arXiv subjects

P. Rubin

Publications and source records attributed to P. Rubin.

At least 19 recordsLinked to original sources

arXiv2023

First observation and study of the $K^{\pm} \rightarrow \pi^{0} \pi^{0} \mu^{\pm} \nu$ decay

The NA48/2 experiment at CERN reports the first observation of the $K^{\pm} \rightarrow \pi^{0} \pi^{0} \mu^{\pm} \nu$ decay based on a sample of 2437 candidates with 15% background contamination collected in 2003--2004. The decay branching ratio in the kinematic region of the squared dilepton mass above $0.03$~GeV$^2/c^4$ is measured to be $(0.65 \pm 0.03) \times 10^{-6}$. The extrapolation to the full kinematic space, using a specific model, is found to be $(3.45 \pm 0.16) \times 10^{-6}$, in agreement with chiral perturbation theory predictions.

hep-ex↗

arXiv2022

Strong enhancement of electromagnetic shower development induced by high-energy photons in a thick oriented tungsten crystal

We have observed a significant enhancement in the energy deposition by $25$--$100~\mathrm{GeV}$ photons in a $1~\mathrm{cm}$ thick tungsten crystal oriented along its $\langle 111 \rangle$ lattice axes. At $100~\mathrm{GeV}$, this enhancement, with respect to the value observed without axial alignment, is more than twofold. This effect, together with the measured huge increase in secondary particle generation is ascribed to the acceleration of the electromagnetic shower development by the strong axial electric field. The experimental results have been critically compared with a newly developed Monte Carlo adapted for use with crystals of multi-$X_0$ thickness. The results presented in this paper may prove to be of significant interest for the development of high-performance photon absorbers and highly compact electromagnetic calorimeters and beam dumps for use at the energy and intensity frontiers.

hep-ex↗

arXiv2019

KLEVER: An experiment to measure BR($K_L\to\pi^0\nu\bar{\nu}$) at the CERN SPS

Precise measurements of the branching ratios for the flavor-changing neutral current decays $K\to\pi\nu\bar{\nu}$ can provide unique constraints on CKM unitarity and, potentially, evidence for new physics. It is important to measure both decay modes, $K^+\to\pi^+\nu\bar{\nu}$ and $K_L\to\pi^0\nu\bar{\nu}$, since different new physics models affect the rates for each channel differently. The goal of the NA62 experiment at the CERN SPS is to measure the BR for the charged channel to within 10%. For the neutral channel, the BR has never been measured. We are designing the KLEVER experiment to measure BR($K_L\to\pi^0\nu\bar{\nu}$) to $\sim$20% using a high-energy neutral beam at the CERN SPS starting in LHC Run 4. The boost from the high-energy beam facilitates the rejection of background channels such as $K_L\to\pi^0\pi^0$ by detection of the additional photons in the final state. On the other hand, the layout poses particular challenges for the design of the small-angle vetoes, which must reject photons from $K_L$ decays escaping through the beam exit amidst an intense background from soft photons and neutrons in the beam. Background from $\Lambda \to n\pi^0$ decays in the beam must also be kept under control. We present findings from our design studies for the beamline and experiment, with an emphasis on the challenges faced and the potential sensitivity for the measurement of BR($K_L\to\pi^0\nu\bar{\nu}$).

hep-ex↗

arXiv2016

FeAs$_2$ formation and electronic nematic ordering: Analysis in terms of structural transformations

By combining DFT-based computational analysis and symmetry constraints in terms of group-subgroup relations, we analysed the formation of the native crystalline structure of loellingite FeAs$_2$. We showed that the ground state of the material exhibits the ordered patterns of the electronic localization which are mainly associated with iron $3d_{x^2 - y^2}$ orbitals and can be characterized in terms of nematic-like ordering. The ordering is the result of the close interplay of the lattice and the electron degrees of freedom. In a structural aspect, it pursues an energy quest to select the orthorhombic crystal lattice attributed to the Pnnm space group. In a charge aspect, the ordering is connected with the valence charge density redistribution that not only provides a high electronic polarizability but also gives rise to an extra-large magnitude of the negative component of the dynamical p-d charge transfer.

cond-mat.mtrl-sci↗

arXiv2016

Model-independent determination of the strong-phase difference between D^0 and D^0-bar-> K^0_S,L h^+ h^- (h=pi,K) and its impact on the measurement of the CKM angle gamma/phi_3

