Search Results (140 total)

Metastable channel of doubly ionized carbon monoxide, CO²⁺, was scantly seen in previous strong-field experiments at the visible wavelength region, but was commonly observed using single high-energy photon or electron excitation. For the first time with near-IR ultrashort-pulse radiation, we observe an abundance of CO²⁺. We show that CO²⁺ results from nonsequential double ionization, while its dissociation counterpart, C⁺+O⁺, results from sequential processes, and CO²⁺ can be obtained through either single high-energy photon or electron excitation or multiphoton ionization with ultrashort pulses before a critical internuclear distance is reached. Our study demonstrates the experimental conditions to converge the outcomes from two vastly different regimes, namely, multiphoton excitation and ionization in strong fields and single high-energy photon or electron excitation and ionization in weak fields.

We report on a measurement 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 data collected with the upgraded Collider Detector at Fermilab in run II, corresponding to an integrated luminosity of 385??pb^-1. The measurement is carried out for jets with rapidity 0.1<|y^jet|<0.7 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 section after the necessary nonperturbative parton-to-hadron corrections are included.

We extend our previous analysis of gauge and Dirac fields in the presence of a chemical potential. We consider an alternative thermal operator which relates in a simple way the Feynman graphs in QED at finite temperature and charge density to those at zero temperature but nonzero chemical potential. Several interesting features of such a factorization are discussed in the context of the thermal photon and fermion self-energies.

We present the first experimental limits on high-q² contributions to charmless semileptonic B decays of the form expected from the weak annihilation (WA) decay mechanism. Such contributions could bias determinations of |V_ub| from inclusive measurements of B?X_ul?. Using a wide range of models based on available theoretical input we set a limit of ?_WA/?_b?u<7.4% (90% confidence level) on the WA fraction, and assess the impact on previous inclusive determinations of |V_ub|.

Two-particle correlations of identical charged pion pairs from Au+Au collisions at sqrt[s_NN]=62.4 and 200 GeV were measured by the PHOBOS experiment at BNL Relativistic Heavy Ion Collider (RHIC). Data for the 15% most central events were analyzed with Bertsch-Pratt and Yano-Koonin-Podgoretskii parametrizations using pairs with rapidities of 0.4<y_??<1.3 and transverse momenta 0.1<k_T<1.4 GeV/c. The Bertsch-Pratt radii R_o and R_? decrease as a function of pair transverse momentum. R_o and R_s are independent of collision energy, while R_? shows a slight increase. The source rapidity y_YKP scales roughly with the pair rapidity y_??, indicating strong dynamical correlations.

We present an experimental and theoretical study of the fluorescence rate of a single molecule as a function of its distance to a laser-irradiated gold nanoparticle. The local field enhancement leads to an increased excitation rate whereas nonradiative energy transfer to the particle leads to a decrease of the quantum yield (quenching). Because of these competing effects, previous experiments showed either fluorescence enhancement or fluorescence quenching. By varying the distance between molecule and particle we show the first experimental measurement demonstrating the continuous transition from fluorescence enhancement to fluorescence quenching. This transition cannot be explained by treating the particle as a polarizable sphere in the dipole approximation.

We measure the dipion mass spectrum in X(3872)?J/??⁺?^- decays using 360??pb^-1 of p? p collisions at sqrt[s]=1.96??TeV collected with the CDF II detector. The spectrum is fit with predictions for odd C-parity (³S₁, ¹P₁, and ³D_J) charmonia decaying to J/??⁺?^-, as well as even C-parity states in which the pions are from ?⁰ decay. The latter case also encompasses exotic interpretations, such as a D⁰D? ^*0 molecule. Only the ³S₁ and J/?? hypotheses are compatible with our data. Since ³S₁ is untenable on other grounds, decay via J/?? is favored, which implies C=+1 for the X(3872). Models for different J/?-? angular momenta L are considered. Flexibility in the models, especially the introduction of ?-? interference, enables good descriptions of our data for both L=0 and 1.

