arXiv subjects

G. Andreassi

Publications and source records attributed to G. Andreassi.

At least 127 records · Page 7Linked to original sources

arXiv2018

Search for CP violation using triple product asymmetries in $Λ^{0}_{b}\to pK^{-}π^{+}π^{-}$, $Λ^{0}_{b}\to pK^{-}K^{+}K^{-}$ and $Ξ^{0}_{b}\to pK^{-}K^{-}π^{+}$ decays

A search for $C$P and $P$ violation using triple-product asymmetries is performed with $Λ^{0}_{b}\to pK^{-}π^{+}π^{-}$, $Λ^{0}_{b}\to pK^{-}K^{+}K^{-}$ and $Ξ^{0}_{b}\to pK^{-}K^{-}π^{+}$ decays. The data sample corresponds to integrated luminosities of 1.0fb$^{-1}$ and 2.0fb$^{-1}$, recorded with the LHCb detector at centre-of-mass energies of 7TeV and 8TeV, respectively. The $CP$- and $P$-violating asymmetries are measured both integrating over all phase space and in specific phase-space regions. No significant deviation from $CP$ or $P$ symmetry is found. The first observation of $Λ^{0}_{b}\to pK^{-}χ_{c0}(1P)(\toπ^{+}π^{-}, K^{+}K^{-})$ decay is also reported.

hep-ex↗

arXiv2018

Observation of a new $Ξ_b^-$ resonance

From samples of $pp$ collision data collected by the LHCb experiment at $\sqrt{s}=7$, $8$ and $13$ TeV corresponding to integrated luminosities of 1.0, 2.0 and 1.5 fb$^{-1}$, respectively, a peak in both the $Λ_b^0K^-$ and $Ξ_b^0π^-$ invariant mass spectra is observed. In the quark model, radially and orbitally excited $Ξ_b^-$ resonances with quark content $bds$ are expected. Referring to this peak as $Ξ_b(6227)^-$, the mass and natural width are measured to be $m_{Ξ_{b}(6227)^-}=6226.9\pm2.0\pm0.3\pm0.2$ MeV/$c^2$ and $Γ_{Ξ_b(6227)^-}=18.1\pm5.4\pm1.8$ MeV/$c^2$, where the first uncertainty is statistical, the second is systematic, and the third, on $m_{Ξ_b(6227)^-}$, is due to the knowledge of the $Λ_b^0$ baryon mass. Relative production rates of the ${Ξ_b(6227)^-\toΛ_b^0K^-}$ and ${Ξ_b(6227)^-\toΞ_b^0π^-}$ decays are also reported.

hep-ex↗

arXiv2018

Measurement of $D_s^{\pm}$ production asymmetry in $pp$ collisions at $\sqrt{s} =7$ and 8 TeV

The inclusive $D_s^{\pm}$ production asymmetry is measured in $pp$ collisions collected by the LHCb experiment at centre-of-mass energies of $\sqrt{s} =7$ and 8 TeV. Promptly produced $D_s^{\pm}$ mesons are used, which decay as $D_s^{\pm}\toϕπ^{\pm}$, with $ϕ\to K^+K^-$. The measurement is performed in bins of transverse momentum, $p_{\rm T}$, and rapidity, $y$, covering the range $2.5<p_{\rm T}<25.0$ GeV$/c$ and $2.0<y<4.5$. No kinematic dependence is observed. Evidence of nonzero $D_s^{\pm}$ production asymmetry is found with a significance of 3.3 standard deviations.

