arXiv subjects

R. Casanova Mohr

Publications and source records attributed to R. Casanova Mohr.

At least 19 recordsLinked to original sources

arXiv2026

Beam-test evaluation of pre-production Low Gain Avalanche Detectors for the ATLAS High Granularity Timing Detector

The High Granularity Timing Detector (HGTD) will be installed in the ATLAS experiment as part of the Phase-II upgrade for the High Luminosity-Large Hadron Collider (HL-LHC). It will mitigate pile-up effects in the forward region, and measure per bunch luminosity. The design of HGTD is based on Low Gain Avalanche Detector (LGAD) sensors. This paper presents the results of beam-test campaigns conducted at CERN and DESY in 2023 and 2024 on single LGADs from HGTD pre-production test structures, before and after neutron irradiation up to fluences of $2.5 \times 10^{15}~\mathrm{n_{eq}/cm^2}$. The tested LGADs can meet HGTD requirements in terms of charge collection, time resolution, and hit efficiency, even under HL-LHC end-of-life conditions, supporting their deployment in the final detector.

physics.ins-det↗

arXiv2025

Thermal Cycling Reliability of Hybrid Pixel Sensor Modules for The ATLAS High Granularity Timing Detector

The reliability of bump connection structures has become a critical aspect of future silicon detectors for particle physics. The High Granularity Timing Detector (HGTD) for the ATLAS experiment at the High-Luminosity Large Hadron Collider will require 8032 hybrid pixel sensor modules, composed of two Low Gain Avalanche Diode sensors bump-bonded to two readout ASICs and glued to a passive PCB. The detector will operate at low temperature (-30 degrees Celsius) to mitigate the impact of irradiation. The thermomechanical reliability of flip-chip bump connections in HGTD modules is a critical concern, particularly due to their characteristically lower bump density (pixel pitch dimensions of 1.3 mm by 1.3 mm). This paper elaborates on the challenges arising from this design characteristic. Finite element analysis and experimental testing were employed to investigate failure modes in the flip-chip bump structures under thermal cycling from -45 degrees Celsius to 40 degrees Celsius and to guide the module redesign. The optimized design demonstrates significantly enhanced robustness and is projected to fulfill the full lifetime requirements of the HGTD.

physics.ins-det↗

arXiv2018

Differential branching fraction and angular analysis of $Λ^{0}_{b} \rightarrow Λμ^+μ^-$ decays

The differential branching fraction of the rare decay $Λ^{0}_{b} \rightarrow Λμ^+μ^-$ is measured as a function of $q^{2}$, the square of the dimuon invariant mass. The analysis is performed using proton-proton collision data, corresponding to an integrated luminosity of $3.0 \mbox{ fb}^{-1}$, collected by the LHCb experiment. Evidence of signal is observed in the $q^2$ region below the square of the $J/ψ$ mass. Integrating over $15 < q^{2} < 20 \mbox{ GeV}^2/c^4$ the branching fraction is measured as $d\mathcal{B}(Λ^{0}_{b} \rightarrow Λμ^+μ^-)/dq^2 = (1.18 ^{+ 0.09} _{-0.08} \pm 0.03 \pm 0.27) \times 10^{-7} ( \mbox{GeV}^{2}/c^{4})^{-1}$, where the uncertainties are statistical, systematic and due to the normalisation mode, $Λ^{0}_{b} \rightarrow J/ψΛ$, respectively. In the $q^2$ intervals where the signal is observed, angular distributions are studied and the forward-backward asymmetries in the dimuon ($A^{l}_{\rm FB}$) and hadron ($A^{h}_{\rm FB}$) systems are measured for the first time. In the range $15 < q^2 < 20 \mbox{ GeV}^2/c^4$ they are found to be $A^{l}_{\rm FB} = -0.05 \pm 0.09 \mbox{ (stat)} \pm 0.03 \mbox{ (syst)}$ and $A^{h}_{\rm FB} = -0.29 \pm 0.07 \mbox{ (stat)} \pm 0.03 \mbox{ (syst)}$.

