Search Results (63 total)

Using 281??pb^-1 of data recorded by the CLEO-c detector in e⁺e^- collisions at the ?(3770), corresponding to 0.78�10⁶ D⁺D^- pairs, we investigate the substructure of the decay D⁺??^-?⁺?⁺ using the Dalitz plot technique. We find that our data are consistent with the following intermediate states: ?(770)?⁺, f₂(1270)?⁺, f₀(1370)?⁺, f₀(1500)?⁺, f₀(980)?⁺, and ??⁺. We confirm large S wave contributions at low ?? mass. We set upper limits on contributions of other possible intermediate states. We consider three models of the ?? S wave and find that all of them adequately describe our data.

We calculate the line shape and linewidths for electromagnetically induced transparency (EIT) in optically thick, Doppler broadened media (buffer gasses are also considered). In generalizing the definition of the EIT linewidth to optically thick media, we find two different linewidth definitions apply depending on whether the experiment is pulsed or continuous wave (cw). Using the cw definition for the EIT line shape we derive analytic expressions describing the linewidth as a function of optical depth. We also review the EIT line shapes in optically thin media and provide physical arguments for how the line shapes change as a function of various parameters.

We present a measurement of the top-quark mass in pp? collisions at sqrt[s]=1.96??TeV which uses events with an inclusive signature of missing transverse energy and jets. The event selection is sensitive to tt? ?W⁺bW^-b? ?l?bqq^?b? independent of the lepton flavor and results in a large acceptance for W??? decays. All-hadronic tt? decays and events with identified electrons or muons are vetoed to provide a statistically independent sample with respect to all previous measurements. The top-quark mass is inferred from the distribution of the scalar sum of all jet transverse energies and the missing transverse energy. Using 311??pb^-1 of integrated luminosity recorded by the Collider Detector at Fermilab, we measure a top-quark mass m_t=172.3_-9.6^+10.8(stat)�10.8(syst)??GeV/c². While the uncertainty on m_t is larger than that of other measurements, the result is statistically uncorrelated with those of other methods and thus can help to reduce the overall m_t uncertainty when combined with other existing measurements.

We present results of a search at CDF�in 929�56??pb^-1 of pp? collisions at 1.96�TeV for the anomalous production of events containing a high-transverse momentum charged lepton (?, either e or ?) and photon (?), accompanied by missing transverse energy (E?_T), and/or additional leptons and photons, and jets (X). We use the same selection criteria as in a previous CDF�Run I search, but with an order-magnitude larger data set, a higher pp? collision energy, and the CDF�II detector. We find 163 ??E?_T+X events, compared to an expectation of 150.6�13.0 events. We observe 74 ???+X events, compared to an expectation of 65.1�7.7 events. We find no events similar to the Run I ee??E?_T event.

We present a measurement of ?(pp? ?W)�B(W?e?) at sqrt[s]=1.96??TeV, using electrons identified in the forward region (1.2<|?|<2.8) of the CDF II detector, in 223??pb^-1 of data. We measure ?�B=2796�13(stat)_-90⁺⁹⁵(syst)�162(lum)??pb. Combining this result with a previous CDF measurement obtained using electrons in the central region (|?|?1), we present the first measurement of the ratio of central-electron to forward-electron W partial cross sections R_exp?=0.925�0.006(stat)�0.032(syst), consistent with theoretical predictions using Coordinated Theoretical-Experimental Project on QCD (CTEQ) and Martin-Roberts-Stirling-Thorne (MRST) parton distribution functions.

This Letter presents measurements of the elliptic flow of charged particles as a function of pseudorapidity and centrality from Cu-Cu collisions at 62.4 and 200�GeV using the PHOBOS detector at the Relativistic Heavy Ion Collider. The elliptic flow in Cu-Cu collisions is found to be significant even for the most central events. For comparison with the Au-Au results, it is found that the detailed way in which the collision geometry (eccentricity) is estimated is of critical importance when scaling out system-size effects. A new form of eccentricity, called the participant eccentricity, is introduced which yields a scaled elliptic flow in the Cu-Cu system that has the same relative magnitude and qualitative features as that in the Au-Au system.

We measure the ratio of cross section times branching fraction, R_p=?_?c2B(?_c2?J/??)/?_?c1B(?_c1?J/??), in 1.1??fb^-1 of pp? collisions at sqrt[s]=1.96??TeV. This measurement covers the kinematic range p_T(J/?)>4.0??GeV/c, |?(J/?)<1.0, and p_T(?)>1.0??GeV/c. For events due to prompt processes, we find R_p=0.395�0.016(stat)�0.015(syst). This result represents a significant improvement in precision over previous measurements of prompt ?_c1,2 hadro production.

We describe a search for anomalous production of events with two leptons (e or ?) of the same electric charge in pp? collisions at a center-of-mass energy of 1.96�TeV. Many extensions to the standard model predict the production of two leptons of the same electric charge. This search has a significant increase in sensitivity compared to earlier searches. Using a data sample corresponding to 1??fb^-1 of integrated luminosity recorded by the CDF II detector, we observe no significant excess in an inclusive selection (expect 33.2�4.7 events, observe 44) or in a supersymmetry-optimized selection (expect 7.8�1.1 events, observe 13.)