hep-ex↗

arXiv2018

Observation of the decay $Λ_b^0 \to Λ_c^+ p \overline{p} π^-$

The decay $Λ_b^0 \to Λ_c^+ p \overline{p} π^-$ is observed using $pp$ collision data collected with the LHCb detector at centre-of-mass energies of $\sqrt{s}=$ 7 and 8 TeV, corresponding to an integrated luminosity of 3 $fb^{-1}$. The ratio of branching fractions between $Λ_b^0 \to Λ_c^+ p \overline{p} π^-$ and $Λ_b^0 \to Λ_c^+ π^-$ decays is measured to be \begin{equation*} \frac{\mathcal{B}(Λ_b^0 \to Λ_c^+ p \overline{p}π^-)}{\mathcal{B}(Λ_b^0 \to Λ_c^+ π^-)} = 0.0540 \pm 0.0023 \pm 0.0032. \end{equation*} Two resonant structures are observed in the $ Λ_c^+ π^-$ mass spectrum of the ${Λ_b^0 \to Λ_c^+ p\overline{p} π^-}$ decays, corresponding to the $Σ_c(2455)^0$ and $Σ_c^{*}(2520)^0$ states. The ratios of branching fractions with respect to the decay $Λ_b^0 \to Λ_c^+ p \overline{p} π^-$ are \begin{align*} \frac{\mathcal{B}(Λ_b^0 \to Σ_c^0 p\overline{p})\times\mathcal{B}(Σ_c^0\to Λ_c^+ π^-)}{\mathcal{B}(Λ_b^0 \to Λ_c^+ p \overline{p}π^-)} = 0.089\pm0.015\pm0.006, \frac{\mathcal{B}(Λ_b^0 \to Σ_c^{*0} p\overline{p})\times\mathcal{B}(Σ_c^{*0}\to Λ_c^+ π^-)}{\mathcal{B}(Λ_b^0 \to Λ_c^+ p \overline{p}π^-)} = 0.119\pm0.020\pm0.014. \end{align*} In all of the above results, the first uncertainty is statistical and the second is systematic. The phase space is also examined for the presence of dibaryon resonances. No evidence for such resonances is found.

hep-ex↗

arXiv2018

Measurement of $Υ$ production in $pp$ collisions at $\sqrt{s}$= 13 TeV

The production cross-sections of $Υ(1S)$, $Υ(2S)$ and $Υ(3S)$ mesons in proton-proton collisions at $\sqrt{s}$= 13 TeV are measured with a data sample corresponding to an integrated luminosity of $277 \pm 11$ $\rm pb^{-1}$ recorded by the LHCb experiment in 2015. The $Υ$ mesons are reconstructed in the decay mode $Υ\toμ^{+}μ^{-}$. The differential production cross-sections times the dimuon branching fractions are measured as a function of the $Υ$ transverse momentum, $p_{\rm T}$, and rapidity, $y$, over the range $0 < p_{\rm T}< 30$ GeV/c and $2.0 < y < 4.5$. The ratios of the cross-sections with respect to the LHCb measurement at $\sqrt{s}$= 8 TeV are also determined. The measurements are compared with theoretical predictions based on NRQCD.

hep-ex↗

arXiv2018

Evidence for the decay $B_{s}^0 \rightarrow \overline{K}{}^{*0}μ^+μ^-$

A search for the decay $B_{s}^0 \rightarrow \overline{K}{}^{*0}μ^+μ^-$ is presented using data sets corresponding to 1.0, 2.0 and 1.6 $\text{fb}^{-1}$ of integrated luminosity collected during $pp$ collisions with the LHCb experiment at centre-of-mass energies of 7, 8 and 13 TeV, respectively. An excess is found over the background-only hypothesis with a significance of 3.4 standard deviations. The branching fraction of the $B_{s}^0 \rightarrow \overline{K}{}^{*0}μ^+μ^-$ decay is determined to be $\mathcal{B}(B_{s}^0 \rightarrow \overline{K}{}^{*0}μ^+μ^-) = [2.9 \pm 1.0~(\text{stat}) \pm 0.2~(\text{syst}) \pm 0.3~(\text{norm})] \times 10^{-8}$, where the first and second uncertainties are statistical and systematic, respectively. The third uncertainty is due to limited knowledge of external parameters used to normalise the branching fraction measurement.

hep-ex↗

arXiv2018

Measurement of the lifetime of the doubly charmed baryon $Ξ_{cc}^{++}$

The first measurement of the lifetime of the doubly charmed baryon $Ξ_{cc}^{++}$ is presented, with the signal reconstructed in the final state $Λ_c^+ K^- π^+ π^+$. The data sample used corresponds to an integrated luminosity of $1.7\,\mathrm{fb}^{-1}$, collected by the LHCb experiment in proton-proton collisions at a centre-of-mass energy of $13\mathrm{\,Te\kern -0.1em V}$. The $Ξ_{cc}^{++}$ lifetime is measured to be $0.256\,^{+0.024}_{-0.022}{\,\rm (stat)\,} \pm 0.014 {\,\rm(syst)}\mathrm{\,ps}$.