hep-ex↗

arXiv2016

First observation and amplitude analysis of the $B^{-}\to D^{+}K^{-}π^{-}$ decay

The $B^{-}\to D^{+}K^{-}π^{-}$ decay is observed in a data sample corresponding to $3.0~\rm{fb}^{-1}$ of $pp$ collision data recorded by the LHCb experiment during 2011 and 2012. Its branching fraction is measured to be ${\cal B}(B^{-}\to D^{+}K^{-}π^{-}) = (7.31 \pm 0.19 \pm 0.22 \pm 0.39) \times 10^{-5}$ where the uncertainties are statistical, systematic and from the branching fraction of the normalisation channel $B^{-}\to D^{+}π^{-}π^{-}$, respectively. An amplitude analysis of the resonant structure of the $B^{-}\to D^{+}K^{-}π^{-}$ decay is used to measure the contributions from quasi-two-body $B^{-}\to D_{0}^{*}(2400)^{0}K^{-}$, $B^{-}\to D_{2}^{*}(2460)^{0}K^{-}$, and $B^{-}\to D_{J}^{*}(2760)^{0}K^{-}$ decays, as well as from nonresonant sources. The $D_{J}^{*}(2760)^{0}$ resonance is determined to have spin~1.

hep-ex↗

arXiv2016

Search for long-lived heavy charged particles using a ring imaging Cherenkov technique at LHCb

A search is performed for heavy long-lived charged particles using 3.0 fb$^{-1}$ of pp collisions collected at $\sqrt{s}$= 7 and 8 TeV with the LHCb detector. The search is mainly based on the response of the ring imaging Cherenkovdetectors to distinguish the heavy, slow-moving particles from muons. No evidence is found for the production of such long-lived states. The results are expressed as limits on the Drell-Yan production of pairs of long-lived particles, with both particles in the LHCb pseudorapidity acceptance, $1.8 < η< 4.9$. The mass-dependent cross-section upper limits are in the range 2-4 fb (at 95\% CL) for masses between 124 and 309 GeV/c$^2$.

hep-ex↗

arXiv2016

First observation of the decay $B_{s}^{0} \to K_{S}^{0} K^{*}(892)^{0}$

A search for $B_{(s)}^{0} \to K_{S}^{0} K^{*}(892)^{0}$ decays is performed using $pp$ collision data, corresponding to an integrated luminosity of $1.0~\text{fb}^{-1}$, collected with the LHCb detector at a centre-of-mass energy of $7~\text{TeV}$. The $B_{s}^{0} \to K_{S}^{0} K^{*}(892)^{0}$ decay is observed for the first time, with a significance of 7.1 standard deviations. The branching fraction is measured to be \begin{equation*} \mathcal{B}(B_{s}^{0} \to \bar{K}^{0} K^{*}(892)^{0}) + \mathcal{B}(B_{s}^{0} \to K^{0} \bar{K}^{*}(892)^{0}) = (16.4 \pm 3.4 \pm 2.3) \times 10^{-6},\\ \end{equation*} where the first uncertainty is statistical and the second is systematic. No evidence is found for the decay $B^{0} \to K_{S}^{0} K^{*}(892)^{0}$ and an upper limit is set on the branching fraction, $\mathcal{B}(B^{0} \to \bar{K}^{0} K^{*}(892)^{0}) + \mathcal{B}(B^{0} \to K^{0} \bar{K}^{*}(892)^{0}) < 0.96 \ \times 10^{-6}, $ at $90\,\% $ confidence level. All results are consistent with Standard Model predictions.

hep-ex↗

arXiv2015

Study of $B^{-}\to DK^-π^+π^-$ and $B^-\to Dπ^-π^+π^-$ decays and determination of the CKM angle $γ$

We report a study of the suppressed $B^-\to DK^-π^+π^-$ and favored $B^-\to Dπ^-π^+π^-$ decays, where the neutral $D$ meson is detected through its decays to the $K^{\mp}π^{\pm}$ and CP-even $K^+K^-$ and $π^+π^-$ final states. The measurement is carried out using a proton-proton collision data sample collected by the LHCb experiment, corresponding to an integrated luminosity of 3.0~fb$^{-1}$. We observe the first significant signals in the CP-even final states of the $D$ meson for both the suppressed $B^-\to DK^-π^+π^-$ and favored $B^-\to Dπ^-π^+π^-$ modes, as well as in the doubly Cabibbo-suppressed $D\to K^+π^-$ final state of the $B^-\to Dπ^-π^+π^-$ decay. Evidence for the ADS suppressed decay $B^{-}\to DK^-π^+π^-$, with $D\to K^+π^-$, is also presented. From the observed yields in the $B^-\to DK^-π^+π^-$, $B^-\to Dπ^-π^+π^-$ and their charge conjugate decay modes, we measure the value of the weak phase to be $γ=(74^{+20}_{-19})^{\rm o}$. This is one of the most precise single-measurement determinations of $γ$ to date.

