arXiv subjects

A. Bitadze

Publications and source records attributed to A. Bitadze.

394 records · Page 22Linked to original sources

arXiv2016

Differential branching fraction and angular moments analysis of the decay $B^0 \to K^+ π^- μ^+ μ^-$ in the $K^*_{0,2}(1430)^0$ region

Measurements of the differential branching fraction and angular moments of the decay $B^0 \to K^+ π^- μ^+ μ^-$ in the $K^+π^-$ invariant mass range $1330<m(K^+ π^-)<1530~MeV/c^2$ are presented. Proton-proton collision data are used, corresponding to an integrated luminosity of 3 $fb^{-1}$ collected by the LHCb experiment. Differential branching fraction measurements are reported in five bins of the invariant mass squared of the dimuon system, $q^2$, between 0.1 and 8.0 $GeV^2/c^4$. For the first time, an angular analysis sensitive to the S-, P- and D-wave contributions of this rare decay is performed. The set of 40 normalised angular moments describing the decay is presented for the $q^2$ range 1.1--6.0 $GeV^2/c^4$.

hep-ex↗

arXiv2016

Measurement of the CKM angle $γ$ from a combination of LHCb results

A combination of measurements sensitive to the CKM angle $γ$ from LHCb is performed. The inputs are from analyses of time-integrated $B^{+}\rightarrow DK^+$, $B^{0} \rightarrow D K^{*0}$, $B^{0} \rightarrow D K^+ π^-$ and $B^{+} \rightarrow D K^+π^+π^-$ tree-level decays. In addition, results from a time-dependent analysis of $B_{s}^{0} \rightarrow D_{s}^{\mp}K^{\pm}$ decays are included. The combination yields $γ= (72.2^{+6.8}_{-7.3})^\circ$, where the uncertainty includes systematic effects. The 95.5% confidence level interval is determined to be $γ\in [55.9,85.2]^\circ$. A second combination is investigated, also including measurements from $B^{+} \rightarrow D π^+$ and $B^{+} \rightarrow D π^+π^-π^+$ decays, which yields compatible results.

hep-ex↗

arXiv2016

Search for Higgs-like bosons decaying into long-lived exotic particles

A search is presented for massive long-lived particles, in the 20-60 GeV mass range with lifetimes between 5 and 100 ps. The dataset used corresponds to 0.62 1\fb of proton-proton collision data collected by the LHCb detector at sqrt(s)=7 TeV. The particles are assumed to be pair-produced by the decay of a Higgs-like boson with mass between 80 and 140 GeV. No excess above the background expectation is observed and limits are set on the production cross-section as a function of the long-lived particle mass and lifetime and of the Higgs-like boson mass.

hep-ex↗

arXiv2016

Study of $B_c^+$ decays to the $K^+K^-π^+$ final state and evidence for the decay $B_c^+\toχ_{c0}π^+$

A study of $B_c^+\to K^+K^-π^+$ decays is performed for the first time using data corresponding to an integrated luminosity of 3.0 $\mathrm{fb}^{-1}$ collected by the LHCb experiment in $pp$ collisions at centre-of-mass energies of $7$ and $8$ TeV. Evidence for the decay $B_c^+\toχ_{c0}(\to K^+K^-)π^+$ is reported with a significance of 4.0 standard deviations, resulting in the measurement of $\frac{σ(B_c^+)}{σ(B^+)}\times\mathcal{B}(B_c^+\toχ_{c0}π^+)$ to be $(9.8^{+3.4}_{-3.0}(\mathrm{stat})\pm 0.8(\mathrm{syst}))\times 10^{-6}$. Here $\mathcal{B}$ denotes a branching fraction while $σ(B_c^+)$ and $σ(B^+)$ are the production cross-sections for $B_c^+$ and $B^+$ mesons. An indication of $\bar b c$ weak annihilation is found for the region $m(K^-π^+)<1.834\mathrm{\,Ge\kern -0.1em V\!/}c^2$, with a significance of 2.4 standard deviations.

