arXiv subjects

Th. Bauer

Publications and source records attributed to Th. Bauer.

At least 19 recordsLinked to original sources

arXiv2026

Linking extended vector wave fields with momentum space topology

Topology describes properties of physical systems that remain constant under continuous deformations. For infinite vector waves, global topological invariants in position space are typically associated with periodic patterns. We demonstrate that even for aperiodic Helmholtz-decomposable wave fields, possessing only the wave's intrinsic periodicity, a topological invariant can be found in momentum space. This invariant, the linking number, represents a Berry phase. By utilizing electromagnetic and hydrodynamic surface waves, we confirm the robustness of the linking number against deformations, and experimentally observe discrete transitions between distinct topological sectors. The linking number captures the topology of vector wave fields across both continuous and discrete momentum spaces. Our work introduces a unified topological framework for vector wave fields, enabling their classification via a global invariant.

physics.optics↗

arXiv2017

Unifying different interpretations of the nonlinear response in glass-forming liquids

This work aims at reconsidering several interpretations coexisting in the recent literature concerning non-linear susceptibilities in supercooled liquids. We present experimental results on glycerol and propylene carbonate showing that the three independent cubic susceptibilities have very similar frequency and temperature dependences, both for their amplitudes and phases. This strongly suggests a unique physical mechanism responsible for the growth of these non-linear susceptibilities. We show that the framework proposed by two of us [BB, Phys. Rev. B 72, 064204 (2005)], where the growth of non-linear susceptibilities is intimately related to the growth of "glassy domains", accounts for all the salient experimental features. We then review several complementary and/or alternative models, and show that the notion of cooperatively rearranging glassy domains is a key (implicit or explicit) ingredient to all of them. This paves the way for future experiments which should deepen our understanding of glasses.

cond-mat.dis-nn↗

arXiv2017

Investigation of nonlinear effects in glassy matter using dielectric methods

We summarize current developments in the investigation of glassy matter using nonlinear dielectric spectroscopy. This work also provides a brief introduction into the phenomenology of the linear dielectric response of glass-forming materials and discusses the main mechanisms that can give rise to nonlinear dielectric response in this material class. Here we mainly concentrate on measurements of the conventional dielectric permittivity at high fields and the higher-order susceptibilities characterizing the 3-omega and 5-omega components of the dielectric response as performed in our group. Typical results on canonical glass-forming liquids and orientationally disordered plastic crystals are discussed, also treating the special case of supercooled monohydroxy alcohols.

cond-mat.dis-nn↗

arXiv2016

Fifth-order susceptibility unveils growth of thermodynamic amorphous order in glass-formers

Glasses are ubiquitous in daily life and technology. However the microscopic mechanisms generating this state of matter remain subject to debate: Glasses are considered either as merely hyper-viscous liquids or as resulting from a genuine thermodynamic phase transition towards a rigid state. We show that third- and fifth-order susceptibilities provide a definite answer to this longstanding controversy. Performing the corresponding high-precision nonlinear dielectric experiments for supercooled glycerol and propylene carbonate, we find strong support for theories based upon thermodynamic amorphous order. Moreover, when lowering temperature, we find that the growing transient domains are compact - that is their fractal dimension d_f = 3. The glass transition may thus represent a class of critical phenomena different from canonical second-order phase transitions for which d_f < 3.

cond-mat.dis-nn↗

arXiv2015

Nonlinear dielectric spectroscopy in a fragile plastic crystal

In this work we provide a thorough examination of the nonlinear dielectric properties of a succinonitrile-glutaronitrile mixture, representing one of the rare example of a plastic crystal with fragile glassy dynamics. The detected alteration of the complex dielectric permittivity under high fields can be explained considering the heterogeneous nature of glassy dynamics and a field-induced variation of entropy. While the first mechanism was also found in structural glass formers, the latter effect seems to be typical for plastic crystals. Morover, the third harmonic component of the dielectric susceptibility is reported, revealing a spectral shape as predicted for cooperative molecular dynamics. In accord with the fragile nature of the glass transition in this plastic crystal, we deduce a relatively strong temperature dependence of the number of correlated molecules, in contrast to the much weaker temperature dependence in plastic-crystalline cyclo-octanol, whose glass transition is of strong nature.

