Searcharxiv⌕ Search

arXiv subjects

A. Beck

Publications and source records attributed to A. Beck.

At least 253 records · Page 14Linked to original sources
arXiv2023

Associated production of prompt $J/ψ$ and $\mathitΥ$ mesons in $pp$ collisions at $\sqrt{s}=13\,\mathrm{TeV}$

The associated production of prompt $J/ψ$ and $\mathit{\mathitΥ}$ mesons in $pp$ collisions at a centre-of-mass energy of $\sqrt{s}=13\,\mathrm{TeV}$ is studied using LHCb data, corresponding to an integrated luminosity of $4\,\mathrm{fb}^{-1}$. The measurement is performed for $J/ψ$ ($\mathitΥ$) mesons with a transverse momentum $p_{\mathrm{T}}<10\,(30)\,\mathrm{GeV}/c$ in the rapidity range $2.0<y<4.5$. In this kinematic range, the cross-section of the associated production of prompt $J/ψ$ and $\mathitΥ(1S)$ mesons is measured to be $133 \pm 22 \pm 7 \pm 3 \, \mathrm{pb}$, with a significance of $7.9\,σ$, and that of prompt $J/ψ$ and $\mathitΥ(2S)$ mesons to be $76\pm 21 \pm 4 \pm 7 \, \mathrm{pb}$, with a significance of $4.9\,σ$. The first uncertainty is statistical, the second systematic, and the third due to uncertainties on the used branching fractions. This is the first observation of the associated production of $J/ψ$ and $\mathitΥ(1S)$ in proton-proton collisions. Differential cross-sections are measured as functions of variables that are sensitive to kinematic correlations between the $J/ψ$ and $\mathitΥ(1S)$ mesons. The effective cross-sections of the associated production of prompt $J/ψ$ and $\mathitΥ$ mesons are obtained and found to be compatible with measurements using other particle productions.

hep-ex↗
arXiv2023

Study of charmonium decays to $K^0_S K π$ in the $B \to (K^0_S K π) K$ channels

A study of the $B^+\to K^0_SK^+K^-π^+$ and $B^+\to K^0_SK^+K^+π^-$ decays is performed using proton-proton collisions at center-of-mass energies of 7, 8 and 13 TeV at the LHCb experiment. The $K^0_SK π$ invariant mass spectra from both decay modes reveal a rich content of charmonium resonances. New precise measurements of the $η_c$ and $η_c(2S)$ resonance parameters are performed and branching fraction measurements are obtained for $B^+$ decays to $η_c$, $J/ψ$, $η_c(2S)$ and $χ_{c1}$ resonances. In particular, the first observation and branching fraction measurement of $B^+ \to χ_{c0} K^0 π^+$ is reported as well as first measurements of the $B^+\to K^0K^+K^-π^+$ and $B^+\to K^0K^+K^+π^-$ branching fractions. Dalitz plot analyses of $η_c \to K^0_SKπ$ and $η_c(2S) \to K^0_SKπ$ decays are performed. A new measurement of the amplitude and phase of the $K π$ $S$-wave as functions of the $K π$ mass is performed, together with measurements of the $K^*_0(1430)$, $K^*_0(1950)$ and $a_0(1700)$ parameters. Finally, the branching fractions of $χ_{c1}$ decays to $K^*$ resonances are also measured.

hep-ex↗
arXiv2023

Observation of a resonant structure near the $D_s^+ D_s^-$ threshold in the $B^+\to D_s^+ D_s^- K^+$ decay

