by GlueX in vicinity of $E_\gamma = 9~\mathrm{GeV}$. The Regge model predicts that the beam polarization asymmetry $\Sigma$ of the scalar meson is opposite to that of pseudoscalar meson photoproduction, however, the cross sections are similar. While the vector natural parity meson exchange is dominant in both cases, the contribution of the pseudovector unnatural parity meson exchange is very small. Using Regge phenomenology, we predicted high energy behavior for double polarized observables $\mathbb{E}$, $\mathbb{F}$, $\mathbb{G}$, and $\mathbb{H}$ for the reactions $\gamma p\to \pi^0p$ and $\gamma p\to a_0^0p$., Comment: 8 pages, 5 figures, several small glitches were fixed

Phenomenological amplitudes obtained in partial-wave analyses (PWA) of single-pion photoproduction are used to evaluate the contribution of this process to the Gerasimov-Drell-Hearn (GDH), Baldin and Gell-Mann-Goldberger-Thirring (GGT) sum rules, by integrating up to 2 GeV in photon energy. Our study confirms that the single-pion contribution to all these sum rules converges even before the highest considered photon energy, but the levels of saturation are very different in the three cases. Single-pion production almost saturates the GDH sum rule for the proton, while a large fraction is missing in the neutron case. The Baldin integrals for the proton and the neutron are both saturated to about four fifths of the predicted total strength. For the GGT sum rule, the wide variability in predictions precludes any definitive statement., Comment: 12 pages, 7 figure, 3 tables; discussion refined, references added, Minor fixes to the authorship list found during production; acknowledgement added; final version accepted by Phys Rev C

A review of our works providing a theoretical description of incoherent pion photoproduction on the deuteron is presented. The existing $\gamma d\to\pi NN$ data are analysed, especially those obtained more recently by the CLAS Collaboration at JLab, the A2 Collaboration at MAMI at Mainz, and the PION@MAX-lab Collaboration at Lund. A procedure, which accounts for the final state interactions (FSI), is applied to extract $\gamma n\to\pi N$ differential cross sections from the deuteron data. The role of FSI is discussed. We also comment on the results of other works in connection with some discrepancies seen in comparing the model with experiment. The electromagnetic properties of baryon $N^\ast$ resonances, improved using the extracted $\gamma n\to\pi N$ differential cross sections, are presented. A model description of the cross section data from charged-pion photoproduction reactions $\gamma d\to\pi^{\pm}NN$ near threshold is also given. The $\gamma d\to\pi^-pp$ data are used to extract the $E_{0+}$ multipole and total crsoss sections of the reaction $\gamma n\to\pi^-p$ near threshold., Comment: 35 pages, 10 figures, 2 tables

Over the past two decades, meson photo- and electroproduction data of unprecedented quality and quantity have been measured at electromagnetic facilities worldwide. By contrast, the meson-beam data for the same hadronic final states are mostly outdated and largely of poor quality, or even non-existent, and thus provide inadequate input to help interpret, analyze, and exploit the full potential of the new electromagnetic data. To reap the full benefit of the high-precision electromagnetic data, new high-statistics data from measurements with meson beams, with good angle and energy coverage for a wide range of reactions, are critically needed to advance our knowledge in baryon and meson spectroscopy and other related areas of hadron physics. To address this situation, a state-of-the-art meson-beam facility needs to be constructed. The present letter summarizes unresolved issues in hadron physics and outlines the vast opportunities and advances that only become possible with such a facility., Comment: 7 pages, 2 figures. arXiv admin note: substantial text overlap with arXiv:1503.07763. That is extension vs published version in EPJA51, 129 (2015)

High-accuracy $\Upsilon$-meson photoproduction data from EIC and EicC experiments will allow the measurement of the near-threshold total cross section of the reaction $\gamma p\to\Upsilon p$, from which the absolute value of the $\Upsilon p$ scattering length, $|\alpha_{\Upsilon p}|$, can be extracted using a Vector-Meson Dominance model. For this evaluation, we used $\Upsilon$-meson photoproduction quasi-data from the QCD approach (the production amplitude can be factorized in terms of gluonic generalized parton distributions and the quarkonium distribution amplitude). A comparative analysis of $|\alpha_{\Upsilon p}|$ with the recently determined scattering lengths for $\omega p$, $\phi p$, and $J/\psi p$ using the A2, CLAS, and GlueX experimental data are performed. The role of the "young" vector-meson effect is evaluated., Comment: 6 pages, 6 figures, 3 tables

