A search for the decay K0S→μ+μ− is performed, based on a data sample of proton-proton collisions corresponding to an integrated luminosity of 3 fb−1, collected by the LHCb experiment at centre-of-mass energies of 7 and 8 TeV. The observed yield is consistent with the background-only hypothesis, yielding a limit on the branching fraction of B(K0S→μ+μ−)<0.8 (1.0)×10−9 at 90% (95%) confidence level. This result improves the previous upper limit on the branching fraction by an order of magnitude.
A search for CP violation in D± → η′ π± and Ds± → η′ π± decays is performed using proton-proton collision data, corresponding to an inte- grated luminosity of 3fb−1, recorded by the LHCb experiment at centre-of- mass energies of 7 and 8 TeV. The measured CP -violating charge asym- metries are ACP(D± → η′π±) = (−0.61 ± 0.72 ± 0.53 ± 0.12)% and ACP (Ds± → η′π±) = (−0.82 ± 0.36 ± 0.22 ± 0.27)%, where the first uncertain- ties are statistical, the second systematic, and the third are the uncertainties on the ACP (D± → KS0π±) and ACP (Ds± → φπ±) measurements used for calibration. The results represent the most precise measurements of these asymmetries to date.
A search for the rare decays Bs0→μ+μ- and B0→μ+μ- is performed at the LHCb experiment using data collected in pp collisions corresponding to a total integrated luminosity of 4.4 fb-1. An excess of Bs0→μ+μ- decays is observed with a significance of 7.8 standard deviations, representing the first observation of this decay in a single experiment. The branching fraction is measured to be B(Bs0→μ+μ-)=(3.0±0.6-0.2+0.3)×10-9, where the first uncertainty is statistical and the second systematic. The first measurement of the Bs0→μ+μ- effective lifetime, τ(Bs0→μ+μ-)=2.04±0.44±0.05 ps, is reported. No significant excess of B0→μ+μ- decays is found, and a 95% confidence level upper limit, B(B0→μ+μ-)<3.4×10-10, is determined. All results are in agreement with the standard model expectations.
The CRAYFIS experiment proposes to use privately owned mobile phones as a ground detector array for Ultra High Energy Cosmic Rays. Upon interacting with Earth’s atmosphere, these events produce extensive particle showers which can be detected by cameras on mobile phones. A typical shower contains minimally-ionizing particles such as muons. As these particles interact with CMOS image sensors, they may leave tracks of faintly-activated pixels that are sometimes hard to distinguish from random detector noise. Triggers that rely on the presence of very bright pixels within an image frame are not efficient in this case. We present a trigger algorithm based on Convolutional Neural Networks which selects images containing such tracks and are evaluated in a lazy manner: the response of each successive layer is computed only if activation of the current layer satisfies a continuation criterion. Usage of neural networks increases the sensitivity considerably comparable with image thresholding, while the lazy evaluation allows for execution of the trigger under the limited computational power of mobile phones.
High-energy physics experiments rely on reconstruction of the trajectories of particles produced at the interaction point. This is a challenging task, especially in the high track multiplicity environment generated by p-p collisions at the LHC energies. A typical event includes hundreds of signal examples (interesting decays) and a significant amount of noise (uninteresting examples). This work describes a modification of the Artificial Retina algorithm for fast track finding: numerical optimization methods were adopted for fast local track search. This approach allows for considerable reduction of the total computational time per event. Test results on simplified simulated model of LHCb VELO (VErtex LOcator) detector are presented. Also this approach is well-suited for implementation of paralleled computations as GPGPU which look very attractive in the context of upcoming detector upgrades.
Using proton-proton collision data corresponding to an integrated luminosity of 3.0fb−1, recorded by the LHCb detector at centre-of-mass energies of 7 and 8TeV, the Bc+ → D0K+ decay is observed with a statistical significance of 5.1 standard deviations. By normalising to B+ → D0π+ decays, a measurement of the branching fraction multiplied by the production rates for Bc+ relative to B+ mesons in the LHCb acceptance is obtained,
R 0 =fc ×B(B+→D0K+)=(9.3+2.8±0.6)×10−7, DKfu c −2.5
where the first uncertainty is statistical and the second is systematic. This decay is expected to proceed predominantly through weak annihilation and penguin amplitudes, and is the first Bc+ decay of this nature to be observed.
