Abstract: A measurement of direct CP violation in the decay $B^{+} \rightarrow K^{+} \pi^{0}$ is reported using a data sample corresponding to an integrated luminosity of 5.4 $\textrm{fb}^{-1}$, collected with the LHCb experiment at a center-of-mass energy of $\sqrt{s}=13$ TeV. The CP asymmetry is measured to be $0.025 \pm 0.015 \pm 0.006 \pm 0.003$, where the uncertainties are statistical, systematic, and due to an external input, respectively. This is the most precise measurement of the CP asymmetry in the decay $B^{+} \rightarrow K^{+} \pi^{0}$ and exceeds the precision on the current world average. This direct CP asymmetry is a key input to studies of a long-standing anomaly in $B$ meson decays, known as the $K\pi$-puzzle. The asymmetry is consistent with the previous measurements of this quantity, confirming and significantly enhancing the observed anomalous difference between the direct CP asymmetries of the $B^{+} \rightarrow K^{+} \pi^{-}$ and $B^{+} \rightarrow K^{+} \pi^{0}$ decays.

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Topics: CP violation (52%)

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5 results found

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Abstract: Based on the flavor structure of four-quark effective operators, we develop an automatic computation program to calculate hadronic two-body $B$ meson decay amplitudes, and apply it to their global analysis in the perturbative QCD (PQCD) approach. Fitting the PQCD factorization formulas for $B\to PP,VP$ decays at leading order in the strong coupling $\alpha_s$ to measured branching ratios and direct CP asymmetries, we determine the Gegenbauer moments in light meson light-cone distribution amplitudes (LCDAs). It is found that most of the fitted Gegenbauer moments of the twist-2 and twist-3 LCDAs for the pseudoscalar meson $P$ ($P=\pi$, $K$) and vector meson $V$ ($V=\rho$, $K^*$) agree with those derived in QCD sum rules. The shape parameter for the $B_s$ meson distribution amplitude and the weak phase $\phi_3(\gamma)=(75.1\pm2.9)^\circ$ consistent with the value in Particle Data Group are also obtained. It is straightforward to extend our analysis to higher orders and higher powers in the PQCD approach, and to the global determination of LCDAs for other hadrons.

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Topics: Vector meson (63%), Pseudoscalar meson (62%), Perturbative QCD (60%) ... read more

4 Citations

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Abstract: We offer a new solution to an old puzzle in the penguin-dominated $B\to\pi K$ decays. The puzzle is the inconsistency among the measurements of the branching ratios and CP asymmetries of the four $B\to\pi K$ decays: $B^+ \to \pi^+ K^0$, $B^+\to \pi^0 K^+$, $B_d^0\to\pi^- K^+$, $B_d^0\to\pi^0 K^0$. We solve the $B\to\pi K$ puzzle by considering the effect of an axion-like particle (ALP) that mixes with the $\pi^0$ and has mass close to the $\pi^0$ mass. We show that the ALP can also explain the anomalies in the electron and muon anomalous magnetic moments.

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Topics: Muon (52%)

3 Citations

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Bhubanjyoti Bhattacharya^{1}, Alakabha Datta^{2}, Danny Marfatia^{3}, Soumitra Nandi^{4} +1 more•Institutions (4)

Abstract: We offer a new solution to an old puzzle in the penguin-dominated $B\ensuremath{\rightarrow}\ensuremath{\pi}K$ decays. The puzzle is the inconsistency among the measurements of the branching ratios and $CP$ asymmetries of the four $B\ensuremath{\rightarrow}\ensuremath{\pi}K$ decays: ${B}^{+}\ensuremath{\rightarrow}{\ensuremath{\pi}}^{+}{K}^{0}$, ${B}^{+}\ensuremath{\rightarrow}{\ensuremath{\pi}}^{0}{K}^{+}$, ${B}_{d}^{0}\ensuremath{\rightarrow}{\ensuremath{\pi}}^{\ensuremath{-}}{K}^{+}$, ${B}_{d}^{0}\ensuremath{\rightarrow}{\ensuremath{\pi}}^{0}{K}^{0}$. We solve the $B\ensuremath{\rightarrow}\ensuremath{\pi}K$ puzzle by considering the effect of an axionlike particle (ALP) that mixes with the ${\ensuremath{\pi}}^{0}$ and has mass close to the ${\ensuremath{\pi}}^{0}$ mass. We show that the ALP can also explain the anomalies in the electron and muon anomalous magnetic moments.

