Understanding the structural phase diagram of nano scale SrTiO3 has important implications on the basic physics and applications of the general class of transition metal oxide perovskites. Pressure ...dependent structural measurements on monodispersed nanoscale SrTiO3 samples with average diameters of 10 to ~80 nm were conducted. A robust pressure independent polar structure was detected in the 10 nm sample for pressures of up to 13 GPa while a size dependent cubic to tetragonal transition occurs (at P = Pc) for larger particle sizes. The results suggest that the growth of ~10 nm STO particles on substrates with large lattice mismatch will not alter the polar state of the system for a large range of strain values, possibly enabling device use.
We report the energy dependence of mid-rapidity (anti-)deuteron production in Au+Au collisions at \(\sqrt{s_\text{NN}} =\ \)7.7, 11.5, 14.5, 19.6, 27, 39, 62.4, and 200 GeV, measured by the STAR ...experiment at RHIC. The yield of deuterons is found to be well described by the thermal model. The collision energy, centrality, and transverse momentum dependence of the coalescence parameter \(B_2\) are discussed. We find that the values of \(B_2\) for anti-deuterons are systematically lower than those for deuterons, indicating that the correlation volume of anti-baryons is larger than that of baryons at \(\sqrt{s_\text{NN}}\) from 19.6 to 39 GeV. In addition, values of \(B_2\) are found to vary with collision energy and show a broad minimum around \(\sqrt{s_\text{NN}}=\ \)20 to 40 GeV, which might imply a change of the equation of state of the medium in these collisions.
Measurements of the production of forward high-energy pi(0) mesons from transversely polarized proton collisions at sqrts=200 GeV are reported. The cross section is generally consistent with ...next-to-leading order perturbative QCD calculations. The analyzing power is small at x(F) below about 0.3, and becomes positive and large at higher x(F), similar to the trend in data at sqrts< or =20 GeV. The analyzing power is in qualitative agreement with perturbative QCD model expectations. This is the first significant spin result seen for particles produced with p(T)>1 GeV/c at a polarized proton collider.
A measurement of the time-dependent ratio of the \(D^0\rightarrow K^+\pi^-\) to \(\overline{D}^0\rightarrow K^+\pi^-\) decay rates is reported. The analysis uses a sample of proton-proton collisions ...corresponding to an integrated luminosity of 6 fb\(^-1\) recorded by the LHCb experiment from 2015 through 2018 at a center-of-mass energy of 13 TeV. The \(D^0\) meson is required to originate from a \(D^{*+}\rightarrow D^0\pi^+\) decay, such that its flavor at production is inferred from the charge of the accompanying pion. The measurement is performed simultaneously for the \(K^+\pi^-\) and \(K^-\pi^+\) final states, allowing both mixing and \(CP\)-violation parameters to be determined. The value of the ratio of the decay rates at production is determined to be \(R_{K\pi} = (343.1 \pm 2.0) \times 10^{-5}\). The mixing parameters are measured to be \(c_{K\pi} = (51.4 \pm 3.5) \times 10^{-4}\) and \(c_{K\pi}^{\prime} = (13 \pm 4) \times 10^{-6}\), where \(\sqrt{R_{K\pi}}c_{K\pi}\) is the linear coefficient of the expansion of the ratio as a function of decay time in units of the \(D^0\) lifetime, and \(c_{K\pi}^{\prime}\) is the quadratic coefficient, both averaged between the \(K^+\pi^-\) and \(K^-\pi^+\) final states. The precision is improved relative to the previous best measurement by approximately 60%. No evidence for \(CP\) violation is found.
The \(\Lambda^0_b \to D^+ D^- \Lambda\) decay is observed for the first time using proton-proton collision data collected by the LHCb experiment at a center-of-mass energy of \(13 \mathrm{TeV}\), ...corresponding to an integrated luminosity of \(5.3 \mathrm{fb}^{-1}\). Using the \(B^0 \to D^+ D^- K_{\mathrm{S}}^0\) decay as a reference channel, the product of the relative production cross-section and decay branching fractions is measured to be $$ {\cal R}=\frac{\sigma_{\Lambda^0_b}}{\sigma_{B^0}} \times \frac{{\cal B}(\Lambda^0_b \to D^+ D^- \Lambda)}{{\cal B}(B^0 \to D^+ D^- K_{\mathrm{S}}^0)}=0.179 \pm 0.022 \pm 0.014 $$ where the first uncertainty is statistical and the second is systematic. The known branching fraction of the reference channel, \({\cal B}(B^0 \to D^+ D^- K_{\mathrm{S}}^0)\), and the cross-section ratio, \(\sigma_{\Lambda^0_b} / \sigma_{B^0}\), previously measured by \(\mathrm{LHCb}\) are used to derive the branching fraction of the \(\Lambda^0_b \to D^+ D^- \Lambda\) decay $$ {\cal B}(\Lambda^0_b \to D^+ D^- \Lambda)=(1.24 \pm 0.15 \pm 0.10 \pm 0.28 \pm 0.11) \times 10^{-4}, $$ where the third and fourth contributions are due to uncertainties of \({\cal B}(B^0 \to D^+ D^- K_{\mathrm{S}}^0)\) and \(\sigma_{\Lambda^0_b} / \sigma_{B^0}\), respectively. Inspection of the \(D^+ \Lambda\) and \(D^+ D^-\) invariant-mass distributions suggests a rich presence of intermediate resonances in the decay. The \(\Lambda^0_b \to D^{*+} D^- \Lambda\) decay is also observed for the first time as a partially reconstructed component in the \(D^+ D^- \Lambda\) invariant mass spectrum.