hep-ex↗

arXiv2016

Measurement of the CKM angle $γ$ using $B^0 \rightarrow D K^{*0}$ with $D \rightarrow K^0_S π^+ π^-$ decays

A model-dependent amplitude analysis of the decay $B^0\rightarrow D(K^0_Sπ^+π^-) K^{*0}$ is performed using proton-proton collision data corresponding to an integrated luminosity of 3.0fb$^{-1}$, recorded at $\sqrt{s}=7$ and $8 TeV$ by the LHCb experiment. The CP violation observables $x_{\pm}$ and $y_{\pm}$, sensitive to the CKM angle $γ$, are measured to be \begin{eqnarray*} x_- &=& -0.15 \pm 0.14 \pm 0.03 \pm 0.01, y_- &=& 0.25 \pm 0.15 \pm 0.06 \pm 0.01, x_+ &=& 0.05 \pm 0.24 \pm 0.04 \pm 0.01, y_+ &=& -0.65^{+0.24}_{-0.23} \pm 0.08 \pm 0.01, \end{eqnarray*} where the first uncertainties are statistical, the second systematic and the third arise from the uncertainty on the $D\rightarrow K^0_S π^+π^-$ amplitude model. These are the most precise measurements of these observables. They correspond to $γ=(80^{+21}_{-22})^{\circ}$ and $r_{B^0}=0.39\pm0.13$, where $r_{B^0}$ is the magnitude of the ratio of the suppressed and favoured $B^0\rightarrow D K^+ π^-$ decay amplitudes, in a $Kπ$ mass region of $\pm50 MeV$ around the $K^*(892)^0$ mass and for an absolute value of the cosine of the $K^{*0}$ decay angle larger than $0.4$.

hep-ex↗

arXiv2016

Measurement of forward $W\to eν$ production in $pp$ collisions at $\sqrt{s}=8\,$TeV

A measurement of the cross-section for $W \to eν$ production in $pp$ collisions is presented using data corresponding to an integrated luminosity of $2\,$fb$^{-1}$ collected by the LHCb experiment at a centre-of-mass energy of $\sqrt{s}=8\,$TeV. The electrons are required to have more than $20\,$GeV of transverse momentum and to lie between 2.00 and 4.25 in pseudorapidity. The inclusive $W$ production cross-sections, where the $W$ decays to $eν$, are measured to be \begin{equation*} σ_{W^{+} \to e^{+}ν_{e}}=1124.4\pm 2.1\pm 21.5\pm 11.2\pm 13.0\,\mathrm{pb}, \end{equation*} \begin{equation*} σ_{W^{-} \to e^{-}\barν_{e}}=\,\,\,809.0\pm 1.9\pm 18.1\pm\,\,\,7.0\pm \phantom{0}9.4\,\mathrm{pb}, \end{equation*} where the first uncertainties are statistical, the second are systematic, the third are due to the knowledge of the LHC beam energy and the fourth are due to the luminosity determination. Differential cross-sections as a function of the electron pseudorapidity are measured. The $W^{+}/W^{-}$ cross-section ratio and production charge asymmetry are also reported. Results are compared with theoretical predictions at next-to-next-to-leading order in perturbative quantum chromodynamics. Finally, in a precise test of lepton universality, the ratio of $W$ boson branching fractions is determined to be \begin{equation*} \mathcal{B}(W \to eν)/\mathcal{B}(W \to μν)=1.020\pm 0.002\pm 0.019, \end{equation*} where the first uncertainty is statistical and the second is systematic.

