arXiv subjects

A. Badalov

Publications and source records attributed to A. Badalov.

At least 271 records · Page 15Linked to original sources

arXiv2014

Measurement of polarization amplitudes and CP asymmetries in $B^0 \to ϕK^*(892)^0$

An angular analysis of the decay $B^0 \to ϕK^*(892)^0$ is reported based on a $pp$ collision data sample, corresponding to an integrated luminosity of 1.0 fb$^{-1}$, collected at a centre-of-mass energy of $\sqrt{s} = 7$ TeV with the LHCb detector. The P-wave amplitudes and phases are measured with a greater precision than by previous experiments, and confirm about equal amounts of longitudinal and transverse polarization. The S-wave $K^+ π^-$ and $K^+K^-$ contributions are taken into account and found to be significant. A comparison of the $B^0 \to ϕK^*(892)^0$ and $\bar{B}^0 \to ϕ\bar{K}^*(892)^0$ results shows no evidence for direct CP violation in the rate asymmetry, in the triple-product asymmetries or in the polarization amplitudes and phases.

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arXiv2014

Measurement of $ψ(2S)$ polarisation in $pp$ collisions at $\sqrt{s}=7$ TeV

The polarisation of prompt $ψ(2S)$ mesons is measured by performing an angular analysis of $ψ(2S)\rightarrow μ^{+} μ^{-}$ decays using proton-proton collision data, corresponding to an integrated luminosity of 1.0 fb$^{-1}$, collected by the LHCb detector at a centre-of-mass energy of 7 TeV. The polarisation is measured in bins of transverse momentum $p_\mathrm{T}$ and rapidity $y$ in the kinematic region $3.5<p_\mathrm{T}<15$ GeV$/c$ and $2.0<y<4.5$, and is compared to theoretical models. No significant polarisation is observed.

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arXiv2014

Search for Majorana neutrinos in $B^- \to π^+μ^-μ^-$ decays

A search for heavy Majorana neutrinos produced in the $B^- \to π^+μ^-μ^-$ decay mode is performed using 3 fb$^{-1}$ of integrated luminosity collected with the LHCb detector in $pp$ collisions at center-of-mass energies of 7 TeV and 8 TeV at the LHC. Neutrinos with masses in the range 250-5000 MeV and lifetimes from zero to 1000 ps are probed. In the absence of a signal, upper limits are set on the branching fraction ${\cal{B}}(B^- \to π^+μ^-μ^-)$ as functions of neutrino mass and lifetime. These limits are on the order of $10^{-9}$ for short neutrino lifetimes of 1 ps or less. Limits are also set on the coupling between the muon and a possible fourth-generation neutrino.

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arXiv2014

Measurement of resonant and $CP$ components in $\overline{B}_s^0\rightarrow J/ψπ^+π^-$ decays

The resonant structure of the decay $\overline{B}_s^0\to J/ψπ^+π^-$ is studied using data corresponding to 3 fb$^{-1}$ of integrated luminosity from $pp$ collisions by the LHC and collected by the LHCb detector. Five interfering $π^+π^-$ states are required to describe the decay: $f_0(980),f_0(1500),f_0(1790),f_2(1270)$, and $f_2^{\prime}(1525)$. An alternative model including these states and a non-resonant $J/ψπ^+π^-$ component also provides a good description of the data. Based on the different transversity components measured for the spin-2 intermediate states, the final state is found to be compatible with being entirely $CP$-odd. The $CP$-even part is found to be $<2.3$% at 95% confidence level. The $f_0(500)$ state is not observed, allowing a limit to be set on the absolute value of the mixing angle with the $f_0(980)$ of $<7.7^{\circ}$ at 90% confidence level, consistent with a tetraquark interpretation of the $f_0(980)$ substructure.

