Search

We report measurements of the photon beam asymmetry $\mathrm{\Sigma }$ for the reactions $\vec{\gamma }p\to p{\pi }^0$ and $\vec{\gamma }p\to p\eta$ from the GlueX experiment using a 9 GeV linearly polarized, tagged photon beam incident on a liquid hydrogen target in Jefferson Lab's Hall D. The asymmetries, measured as a function of the proton momentum transfer, possess greater precision than previous ${\pi }^0$ measurements and are the first $\eta$ measurements in this energy regime. The results are compared with theoretical predictions based on $t$-channel, quasiparticle exchange and constrain the axial-vector component of the neutral meson production mechanism in these models.

We demonstrate the hohlraum radiation temperature and symmetry required for ignition-scale inertial confinement fusion capsule implosions. Cryogenic gas-filled hohlraums with 2.2 mm-diameter capsules are heated with unprecedented laser energies of 1.2 MJ delivered by 192 ultraviolet laser beams on the National Ignition Facility. Laser backscatter measurements show that these hohlraums absorb 87% to 91% of the incident laser power resulting in peak radiation temperatures of $T_{\mathrm{RAD}}=300\mathrm{eV}$ and a symmetric implosion to a $100\mu \mathrm{m}$ diameter hot core.

We report on the measurement of spin density matrix elements of the $\mathrm{\Lambda }\left(1520\right)$ in the photoproduction reaction $\gamma p\to \mathrm{\Lambda }\left(1520\right)K^{+}$, via its subsequent decay to $K^{-}p$. The measurement was performed as part of the GlueX experimental program in Hall D at Jefferson Laboratory using a linearly polarized photon beam with $E_{\gamma }=8.2\mathrm{GeV}\text{–}8.8\mathrm{GeV}$. These are the first such measurements in this photon energy range. Results are presented in bins of momentum transfer squared, $-(t-t_{\text{0}})$. We compare the results with a Reggeon exchange model and determine that natural exchange amplitudes are dominant in $\mathrm{\Lambda }\left(1520\right)$ photoproduction.

Based on $334{\mathrm{pb}}^{-1}$ of photoproduction data collected with the GlueX detector at Jefferson Lab, we have measured for the first time the cross section of the exclusive reaction $\gamma +p\to \varphi (1020){\pi }^{+}{\pi }^{-}p$ by reconstructing the final state $K^{+}{K}^{-}{\pi }^{+}{\pi }^{-}p$ produced with a photon beam of energies between 8.0 and 11.6 GeV. Based on the measured differential cross section, we have performed a search for the strangeoniumlike exotic candidate $Y(2175)$, recently renamed to $\varphi (2170)$. This state has been reported by different $e^{+}{e}^{-}$ annihilation experiments and it is addressed here for the first time in a photoproduction experiment. We do not find evidence for this state when using the resonance parameters quoted by the Particle Data Group and provide upper limits on the photoproduction cross section. Instead, we find a structure at a mass of $m(\varphi {\pi }^{+}{\pi }^{-})=2.24\mathrm{GeV}/c^2$ with a statistical significance of about $5\sigma$. The parameters of this structure differ from those quoted by the Particle Data Group for the $\varphi (2170)$ and are consistent with a previous observation in $e^{+}{e}^{-}$ annihilation. In addition, there is evidence for a second structure at $1.82\mathrm{GeV}/c^2$.

We report on the measurement of the beam asymmetry $\mathrm{\Sigma }$ for the reactions $\vec{\gamma }p\to p\eta$ and $\vec{\gamma }p\to p{\eta }^{\prime }$ from the GlueX experiment using an 8.2–8.8-GeV linearly polarized tagged photon beam incident on a liquid hydrogen target in Hall D at Jefferson Laboratory. These measurements are made as a function of momentum transfer $-t$ with significantly higher statistical precision than our earlier $\eta$ measurements and are the first measurements of ${\eta }^{\prime }$ in this energy range. We compare the results to theoretical predictions based on $t$-channel quasiparticle exchange. We also compare the ratio of ${\mathrm{\Sigma }}_{\eta }$ to ${\mathrm{\Sigma }}_{{\eta }^{\prime }}$ to these models as this ratio is predicted to be sensitive to the amount of $s\overline{s}$ exchange in the production. We find that photoproduction of both $\eta$ and ${\eta }^{\prime }$ is dominated by natural parity exchange with little dependence on $-t$.