We search for the technicolor process pp? ??_T/?_T?W?_T in events containing one electron and two jets, in data corresponding to an integrated luminosity of 390??pb^-1, recorded by the D0 experiment at the Fermilab Tevatron. Technicolor predicts that technipions ?_T decay dominantly into bb? , bc? , or b? c, depending on their charge. In these events b and c quarks are identified by their secondary decay vertices within jets. Two analysis methods based on topological variables are presented. Since no excess above the standard model prediction was found, the result is presented as an exclusion in the ?_T vs ?_T mass plane for a given set of model parameters.

We present a search for electroweak production of single top quarks in the s-channel (pp? ?tb? +X) and t-channel (pp? ?tqb? +X) modes. We have analyzed 230??pb^-1 of data collected with the D0 detector at the Fermilab Tevatron Collider at a center-of-mass energy of sqrt[s]=1.96??TeV. No evidence for a single top quark signal is found. We set 95% confidence level upper limits on the production cross sections, based on binned likelihoods formed from a neural network output. The observed (expected) limits are 6.4�pb (4.5�pb) in the s-channel and 5.0�pb (5.8�pb) in the t-channel.

We present results on two-particle angular correlations in proton-proton collisions at center-of-mass energies of 200 and 410 GeV. The PHOBOS experiment at the BNL Relativistic Heavy Ion Collider has a uniquely large coverage for charged particles, giving the opportunity to explore the correlations at both short- and long-range scales. At both energies, a complex two-dimensional correlation structure in ?? and ?? is observed. In the context of an independent cluster model of short-range correlations, the cluster size and its decay width are extracted from the two-particle pseudorapidity correlation function and compared with previous measurements in proton-proton and proton-antiproton collisions, as well as PYTHIA and HIJING predictions.

We report on measurements of the inclusive jet production cross section as a function of the jet transverse momentum in pp? collisions at sqrt[s]=1.96??TeV, using the k_T algorithm and a data sample corresponding to 1.0??fb^-1 collected with the Collider Detector at Fermilab in run�II. The measurements are carried out in five different jet rapidity regions with |y^jet|<2.1 and transverse momentum in the range 54<p_T^jet<700??GeV/c. Next-to-leading order perturbative QCD predictions are in good agreement with the measured cross sections.

We present a measurement of the inclusive production cross section for Z bosons decaying to tau leptons in pp? collisions at sqrt[s]=1.96??TeV. We use a channel with one hadronically-decaying and one electronically-decaying tau. This measurement is based on 350??pb^-1 of CDF Run II data. Using a sample of 504 opposite sign e? events with a total expected background of 190 events, we obtain ?(pp? ?4Z)�B(Z???)=264�23(stat)�14(syst)�15(lumi)??pb, in agreement with the next-to-next-to-leading order QCD prediction. This is the first CDF cross section measurement using hadronically-decaying taus in Run II.

It was shown some years ago that the spectrum of a stochastic scalar field depends not only on the source spectrum but also on the degree of coherence of the source. In this paper we show that there are electromagnetic fields for which not only the state of coherence of the source, but also its degree of polarization affect the spectrum of the radiated field. We illustrate the analysis by diagrams which show the far-zone spectra of some stochastic electromagnetic beams generated by sources of different states of coherence and different degrees of polarization. The spectra of the radiated field depend both on coherence properties of the source and its degree of polarization and are found to be different in different directions of observation.

We consider scattering of stochastic scalar fields on deterministic as well as on random media, occupying a finite domain. The scattering is characterized by a generalized scattering matrix which transforms the angular correlation function of the incident field into the angular correlation function of the scattered field. Within the accuracy of the first Born approximation this matrix can be expressed in a simple manner in terms of the scattering potential of the scatterer. Apart from determining the angular distribution of the spectral intensity of the scattered field, the scattering matrix makes it possible also to determine the changes in the state of coherence of the field produced on scattering.

We employ a surface plasmon technique to resolve the dynamics of femtosecond-laser-induced coherent acoustic phonons in noble metals. Clear acoustic oscillations are observed in our experiments. We further study the dependence of the initial phase of the oscillations on pump fluence, and we find that the initial phase decreases linearly with pump fluence. Our model calculations show that hot electrons instantaneously excited by femtosecond pulses contribute to the generation of coherent acoustic phonons in metals.

A measurement of the top quark mass using events with one charged lepton, missing transverse energy, and jets in the final state, collected by the D0 detector from pp? collisions at sqrt[s]=1.96??TeV at the Fermilab Tevatron collider, is presented. A constrained fit is used to fully reconstruct the kinematics of the events. For every event a top quark mass likelihood is calculated taking into account all possible jet assignments and the probability that an event is signal or background. Lifetime-based identification of b jets is employed to enhance the separation between tt? signal and background from other physics processes and to improve the assignment of the observed jets to the quarks in the tt? hypothesis. We extract a multiplicative jet energy scale (JES) factor in situ, greatly reducing the systematic effect related to the jet energy measurement. In a data sample with an integrated luminosity of 425??pb^-1, we observe 230 candidate events, with an estimated background of 123 events, and measure m_t=173.7�4.4(stat+JES)_-2.0^+2.1(syst)??GeV. This result represents the first application of the ideogram technique to the measurement of the top quark mass in lepton+jets events.