The spectroscopy of neutron-rich ^{109,110,111,112}Ru nuclei was studied by measuring the prompt ? rays that originate from fission fragments, produced by the ²³⁸U(?,f) fusion-fission reaction, in coincidence with the detection of both fragments. For ^109,111Ru, both the negative-parity (h_11/2 orbitals) and K=5/2 positive-parity (mainly g_7/2 and d_5/2 orbitals) bands were extended to substantially higher spin and excitation energy than known previously. The ground-state and ?-vibrational bands of ^110,112Ru also were extended to higher spin, allowing observation of the second band crossing at the rotational frequency of ?450 keV in ¹¹²Ru, which is ?50 keV above the first band crossing. At a similar rotational frequency, the first band crossing for the h_11/2 band in ¹¹¹Ru was observed, which is absent in ¹⁰⁹Ru. These band crossings most likely are caused by the alignment of the g_9/2 proton pair. This early onset of the band crossing for the aligned ?g_9/2 orbitals may be evidence of a triaxial shape transition from prolate to oblate occurring in ¹¹¹Ru. The data together with a comparison of cranked shell?model predictions are presented.

We show that entanglement entropy of free fermions scales faster than area law, as opposed to the scaling L^d-1 for the harmonic lattice, for example. We also suggest and provide evidence in support of an explicit formula for the entanglement entropy of free fermions in any dimension d, S?  c(??,??)L^d-1log?L as the size of a subsystem L??, where ?? is the Fermi surface and ?? is the boundary of the region in real space. The expression for the constant c(??,??) is based on a conjecture due to Widom. We prove that a similar expression holds for the particle number fluctuations and use it to prove a two sided estimate on the entropy S.

We determine the dielectron widths of the ?(1S), ?(2S), and ?(3S) resonances with better than 2% precision by integrating the cross section of e⁺e^-?? over the e⁺e^- center-of-mass energy. Using e⁺e^- energy scans of the ? resonances at the Cornell Electron Storage Ring and measuring ? production with the CLEO detector, we find dielectron widths of 1.252±0.004(?_stat)±0.019(?_syst)??keV, 0.581±0.004±0.009??keV, and 0.413±0.004±0.006??keV for the ?(1S), ?(2S), and ?(3S), respectively.

Using the mixed space representation, we extend our earlier analysis to the case of Dirac and gauge fields and show that in the absence of a chemical potential, the finite temperature Feynman diagrams can be related to the corresponding zero temperature graphs through a thermal operator. At nonzero chemical potential we show explicitly in the case of the fermion self-energy that such a factorization is violated because of the presence of a singular contact term. Such a temperature dependent term which arises only at finite density and has a quadratic mass singularity cannot be related, through a regular thermal operator, to the fermion self-energy at zero temperature which is infrared finite. Furthermore, we show that the thermal radiative corrections at finite density have a screening effect for the chemical potential leading to a finite renormalization of the potential.

We measure the cross section for e⁺e^-??(3770)?hadrons at E_c.m.=3773??MeV to be (6.38±0.08_-0.30^+0.41)??nb using the CLEO detector at the CESR e⁺e^- collider. The difference between this and the e⁺e^-??(3770)?DD? cross section at the same energy is found to be (-0.01±0.08_-0.30^+0.41)??nb. With the observed total cross section, we extract ?_ee(?(3770))=(0.204±0.003_-0.027^+0.041)??keV. Uncertainties shown are statistical and systematic, respectively.

We report on a search for gravitational waves from binary black hole inspirals in the data from the second science run of the LIGO interferometers. The search focused on binary systems with component masses between 3 and 20M_?. Optimally oriented binaries with distances up to 1 Mpc could be detected with efficiency of at least 90%. We found no events that could be identified as gravitational waves in the 385.6 hours of data that we searched.

We report on precision measurements of the masses and widths of the narrow, orbitally excited states D₁⁰ and D₂^*0 using the CDF II detector at the Fermilab Tevatron. Both states (collectively called D^**) are reconstructed in the decay channel D^**?D^*+?^-. The D₂^*0 is also reconstructed in the D^**?D⁺?^- channel. Using a data set with an integrated luminosity of 210??pb^-1, the measured masses and widths for the D₁⁰ are 2421.7±0.7±0.6???MeV/c² and 20.0±1.7±1.3???MeV/c² respectively, while for the D₂^*0 they are 2463.3±0.6±0.8???MeV/c² and 49.2±2.3±1.2???MeV/c². These values are currently the single best measurements available.