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arXiv2014

Measurements of indirect CP asymmetries in $D^0\to K^-K^+$ and $D^0\toπ^-π^+$ decays

A study of indirect CP violation in $D^0$ mesons through the determination of the parameter $A_Γ$ is presented using a data sample of $pp$ collisions, corresponding to an integrated luminosity of 1.0 fb$^{-1}$, collected with the LHCb detector and recorded at the centre-of-mass energy of 7 TeV at the LHC. The parameter $A_Γ$ is the asymmetry of the effective lifetimes measured in decays of $D^0$ and $\bar{D}^0$ mesons to the CP eigenstates $K^-K^+$ and $π^-π^+$. Fits to the data sample yield $A_Γ(KK)=(-0.35\pm0.62\pm0.12)\times 10^{-3}$ and $A_Γ(ππ)=(0.33\pm1.06\pm0.14)\times 10^{-3}$, where the first uncertainties are statistical and the second systematic. The results represent the world's best measurements of these quantities. They show no difference in $A_Γ$ between the two final states and no indication of CP violation.

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arXiv2014

Measurement of the $B_c^+$ meson lifetime using $B_c^+ \to J\!/\!ψμ^+ ν_μ X$ decays

The lifetime of the $B_c^+$ meson is measured using semileptonic decays having a $J\!/\!ψ$ meson and a muon in the final state. The data, corresponding to an integrated luminosity of $2\mathrm{~fb^{-1}}$, are collected by the LHCb detector in $pp$ collisions at a centre-of-mass energy of $8\,\mathrm{TeV}$. The measured lifetime is $$τ= 509 \pm 8 \pm 12 \mathrm{~fs},$$ where the first uncertainty is statistical and the second is systematic.

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arXiv2014

Updated measurements of exclusive $J/ψ$ and $ψ(2S)$ production cross-sections in $pp$ collisions at $\sqrt{s}=7$ TeV

The differential cross-section as a function of rapidity has been measured for the exclusive production of $J/ψ$ and $ψ(2S)$ mesons in proton-proton collisions at $\sqrt{s}=7$ TeV, using data collected by the LHCb experiment, corresponding to an integrated luminosity of 930 pb$^{-1}$. The cross-sections times branching fractions to two muons having pseudorapidities between 2.0 and 4.5 are measured to be $$\begin{array}{rl} σ_{pp\rightarrow J/ψ\rightarrow{μ^+}{μ^-}}(2.0<η_{μ^\pm }<4.5)=&291\pm 7\pm19 {\rm \ pb},\\ σ_{pp\rightarrowψ(2S)\rightarrow{μ^+}{μ^-}}(2.0<η_{μ^\pm}<4.5)=&6.5\pm 0.9\pm 0.4 {\rm \ pb},\end{array}$$ where the first uncertainty is statistical and the second is systematic. The measurements agree with next-to-leading order QCD predictions as well as with models that include saturation effects.

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arXiv2014

Observation of B^0_(s) -> J/ψf_1(1285) decays and measurement of the f_1(1285) mixing angle

Decays of Bs and B0 mesons into J/ψπ+π-π+π- final states, produced in pp collisions at the LHC, are investigated using data corresponding to an integrated luminosity of 3/fb collected with the LHCb detector. B^0_(s) -> Jψf_1(1285) decays are seen for the first time, and the branching fractions are measured. Using these rates, the f_1(1285) mixing angle between strange and non-strange components of its wave function in the q-qbar structure model is determined to be \pm (24.0^{+3.1+0.6}_{-2.6-0.8}) degrees. Implications on the possible tetraquark nature of the f_1(1285) are discussed.

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arXiv2014

Observation of associated production of a $Z$ boson with a $D$ meson in the~forward region

A search for associated production of a $Z$ boson with an open charm meson is presented using a data sample, corresponding to an integrated luminosity of $1.0\,\mathrm{fb}^{-`}$ of proton--proton collisions at a centre-of-mass energy of 7\,TeV, collected by the LHCb experiment. %% Seven candidate events for associated production of a $Z$ boson with a $D^0$ meson and four candidate events for a $Z$ boson with a $D^+$ meson are observed with a combined significance of 5.1standard deviations. The production cross-sections in the forward region are measured to be $$σ_{Z\rightarrowμ^+μ^-\!,D^0} = 2.50\pm1.12\pm0.22pb$$ $$σ_{Z\rightarrowμ^+μ^-\!,D^+} = 0.44\pm0.23\pm0.03pb,$$ where the first uncertainty is statistical and the second systematic.