We present our femtosecond optical pump-probe studies of proximized ferromagnet-superconductor nanobilayers. The weak ferromagnetic nature of a thin NiCu film makes it possible to observe the dynamics of the nonequilibrium carriers through the near-surface optical reflectivity change measurements. The subpicosecond biexponential reflectivity decay has been identified as electron-phonon Debye and acoustic phonon relaxation times, and the decay of Debye phonons versus temperature dependence was used to evaluate the electron-phonon coupling constants for both the pure Nb and proximized Nb?NiCu heterostructures down to low temperatures. We have also demonstrated that the NiCu overlay on top of Nb dramatically reduced the slow, bolometric component of the photoresponse component, making such bilayers attractive for future radiation detector applications.

We show that, although the amount of mutual entanglement of photons propagating in free space is fixed, the type of correlations between the photons that determine the entanglement can dramatically change during propagation. We show that this amounts to a migration of entanglement in Hilbert space, rather than real space. For the case of spontaneous parametric down-conversion, the migration of entanglement in transverse coordinates takes place from modulus to phase of the biphoton state and back again. We propose an experiment to observe this migration in Hilbert space and to determine the full entanglement.

We present calculations for a coherent population transfer [stimulated Raman adiabatic passage (STIRAP)] between the two lowest electronic ground states of the KRb molecule. In contrast to previous work on STIRAP in molecular systems, position dependent transition dipole moments are included in the calculation to take the mixed singlet-triplet nature of the intermediate state into account. Additionally, we incorporate the kinetic energy term and position dependent electronic states of the molecule. Transfer efficiencies of up to 58% can be achieved for moderate laser pulses in the picosecond range. Calculations with constant transition dipole moments show a much higher transfer of 94% and thus overestimate the efficiency significantly.

The D0 Collaboration presents first evidence for the production of single top quarks at the Fermilab Tevatron pp? collider. Using a 0.9??fb^-1 dataset, we apply a multivariate analysis to separate signal from background and measure ?(pp? ?tb+X,tqb+X)=4.9�1.4??pb. The probability to measure a cross section at this value or higher in the absence of a signal is 0.035%, corresponding to a 3.4�standard deviation significance. We use the cross section measurement to directly determine the Cabibbo-Kobayashi-Maskawa matrix element that describes the Wtb coupling and find 0.68<|V_tb|?1 at 95% C.L. within the standard model.

We present the results of asearch for W^? boson decaying to electron-neutrinopairs in pp? collisionsat a center-of-mass energy of 1.96�TeV, using a data sample corresponding to 205??pb^-1 of integrated luminosity collected by the CDFII detector at Fermilab. We observe no evidence for this decay mode and set limits on the production cross section times branching fraction, assumingthe neutrinos from W^? boson decays to be light. Ifwe assume the manifest left-right symmetric model, we exclude a W^? boson with mass less than 788??GeV/c²at the 95% confidence level.

We report the first observation of the associated production of a W boson and a Z boson. This result is based on 1.1??fb^-1 of integrated luminosity from pp? collisions at sqrt[s]=1.96??TeV collected with the CDF�II detector at the Fermilab Tevatron. We observe 16�WZ candidates passing our event selection with an expected background of 2.7�0.4�events. A fit to the missing transverse energy distribution indicates an excess of events compared to the background expectation corresponding to a significance equivalent to 6�standard deviations. The measured cross section is ?(pp? ?WZ)=5.0_-1.6^+1.8??pb, consistent with the standard model expectation.

We have performed the first direct measurement of the time-integrated flavor untagged charge asymmetry in semileptonic B_s⁰ decays A_SL^s,unt by comparing the decay rate of B_s⁰??⁺D_s^-?X, where D_s^-???^- and ??K⁺K^-, with the charge-conjugate B? _s⁰ decay rate. This sample was selected from 1.3??fb^-1 of data collected by the D0 experiment in run�II of the Fermilab Tevatron collider. We obtain A_SL^s,unt=[1.23�0.97(stat)�0.17(syst)]�10^-2. Assuming that ?m_s/?? _s?1, this result can be translated into a measurement of the CP-violating phase in B_s⁰ mixing: ??_s/?m_stan??_s= �[2.45�1.93(stat)�0.35(syst)]�10^-2.

In this paper, we study nonsequential double ionization in various molecular fragments for laser polarization aligning either parallel or perpendicular to the molecular axis. In the diatomic molecule O₂, we find that nonsequential double ionization can be turned on and off when we simply switch the laser polarization between perpendicular and parallel ionization. Furthermore, we find that the dependence of kinetic energy release on intensity can be used to distinguish sequential versus nonsequential ionization in molecules. The results in this paper allow us to gain better understanding of the role of nonsequential ionization in molecular dissociative ionization.

We demonstrate an all-optical delay line in hot cesium vapor that tunably delays 275�ps input pulses up to 6.8�ns and 740 input ps pulses up to 59�ns (group index of approximately 200) with little pulse distortion. The delay is made tunable with a fast reconfiguration time (hundreds of ns) by optically pumping out of the atomic ground states.

