arXiv subjects

G. Bauer

Publications and source records attributed to G. Bauer.

At least 55 records · Page 3Linked to original sources

arXiv2011

Measurement of branching ratio and Bs0 lifetime in the decay Bs0 -> J/psi f0(980) at CDF

We present a study of Bs0 decays to the CP-odd final state J/psi f0(980) with J/psi -> mu+ mu- and f0(980) -> pi+ pi-. Using ppbar collision data with an integrated luminosity of 3.8/fb collected by the CDF II detector at the Tevatron we measure a Bs0 lifetime of tau(Bs0 -> J/psi f0(980)) = 1.70 -0.11+0.12(stat) +-0.03(syst) ps. This is the first measurement of the Bs0 lifetime in a decay to a CP eigenstate and corresponds in the standard model to the lifetime of the heavy Bs0 eigenstate. We also measure the product of branching fractions of Bs0 -> J/psi f0(980) and f0(980) -> pi+ pi- relative to the product of branching fractions of Bs0 -> J/psi phi and phi -> K+ K- to be R_f0/phi = 0.257 +_0.020(stat) +-0.014(syst), which is the most precise determination of this quantity to date.

hep-ex↗

arXiv2011

On the Existence of Dynamics of Wheeler-Feynman Electromagnetism

We study the equations of Wheeler-Feynman electrodynamics which is an action-at-a-distance theory about world-lines of charges that interact through their corresponding advanced and retarded Liénard-Wiechert field terms. The equations are non-linear, neutral, and involve time-like advanced as well as retarded arguments of unbounded delay. Using a reformulation in terms of Maxwell-Lorentz electrodynamics without self-interaction, which we have introduced in a preceding work, we are able to establish the existence of conditional solutions. These are solutions that solve the Wheeler-Feynman equations on any finite time interval with prescribed continuations outside of this interval. As a byproduct we also prove existence and uniqueness of solutions to the Synge equations on the time half-line for a given history of charge trajectories.

math-ph↗

arXiv2011

Search for New Dielectron Resonances and Randall-Sundrum Gravitons at the Collider Detector at Fermilab

A search for new dielectron mass resonances using data recorded by the CDF II detector and corresponding to an integrated luminosity of 5.7/fb is presented. No significant excess over the expected standard model prediction is observed. In this dataset, an event with the highest dielectron mass ever observed (960 GeV/c^2) was recorded. The results are interpreted in the Randall-Sundrum (RS) model. Combined with the 5.4/fb diphoton analysis, the RS-graviton lower mass limit for the coupling k/\bar{M}_{Pl}=0.1 is 1058 GeV/c^2, making it the strongest limit to date.

hep-ex↗

arXiv2011

Maxwell-Lorentz Dynamics of Rigid Charges

We establish global existence and uniqueness of the dynamics of classical electromagnetism with extended, rigid charges and fields which need not to be square integrable. We consider also a modified theory of electromagnetism where no self-fields occur. That theory and our results are crucial for approaching the as yet unsolved problem of the general existence of dynamics of Wheeler Feynman electromagnetism, which we shall address in the follow up paper.

math-ph↗

arXiv2010

Strain determination in the Si channel above a single SiGe island inside a field effect transistor using nanobeam x-ray diffraction

SiGe islands are used to induce tensile strain in the Si channel of Field Effect Transistors to achieve larger transconductance and higher current driveabilities. We report on x-ray diffraction experiments on a single fully-processed and functional device with a TiN+Al gate stack and source, gate, and drain contacts in place. The strain fields in the Si channel were explored using an x-ray beam focused to 400 nm diameter combined with finite element simulations. A maximum in-plane tensile strain of about 1% in the Si channel was found, which is by a factor of three to four higher than achievable for dislocation-free tensile strained Si in state-of-the-art devices.

cond-mat.mes-hall↗

arXiv2010

Contact superconductivity in In-PbTe junctions

The authors report on electron transport studies on superconductor-semiconductor hybrid structures of indium and n-type lead telluride, either in the form of quantum wells or bulk crystals. In-PbTe contacts form by spontaneous alloying, which occurs already at room temperature. The alloyed phase penetrates deeply into PbTe and forms metallic contacts even in the presence of depletion layers at the semiconductor surface. Although the detailed structure of this phase is unknown, we observe that it exhibits a superconducting transition at temperatures below 10 K. This causes such substantial reduction of the contact resistances that they even become comparable to those predicted for ideal superconductor-normal conductor contacts. Most importantly, this result indicates that the interface phase in the superconducting state becomes nearly homogeneous - in contrast to the structure expected for alloyed contacts. We suggest that the unusual interface superconductivity is linked to the unique properties of PbTe, namely, its huge static dielectric constant. Apparently the alloyed interface phase contains superconducting precipitates randomly distributed within the depletion layers, and their Coulomb charging energies are extremely small. According to the existing models of the granular superconductivity, even very weak Josephson coupling between the neighboring precipitates gives rise to the formation of a global superconducting phase which explains our observations.

cond-mat.supr-con↗

arXiv2010

Studying the Underlying Event in Drell-Yan and High Transverse Momentum Jet Production at the Tevatron

