Strange Hadron Spectroscopy with a Secondary KL Beam at GlueX

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. A flux on the order of 3 x 10^4 KL/s will allow a broad range of measurements to be made by improving the statistics of previous data obtained on hydrogen targets by three orders of magnitude. Use of a deuteron target will provide first measurements on the neutron which is {\it terra incognita}. 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 c.m. cos{\theta} from -0.95 to 0.95 in the c.m. range above W = 1490 MeV and up to 3500 MeV. These new GlueX data will greatly constrain partial-wave analyses and reduce model-dependent uncertainties in the extraction of strange resonance properties (including pole positions), and provide a new benchmark for comparisons with QCD-inspired models and lattice QCD calculations. The proposed facility will also have an impact in the strange meson sector by providing measurements of the final-state K{\pi} system from threshold up to 2 GeV invariant mass to establish and improve on the pole positions and widths of all K*(K{\pi}) P-wave states as well as for the S-wave scalar meson {\kappa}(800).Comment: 97 pages, 63 figures, Proposal for JLab PAC45, PR12-17-001; v3 missed citation in Sec 9 (pg 22

First Measurement of Near-Threshold J/ᴪ Exclusive Photoproduction Off the Proton

We report on the measurement of the γp -\u3e J/ψp cross section from Eγ = 11.8 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 dσ/dt has an exponential slope of 1.67 ± 0.39 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 β(P+c → J/ψp) and cross sections σ(γp → P+c ) x β(P+c → J/ψp)

Beam Asymmetry Σ for π+ and π0 Photoproduction on the Proton for Photon Energies From 1.102 to 1.862 GeV

Beam asymmetries for the reactions ˠp -\u3e pπ0 and ˠp -\u3e nπ+have been measured with the CEBAF Large Acceptance Spectrometer (CLAS) and a tagged, linearly polarized photon beam with energies from 1.102-1.862 GeV. A Fourier moment technique for extracting beam asymmetries from experimental data is described. The results reported here possess greater precision and finer energy resolution than previous measurements. Our data for both pion reactions appear to favor the SAID and Bonn-Gatchina scattering analyses over the older Mainz MAID predictions. After incorporating the present set of beam asymmetries into the world database, exploratory fits made with the SAID analysis indicate that the largest changes from previous fits are for properties of the Δ(1700)3/2- and Δ(1905) 5/2+ states

Induced Polarization of Λ1116 in Kaon Electroproduction

We have measured. the induced polarization of the Λ (1116) in the reaction ep →e′K+Λ , detecting the scattered e′ and K+ in the final state along with the proton from the decay Λ → pπ− . The present study used the CEBAF Large Acceptance Spectrometer (CLAS), which allowed for a large kinematic acceptance in invariant energy W (1.6≤ W ≤ 2.7 GeV) and covered the full range of the kaon production angle at an average momentum transfer Q2 = 1.90GeV2 . In this experiment a 5.50-GeV electron beam was incident upon an unpolarized liquid-hydrogen target. We have mapped out the W and kaon production angle dependencies of the induced polarization and found striking differences from photoproduction data over most of the kinematic range studied. However, we also found that the induced polarization is essentially Q2 independent in our kinematic domain, suggesting that somewhere below the Q2 covered here there must be a strong Q2 dependence. Along with previously published photo- and electroproduction cross sections and polarization observables, these data are needed for the development of models, such as effective field theories, and as input to coupled-channel analyses that can provide evidence of previously unobserved s -channel resonances

First Measurement of Direct Photoproduction of the a\u3csub\u3e2\u3c/sub\u3e(1320)⁰ Meson on the Proton

We present the first measurement of the reaction p -\u3e a₂(1320)⁰ p in the photon energy range 3.5-5.5 GeV and four-momentum transfer squared 0.2 \u3c -t \u3c 2.0 GeV2. Data were collected with the CEBAF Large Acceptance Spectrometer detector at the Thomas Jefferson National Accelerator Facility. The a2resonance was detected by measuring the reaction p → π0ηp and reconstructing the π0η invariant mass. The most prominent feature of the differential cross section is a dip at -t ≈ 0.55 GeV2. This can be described in the framework of Regge phenomenology, where the exchange degeneracy hypothesis predicts a zero in the reaction amplitude for this value of the four-momentum transfer

