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J. Anderson

Publications and source records attributed to J. Anderson.

At least 199 records · Page 11Linked to original sources
arXiv2015

Measurement of the branching fraction ratio $\mathcal{B}(B_c^+ \rightarrow ψ(2S)π^+)/\mathcal{B}(B_c^+ \rightarrow J/ψπ^+)$

Using $pp$ collision data collected by LHCb at center-of-mass energies $\sqrt{s}$ = 7 TeV and 8 TeV, corresponding to an integrated luminosity of 3 fb$^{-1}$, the ratio of the branching fraction of the $B_c^+ \rightarrow ψ(2S)π^+$ decay relative to that of the $B_c^+ \rightarrow J/ψπ^+$ decay is measured to be 0.268 $\pm$ 0.032 (stat) $\pm$ 0.007 (syst) $\pm$ 0.006 (BF). The first uncertainty is statistical, the second is systematic, and the third is due to the uncertainties on the branching fractions of the $J/ψ\rightarrow μ^+μ^-$ and $ψ(2S) \rightarrow μ^+μ^-$ decays. This measurement is consistent with the previous LHCb result, and the statistical uncertainty is halved.

hep-ex↗
arXiv2015

Measurement of the time-integrated $CP$ asymmetry in $D^0 \to K^0_S K^0_S$ decays

The time-integrated $CP$ asymmetry in the decay $D^0 \to K^0_S K^0_S$ is measured using $3 fb^{-1}$ of proton-proton collision data collected by the LHCb experiment at centre-of-mass energies of 7 and 8 TeV. The flavour of the $D^0$ meson is determined by use of the decay $D^{*+} \to D^0 π^+$ and its charge conjugate mode. The result is \[ {\cal A}_{CP} = -0.029 \pm 0.052 \pm 0.022, \] where the first uncertainty is statistical and the second systematic. The result is consistent with Standard Model expectations and improves the uncertainty with respect to the only previous measurement of this quantity by more than a factor of three.

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arXiv2015

Search for hidden-sector bosons in $B^0 \!\to K^{*0}μ^+μ^-$ decays

A search is presented for hidden-sector bosons, $χ$, produced in the decay ${B^0\!\to K^*(892)^0χ}$, with $K^*(892)^0\!\to K^{+}π^{-}$ and $χ\!\toμ^+μ^-$. The search is performed using $pp$-collision data corresponding to 3.0 fb$^{-1}$ collected with the LHCb detector. No significant signal is observed in the accessible mass range $214 \leq m(χ) \leq 4350$ MeV, and upper limits are placed on the branching fraction product $\mathcal{B}(B^0\!\to K^*(892)^0χ)\times\mathcal{B}(χ\!\toμ^+μ^-)$ as a function of the mass and lifetime of the $χ$ boson. These limits are of the order of $10^{-9}$ for $χ$ lifetimes less than 100 ps over most of the $m(χ)$ range, and place the most stringent constraints to date on many theories that predict the existence of additional low-mass bosons.

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arXiv2015

Measurement of the $B_s^0 \to ϕϕ$ branching fraction and search for the decay $B^0 \to ϕϕ$

Using a dataset 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 $B_s^0 \to ϕϕ$ branching fraction is measured to be \[ \mathcal{B}(B_s^0 \to ϕϕ) = ( 1.84 \pm 0.05 (\text{stat}) \pm 0.07 (\text{syst}) \pm 0.11 (f_s/f_d) \pm 0.12 (\text{norm}) ) \times 10^{-5}, \] where $f_s/f_d$ represents the ratio of the $B_s^0$ to $B^0$ production cross-sections, and the $B^0 \to ϕK^*(892)^0$ decay mode is used for normalization. This is the most precise measurement of this branching fraction to date, representing a factor five reduction in the statistical uncertainty compared with the previous best measurement. A search for the decay $B^0 \to ϕϕ$ is also made. No signal is observed, and an upper limit on the branching fraction is set as \[ \mathcal{B}(B^0 \to ϕϕ) < 2.8 \times 10^{-8} \] at 90% confidence level. This is a factor of seven improvement compared to the previous best limit.