We report the first determination of the relative strong-phase difference between D^0 -> K^0_S,L K^+ K^- and D^0-bar -> K^0_S,L K^+ K^-. In addition, we present updated measurements of the relative strong-phase difference between D^0 -> K^0_S,L pi^+ pi^- and D^0-bar -> K^0_S,L pi^+ pi^-. Both measurements exploit the quantum coherence between a pair of D^0 and D^0-bar mesons produced from psi(3770) decays. The strong-phase differences measured are important for determining the Cabibbo-Kobayashi-Maskawa angle gamma/phi_3 in B^- -> K^- D^0-tilde decays, where D^0-tilde is a D^0 or D^0-bar meson decaying to K^0_S h^+ h^- (h=pi,K), in a manner independent of the model assumed to describe the D^0 -> K^0_S h^+ h^- decay. Using our results, the uncertainty in gamma/phi_3 due to the error on the strong-phase difference is expected to be between 1.7 and 3.9 degrees for an analysis using B^- K^- D^0-tilde D^0-tilde -> K^0_S pi^+ pi^- decays, and between 3.2 and 3.9 degrees for an analysis based on B^- -> K^- D^0-tilde, D^0-tilde -> K^0_S K^+ K^- decays. A measurement is also presented of the CP-odd fraction, F_-, of the decay D^0 -> K^0_S K^+ K^- in the region of the phi -> K^+ K^- resonance. We find that in a region within 0.01 GeV^2/c^4 of the nominal phi mass squared F_- > 0.91 at the 90% confidence level.

hep-ex↗

arXiv2014

Exact diagonalization study of the spin-1 two-dimensional $J_1$-$J_3$ Heisenberg model on a triangular lattice

The spin-1 Heisenberg model on a triangular lattice with the ferromagnetic nearest- and antiferromagnetic third-nearest-neighbor exchange interactions, $J_1=-(1-p)J$ and $J_2=pJ$, $J>0$ $ (0 \leq p \leq 1)$, is studied with the use of the SPINPACK code. This model is applicable for the description of the magnetic properties of NiGa$_2$S$_4$. The ground, low-lying excited state energies and spin-spin correlation functions have been found for lattices with N=16 and N=20 sites with the periodic boundary conditions. These results are in qualitative agreement with earlier authors' results obtained with Mori's projection operator technique.

cond-mat.str-el↗

arXiv2014

The pseudogaps in multiband electron-doped cuprate superconductivity

The pseudogap (PG) excitations in the framework of multiband superconductivity are analysed. Calculations for the doping phase diagram of electron-doped cuprate superconductors have been made. A nonrigid multiband model has been used. The interband pairing acts between the upper Hubbard band (UHB) and midgap states created (and shifted upwards) by doping. The appearance of two PG and two phase diagram critical points (CP) is suggested. The larger antinodal PG reflects the destruction of the long-range antiferromagnetic (AF) order. The second, smaller PG is a near-nodal event with exposed doping dependence behind the first CP. It reaches the T$_c$ - dome. Model calculations have been made. The peculiarities of the phase diagram are determined by the doping-stimulated band overlap dynamics. The observation of ,,foreign`` carriers as compared to the ones introduced by doping is expected to start with the vanishing PG.

cond-mat.supr-con↗

arXiv2014

Updated measurements of absolute $D^+$ and $D^0$ hadronic branching fractions and $σ(e^+e^-\to D\overline{D})$ at $E_\mathrm{cm} = 3774$ MeV

Utilizing the full CLEO-c data sample of 818 pb$^{-1}$ of $e^+e^-$ data taken at the $ψ(3770)$ resonance, we update our measurements of absolute hadronic branching fractions of charged and neutral $D$ mesons. We previously reportedresults from subsets of these data. Using a double tag technique we obtain branching fractions for three $D^0$ and six $D^+$ modes, including the reference branching fractions $\mathcal{B} (D^0\to K^-π^+)=(3.934 \pm 0.021 \pm 0.061)\%$ and $\mathcal{B} (D^+ \to K^- π^+π^+)=(9.224 \pm 0.059 \pm 0.157)\%$. The uncertainties are statistical and systematic, respectively. In these measurements we include the effects of final-state radiation by allowing for additional unobserved photons in the final state, and the systematic errors include our estimates of the uncertainties of these effects. Furthermore, using an independent measurement of the luminosity, we obtain the cross sections $σ(e^+e^-\to D^0\overline{D}{}^0)=(3.607\pm 0.017 \pm 0.056) \ \mathrm{nb}$ and $σ(e^+e^-\to D^+D^-)=(2.882\pm 0.018 \pm 0.042) \ \mathrm{nb}$ at a center of mass energy, $E_\mathrm{cm} = 3774 \pm 1$ MeV.

hep-ex↗

arXiv2014

Magnetic properties of the spin-1 two-dimensional $J_1-J_3$ Heisenberg model on a triangular lattice