hep-ex↗

arXiv2016

Amplitude analysis of $B^{-} \to D^{+} π^{-} π^{-}$ decays

The Dalitz plot analysis technique is used to study the resonant substructures of $B^{-} \to D^{+} π^{-} π^{-}$ decays in a data sample corresponding to 3.0 ${\rm fb}^{-1}$ of $pp$ collision data recorded by the LHCb experiment during 2011 and 2012. A model-independent analysis of the angular moments demonstrates the presence of resonances with spins 1, 2 and 3 at high $D^{+}π^{-}$ mass. The data are fitted with an amplitude model composed of a quasi-model-independent function to describe the $D^{+}π^{-}$ S-wave together with virtual contributions from the $D^{*}(2007)^{0}$ and $B^{*0}$ states, and components corresponding to the $D^{*}_{2}(2460)^{0}$, $D^{*}_{1}(2680)^{0}$, $D^{*}_{3}(2760)^{0}$ and $D^{*}_{2}(3000)^{0}$ resonances. The masses and widths of these resonances are determined together with the branching fractions for their production in $B^{-} \to D^{+} π^{-} π^{-}$ decays. The $D^{+}π^{-}$ S-wave has phase motion consistent with that expected due to the presence of the $D^{*}_{0}(2400)^{0}$ state. These results constitute the first observations of the $D^{*}_{3}(2760)^{0}$ and $D^{*}_{2}(3000)^{0}$ resonances.

hep-ex↗

arXiv2016

Measurement of the forward Z boson production cross-section in pp collisions at $\sqrt{s} = 13$ TeV

A measurement of the production cross-section of Z bosons in pp collisions at $\sqrt{s} = 13$ TeV is presented using dimuon and dielectron final states in LHCb data. The cross-section is measured for leptons with pseudorapidities in the range $2.0 < η< 4.5$, transverse momenta $p_\text{T} > 20$ GeV and dilepton invariant mass in the range $60<m(\ell\ell)<120$ GeV. The integrated cross-section from averaging the two final states is \begin{equation*}σ_{\text{Z}}^{\ell\ell} = 194.3 \pm 0.9 \pm 3.3 \pm 7.6\text{ pb,}\end{equation*} where the first uncertainty is statistical, the second is due to systematic effects, and the third is due to the luminosity determination. In addition, differential cross-sections are measured as functions of the Z boson rapidity, transverse momentum and the angular variable $ϕ^*_η$.

hep-ex↗

arXiv2016

Evidence for exotic hadron contributions to $Λ_b^0 \to J/ψp π^-$ decays

A full amplitude analysis of $Λ_b^0 \to J/ψp π^-$ decays is performed with a data sample acquired with the LHCb detector from 7 and 8 TeV $pp$ collisions, corresponding to an integrated luminosity of 3 fb$^{-1}$. A significantly better description of the data is achieved when, in addition to the previously observed nucleon excitations $N\to pπ^-$, either the $P_c(4380)^+$ and $P_c(4450)^+\to J/ψp$ states, previously observed in $Λ_b^0 \to J/ψp K^-$ decays, or the $Z_c(4200)^-\to J/ψπ^-$ state, previously reported in $B^0 \to J/ψK^+ π^-$ decays, or all three, are included in the amplitude models. The data support a model containing all three exotic states, with a significance of more than three standard deviations. Within uncertainties, the data are consistent with the $P_c(4380)^+$ and $P_c(4450)^+$ production rates expected from their previous observation taking account of Cabibbo suppression.

hep-ex↗

arXiv2016

Measurement of the $CP$ asymmetry in $B_s^0-\overline{B}{}_s^0$ mixing

The $CP$ asymmetry in the mixing of $B_s^0$ and $\overline{B}{}_s^0$ mesons is measured in proton-proton collision data corresponding to an integrated luminosity of 3.0 fb$^{-1}$, recorded by the LHCb experiment at centre-of-mass energies of 7 and 8 TeV. Semileptonic $B_s^0$ and $\overline{B}{}_s^0$ decays are studied in the inclusive mode $D_s^{\mp} μ^{\pm} ν_μ X$ with the $D_s^{\mp}$ mesons reconstructed in the $K^+ K^- π^{\mp}$ final state. Correcting the observed charge asymmetry for detection and background effects, the $CP$ asymmetry is found to be $a_{\text{sl}}^s = (0.39 \pm 0.26 \pm 0.20) \% $, where the first uncertainty is statistical and the second systematic. This is the most precise measurement of $a_{\text{sl}}^s$ to date. It is consistent with the prediction from the Standard Model and will constrain new models of particle physics.

hep-ex↗

arXiv2016

Observation of $η_{c}(2S) \to p \bar p$ and search for $X(3872) \to p \bar p$ decays