An amplitude analysis of the $B^+\to D_s^+ D_s^- K^+$ decay is carried out to study for the first time its intermediate resonant contributions, using proton-proton collision data collected with the LHCb detector at centre-of-mass energies of 7, 8 and 13 TeV. A near-threshold peaking structure, referred to as $X(3960)$, is observed in the $D_s^+ D_s^-$ invariant-mass spectrum with significance greater than 12 standard deviations. The mass, width and the quantum numbers of the structure are measured to be $3956\pm5\pm10$ MeV, $43\pm13\pm8$ MeV and $J^{PC}=0^{++}$, respectively, where the first uncertainties are statistical and the second systematic. The properties of the new structure are consistent with recent theoretical predictions for a state composed of $c\bar{c}s\bar{s}$ quarks. Evidence for an additional structure is found around 4140 MeV in the $D_s^+ D_s^-$ invariant mass, which might be caused either by a new resonance with the $0^{++}$ assignment or by a $J/ψϕ\leftrightarrow D_s^+ D_s^-$ coupled-channel effect.

hep-ex↗
arXiv2023

Search for $D^{*}(2007)^0\toμ^+μ^-$ in $B^-\toπ^-μ^+μ^-$ decays

The very rare $D^{*}(2007)^0\toμ^+μ^-$ decay is searched for by analysing $B^-\toπ^-μ^+μ^-$ decays. The analysis uses a sample of beauty mesons produced in proton-proton collisions collected with the LHCb detector between 2011 and 2018, corresponding to an integrated luminosity of 9 fb$^{-1}$. The signal signature corresponds to simultaneous peaks in the $μ^+μ^-$ and $π^-μ^+μ^-$ invariant masses. No evidence for an excess of events over background is observed and an upper limit is set on the branching fraction of the decay at ${\cal B}(D^{*}(2007)^0\toμ^+μ^-) < 2.6\times 10^{-8}$ at $90\%$ confidence level. This is the first limit on the branching fraction of $D^{*}(2007)^0\toμ^+μ^-$ decays and the most stringent limit on $D^{*}(2007)^0$ decays to leptonic final states. The analysis is the first search for a rare charm-meson decay exploiting production via beauty decays.

hep-ex↗
arXiv2023

Observation of sizeable $ω$ contribution to $χ_{c1}(3872)\toπ^+π^-J/ψ$ decays

Resonant structures in the dipion mass spectrum from $χ_{c1}(3872)\toπ^+π^- J/ψ$ decays, produced via $B^+\to K^+χ_{c1}(3872)$ decays, are analyzed using proton-proton collision data collected by the LHCb experiment, corresponding to an integrated luminosity of 9 $fb^{-1}$. A sizeable contribution from the isospin conserving $χ_{c1}(3872)\toωJ/ψ$ decay is established for the first time, $(21.4\pm2.3\pm2.0)\%$, with a significance of more than $7.1σ$. The amplitude of isospin violating decay, $χ_{c1}(3872)\toρ^0 J/ψ$, relative to isospin conserving decay, $χ_{c1}(3872)\toωJ/ψ$, is properly determined, and it is a factor of six larger than expected for a pure charmonium state.

hep-ex↗
arXiv2023

Search for the lepton-flavour violating decays $B^0 \to K^{*0} μ^\pm e^\mp$ and $B_s^0 \to ϕμ^\pm e^\mp$

A search for the lepton-flavour violating decays $B^0 \to K^{*0} μ^\pm e^\mp$ and $B_s^0 \to ϕμ^\pm e^\mp$ is presented, using proton-proton collision data collected by the LHCb detector at the LHC, corresponding to an integrated luminosity of $9\,\text{fb}^{-1}$. No significant signals are observed and upper limits of \begin{align} {\cal B}( B^0 \to K^{*0} μ^+ e^- ) &< \phantom{1}5.7\times 10^{-9}~(6.9\times 10^{-9}),\newline {\cal B}( B^0 \to K^{*0} μ^- e^+ ) &< \phantom{1}6.8\times 10^{-9}~(7.9\times 10^{-9}),\newline {\cal B}( B^0 \to K^{*0} μ^\pm e^\mp ) &< 10.1\times 10^{-9}~(11.7\times 10^{-9}),\newline {\cal B}( B_s^0 \to ϕμ^\pm e^\mp ) &< 16.0\times 10^{-9}~(19.8\times 10^{-9}) \end{align} are set at $90\%~(95\%)$ confidence level. These results constitute the world's most stringent limits to date, with the limit on the decay $B_s^0 \to ϕμ^\pm e^\mp$ the first being set. In addition, limits are reported for scalar and left-handed lepton-flavour violating New Physics scenarios.