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arXiv2014

Search for CP violation in the decay $D^+ \to π^-π^+π^+$

A search for CP violation in the phase space of the decay $D^+\toπ^-π^+π^+$ is reported using $pp$ collision data, corresponding to an integrated luminosity of 1.0 fb$^{-1}$, collected by the LHCb experiment at a centre-of-mass energy of 7 TeV. The Dalitz plot distributions for $3.1\times 10^6$ $D^+$ and $D^-$ candidates are compared with binned and unbinned model-independent techniques. No evidence for CP violation is found.

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arXiv2014

Search for the doubly charmed baryon Xi_cc^+

A search for the doubly charmed baryon Xi_cc^+ in the decay mode Xi_cc^+ -> Lambda_c^+ K^- pi^+ is performed with a data sample, corresponding to an integrated luminosity of 0.65/fb, of pp collisions recorded at a centre-of-mass energy of 7 TeV. No significant signal is found in the mass range 3300-3800 MeV/c^2. Upper limits at the 95% confidence level on the ratio of the Xi_cc^+ production cross-section times branching fraction to that of the Lambda_c^+, R, are given as a function of the Xi_cc^+ mass and lifetime. The largest upper limits range from R < 1.5 x 10^-2 for a lifetime of 100 fs to R < 3.9 x 10^-4 for a lifetime of 400 fs.

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arXiv2013

Search for the decay D0 to π+ π- μ+ μ-

A search for the D0 to π+ π- μ+ μ- decay, where the muon pair does not originate from a resonance, is performed using proton-proton collision data corresponding to an integrated luminosity of 1.0 fb-1 recorded by the LHCb experiment at a centre-of-mass energy of 7 TeV. No signal is observed and an upper limit on the relative branching fraction with respect to the resonant decay mode D0 to π+ π- ϕ(to μ+ μ-), under the assumption of a phase-space model, is found to be B(D0 to π+ π- mu+ mu-)/B(D0 to π+ π- ϕ(to μ+ μ-)) < 0.96 at the 90% confidence level. The upper limit on the absolute branching fraction is evaluated to be B(D0 to π+ π- μ+ μ-) < 5.5 x 10-7 at 90% confidence level. This is the most stringent to date.

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arXiv2013

Measurement of the charge asymmetry in $B^{\pm}\rightarrow ϕK^{\pm}$ and search for $B^{\pm}\rightarrow ϕπ^{\pm}$ decays

The \CP-violating charge asymmetry in $B^{\pm}\rightarrow ϕK^{\pm}$ decays is measured in a sample of $pp$ collisions at 7 TeV centre-of-mass energy, corresponding to an integrated luminosity of 1.0 fb$^{-1}$ collected by the LHCb experiment. The result is $\mathcal{A}_{CP}(B^{\pm}\rightarrow ϕK^{\pm}) = \rm 0.022\pm 0.021 \pm 0.009$, where the first uncertainty is statistical and the second systematic. In addition, a search for the $B^{\pm}\rightarrow ϕπ^{\pm}$ decay mode is performed, using the $B^{\pm}\rightarrow ϕK^{\pm}$ decay rate for normalization. An upper limit on the branching fraction $\mathcal{B}(B^{\pm}\rightarrow ϕπ^{\pm})< 1.5\times 10^{-7}$ is set at 90% confidence level.

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arXiv2013

Study of forward Z+jet production in pp collisions at $\sqrt{s} = 7$ TeV

A measurement of the $Z(\rightarrowμ^+μ^-)$+jet production cross-section in $pp$ collisions at a centre-of-mass energy $\sqrt{s} = 7$ TeV is presented. The analysis is based on an integrated luminosity of $1.0\,\text{fb}^{-1}$ recorded by the LHCb experiment. Results are shown with two jet transverse momentum thresholds, 10 and 20 GeV, for both the overall cross-section within the fiducial volume, and for six differential cross-section measurements. The fiducial volume requires that both the jet and the muons from the Z boson decay are produced in the forward direction ($2.0<η<4.5$). The results show good agreement with theoretical predictions at the second-order expansion in the coupling of the strong interaction.

