arXiv subjects

G. Morello

Publications and source records attributed to G. Morello.

At least 91 records · Page 5Linked to original sources

arXiv2016

Optimization of electrospinning techniques for the realization of nanofiber plastic lasers

Electrospinning technologies for the realization of active polymeric nanomaterials can be easily up-scaled, opening perspectives to industrial exploitation, and due to their versatility they can be employed to finely tailor the size, morphology and macroscopic assembly of fibers as well as their functional properties. Light-emitting or other active polymer nanofibers, made of conjugated polymers or of blends embedding chromophores or other functional dopants, are suitable for various applications in advanced photonics and sensing technologies. In particular, their almost one-dimensional geometry and finely tunable composition make them interesting materials for developing novel lasing devices. However, electrospinning techniques rely on a large variety of parameters and possible experimental geometries, and they need to be carefully optimized in order to obtain suitable topographical and photonic properties in the resulting nanostructures. Targeted features include smooth and uniform fiber surface, dimensional control, as well as filament alignment, enhanced light emission, and stimulated emission. We here present various optimization strategies for electrospinning methods which have been implemented and developed by us for the realization of lasing architectures based on polymer nanofibers. The geometry of the resulting nanowires leads to peculiar light-scattering from spun filaments, and to controllable lasing characteristics.

cond-mat.mtrl-sci↗

arXiv2016

Limit on the production of a new vector boson in $\mathrm{e^+ e^-}\rightarrow {\rm U}γ$, U$\rightarrow π^+π^-$ with the KLOE experiment

The recent interest in a light gauge boson in the framework of an extra U(1) symmetry motivates searches in the mass range below 1 GeV. We present a search for such a particle, the dark photon, in ${\rm e^+ e^-}\rightarrow {\rm U}γ$, U$\rightarrow π^+π^-$ based on 28 million $\mathrm{e^+ e^-} \rightarrow π^+ π^-γ$ events collected at DA$Φ$NE by the KLOE experiment. The $π^+ π^-$ production by initial-state radiation compensates for a loss of sensitivity of previous KLOE ${\rm U} \rightarrow \mathrm{e^+ e^-}$, $μ^+μ^-$ searches due to the small branching ratios in the $ρ-ω$ resonance region. We found no evidence for a signal and set a limit at 90\% CL on the mixing strength between the photon and the dark photon, $\varepsilon^2$, in the U mass range between $527$ and $987$~MeV. Above 700 MeV this new limit is more stringent than previous ones.

hep-ex↗

arXiv2016

Detection of an atmosphere around the super-Earth 55 Cancri e

We report the analysis of two new spectroscopic observations of the super-Earth 55 Cancri e, in the near infrared, obtained with the WFC3 camera onboard the HST. 55 Cancri e orbits so close to its parent star, that temperatures much higher than 2000 K are expected on its surface. Given the brightness of 55 Cancri, the observations were obtained in scanning mode, adopting a very long scanning length and a very high scanning speed. We use our specialized pipeline to take into account systematics introduced by these observational parameters when coupled with the geometrical distortions of the instrument. We measure the transit depth per wavelength channel with an average relative uncertainty of 22 ppm per visit and find modulations that depart from a straight line model with a 6$σ$ confidence level. These results suggest that 55 Cancri e is surrounded by an atmosphere, which is probably hydrogen-rich. Our fully Bayesian spectral retrieval code, T-REx, has identified HCN to be the most likely molecular candidate able to explain the features at 1.42 and 1.54 $μ$m. While additional spectroscopic observations in a broader wavelength range in the infrared will be needed to confirm the HCN detection, we discuss here the implications of such result. Our chemical model, developed with combustion specialists, indicates that relatively high mixing ratios of HCN may be caused by a high C/O ratio. This result suggests this super-Earth is a carbon-rich environment even more exotic than previously thought.

astro-ph.EP↗

arXiv2016

Precision measurement of the $η\toπ^+π^-π^0$ Dalitz plot distribution with the KLOE detector

Using $1.6$ fb$^{-1}$ of $e^+ e^-\toϕ\toηγ$ data collected with the KLOE detector at DA$Φ$NE, the Dalitz plot distribution for the $η\to π^+ π^- π^0$ decay is studied with the world's largest sample of $\sim 4.7 \cdot 10^6$ events. The Dalitz plot density is parametrized as a polynomial expansion up to cubic terms in the normalized dimensionless variables $X$ and $Y$. The experiment is sensitive to all charge conjugation conserving terms of the expansion, including a $gX^2Y$ term. The statistical uncertainty of all parameters is improved by a factor two with respect to earlier measurements.