hep-ex↗
arXiv2023

Search for the doubly heavy baryon $\itΞ_{bc}^{+}$ decaying to $J/\itψ \itΞ_{c}^{+}$

A first search for the $\itΞ_{bc}^{+}\to J/\itψ\itΞ_{c}^{+}$ decay is performed by the LHCb experiment with a data sample of proton-proton collisions, corresponding to an integrated luminosity of $9\,\mathrm{fb}^{-1}$ recorded at centre-of-mass energies of 7, 8, and $13\mathrm{\,Te\kern -0.1em V}$. Two peaking structures are seen with a local (global) significance of $4.3\,(2.8)$ and $4.1\,(2.4)$ standard deviations at masses of $6571\,\mathrm{Me\kern -0.1em V\!/}c^2$ and $6694\,\mathrm{Me\kern -0.1em V\!/}c^2$, respectively. Upper limits are set on the $\itΞ_{bc}^{+}$ baryon production cross-section times the branching fraction relative to that of the $B_{c}^{+}\to J/\itψ D_{s}^{+}$ decay at centre-of-mass energies of 8 and $13\mathrm{\,Te\kern -0.1em V}$, in the $\itΞ_{bc}^{+}$ and in the $B_{c}^{+}$ rapidity and transverse-momentum ranges from 2.0 to 4.5 and 0 to $20\,\mathrm{Ge\kern -0.1em V\!/}c$, respectively. Upper limits are presented as a function of the $\itΞ_{bc}^{+}$ mass and lifetime.

hep-ex↗
arXiv2023

Amplitude analysis of $B^0 \rightarrow \overline{D}^0 D_s^+ π^-$ and $B^+ \rightarrow D^- D_s^+ π^+$ decays

Resonant contributions in $B^0 \rightarrow \overline{D}^0 D^+_sπ^-$ and $B^+\rightarrow D^- D^+_sπ^+$ decays are determined with an amplitude analysis, which is performed both separately and simultaneously, where in the latter case isospin symmetry between the decays is assumed. The analysis is based on data collected by the LHCb detector in proton-proton collisions at center-of-mass energies of 7, 8 and 13 $\rm{TeV}$. The full data sample corresponds to an integrated luminosity of 9 $\rm fb^{-1}$. A doubly charged spin-0 open-charm tetraquark candidate together with a neutral partner, both with masses near $2.9\,\rm{GeV}$, are observed in the $D_sπ$ decay channel.

hep-ex↗
arXiv2023

First observation of a doubly charged tetraquark and its neutral partner

A combined amplitude analysis is performed for the decays $B^0 \rightarrow \overline{D}^0 D^+_sπ^-$ and $B^+\rightarrow D^- D^+_sπ^+$, which are related by isospin symmetry. The analysis is based on data collected by the LHCb detector in proton-proton collisions at center-of-mass energies of 7, 8 and 13$\,\rm{TeV}$. The full data sample corresponds to an integrated luminosity of 9$\,\rm{fb^{-1}}$. Two new resonant states with masses of $2.908\pm0.011\pm0.020\,\rm{GeV}$ and widths of $0.136\pm0.023\pm0.011\,\rm{GeV}$ are observed, which decay to $D^+_sπ^+$ and $D^+_sπ^-$ respectively. The former state indicates the first observation of a doubly charged open-charm tetraquark state with minimal quark content $[c\bar{s}u\bar{d}]$, and the latter state is a neutral tetraquark composed of $[c\bar{s}\bar{u}d]$ quarks. Both states are found to have spin-parity $0^+$, and their resonant parameters are consistent with each other, which suggests that they belong to an isospin triplet.