The first observation of the decay $η_{c}(2S) \to p \bar p$ is reported using proton-proton collision data corresponding to an integrated luminosity of $3.0\rm \, fb^{-1}$ recorded by the LHCb experiment at centre-of-mass energies of 7 and 8 TeV. The $η_{c}(2S)$ resonance is produced in the decay $B^{+} \to [c\bar c] K^{+}$. The product of branching fractions normalised to that for the $J/ψ$ intermediate state, ${\cal R}_{η_{c}(2S)}$, is measured to be \begin{align*} {\cal R}_{η_{c}(2S)}\equiv\frac{{\mathcal B}(B^{+} \to η_{c}(2S) K^{+}) \times {\mathcal B}(η_{c}(2S) \to p \bar p)}{{\mathcal B}(B^{+} \to J/ψK^{+}) \times {\mathcal B}(J/ψ\to p \bar p)} =~& (1.58 \pm 0.33 \pm 0.09)\times 10^{-2}, \end{align*} where the first uncertainty is statistical and the second systematic. No signals for the decays $B^{+} \to X(3872) (\to p \bar p) K^{+}$ and $B^{+} \to ψ(3770) (\to p \bar p) K^{+}$ are seen, and the 95\% confidence level upper limits on their relative branching ratios are % found to be ${\cal R}_{X(3872)}<0.25\times10^{-2}$ and ${\cal R}_{ψ(3770))}<0.10$. In addition, the mass differences between the $η_{c}(1S)$ and the $J/ψ$ states, between the $η_{c}(2S)$ and the $ψ(2S)$ states, and the natural width of the $η_{c}(1S)$ are measured as \begin{align*} M_{J/ψ} - M_{η_{c}(1S)} =~& 110.2 \pm 0.5 \pm 0.9 \rm \, MeV, M_{ψ(2S)} -M_{η_{c}(2S)} =~ & 52.5 \pm 1.7 \pm 0.6 \rm \, MeV, Γ_{η_{c}(1S)} =~& 34.0 \pm 1.9 \pm 1.3 \rm \, MeV. \end{align*}

hep-ex↗

arXiv2016

Measurement of forward $W$ and $Z$ boson production in association with jets in proton-proton collisions at $\sqrt{s}=8$ TeV

The production of $W$ and $Z$ bosons in association with jets is studied in the forward region of proton-proton collisions collected at a centre-of-mass energy of 8 TeV by the LHCb experiment, corresponding to an integrated luminosity of 1.98 $\pm$ 0.02 fb$^{-1}$. The $W$ boson is identified using its decay to a muon and a neutrino, while the $Z$ boson is identified through its decay to a muon pair. Total cross-sections are measured and combined into charge ratios, asymmetries, and ratios of $W+$jet and $Z$+jet production cross-sections. Differential measurements are also performed as a function of both boson and jet kinematic variables. All results are in agreement with Standard Model predictions.

hep-ex↗

arXiv2015

A Proposal for a Three Detector Short-Baseline Neutrino Oscillation Program in the Fermilab Booster Neutrino Beam

A Short-Baseline Neutrino (SBN) physics program of three LAr-TPC detectors located along the Booster Neutrino Beam (BNB) at Fermilab is presented. This new SBN Program will deliver a rich and compelling physics opportunity, including the ability to resolve a class of experimental anomalies in neutrino physics and to perform the most sensitive search to date for sterile neutrinos at the eV mass-scale through both appearance and disappearance oscillation channels. Using data sets of 6.6e20 protons on target (P.O.T.) in the LAr1-ND and ICARUS T600 detectors plus 13.2e20 P.O.T. in the MicroBooNE detector, we estimate that a search for muon neutrino to electron neutrino appearance can be performed with ~5 sigma sensitivity for the LSND allowed (99% C.L.) parameter region. In this proposal for the SBN Program, we describe the physics analysis, the conceptual design of the LAr1-ND detector, the design and refurbishment of the T600 detector, the necessary infrastructure required to execute the program, and a possible reconfiguration of the BNB target and horn system to improve its performance for oscillation searches.