hep-ex↗

arXiv2015

Observation of the $B^0_s\toη'η'$ decay

The first observation of the $B^0_s\toη'η'$ decay is reported. The study is based on a sample of proton-proton collisions corresponding to $3.0$ ${\rm fb^{-1}}$ of integrated luminosity collected with the LHCb detector. The significance of the signal is $6.4$ standard deviations. The branching fraction is measured to be $[3.31 \pm 0.64\,{\rm (stat)} \pm 0.28\,{\rm (syst)} \pm 0.12\,{\rm (norm)}]\times10^{-5}$, where the third uncertainty comes from the $B^{\pm}\toη' K^{\pm}$ branching fraction that is used as a normalisation. In addition, the charge asymmetries of $B^{\pm}\toη' K^{\pm}$ and $B^{\pm}\toϕK^{\pm}$, which are control channels, are measured to be $(-0.2 \pm1.3)\%$ and $(+1.7\pm1.3)\%$, respectively. All results are consistent with theoretical expectations.

hep-ex↗

arXiv2015

Search for the $Λ_b \rightarrow Λη^\prime$ and $Λ_b \rightarrow Λη$ decays with the LHCb detector

A search is performed for the as yet unobserved baryonic $Λ_b \rightarrow Λη^\prime$ and $Λ_b \rightarrow Λη$ decays with 3$fb^{-1}$ of proton-proton collision data recorded by the LHCb experiment. The $B^0 \rightarrow K_S^0 η^\prime$ decay is used as a normalisation channel. No significant signal is observed for the $Λ_b \rightarrow Λη^\prime$ decay. An upper limit is found on the branching fraction of $\mathcal{B}(Λ_b \rightarrow Λη^\prime)<3.1\times10^{-6}$} at 90\% confidence level. Evidence is seen for the presence of the $Λ_b \rightarrow Λη$ decay at the level of $3σ$ significance, with a branching fraction $\mathcal{B}(Λ_b \rightarrow Λη)=(9.3^{+7.3}_{-5.3})\times10^{-6}$}.

hep-ex↗

arXiv2015

Observation of the decay $\overline{B}_s^0 \rightarrow ψ(2S) K^+ π^-$

The decay $\overline{B}_s^0 \rightarrow ψ(2S) K^+ π^-$ is observed using a data set corresponding to an integrated luminosity of $3.0fb^{-1}$ collected by the LHCb experiment in $pp$ collisions at centre-of-mass energies of 7 and 8 TeV. The branching fraction relative to the $B^0\rightarrow ψ(2S) K^+ π^-$ decay mode is measured to be \begin{equation} \frac{{\cal B}(\overline{B}^0_s \rightarrow ψ(2S) K^+ π^-)}{{\cal B}(B^0 \rightarrow ψ(2S) K^+ π^-)} = 5.38 \pm 0.36 (stat) \pm 0.22 (syst) \pm 0.31 \, (f_s/f_d) \, \%,\nonumber \end{equation} where $f_s/f_d$ indicates the uncertainty due to the ratio of probabilities for a $b$ quark to hadronise into a $B_s^0$ or $B^0$ meson. Using an amplitude analysis, the fraction of decays proceeding via an intermediate $K^*(892)^0$ meson is measured to be $0.645 \pm 0.049 (stat) \pm 0.049 (syst)$ and its longitudinal polarisation fraction is $0.524 \pm 0.056 (stat) \pm 0.029 (syst)$. The relative branching fraction for this component is determined to be \begin{equation} \frac{{\cal B}(\overline{B}^0_s \rightarrow ψ(2S) K^*(892)^0)}{{\cal B}(B^0 \rightarrow ψ(2S) K^*(892)^0)} = 5.58 \pm 0.57 (stat) \pm 0.40 (syst) \pm 0.32 \, (f_s/f_d) \, \%. \nonumber \end{equation} In addition, the mass splitting between the $B_s^0$ and $B^0$ mesons is measured as \begin{equation} M(B^0_s) - M(B^0) = 87.45 \pm 0.44 (stat) \pm 0.07 (syst) MeV/c^2. \nonumber \end{equation}

hep-ex↗

arXiv2015

Observation of the ${B^0 \to ρ^0 ρ^0}$ decay from an amplitude analysis of ${B^0 \to (π^+π^-)(π^+π^-)}$ decays