hep-ex↗
arXiv2023

Amplitude analysis of the $Λ^+_c\to pK^-π^+$ decay and $Λ^+_c$ baryon polarization measurement in semileptonic beauty hadron decays

An amplitude analysis of $Λ^+_c \to pK^-π^+$ decays together with a measurement of the $Λ^+_c$ polarization vector in semileptonic beauty hadron decays is presented. A sample of $400\,000$ candidates is selected from proton-proton collisions recorded by the LHCb detector at a center-of-mass energy of 13 TeV. An amplitude model is developed and the resonance fractions as well as two- and three-body decay parameters are reported. The mass and width of the $Λ(2000)$ state are also determined. A significant $Λ^+_c$ polarization is found. A large sensitivity of the $Λ^+_c \to pK^-π^+$ decay to the polarization is seen, making the amplitude model suitable for $Λ^+_c$ polarization measurements in other systems.

hep-ex↗
arXiv2023

Nuclear modification factor of neutral pions in the forward and backward regions in $p$-Pb collisions

The nuclear modification factor of neutral pions is measured in proton-lead collisions collected at a center-of-mass energy per nucleon of $8.16~{\rm TeV}$ with the LHCb detector. The $π^0$ production cross section is measured differentially in transverse momentum ($p_{\rm T}$) for $1.5<p_{\rm T}<10.0~{\rm GeV}$ and in center-of-mass pseudorapidity ($η_{\rm c.m.}$) regions $2.5<η_{\rm c.m.}<3.5$ (forward) and $-4.0<η_{\rm c.m.}<-3.0$ (backward) defined relative to the proton beam direction. The forward measurement shows a sizable suppression of $π^0$ production, while the backward measurement shows the first evidence of $π^0$ enhancement in proton-lead collisions at the LHC. Together, these measurements provide precise constraints on models of nuclear structure and particle production in high-energy nuclear collisions.

nucl-ex↗
arXiv2023

Measurement of the ratio of branching fractions $\mathcal{B}(B_c^+ \to B_s^0 π^+)/\mathcal{B}(B_c^+ \to J/ψπ^+)$

The ratio of branching fractions of $B_c^+ \to B_s^0 π^+$ and $B_c^+ \to J/ψπ^+$ decays is measured with proton-proton collision data of a centre-of-mass energy of $13\text{TeV}$. The data were collected with the LHCb experiment during 2016--2018, corresponding to an integrated luminosity of $5.4 \text{fb}^{-1}$. The $B_s^0$ mesons are reconstructed via the decays $B_s^0 \to J/ψϕ$ and $B_s^0 \to D_s^- π^+$. The ratio of branching fractions is measured to be $\mathcal{B}(B_c^+ \to B_s^0 π^+)/\mathcal{B}(B_c^+ \to J/ψπ^+) = 91 \pm 10 \pm 8 \pm 3$ where the first uncertainty is statistical, the second is systematic and the third is due to the knowledge of the branching fractions of the intermediate state decays.

hep-ex↗
arXiv2023

First observation and branching fraction measurement of the $Λ_b^0\to D_s^- p$ decay

The first observation of the $Λ_b^0\to D_s^- p$ decay is presented using proton-proton collision data collected by the LHCb experiment at a centre-of-mass energy of ${\sqrt{s}=13 \,\textrm{TeV}}$, corresponding to a total integrated luminosity of $6\,\textrm{fb}^{-1}$. Using the $Λ_b^0\toΛ_c^+π^-$ decay as the normalisation mode, the branching fraction of the $Λ_b^0\to D_s^- p$ decay is measured to be ${\mathcal{B}(Λ_b^0\to D_s^- p)=(12.6 \pm 0.5 \pm 0.3 \pm 1.2 )\times 10^{-6}}$, where the first uncertainty is statistical, the second systematic and the third due to uncertainties in the branching fractions of the $Λ_b^0\toΛ_c^+π^-$, $D_s^- \to K^-K^+π^-$ and $Λ_c^+\to p K^- π^+$ decays.