hep-ex↗

arXiv2015

Limit on the production of a low-mass vector boson in $\mathrm{e}^{+}\mathrm{e}^{-} \to \mathrm{U}γ$, $\mathrm{U} \to \mathrm{e}^{+}\mathrm{e}^{-}$ with the KLOE experiment

The existence of a new force beyond the Standard Model is compelling because it could explain several striking astrophysical observations which fail standard interpretations. We searched for the light vector mediator of this dark force, the $\mathrm{U}$ boson, with the KLOE detector at the DA$Φ$NE $\mathrm{e}^{+}\mathrm{e}^{-}$ collider. Using an integrated luminosity of 1.54 fb$^{-1}$, we studied the process $\mathrm{e}^{+}\mathrm{e}^{-} \to \mathrm{U}γ$, with $\mathrm{U} \to \mathrm{e}^{+}\mathrm{e}^{-}$, using radiative-return to search for a resonant peak in the dielectron invariant-mass distribution. We did not find evidence for a signal, and set a 90\%~CL upper limit on the mixing strength between the Standard Model photon and the dark photon, $\varepsilon^2$, at $10^{-6}$--$10^{-4}$ in the 5--520~MeV/c$^2$ mass range.

hep-ex↗

arXiv2015

Search for dark Higgsstrahlung in e+ e- -> mu+ mu- and missing energy events with the KLOE experiment

We searched for evidence of a Higgsstrahlung process in a secluded sector, leading to a final state with a dark photon U and a dark Higgs boson h', with the KLOE detector at DAFNE. We investigated the case of h' lighter than U, with U decaying into a muon pair and h' producing a missing energy signature. We found no evidence of the process and set upper limits to its parameters in the range 2m_mu<m_U<1000 MeV, m_h'<m_U.

hep-ex↗

arXiv2015

Revisiting Spitzer transit observations with Independent Component Analysis: new results for the GJ436 system

We analyzed four Spitzer/IRAC observations at 3.6 and 4.5 μm of the primary transit of the exoplanet GJ436b, by using blind source separation techniques. These observations are important to investigate the atmospheric composition of the planet GJ436b. Previous analyses claimed strong inter-epoch variations of the transit parameters due to stellar variability, casting doubts on the possibility to extract conclusively an atmospheric signal; those analyses also reported discrepant results, hence the necessity of this reanalysis. The method we used has been proposed in Morello et al. (2014) to analyze 3.6 μm transit light-curves of the hot Jupiter HD189733b; it performes an Independent Component Analysis (ICA) on a set of pixel-light-curves, i.e. time series read by individual pixels, from the same photometric observation. Our method only assumes the independence of instrumental and astrophysical signals, and therefore guarantees a higher degree of objectivity compared to parametric detrending techniques published in the literature. The datasets we analyzed in this paper represent a more challenging test compared to the previous ones. Contrary to previous results reported in the literature, our results (1) do not support any detectable inter-epoch variations of orbital and stellar parameters, (2) are photometrically stable at the level 10e-4 in the IR, and (3) the transit depth measurements at the two wavelengths are consistent within 1σ. We also (4) detect a possible transit duration variation (TDV) of 80 s (2 σ significance level), that has not been pointed out in the literature, and (5) confirm no transit timing variations (TTVs) >30 s.

astro-ph.EP↗

arXiv2015

Commissioning of the Inner Tracker of the KLOE-2 experiment

The KLOE-2 experiment is undergoing commissioning at the DA$Φ$NE $e^{+}e^{-}$ collider of the Frascati National Laboratory of the INFN, after the integration of new detectors in the former KLOE apparatus. The Inner Tracker, a very light detector (material budget $<2\%X_{0}$), is one of the new subdetectors and it is composed of 4 cylindrical triple-GEM with a stereo X-V strips/pads readout. The commissioning phase of the Inner Tracker consists in the characterization of the detector response and in its performance evaluation. The method used to evaluate its detection efficiency is reported, together with some preliminary results.

physics.ins-det↗

arXiv2014

The Resistive-WELL detector: a compact spark-protected single amplification-stage MPGD

In this work we present a novel idea for a compact spark-protected single amplification stage Micro-Pattern Gas Detector (MPGD). The detector amplification stage, realized with a structure very similar to a GEM foil, is embedded through a resistive layer in the readout board. A cathode electrode, defining the gas conversion/drift gap, completes the detector mechanics. The new structure, that we call Resistive-WELL (R-WELL), has some characteristics in common with previous MPGDs, such as C.A.T. and WELL, developed more than ten years ago. The prototype object of the present study has been realized in the 2009 by TE-MPE-EM Workshop at CERN. The new architecture is a very compact MPGD, robust against discharges and exhibiting a large gain ($\sim$6$\times$10$^3$), simple to construct and easy for engineering and then suitable for large area tracking devices as well as huge calorimetric apparata.

