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Bifani, S.

Publications and source records attributed to Bifani, S..

At least 91 records · Page 5
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DOE OSTI2021

Search for long-lived particles decaying to e± μ∓ ν

Long-lived particles decaying to e±μ∓ν, with masses between 7 and 50GeV/c 2 and lifetimes between 2 and 50 ps, are searched for by looking at displaced vertices containing electrons and muons of opposite charges. The search is performed using 5.4 fb -1 of p p collisions collected with the LHCb detector at a centre-of-mass energy of $\sqrt{s}$=13TeV. Three mechanisms of production of long-lived particles are considered: the direct pair production from quark interactions, the pair production from the decay of a Standard-Model-like Higgs boson with a mass of 125GeV/c 2 , and the charged current production from an on-shell W boson with an additional lepton. No evidence of these long-lived states is obtained and upper limits on the production cross-section times branching fraction are set on the different production modes.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2021

Search for heavy neutral leptons in $W^+\rightarrow \mu ^{+}\mu ^{\pm }\, \text {jet}$ decays

A search is performed for heavy neutrinos in the decay of a W boson into two muons and a jet. The data set corresponds to an integrated luminosity of approximately 3.0fb –1 of proton–proton collision data at centre-of-mass energies of 7 and 8 TeV collected with the LHCb experiment. Both same-sign and opposite-sign muons in the final state are considered. Data are found to be consistent with the expected background. Upper limits on the coupling of a heavy neutrino with the Standard Model neutrino are set at 95% confidence level in the heavy-neutrino mass range from 5 to 50GeV/c 2 . These are of the order of 10 –3 for lepton-number-conserving decays and of the order of 10 –4 for lepton-number-violating heavy-neutrino decays.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2021

Observation of the ${B}_s^0 $ → D*±D∓ decay

A search for the B 0 → D *± D ∓ decay is performed using proton-proton collision data at centre-of-mass energies of 7, 8 and 13 TeV collected by the LHCb experiment, corresponding to an integrated luminosity of 9 fb -1 . The decay is observed with a high significance and its branching fraction relative to the B 0 → D *± D ∓ decay is measured to be $\frac{\mathrm{\mathcal{B}}\left({B}_s^0\to {D}^{\ast \pm }{D}^{\mp}\right)}{\mathrm{\mathcal{B}}\left({B}^0\to {D}^{\ast \pm }{D}^{\mp}\right)}=0.137\pm 0.017\pm 0.002\pm 0.006$, where the first uncertainty is statistical, the second systematic and the third is due to the uncertainty on the ratio of the $B_{s}^{0}$ and $B^{0}$ hadronisation fractions.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2021

Measurement of the CKM angle γ in B ± → DK ± and B ± → Dπ ± decays with D → $ {K}_{\mathrm{S}}^0 $h + h -

A measurement of CP -violating observables is performed using the decays B ± → DK ± and B ± → Dπ ± , where the D meson is reconstructed in one of the self-conjugate three-body final states \( {K}_{\mathrm{S}}^0 \) π + π - and \( {K}_{\mathrm{S}}^0 \) K + K - (commonly denoted \( {K}_{\mathrm{S}}^0 \) h + h - ). The decays are analysed in bins of the D -decay phase space, leading to a measurement that is independent of the modelling of the D -decay amplitude. The observables are inter- preted in terms of the CKM angle γ . Using a data sample corresponding to an integrated luminosity of 9 fb - 1 collected in proton-proton collisions at centre-of mass energies of 7, 8, and 13 TeV with the LHCb experiment, γ is measured to be \( \left({68.7}_{-5.1}^{+5.2}\right){}^{\circ} \) . The hadronic parameters \( {r}_B^{D K},{r}_B^{D\pi},{\delta}_B^{D K},\kern0.5em \mathrm{and}\kern0.5em {\delta}_B^{D\pi} \) , which are the ratios and strong-phase differences of the suppressed and favoured B ± decays, are also reported.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2021

Measurement of differential $ b\overline{b} $- and $ c\overline{c} $-dijet cross-sections in the forward region of pp collisions at $ \sqrt{s} $ = 13 TeV

The inclusive \( b\overline{b} \) - and \( c\overline{c} \) -dijet production cross-sections in the forward region of pp collisions are measured using a data sample collected with the LHCb detector at a centre-of-mass energy of 13 TeV in 2016. The data sample corresponds to an integrated luminosity of 1.6 fb - 1 . Differential cross-sections are measured as a function of the transverse momentum and of the pseudorapidity of the leading jet, of the rapidity difference between the jets, and of the dijet invariant mass. A fiducial region for the measurement is defined by requiring that the two jets originating from the two b or c quarks are emitted with transverse momentum greater than 20 GeV/ c , pseudorapidity in the range 2 . 2 < η < 4 . 2, and with a difference in the azimuthal angle between the two jets greater than 1.5. The integrated \( b\overline{b} \) -dijet cross-section is measured to be 53 . 0 ± 9 . 7 nb, and the total \( c\overline{c} \) -dijet cross-section is measured to be 73 ± 16 nb. The ratio between \( c\overline{c} \) - and \( b\overline{b} \) -dijet cross-sections is also measured and found to be 1 . 37 ± 0 . 27. The results are in agreement with theoretical predictions at next-to-leading order.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2021