Proton-proton collision data recorded in 2011 and 2012 by the \lhcb experiment, co\-rres\-pon\-ding to an integrated luminosity of 3.0\invfb, are a\-na\-lysed to search for the charmless ${B^0 \to ρ^0 ρ^0}$ decay. More than 600 ${\B^0 \to (π^+π^-)(π^+π^-)}$ signal decays are selected and used to perform an amplitude analysis from which the ${B^0 \to ρ^0 ρ^0}$ decay is observed for the first time with 7.1 standard deviations significance. The fraction of ${B^0 \to ρ^0 ρ^0}$ decays yielding a longitudinally polarised final state is measured to be $\fL = 0.745^{+0.048}_{-0.058} ({\rm stat}) \pm 0.034 ({\rm syst})$. The ${B^0 \to ρ^0 ρ^0}$ branching fraction, using the ${\B^0 \to ϕK^*(892)^{0}}$ decay as reference, is also reported as ${\BF(B^0 \to ρ^0 ρ^0) = (0.94 \pm 0.17 ({\rm stat}) \pm 0.09 ({\rm syst}) \pm 0.06 ({\rm BF})) \times 10^{-6}}$.

hep-ex↗

arXiv2015

Measurement of the exclusive $Υ$ production cross-section in $pp$ collisions at $\sqrt{s}=$7 TeV and 8 TeV

A study is presented of central exclusive production of $Υ(nS)$ states, where the $Υ(nS)$ resonances decay to the $μ^+μ^-$ final state, using $pp$ collision data recorded by the LHCb experiment. The cross-section is measured in the rapidity range $2<y(Υ)<4.5$ where the muons are reconstructed in the pseudorapidity range $2<η(μ^\pm)<4.5$. The data sample corresponds to an integrated luminosity of 2.9 fb$^{-1}$ and was collected at centre-of-mass energies of $7$ TeV and $8$ TeV. The measured $Υ(1S)$ and $Υ(2S)$ production cross-sections are \begin{eqnarray} σ(pp \to pΥ(1S)p) &=& 9.0 \pm 2.1 \pm 1.7\textrm{ pb and}\nonumber\\ σ(pp \to pΥ(2S)p) &=& 1.3 \pm 0.8 \pm 0.3\textrm{ pb},\nonumber \end{eqnarray} where the first uncertainties are statistical and the second are systematic. The $Υ(1S)$ cross-section is also measured as a function of rapidity and is found to be in good agreement with Standard Model predictions. An upper limit is set at 3.4 pb at the 95\% confidence level for the exclusive $Υ(3S)$ production cross-section, including possible contamination from $χ_b(3P)\toΥ(3S)γ$ decays.

hep-ex↗

arXiv2015

Measurement of the forward $Z$ boson production cross-section in $pp$ collisions at $\sqrt{s}$ = 7 TeV

A measurement of the production cross-section for $Z$ bosons that decay to muons is presented. The data were recorded by the LHCb detector during $pp$ collisions at a centre-of-mass energy of 7 TeV, and correspond to an integrated luminosity of 1.0 fb$^{-1}$. The cross-section is measured for muons in the pseudorapidity range $2.0 < η< 4.5$ with transverse momenta $p_{T} > 20$ GeV/c. The dimuon mass is restricted to $60 < M_{μ^{+}μ^{-}} < 120$ GeV/c$^{2}$. The measured cross-section is $$σ_{Z\rightarrowμ^{+}μ^{-}} = (76.0 \pm 0.3 \pm 0.5 \pm 1.0 \pm 1.3) \, \text{pb}$$ where the uncertainties are due to the sample size, systematic effects, the beam energy and the luminosity. This result is in good agreement with theoretical predictions at next-to-next-to-leading order in perturbative quantum chromodynamics. The cross-section is also measured differentially as a function of kinematic variables of the $Z$ boson. Ratios of the production cross-sections of electroweak bosons are presented using updated LHCb measurements of $W$ boson production. A precise test of the Standard Model is provided by the measurement of the ratio $$\frac{σ_{W^{+}\rightarrowμ^{+}ν_μ} + σ_{W^{-}\rightarrowμ^{-}\barν_μ}}{σ_{Z\rightarrowμ^{+}μ^{-}}} = 20.63\pm0.09\pm0.12\pm0.05,$$ where the uncertainty due to luminosity cancels.

hep-ex↗

arXiv2015

Measurement of $CP$ asymmetries and polarisation fractions in $B_s^0 \rightarrow K^{0}\bar{K}{}^{0}$ decays