Motivated by the recent experiment in NiGa$_2$S$_4$, the spin-1 Heisenberg model on a triangular lattice with the ferromagnetic nearest- and antiferromagnetic third-nearest-neighbor exchange interactions, $J_1 = -(1-p)J$ and $J_3 = pJ, J > 0$, is studied in the range of the parameter $0 \leq p \leq 1$. Mori's projection operator technique is used as a method, which retains the rotation symmetry of spin components and does not anticipate any magnetic ordering. For zero temperature several phase transitions are observed. At $ p \approx 0.2$ the ground state is transformed from the ferromagnetic order into a disordered state, which in its turn is changed to an antiferromagnetic long-range ordered state with the incommensurate ordering vector at $p \approx 0.31$. With growing $p$ the ordering vector moves along the line to the commensurate point $Q_c = (2 π/3, 0)$, which is reached at $p = 1$. The final state with the antiferromagnetic long-range order can be conceived as four interpenetrating sublattices with the $120°$ spin structure on each of them. Obtained results offer a satisfactory explanation for the experimental data in NiGa$_2$S$_4$.

cond-mat.str-el↗

arXiv2013

Report of the Quark Flavor Physics Working Group

This report represents the response of the Intensity Frontier Quark Flavor Physics Working Group to the Snowmass charge. We summarize the current status of quark flavor physics and identify many exciting future opportunities for studying the properties of strange, charm, and bottom quarks. The ability of these studies to reveal the effects of new physics at high mass scales make them an essential ingredient in a well-balanced experimental particle physics program.

hep-ex↗

arXiv2013

Improved Measurement of Absolute Hadronic Branching Fractions of the Ds+ Meson

The branching fractions of Ds meson decays serve to normalize many measurements of processes involving charm quarks. Using 586 pb^-1 of e+ e- collisions recorded at a center of mass energy of 4.17 GeV, we determine absolute branching fractions for 13 Ds decays in 16 reconstructed final states with a double tag technique. In particular we make a precise measurement of the branching fraction B(Ds -> K- K+ pi+) = (5.55 +- 0.14 +- 0.13)%, where the uncertainties are statistical and systematic respectively. We find a significantly reduced value of B(Ds -> pi+ pi0 eta') compared to the world average, and our results bring the inclusively and exclusively measured values of B(Ds -> eta' X)$ into agreement. We also search for CP-violating asymmetries in Ds decays and measure the cross-section of e+ e- -> Ds* Ds at Ecm = 4.17 GeV.

hep-ex↗

arXiv2013

Measurement of the branching ratio of the decay $Ξ^{0}\rightarrow Σ^{+} μ^{-} \barν_μ$

From the 2002 data taking with a neutral kaon beam extracted from the CERN-SPS, the NA48/1 experiment observed 97 $Ξ^{0}\rightarrow Σ^{+} μ^{-} \barν_μ$ candidates with a background contamination of $30.8 \pm 4.2$ events. From this sample, the BR($Ξ^{0}\rightarrow Σ^{+} μ^{-} \barν_μ$) is measured to be $(2.17 \pm 0.32_{\mathrm{stat}}\pm 0.17_{\mathrm{syst}})\times10^{-6}$.

hep-ex↗

arXiv2012

Updated Measurement of the Strong Phase in D0 --> K+pi- Decay Using Quantum Correlations in e+e- --> D0 D0bar at CLEO

We analyze a sample of 3 million quantum-correlated D0 D0bar pairs from 818 pb^-1 of e+e- collision data collected with the CLEO-c detector at E_cm = 3.77 GeV, to give an updated measurement of \cosδand a first determination of \sinδ, where δis the relative strong phase between doubly Cabibbo-suppressed D0 --> K+pi- and Cabibbo-favored D0bar --> K+pi- decay amplitudes. With no inputs from other experiments, we find \cosδ= 0.81 +0.22+0.07 -0.18-0.05, \sinδ= -0.01 +- 0.41 +- 0.04, and |δ| = 10 +28+13 -53-0 degrees. By including external measurements of mixing parameters, we find alternative values of \cosδ= 1.15 +0.19+0.00 -0.17-0.08, \sinδ= 0.56 +0.32+0.21 -0.31-0.20, and δ= (18 +11-17) degrees. Our results can be used to improve the world average uncertainty on the mixing parameter y by approximately 10%.

hep-ex↗

arXiv2012

Amplitude analysis of D0->K+K-pi+pi-

The first flavor-tagged amplitude analysis of the decay D0 to the self-conjugate final state K+K-pi+pi- is presented. Data from the CLEO II.V, CLEO III, and CLEO-c detectors are used, from which around 3000 signal decays are selected. The three most significant amplitudes, which contribute to the model that best fits the data, are phirho0, K1(1270)+-K-+, and non-resonant K+K-pi+pi-. Separate amplitude analyses of D0 and D0-bar candidates indicate no CP violation among the amplitudes at the level of 5% to 30% depending on the mode. In addition, the sensitivity to the CP-violating parameter gamma/phi3 of a sample of 2000 B+ -> D0-tilde(K+K-pi+pi-)K+ decays, where D0-tilde is a D0 or D0-bar, collected at LHCb or a future flavor facility, is estimated to be (11.3 +/- 0.3) degrees using the favored model.