We evaluated recent CLAS Collaboration measurements for the $90^\circ$ meson photoproduction off the nucleon using a tagged photon beam spanning the energy interval $s = 3 - 11$ GeV$^2$. The results are compared with the "Quark Counting Rules" predictions., Comment: 9 pages, 5 figures, 1 table, revised version

We propose a high-statistics measurement of few body nuclear structure and short range correlations in quasi-elastic scattering at 6.6 GeV from $^2$H, $^3$He and $^3$H targets in Hall B with the CLAS12 detector. We will measure absolute cross sections for $(e,e'p)$ and $(e,e'pN)$ quasi-elastic reaction channels up to a missing momentum $p_{miss} \approx 1$ GeV/c over a wide range of $Q^2$ and $x_B$ and construct the isoscalar sum of $^3$H and $^3$He. We will compare $(e,e'p)$ cross sections to nuclear theory predictions using a wide variety of techniques and $NN$ interactions in order to constrain the $NN$ interaction at short distances. We will measure $(e,e'pN)$ quasi-elastic reaction cross sections and $(e,e'pN)/(e,e'p)$ ratios to understand short range correlated (SRC) $NN$ pairs in the simplest non-trivial system. $^3$H and $^3$He, being mirror nuclei, exploit the maximum available isospin asymmetry. They are light enough that their ground states are readily calculable, but they already exhibit complex nuclear behavior, including $NN$ SRCs. We will also measure $^2$H$(e,e'p)$ in order to help theorists constrain non-quasielastic reaction mechanisms in order to better calculate reactions on $A=3$ nuclei. Measuring all three few body nuclei together is critical, in order to understand and minimize different reaction effects, such as single charge exchange final state interactions, in order to test ground-state nuclear models. We will also measure the ratio of inclusive $(e,e')$ quasi-elastic cross sections (integrated over $x_B$) from $^3$He and $^3$H in order to extract the neutron magnetic form factor $G_M^n$ at small and moderate values of $Q^2$. We will measure this at both 6.6 GeV and 2.2 GeV., Comment: Final version of the Proposal [PR12-20-005] approved by JLab PAC48

We propose to create a secondary beam of neutral kaons in Hall D at Jefferson Lab to be used with the GlueX experimental setup for strange hadron spectroscopy. The superior CEBAF electron beam will enable a flux on the order of $1\times 10^4~K_L/sec$, which exceeds the flux of that previously attained at SLAC by three orders of magnitude. The use of a deuteron target will provide first measurements ever with neutral kaons on neutrons. The experiment will measure both differential cross sections and self-analyzed polarizations of the produced $\Lambda$, $\Sigma$, $\Xi$, and $\Omega$ hyperons using the GlueX detector at the Jefferson Lab Hall D. The measurements will span CM $\cos\theta$ from $-0.95$ to 0.95 in the range W = 1490 MeV to 2500 MeV. The new data will significantly constrain the partial wave analyses and reduce model-dependent uncertainties in the extraction of the properties and pole positions of the strange hyperon resonances, and establish the orbitally excited multiplets in the spectra of the $\Xi$ and $\Omega$ hyperons. Comparison with the corresponding multiplets in the spectra of the charm and bottom hyperons will provide insight into he accuracy of QCD-based calculations over a large range of masses. The proposed facility will have a defining impact in the strange meson sector through measurements of the final state $K\pi$ system up to 2 GeV invariant mass. This will allow the determination of pole positions and widths of all relevant $K^\ast(K\pi)$ $S$-,$P$-,$D$-,$F$-, and $G$-wave resonances, settle the question of the existence or nonexistence of scalar meson $\kappa/K_0^\ast(700)$ and improve the constrains on their pole parameters. Subsequently improving our knowledge of the low-lying scalar nonet in general., Comment: Final version of the KLF Proposal [C12-19-001] approved by JLab PAC48. The intermediate version of the proposal was posted in arXiv:1707.05284 [hep-ex]. 103 pages, 52 figures, 8 tables, 324 references. Several typos were fixed