physics.ins-det↗

arXiv2012

Development of a custom on-line ultrasonic vapour analyzer/flowmeter for the ATLAS inner detector, with application to gaseous tracking and Cherenkov detectors

Precision sound velocity measurements can simultaneously determine binary gas composition and flow. We have developed an analyzer with custom electronics, currently in use in the ATLAS inner detector, with numerous potential applications. The instrument has demonstrated ~0.3% mixture precision for C3F8/C2F6 mixtures and < 10-4 resolution for N2/C3F8 mixtures. Moderate and high flow versions of the instrument have demonstrated flow resolutions of +/- 2% F.S. for flows up to 250 l.min-1, and +/- 1.9% F.S. for linear flow velocities up to 15 ms-1; the latter flow approaching that expected in the vapour return of the thermosiphon fluorocarbon coolant recirculator being built for the ATLAS silicon tracker.

physics.ins-det↗

arXiv2012

A combined ultrasonic flow meter and binary vapour mixture analyzer for the ATLAS silicon tracker

An upgrade to the ATLAS silicon tracker cooling control system may require a change from C3F8 (octafluoro-propane) evaporative coolant to a blend containing 10-25% of C2F6 (hexafluoro-ethane). Such a change will reduce the evaporation temperature to assure thermal stability following radiation damage accumulated at full LHC luminosity. Central to this upgrade is a new ultrasonic instrument in which sound transit times are continuously measured in opposite directions in flowing gas at known temperature and pressure to deduce the C3F8/C2F6 flow rate and mixture composition. The instrument and its Supervisory, Control and Data Acquisition (SCADA) software are described in this paper. Several geometries for the instrument are in use or under evaluation. An instrument with a pinched axial geometry intended for analysis and measurement of moderate flow rates has demonstrated a mixture resolution of 3.10-3 for C3F8/C2F6 molar mixtures with 20%C2F6, and a flow resolution of 2% of full scale for mass flows up to 30gs-1. In mixtures of widely-differing molecular weight (mw), higher mixture precision is possible: a sensitivity of <5.10-5 to leaks of C3F8 into part of the ATLAS tracker nitrogen envelope (mw difference 160) has been seen. An instrument with an angled sound path geometry has been developed for use at high fluorocarbon mass flow rates of around 1.2 kgs-1 - corresponding to full flow in a new 60kW thermosiphon recirculator under construction for the ATLAS silicon tracker. Extensive computational fluid dynamics studies were performed to determine the preferred geometry (ultrasonic transducer spacing and placement, together with the sound crossing angle with respect to the vapour flow direction). A prototype with 45deg crossing angle has demonstrated a flow resolution of 1.9% of full scale for linear flow velocities up to 15 ms-1. The instrument has many potential applications.

physics.ins-det↗

arXiv2012

A Combine On-Line Acoustic Flowmeter and Fluorocarbon Coolant Mixture Analyzer for The ATLAS Silicon Tracker

An upgrade to the ATLAS silicon tracker cooling control system may require a change from C3F8 (octafluoro-propane) to a blend containing 10-30% of C2F6 (hexafluoro-ethane) to reduce the evaporation temperature and better protect the silicon from cumulative radiation damage with increasing LHC luminosity. Central to this upgrade is a new acoustic instrument for the real-time measurement of the C3F8/C2F6 mixture ratio and flow. The instrument and its Supervisory, Control and Data Acquisition (SCADA) software are described in this paper. The instrument has demonstrated a resolution of 3.10-3 for C3F8/C2F6 mixtures with ~20%C2F6, and flow resolution of 2% of full scale for mass flows up to 30gs-1. In mixtures of widely-differing molecular weight (mw), higher mixture precision is possible: a sensitivity of < 5.10-4 to leaks of C3F8 into the ATLAS pixel detector nitrogen envelope (mw difference 160) has been seen. The instrument has many potential applications, including the analysis of mixtures of hydrocarbons, vapours for semi-conductor manufacture and anaesthesia.

physics.acc-ph↗