arXiv subjects

H. Brown

Publications and source records attributed to H. Brown.

At least 19 recordsLinked to original sources

arXiv2024

Stratospheric aerosol source inversion: Noise, variability, and uncertainty quantification

Stratospheric aerosols play an important role in the earth system and can affect the climate on timescales of months to years. However, estimating the characteristics of partially observed aerosol injections, such as those from volcanic eruptions, is fraught with uncertainties. This article presents a framework for stratospheric aerosol source inversion which accounts for background aerosol noise and earth system internal variability via a Bayesian approximation error approach. We leverage specially designed earth system model simulations using the Energy Exascale Earth System Model (E3SM). A comprehensive framework for data generation, data processing, dimension reduction, operator learning, and Bayesian inversion is presented where each component of the framework is designed to address particular challenges in stratospheric modeling on the global scale. We present numerical results using synthesized observational data to rigorously assess the ability of our approach to estimate aerosol sources and associate uncertainty with those estimates.

cs.LG↗

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.

hep-ex↗

arXiv2015

Measurement of the $η_c (1S)$ production cross-section in proton-proton collisions via the decay $η_c (1S) \rightarrow p \bar{p}$

The production of the $η_c (1S)$ state in proton-proton collisions is probed via its decay to the $p \bar{p}$ final state with the LHCb detector, in the rapidity range $2.0 < y < 4.5$ and in the meson transverse-momentum range $p_T > 6.5$ GeV/c. The cross-section for prompt production of $η_c (1S)$ mesons relative to the prompt $J/ψ$ cross-section is measured, for the first time, to be $σ_{η_c (1S)}/σ_{J/ψ} = 1.74 \pm 0.29 \pm 0.28 \pm 0.18 _{B}$ at a centre-of-mass energy $\sqrt{s} = 7$ TeV using data corresponding to an integrated luminosity of 0.7 fb$^{-1}$, and $σ_{η_c (1S)}/σ_{J/ψ} = 1.60 \pm 0.29 \pm 0.25 \pm 0.17 _{B}$ at $\sqrt{s} = 8$ TeV using 2.0 fb$^{-1}$. The uncertainties quoted are, in order, statistical, systematic, and that on the ratio of branching fractions of the $η_c (1S)$ and $J/ψ$ decays to the $p \bar{p}$ final state. In addition, the inclusive branching fraction of $b$-hadron decays into $η_c (1S)$ mesons is measured, for the first time, to be $B ( b \rightarrow η_c X ) = (4.88 \pm 0.64 \pm 0.29 \pm 0.67 _{B}) \times 10^{-3}$, where the third uncertainty includes also the uncertainty on the $J/ψ$ inclusive branching fraction from $b$-hadron decays. The difference between the $J/ψ$ and $η_c (1S)$ meson masses is determined to be $114.7 \pm 1.5 \pm 0.1$ MeV/c$^2$.

hep-ex↗

arXiv2015

Measurement of $B_c^+$ production in proton-proton collisions at $\sqrt{s}=8$ TeV

Production of $B_c^+$ mesons in proton-proton collisions at a center-of-mass energy of 8 TeV is studied with data corresponding to an integrated luminosity of $2.0~{\rm fb}^{-1}$ recorded by the LHCb experiment. The ratio of production cross-sections times branching fractions between the $B_c^+\to J/ψπ^+$ and $B^+\to J/ψK^+$ decays is measured as a function of transverse momentum and rapidity in the regions $0 < p_{\rm T} < 20~{\rm GeV}/c$ and $2.0 < y < 4.5$. The ratio in this kinematic range is measured to be $(0.683\pm0.018\pm0.009)\%$, where the first uncertainty is statistical and the second systematic.

hep-ex↗

arXiv2015

Search for the lepton flavour violating decay $τ^-\to μ^-μ^+μ^-$

A search for the lepton flavour violating decay $τ^-\to μ^-μ^+μ^-$ is performed with the LHCb experiment. The data sample corresponds to an integrated luminosity of $1.0\mathrm{\,fb}^{-1}$ of proton-proton collisions at a centre-of-mass energy of $7\mathrm{\,Te\kern -0.1em V}$ and $2.0\mathrm{\,fb}^{-1}$ at $8\mathrm{\,Te\kern -0.1em V}$. No evidence is found for a signal, and a limit is set at $90\%$ confidence level on the branching fraction, $\mathcal{B}(τ^-\to μ^-μ^+μ^-) < 4.6 \times 10^{-8}$.