We report the first measurement of the top quark mass using the decay length technique in pp? collisions at a center-of-mass energy of 1.96�TeV. This technique uses the measured flight distance of the b hadron to infer the mass of the top quark in lepton plus jets events with missing transverse energy. It relies solely on tracking and avoids the jet energy scale uncertainty that is common to all other methods used so far. We apply our novel method to a 695??pb^-1 data sample recorded by the CDF II detector at Fermilab and extract a measurement of m_t=180.7_-13.4^+15.5(stat.)�8.6(syst.)??GeV/c². While the uncertainty of this result is larger than that of other measurements, the dominant uncertainties in the decay length technique are uncorrelated with those in other methods. This result can help reduce the overall uncertainty when combined with other existing measurements of the top quark mass.

We report on a study of exclusive radiative decays of the ?(1S) resonance into the final states ??⁰?⁰, ??? and ??⁰?, using 1.13??fb^-1 of e⁺e^- annihilation data collected at sqrt[s]=9.46??GeV with the CLEO�III detector operating at the Cornell Electron Storage Ring. In the channel ??⁰?⁰, we measure the branching ratio for the decay mode ?(1S)??f₂(1270) to be (10.5�1.6(stat)_-1.8^+1.9(syst))�10^-5. We place upper limits on the product branching ratios for the isoscalar resonances f₀(1500) and f₀(1710) for the ?⁰?⁰ and ?? decay channels. We also set an upper limit on the ?(1S) radiative decay into ?⁰?.

Using a sample of 3�10⁶ ?(2S) decays collected by the CLEO III and CLEO-c detector configurations, we present results of a study of ?_c0 and ?_c2 decays into ??, ??^?, and ?^??^? final states. We find B(?_c0???)=(0.31�0.05�0.04�0.02)%, B(?_c0???^?)<0.05% at the 90% confidence level, and B(?_c0??^??^?)=(0.17�0.04�0.02�0.01)%. We also present upper limits for the decays of ?_c2 into these final states. These results give information on the decay mechanism of ?_c states into pseudoscalars.

We present a measurement of the top-quark mass M_top in the all-hadronic decay channel tt? ?W⁺bW^-b? ?q₁q? ₂bq₃q? ₄b? . The analysis is performed using 310??pb^-1 of sqrt[s]=1.96??TeV pp? collisions collected with the CDF II detector using a multijet trigger. The mass measurement is based on an event-by-event likelihood which depends on both the sample purity and the value of the top-quark mass, using 90 possible jet-to-parton assignments in the six-jet final state. The joint likelihood of 290 selected events yields a value of M_top=177.1�4.9(stat)�4.7(syst)??GeV/c².

We report a search for the anomalous production of events with multiple charged leptons in pp? collisions at sqrt[s]=1.96??TeV using a data sample corresponding to an integrated luminosity of 346??pb^-1 collected by the CDF�II detector at the Fermilab Tevatron. The search is divided into three-lepton and four-or-more-lepton data samples. We observe six events in the three-lepton sample and zero events in the ?4-lepton sample. Both numbers of events are consistent with standard model background expectations. Within the framework of an R-parity-violating supergravity model, the results are interpreted as mass limits on the lightest neutralino (??₁⁰) and chargino (??₁^�) particles. For one particular choice of model parameters, the limits are M(??₁⁰)>110??GeV/c² and M(??₁^�)>203??GeV/c² at 95% confidence level; the variation of these mass limits with model parameters is presented.

We generalize the stochastic path integral formalism by considering Hamiltonian dynamics in the presence of general Markovian noise. Kramers? solution of the activation rate for escape over a barrier is generalized for non-Gaussian driving noise in both the overdamped and underdamped limit. We apply our general results to a Josephson junction detector measuring the electron counting statistics of a mesoscopic conductor. The activation rate dependence on the third current cumulant includes an additional term originating from the backaction of the measurement circuit.

We present an analysis of angular distributions and correlations of the X(3872) particle in the exclusive decay mode X(3872)?J/??⁺?^- with J/???⁺?^-. We use 780??pb^-1 of data from pp? collisions at sqrt[s]=1.96??TeV collected with the CDF II detector at the Fermilab Tevatron. We derive constraints on spin, parity, and charge conjugation parity of the X(3872) particle by comparing measured angular distributions of the decay products with predictions for different J^PC hypotheses. The assignments J^PC=1⁺⁺ and 2^-+ are the only ones consistent with the data.

In a rotating two-component Bose-Einstein condensate (BEC), the traditional triangular vortex lattice can be replaced by a rectangular vortex lattice or even a structure characterized in terms of vortex sheets, depending on the interspecies interactions. We study the dynamics of this system by analyzing the Bogoliubov excitation spectrum. Excitations familiar to BEC vortex systems are found such as Tkachenko modes, hydrodynamic modes, and surface waves, however, the complex two-component morphology also gives rise to phenomena including shear flow between vortex sheets.