Charmonium production cross-section in proton-proton collisions is measured at the centre-of-mass energy \(\sqrt{s}=13\,TeV\) using decays to \(p\bar{p}\) final state. The study is performed using a ...data sample corresponding to an integrated luminosity of \(2.2\,{fb}^{-1}\) collected in 2018 with the \(LHCb\) detector. The production cross-section of the \(\eta_c\) meson is measured in a rapidity range of \(2.0 < y < 4.0\) and in a transverse momentum range of \(5.0 < p_{T} < 20.0\,{GeV/\it{c}}\), which is extended compared with previous \(LHCb\) analyses. The differential cross-section is measured in bins of \(p_{T}\) and, for the first time, of \(y\). Upper limits, at 90% and 95% confidence levels, on the \(\eta_c(2S)\) and \(h_c(1P)\) prompt production cross-sections are determined for the first time.
The first study of \(J/\psi\phi\) production in diffractive processes in proton-proton collisions is presented. The study is based on an LHCb dataset recorded at centre-of-mass energy of 13 TeV, ...corresponding to an integrated luminosity of 5 fb\(^{-1}\). The data disfavour a nonresonant \(J/\psi\phi\) production but are consistent with a resonant model including several resonant states observed previously only in \(B^+ \to J/\psi\phi K^+\) decays. The \(\chi_{c0}(4500)\) state is observed with a significance over \(5\sigma\) and the \(\chi_{c1}(4274)\) is confirmed with a significance of more than \(4\sigma\).
The first full amplitude analysis of \(B^+ \to \psi(2S) K^+ \pi^+ \pi^-\) decays is performed using proton-proton collision data corresponding to an integrated luminosity of \(9\,\text{fb}^{-1}\) ...recorded with the LHCb detector. The rich \(K^+ \pi^+ \pi^-\) spectrum is studied and the branching fractions of the resonant substructure associated with the prominent \(K_1(1270)^+\) contribution are measured. The data cannot be described by conventional strange and charmonium resonances only. An amplitude model with 53 components is developed comprising 11 hidden-charm exotic hadrons. New production mechanisms for charged charmonium-like states are observed. Significant resonant activity with spin-parity \(J^P = 1^+\) in the \(\psi(2S) \pi^+\) system is confirmed and a multi-pole structure is demonstrated. The spectral decomposition of the \(\psi(2S) \pi^+ \pi^-\) invariant-mass structure, dominated by \(X^0 \to \psi(2S) \rho(770)^0\) decays, broadly resembles the \(J/\psi \phi\) spectrum observed in \(B^+ \to J/\psi \phi K^+\) decays. Exotic \(\psi(2S) K^+ \pi^-\) resonances are observed for the first time.
A search for the fully reconstructed \(B_s^0 \rightarrow \mu^+\mu^-\gamma\) decay is performed at the LHCb experiment using proton-proton collisions at \(\sqrt{s}=13\)\,TeV corresponding to an ...integrated luminosity of \(5.4\,\mathrm{fb^{-1}}\). No significant signal is found and upper limits on the branching fraction in intervals of the dimuon mass are set \begin{align} {\cal B}(B_s^0 \rightarrow \mu^+\mu^-\gamma) < 4.2\times10^{-8},~&m(\mu\mu)\in2m_\mu,~1.70\,\mathrm{GeV/c^2} ,\nonumber {\cal B}(B_s^0 \rightarrow \mu^+\mu^-\gamma) < 7.7\times10^{-8},~&m(\mu\mu)\in1.70,~2.88\,\mathrm{GeV/c^2},\nonumber {\cal B}(B_s^0 \rightarrow \mu^+\mu^-\gamma) < 4.2\times10^{-8},~&m(\mu\mu)\in3.92 ,~m_{B_s^0}\,\mathrm{GeV/c^2},\nonumber \end{align} at 95\% confidence level. Additionally, upper limits are set on the branching fraction in the \(2m_\mu,~1.70\,\mathrm{GeV/c^2}\) dimuon mass region excluding the contribution from the intermediate \(\phi(1020)\) meson, and in the region combining all dimuon-mass intervals.
A search for the nonresonant \(\Lambda_c^+ \to p \mu^+ \mu^-\) decay is performed using proton-proton collision data recorded at a centre-of-mass energy of 13 TeV by the LHCb experiment, ...corresponding to an integrated luminosity of 5.4 fb\(^{-1}\). No evidence for the decay is found in the dimuon invariant-mass regions where the expected contributions of resonances is subdominant. The upper limit on the branching fraction of the \(\Lambda_c^+ \to p \mu^+ \mu^-\) decay is determined to be \(2.9~(3.2) \times 10^{-8}\) at 90% (95%) confidence level. The branching fractions in the dimuon invariant-mass regions dominated by the \(\eta\), \(\rho\) and \(\omega\) resonances are also determined.
