arXiv subjects

S. Dobbs

Publications and source records attributed to S. Dobbs.

At least 37 records · Page 2Linked to original sources

arXiv2019

Beam Asymmetry $\mathbfΣ$ for the Photoproduction of $\mathbfη$ and $\mathbf{η^{\prime}}$ Mesons at $\mathbf{E_γ=8.8}$GeV

We report on the measurement of the beam asymmetry $Σ$ for the reactions $\vecγp\rightarrow pη$ and $\vecγp \rightarrow pη^{\prime}$ 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 Lab. These measurements are made as a function of momentum transfer $-t$, with significantly higher statistical precision than our earlier $η$ measurements, and are the first measurements of $η^{\prime}$ in this energy range. We compare the results to theoretical predictions based on $t$--channel quasi-particle exchange. We also compare the ratio of $Σ_η$ to $Σ_{η^{\prime}}$ to these models, as this ratio is predicted to be sensitive to the amount of $s\bar{s}$ exchange in the production. We find that photoproduction of both $η$ and $η^{\prime}$ is dominated by natural parity exchange with little dependence on $-t$.

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arXiv2019

First measurement of near-threshold J/$ψ$ exclusive photoproduction off the proton

We report on the measurement of the $γp \rightarrow J/ψp$ cross section from $E_γ= 11.8$ GeV down to the threshold at $8.2$ GeV using a tagged photon beam with the GlueX experiment. We find 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 $1.67 \pm 0.39$ 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 $\mathcal{B}(P_c^+ \rightarrow J/ψp)$ and cross sections $σ(γp \to P_c^+)\times\mathcal{B}(P_c^+ \to J/ψp) $.

nucl-ex↗

arXiv2018

Measurements of $Ω^-$ Branching Fractions

Using $e^+e^-$ annihilation data taken at the CESR collider with the CLEO-c detector, measurements of two main $Ω^-$ branching fractions have been made using the reaction $ψ(2S)\toΩ^-\overlineΩ^+$, hyperon pair production at $\sqrt{s}=3.69$~GeV, the peak of the $ψ(2S)$ resonance. $Ω^-$ decay channels are identified through momentum distributions of charged particles, and systematics of the $Ω^-$ branching fractions have been studied. The result gives: $\mathcal{B}(Ω^- \to Λ^0 K^-) = (68.9\pm9.5\pm4.3)\%$, and $ \mathcal{B}(Ω^- \to Ξ^0 π^-) = (19.0\pm4.0\pm1.2)\%$.

hep-ex↗

arXiv2018

Nucleon and nuclear structure through dilepton production

Transverse momentum distributions and generalized parton distributions provide a comprehensive framework for the three-dimensional imaging of the nucleon and the nucleus experimentally using deeply virtual semi-exclusive and exclusive processes. The advent of combined high luminosity facilities and large acceptance detector capabilities enables experimental investigation of the partonic structure of hadrons with time-like virtual probes, in complement to the rich on-going space-like virtual probe program. The merits and benefits of the dilepton production channel for nuclear structure studies are discussed within the context of the International Workshop on Nucleon and Nuclear Structure through Dilepton Production taking place at the European Center for Theoretical Studies in Nuclear Physics and Related Areas (ECT$^{\star}$) of Trento. Particularly, the double deeply virtual Compton scattering, the time-like Compton scattering, the deeply virtual meson production, and the Drell-Yan processes are reviewed and a strategy for high impact experimental measurements is proposed.

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arXiv2017

Precision Measurement of the Hadronic Contribution to the Muon Anomalous Magnetic Moment

We report on a precision measurement of the cross section for the reaction $e^+e^-\toπ^+π^-$ in the mass range $0.30<M_{ππ}<1.00$ GeV with the initial state radiation (ISR) method, using 817 pb$^{-1}$ of data at $e^+e^-$ center-of-mass energies near 3.77 GeV and 586 pb$^{-1}$ of data at $e^+e^-$ center-of-mass energies near 4.17 GeV, collected with the CLEO-c detector at the CESR $e^+e^-$ collider at Cornell University. The integrated cross sections in the range $0.30<M_{ππ}<1.00$ GeV for the process $e^+e^-\toπ^+π^-$ are determined with a statistical uncertainty of $0.7\%$ and a systematic uncertainty of $1.5\%$. The leading-order hadronic contribution to the muon anomalous magnetic moment calculated using these measured $e^+e^-\toπ^+π^-$ cross sections in the range $M_{ππ}=0.30$ to 1.00 GeV is calculated to be $(500.4\pm3.6 (\mathrm{stat})\pm 7.5(\mathrm{syst}))\times10^{-10}$.