From an analysis of the decay B_s⁰?J/??, we obtain the width difference between the light and heavy mass eigenstates ???(?_L-?_H)=0.17�0.09(stat)�0.02(syst)??ps^-1 and the CP-violating phase ?_s=-0.79�0.56(stat)_-0.01^+0.14(syst). Under the hypothesis of no CP violation (?_s?0), we obtain 1/?? = �?? (B_s⁰)=1.52�0.08(stat)_-0.03^+0.01(syst)??ps and ??=0.12_-0.10^+0.08(stat)�0.02(syst)??ps^-1. The data sample corresponds to an integrated luminosity of about 1.1??fb^-1 accumulated with the D0 detector at the Fermilab Tevatron collider. This is the first direct measurement of the CP-violating mixing phase in the B_s⁰ system.

We present the first observation of the baryon decay ?_b⁰??_c⁺?^- followed by ?_c⁺?pK^-?⁺ in 106??pb^-1 pp? collisions at sqrt[s]=1.96??TeV in the CDF experiment. In order to reduce systematic error, the measured rate for ?_b⁰ decay is normalized to the kinematically similar meson decay B? ⁰?D⁺?^- followed by D⁺??⁺K^-?⁺. We report the ratio of production cross sections (?) times the ratio of branching fractions (B) for the momentum region integrated above p_T>6??GeV/c and pseudorapidity range |?|<1.3: ?(pp? ??_b⁰X)/?(pp? ?B? ⁰X)�B(?_b⁰??_c⁺?^-)/B(B? ⁰?D⁺?^-)=0.82� �0.08(stat)�0.11(syst)�0.22[B(?_c⁺?pK^-?⁺)].

We report a measurement of the ?_b⁰ lifetime in the exclusive decay ?_b⁰?J/??⁰ in pp? collisions at sqrt[s]=1.96??TeV using an integrated luminosity of 1.0??fb^-1 of data collected by the CDF�II detector at the Fermilab Tevatron. Using fully reconstructed decays, we measure ?(?_b⁰)=1.593_-0.078^+0.083(stat)�0.033(syst)??ps. This is the single most precise measurement of ?(?_b⁰) and is 3.2? higher than the current world average.

The combined data of two Coulomb excitation experiments has verified the purely electromagnetic population of the K^?=4⁺,6⁺,8^-, and 16⁺ rotational bands in ¹⁷⁸Hf via 2???14 K-forbidden transitions, quantifying the breakdown of the K-selection rule with increasing spin in the low-K bands. The ?-, 4⁺, and 6⁺ bands were extended, and four new states in a rotational band were tentatively assigned to a previously known K^?=0⁺ band. The quasiparticle structure of the 6⁺ (t_{1 / 2}=77 ns) and 8^- (t_{1 / 2}=4 s) isomer bands were evaluated, showing that the gyromagnetic ratios of the 6⁺ isomer band are consistent with a pure ?7 / 2⁺[404],?5 / 2⁺[402] structure. The 8^- isomer band at 1147 keV and the second 8^- band at 1479 keV, thought to be predominantly ?7 / 2^-[514],?9 / 2⁺[624] and ?9 / 2^-[514],?7 / 2⁺[404], respectively, are mixed to a degree approaching the strong-mixing limit. Based on measured ?K^?=16⁺?E2?K^?=0⁺? matrix elements, it was shown that heavy-ion bombardment could depopulate the 16⁺ isomer at the ~1% level, although no states were found that would mediate photodeexcitation of the isomer via low-energy x-ray absorption.

We present a measurement of the fractions F₀ and F₊ of longitudinally polarized and right-handed W bosons in top-quark decays using data collected with the CDF II detector. The data set used in the analysis corresponds to an integrated luminosity of approximately 318??pb^-1. We select tt? candidate events with one lepton, at least four jets, and missing transverse energy. Our helicity measurement uses the decay angle ?^*, which is defined as the angle between the momentum of the charged lepton in the W boson rest frame and the W momentum in the top-quark rest frame. The cos??^* distribution in the data is determined by full kinematic reconstruction of the tt? candidates. We find F₀=0.85_-0.22^+0.15(stat)�0.06(syst) and F₊=0.05_-0.05^+0.11(stat)�0.03(syst), which is consistent with the standard model prediction. We set an upper limit on the fraction of right-handed W bosons of F₊<0.26 at the 95% confidence level.

High-spin states in neutron-rich ¹⁸⁰Hf and ¹⁸²Hf nuclei were populated through inelastic and transfer reactions with a ¹³⁶Xe beam incident on a thin ¹⁸⁰Hf target, and investigated using particle-? coincidence techniques. New collective band structures were observed, and previously known rotational and vibrational bands in these nuclei were extended to higher angular momenta. No obvious nucleon alignment was observed in the ground state band of either nucleus up to ??=0.43 MeV, a significant delay compared to lighter even-even Hf isotopes. Woods-Saxon cranking calculations were performed to predict the nature of the first band crossings and shape evolution in ^180,182Hf.