We observe signals for the decays ?(3770)?XJ/? from data acquired with the CLEO detector operating at the CESR e⁺e^- collider with sqrt[s]=3773??MeV. We measure the following branching fractions B(?(3770)?XJ/?) and significances: (189±20±20)×10^-5 (11.6?) for X=?⁺?^-, (80±25±16)×10^-5 (3.4?) for X=?⁰?⁰, and (87±33±22)×10^-5 (3.5?) for X=?, where the errors are statistical and systematic, respectively. The radiative return process e⁺e^-???(2S) populates the same event sample and is used to measure ?_ee[?(2S)]=(2.54±0.03±0.11)??keV.

We present the first measurement of the A₂ and A₃ angular coefficients of the W boson produced in proton-antiproton collisions. We study W?e?_e and W???_? candidate events produced in association with at least one jet at CDF, during Run Ia and Run Ib of the Tevatron at sqrt[s]=1.8??TeV. The corresponding integrated luminosity was 110??pb^-1. The jet balances the transverse momentum of the W and introduces QCD effects in W boson production. The extraction of the angular coefficients is achieved through the direct measurement of the azimuthal angle of the charged lepton in the Collins-Soper rest-frame of the W boson. The angular coefficients are measured as a function of the transverse momentum of the W boson. The electron, muon, and combined results are in good agreement with the standard model prediction, up to order ?_s² in QCD.

Using data acquired with the CLEO detector at the CESR e⁺e^- collider at sqrt[s]=3.773??GeV, we measure the cross section for the radiative return process e⁺e^-??J/?, J/???⁺?^-, resulting in B(J/???⁺?^-)×?_ee(J/?)=0.3384±0.0058±0.0071??keV, ?_ee(J/?)=5.68±0.11±0.13??keV, and ?_tot(J/?)=95.5±2.4±2.4??keV, in which the errors are statistical and systematic, respectively. We also determine the ratio ?_ee[?(2S)]/?_ee(J/?)=0.45±0.01±0.02.

We report on the experimental demonstration of high energy-time entanglement in two-photon states created in the process of spontaneous parametric down-conversion. We show that the classical variance product, which we violate by three orders of magnitude, actually represents a lower bound estimate of the number of information eigenmodes K. Explicit measurements estimate K to be greater than 100, with theoretical estimates predicting a value of as high as 1×10⁶. These results provide incentive for the practical feasibility of large bandwidth quantum information processing, particularly in cryptography over large distances.

We present a search for Higgs bosons decaying into bb? and produced in association with W bosons in pp? collisions at sqrt[s]=1.96??TeV. This search uses 320??pb^-1 of the data set accumulated by the upgraded Collider Detector at Fermilab. Events are selected that have a high-transverse momentum electron or muon, missing transverse energy, and two jets, at least one of which is consistent with the hadronization of a b quark. Both the number of events and the dijet mass distribution are consistent with standard model background expectations, and we set 95% confidence level upper limits on the production cross section times branching ratio for the Higgs boson or any new particle with similar decay kinematics. These upper limits range from 10 pb for m_H=110??GeV/c² to 3 pb for m_H=150??GeV/c².

Results on a search for pair production of second-generation scalar leptoquark in pp? collisions at sqrt[s]=1.96??TeV are reported. The data analyzed were collected by the CDF detector during the 2002?2003 Tevatron Run II and correspond to an integrated luminosity of 198??pb^-1. Leptoquarks (LQ) are sought through their decay into (charged) leptons and quarks, with final state signatures represented by two muons and jets and one muon, large transverse missing energy and jets. We observe no evidence for LQ production and derive 95% C.L. upper limits on the LQ production cross sections as well as lower limits on their mass as a function of ?, where ? is the branching fraction for LQ??q.