hep-ex↗

arXiv2017

Hyperon Form Factors & Diquark Correlations

Using $e^+e^-$ annihilation data taken at the CESR collider with the CLEO-c detector, measurements of hyperon pair production cross sections and elastic and transition electromagnetic form factors have been made at the charmonium resonances: $ψ(2S)$, $\sqrt{s}=3.69$ GeV, $|Q^2|=13.6$ GeV$^2$, $\mathcal{L}=48$~pb$^{-1}$; $ψ(3770)$, $\sqrt{s}=3.77$ GeV, $|Q^2|=14.2$ GeV$^2$, $\mathcal{L}=805$~pb$^{-1}$; and $ψ(4170)$, $\sqrt{s}=4.17$ GeV, $|Q^2|=17.4$ GeV$^2$, $\mathcal{L}=586$~pb$^{-1}$. %High efficiency particle identification has resulted in good statistical precision in the results. Results with good statistical precision are obtained with high efficiency particle identification. Systematics of pair production cross sections, and form factors with respect to the number of strange quarks in the hyperons are studied, and evidence is presented for effects of diquark correlations in comparative results for $Λ^0$ and $Σ^0$, both of which have the same $uds$ quark content.

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arXiv2017

Measurement of the beam asymmetry $Σ$ for $π^0$ and $η$ photoproduction on the proton at $E_γ= 9$ GeV

We report measurements of the photon beam asymmetry $Σ$ for the reactions $\vecγp\to pπ^0$ and $\vecγp\to pη$ 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 $π^0$ measurements and are the first $η$ measurements in this energy regime. The results are compared with theoretical predictions based on $t$-channel, quasi-particle exchange and constrain the axial-vector component of the neutral meson production mechanism in these models.

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arXiv2016

Studies of the decays D^0 \rightarrow K_S^0K^-π^+ and D^0 \rightarrow K_S^0K^+π^-

The first measurements of the coherence factor R_{K_S^0Kπ} and the average strong--phase difference δ^{K_S^0Kπ} in D^0 \to K_S^0 K^\mpπ^\pm decays are reported. These parameters can be used to improve the determination of the unitary triangle angle γ in B^- \rightarrow $\widetilde{D}K^-$ decays, where $\widetilde{D}$ is either a D^0 or a D^0-bar meson decaying to the same final state, and also in studies of charm mixing. The measurements of the coherence factor and strong-phase difference are made using quantum-correlated, fully-reconstructed D^0D^0-bar pairs produced in e^+e^- collisions at the ψ(3770) resonance. The measured values are R_{K_S^0Kπ} = 0.70 \pm 0.08 and δ^{K_S^0Kπ} = (0.1 \pm 15.7)$^\circ$ for an unrestricted kinematic region and R_{K*K} = 0.94 \pm 0.12 and δ^{K*K} = (-16.6 \pm 18.4)$^\circ$ for a region where the combined K_S^0 π^\pm invariant mass is within 100 MeV/c^2 of the K^{*}(892)^\pm mass. These results indicate a significant level of coherence in the decay. In addition, isobar models are presented for the two decays, which show the dominance of the K^*(892)^\pm resonance. The branching ratio {B}(D^0 \rightarrow K_S^0K^+π^-)/{B}(D^0 \rightarrow K_S^0K^-π^+) is determined to be 0.592 \pm 0.044 (stat.) \pm 0.018 (syst.), which is more precise than previous measurements.

hep-ex↗

arXiv2016

Model-independent determination of the strong-phase difference between D^0 and D^0-bar-> K^0_S,L h^+ h^- (h=pi,K) and its impact on the measurement of the CKM angle gamma/phi_3

We report the first determination of the relative strong-phase difference between D^0 -> K^0_S,L K^+ K^- and D^0-bar -> K^0_S,L K^+ K^-. In addition, we present updated measurements of the relative strong-phase difference between D^0 -> K^0_S,L pi^+ pi^- and D^0-bar -> K^0_S,L pi^+ pi^-. Both measurements exploit the quantum coherence between a pair of D^0 and D^0-bar mesons produced from psi(3770) decays. The strong-phase differences measured are important for determining the Cabibbo-Kobayashi-Maskawa angle gamma/phi_3 in B^- -> K^- D^0-tilde decays, where D^0-tilde is a D^0 or D^0-bar meson decaying to K^0_S h^+ h^- (h=pi,K), in a manner independent of the model assumed to describe the D^0 -> K^0_S h^+ h^- decay. Using our results, the uncertainty in gamma/phi_3 due to the error on the strong-phase difference is expected to be between 1.7 and 3.9 degrees for an analysis using B^- K^- D^0-tilde D^0-tilde -> K^0_S pi^+ pi^- decays, and between 3.2 and 3.9 degrees for an analysis based on B^- -> K^- D^0-tilde, D^0-tilde -> K^0_S K^+ K^- decays. A measurement is also presented of the CP-odd fraction, F_-, of the decay D^0 -> K^0_S K^+ K^- in the region of the phi -> K^+ K^- resonance. We find that in a region within 0.01 GeV^2/c^4 of the nominal phi mass squared F_- > 0.91 at the 90% confidence level.