cond-mat.dis-nn↗

arXiv2015

Quantum numbers of the $X(3872)$ state and orbital angular momentum in its $\rho^0 J\psi$ decay

Angular correlations in $B^+\to X(3872) K^+$ decays, with $X(3872)\to \rho^0 J/\psi$, $\rho^0\to\pi^+\pi^-$ and $J/\psi \to\mu^+\mu^-$, are used to measure orbital angular momentum contributions and to determine the $J^{PC}$ value of the $X(3872)$ meson. The data correspond to an integrated luminosity of 3.0 fb$^{-1}$ of proton-proton collisions collected with the LHCb detector. This determination, for the first time performed without assuming a value for the orbital angular momentum, confirms the quantum numbers to be $J^{PC}=1^{++}$. The $X(3872)$ is found to decay predominantly through S wave and an upper limit of $4\%$ at $95\%$ C.L. is set on the fraction of D wave.

hep-ex↗

arXiv2015

Cooperativity and Heterogeneity in Plastic Crystals Studied by Nonlinear Dielectric Spectroscopy

The glassy dynamics of plastic-crystalline cyclo-octanol and ortho-carborane, where only the molecular reorientational degrees of freedom freeze without long-range order, is investigated by nonlinear dielectric spectroscopy. Marked differences to canonical glass formers show up: While molecular cooperativity governs the glassy freezing, it leads to a much weaker slowing down of molecular dynamics than in supercooled liquids. Moreover, the observed nonlinear effects cannot be explained with the same heterogeneity scenario recently applied to canonical glass formers. This supports ideas that molecular relaxation in plastic crystals may be intrinsically non-exponential. Finally, no nonlinear effects were detected for the secondary processes in cyclo-octanol.

cond-mat.dis-nn↗

arXiv2014

Study of the kinematic dependences of $Λ_b^0$ production in $pp$ collisions and a measurement of the $Λ_b^0 \rightarrow Λ_c^+ π^-$ branching fraction

The kinematic dependences of the relative production rates, $f_{Λ_b^0}/f_d$, of $Λ_b^0$ baryons and $\bar{B}^0$ mesons are measured using $Λ_b^0 \rightarrow Λ_c^+ π^-$ and $\bar{B}^0 \rightarrow D^+ π^-$ decays. The measurements use proton-proton collision data, corresponding to an integrated luminosity of 1 fb$^{-1}$ at a centre-of-mass energy of 7 TeV, recorded in the forward region with the LHCb experiment. The relative production rates are observed to depend on the transverse momentum, $p_T$, and pseudorapidity, $η$, of the beauty hadron, in the studied kinematic region $1.5 < p_T < 40$ GeV/$c$ and $2 < η< 5$. Using a previous LHCb measurement of $f_{Λ_b^0}/f_d$ in semileptonic decays, the branching fraction $\mathcal{B}(Λ_b^0 \rightarrow Λ_c^+ π^-) = \Big( 4.30 \pm 0.03 \,\, ^{+0.12}_{-0.11} \pm 0.26 \pm 0.21 \Big) \times 10^{-3}$ is obtained, where the first uncertainty is statistical, the second is systematic, the third is from the previous LHCb measurement of $f_{Λ_b^0}/f_d$ and the fourth is due to the $\bar{B}^0 \rightarrow D^+ π^-$ branching fraction. This is the most precise measurement of a $Λ_b^0$ branching fraction to date.

hep-ex↗

arXiv2014

Effective lifetime measurements in the $B_{s}^{0} \rightarrow K^{+}K^{-}$, $B^{0} \rightarrow K^{+}π^{-}$ and $B_{s}^{0} \rightarrow π^{+}K^{-}$ decays