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arXiv2013

Measurement of the $\bar{B}_s^0\to D_s^-D_s^+$ and $\bar{B}_s^0\to D^-D_s^+$ effective lifetimes

The first measurement of the effective lifetime of the $\bar{B}_s^0$ meson in the decay $\bar{B}_s^0\to D_s^-D_s^+$ is reported using a proton-proton collision dataset, corresponding to an integrated luminosity of 3 fb$^{-1}$, collected by the LHCb experiment. The measured value of the $\bar{B}_s^0\to D_s^-D_s^+$ effective lifetime is $1.379\pm0.026\pm0.017$ ps, where the uncertainties are statistical and systematic, respectively. This lifetime translates into a measurement of the decay width of the light $\bar{B}_s^0$ mass eigenstate of Γ_L$=0.725\pm0.014\pm0.009$ ps$^{-1}$. The $\bar{B}_s^0$ lifetime is also measured using the flavor-specific $\bar{B}_s^0\to D^-D_s^+$ decay to be $1.52\pm0.15\pm0.01 {\rm ps}$.

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arXiv2013

Studies of beauty baryon decays to $D^0 p h^-$ and $Λ_c^+ h^-$ final states

Decays of beauty baryons to the $D^0 p h^-$ and $Λ_c^+ h^-$ final states (where $h$ indicates a pion or a kaon) are studied using a data sample of $pp$ collisions, corresponding to an integrated luminosity of 1.0 fb$^{-1}$, collected by the LHCb detector. The Cabibbo-suppressed decays $Λ_b^0\to D^0 p K^-$ and $Λ_b^0\to Λ_c^+ K^-$ are observed and their branching fractions are measured with respect to the decays $Λ_b^0\to D^0 p π^-$ and $Λ_b^0\to Λ_c^+ π^-$. In addition, the first observation is reported of the decay of the neutral beauty-strange baryon $Ξ_b^0$ to the $D^0 p K^-$ final state, and a measurement of the $Ξ_b^0$ mass is performed. Evidence of the $Ξ_b^0\to Λ_c^+ K^-$ decay is also reported.

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arXiv2013

Measurement of CP violation in the phase space of $B^{\pm} \rightarrow K^{+} K^{-} π^{\pm}$ and $B^{\pm} \rightarrow π^{+} π^{-} π^{\pm}$ decays

The charmless decays $B^{\pm} \rightarrow K^{+}K^{-}π^{\pm}$ and $B^{\pm} \rightarrow π^{+}π^{-}π^{\pm}$ are reconstructed in a data set, corresponding to an integrated luminosity of 1.0 fb$^{-1}$ of pp collisions at a center-of-mass energy of 7 TeV, collected by LHCb in 2011. The inclusive charge asymmetries of these modes are measured to be $A_{CP}(B^{\pm} \rightarrow K^{+}K^{-}π^{\pm}) =-0.141 \pm 0.040 (stat) \pm 0.018 (syst) \pm 0.007 (J/ψK^{\pm})$ and $A_{CP}(B^{\pm} \rightarrow π^{+}π^{-}π^{\pm}) = 0.117 \pm 0.021 (stat) \pm 0.009 (syst) \pm 0.007 (J/ψK^{\pm})$, where the third uncertainty is due to the CP asymmetry of the $B^{\pm} \rightarrow J/ψK^{\pm}$ reference mode. In addition to the inclusive CP asymmetries, larger asymmetries are observed in localized regions of phase space.

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arXiv2013

Measurement of the $B^0_s \to μ^+ μ^-$ branching fraction and search for $B^0 \to μ^+ μ^-$ decays at the LHCb experiment

A search for the rare decays $B^0_s \toμ^+μ^-$ and $B^0 \toμ^+μ^-$ is performed at the LHCb experiment. The data analysed correspond to an integrated luminosity of 1 fb$^{-1}$ of $pp$ collisions at a centre-of-mass energy of 7 TeV and 2 fb$^{-1}$ at 8 TeV. An excess of $B^0_s \toμ^+μ^-$ signal candidates with respect to the background expectation is seen with a significance of 4.0 standard deviations. A time-integrated branching fraction of ${\cal B}(B^0_s \toμ^+μ^-) = (2.9^{+1.1}_{-1.0})\times 10^{-9}$ is obtained and an upper limit of ${\cal B}(B^0 \toμ^+μ^-) < 7.4\times 10^{-10}$ at 95% confidence level is set. These results are consistent with the Standard Model expectations.

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