hep-ex↗
arXiv2023

Observation of the $B^0_s\!\to D^{*+}D^{*-}$ decay

The first observation of the $B^0_s\!\to D^{*+}D^{*-}$ decay and the measurement of its branching ratio relative to the $B^0\!\to D^{*+}D^{*-}$ decay are presented. The data sample used corresponds to an integrated luminosity of $9\,\text{fb}^{-1}$ of proton-proton collisions recorded by the LHCb experiment at centre-of-mass energies of 7, 8 and $13\,\text{TeV}$ between 2011 and 2018. The decay is observed with more than $10$ standard deviations and the time-integrated ratio of branching fractions is determined to be \begin{align*} \frac{\mathcal{B}(B^0_s\!\to D^{*+}D^{*-})}{\mathcal{B}(B^0\!\to D^{*+}D^{*-})} = 0.269 \pm 0.032 \pm 0.011 \pm 0.008\, , \end{align*} where the first uncertainty is statistical, the second systematic and the third due to the uncertainty of the fragmentation fraction ratio $f_s/f_d$. The $B^0_s\!\to D^{*+}D^{*-}$ branching fraction is calculated to be \begin{align*} \mathcal{B}(B^0_s\!\to D^{*+}D^{*-}) = (2.15 \pm 0.26 \pm 0.09 \pm 0.06 \pm 0.16)\times 10^{-4} \,, \end{align*} where the fourth uncertainty is due to the $B^0\!\to D^{*+}D^{*-}$branching fraction. These results are calculated using the average $B^0_s$ meson lifetime in simulation. Correction factors are reported for scenarios where either a purely heavy or a purely light $B^0_s$ eigenstate is considered.

hep-ex↗
arXiv2023

Effect of carbon content on electronic structure of uranium carbides

The electronic structure of UC$_x$ (x=0.9, 1.0, 1.1, 2.0) was studied by means of x-ray absorption spectroscopy (XAS) at the C $K$ edge and measurements in the high energy resolution fluorescence detection (HERFD) mode at the U $M_4$ and $L_3$ edges. The full-relativistic density functional theory calculations taking into account the $5f-5f$ Coulomb interaction $U$ and spin-orbit coupling (DFT+$U$+SOC) were also performed for UC and UC$_2$. While the U $L_3$ HERFD-XAS spectra of the studied samples reveal little difference, the U $M_4$ HERFD-XAS spectra show certain sensitivity to the varying carbon content in uranium carbides. The observed gradual changes in the U $M_4$ HERFD spectra suggest an increase in the C $2p$-U $5f$ charge transfer, which is supported by the orbital population analysis in the DFT+$U$+SOC calculations, indicating an increase in the U $5f$ occupancy in UC$_2$ as compared to that in UC. On the other hand, the density of states at the Fermi level were found to be significantly lower in UC$_2$, thus affecting the thermodynamic properties. Both the x-ray spectroscopic data (in particular, the C $K$ XAS measurements) and results of the DFT+$U$+SOC indicate the importance of taking into account $U$ and SOC for the description of the electronic structure of actinide carbides.