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arXiv2015

$B$ flavour tagging using charm decays at the LHCb experiment

An algorithm is described for tagging the flavour content at production of neutral $B$ mesons in the LHCb experiment. The algorithm exploits the correlation of the flavour of a $B$ meson with the charge of a reconstructed secondary charm hadron from the decay of the other $b$ hadron produced in the proton-proton collision. Charm hadron candidates are identified in a number of fully or partially reconstructed Cabibbo-favoured decay modes. The algorithm is calibrated on the self-tagged decay modes $B^+ \to J/ψ\, K^+$ and $B^0 \to J/ψ\, K^{*0}$ using $3.0\mathrm{\,fb}^{-1}$ of data collected by the LHCb experiment at $pp$ centre-of-mass energies of $7\mathrm{\,TeV}$ and $8\mathrm{\,TeV}$. Its tagging power on these samples of $B \to J/ψ\, X$ decays is $(0.30 \pm 0.01 \pm 0.01) \%$.

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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

The Hubble Space Telescope UV Legacy Survey of Galactic Globular Clusters. V. Constraints on Formation Scenarios

We build on the evidence provided by our Legacy Survey of Galactic globular clusters (GC) to submit to a crucial test four scenarios currently entertained for the formation of multiple stellar generations in GCs. The observational constraints on multiple generations to be fulfilled are manifold, including GC specificity, ubiquity, variety, predominance, discreteness, supernova avoidance, p-capture processing, helium enrichment and mass budget. We argue that scenarios appealing to supermassive stars, fast rotating massive stars and massive interactive binaries violate in an irreparable fashion two or more among such constraints. Also the scenario appealing to AGB stars as producers of the material for next generation stars encounters severe difficulties, specifically concerning the mass budget problem and the detailed chemical composition of second generation stars. We qualitatively explore ways possibly allowing one to save the AGB scenario, specifically appealing to a possible revision of the cross section of a critical reaction rate destroying sodium, or alternatively by a more extensive exploration of the vast parameter space controlling the evolutionary behavior of AGB stellar models. Still, we cannot ensure success for these efforts and totally new scenarios may have to be invented to understand how GCs formed in the early Universe.

astro-ph.GA↗
arXiv2015

Angular analysis and differential branching fraction of the decay $B^0_s\toϕμ^+μ^-$

An angular analysis and a measurement of the differential branching fraction of the decay $B^0_s\toϕμ^+μ^-$ are presented, using data corresponding to an integrated luminosity of $3.0\, {\rm fb^{-1}}$ of $pp$ collisions recorded by the LHCb experiment at $\sqrt{s} = 7$ and $8\, {\rm TeV}$. Measurements are reported as a function of $q^{2}$, the square of the dimuon invariant mass and results of the angular analysis are found to be consistent with the Standard Model. In the range $1<q^2<6\, {\rm GeV}^{2}/c^{4}$, where precise theoretical calculations are available, the differential branching fraction is found to be more than $3\,σ$ below the Standard Model predictions.

hep-ex↗
arXiv2015

Study of $W$ boson production in association with beauty and charm

The associated production of a $W$ boson with a jet originating from either a light parton or heavy-flavor quark is studied in the forward region using proton-proton collisions. The analysis uses data corresponding to integrated luminosities of 1.0 and $2.0\,{\rm fb}^{-1}$ collected with the LHCb detector at center-of-mass energies of 7 and 8 TeV, respectively. The $W$ bosons are reconstructed using the $W\toμν$ decay and muons with a transverse momentum, $p_{\rm T}$, larger than 20 GeV in the pseudorapidity range $2.0<η<4.5$. The partons are reconstructed as jets with $p_{\rm T} > 20$ GeV and $2.2 < η< 4.2$. The sum of the muon and jet momenta must satisfy $p_{\rm T} > 20$ GeV. The fraction of $W+$jet events that originate from beauty and charm quarks is measured, along with the charge asymmetries of the $W\!+\!b$ and $W\!+\!c$ production cross-sections. The ratio of the $W+$jet to $Z+$jet production cross-sections is also measured using the $Z\toμμ$ decay. All results are in agreement with Standard Model predictions.