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arXiv2016

First Results from The GlueX Experiment

The GlueX experiment at Jefferson Lab ran with its first commissioning beam in late 2014 and the spring of 2015. Data were collected on both plastic and liquid hydrogen targets, and much of the detector has been commissioned. All of the detector systems are now performing at or near design specifications and events are being fully reconstructed, including exclusive production of $π^{0}$, $η$ and $ω$ mesons. Linearly-polarized photons were successfully produced through coherent bremsstrahlung and polarization transfer to the $ρ$ has been observed.

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arXiv2015

A Comprehensive Study of the Radiative Decays of $J/ψ$ and $ψ(2S)$ to Pseudoscalar Meson Pairs, and Search for Glueballs

Using 53 pb$^{-1}$ of $e^+e^-$ annihilation data taken at $\sqrt{s}=3.686$ GeV, a comprehensive study has been made of the radiative decays of samples of 5.1 million $J/ψ$ and 24.5 million $ψ(2S)$ into pairs of pseudoscalar mesons, $π^+π^-$, $π^0π^0$, $K^+K^-$, $K_S^0K_S^0$, and $ηη$. Product branching fractions for the radiative decays of $J/ψ$ and $ψ(2S)$ to scalar resonances $f_0(1370,1500,1710,2100, \text{and} 2200)$, and tensor resonances $f_2(1270,1525, \text{and} 2230)$ have been determined, and are discussed in relation to predicted glueballs. For $ψ(2S)$ radiative decays the search for glueballs has been extended to masses between 2.5 GeV and 3.3 GeV.

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arXiv2015

Precision Measurement of the Mass of the $D^{0}$ Meson and the Binding Energy of the $X(3872)$ Meson as a $D^0\overline{D^{0}}$ Molecule

A precision measurement of the mass difference between the $D^0$ and $D^{*0}$ mesons has been made using 316~pb$^{-1}$ of $e^{+}e^{-}$ annihilation data taken at $\sqrt{s}=4170$~MeV using the CLEO-c detector. We obtain $ΔM \equiv M(D^{*0})-M(D^0) =142.007\pm0.015$(stat)~$\pm$~0.014(syst)~MeV, as the average for the two decays, $D^0\to K^-π^+$ and $D^0\to K^-π^+π^-π^+$. The new measurement of $ΔM$ leads to $M(D^{*0})=2006.850\pm0.049$~MeV, and the currently most precise measurement of the binding energy of the ``exotic'' meson X(3872) if interpreted as a $D^0D^{*0}$ hadronic molecule, $E_{b}(\text{X}(3872))\equiv M(D^0D^{*0})-M(\text{X}(3872))=3\pm192$ keV.

hep-ex↗

arXiv2014

First Measurements of Timelike Form Factors of the Hyperons, Lambda0, Sigma0, Sigma+, Xi0, Xi-, and Omega-, and Evidence of Diquark Correlations

Using 805 pb^-1 of e+e- annihilation data taken with the CLEO-c detector at psi(3770), sqrt{s}=3770 MeV, we report the first measurements of the electromagnetic form factors of the Lambda0, Sigma0, Sigma+, Xi0, Xi-, and Omega- hyperons for the large timelike momentum transfer of |Q^2|=14.2 GeV^2. The form factors for the different hyperons are found to vary by nearly a factor two. It is found that |G_M(Lambda0)|=1.66(24) x |G_M(Sigma0)|. The Lambda0 and Sigma0 hyperons have the same uds quark content, but differ in their isospin, and therefore the spin of the $ud$ quark pair. It is suggested that the spatial correlation implied by the singlet spin--isospin configuration in the Lambda0 is an example of strong diquark correlations in the Lambda0, as anticipated by Jaffe and Wilczek. Improved measurements of the branching fractions of psi(2S) -> p pbar and hyperon--antihyperon pairs are also reported.

hep-ex↗

arXiv2014

Updated measurements of absolute $D^+$ and $D^0$ hadronic branching fractions and $σ(e^+e^-\to D\overline{D})$ at $E_\mathrm{cm} = 3774$ MeV