hep-ex↗

arXiv2018

Measurement of the $CP$ asymmetry in $B^-\to D_s^-D^0$ and $B^-\to D^-D^0$ decays

The $CP$ asymmetry in $B^-\to D_s^-D^0$ and $B^-\to D^-D^0$ decays is measured using LHCb data corresponding to an integrated luminosity of 3.0 fb$^{-1}$, collected in $pp$ collisions at centre-of-mass energies of 7 and 8 TeV. The results are $A^{CP}(B^-\to D_s^-D^0)=(-0.4\pm 0.5\pm 0.5)\%$ and $A^{CP}(B^-\to D^-D^0)=( 2.3\pm 2.7\pm 0.4)\%$, where the first uncertainties are statistical and the second systematic. This is the first measurement of $A^{CP}(B^-\to D_s^-D^0)$ and the most precise determination of $A^{CP}(B^-\to D^-D^0)$. Neither result shows evidence of $CP$ violation.

hep-ex↗

arXiv2018

Search for $B_c^+$ decays to two charm mesons

A search for decays of $B_c^+$ mesons to two charm mesons is performed for the first time using data corresponding to an integrated luminosity of 3.0 fb$^{-1}$, collected by the LHCb experiment in $pp$ collisions at centre-of-mass energies of 7 and 8 TeV. The decays considered are $B_c^+\to D^{(*)+}_{(s)} \overline{D}^{(*)0}$ and $B_c^+\to D^{(*)+}_{(s)} D^{(*)0}$, which are normalised to high-yield $B^+\to D^+_{(s)} \overline{D}^0$ decays. No evidence for a signal is found and limits are set on twelve $B_c^+$ decay modes.

hep-ex↗

arXiv2018

Measurement of the inelastic $pp$ cross-section at a centre-of-mass energy of 13\,TeV

The cross-section for inelastic proton-proton collisions at a centre-of-mass energy of 13\,TeV is measured with the LHCb detector. The fiducial cross-section for inelastic interactions producing at least one prompt long-lived charged particle with momentum $p>2$\,GeV/$c$ in the pseudorapidity range $2<η<5$ is determined to be $σ_{\rm acc}= 62.2 \pm 0.2 \pm 2.5$\,mb. The first uncertainty is the intrinsic systematic uncertainty of the measurement, the second is due to the uncertainty on the integrated luminosity. The statistical uncertainty is negligible. Extrapolation to full phase space yields the total inelastic proton-proton cross-section $σ_{\rm inel}= 75.4 \pm 3.0 \pm 4.5$\,mb, where the first uncertainty is experimental and the second due to the extrapolation. An updated value of the inelastic cross-section at a centre-of-mass energy of 7\,TeV is also reported.

hep-ex↗

arXiv2018

Measurement of $CP$ violation in $B^{0}\rightarrow D^{\mp}π^{\pm}$ decays

A measurement of the $CP$ asymmetries $S_{f}$ and $S_{\bar{f}}$ in $B^0\to D^{\mp}π^{\pm}$ decays is reported. The decays are reconstructed in a dataset collected with the LHCb experiment in proton-proton collisions at centre-of-mass energies of 7 and 8 TeV and corresponding to an integrated luminosity of $3.0 \rm{ fb}^{-1}$. The $CP$ asymmetries are measured to be $S_{f} = 0.058 \pm 0.020 (\rm{stat}) \pm 0.011(\rm{syst})$ and $S_{\bar{f}} = 0.038\pm 0.020 (\text{stat})\pm 0.007 (\text{syst})$. These results are in agreement with, and more precise than, previous determinations. They are used to constrain $|\sin\left(2β+γ\right)|$ and $γ$ to intervals that are consistent with the current world-average values.