We present the first observation of exclusive e⁺e^- production in hadron-hadron collisions, using pp? collision data at sqrt[s]=1.96??TeV taken by the run II Collider Detector at Fermilab, and corresponding to an integrated luminosity of 532??pb^-1. We require the absence of any particle signatures in the detector except for an electron and a positron candidate, each with transverse energy E_T>5??GeV and pseudorapidity |?|<2. With these criteria, 16 events are observed compared to a background expectation of 1.9�0.3 events. These events are consistent in cross section and properties with the QED process pp? ?p+e⁺e^-+p? through two-photon exchange. The measured cross section is 1.6_-0.3^+0.5(stat)�0.3(syst)??pb. This agrees with the theoretical prediction of 1.71�0.01??pb.

Specific heat measurements show that the introduction of amorphous columnar defects considerably affects the transition from the normal to the superconducting state in zero magnetic field. Experimental results are compared to numerical simulations of the three-dimensional XY model for both the pure system and the system containing random columnar disorder. The numerics reproduce the salient features of experiment, showing in particular that the specific heat peak changes from cusplike to smoothly rounded when columnar defects are added. By considering the specific heat critical exponent ?, we argue that such behavior is consistent with recent numerical work [A. Vestergren , Phys. Rev. B 70, 054508 (2004)] showing that the introduction of columnar defects changes the universality class of the transition.

A precision measurement of the D⁰ meson mass has been made using ?281??pb^-1 of e⁺e^- annihilation data taken with the CLEO-c detector at the ?(3770) resonance. The exclusive decay D⁰?K_S? has been used to obtain M(D⁰)=1864.847�0.150(stat)�0.095(syst)??MeV. This corresponds to M(D⁰D? ^*0)=3871.81�0.36??MeV, and leads to a well-constrained determination of the binding energy of the proposed D⁰D? ^*0 molecule X(3872), as E_b=0.6�0.6??MeV.

Transverse momentum spectra of pions, kaons, protons, and antiprotons from Au+Au collisions at sqrt[s_NN] = 62.4 GeV have been measured by the PHOBOS experiment at the Relativistic Heavy Ion Collider at Brookhaven National Laboratory. The identification of particles relies on three different methods: low momentum particles stopping in the first detector layers; the specific energy loss (dE/dx) in the silicon spectrometer, and time-of-flight measurement. These methods cover the transverse momentum ranges 0.03?0.2, 0.2?1.0, and 0.5?3.0 GeV/c, respectively. Baryons are found to have substantially harder transverse momentum spectra than mesons. The p_T region in which the proton to pion ratio reaches unity in central Au+Au collisions at sqrt[s_NN] = 62.4 GeV fits into a smooth trend as a function of collision energy. At low transverse mass, the spectra of various species exhibit a significant deviation from transverse mass scaling. The observed particle yields at very low p_T are comparable to extrapolations from higher p_T for kaons, protons and antiprotons. By comparing our results to Au+Au collisions at sqrt[s_NN] = 200 GeV, we conclude that the net proton yield at midrapidity is proportional to the number of participant nucleons in the collision.

We report a measurement of the top-quark mass, M_t, in the dilepton decay channel of tt? ?b?^?+?_?^?b? ?^-?? _? using an integrated luminosity of 1.0??fb^-1 of pp? collisions collected with the CDF II detector. We apply a method that convolutes a leading-order matrix element with detector resolution functions to form event-by-event likelihoods; we have enhanced the leading-order description to describe the effects of initial-state radiation. The joint likelihood is the product of the likelihoods from 78 candidate events in this sample, which yields a measurement of M_t=164.5�3.9(stat.)�3.9(syst.)??GeV/c², the most precise measurement of M_t in the dilepton channel.

We report an upper limit on the fraction of V+A current, f_V+A, in top-quark decays, using approximately 700??pb^-1 of pp? collisions at sqrt[s]=1.96??TeV acquired by the upgraded Collider Detector at Fermilab. For the decay t?Wb???b (where ?=e or ?), the invariant mass of the charged lepton and the bottom quark jet is sensitive to the polarization of the W boson. We determine f_V+A=-0.06�0.25 given a top-quark mass of 175??GeV/c². We set an upper limit on f_V+A of 0.29 at the 95% confidence level, an improvement by a factor of 2 on the previous best direct limit.

We present a measurement of the branching fraction of invisible ?(1S) decays, using 1.2??fb^-1 of data collected at the ?(2S) resonance with the CLEO�III detector at CESR. After subtracting expected backgrounds from events that pass selection criteria for invisible ?(1S) decay in ?(2S)??⁺?^-?(1S), we deduce a 90% C.L. upper limit of B[?(1S)?invisible]<0.39%.

We present a protocol for large-alphabet quantum key distribution (QKD) using energy-time entangled biphotons. Binned, high-resolution timing measurements are used to generate a large-alphabet key with over 10 bits of information per photon pair, albeit with large noise. QKD with 5% bit error rate is demonstrated with 4�bits of information per photon pair, where the security of the quantum channel is determined by the visibility of Franson interference fringes. The protocol is easily generalizable to even larger alphabets, and utilizes energy-time entanglement which is robust to transmission over large distances in fiber.