Utilizing the full CLEO-c data sample of 818 pb$^{-1}$ of $e^+e^-$ data taken at the $ψ(3770)$ resonance, we update our measurements of absolute hadronic branching fractions of charged and neutral $D$ mesons. We previously reportedresults from subsets of these data. Using a double tag technique we obtain branching fractions for three $D^0$ and six $D^+$ modes, including the reference branching fractions $\mathcal{B} (D^0\to K^-π^+)=(3.934 \pm 0.021 \pm 0.061)\%$ and $\mathcal{B} (D^+ \to K^- π^+π^+)=(9.224 \pm 0.059 \pm 0.157)\%$. The uncertainties are statistical and systematic, respectively. In these measurements we include the effects of final-state radiation by allowing for additional unobserved photons in the final state, and the systematic errors include our estimates of the uncertainties of these effects. Furthermore, using an independent measurement of the luminosity, we obtain the cross sections $σ(e^+e^-\to D^0\overline{D}{}^0)=(3.607\pm 0.017 \pm 0.056) \ \mathrm{nb}$ and $σ(e^+e^-\to D^+D^-)=(2.882\pm 0.018 \pm 0.042) \ \mathrm{nb}$ at a center of mass energy, $E_\mathrm{cm} = 3774 \pm 1$ MeV.

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arXiv2014

A study of decays to strange final states with GlueX in Hall D using components of the BaBar DIRC

We propose to enhance the kaon identification capabilities of the GlueX detector by constructing an FDIRC (Focusing Detection of Internally Reflected Cherenkov) detector utilizing the decommissioned BaBar DIRC components. The GlueX FDIRC would significantly enhance the GlueX physics program by allowing one to search for and study hybrid mesons decaying into kaon final states. Such systematic studies of kaon final states are essential for inferring the quark flavor content of hybrid and conventional mesons. The GlueX FDIRC would reuse one-third of the synthetic fused silica bars that were utilized in the BaBar DIRC. A new focussing photon camera, read out with large area photodetectors, would be developed. We propose operating the enhanced GlueX detector in Hall D for a total of 220 days at an average intensity of 5x10^7 γ/s, a program that was conditionally approved by PAC39

physics.ins-det↗

arXiv2014

First Measurement of the Electromagnetic Form Factor of the Neutral Kaon at a Large Momentum Transfer and the Effect of $SU(3)$ Breaking

At large momentum transfers the photon interacts with the charges and spins of the constituent partons in a hadron. It is expected that the neutral kaon can acquire finite electromagnetic form factors because its wave function is affected by the order of magnitude difference between the mass of the strange quark and that of the down quark, or flavor $SU(3)$ breaking. We report on the first measurement of the form factor of neutral kaons at the large timelike momentum transfer of $|Q^2|=17.4$ GeV$^2$ by measuring the cross section for $e^+e^-\to K_SK_L$ at $\sqrt{s}=4.17$ GeV using CLEO-c data with an integrated luminosity of 586 pb$^{-1}$. We obtain $F_{K_SK_L}(17.4~\textrm{GeV}^2)=5.3\times10^{-3}$, with a 90% C.L. interval of $(2.9-8.2)\times10^{-3}$. This is nearly an order of magnitude smaller than $F_{K^+K^-}(17.4~\textrm{GeV}^2)=(44\pm1)\times10^{-3}$, and indicates that the effect of $SU(3)$ breaking is small. In turn, this makes it unlikely that the recently observed strong violation of the pQCD prediction, $F_{π^+π^-}(|Q^2|)/F_{K^+K^-}(|Q^2|)=f_π^2/f_K^2$, which is based on the assumption of similar wave functions for the pions and kaons, can be attributed to $SU(3)$ breaking alone.

hep-ex↗

arXiv2014

High precision measurement of the masses of the $D^0$ and $K_S$ mesons

Using 580 pb$^{-1}$ of $e^+e^-$ annihilation data taken with the CLEO--c detector at $ψ(3770)$, the decay $D^0(\overline{D}^0)\to K^\pmπ^\mp π^+π^-$ has been studied to make the highest precision measurement of $D^0$ mass, $M(D^0)=1864.845\pm0.025\pm0.022\pm0.053$ MeV, where the first error is statistical, the second error is systematic, and the third error is due to uncertainty in kaon masses. As an intermediate step of the present investigation the mass of the $K_S$ meson has been measured to be $M(K_S)=497.607\pm0.007\pm0.015$ MeV. Both $M(D^0)$ and $M(K_S)$ are the most precise single measurements of the masses of these mesons.

hep-ex↗

arXiv2013

Report of the Quark Flavor Physics Working Group

This report represents the response of the Intensity Frontier Quark Flavor Physics Working Group to the Snowmass charge. We summarize the current status of quark flavor physics and identify many exciting future opportunities for studying the properties of strange, charm, and bottom quarks. The ability of these studies to reveal the effects of new physics at high mass scales make them an essential ingredient in a well-balanced experimental particle physics program.

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