physics.ins-det↗

arXiv2014

Study of Dalitz decay phi -> eta e+e- with KLOE detector

We have studied the vector to pseudoscalar conversion decay phi -> eta e+e-, with eta -> pi0pi0pi0, with the KLOE detector at DAPHNE. The data set of 1.7 fb-1 of e+e- collisions at sqrt(s)~Mphi contains a clear conversion decay signal of ~31,000 events from which we measured a value of BR(phi -> eta e+e-)=(1.075+-0.007+-0.038)x10-4. The same sample is used to determine the transition form factor by a fit to the e+e- invariant mass spectrum, obtaining b(phi eta) =(1.17 +- 0.10 + 0.07) GeV-2, that improves by a factor of five the precision of the previous measurement and is in good agreement with VMD expectations.

hep-ex↗

arXiv2014

Search for light vector boson production in $e^+e^- \rightarrow μ^+ μ^- γ$ interactions with the KLOE experiment

We have searched for a light vector boson $U$, the possible carrier of a "dark force", with the KLOE detector at the DA$Φ$NE \epm\ collider, motivated by astrophysical evidence for the presence of dark matter in the universe. Using \epm\ collisions collected with an integrated luminosity of $239.3$~pb$^{-1}$, we look for a dimuon mass peak in the reaction \epm\to$μ^+ μ^-$\gam, corresponding to the decay $U\toμ^+μ^-$. We find no evidence for a $U$ vector boson signal. We set a 90\% CL upper limit for the mixing parameter squared between the photon and the $U$ boson of 1.6$\times$10$^{-5}$ to 8.6$\times$10$^{-7}$ for the mass region $520<m_{\rm U}<980$ MeV.

hep-ex↗

arXiv2014

Test of CPT and Lorentz symmetry in entangled neutral kaons with the KLOE experiment

Neutral kaon pairs produced in phi decays in anti-symmetric entangled state can be exploited to search for violation of CPT symmetry and Lorentz invariance. We present an analysis of the CP-violating process phi->K_S K_L->pi+pi-pi+pi- based on 1.7 fb-1 of data collected by the KLOE experiment at the Frascati phi-factory DAFNE. The data are used to perform a measurement of the CPT-violating parameters Delta_amu for neutral kaons in the contest of the Standard Model Extension framework. The parameters measured in the reference frame of the fixed stars are: Delta_ao = (-6.0 +- 7.7_{stat} +- 3.1_{syst}) x 10^{-18} GeV Delta_ax = ( 0.9 +- 1.5_{stat} +- 0.6_{syst}) x 10^{-18} GeV Delta_ay = (-2.0 +- 1.5_{stat} +- 0.5_{syst}) x 10^{-18} GeV Delta_az = ( 3.1 +- 1.7_{stat} +- 0.5_{syst}) x 10^{-18} GeV These are presently the most precise measurements in the quark sector of the Standard Model Extension.

hep-ex↗

arXiv2013

Recent results on hadron physics at KLOE

One of the basic motivations of the KLOE and KLOE-2 collaborations is the test of fundamental symmetries and the search for phenomena beyond the Standard Model via the hadronic and leptonic decays of ground-state mesons and via their production in the fusion of virtual gamma quanta exchanged between colliding electrons and positrons. This contribution includes brief description of results of recent analysis of the KLOE data aimed at (i) the search for the dark matter boson, (ii) determination of the hadronic and light-by-light contributions to the g-2 muon anomaly and (iii) tests of QCD anomalies.

hep-ex↗

arXiv2013

A new limit on the CP violating decay KS -> 3pi0 with the KLOE experiment

We have carried out a new direct search for the CP violating decay KS -> 3pi0 with 1.7 fb^-1 of e+e- collisions collected by the KLOE detector at the phi-factory DAFNE. We have searched for this decay in a sample of about 5.9 x 10^8 KS KL events tagging the KS by means of the KL interaction in the calorimeter and requiring six prompt photons. With respect to our previous search, the analysis has been improved by increasing of a factor four the tagged sample and by a more effective background rejection of fake KS tags and spurious clusters. We find no candidates in data and simulated background samples, while we expect 0.12 standard model events. Normalizing to the number of KS -> 2pi0 events in the same sample, we set the upper limit on BR(KS -> 3pi0 < 2.6 x 10^-8 at 90% C.L., five times lower than the previous limit. We also set the upper limit on the eta_000 parameter, |eta_000 | < 0.0088 at 90% C.L., improving by a factor two the latest direct measurement.