A search for a manifestly exotic S=-2 baryon state decaying to ?^-?^-, and its neutral partner decaying to ?^-?⁺, has been performed using 220??pb^-1 of pp? collisions at sqrt[s]=1.96??TeV collected by the Collider Detector at Fermilab. The ?^- trajectories were measured in a silicon tracker before their decay, resulting in a sample with low background and excellent position resolution. No evidence was found for S=-2 pentaquark candidates in the invariant mass range of 1600?2100??MeV/c². Upper limits on the product of pentaquark production cross section times its branching fraction to ?^-?^+,-, relative to the cross section of the well-established ?(1530) resonance, are presented for neutral and doubly negative candidates with p_T>2??GeV/c and |y|<1 as a function of pentaquark mass. At 1862??MeV/c², these upper limits for neutral and doubly negative final states were found to be 3.2% and 1.7% at the 90% confidence level, respectively.

Using 355??pb^-1 of data collected by the CDF�II detector in pp? collisions at sqrt[s]=1.96??TeV at the Fermilab Tevatron, we study the fully reconstructed hadronic decays B_(s)⁰?D_(s)^-?⁺ and B_(s)⁰?D_(s)^-?⁺?⁺?^-. We present the first measurement of the ratio of branching fractions B(B_s⁰?D_s^-?⁺?⁺?^-)/B(B⁰?D^-?⁺?⁺?^-)=1.05�0.10(stat)�0.22(syst). We also update our measurement of B(B_s⁰?D_s^-?⁺)/B(B⁰?D^-?⁺) to 1.13�0.08(stat)�0.23(syst), improving the statistical uncertainty by more than a factor of 2. We find B(B_s⁰?D_s^-?⁺)=[3.8�0.3(stat)�1.3(syst)]�10^-3 and B(B_s⁰?D_s^-?⁺?⁺?^-)=[8.4�0.8(stat)�3.2(syst)]�10^-3.

Using a sample of 3�10⁶ ?(2S) decays recorded by the CLEO detector, we study three-body decays of the ?_c0, ?_c1, and ?_c2 produced in radiative decays of the ?(2S). We consider the final states ?⁺?^-?, K⁺K^-?, pp? ?, ?⁺?^-?^?, K⁺K^-?⁰, pp? ?⁰, ?⁺K^-K_S⁰, and K⁺p? ?, measuring branching fractions or placing upper limits. For ?_c1??⁺?^-?, K⁺K^-?⁰, and ?⁺K^-K_S⁰ our observed samples are large enough to indicate the largest contributions to the substructure.

We present a measurement of the fraction f₊ of right-handed W bosons produced in top quark decays, based on a candidate sample of tt? events in the ?+jets and dilepton decay channels corresponding to an integrated luminosity of 370??pb^-1 collected by the D0 detector at the Fermilab Tevatron pp? Collider at sqrt[s]=1.96??TeV. We reconstruct the decay angle ?^* for each lepton. By comparing the cos??^* distribution from the data with that for the expected background and signal for various values of f₊ (where we assume that the fraction of longitudinally-polarized W bosons has the standard model value of 0.70), we find f₊=0.056�0.080(stat)�0.057(syst) (f₊<0.23 at 95% C.L.), consistent with the standard model prediction of f₊=3.6�10^-4.

We present a general quantum theory capable of describing photon statistics under the combined effects of four-wave mixing and Raman scattering inside optical fibers. Our theory is vectorial in nature and includes all polarization effects. Our analysis shows that spontaneous Raman scattering degrades the pair correlation in all cases but the extent of degradation depends on the pumping configuration employed. In a single-pump configuration, photon pairs can be created with polarization either parallel or orthogonal to the pump. Our results show that the orthogonal configuration can improve the extent of quantum correlation considerably over a broad bandwidth. In the case of a dual-pump configuration, we show that imbalance of two pump powers can be used to improve the quality of photon pairs. We show that orthogonally polarized pumps can generate photon pairs automatically in a polarization-entangled state. In particular, orthogonal pumping with circular polarizations produces such an entangled state with relatively high quality. We also quantify the quality of polarization entanglement as well as energy-time entanglement constructed using correlated photon pairs.

Using data collected with the CLEO III detector at the CESR e⁺e^- collider, we report on a first observation of the decay ?(3S)??⁺?^-, and precisely measure the ratio of branching fractions of ?(nS), n=1, 2, 3, to ?⁺?^- and ?⁺?^- final states, finding agreement with expectations from lepton universality. We derive absolute branching fractions for these decays, and also set a limit on the influence of a low mass CP-odd Higgs boson in the decay of the ?(1S).

We present a new measurement of the B⁺ meson differential cross section d?/dp_T at sqrt[s]=1960??GeV. The data correspond to an integrated luminosity of 739??pb^-1 collected with the upgraded CDF detector (CDF II) at the Fermilab Tevatron collider. B⁺ candidates are reconstructed through the decay B⁺?J/?K⁺, with J/???⁺?^-. The integrated cross section for producing B⁺ mesons with p_T?6??GeV/c and |y|?1 is measured to be 2.78�0.24???b.