We present a search for anomalous semileptonic decays of heavy flavor hadrons produced in association with a W boson in proton-antiproton collisions at sqrt[s]=1.96??TeV. We use 162??pb^-1 of data collected with the CDF II detector at the Fermilab Tevatron Collider. We select events with one W boson and at least one jet with an identified secondary vertex. In the jets with a secondary vertex we look for a semileptonic decay to a muon. We compare the number of jets with both a secondary vertex and a semileptonic decay and the kinematic properties of these jets, with the standard model expectation of W plus heavy flavor production and decay. No discrepancy is seen between the observation and the expectation, and we set limits on the production cross section of a B-like hadron with an anomalously high semileptonic branching ratio.

We report the first evidence for a fully reconstructed decay mode of the B_c^± meson in the channel B_c^±?J/??^±, with J/???⁺?^-. The analysis is based on an integrated luminosity of 360??pb^-1 in pp? collisions at 1.96 TeV center of mass energy collected by the Collider Detector at Fermilab. We observe 14.6±4.6 signal events with a background of 7.1±0.9 events, and a fit to the J/??^± mass spectrum yields a B_c^± mass of 6285.7±5.3(stat)±1.2(syst)??MeV/c². The probability of a peak of this magnitude occurring by random fluctuation in the search region is estimated as 0.012%.

Using 281??pb^-1 of data collected with the CLEO-c detector, we report on first observations and measurements of Cabibbo-suppressed decays of D mesons in the following six decay modes: ?⁺?^-?⁰?⁰, ?⁺?⁺?^-?^-?⁰, ?⁺?⁰?⁰, ?⁺?⁺?^-?⁰, ??⁰, and ??⁺?^-. Improved branching fraction measurements in eight other multipion decay modes are also presented. The measured D??? rates allow us to extract the ratio of isospin amplitudes A(?I=3/2)/A(?I=1/2)=0.420±0.014(stat)±0.016(syst) and the strong phase shift of ?_I=(86.4±2.8±3.3)°, which is quite large and now more precisely determined.

This article presents a measurement of the top quark mass using the CDF II detector at Fermilab. Colliding beams of protons and antiprotons at Fermilab?s Tevatron (sqrt[s]=1.96??TeV) produce top/antitop pairs, which decay to W⁺W^-bb? ; events are selected where one W decays to hadrons and the other W decays to either e or ? plus a neutrino. The data sample corresponds to an integrated luminosity of approximately 318??pb^-1. A total of 165 tt? events are separated into four subsamples based on jet transverse energy thresholds and the number of b jets identified by reconstructing a displaced vertex. In each event, the reconstructed top quark invariant mass is determined by minimizing a ?² for the overconstrained kinematic system. At the same time, the mass of the hadronically decaying W boson is measured in the same event sample. The observed W boson mass provides an in situ improvement in the determination of the hadronic jet energy scale. A simultaneous likelihood fit of the reconstructed top quark masses and the W boson invariant masses in the data sample to distributions from simulated signal and background events gives a top quark mass of 173.5_-3.8^+3.9??GeV/c².

We consider QCD tt? Z production at the LHC with Z??? ? and all-hadronic tt? decays, i.e. pp?p?_Tbb? +4 jets, as a tool to measure ttZ couplings. This channel has a significantly larger cross section than those where the Z boson decays leptonically. However, tt? , bb? +4 jet, tt? j, and tt? jj production give rise to potentially large backgrounds. We show that these processes can be suppressed to an acceptable level with suitable cuts, and find that adding the p?_Tbb? +4 jet channel to the final states used in previous ttZ couplings analyses will improve the sensitivity by 10%?60%. We also discuss how the measurement of the ttZ couplings may constrain Little Higgs models.

We report that measurements of the Raman intensity versus applied voltage are sensitive to filling of the density of states and enable us to measure the second band gap in specific semiconducting single-walled carbon nanotubes (SWNTs). Raman scattering preferentially selects sets of SWNTs whose excitonic transitions are resonant with the incident or scattered photon energies. Simultaneous measurement of the electronic gap and exciton resonance allows us to infer binding energies for the exciton of 0.49±0.05 and 0.62±0.05??eV for tubes of (10,3) and (7,5), respectively. Metallic SWNTs exhibit no excitonic feature.