hep-ex↗

arXiv2018

Studies of the resonance structure in $D^{0} \to K^\mp π^\pm π^\pm π^\mp$ decays

Amplitude models are constructed to describe the resonance structure of ${D^{0}\to K^{-}π^{+}π^{+}π^{-}}$ and ${D^{0} \to K^{+}π^{-}π^{-}π^{+}}$ decays using $pp$ collision data collected at centre-of-mass energies of 7 and 8 TeV with the LHCb experiment, corresponding to an integrated luminosity of $3.0\mathrm{fb}^{-1}$. The largest contributions to both decay amplitudes are found to come from axial resonances, with decay modes $D^{0} \to a_1(1260)^{+} K^{-}$ and $D^{0} \to K_1(1270/1400)^{+} π^{-}$ being prominent in ${D^{0}\to K^{-}π^{+}π^{+}π^{-}}$ and $D^{0}\to K^{+}π^{-}π^{-}π^{+}$, respectively. Precise measurements of the lineshape parameters and couplings of the $a_1(1260)^{+}$, $K_1(1270)^{-}$ and $K(1460)^{-}$ resonances are made, and a quasi model-independent study of the $K(1460)^{-}$ resonance is performed. The coherence factor of the decays is calculated from the amplitude models to be $R_{K3π} = 0.459\pm 0.010\,(\mathrm{stat}) \pm 0.012\,(\mathrm{syst}) \pm 0.020\,(\mathrm{model})$, which is consistent with direct measurements. These models will be useful in future measurements of the unitary-triangle angle $γ$ and studies of charm mixing and $C\!P$ violation.

hep-ex↗

arXiv2018

Evidence for the rare decay $Σ^+ \to p μ^+ μ^-$

A search for the rare decay $Σ^+ \to p μ^+ μ^-$ is performed using $pp$ collision data recorded by the LHCb experiment at centre-of-mass energies $\sqrt{s} = 7$ and $8$ TeV, corresponding to an integrated luminosity of $3 fb^{-1}$. An excess of events is observed with respect to the background expectation, with a signal significance of 4.1 standard deviations. No significant structure is observed in the dimuon invariant mass distribution, in contrast with a previous result from the HyperCP experiment. The measured $Σ^+ \to p μ^+ μ^-$ branching fraction is $(2.2\,^{+\,1.8}_{-\,1.3})\times 10^{-8}$, where statistical and systematic uncertainties are included, which is consistent with the Standard Model prediction.

hep-ex↗

arXiv2018

Search for massive long-lived particles decaying semileptonically in the LHCb detector

A search is presented for massive long-lived particles decaying into a muon and two quarks. The dataset consists of proton-proton interactions at centre-of-mass energies of 7 and 8 TeV, corresponding to integrated luminosities of 1 and 2 1/fb, respectively. The analysis is performed assuming a set of production mechanisms with simple topologies, including the production of a Higgs-like particle decaying into two long-lived particles. The mass range from 20 to 80 GeV and lifetimes from 5 to 100 ps are explored. Results are also interpreted in terms of neutralino production in different supersymmetric models, with masses in the 23-198 GeV range. No excess above the background expectation is observed and upper limits are set on the production cross-section for various points in the parameter space of theoretical models.

hep-ex↗

arXiv2018

Observation of the $Λ_b^0\toΛϕ$ decay

The $Λ_b^0\toΛϕ$ decay is observed using data corresponding to an integrated luminosity of 3.0fb$^{-1}$ recorded by the LHCb experiment. The decay proceeds at leading order via a $b\to s\bar{s}s$ loop transition and is therefore sensitive to the possible presence of particles beyond the Standard Model. A first observation is reported with a significance of $5.9$ standard deviations. The value of the branching fraction is measured to be $(5.18\pm1.04\pm0.35\,^{+0.67}_{-0.62})\times10^{-6}$, where the first uncertainty is statistical, the second is systematic, and the third is related to external inputs. Triple-product asymmetries are measured to be consistent with zero.

hep-ex↗

arXiv2018

Search for the rare decay $Λ_{c}^{+} \to pμ^+μ^-$

A search for the flavor-changing neutral-current decay $Λ_{c}^{+} \to pμ^+μ^-$ is reported using a data set corresponding to an integrated luminosity of $3.0\rm fb^{-1}$ collected by the LHCb collaboration. No significant signal is observed outside of the dimuon mass regions around the $ϕ$ and $ω$ resonances and an upper limit is placed on the branching fraction of $\mathcal{B} (Λ_{c}^{+} \to pμ^+μ^-) < 7.7~(9.6)\times 10^{-8}~{\rm at}~90\%~(95\%)$ confidence level. A significant signal is observed in the $ω$ dimuon mass region for the first time.