An angular analysis of the decay $B_s^0 \rightarrow K^{*0}\bar{K}{}^{*0}$ is performed using $pp$ collisions corresponding to an integrated luminosity of $1.0$ ${fb}^{-1}$ collected by the LHCb experiment at a centre-of-mass energy $\sqrt{s} = 7$ TeV. A combined angular and mass analysis separates six helicity amplitudes and allows the measurement of the longitudinal polarisation fraction $f_L = 0.201 \pm 0.057 {(stat.)} \pm 0.040{(syst.)}$ for the $B_s^0 \rightarrow K^*(892)^0 \bar{K}{}^*(892)^0$ decay. A large scalar contribution from the $K^{*}_{0}(1430)$ and $K^{*}_{0}(800)$ resonances is found, allowing the determination of additional $CP$ asymmetries. Triple product and direct $CP$ asymmetries are determined to be compatible with the Standard Model expectations. The branching fraction $\mathcal{B}(B_s^0 \rightarrow K^*(892)^0 \bar{K}{}^*(892)^0)$ is measured to be $(10.8 \pm 2.1 {\ \rm (stat.)} \pm 1.4 {\ \rm (syst.)} \pm 0.6 \ (f_d/f_s) ) \times 10^{-6}$.

hep-ex↗

arXiv2015

Search for the decay $B_s^0 \to \overline{D}^{0} f_{0}(980)$

A search for $B_s^0 \to \overline{D}^{0} f_{0}(980)$ decays is performed using $3.0\, {\rm fb}^{-1}$ of $pp$ collision data recorded by the LHCb experiment during 2011 and 2012. The $f_{0}(980)$ meson is reconstructed through its decay to the $π^{+}π^{-}$ final state in the mass window $900\, {\rm MeV}/c^{2} < m(π^{+}π^{-}) < 1080\, {\rm MeV}/c^{2}$. No significant signal is observed. The first upper limits on the branching fraction of $\mathcal{B}(B_s^0 \to \overline{D}^{0} f_{0}(980)) < 3.1\,(3.4) \times 10^{-6}$ are set at $90\,\%$ ($95\,\%$) confidence level.

hep-ex↗

arXiv2015

Amplitude analysis of $B^0 \rightarrow \bar{D}^0 K^+ π^-$ decays

The Dalitz plot distribution of $B^0 \rightarrow \bar{D}^0 K^+ π^-$ decays is studied using a data sample corresponding to $3.0\rm{fb}^{-1}$ of $pp$ collision data recorded by the LHCb experiment during 2011 and 2012. The data are described by an amplitude model that contains contributions from intermediate $K^*(892)^0$, $K^*(1410)^0$, $K^*_2(1430)^0$ and $D^*_2(2460)^-$ resonances. The model also contains components to describe broad structures, including the $K^*_0(1430)^0$ and $D^*_0(2400)^-$ resonances, in the $Kπ$ S-wave and the $Dπ$ S- and P-waves. The masses and widths of the $D^*_0(2400)^-$ and $D^*_2(2460)^-$ resonances are measured, as are the complex amplitudes and fit fractions for all components included in the amplitude model. The model obtained will be an integral part of a future determination of the angle $γ$ of the CKM quark mixing matrix using $B^0 \rightarrow D K^+ π^-$ decays.

hep-ex↗

arXiv2015

Determination of the quark coupling strength $|V_{ub}|$ using baryonic decays

In the Standard Model of particle physics, the strength of the couplings of the $b$ quark to the $u$ and $c$ quarks, $|V_{ub}|$ and $|V_{cb}|$, are governed by the coupling of the quarks to the Higgs boson. Using data from the LHCb experiment at the Large Hadron Collider, the probability for the $Λ^0_b$ baryon to decay into the $p μ^- \overlineν_μ$ final state relative to the $Λ^+_c μ^- \overlineν_μ$ final state is measured. Combined with theoretical calculations of the strong interaction and a previously measured value of $|V_{cb}|$, the first $|V_{ub}|$ measurement to use a baryonic decay is performed. This measurement is consistent with previous determinations of $|V_{ub}|$ using $B$ meson decays to specific final states and confirms the existing incompatibility with those using an inclusive sample of final states.

hep-ex↗

arXiv2015

Identification of beauty and charm quark jets at LHCb

Identification of jets originating from beauty and charm quarks is important for measuring Standard Model processes and for searching for new physics. The performance of algorithms developed to select $b$- and $c$-quark jets is measured using data recorded by LHCb from proton-proton collisions at $\sqrt{s}=7$ TeV in 2011 and at $\sqrt{s}=8$ TeV in 2012. The efficiency for identifying a $b(c)$ jet is about 65%(25%) with a probability for misidentifying a light-parton jet of 0.3% for jets with transverse momentum $p_{\rm T} > 20$ GeV and pseudorapidity $2.2 < η< 4.2$. The dependence of the performance on the $p_{\rm T}$ and $η$ of the jet is also measured.

hep-ex↗