Using CLEO data, we study the production of the antideuteron, d? , in ?(nS) resonance decays and the nearby continuum. The branching ratios obtained are B^dir(?(1S)?d? X)=(3.36�0.23�0.25)�10^-5, B(?(1S)?d? X)=(2.86�0.19�0.21)�10^-5, and B(?(2S)?d? X)=(3.37�0.50�0.25)�10^-5, where the ?dir? superscript indicates that decays produced via reannihilation of the bb? pair to a ?^* are removed from both the signal and the normalizing number of ?(1S) decays in order to isolate direct decays of the ?(1S) to ggg, gg?. Upper limits at 90%�C.L.�are given for B(?(4S)?d? X)<1.3�10^-5, and continuum production ?(e⁺e^-?d? X)<0.031??pb. The ?(2S) data is also used to extract a limit on ?_bJ?d? X. The results indicate enhanced deuteron production in ggg, gg? hadronization compared to ?^*?qq? . Baryon number compensation is also investigated with the large ?(1S)?d? X sample.

We derive the properties of hard thermal effective actions in gauge theories from the point of view of Schwinger?s proper time formulation. This analysis is simplified by introducing a set of generalized energy and momenta which are conserved and are nonlocal in general. These constants of motion, which embody energy-momentum exchanges between the fields and the particles along their trajectories, can be related to a class of gauge invariant or covariant potentials in the hard thermal regime. We show that in this regime the generalized energy, which is nonlocal in general, generates the characteristic nonlocal behavior of the hard thermal effective actions.

Two-dimensional images carried by optical pulses (2�ns) are delayed by up to 10�ns in a 10�cm cesium vapor cell. By interfering the delayed images with a local oscillator, the transverse phase and amplitude profiles of the images are shown to be preserved. It is further shown that delayed images can be well preserved even at very low light levels, where each pulse contains on average less than one photon.

We present the first experimental discrimination between the 2e/3 and 4e/3 top quark electric charge scenarios, using top quark pairs (tt? ) produced in pp? collisions at sqrt[s]=1.96??TeV by the Fermilab Tevatron Collider. We use 370??pb^-1 of data collected by the D0 experiment and select events with at least one high transverse momentum electron or muon, high transverse energy imbalance, and four or more jets. We discriminate between b- and b? -quark jets by using the charge and momenta of tracks within the jet cones. The data are consistent with the expected electric charge, |q|=2e/3. We exclude, at the 92% C.L., that the sample is solely due to the production of exotic quark pairs QQ? with |q|=4e/3. We place an upper limit on the fraction of QQ? pairs ?<0.80 at the 90% C.L.

Thick, 40???m plastic shells filled with 25?35�atm of D₂ or D³He were imploded on a low-adiabat (??1.3) and with a low-implosion velocity (?2�10⁷??cm/s) on the OMEGA laser to generate massive cores of compressed plasma with high areal densities optimal for fast ignition. The targets are driven by 20-kJ relaxation adiabat-shaping laser pulses to keep the inner portion of the shell nearly Fermi degenerate. The measured kinetic energy downshift of proton spectra is in good agreement with the theoretical predictions yielding burn-averaged areal densities of 0.130�0.017??g/cm² and peak ?R during the burn of about 0.24�0.018??g/cm², the largest ?R measured on OMEGA to date. The same implosions with empty plastic shells are expected to reach 1.3??g/cm² across the core (i.e., 2?R) enough to stop fast electrons with energies up to 4.5�MeV typical of fast ignition scenarios.

Using 5.63??pb^-1 of data accumulated at the ?(2S) resonance with the CLEO III and CLEO-c detectors corresponding to 3.08�10⁶ ?(2S) decays, a search is performed for the decay ?(2S)??_c?⁺?^-?⁰ to test a theoretical prediction based upon the assumption that the cc? pair in the ?(2S) does not annihilate directly into three gluons but rather survives before annihilating. No signal is observed, and a combined upper limit from six ?_c decay modes is determined to be B(?(2S)??_c?⁺?^-?⁰)?1.0�10^-3 at 90% C.L. This upper limit is about an order of magnitude below the theoretical expectation.

Knowledge of the B_s decay fraction of the ?(5S) resonance, f_S, is important for B_s meson studies at the ?(5S) energy. Using a data sample collected by the CLEO III detector at CESR consisting of 0.423??fb^-1 on the ?(5S) resonance, 6.34??fb^-1 on the ?(4S) and 2.32??fb^-1 in the continuum below the ?(4S), we measure B(?(5S)??X)=(13.8�0.7_-1.5^+2.3)% and B(?(4S)??X)=(7.1�0.1�0.6)%; the ratio of the two rates is (1.9�0.1_-0.2^+0.3). This is the first measurement of the ? meson yield from the ?(5S). Using these rates, and a model dependent estimate of B(B_s??X), we determine f_S=(24.6�2.9_-5.3^+11.0)%. We also update our previous independent measurement of f_S made using the inclusive D_s yields to now be (16.8�2.6_-3.4^+6.7)%, due to a better estimate of the number of hadronic events. We also report the total ?(5S) hadronic cross section above continuum to be ?(e⁺e^-??(5S))=(0.301�0.002�0.039)??nb. This allows us to extract the fraction of B mesons as (58.9�10.0�9.2)%, equal to 1-f_S. Averaging the three methods gives a model dependent result of f_S=(21_-3⁺⁶)%.

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