The Muon Scattering Experiment at the Paul Scherrer Institut uses a mixed beam of electrons, muons, and pions, necessitating precise timing to identify the beam particles and reactions they cause. We describe the design and performance of three timing detectors using plastic scintillator read out with silicon photomultipliers that have been built for the experiment. The Beam Hodoscope, upstream of the scattering target, counts the beam flux and precisely times beam particles both to identify species and provide a starting time for time-of-flight measurements. The Beam Monitor, downstream of the scattering target, counts the unscattered beam flux, helps identify background in scattering events, and precisely times beam particles for time-of-flight measurements. The Beam Focus Monitor, mounted on the target ladder under the liquid hydrogen target inside the target vacuum chamber, is used in dedicated runs to sample the beam spot at three points near the target center, where the beam should be focused., Comment: Fixed typos, added references, and rephrased some sections to be clearer. Changed numbering of tables and figures in Appendix

The Kaon Production Target (KPT) is an important component of the proposed K-Long facility which will be operated in JLab Hall~D, targeting strange baryon and meson spectroscopy. In this note we present a conceptual design for the Be-target assembly for the planned K-Long beam line, which will be used along with the GlueX spectrometer in its standard configuration for the proposed experiments. The high quality 12-GeV CEBAF electron beam enables production of a K$_L$ flux at the GlueX target on the order of $1\times 10^4 K_L/sec$, which exceeds the K$_L$ flux previously attained at SLAC by three orders of magnitude. An intense K$_L$ beam would open a new window of opportunity not only to locate "missing resonances" in the strange hadron spectrum, but also to establish their properties by studying different decay channels systematically. The most important and radiation damaging background in K$_L$ production is due to neutrons. The Monte Carlo simulations for the proposed conceptual design of KPT show that the resulting neutron and gamma flux lead to a prompt radiation dose rate for the KLF experiment that is below the JLab Radiation Control Department radiation dose rate limits in the experimental hall and at the site boundary, and will not substantially affect the performance of the spectrometer., Comment: 9 pages, 9 figures

Modern experimental facilities, such as CBELSA, ELPH, JLab, MAMI and SPring-8 have provided a tremendous volume of data, often with wide energy and angular coverage, and with increasing precision. For reactions with two hadrons in the final state, these data are often presented as multiple sets of panels, with angular distributions at numerous specific energies. Such presentations have limited visual appeal, and their physical content is typically extracted through some model- dependent treatment. Instead, we explore the use of a Legendre series expansion with a relatively small number of essential coefficients. This approach has been applied in several recent experimental investigations. We present some general properties of the Legendre coefficients in the helicity framework and consider what physical information can be extracted without any model-dependent assumptions., Comment: 13 pgs, 3 figs

Energy-dependent and single-energy fits to the existing nucleon-nucleon database have been updated to incorporate recent measurements. The fits cover a region from threshold to 3 GeV, in the laboratory kinetic energy, for proton-proton scattering, with an upper limit of 1.3 GeV for neutron-proton scattering. Experiments carried out at the COSY-WASA and COSY-ANKE facilities have had a significant impact on the partial-wave solutions. Results are discussed in terms of both partial-wave and direct reconstruction amplitudes., Comment: 15 pages, 14 figures

The measurement was performed with circularly polarized photons incident on longitudinally polarized target in Hall B at the Thomas Jefferson National Accelerator Facility. The helicity asymmetry E for $\vec{\gamma}\vec{p}\to\pi^0p$ was determined at CM energies between 1450 MeV and 2050 MeV and compared to the SAID, MAID, and BnGa partial-wave analyses., Comment: 5 pages, 5 figures; Hadron 2015 Proceedings

An overview of the GW SAID and ITEP groups' effort to analyze pion photoproduction on the neutron-target will be given. The disentanglement of the isoscalar and isovector EM couplings of N* and Delta* resonances does require compatible data on both proton and neutron targets. The final-state interaction plays a critical role in the state-of-the-art analysis in extraction of the gn-->piN data from the deuteron target experiments. Then resonance couplings determined by the SAID PWA technique are then compared to previous findings. The neutron program is important component of the current JLab, MAMI-C, SPring-8, ELSA, and ELPH studies., Comment: 6 pages, 7 figures, 1 table; Hadron 2015 Proceedings. arXiv admin note: substantial text overlap with arXiv:1501.02510