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1 Citations

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Abstract: The Standard Model (SM) predicts that $\Delta A_{\rm CP}$, the difference between the direct CP asymmetries for the modes $B^+\to \pi^0 K^+$ and $B^0\to \pi^- K^+$ that are related by weak isospin, should be close to zero. There has been a recent claim by the LHCb Collaboration that the measured value of $\Delta A_{\rm CP}$ shows an uncomfortable tension with the SM prediction, almost at the $8\sigma$ level. Motivated by this claim, we critically re-examine the data on all the $B\to \pi K$ modes, including the CP asymmetries and CP-averaged branching fractions. From a combined Bayesian analysis with the topological amplitudes and their phases as the free parameters, we find that the best-fit region has a large overlap with the parameter space favoured in the SM, albeit with some enhancement for the electroweak penguin and the colour-suppressed tree amplitudes, consistent with the findings of earlier studies. We find that in this SM-like region, $\Delta A_{\rm CP}$ is more than 5$\sigma$ away from zero and the tension with the global average, as well as the LHCb result, is within $2\sigma$. Thus we conclude that there is not yet enough motivation to go beyond the SM.

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46 results found

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Abstract: G eant 4 is a toolkit for simulating the passage of particles through matter. It includes a complete range of functionality including tracking, geometry, physics models and hits. The physics processes offered cover a comprehensive range, including electromagnetic, hadronic and optical processes, a large set of long-lived particles, materials and elements, over a wide energy range starting, in some cases, from 250 eV and extending in others to the TeV energy range. It has been designed and constructed to expose the physics models utilised, to handle complex geometries, and to enable its easy adaptation for optimal use in different sets of applications. The toolkit is the result of a worldwide collaboration of physicists and software engineers. It has been created exploiting software engineering and object-oriented technology and implemented in the C++ programming language. It has been used in applications in particle physics, nuclear physics, accelerator design, space engineering and medical physics.

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Topics: Applied physics (54%)

16,046 Citations

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Abstract: SUMMARY A generalized form of the cross-validation criterion is applied to the choice and assessment of prediction using the data-analytic concept of a prescription. The examples used to illustrate the application are drawn from the problem areas of univariate estimation, linear regression and analysis of variance.

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Topics: Univariate (59%), Linear regression (57%)

7,009 Citations

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Abstract: The Pythia program can be used to generate high-energy-physics ''events'', i.e. sets of outgoing particles produced in the interactions between two incoming particles. The objective is to provide as accurate as possible a representation of event properties in a wide range of reactions, within and beyond the Standard Model, with emphasis on those where strong interactions play a role, directly or indirectly, and therefore multihadronic final states are produced. The physics is then not understood well enough to give an exact description; instead the program has to be based on a combination of analytical results and various QCD-based models. This physics input is summarized here, for areas such as hard subprocesses, initial- and final-state parton showers, underlying events and beam remnants, fragmentation and decays, and much more. Furthermore, extensive information is provided on all program elements: subroutines and functions, switches and parameters, and particle and process data. This should allow the user to tailor the generation task to the topics of interest.

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Topics: Parton shower (57%), Event generator (51%)

5,971 Citations

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John Allison^{1}, K. Amako^{2}, John Apostolakis^{3}, Henrique Araujo^{4} +69 more•Institutions (17)

Abstract: Geant4 is a software toolkit for the simulation of the passage of particles through matter. It is used by a large number of experiments and projects in a variety of application domains, including high energy physics, astrophysics and space science, medical physics and radiation protection. Its functionality and modeling capabilities continue to be extended, while its performance is enhanced. An overview of recent developments in diverse areas of the toolkit is presented. These include performance optimization for complex setups; improvements for the propagation in fields; new options for event biasing; and additions and improvements in geometry, physics processes and interactive capabilities

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Topics: Event (computing) (50%)

5,363 Citations

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Torbjörn Sjöstrand^{1}, Torbjörn Sjöstrand^{2}, Stephen Mrenna^{3}, Peter Skands^{2} +1 more•Institutions (3)

Abstract: The Pythia program is a standard tool for the generation of high-energy collisions, comprising a coherent set of physics models for the evolution from a few-body hard process to a complex multihadronic nal state. It contains a library of hard processes and models for initial- and nal-state parton showers, multiple partonparton interactions, beam remnants, string fragmentation and particle decays. It also has a set of utilities and interfaces to external programs. While previous versions were written in Fortran, Pythia 8 represents a complete rewrite in C++. The current release is the rst main one after this transition, and does not yet in every respect replace the old code. It does contain some new physics aspects, on the other hand, that should make it an attractive option especially for LHC physics studies.

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Topics: Parton shower (56%)

4,713 Citations