hep-ex↗

arXiv2012

Studies of the decays D^0 \rightarrow K_S^0K^-\pi^+ and D^0 \rightarrow K_S^0K^+\pi^-

The first measurements of the coherence factor R_{K_S^0K\pi} and the average strong--phase difference \delta^{K_S^0K\pi} in D^0 \to K_S^0 K^\mp\pi^\pm decays are reported. These parameters can be used to improve the determination of the unitary triangle angle \gamma\ in B^- \rightarrow $\widetilde{D}K^-$ decays, where $\widetilde{D}$ is either a D^0 or a D^0-bar meson decaying to the same final state, and also in studies of charm mixing. The measurements of the coherence factor and strong-phase difference are made using quantum-correlated, fully-reconstructed D^0D^0-bar pairs produced in e^+e^- collisions at the \psi(3770) resonance. The measured values are R_{K_S^0K\pi} = 0.70 \pm 0.08 and \delta^{K_S^0K\pi} = (0.1 \pm 15.7)$^\circ$ for an unrestricted kinematic region and R_{K*K} = 0.94 \pm 0.12 and \delta^{K*K} = (-16.6 \pm 18.4)$^\circ$ for a region where the combined K_S^0 \pi^\pm invariant mass is within 100 MeV/c^2 of the K^{*}(892)^\pm mass. These results indicate a significant level of coherence in the decay. In addition, isobar models are presented for the two decays, which show the dominance of the K^*(892)^\pm resonance. The branching ratio {B}(D^0 \rightarrow K_S^0K^+\pi^-)/{B}(D^0 \rightarrow K_S^0K^-\pi^+) is determined to be 0.592 \pm 0.044 (stat.) \pm 0.018 (syst.), which is more precise than previous measurements.

hep-ex↗

arXiv2012

Amplitude analyses of the decays chi_c1 -> eta pi+ pi- and chi_c1 -> eta' pi+ pi-

Using a data sample of 2.59 x 10^7 psi(2S) decays obtained with the CLEO-c detector, we perform amplitude analyses of the complementary decay chains chi_c1 -> eta pi+ pi- and chi_c1 -> eta' pi+ pi-. We find evidence for a P-wave eta' pi scattering amplitude, which, if interpreted as a resonance, would have exotic J^PC = 1^-+ and parameters consistent with the pi_1(1600) state reported in other production mechanisms. We also make the first observation of the decay a_0(980) -> eta' pi and measure the ratio of branching fractions B(a_0(980) -> eta' pi)/B(a_0(980) -> eta pi) = 0.064 +- 0.014 +- 0.014. The pi pi spectrum produced with a recoiling eta is compared to that with eta' recoil.

hep-ex↗

arXiv2011

First Measurement of the Form Factors in the Decays D0 to rho- e+ nu_e and D+ to rho0 e+ nu_e

Using the entire CLEO-c psi(3770) to DDbar event sample, corresponding to an integrated luminosity of 818 pb^-1 and approximately 5.4 x 10^6 DDbar events, we measure the form factors for the decays D0 to rho- e+ nu_e and D+ to rho0 e+ nu_e for the first time and the branching fractions with improved precision. A four-dimensional unbinned maximum likelihood fit determines the form factor ratios to be: V(0)/A_1(0) = 1.48 +- 0.15 +- 0.05 and A_2(0)/A_1(0)= 0.83 +- 0.11 +- 0.04. Assuming CKM unitarity, the known D meson lifetimes and our measured branching fractions we obtain the form factor normalizations A_1(0), A_2(0), and V(0). We also present a measurement of the branching fraction for D^+ to omega e^+ nu_e with improved precision.

hep-ex↗

arXiv2011

Observation of the h_c(1P) using e^+e^- collisions above DDbar threshold

Using 586pb^-1 of e^+e^- collision data at E_CM = 4170MeV, produced at the CESR collider and collected with the CLEO-c detector, we observe the process e^+e^- --> pi^+ pi^- h_c(1P). We measure its cross section to be 15.6+-2.3+-1.9+-3.0pb, where the third error is due to the external uncertainty on the branching fraction of psi(2S) --> pi^0 h_c(1P), which we use for normalization. We also find evidence for e^+e^- --> eta h_c(1P) at 4170MeV at the 3sigma level, and see hints of a rise in the e^+e^- --> pi^+ pi^- h_c(1P) cross section at 4260MeV.

hep-ex↗