Measurements of the effective lifetimes in the $B_{s}^{0} \rightarrow K^{+}K^{-}$, $B^{0} \rightarrow K^{+}π^{-}$ and $B_{s}^{0} \rightarrow π^{+}K^{-}$ decays are presented using $1.0~\mathrm{fb^{-1}}$ of $pp$ collision data collected at a centre-of-mass energy of 7 TeV by the LHCb experiment. The analysis uses a data-driven approach to correct for the decay time acceptance. The measured effective lifetimes are $τ_{B_{s}^{0} \rightarrow K^{+}K^{-}}$ = $1.407~\pm~0.016~\pm~0.007~\mathrm{ps}$, $τ_{B^{0} \rightarrow K^{+}π^{-}}$ = $1.524~\pm~0.011~\pm~0.004~\mathrm{ps}$, $τ_{B_{s}^{0} \rightarrow π^{+}K^{-}}$ = $1.60~\pm~0.06~\pm~0.01~\mathrm{ps}$. This is the most precise determination to date of the effective lifetime in the $B_{s}^{0} \rightarrow K^{+}K^{-}$ decay and provides constraints on contributions from physics beyond the Standard Model to the $B_{s}^{0}$ mixing phase and the width difference $ΔΓ_{s}$.

hep-ex↗

arXiv2014

Measurement of the $Ξ_b^-$ and $Ω_b^-$ baryon lifetimes

Using a data sample of pp collisions corresponding to an integrated luminosity of $3~ \rm fb^{-1}$, the $Ξ_b^-$ and $Ω_b^-$ baryons are reconstructed in the $Ξ_b^- \rightarrow J/ψΞ^-$ and $Ω_b^- \rightarrow J/ψΩ^-$ decay modes and their lifetimes measured to be $τ(Ξ_b^-) = 1.55\, ^{+0.10}_{-0.09}~{\rm(stat)} \pm 0.03\,{\rm(syst)}$ ps, $τ(Ω_b^-) = 1.54\, ^{+0.26}_{-0.21}~{\rm(stat)} \pm 0.05\,{\rm(syst)}$ ps. These are the most precise determinations to date. Both measurements are in good agreement with previous experimental results and with theoretical predictions.

hep-ex↗

arXiv2014

Measurement of $CP$ asymmetry in $D^0 \rightarrow K^- K^+$ and $D^0 \rightarrow π^- π^+$ decays

Time-integrated $CP$ asymmetries in $D^0$ decays to the final states $K^- K^+$ and $π^- π^+$ are measured using proton-proton collisions corresponding to $3\mathrm{\,fb}^{-1}$ of integrated luminosity collected at centre-of-mass energies of $7\mathrm{\,Te\kern -0.1em V}$ and $8\mathrm{\,Te\kern -0.1em V}$. The $D^0$ mesons are produced in semileptonic $b$-hadron decays, where the charge of the accompanying muon is used to determine the initial flavour of the charm meson. The difference in $CP$ asymmetries between the two final states is measured to be \begin{align} ΔA_{CP} = A_{CP}(K^-K^+)-A_{CP}(π^-π^+) = (+0.14 \pm 0.16\mathrm{\,(stat)} \pm 0.08\mathrm{\,(syst)})\% \ . \nonumber \end{align} A measurement of $A_{CP}(K^-K^+)$ is obtained assuming negligible $CP$ violation in charm mixing and in Cabibbo-favoured $D$ decays. It is found to be \begin{align} A_{CP}(K^-K^+) = (-0.06 \pm 0.15\mathrm{\,(stat)} \pm 0.10\mathrm{\,(syst)}) \% \ ,\nonumber \end{align} where the correlation coefficient between $ΔA_{CP}$ and $A_{CP}(K^-K^+)$ is $ρ=0.28$. By combining these results, the $CP$ asymmetry in the $D^0\rightarrowπ^-π^+$ channel is $A_{CP}(π^-π^+)=(-0.20\pm0.19\mathrm{\,(stat)}\pm0.10\mathrm{\,(syst)})\%$.

hep-ex↗

arXiv2014

Measurement of the resonant and CP components in $\overline{B}^0\rightarrow J/ψπ^+π^-$ decays