We study the underlying event in proton-antiproton collisions by examining the behavior of charged particles (transverse momentum pT > 0.5 GeV/c, pseudorapidity |η| < 1) produced in association with large transverse momentum jets (~2.2 fb-1) or with Drell-Yan lepton-pairs (~2.7 fb-1) in the Z-boson mass region (70 < M(pair) < 110 GeV/c2) as measured by CDF at 1.96 TeV center-of-mass energy. We use the direction of the lepton-pair (in Drell-Yan production) or the leading jet (in high-pT jet production) in each event to define three regions of η-ϕspace; toward, away, and transverse, where ϕis the azimuthal scattering angle. For Drell-Yan production (excluding the leptons) both the toward and transverse regions are very sensitive to the underlying event. In high-pT jet production the transverse region is very sensitive to the underlying event and is separated into a MAX and MIN transverse region, which helps separate the hard component (initial and final-state radiation) from the beam-beam remnant and multiple parton interaction components of the scattering. The data are corrected to the particle level to remove detector effects and are then compared with several QCD Monte-Carlo models. The goal of this analysis is to provide data that can be used to test and improve the QCD Monte-Carlo models of the underlying event that are used to simulate hadron-hadron collisions.

hep-ex↗

arXiv2010

Embedded magnetic phases in (Ga,Fe)N: the key role of growth temperature

The local chemistry, structure, and magnetism of (Ga,Fe)N nanocomposites grown by metal organic vapor phase epitaxy is studied by high resolution synchrotron x-ray diffraction and absorption, transmission electron microscopy, and superconducting quantum interference device magnetometry as a function of the growth temperature $T_{\mathrm{g}}$. Three contributions to the magnetization are identified: i) paramagnetic -- originating from dilute and non-interacting Fe$^{3+}$ ions substitutional of Ga, and dominating in layers obtained at the lowest considered $T_{\mathrm{g}}$ (800$^{\circ}$C); ii) superparamagnetic-like -- brought about mainly by ferromagnetic nanocrystals of $ε-$Fe$_3$N but also by $γ'$-Fe$_4$N and by inclusions of elemental $α$- and $γ$-Fe, and prevalent in films obtained in the intermediate $T_{\mathrm{g}}$ range; iii) component linear in the magnetic field and associated with antiferromagnetic interactions -- found to originate from highly nitridated Fe$_x$N ($x \leq$ 2) phases, like $ζ$-Fe$_2$N, and detected in samples deposited at the highest employed temperature, $T_{\mathrm{g}}$ = 950$^{\circ}$C. Furthermore, depending on $T_{\mathrm{g}}$, the Fe-rich nanocrystals segregate towards the sample surface or occupy two-dimensional planes perpendicular to the growth direction.

cond-mat.mtrl-sci↗

arXiv2009

Spin-induced optical second harmonic generation in the centrosymmetric magnetic semiconductors EuTe and EuSe

Spectroscopy of the centrosymmetric magnetic semiconductors EuTe and EuSe reveals spin-induced optical second harmonic generation (SHG) in the band gap vicinity at 2.1-2.4eV. The magnetic field and temperature dependence demonstrates that the SHG arises from the bulk of the materials due to a novel type of nonlinear optical susceptibility caused by the magnetic dipole contribution combined with spontaneous or induced magnetization. This spin-induced susceptibility opens access to a wide class of centrosymmetric systems by harmonics generation spectroscopy.

cond-mat.mtrl-sci↗

arXiv2008

Controlled aggregation of magnetic ions in a semiconductor. Experimental demonstration

The control on the distribution of magnetic ions into a semiconducting host is crucial for the functionality of magnetically doped semiconductors. Through a structural analysis at the nanoscale, we give experimental evidence that the aggregation of Fe ions in (Ga,Fe)N and consequently the magnetic response of the material are affected by growth rate and co-doping with shallow impurities.

cond-mat.mtrl-sci↗

arXiv2005

The X(3872) at the Tevatron

I report results on the X(3872) from the Tevatron. Mass and other properties have been studied, with a focus on new results on the dipion mass spectrum in X -> J/PsiPi^+Pi^- decays. Dipions favor interpreting the decay as J/PsiRho, implying even C-parity for the X. Modeling uncertainties do not allow distinguishing between S- and P-wave decays of the J/PsiRho mode. Effects of Rho-Omega interference in X decay are also introduced.

hep-ex↗

arXiv2005

Disorder suppression and precise conductance quantization in constrictions of PbTe quantum wells

Conductance quantization was measured in submicron constrictions of PbTe, patterned into narrow,12 nm wide quantum wells deposited between Pb$_{0.92}$Eu$_{0.08}$Te barriers. Because the quantum confinement imposed by the barriers is much stronger than the lateral one, the one-dimensional electron energy level structure is very similar to that usually met in constrictions of AlGaAs/GaAs heterostructures. However, in contrast to any other system studied so far, we observe precise conductance quantization in $2e^2/h$ units, {\it despite of significant amount of charged defects in the vicinity of the constriction}. We show that such extraordinary results is a consequence of the paraelectric properties of PbTe, namely, the suppression of long-range tails of the Coulomb potentials due to the huge dielectric constant.