We report on the measurement of the $\gamma p\to J/\psi p$ cross section from $E_{\gamma }=11.8\mathrm{GeV}$ down to the threshold at 8.2 GeV using a tagged photon beam with the GlueX experiment. We find that the total cross section falls toward the threshold less steeply than expected from two-gluon exchange models. The differential cross section $d\sigma /dt$ has an exponential slope of $1.67\pm 0.39{\mathrm{GeV}}^{-2}$ at 10.7 GeV average energy. The LHCb pentaquark candidates $P_c^{+}$ can be produced in the $s$ channel of this reaction. We see no evidence for them and set model-dependent upper limits on their branching fractions $\mathcal{B}(P_c^{+}\to J/\psi p)$ and cross sections $\sigma (\gamma p\to P_c^{+})\times \mathcal{B}(P_c^{+}\to J/\psi p)$.

We report a measurement of the ${\pi }^{-}$ photoproduction beam asymmetry for the reaction $\vec{\gamma }p\to {\pi }^{-}{\mathrm{\Delta }}^{++}$ using data from the GlueX experiment in the photon beam energy range 8.2–8.8 GeV. The asymmetry $\mathrm{\Sigma }$ is measured as a function of four-momentum transfer $t$ to the ${\mathrm{\Delta }}^{++}$ and compared to phenomenological models. We find that $\mathrm{\Sigma }$ varies as a function of $t$: negative at smaller values and positive at higher values of $\left|t\right|$. The reaction can be described theoretically by $t$-channel particle exchange requiring pseudoscalar, vector, and tensor intermediaries. In particular, this reaction requires charge exchange, allowing us to probe pion exchange and the significance of higher-order corrections to one-pion exchange at low momentum transfer. Constraining production mechanisms of conventional mesons may aid in the search for and study of unconventional mesons. This is the first measurement of the process at this energy.

The spin-exotic hybrid meson ${\pi }_1(1600)$ is predicted to have a large decay rate to the $\omega \pi \pi$ final state. Using $76.6{\mathrm{pb}}^{-1}$ of data collected with the GlueX detector, we measure the cross sections for the reactions $\gamma p\to \omega {\pi }^{+}{\pi }^{-}p$, $\gamma p\to \omega {\pi }^0{\pi }^{0}p$, and $\gamma p\to \omega {\pi }^{-}{\pi }^0{\mathrm{\Delta }}^{++}$ in the range $E_{\gamma }=8–10\mathrm{GeV}$. Using isospin conservation, we set the first upper limits on the photoproduction cross sections of the ${\pi }_1^0(1600)$ and ${\pi }_1^{-}(1600)$. We combine these limits with lattice calculations of decay widths and find that photoproduction of ${\eta }^{\prime }\pi$ is the most sensitive two-body system to search for the ${\pi }_1(1600)$.

The GlueX experiment at Jefferson Lab studies photoproduction of mesons using linearly polarized $8.5\text{GeV}$ photons impinging on a hydrogen target which is contained within a detector with near-complete coverage for charged and neutral particles. We present measurements of spin-density matrix elements for the photoproduction of the vector meson $\rho$(770). The statistical precision achieved exceeds that of previous experiments for polarized photoproduction in this energy range by orders of magnitude. We confirm a high degree of $s$-channel helicity conservation at small squared four-momentum transfer $t$ and are able to extract the $t$ dependence of natural- and unnatural-parity exchange contributions to the production process in detail. We confirm the dominance of natural-parity exchange over the full $t$ range. We also find that helicity amplitudes in which the helicity of the incident photon and the photoproduced $\rho \left(770\right)$ differ by two units are negligible for $-t<0.5{\text{GeV}}^2/c^2$.

We measure for the first time the differential photoproduction cross section $d\sigma /dt$ of the $a_2\left(1320\right)$ meson at an average photon beam energy of 8.5 GeV, using data with an integrated luminosity of 104 ${\mathrm{pb}}^{-1}$ collected by the GlueX experiment. We fully reconstruct the $\gamma p\to \eta {\pi }^{0}p$ reaction and perform a partial-wave analysis in the $a_2\left(1320\right)$ mass region with amplitudes that incorporate the linear polarization of the beam. This allows us to separate for the first time the contributions of natural- and unnatural-parity exchanges. These measurements provide novel information about the photoproduction mechanism, which is critical for the search for spin-exotic states.