Differential Cross Sections for Λ (1520) Using Photoproduction at CLAS

The reaction p → K+Λ (1520) using photoproduction data from the CLAS g12 experiment at Jefferson Lab is studied. The decay of Λ(1520) into two exclusive channels, Σπ+π- and Σ-π+, is studied from the detected K+, π+, and π- particles. A good agreement is established for the Λ(1520) differential cross sections with the previous CLAS measurements. The differential cross sections as a function of center-of-mass angle are extended to higher photon energies. Newly added are the differential cross sections as a function of invariant four-momentum transfer t, which is the natural variable to use for a theoretical model based on a Regge-exchange reaction mechanism. No new N* resonances decaying into the K+Λ (1520) final state are found

Observation of a narrow structure in p(gamma,K_s)X via interference with phi-meson production

We report observation of a narrow peak structure at ~1.54 GeV with a Gaussian width sigma=6 MeV in the missing of K_s in the reaction gamma+p = pK_sK_L. The observed structure may be due to the interference between a strange (or anti-strange) baryon resonance in the pK_L system and the phi(K_sK_L) photoproduction leading to the same final state. The statistical significance of the observed excess of events estimated as the log likelihood ratio of the resonant signal+background hypothesis and the phi-production based background only hypothesis corresponds to 5.3 sigma.Comment: Accepted for publication in Physical Review C, 9 pages, 11 figures, 1 table added, revise

Extraction of Beam-Spin Asymmetries from the Hard Exclusive π⁺ Channel Off Protons in a Wide Range of Kinematics

We have measured beam-spin asymmetries to extract the sinϕ moment ALUsinϕ from the hard exclusive e→p → e\u27nπ+ reaction above the resonance region, for the first time with nearly full coverage from forward to backward angles in the center of mass. The ALUsinϕ moment has been measured up to 6.6  GeV2 in -t, covering the kinematic regimes of generalized parton distributions (GPD) and baryon-to-meson transition distribution amplitudes (TDA) at the same time. The experimental results in very forward kinematics demonstrate the sensitivity to chiral-odd and chiral-even GPDs. In very backward kinematics where the TDA framework is applicable, we found ALUsinϕ to be negative, while a sign change was observed near 90° in the center of mass. The unique results presented in this Letter will provide critical constraints to establish reaction mechanisms that can help to further develop the GPD and TDA frameworks

Center of Mass Motion of Short-Range Correlated Nucleon Pairs Studied Via the A(e, e\u27pp) Reaction

Short-range correlated (SRC) nucleon pairs are a vital part of the nucleus, accounting for almost all nucleons with momentum greater than the Fermi momentum (kF). A fundamental characteristic of SRC pairs is having large relative momenta as compared to kF, and smaller center of mass (c.m.) which indicates a small separation distance between the nucleons in the pair. Determining the c.m. momentum distribution of SRC pairs is essential for understanding their formation process. We report here on the extraction of the c.m. motion of proton-proton (pp) SRC pairs in carbon and, for the first time in heavier and ansymetric nuclei: aluminum, iron, and lead, from measurements of the A(e,e′pp) reaction. We find that the pair c.m. motion for these nuclei can be described by a three-dimensional Gaussian with a narrow width ranging from 140 to 170  MeV/c , approximately consistent with the sum of two mean-field nucleon momenta. Comparison with calculations appears to show that the SRC pairs are formed from mean-field nucleons in specific quantum states

Beam Spin Asymmetry in Semi-Inclusive Electroproduction of Hadron Pairs

A first measurement of the longitudinal beam spin asymmetry ALU in the semi-inclusive electroproduction of pairs of charged pions is reported. ALU is a higher-twist observable and offers the cleanest access to the nucleon twist-3 parton distribution function e(x). Data have been collected in the Hall-B at Jefferson Lab by impinging a 5.498-GeV electron beam on a liquid-hydrogen target, and reconstructing the scattered electron and the pion pair with the CLAS detector. One-dimensional projections of the AsinLUϕR moments are extracted for the kinematic variables of interest in the valence quark region. The understanding of dihadron production is essential for the interpretation of observables in single-hadron production in semi-inclusive DIS, and pioneering measurements of single-spin asymmetries in dihadron production open a new avenue in studies of QCD dynamics