hep-ex↗

arXiv2018

Test of Lepton Flavor Universality by the measurement of the $B^0 \to D^{*-} τ^+ ν_τ$ branching fraction using three-prong $τ$ decays

The ratio of branching fractions ${\cal{R}}(D^{*-})\equiv {\cal{B}}(B^0 \to D^{*-} τ^+ ν_τ)/{\cal{B}}(B^0 \to D^{*-} μ^+ν_μ)$ is measured using a data sample of proton-proton collisions collected with the LHCb detector at center-of-mass energies of 7 and 8 TeV, corresponding to an integrated luminosity of 3$~$fb$^{-1}$. The $τ$ lepton is reconstructed with three charged pions in the final state. A novel method is used that exploits the different vertex topologies of signal and backgrounds to isolate samples of semitauonic decays of $b$ hadrons with high purity. Using the $B^0 \to D^{*-}π^+π^-π^+$ decay as the normalization channel, the ratio ${\cal{B}}(B^0 \to D^{*-} τ^+ ν_τ)/{\cal{B}}(B^0 \to D^{*-}π^+π^-π^+)$ is measured to be $1.97 \pm 0.13 \pm 0.18$, where the first uncertainty is statistical and the second systematic. An average of branching fraction measurements for the normalization channel is used to derive ${\cal{B}}(B^0 \to D^{*-} τ^+ ν_τ) = (1.42 \pm 0.094 \pm 0.129 \pm 0.054) \%$, where the third uncertainty is due to the limited knowledge of ${\cal{B}}(B^0\to D^{*-}π^+π^-π^+)$. A test of lepton flavor universality is performed using the well-measured branching fraction ${\cal{B}}(B^0 \to D^{*-} μ^+ν_μ)$ to compute ${\cal{R}}(D^{*-}) = 0.291 \pm 0.019 \pm 0.026 \pm 0.013$, where the third uncertainty originates from the uncertainties on ${\cal{B}}(B^0 \to D^{*-}π^+π^-π^+)$ and ${\cal{B}}(B^0 \to D^{*-} μ^+ν_μ)$. This measurement is in agreement with the Standard Model prediction and with previous measurements.

hep-ex↗

arXiv2018

Measurement of the ratio of the $B^0 \to D^{-} τ^+ ν_τ$ and $B^0 \to D^{-} μ^+ ν_μ$ branching fractions using three-prong $τ$-lepton decays

The ratio of branching fractions ${\cal{R}}(D^{*-})\equiv {\cal{B}}(B^0 \to D^{*-} τ^+ ν_τ)/{\cal{B}}(B^0 \to D^{*-} μ^+ν_μ)$ is measured using a data sample of proton-proton collisions collected with the LHCb detector at center-of-mass energies of 7 and 8 Tev, corresponding to an integrated luminosity of 3$~$fb$^{-1}$. For the first time ${\cal{R}}(D^{*-})$ is determined using the $τ$ lepton decays with three charged pions in the final state. The $B^0 \to D^{*-} τ^+ν_τ$ yield is normalized to that of the $B^0\to D^{*-} π^+π^-π^+$ mode, providing a measurement of ${\cal{B}}(B^0\to D^{*-}τ^+ν_τ)/{\cal{B}}(B^0\to D^{*-}π^+π^-π^+) = 1.97 \pm 0.13 \pm 0.18$, where the first uncertainty is statistical and the second systematic. The value of ${\cal{B}}(B^0 \to D^{*-} τ^+ ν_τ) = (1.42 \pm 0.094 \pm 0.129 \pm 0.054)\% $ is obtained, where the third uncertainty is due to the limited knowledge of the branching fraction of the normalization mode. Using the well-measured branching fraction of the $B^0 \to D^{*-} μ^+ν_μ$ decay, a value of ${\cal{R}}(D^{*-}) = 0.291 \pm 0.019 \pm 0.026 \pm 0.013$ is established, where the third uncertainty is due to the limited knowledge of the branching fractions of the normalization and $B^0\to D^{*-}μ^+ν_μ$ modes. This measurement is in agreement with the Standard Model prediction and with previous results.

hep-ex↗