We measure the spin-density matrix elements (SDMEs) for the photoproduction of $\varphi \left(1020\right)$ off of the proton in its decay to $K_S^0{K}_L^0$, using 105 ${\mathrm{pb}}^{-1}$ of data collected with a linearly polarized photon beam using the GlueX experiment. The SDMEs are measured in nine bins of the squared four-momentum transfer $t$ in the range $-t=0.15-1.0$ ${\mathrm{GeV}}^2$, providing the first measurement of their $t$ dependence for photon beam energies of $E_{\gamma }=8.2-8.8$ GeV. We confirm the dominance of Pomeron exchange in this region and put constraints on the contribution of other Regge exchanges. We also find that helicity amplitudes where the helicity of the photon and $\varphi \left(1020\right)$ differ by two units are negligible.

We report measurements of the photon beam asymmetry $\mathrm{\Sigma }$ for the reaction $\vec{\gamma }p\to K^{+}{\mathrm{\Sigma }}^0$(1193) using the GlueX spectrometer in Hall D at Jefferson Lab. Data were collected by using a linearly polarized photon beam in the energy range of 8.2–8.8 GeV incident on a liquid hydrogen target. The beam asymmetry $\mathrm{\Sigma }$ was measured as a function of the Mandelstam variable $t$, and a single value of $\mathrm{\Sigma }$ was extracted for events produced in the $u$ channel. These are the first exclusive measurements of the photon beam asymmetry $\mathrm{\Sigma }$ for the reaction in this energy range. For the $t$ channel, the measured beam asymmetry is close to unity over the $t$ range studied, $-t=(0.1–1.4)$($\mathrm{GeV}/{c)}^2$, with an average value of $\mathrm{\Sigma }=1.00\pm 0.05$. This agrees with theoretical models that describe the reaction via the natural-parity exchange of the $K^{*}$(892) Regge trajectory. A value of $\mathrm{\Sigma }=0.41\pm 0.09$ is obtained for the $u$ channel integrated up to $-u=2.0$ ($\mathrm{GeV}/{c)}^2$.

We report the total and differential cross sections for $J/\psi$ photoproduction with the large acceptance GlueX spectrometer for photon beam energies from the threshold at 8.2 GeV up to 11.44 GeV and over the full kinematic range of momentum transfer squared, $t$. Such coverage facilitates the extrapolation of the differential cross sections to the forward ($t=0$) point beyond the physical region. The forward cross section is used by many theoretical models and plays an important role in understanding $J/\psi$ photoproduction and its relation to the $J/\psi$-proton interaction. These measurements of $J/\psi$ photoproduction near threshold are also crucial inputs to theoretical models that are used to study important aspects of the gluon structure of the proton, such as the gluon generalized parton distribution of the proton, the mass radius of the proton, and the trace anomaly contribution to the proton mass. We observe possible structures in the total cross section energy dependence and find evidence for contributions beyond gluon exchange in the differential cross section close to threshold, both of which are consistent with contributions from open-charm intermediate states.

We present a search for axionlike particles, $a$, produced in photon-proton collisions at a center-of-mass energy of approximately 4 GeV, focusing on the scenario where the $a$-gluon coupling is dominant. The search uses $a\to \gamma \gamma$ and $a\to {\pi }^{+}{\pi }^{-}{\pi }^0$ decays, and a data sample corresponding to an integrated luminosity of $168{\mathrm{pb}}^{-1}$ collected with the GlueX detector. The search for $a\to \gamma \gamma$ decays is performed in the mass range of $180<m_a<480\mathrm{MeV}$, while the search for $a\to {\pi }^{+}{\pi }^{-}{\pi }^0$ decays explores the $600<m_a<720\mathrm{MeV}$ region. No evidence for a signal is found, and 90% confidence-level exclusion limits are placed on the $a$-gluon coupling strength. These constraints are the most stringent to date over much of the mass ranges considered.

The GlueX experiment at Jefferson Lab has observed $p\overline{p}$ and, for the first time, $\mathrm{\Lambda }\overline{\mathrm{\Lambda }}$ and $p\overline{\mathrm{\Lambda }}$ photoproduction from a proton target at photon energies up to 11.6 GeV. The angular distributions are forward peaked for all produced pairs, consistent with Regge-like $t$-channel exchange. Asymmetric wide-angle antibaryon distributions show the presence of additional processes. In a phenomenological model, we find consistency with a double-$t$-channel exchange process where antibaryons are created only at the middle vertex. The model matches all observed distributions with a small number of free parameters. In the hyperon channels, we observe a clear distinction between photoproduction of the $\mathrm{\Lambda }\overline{\mathrm{\Lambda }}$ and $p\overline{\mathrm{\Lambda }}$ systems but general similarity to the $p\overline{p}$ system. We report both total cross sections and cross sections differential with respect to momentum transfer and the invariant masses of the created particle pairs. No narrow resonant structures were found in these reaction channels. The suppression of $s\overline{s}$ quark pairs relative to $d\overline{d}$ quark pairs is similar to what has been seen in other reactions.