Study of ${\mathrm{B}}_{\mathrm{s}}^0$ → J/ψπ + π – K + K – decays

The decays ${\mathrm{B}}_{\mathrm{s}}^0$ → J/ψπ + π – K + K – are studied using a data set corresponding to an integrated luminosity of 9 fb –1 , collected with the LHCb detector in proton-proton collisions at centre-of-mass energies of 7, 8 and 13 TeV. The decays ${\mathrm{B}}_{\mathrm{s}}^0$ → $\mathrm{J}/{ψ \mathrm{K}}^{\ast 0}{\overline{\mathrm{K}}}^{\ast 0}$ and ${\mathrm{B}}_{\mathrm{s}}^0$ → χ c1 (3872)K + K – , where the K + K – pair does not originate from a Φ meson, are observed for the first time. Precise measurements of the ratios of branching fractions between intermediate χ c1 (3872)Φ, $\mathrm{J}/{ψ \mathrm{K}}^{\ast 0}{\overline{\mathrm{K}}}^{\ast 0}$, ψ(2S)Φ and χ c1 (3872)K + K – states are reported. A structure, denoted as X(4740), is observed in the J/ψΦ mass spectrum and, assuming a Breit-Wigner parameterisation, its mass and width are determined to be ${\displaystyle \begin{array}{c}{m}_{\mathrm{X}(4740)}=4741\pm 6\pm 6\kern0.5em \mathrm{MeV}/{c}^2,\\ {}{\Gamma}_{\mathrm{X}(4740)}=53\pm 15\pm 11\kern0.5em \mathrm{MeV},\end{array}}$ where the first uncertainty is statistical and the second is systematic. In addition, the most precise single measurement of the mass of the ${\mathrm{B}}_{\mathrm{s}}^0$ meson is performed and gives a value of ${m}_{{\mathrm{B}}_{\mathrm{s}}^0}=5366.98\pm 0.07\pm 0.13\kern0.5em \mathrm{MeV}/{c}^2.$

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2021

Search for the rare decay $ B^0\to J/ \psi\phi$*

A search for the rare decay $ B^0\to J/ \psi\phi$ is performed using $ pp$ collision data collected with the LHCb dete-ctor at centre-of-mass energies of 7, 8 and 13 TeV, corresponding to an integrated luminosity of 9 fb -1 . No significant signal of the decay is observed and an upper limit of $ 1.1 \times 10^{-7}$ at 90% confidence level is set on the branching fraction.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2020

Strong constraints on the b → sγ photon polarisation from B0 → K*0e+e-decays

An angular analysis of the B 0 → K* 0 e + e - decay is performed using a data sample corresponding to an integrated luminosity of 9 fb - 1 of pp collisions collected with the LHCb experiment. The analysis is conducted in the very low dielectron mass squared ( q 2 ) interval between 0 . 0008 and 0 . 257 GeV 2 , where the rate is dominated by the B 0 → K * 0 γ transition with a virtual photon. The fraction of longitudinal polarisation of the K * 0 meson, F L , is measured to be F L = (4 . 4 ± 2 . 6 ± 1 . 4)%, where the first uncertainty is statistical and the second systematic. The \( {A}_{\mathrm{T}}^{\mathrm{Re}} \) observable, which is related to the lepton forward-backward asymmetry, is measured to be \( {A}_{\mathrm{T}}^{\mathrm{Re}} \) = - 0 . 06 ± 0 . 08 ± 0 . 02. The \( {A}_{\mathrm{T}}^{(2)} \) and \( {A}_{\mathrm{T}}^{\mathrm{Im}} \) transverse asymmetries, which are sensitive to the virtual photon polarisation, are found to be \( {A}_{\mathrm{T}}^{(2)} \) = 0 . 11 ± 0 . 10 ± 0 . 02 and \( {A}_{\mathrm{T}}^{\mathrm{Im}} \) = 0 . 02 ± 0 . 10 ± 0 . 01. The results are consistent with Standard Model predictions and provide the world’s best constraint on the b → sγ photon polarisation.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2020

Amplitude analysis of the B + → D + D - K + decay

Results are reported from an amplitude analysis of the B + → D + D - K + decay. The analysis is carried out using LHCb proton-proton collision data taken at $\sqrt{s}$ = 7, 8, and 13 TeV, corresponding to a total integrated luminosity of 9 fb -1 . In order to obtain a good description of the data, it is found to be necessary to include new spin-0 and spin-1 resonances in the D - K + channel with masses around 2.9 GeV/c 2 , and a new spin-0 charmonium resonance in proximity to the spin-2 χ c2 (3930) state.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2020

Model-Independent Study of Structure in B + → D + D - K + Decays

The only anticipated resonant contributions to B + → D + D - K + decays are charmonium states in the D + D - channel. A model-independent analysis, using LHCb proton-proton collision data taken at center of-mass energies of $\sqrt{s}$ = 7, 8, and 13 TeV, corresponding to a total integrated luminosity of 9 fb -1 , is carried out to test this hypothesis. The description of the data assuming that resonances only manifest in decays to the D + D - pair is shown to be incomplete. This constitutes evidence for a new contribution to the decay, potentially one or more new charm-strange resonances in the D + K - channel with masses around 2.9 GeV/c 2

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2020

Observation of Enhanced Double Parton Scattering in Proton-Lead Collisions at $\sqrt{s_{NN}}$= 8.16 TeV

A study of prompt charm-hadron pair production in proton-lead collisions at $\sqrt{s_{NN}$ = 8.16 TeV is performed using data corresponding to an integrated luminosity of about 30 nb -1 , collected with the LHCb experiment. Production cross sections for different pairs of charm hadrons are measured and kinematic correlations between the two charm hadrons are investigated. This is the first measurement of associated production of two charm hadrons in proton-lead collisions. The results confirm the predicted enhancement of double parton scattering production in proton-lead collisions compared to the single parton scattering production.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