We report the results of a search for a charged Higgs boson in the decays of top quarks produced in pp? collisions at a center-of-mass energy of 1.96 TeV. We use a data sample corresponding to an integrated luminosity of 193??pb^-1 collected by the upgraded Collider Detector at Fermilab. No evidence for charged Higgs production is found, allowing 95% C.L. upper limits to be placed on BR(t?H⁺b) for different charged Higgs decay scenarios. In addition, we present in the minimal supersymmetric standard model (m_H^±,tan??) plane the first exclusion regions with radiative and Yukawa coupling corrections.

Using data obtained with the CLEO III detector, running at the Cornell Electron Storage Ring (CESR), we report on a new study of exclusive radiative ?(1S) decays into the final states ??⁺?^-, ?K⁺K^-, and ?pp? . We present branching ratio measurements for the decay modes ?(1S)??f₂(1270), ?(1S)??f₂^?(1525), and ?(1S)??K⁺K^-; helicity production ratios for f₂(1270) and f₂^?(1525); upper limits for the decay ?(1S)??f_J(2200), with f_J(2220)??⁺?^-, K⁺K^-, pp? ; and an upper limit for the decay ?(1S)??X(1860), with X(1860)??pp? .

Coulomb activation of the four quasiparticle K^?=16^{+ 178}Hf isomer (t_1/2=31??y) has led to the measurement of a set of E? matrix elements coupling the isomer band to the ground band. The present data combined with earlier ¹⁷⁸Hf Coulomb excitation data have probed the K components in the wave functions and revealed the onset and saturation of K mixing in low-K bands, whereas the mixing is negligible in the high-K bands. The implications can be applied to other quadrupole-deformed nuclei.

We report on an experimental demonstration of electron cooling of high-energy antiprotons circulating in a storage ring. In our experiments, electron cooling, a well-established method at low energies (<500??MeV/nucleon), was carried out in a new region of beam parameters, requiring a multi-MeV dc electron beam and an unusual beam transport line. In this Letter, we present the results of the longitudinal cooling force measurements and compare them with theoretical predictions.

Using data collected at the ?(3770) resonance with the CLEO-c detector at the Cornell e⁺e^- storage ring, we present searches for 25 charmless decay modes of the ?(3770), mostly multibody final states. No evidence for charmless decays is found.

We report two measurements of the top-quark mass M_top using the CDF II detector at the Fermilab Tevatron in a 318??pb^-1 data sample of tt? events in the lepton+jets final state. One method uses an event-based likelihood technique resulting in M_top=173.2_-2.4^+2.6(stat)±3.2(syst)??GeV/c² or 173.2_-4.0^+4.1??GeV/c². The second method reconstructs a top-quark mass in each event using the measured invariant mass of the hadronically decaying W boson to constrain the jet energy scale to obtain a value for M_top of 173.5_-3.6^+3.7(stat)±1.3(syst)??GeV/c² or 173.5_-3.8^+3.9??GeV/c². We take the latter, which is more precise, as our result.

We have searched for the di-pion transition ?_b(2P)????_b(1P) in the CLEO III sample of ?(3S) decays in the exclusive decay chain: ?(3S)???_b(2P), ?_b(2P)????_b(1P), ?_b(1P)???(1S), ?(1S)??⁺?^-. Our studies include both ?⁺?^- and ?⁰?⁰, each analyzed both in fully-reconstructed events and in events with one pion undetected. We show that the null hypothesis is not substantiated. Under reasonable assumptions, we find the partial decay width to be ?(?_b(2P)????_b(1P))=(0.83±0.22±0.08±0.19)??keV, with the uncertainties being statistical, internal CLEO systematics, and common systematics from outside sources.