cond-mat.mes-hall↗

arXiv2005

Search for First-Generation Scalar Leptoquarks in $\bm{p \bar{p}}$ collisions at $\sqrt{s}$=1.96 TeV

We report on a search for pair production of first-generation scalar leptoquarks ($LQ$) in $p \bar{p}$ collisions at $\sqrt{s}$=1.96 TeV using an integrated luminosity of 203 $pb^{-1}$ collected at the Fermilab Tevatron collider by the CDF experiment. We observe no evidence for $LQ$ production in the topologies arising from $LQ \bar{LQ} \to eqeq$ and $LQ \bar{LQ} \to eq νq$, and derive 95% C.L. upper limits on the $LQ$ production cross section. %as a function of $β$, where $β$ is the branching fraction for $LQ \to eq$. The results are combined with those obtained from a separately reported CDF search in the topology arising from $LQ\bar{LQ} \to νq νq$ and 95% C.L. lower limits on the LQ mass as a function of $β= BR(LQ \to eq) $ are derived. The limits are 236, 205 and 145 GeV/c$^2$ for $β$ = 1, $β$ = 0.5 and $β$ = 0.1, respectively.

hep-ex↗

arXiv2005

The X(3872) Meson and "Exotic" Spectroscopy at CDF II

A spate of remarkable new hadrons reported in 2003 may lead to unequivocal proof of states beyond conventional $q\bar{q}$ and $qqq$ structure. Claimed baryonic states Theta+, Phi, and Theta^0_c would consist of five quarks, and new D_{sJ}-states and/or X(3872) might contain four quarks. I review efforts to search for and study this ``new'' spectroscopy in pbarp-collisions with the CDF II detector. Pentaquark searches are negative, and no evidence for exotic analogs of D_{sJ}-states was found. CDF has confirmed the X(3872). My main focus is the production and decay properties of the X(3872), and its possible interpretations. (Contains Copyrighted material, Readers may view, browse, and/or download material for temporary copying purposes only, provided these uses are for noncomercial personal purposes. Execpt as provided by law, this material may not be further reproduced, distributed, transmitted, modified, adapted, performed, displayed, published, or sold in whole or part, without written permission from the publisher.)

hep-ex↗

arXiv2005

Nonmonotonic Temperature Dependence of the Hall Resistance for 2D Electron System in Si

Weak field Hall resistance Rxy(T) of the 2D electron system in Si was measured over the range of temperatures 1-35 K and densities, where the diagonal resistivity exhibits a ``metallic'' behavior. The Rxy(T) dependence was found to be non-monotonic with a maximum at temperatures Tm~0.16Tf. The Rxy(T) variations in the low-temperature domain (T Tm), the Rxy(T) dependence can be qualitatively explained in terms of either a semiclassical T-dependence of a transport time, or a thermal activation of carries from a localized band.

cond-mat.str-el↗

arXiv2004

Comparison of Three-jet Events in Proton-Antiproton Collisions at Center-of-mass Energy 1.8 TeV to Predictions from a Next-to-leading Order QCD Calculation

The properties of three-jet events with total transverse energy greater than 320 GeV and individual jet energy greater than 20 GeV have been analyzed and compared to absolute predictions from a next-to-leading order (NLO) perturbative QCD calculation. These data, of integrated luminosity 86 pb^-1, were recorded by the CDF Experiment for proton-antiproton collisions at sqrt{s}=1.8 TeV. This study tests a model of higher order QCD processes that result in gluon emission and can be used to estimate the magnitude of the contribution of processes higher than NLO. The total cross section is measured to be 466 +/- 3(stat.)^{+207}_{-70}(syst.) pb. The differential cross section is furthermore measured for all kinematically accessible regions of the Dalitz plane, including those for which the theoretical prediction is unreliable. While the measured cross section is consistent with the theoretical prediction in magnitude, the two differ somewhat in shape in the Dalitz plane.

hep-ex↗

arXiv2004

The X(3872) at CDF II

Last year's X(3872) discovery was confirmed with the CDF II detector in pbarp collisions. We measure its mass to be $3871.3 \pm 0.7 \pm 0.4 MeV/c2$. The source of X-mesons in the large CDF sample is resolved by studying their vertex displacement. We find $16.1 \pm 4.9 \pm 2.0$% of our X-sample comes from decays of b-hadrons, and the remainder from prompt sources: either direct production or by decay of (unknown) short-lived particles. The mix of production sources is similar to that observed for the psi(2S) charmonium state.

hep-ex↗

arXiv2004

Reply to Comment (cond-mat/0311174)

We demonstrate that the experimental data on the temperature dependence of the resistivity and conductivity for high-mobility Si-MOS structures, obtained for a wide range of densities (~ 1:7) at intermediate temperatures, agree quantitatively with theory of interaction corrections in the ballistic regime, Tτ>1. Our comparison does not involve any fitting parameters.

cond-mat.str-el↗