The resonant structure of the reaction $\overline{B}^0\rightarrow J/ψπ^+π^-$ is studied using data from 3 fb$^{-1}$ of integrated luminosity collected by the LHCb experiment, one-third at 7 Tev center-of-mass energy and the remainder at 8 Tev. The invariant mass of the $π^+π^-$ pair and three decay angular distributions are used to determine the fractions of the resonant and non-resonant components. Six interfering $π^+π^-$ states: $ρ(770)$, $f_0(500)$, $f_2(1270)$, $ρ(1450)$, $ω(782)$ and $ρ(1700)$ are required to give a good description of invariant mass spectra and decay angular distributions. The positive and negative CP fractions of each of the resonant final states are determined. The $f_0(980)$ meson is not seen and the upper limit on its presence, compared with the observed $f_0(500)$ rate, is inconsistent with a model of tetraquark substructure for these scalar mesons at the eight standard deviation level. In the $q\overline{q}$ model, the absolute value of the mixing angle between the $f_0(980)$ and the $f_0(500)$ scalar mesons is limited to be less than $17^{\circ}$ at 90% confidence level.

hep-ex↗

arXiv2014

Differential branching fractions and isospin asymmetries of $B \to K^{(*)}μ^{+}μ^{-}$ decays

The isospin asymmetries of $B \to Kμ^+μ^-$ and $B \to K^{*}μ^+μ^-$ decays and the partial branching fractions of the $B^0 \to K^0μ^+μ^-$, $B^+ \to K^+μ^+μ^-$ and $B^+ \to K^{*+}μ^+μ^-$ decays are measured as functions of the dimuon mass squared, $q^2$. The data used correspond to an integrated luminosity of 3$~$fb$^{-1}$ from proton-proton collisions collected with the LHCb detector at centre-of-mass energies of 7$\,$TeV and 8$\,$TeV in 2011 and 2012, respectively. The isospin asymmetries are both consistent with the Standard Model expectations. The three measured branching fractions, while individually consistent, all favour lower values than their respective Standard Model predictions.

hep-ex↗

arXiv2014

Searches for $Λ^0_{b}$ and $Ξ^{0}_{b}$ decays to $K^0_{\rm S} p π^{-}$ and $K^0_{\rm S}p K^{-}$ final states with first observation of the $Λ^0_{b} \rightarrow K^0_{\rm S}p π^{-}$ decay

A search for previously unobserved decays of beauty baryons to the final states $K^0_{\rm\scriptscriptstyle S} p π^{-}$ and $K^0_{\rm\scriptscriptstyle S}p K^{-}$ is reported. The analysis is based on a data sample corresponding to an integrated luminosity of $1.0\,$fb$^{-1}$ of $pp$ collisions. The $Λ^0_{b} \rightarrow \overline{\kern -0.2em K}^0_{\rm\scriptscriptstyle S}p π^{-}$ decay is observed with a significance of $8.6\,σ$, with branching fraction \begin{eqnarray*} {\cal{B}}(Λ^0_{b} \rightarrow \overline{\kern -0.2em K}^0 p π^{-}) & = & \left(1.26 \pm 0.19 \pm 0.09 \pm 0.34 \pm 0.05 \right) \times 10^{-5} \,, \end{eqnarray*} where the uncertainties are statistical, systematic, from the ratio of fragmentation fractions $f_Λ/f_{d}$, and from the branching fraction of the $B^0 \rightarrow K^0_{\rm\scriptscriptstyle S}π^{+}π^{-}$ normalisation channel, respectively. A first measurement is made of the $CP$ asymmetry, giving \begin{eqnarray*} A_{C/!P} (Λ^0_{b} \rightarrow \overline{\kern -0.2em K}^0 p π^{-}) & = & 0.22 \pm 0.13\mathrm{\,(stat)} \pm 0.03\mathrm{\,(syst)} \, . \end{eqnarray*} No significant signals are seen for $Λ^0_{b} \rightarrow K^0_{\rm\scriptscriptstyle S}p K^{-}$ decays, $Ξ^{0}_{b}$ decays to both the $K^0_{\rm\scriptscriptstyle S}p π^{-}$ and $K^0_{\rm\scriptscriptstyle S}p K^{-}$ final states, and the $Λ^0_{b} \rightarrow D^{-}_{s} (\rightarrow K^0_{\rm\scriptscriptstyle S} K^{-}) p$ decay, and upper limits on their branching fractions are reported.