Over the past two decades, meson photo- and electro-production data of unprecedented quality and quantity have been measured at electromagnetic facilities worldwide. By contrast, the meson-beam data for the same hadronic final states are mostly outdated and largely of poor quality, or even nonexistent, and thus provide inadequate input to help interpret, analyze, and exploit the full potential of the new electromagnetic data. To reap the full benefit of the high-precision electromagnetic data, new high-statistics data from measurements with meson beams, with good angle and energy coverage for a wide range of reactions, are critically needed to advance our knowledge in baryon and meson spectroscopy and other related areas of hadron physics. To address this situation, a state of-the-art meson-beam facility needs to be constructed. The present paper summarizes unresolved issues in hadron physics and outlines the vast opportunities and advances that only become possible with such a facility., Comment: 46 pages, 10 figures, 4 tables

An overview of the GW SAID and ITEP groups effort to analyze pion photoproduction on the neutron-target will be given. The disentanglement the isoscalar and isovector EM couplings of N* and Delta* resonances does require compatible data on both proton and neutron targets. The final-state interaction plays a critical role in the state-of-the-art analysis in extraction of the gamma n --> pi N data from the deuteron target experiments. It is important component of the current JLab, MAMI-C, SPring-8, ELSA, and ELPH programs, Comment: 7 pages, 7 figures, 1 table; Proceedings of International Conference Dark Matter, Hadron Physics and Fusion Physics, Messina, Italy, Sept. 2014; will be published in EPJ Web of Conferences

We present an overview of the GW SAID group effort to analyze on new pion photoproduction on both proton- and neutron-targets. The main database contribution came from the recent CLAS and MAMI unpolarized and polarized measurements. The differential cross section for the processes gamma n --> pi- p was extracted from new measurements accounting for Fermi motion effects in the impulse approximation (IA) as well as NN and piN effects beyond the IA. The EM coupling results are compared to other recent studies., Comment: 4 pages, 3 figures, 2 tables; Contribution to the proceedings of the 13th International Conference on Meson-Nucleon Physics and Structure of Nucleon (MENU 2013), Rome, Italy, Sept. - Oct. 2013

A unified description of single-pion photoproduction data, together with pion- and eta-hadroproduction data, has been achieved in a Chew-Mandelstam parametrization which is consistent with unitarity at the two-body level. Energy-dependent and single-energy partial wave analyses of pion photoproduction data have been performed and compared to previous SAID fits and multipoles from the Mainz and Bonn-Gatchina groups., Comment: 11 pages, 9 figures, and 2 tables

We report the first extraction of the pion-nucleon multipoles near the production threshold for the $n\pi^+$ channel at relatively high momentum transfer ($Q^2$ up to 4.2 $\rm{GeV^2}$). The dominance of the s-wave transverse multipole ($E_{0+}$), expected in this region, allowed us to access the generalized form factor $G_1$ within the light-cone sum rule (LCSR) framework as well as the axial form factor $G_A$. The data analyzed in this work were collected by the nearly $4\pi$ CEBAF Large Acceptance Spectrometer (CLAS) using a 5.754 $\rm{GeV}$ electron beam on a proton target. The differential cross section and the $\pi-N$-multipole $E_{0+}/G_D$ were measured using two different methods, the LCSR and a direct multipole fit. The results from the two methods are found to be consistent and almost $Q^2$ independent., Comment: 17pages, 22 figures, Journal article (Physical Review C)

Energy-dependent and single-energy fits to the existing pion photoproduction database have been updated to cover the region from threshold to 2.7 GeV in the laboratory photon energy. Revised resonance photo-decay couplings have been extracted and compared to previous determinations. The influence of recent measurements is displayed. Remaining problems and future approaches are discussed., Comment: 9 pages, 6 figures, 3 tables

Model dependence of multipole analysis has been explored through energy-dependent and single-energy fits to pion photoproduction data. The MAID energy-dependent solution has been used as input for an event generator producing realistic pseudo data. These were fitted using the SAID parametrization approach to determine single-energy and energy-dependent solutions over a range of lab photon energies from 200 to 1200 MeV. The resulting solutions were found to be consistent with the input amplitudes from MAID. Fits with a $\chi$-squared per datum of unity or less were generally achieved. We discuss energy regions where consistent results are expected, and explore the sensitivity of fits to the number of included single- and double-polarization observables. The influence of Watson's theorem is examined in detail., Comment: 12 pages, 8 figures