A highly significant structure is observed in the Λ+cK−π+π+ mass spectrum, where the Λ+c baryon is reconstructed in the decay mode pK−π+. The structure is consistent with originating from a weakly decaying particle, identified as the doubly charmed baryon Ξ++cc. The difference between the masses of the Ξ++cc and Λ+c states is measured to be 1334.94±0.72(stat)±0.27(syst MeV/c2, and the Ξ++cc mass is then determined to be 3621.40±0.72(stat)±0.27(syst±0.14(Λ+c) MeV/c2, where the last uncertainty is due to the limited knowledge of the Λ+c mass. The state is observed in a sample of proton-proton collision data collected by the LHCb experiment at a center-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 1.7 fb−1, and confirmed in an additional sample of data collected at 8 TeV.
In this paper we suggest an algorithm for ringing suppression based on a sparse representation method. As one of its steps, the suggested method includes image deblurring based on the Wiener-Hunt deconvolution algorithm. The ringing suppression algorithm uses the signals' mutual coherence and sparsities analysis when dealing with the ringing effect based on the sparse representation method. We also analyze the mutual coherence and sparsities for blurred images and images with white Gaussian noise.
A search for the rare decays Bs0→τ+τ- and B0→τ+τ- is performed using proton–proton collision data collected with the LHCb detector. The data sample corresponds to an integrated luminosity of 3 fb-1 collected in 2011 and 2012. The τ leptons are reconstructed through the decay τ-→π-π+π-ντ. Assuming no contribution from B0→τ+τ- decays, an upper limit is set on the branching fraction B(Bs0→τ+τ-)<6.8×10-3 at the 95% confidence level. If instead no contribution from Bs0→τ+τ- decays is assumed, the limit is B(B0→τ+τ-)<2.1×10-3 at the 95% confidence level. These results correspond to the first direct limit on B(Bs0→τ+τ-) and the world’s best limit on B(B0→τ+τ-).
Using decays to ϕ-meson pairs, the inclusive production of charmonium states in b-hadron decays is studied with pp collision data corresponding to an integrated luminosity of 3.0fb−1, collected by the LHCb experiment at centre-of-mass energies of 7 and 8 TeV. Denoting by BC≡B(b→CX)×B(C→ϕϕ) the inclusive branching fraction of a b hadron to a charmonium state C that decays into a pair of ϕ mesons, ratios RC1C2≡BC1/BC2 are determined as Rχc0ηc(1S)=0.147±0.023±0.011, Rχc1ηc(1S)=0.073±0.016±0.006, Rχc2ηc(1S)=0.081±0.013±0.005, Rχc1χc0=0.50±0.11±0.01, Rχc2χc0=0.56±0.10±0.01 and Rηc(2S)ηc(1S)=0.040±0.011±0.004. Here and below the first uncertainties are statistical and the second systematic. Upper limits at 90% confidence level for the inclusive production of X(3872), X(3915) and χc2(2P) states are obtained as RX(3872)χc1<0.34, RX(3915)χc0<0.12 and Rχc2(2P)χc2<0.16. Differential cross-sections as a function of transverse momentum are measured for the ηc(1S) and χc states. The branching fraction of the decay B0s→ϕϕϕ is measured for the first time, B(B0s→ϕϕϕ)=(2.15±0.54±0.28±0.21B)×10−6. Here the third uncertainty is due to the branching fraction of the decay B0s→ϕϕ, which is used for normalization. No evidence for intermediate resonances is seen. A preferentially transverse ϕ polarization is observed. The measurements allow the determination of the ratio of the branching fractions for the ηc(1S) decays to ϕϕ and pp¯ as B(ηc(1S)→ϕϕ)/B(ηc(1S)→pp¯)=1.79±0.14±0.32.
Daily operation of a large-scale experiment is a challenging task, particularly from perspectives of routine monitoring of quality for data being taken. We describe an approach that uses Machine Learning for the automated system to monitor data quality, which is based on partial use of data qualified manually by detector experts. The system automatically classifies marginal cases: both of good an bad data, and use human expert decision to classify remaining “grey area” cases. This study uses collision data collected by the CMS experiment at LHC in 2010. We demonstrate that proposed workflow is able to automatically process at least 20% of samples without noticeable degradation of the result.