hep-ex↗

arXiv2014

Measurement of charged particle multiplicities and densities in $pp$ collisions at $\sqrt{s}=7\;$TeV in the forward region

Charged particle multiplicities are studied in proton-proton collisions in the forward region at a centre-of-mass energy of $\sqrt{s} = 7\;$TeV with data collected by the LHCb detector. The forward spectrometer allows access to a kinematic range of $2.0<η<4.8$ in pseudorapidity, momenta down to $2\;$GeV/$c$ and transverse momenta down to $0.2\;$GeV/$c$. The measurements are performed using minimum-bias events with at least one charged particle in the kinematic acceptance. The results are presented as functions of pseudorapidity and transverse momentum and are compared to predictions from several Monte Carlo event generators.

hep-ex↗

arXiv2014

A study of CP violation in $B^\pm \to D K^\pm$ and $B^\pm \to D π^\pm$ decays with $D \to K^0_{\rm S} K^\pm π^\mp$ final states

A first study of CP violation in the decay modes $B^\pm\to [K^0_{\rm S} K^\pm π^\mp]_D h^\pm$ and $B^\pm\to [K^0_{\rm S} K^\mp π^\pm]_D h^\pm$, where $h$ labels a $K$ or $π$ meson and $D$ labels a $D^0$ or $\overline{D}^0$ meson, is performed. The analysis uses the LHCb data set collected in $pp$ collisions, corresponding to an integrated luminosity of 3 fb$^{-1}$. The analysis is sensitive to the CP-violating CKM phase $γ$ through seven observables: one charge asymmetry in each of the four modes and three ratios of the charge-integrated yields. The results are consistent with measurements of $γ$ using other decay modes.

hep-ex↗

arXiv2014

Observation of photon polarization in the $b \to sγ$ transition

This Letter presents a study of the flavor-changing neutral current radiative $B^{\pm} \to K^{\pm}π^{\mp}π^{\pm}γ$ decays performed using data collected in proton-proton collisions with the LHCb detector at $7$ and $8\,$TeV center-of-mass energies. In this sample, corresponding to an integrated luminosity of $3\,\text{fb}^{-1}$, nearly $14\,000$ signal events are reconstructed and selected, containing all possible intermediate resonances with a $K^{\pm}π^{\mp}π^{\pm}$ final state in the $[1.1, 1.9]\,$GeV/$c^{2}$ mass range. The distribution of the angle of the photon direction with respect to the plane defined by the final-state hadrons in their rest frame is studied in intervals of $K^{\pm}π^{\mp}π^{\pm}$ mass and the asymmetry between the number of signal events found on each side of the plane is obtained. The first direct observation of the photon polarization in the $b \to sγ$ transition is reported with a significance of $5.2\,σ$.

hep-ex↗

arXiv2014

Nonlinear dielectric response of Debye, alpha, and beta relaxation in 1-propanol

We present nonlinear dielectric measurements of glass-forming 1-propanol, a prototypical example for the monohydroxy alcohols that are known to exhibit unusual relaxation dynamics, namely an additional Debye relaxation, slower than the structural alpha relaxation. Applying high ac fields of 468 kV/cm allows for a detailed investigation of the nonlinear properties of all three relaxation processes occurring in 1-propanol, namely the Debye, alpha, and beta relaxation. Both the field-induced variations of dielectric constant and loss are reported. Polarization saturation and the absorption of field energy govern the findings in the Debye-relaxation regime, well consistent with the suggested cluster-like nature of the relaxing entities. The behavior of the alpha relaxation is in good accord with the expectations for a heterogeneous relaxation scenario. Finally, the Johari-Goldstein beta-relaxation in 1-propanol seems to exhibit no or only weak field dependence, in agreement with recent findings for the excess wing of canonical glass formers.

cond-mat.soft↗