hep-ex↗

arXiv2015

Mu2e Technical Design Report

The Mu2e experiment at Fermilab will search for charged lepton flavor violation via the coherent conversion process mu- N --> e- N with a sensitivity approximately four orders of magnitude better than the current world's best limits for this process. The experiment's sensitivity offers discovery potential over a wide array of new physics models and probes mass scales well beyond the reach of the LHC. We describe herein the preliminary design of the proposed Mu2e experiment. This document was created in partial fulfillment of the requirements necessary to obtain DOE CD-2 approval.

physics.ins-det↗

arXiv2015

LHCb Detector Performance

The LHCb detector is a forward spectrometer at the Large Hadron Collider (LHC) at CERN. The experiment is designed for precision measurements of CP violation and rare decays of beauty and charm hadrons. In this paper the performance of the various LHCb sub-detectors and the trigger system are described, using data taken from 2010 to 2012. It is shown that the design criteria of the experiment have been met. The excellent performance of the detector has allowed the LHCb collaboration to publish a wide range of physics results, demonstrating LHCb's unique role, both as a heavy flavour experiment and as a general purpose detector in the forward region.

hep-ex↗

arXiv2015

Measurement of the track reconstruction efficiency at LHCb

The determination of track reconstruction efficiencies at LHCb using $J/ψ\rightarrowμ^{+}μ^{-}$ decays is presented. Efficiencies above $95\%$ are found for the data taking periods in 2010, 2011, and 2012. The ratio of the track reconstruction efficiency of muons in data and simulation is compatible with unity and measured with an uncertainty of $0.8\,\%$ for data taking in 2010, and at a precision of $0.4\,\%$ for data taking in 2011 and 2012. For hadrons an additional $1.4\,\%$ uncertainty due to material interactions is assumed. This result is crucial for accurate cross section and branching fraction measurements in LHCb.

hep-ex↗

arXiv2015

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

The semileptonic $CP$ asymmetry in $B^0-\overline{B}{}^0$ mixing, $a_{\rm sl}^d$, is measured in proton-proton collision data, corresponding to an integrated luminosity of 3.0 fb$^{-1}$, recorded by the LHCb experiment. Semileptonic $B^0$ decays are reconstructed in the inclusive final states $D^-μ^+$ and $D^{*-}μ^+$, where the $D^-$ meson decays into the $K^+π^-π^-$ final state, and the $D^{*-}$ meson into the $\overline{D}{}^0(\rightarrow K^+π^-)π^-$ final state. The asymmetry between the numbers of $D^{(*)-}μ^+$ and $D^{(*)+}μ^-$ decays is measured as a function of the decay time of the $B^0$ mesons. The $CP$ asymmetry is measured to be $a_{\rm sl}^d = (-0.02 \pm 0.19 \pm 0.30)\%$, where the first uncertainty is statistical and the second systematic. This is the most precise measurement of $a_{\rm sl}^d$ to date and is consistent with the prediction from the Standard Model.

hep-ex↗

arXiv2014

Determination of gamma and -2beta_s from charmless two-body decays of beauty mesons

Using the latest LHCb measurements of time-dependent CP violation in the B^0_s -> K^+K^- decay, a U-spin relation between the decay amplitudes of B^0_s -> K^+K^- and B^0 -> π^+π^- decay processes allows constraints to be placed on the angle gamma of the unitarity triangle and on the B^0_s mixing phase -2β_s. Results from an extended approach, which uses additional inputs on B^0 -> π^0π^0 and B^+ -> π^+π^0 decays from other experiments and exploits isospin symmetry, are also presented. The dependence of the results on the maximum allowed amount of U-spin breaking is studied. At 68% probability, the value γ= ( 63.5 +7.2 -6.7 ) degrees modulo 180 degrees is determined. In an alternative analysis, the value -2β_s = -0.12 +0.14 -0.16 rad is found. In both measurements, the uncertainties due to U-spin breaking effects up to 50% are included.