hep-ex↗
arXiv2015

First observation of top quark production in the forward region

Top quark production in the forward region in proton-proton collisions is observed for the first time. The $W\!+\!b$ final state with $W\toμν$ is reconstructed using muons with a transverse momentum, $p_{\rm T}$, larger than 25 GeV in the pseudorapidity range $2.0<η<4.5$. The $b$ jets are required to have $50 < p_{\rm T} < 100$ GeV and $2.2 < η< 4.2$, while the transverse component of the sum of the muon and $b$-jet momenta must satisfy $p_{\rm T} > 20$ GeV. The results are based on data corresponding to integrated luminosities of 1.0 and $2.0$ fb$^{-1}$ collected at center-of-mass energies of 7 and 8 TeV by LHCb. The inclusive top quark production cross-sections in the fiducial region are $σ({\rm top})[7\rm{TeV}] = 239\pm53({\rm stat})\pm33({\rm syst})\pm24({\rm theory})\,{\rm fb}$ and $σ({\rm top})[8\rm{TeV}] = 289\pm43({\rm stat})\pm40({\rm syst})\pm29({\rm theory})\,{\rm fb}$. These results, along with the observed differential yields and charge asymmetries, are in agreement with next-to-leading order Standard Model predictions.

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 ratio of branching fractions $\mathcal{B}(\overline{B}^0 \to D^{*+}τ^{-}\overlineν_τ)/\mathcal{B}(\overline{B}^0 \to D^{*+}μ^{-}\overlineν_μ)$

The branching fraction ratio $\mathcal{R}(D^{*}) \equiv \mathcal{B}(\overline{B}^0 \to D^{*+}τ^{-}\overlineν_τ)/\mathcal{B}(\overline{B}^0 \to D^{*+}μ^{-}\overlineν_μ)$ is measured using a sample of proton-proton collision data corresponding to 3.0\invfb of integrated luminosity recorded by the LHCb experiment during 2011 and 2012. The tau lepton is identified in the decay mode $τ^{-} \to μ^{-}\overlineν_μν_τ$. The semitauonic decay is sensitive to contributions from non-Standard-Model particles that preferentially couple to the third generation of fermions, in particular Higgs-like charged scalars. A multidimensional fit to kinematic distributions of the candidate $\overline{B}^0$ decays gives $\mathcal{R}(D^{*}) = 0.336 \pm 0.027(stat) \pm 0.030 (syst)$. This result, which is the first measurement of this quantity at a hadron collider, is 2.1 standard deviations larger than the value expected from lepton universality in the Standard Model.

hep-ex↗
arXiv2015

Quantum numbers of the $X(3872)$ state and orbital angular momentum in its $ρ^0 Jψ$ decay

Angular correlations in $B^+\to X(3872) K^+$ decays, with $X(3872)\to ρ^0 J/ψ$, $ρ^0\toπ^+π^-$ and $J/ψ\toμ^+μ^-$, are used to measure orbital angular momentum contributions and to determine the $J^{PC}$ value of the $X(3872)$ meson. The data correspond to an integrated luminosity of 3.0 fb$^{-1}$ of proton-proton collisions collected with the LHCb detector. This determination, for the first time performed without assuming a value for the orbital angular momentum, confirms the quantum numbers to be $J^{PC}=1^{++}$. The $X(3872)$ is found to decay predominantly through S wave and an upper limit of $4\%$ at $95\%$ C.L. is set on the fraction of D wave.