hep-ex↗

arXiv2013

Precision measurement of $σ(e^+e^-\rightarrowπ^+π^-γ)/σ(e^+e^-\rightarrow μ^+μ^-γ)$ and determination of the $π^+π^-$ contribution to the muon anomaly with the KLOE detector

We have measured the ratio $σ(e^+e^-\rightarrowπ^+π^-γ)/σ(e^+e^-\rightarrow μ^+μ^-γ)$, with the KLOE detector at DA$Φ$NE for a total integrated luminosity of $\sim$ 240 pb$^{-1}$. From this ratio we obtain the cross section $σ(e^+e^-\rightarrowπ^+π^-)$. From the cross section we determine the pion form factor $|F_π|^2$ and the two-pion contribution to the muon anomaly $a_μ$ for $0.592<M_{ππ}<0.975$ GeV, $Δ^{ππ} a_μ$= $({\rm 385.1\pm1.1_{stat}\pm2.7_{sys+theo}})\times10^{-10}$. This result confirms the current discrepancy between the Standard Model calculation and the experimental measurement of the muon anomaly.

hep-ex↗

arXiv2013

Limit on the production of a light vector gauge boson in phi meson decays with the KLOE detector

We present a new limit on the production of a light dark-force mediator with the KLOE detector at DAPHNE. This boson, called U, has been searched for in the decay phi --> eta U, U --> e+ e-, analyzing the decay eta --> pi0 pi0 pi0 in a data sample of 1.7 fb-1. No structures are observed in the e+e- invariant mass distribution over the background. This search is combined with a previous result obtained from the decay eta --> pi+ pi- pi0, increasing the sensitivity. We set an upper limit at 90% C.L. on the ratio between the U boson coupling constant and the fine structure constant of alpha'/alpha < 1.7x10^-5 for 30<M_U<400 MeV and alpha'/alpha < 8x10^-6 for the sub-region 50<M_U<210 MeV. This result assumes the Vector Meson Dominance expectations for the phietagamma^* transition form factor. The dependence of this limit on the transition form factor has also been studied.

hep-ex↗

arXiv2012

Measurement of η meson production in γγ interactions and Γ(η-->γγ) with the KLOE detector

We present a measurement of η meson production in photon-photon interactions produced by electron-positron beams colliding with \sqrt{s}=1 GeV. The measurement is done with the KLOE detector at the ϕ-factory DAΦNE with an integrated luminosity of 0.24 fb^{-1}. The e^+e^- --> e^+e^-η cross section is measured without detecting the outgoing electron and positron, selecting the decays η-->π^+π^-π^0 and η-->π^0π^0π^0. The most relevant background is due to e^+e^- --> ηγ when the monochromatic photon escapes detection. The cross section for this process is measured as σ(e^+e^- -->ηγ) = (856 \pm 8_{stat} \pm 16_{syst}) pb. The combined result for the e^+e^- -->e^+e^-η cross section is σ(e^+e^- -->e^+e^-η) = (32.72 \pm 1.27_{stat} \pm 0.70_{syst}) pb. From this we derive the partial width Γ(η-->γγ) = (520 \pm 20_{stat} \pm 13_{syst}) eV. This is in agreement with the world average and is the most precise measurement to date.

hep-ex↗

arXiv2012

Measurement of Γ(η-> π^+π^-γ)/Γ(η-> π^+π^-π^0) with the KLOE Detector

The ratio R_η=Γ(η-> π^+π^-γ)/Γ(η-> π^+π^-π^0) has been measured by analyzing 22 million ϕ\to ηγdecays collected by the KLOE experiment at DA\PhiNE, corresponding to an integrated luminosity of 558 pb^{-1}. The η\to π^+π^-γproceeds both via the ρresonant contribution, and possibly a non-resonant direct term, connected to the box anomaly. Our result, R_η= 0.1856\pm 0.0005_{stat} \pm 0.0028_{syst}, points out a sizable contribution of the direct term to the total width. The di-pion invariant mass for the η-> π^+π^-γdecay could be described in a model-independent approach in terms of a single free parameter, α. The determined value of the parameter αis α= (1.32 \pm 0.08_{stat} +0.10/-0.09_{syst}\pm 0.02_{theo}) GeV^{-2}

hep-ex↗