physics.chem-ph↗
arXiv2023

Observation of the decay $ Λ_b^0\rightarrow Λ_c^+τ^-\overlineν_τ$

The first observation of the semileptonic $b$-baryon decay $ Λ_b^0 \rightarrow Λ_c^+ τ^-\overlineν_τ$, with a significance of $6.1\,σ$, is reported using a data sample corresponding to 3 fb$^{-1}$ of integrated luminosity, collected by the LHCb experiment at centre-of-mass energies of 7 and 8 TeV at the LHC. The $τ^-$ lepton is reconstructed in the hadronic decay to three charged pions. The branching fraction ${\mathcal{B}}(Λ_b^0 \rightarrow Λ_c^+τ^-\overlineν_τ) = (1.50 \pm 0.16\pm 0.25\pm 0.23)\%$ is obtained, where uncertainties are statistical, systematic and from the external branching fraction of the normalisation channel $Λ_b^0\rightarrow Λ_c^+π^-π^+π^-$. The ratio of semileptonic branching fractions ${\mathcal{R}}( Λ_c^+)\equiv {\mathcal{B}}( Λ_b^0 \rightarrow Λ_c^+ τ^-\overlineν_τ)/{\mathcal{B}}( Λ_b^0 \rightarrow Λ_c^+ μ^-\overlineν_μ)$ is derived to be $0.242 \pm 0.026 \pm 0.040\pm 0.059$, where the external branching fraction uncertainty from the channel $Λ_b^0\rightarrow Λ_c^+μ^-\overlineν_μ$ contributes to the last term. This result is in agreement with the Standard Model prediction.

hep-ex↗
arXiv2022

Optimization and first electronic implementation of the Constant-Fraction Time-Over-Threshold pulse shape discrimination method

In this contribution we report on further investigations of the recently-evaluated Constant-Fraction Time-over-Threshold (CF-ToT) method for neutron/gamma-ray pulse shape discrimination (PSD). The superiority of the CF-ToT PSD method over the constant-threshold (CT-ToT) method was previously demonstrated, down to low neutron energy thresholds of 100 keVee. Here, we report on a quantitative comparison between the traditionally used Charge Comparison (CC) method and the CF-ToT method using a stilbene scintillator coupled to a silicon photomultiplier, implementing an offline analysis of recorded fast-neutron and gamma-ray waveforms. An optimization of the constant fraction value indicates that a 20%-fraction yields the optimum figure-of-merit (FOM) and gamma-ray peak-to-valley (P/V) ratio. The results obtained for a particle energy threshold of 100 keVee show that the FOM and P/V values achieved with the CF-ToT method are superior to those obtained using the standard CC method. In addition, a first electronic implementation of the CF-ToT method was performed using simple circuitry suitable for multichannel architecture. Initial results obtained with this circuit prototype are presented.

physics.ins-det↗
arXiv2022

Revealing the short-range structure of the "mirror nuclei" $^3$H and $^3$He

When protons and neutrons (nucleons) are bound into atomic nuclei, they are close enough together to feel significant attraction, or repulsion, from the strong, short-distance part of the nucleon-nucleon interaction. These strong interactions lead to hard collisions between nucleons, generating pairs of highly-energetic nucleons referred to as short-range correlations (SRCs). SRCs are an important but relatively poorly understood part of nuclear structure and mapping out the strength and isospin structure (neutron-proton vs proton-proton pairs) of these virtual excitations is thus critical input for modeling a range of nuclear, particle, and astrophysics measurements. Hitherto measurements used two-nucleon knockout or ``triple-coincidence'' reactions to measure the relative contribution of np- and pp-SRCs by knocking out a proton from the SRC and detecting its partner nucleon (proton or neutron). These measurementsshow that SRCs are almost exclusively np pairs, but had limited statistics and required large model-dependent final-state interaction (FSI) corrections. We report on the first measurement using inclusive scattering from the mirror nuclei $^3$H and $^3$He to extract the np/pp ratio of SRCs in the A=3 system. We obtain a measure of the np/pp SRC ratio that is an order of magnitude more precise than previous experiments, and find a dramatic deviation from the near-total np dominance observed in heavy nuclei. This result implies an unexpected structure in the high-momentum wavefunction for $^3$He and $^3$H. Understanding these results will improve our understanding of the short-range part of the N-N interaction.

nucl-ex↗