hep-ex↗

arXiv2014

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

A measurement of the inclusive $W \to μν$ production cross-section using data from $pp$ collisions at a centre-of-mass energy of $\sqrt{s} = 7 {\rm \, TeV}$ is presented. The analysis is based on an integrated luminosity of about $1.0 {\rm \, fb}^{-1}$ recorded with the LHCb detector. Results are reported for muons with a transverse momentum greater than $20 {\rm \, Ge\kern -0.1em V\!/}c$ and pseudorapidity between 2.0 and 4.5. The $W^{+}$ and $W^{-}$ production cross-sections are measured to be $$σ_{W^{+} \to μ^{+}ν} = 861.0 \pm 2.0 \pm 11.2 \pm 14.7 {\rm \, pb},$$ $$σ_{W^{-} \to μ^{-}\overlineν} = 675.8 \pm 1.9 \pm 8.8 \pm 11.6 {\rm \, pb},$$ where the first uncertainty is statistical, the second is systematic and the third is due to the luminosity determination. Cross-section ratios and differential distributions as functions of the muon pseudorapidity are also presented. The ratio of $W^{+}$ to $W^{-}$ cross-sections in the same fiducial kinematic region is determined to be $$\frac{σ_{W^{+} \to μ^{+}ν}}{σ_{W^{-} \to μ^{-}\overlineν}} = 1.274 \pm 0.005 \pm 0.009,$$ where the uncertainties are statistical and systematic, respectively. Results are in good agreement with theoretical predictions at next-to-next-to-leading order in perturbative quantum chromodynamics.

hep-ex↗

arXiv2014

Measurements of $C\!P$ violation in the three-body phase space of charmless $B^{\pm}$ decays

The charmless three-body decay modes $B^{\pm} \rightarrow K^{\pm} π^{+} π^{-}$, $B^{\pm} \rightarrow K^{\pm} K^{+} K^{-}$, $B^{\pm} \rightarrow π^{\pm} K^{+} K^{-}$ and $B^{\pm} \rightarrow π^{\pm} π^{+} π^{-}$ are reconstructed using data, corresponding to an integrated luminosity of 3.0\;$\mbox{\,fb}^{-1}$, collected by the LHCb detector. The inclusive $C\!P$ asymmetries of these modes are measured to be $$ A_{C\!P}(B^{\pm} \rightarrow K^{\pm} π^{+} π^{-})= +0.025 \pm 0.004 \pm 0.004 \pm 0.007 \\ A_{C\!P}(B^{\pm} \rightarrow K^{\pm} K^{+} K^{-}) = -0.036 \pm 0.004 \pm 0.002 \pm 0.007 \\ A_{C\!P}(B^{\pm} \rightarrow π^{\pm} π^{+} π^{-})= +0.058 \pm 0.008 \pm 0.009 \pm 0.007 \\ A_{C\!P}(B^{\pm} \rightarrow π^{\pm} K^{+} K^{-})= -0.123 \pm 0.017 \pm 0.012 \pm 0.007 $$ %% where the first uncertainty is statistical, the second systematic, and the third is due to the $C\!P$ asymmetry of the $B^{\pm} \rightarrow J/ψK^{\pm}$ reference mode. The distributions of these asymmetries are also studied as functions of position in the Dalitz plot and suggest contributions from rescattering and resonance interference processes.

hep-ex↗

arXiv2014

Search for CP violation in $D^0\toπ^-π^+π^0$ decays with the energy test

A search for time-integrated CP violation in the Cabibbo-suppressed decay $D^0\toπ^-π^+π^0$ is performed using for the first time an unbinned model-independent technique known as the energy test. Using proton-proton collision data, corresponding to an integrated luminosity of 2.0 fb$^{-1}$ collected by the LHCb detector at a centre-of-mass energy of $\sqrt{s}$ = 8 TeV, the world's best sensitivity to CP violation in this decay is obtained. The data are found to be consistent with the hypothesis of CP symmetry with a p-value of (2.6 +/- 0.5)%.

hep-ex↗

arXiv2014

Precision measurement of the mass and lifetime of the Xi_b^- baryon

We report on measurements of the mass and lifetime of the Xi_b^- baryon using about 1800 Xi_b^- decays reconstructed in a proton-proton collision data set corresponding to an integrated luminosity of 3.0 fb^{-1} collected by the LHCb experiment. The decays are reconstructed in the Xi_b^- --> Xi_c^0 pi^-, Xi_c^0 --> pK-K-pi+ channel and the mass and lifetime are measured using the Lambda_b^0 --> Lambda_c^+ pi- mode as a reference. We measure M(Xi_b^-) - M(Lambda_b^0) = 178.36 +- 0.46 +- 0.16 MeV/c^2 and tau(Xi_b^-)/tau(Lambda_b^0) = 1.089 +- 0.026 +- 0.011, where the uncertainties are statistical and systematic, respectively. These results lead to a factor of two better precision on the Xi_b^- mass and lifetime compared to previous best measurements, and are consistent with theoretical expectations.