Using the CLEO detector at the Cornell Electron Storage Ring, we have observed the B_s meson in e⁺e^- annihilation at the ?(5S) resonance. We find 14 candidates consistent with B_s decays into final states with a J/? or a D_s^(*)-. The probability that we have observed a background fluctuation is less than 8×10^-10. We have established that at the energy of the ?(5S) resonance B_s production proceeds predominantly through the creation of B_s^*B? _s^* pairs. We find ?(e⁺e^-?B_s^*B? _s^*)=[0.11_-0.03^+0.04(stat)±0.02(syst)]??nb, and set the following limits: ?(e⁺e^-?B_sB? _s)/?(e⁺e^-?B_s^*B? _s^*)<0.16 and [?(e⁺e^-?B_sB? _s^*)+?(e⁺e^-?B_s^*B? _s)]/?(e⁺e^-?B_s^*B? _s^*)<0.16 (90% C.L.). The mass of the B_s^* meson is measured to be M_Bs^*=[5.414±0.001(stat)±0.003(syst)]??GeV/c².

We describe a search for ?(3770) decay to two-body non-DD? final states in e⁺e^- data produced by the CESR collider and analyzed with the CLEO-c detector. Vector-pseudoscalar production ?⁰?⁰, ?⁺?^-, ??⁰, ??⁰, ??, ??, ??, ??^?, ??^?, ??^?, K^*0K⁰? , and K^*+K^- is studied along with that of b₁? (b₁⁰?⁰ and b₁⁺?^-) and ?⁺?^-?⁰. The largest amount of disagreement between the expected rate for e⁺e^-??^*?X and that for e⁺e^-?X at sqrt[s]=3.773???GeV is found for X=??, at an excess cross section of (2.4±0.6)???pb [?_??^?(3770)=(7.4±1.6)???keV], and a suggestive suppression is seen for ?⁺?^-?⁰ and ??. We conclude with form factor determinations for ??⁰, ??, and ??^?.

Top quark pair production at proton-antiproton colliders is known to exhibit a forward-backward asymmetry due to higher-order QCD effects. We explore how this asymmetry might be studied at the Fermilab Tevatron, including how the asymmetry depends on the kinematics of extra hard partons. We consider results for top quark pair events with one and two additional hard jets. We further note that a similar asymmetry, correlated with the presence of jets, arises in specific models for parton showers in Monte Carlo simulations. We conclude that the measurement of this asymmetry at the Tevatron will be challenging, but important both for our understanding of QCD and for our efforts to model it.

We present a study of the dijet invariant mass distribution for the reaction p? p?two???jets+?+X, at a center of mass energy of 1.8 TeV, using data collected by the CDF experiment. We compare the data to predictions for the production of a photon with two jets, together with the resonant processes p? p?W/Z+?+X, in which the W and Z bosons decay hadronically. A fit is made to the dijet invariant mass distribution combining the nonresonant background and resonant processes. We use the result to establish a limit for the inclusive production cross section of W/Z+? with hadronic decay of the W and Z bosons.

We present a search for neutral supersymmetric Higgs bosons decaying to ? pairs produced in pp? collisions at sqrt[s]=1.96??TeV. The data, corresponding to 310??pb^-1 integrated luminosity, were collected with the Collider Detector at Fermilab in run II of the Tevatron. No significant excess above the standard model backgrounds is observed. We set exclusion limits on the production cross section times branching fraction to ? pairs for Higgs boson masses in the range from 90 to 250??GeV/c².

We present a search for the standard model Higgs boson in H?WW^(*) decays with e⁺e^-, e^±?^?, and ?⁺?^- final states in pp? collisions at a center-of-mass energy of sqrt[s]=1.96??TeV. The data, collected from April 2002 to June 2004 with the D0 detector, correspond to an integrated luminosity of 300?325??pb^-1, depending on the final state. The number of events observed is consistent with the expectation from backgrounds. Limits from the combination of all three channels on the Higgs boson production cross section times branching ratio ?×BR(H?WW^(*)) are presented.

We introduce a background-free real-time detection scheme capable of recognizing low-index nanoparticles such as single viruses in water. The method is based on interferometrically measuring the electromagnetic field amplitude of the scattered light. A split detector is used to generate a background-free signal that renders unprecedented sensitivity for small particles. In its current configuration the sensor is capable of detecting low-index particles in water down to 10 nm in radius or single gold particles as small as 5 nm. We demonstrate the detection of such small particles in a microfluidic system with a time resolution of 1 ms and we discuss the theoretical limits of this novel detection scheme.