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arXiv2015

The LOFAR Multifrequency Snapshot Sky Survey (MSSS) I. Survey description and first results

We present the Multifrequency Snapshot Sky Survey (MSSS), the first northern-sky LOFAR imaging survey. In this introductory paper, we first describe in detail the motivation and design of the survey. Compared to previous radio surveys, MSSS is exceptional due to its intrinsic multifrequency nature providing information about the spectral properties of the detected sources over more than two octaves (from 30 to 160 MHz). The broadband frequency coverage, together with the fast survey speed generated by LOFAR's multibeaming capabilities, make MSSS the first survey of the sort anticipated to be carried out with the forthcoming Square Kilometre Array (SKA). Two of the sixteen frequency bands included in the survey were chosen to exactly overlap the frequency coverage of large-area Very Large Array (VLA) and Giant Metrewave Radio Telescope (GMRT) surveys at 74 MHz and 151 MHz respectively. The survey performance is illustrated within the "MSSS Verification Field" (MVF), a region of 100 square degrees centered at J2000 (RA,Dec)=(15h,69deg). The MSSS results from the MVF are compared with previous radio survey catalogs. We assess the flux and astrometric uncertainties in the catalog, as well as the completeness and reliability considering our source finding strategy. We determine the 90% completeness levels within the MVF to be 100 mJy at 135 MHz with 108" resolution, and 550 mJy at 50 MHz with 166" resolution. Images and catalogs for the full survey, expected to contain 150,000-200,000 sources, will be released to a public web server. We outline the plans for the ongoing production of the final survey products, and the ultimate public release of images and source catalogs.

astro-ph.IM↗
arXiv2015

First measurement of the differential branching fraction and $C\!P$ asymmetry of the $B^\pm\toπ^\pmμ^+μ^-$ decay

The differential branching fraction with respect to the dimuon invariant mass squared, and the $C\!P$ asymmetry of the $B^\pm\toπ^\pmμ^+μ^-$ decay are measured for the first time. The CKM matrix elements $|V_{td}|$ and $|V_{ts}|$, and the ratio $|V_{td}/V_{ts}|$ are determined. The analysis is performed using proton-proton collision data corresponding to an integrated luminosity of 3.0 fb$^{-1}$, collected by the LHCb experiment at centre-of-mass energies of 7 and 8 TeV. The total branching fraction and $C\!P$ asymmetry of $B^\pm\toπ^\pmμ^+μ^-$ decays are measured to be \begin{eqnarray} \mathcal{B}(B^\pm\toπ^\pmμ^+μ^-) &=& (1.83 \pm 0.24 \pm 0.05) \times 10^{-8}\,\,\,\mathrm{and} \nonumber\\ \mathcal{A}_{C\!P}(B^\pm\toπ^\pmμ^+μ^-) &=& -0.11 \pm 0.12 \pm 0.01\,, \nonumber \end{eqnarray} where the first uncertainties are statistical and the second are systematic. These are the most precise measurements of these observables to date, and they are compatible with the predictions of the Standard Model.

hep-ex↗
arXiv2015

Discovery of near-ultraviolet counterparts to millisecond pulsars in the globular cluster 47 Tucanae

We report the discovery of the likely white dwarf companions to radio millisecond pulsars 47 Tuc Q and 47 Tuc S in the globular cluster 47 Tucanae. These blue stars were found in near-ultraviolet images from the Hubble Space Telescope for which we derived accurate absolute astrometry, and are located at positions consistent with the radio coordinates to within 0.016 arcsec (0.2sigma). We present near-ultraviolet and optical colours for the previously identified companion to millisecond pulsar 47 Tuc U, and we unambiguously confirm the tentative prior identifications of the optical counterparts to 47 Tuc T and 47 Tuc Y. For the latter, we present its radio-timing solution for the first time. We find that all five near-ultraviolet counterparts have U300-B390 colours that are consistent with He white dwarf cooling models for masses ~0.16-0.3 Msun and cooling ages within ~0.1-6 Gyr. The Ha-R625 colours of 47 Tuc U and 47 Tuc T indicate the presence of a strong Ha absorption line, as expected for white dwarfs with an H envelope.

astro-ph.SR↗
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.

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