hep-ex↗

arXiv2014

Measurement of the inelastic $pp$ cross-section at a centre-of-mass energy of $\sqrt{s}=7$ TeV

The cross-section for inelastic proton-proton collisions, with at least one prompt long-lived charged particle of transverse momentum $p_{\rm T}>0.2$ GeV/$c$ in the pseudorapidity range $2.0<η<4.5$, is measured by the LHCb experiment at a centre-of-mass energy of $\sqrt{s}=7$ TeV. The cross-section in this kinematic range is determined to be $σ_{\rm inel}^{\rm acc} = 55.0 \pm 2.4$ mb within the spectrometer acceptance with an experimental uncertainty that is dominated by systematic contributions. Extrapolation to the full phase space, using PYTHIA 6, yields $σ_{\rm inel} = 66.9 \pm 2.9 \pm 4.4$ mb, where the first uncertainty is experimental and the second is due to the extrapolation.

hep-ex↗

arXiv2014

Precision luminosity measurements at LHCb

Measuring cross-sections at the LHC requires the luminosity to be determined accurately at each centre-of-mass energy $\sqrt{s}$. In this paper results are reported from the luminosity calibrations carried out at the LHC interaction point 8 with the LHCb detector for $\sqrt{s}$ = 2.76, 7 and 8 TeV (proton-proton collisions) and for $\sqrt{s_{NN}}$ = 5 TeV (proton-lead collisions). Both the "van der Meer scan" and "beam-gas imaging" luminosity calibration methods were employed. It is observed that the beam density profile cannot always be described by a function that is factorizable in the two transverse coordinates. The introduction of a two-dimensional description of the beams improves significantly the consistency of the results. For proton-proton interactions at $\sqrt{s}$ = 8 TeV a relative precision of the luminosity calibration of 1.47% is obtained using van der Meer scans and 1.43% using beam-gas imaging, resulting in a combined precision of 1.12%. Applying the calibration to the full data set determines the luminosity with a precision of 1.16%. This represents the most precise luminosity measurement achieved so far at a bunched-beam hadron collider.

hep-ex↗

arXiv2014

Measurement of CP violation parameters in B0->D K*0 decays

An analysis of B0->D K*0 decays is presented, where D represents an admixture of D0 and D0b mesons reconstructed in four separate final states: K-pi+, pi-K+, K+K- and pi+pi-. The data sample corresponds to 3.0fb-1 of proton-proton collision, collected by the LHCb experiment. Measurements of several observables are performed, including CP asymmetries. The most precise determination is presented of rB(DK*0), the magnitude of the ratio of the amplitudes of the decay B0->D K+ pi- with a b->u or a b->c transition, in a K pi mass region of +/-50 MeV/c2 around the K*(892) mass and for an absolute value of the cosine of the K*0 helicity angle larger than 0.4.

hep-ex↗

arXiv2014

Observation of $B^0_s \to K^{\pm}K^\mp$ and evidence for $B^0_s \to K^{-}π^+$ decays

Measurements of the branching fractions of $B^0_s \to K^{*\pm}K^\mp$ and $B^0_s \to K^{*\pm}π^\mp$ decays are performed using a data sample corresponding to $1.0 \ {\rm fb}^{-1}$ of proton-proton collision data collected with the LHCb detector at a centre-of-mass energy of $7\mathrm{\,TeV}$, where the $K^{*\pm}$ mesons are reconstructed in the $K^0_{\rm S}π^\pm$ final state. The first observation of the $B^0_s \to K^{*\pm}K^\mp$ decay and the first evidence for the $B^0_s \to K^{*-}π^+$ decay are reported with branching fractions \begin{eqnarray} {\cal B}(B^0_s \to K^{*\pm}K^\mp) & = & (12.7\pm1.9\pm1.9) \times 10^{-6}, \\ {\cal B}(B^0_s \to K^{*-}π^+) & = & ~(3.3\pm1.1\pm0.5) \times 10^{-6}, \end{eqnarray} where the first uncertainties are statistical and the second are systematic. In addition, an upper limit of ${\cal B}(B^0 \to K^{*\pm}K^\mp) < 0.4 \ (0.5) \times 10^{-6}$ is set at $90\,% \ (95\,%)$ confidence level.

hep-ex↗