The oscillation frequency, TeV">TeVTeV. A combination of the two decay modes gives <span data-mathml="nsΔmd=(505.0±2.1±1.0)ns−1Δmd=(505.0±2.1±1.0)ns−1, where the first uncertainty is statistical and the second is systematic. This is the most precise single measurement of this parameter. It is consistent with the current world average and has similar precision.
This paper aims to tackle the problem of brain network classification with machine learning algorithms using spectra of networks' matrices. Two approaches are discussed: first, linear and tree-based models are trained on the vectors of sorted eigenvalues of the adjacency matrix, the Laplacian matrix and the normalized Laplacian; next, SVM classifier is trained with kernels based on information divergence between the eigenvalue distributions. The latter approach gives promising results in the classification of autism spectrum disorder versus typical development and of the carriers versus noncarriers of an allele associated with the high risk of Alzheimer disease.
A search for exclusive or quasi-exclusive γγ → W+W− production, via pp → p(*)W+W−p(*) →p(*)μ±e∓p(*) at s√=8s=8 TeV, is reported using data corresponding to an integrated luminosity of 19.7 fb−1. Events are selected by requiring the presence of an electron-muon pair with large transverse momentum pT(μ±e∓) > 30 GeV, and no associated charged particles detected from the same vertex. The 8 TeV results are combined with the previous 7 TeV results (obtained for 5.05 fb−1 of data). In the signal region, 13 (2) events are observed over an expected background of 3.9 ± 0.6 (0.84 ± 0.15) events for 8 (7) TeV, resulting in a combined excess of 3.4σ over the background-only hypothesis. The observed yields and kinematic distributions are compatible with the standard model prediction for exclusive and quasi-exclusive γγ → W+W− production. Upper limits on the anomalous quartic gauge coupling operators a0,CW (dimension-6) andfM0,1,2,3 (dimension-8), the most stringent to date, are derived from the measured dilepton transverse momentum spectrum.
A full amplitude analysis of Λ 0 b → J/ψ pπ− 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 → pπ−, either the Pc(4380)+ and Pc(4450)+ → J/ψ p states, previously observed in Λ 0 b → J/ψ pK− decays, or the Zc(4200)− → J/ψ π− state, previously reported in B0 → J/ψ K+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 Pc(4380)+ and Pc(4450)+ production rates expected from their previous observation taking account of Cabibbo suppression.
Charm meson oscillations are observed in a time-dependent analysis of the ratio of D0 → K+π −π +π − to D0 → K−π +π −π + decay rates, using data corresponding to an integrated luminosity of 3.0 fb−1 recorded by the LHCb experiment. The measurements presented are sensitive to the phase-space averaged ratio of doubly Cabibbo-suppressed to Cabibbo-favoured amplitudes r K3π D and the product of the coherence factor RK3π D and a charm mixing parameter y 0 K3π . The constraints measured are r K3π D = (5.67±0.12)×10−2 , which is the most precise determination to date, and RK3π D · y 0 K3π = (0.3 ± 1.8) × 10−3 , which provides useful input for determinations of the CP-violating phase γ in B±→ DK±, D→ K∓π ±π ∓π ± decays. The analysis also gives the most precise measurement of the D0 → K+π −π +π − branching fraction, and the first observation of D0–D0 oscillations in this decay mode, with a significance of 8.2 standard deviations.
A time-dependent angular analysis of Bs0→ψ(2S)ϕ decays is performed using data recorded by the LHCb experiment. The data set corresponds to an integrated luminosity of 3.0fb−1 collected during Run 1 of the LHC. The CP -violating phase and decay-width difference of the Bs0 system are measured to be ϕs=0.23−0.28+0.29±0.02rad and ΔΓs=0.066−0.044+0.041±0.007ps−1 , respectively, where the first uncertainty is statistical and the second systematic. This is the first time that ϕs and ΔΓs have been measured in a decay containing the ψ(2S) resonance.