We present a measurement of the charge asymmetry ${\delta }_L$ in the mode $K_L\to {\pi }^{\pm }{e}^{\mp }\nu$ based on $298\times {10}^6$ analyzed decays. We measure a value of ${\delta }_L=[3322\pm 58(\mathrm{stat})\pm 47(\mathrm{syst}\left)\right]\times 10^{-6\mathrm{}}$, in good agreement with previous measurements and 2.4 times more precise than the current best published result. The result is used to place more stringent limits on $\mathrm{CPT}$ and $\Delta S=\Delta Q$ violation in the neutral kaon system.

We present a series of measurements based on $K_{L,S}\to {\pi }^{+}{\pi }^{-}$ and $K_{L,S}\to {\pi }^0{\pi }^0$ decays collected in 1996–1997 by the $\mathrm{KTeV}$ experiment (E832) at Fermilab. We compare these four $\overrightarrow{K}\pi \pi$ decay rates to measure the direct $\mathrm{CP}$ violation parameter $\mathrm{Re}({\epsilon }^{\prime }/\epsilon )=(20.7\mathrm{}\pm 2.8)\times {10}^{-4}.$ We also test $\mathrm{CPT}$ symmetry by measuring the relative phase between the $\mathrm{CP}$ violating and $\mathrm{CP}$ conserving decay amplitudes for $\overrightarrow{K}{\pi }^{+}{\pi }^{-}$ $\left({\phi }_{+-}\right)$ and for $\overrightarrow{K}{\pi }^0{\pi }^0$ $\left({\phi }_{00}\right).\mathrm{}$ We find the difference between the relative phases to be $\Delta \phi \equiv {\phi }_{00}-{\phi }_{+-}=(+0.39\mathrm{}\pm 0.50)°,$ and the deviation of ${\phi }_{+-}$ from the superweak phase to be ${\phi }_{+-}-{\phi }_{\mathrm{SW}}=(+0.61\mathrm{}\pm 1.19)°;$ both results are consistent with $\mathrm{CPT}$ symmetry. In addition, we present new measurements of the $K_L$-$K_S$ mass difference and $K_S$ lifetime: $\Delta m=(5261\mathrm{}\pm 15)\times {10}^6ħ{\mathrm{s}}^{-1}$ and ${\tau }_S=(89.65\mathrm{}\pm 0.07)\times {10}^{-12}\mathrm{s}.$

We present a determination of the Cabibbo-Kobayashi-Maskawa parameter $|V_{us}|$ based on new measurements of the six largest $K_L$ branching fractions and semileptonic form factors by the KTeV (E832) experiment at Fermilab. We find $|{\mathrm{V}}_{\mathrm{u}\mathrm{s}}|=0.2252\pm {0.0008}_{\mathrm{K}\mathrm{T}\mathrm{e}\mathrm{V}}\pm {0.0021}_{\mathrm{e}\mathrm{x}\mathrm{t}}$, where the errors are from KTeV measurements and from external sources. We also use the measured branching fractions to determine the CP violation parameter $|{\eta }_{+-}|=(2.228\pm {0.005}_{\mathrm{K}\mathrm{T}\mathrm{e}\mathrm{V}}\pm {0.009}_{\mathrm{e}\mathrm{x}\mathrm{t}})\times {10}^{-3}$.

We present the first measurement of the form factor ratios $g_1{/f}_1$ (direct axial vector to vector), $g_2{/f}_1$ (second class current), and $f_2{/f}_1$ (weak magnetism) for the decay ${\Xi }^0\to {\Sigma }^{+}{e}^{-}{\overline{\nu }}_e$ using the KTeV (E799) beam line and detector at Fermilab. From the ${\Sigma }^{+}$ polarization measured with the decay ${\Sigma }^{+}\to p{\pi }^0$ and the $e^{-}-\overline{\nu }$ correlation, we measure $g_1{/f}_1$ to be $1.32{\pm }_{0.17}^{0.21}\left(\mathrm{stat}\right)\pm 0.05\left(\mathrm{syst}\right)$, assuming the $\mathrm{SU}(3{)}_f$ (flavor) values for $g_2{/f}_1$ and $f_2{/f}_1$. Our results are all consistent with exact $\mathrm{SU}(3{)}_f$ symmetry.