Publications

In this work, we propose an approach for electromagnetic shower generation on a track level. Currently, Monte Carlo simulation occupies 50-70\% of total computing resources that are used by physicists experiments worldwide. Thus, speedup of the simulation step allows to reduce simulation cost and accelerate synthetic experiments. In this paper, we suggest dividing the problem of shower generation into two separate issues: graph generation and tracks features generation. Both these problems can be efficiently solved with a cascade of deep autoregressive generative network and graph convolution network. The novelty of the proposed approach lies in the Neural networks application to the generation of the complex recursive physical process.

The increasing luminosities of future Large Hadron Collider runs and next generation of collider experiments will require an unprecedented amount of simulated events to be produced. Such large scale productions are extremely demanding in terms of computing resources. Thus new approaches to event generation and simulation of detector responses are needed. In LHCb, the accurate simulation of Cherenkov detectors takes a sizeable fraction of CPU time. An alternative approach is described here, when one generates high-level reconstructed observables using a generative neural network to bypass low level details. This network is trained to reproduce the particle species likelihood function values based on the track kinematic parameters and detector occupancy. The fast simulation is trained using real data samples collected by LHCb during run 2. We demonstrate that this approach provides high-fidelity results.

We report four narrow peaks in the Ξb0K- mass spectrum obtained using pp collisions at center-of-mass energies of 7, 8, and 13 TeV, corresponding to a total integrated luminosity of 9  fb-1 recorded by the LHCb experiment. Referring to these states by their mass, the mass values are m[Ωb(6316)-]=6315.64±0.31±0.07±0.50  MeV, m[Ωb(6330)-]=6330.30±0.28±0.07±0.50  MeV, m[Ωb(6340)-]=6339.71±0.26±0.05±0.50  MeV, m[Ωb(6350)-]=6349.88±0.35±0.05±0.50  MeV, where the uncertainties are statistical, systematic, and the last is due to the knowledge of the Ξb0 mass. The natural widths of the three lower mass states are consistent with zero, and the 90% confidence-level upper limits are determined to be Γ[Ωb(6316)-]<2.8  MeV, Γ[Ωb(6330)-]<3.1  MeV and Γ[Ωb(6340)-]<1.5  MeV. The natural width of the Ωb(6350)- peak is 1.4-0.8+1.0±0.1  MeV, which is 2.5σ from zero and corresponds to an upper limit of 2.8 MeV. The peaks have local significances ranging from 3.6σ to 7.2σ. After accounting for the look-elsewhere effect, the significances of the Ωb(6316)- and Ωb(6330)- peaks are reduced to 2.1σ and 2.6σ, respectively, while the two higher mass peaks exceed 5σ. The observed peaks are consistent with expectations for excited Ωb- resonances.

Ratios of isospin amplitudes in hadron decays are a useful probe of the interplay between weak and strong interactions and allow searches for physics beyond the standard model. We present the first results on isospin amplitudes in b-baryon decays, using data corresponding to an integrated luminosity of 8.5  fb-1, collected with the LHCb detector in pp collisions at center of mass energies of 7, 8, and 13 TeV. The isospin amplitude ratio |A1(Λb0→J/ψΣ0)/A0(Λb0→J/ψΛ)|, where the subscript on A indicates the final-state isospin, is measured to be less than 1/21.8 at 95% confidence level. The Cabibbo suppressed Ξb0→J/ψΛ decay is observed for the first time, allowing for the measurement |A0(Ξb0→J/ψΛ)/A1/2(Ξb0→J/ψΞ0)|=0.37±0.06±0.02, where the uncertainties are statistical and systematic, respectively.

We study measurable dependence of measures on a parameter in the following two classical problems: constructing conditional measures and the Kantorovich optimal transportation. For parametric families of measures and mappings we prove the existence of conditional measures measurably depending on the parameter. A particular emphasis is made on the Borel measurability (which cannot be always achieved). Our second main result gives sufficient conditions for the Borel measurability of optimal transports and transportation costs with respect to a parameter in the case where marginal measures and cost functions depend on a parameter. As a corollary we obtain the Borel measurability with respect to the parameter for disintegrations of optimal plans. Finally, we show that the Skorohod parametrization of measures by mappings can be also made measurable with respect to a parameter.

The cross-sections of 𝜓(2𝑆) meson production in proton-proton collisions at 𝑠√=13 TeV are measured with a data sample collected by the LHCb detector corresponding to an integrated luminosity of 275 pb−1. The production cross-sections for prompt 𝜓(2𝑆) mesons and those for 𝜓(2𝑆) mesons from b-hadron decays (𝜓(2𝑆)-from- 𝑏) are determined as functions of the transverse momentum, 𝑝T, and the rapidity, y, of the 𝜓(2𝑆) meson in the kinematic range 2<𝑝T<20 GeV/𝑐 and 2.0<𝑦<4.5

. The production cross-sections integrated over this kinematic region are

𝜎( prompt 𝜓(2𝑆),13 TeV)=1.430±0.005 (stat)±0.099 (syst)μb,𝜎(𝜓(2𝑆)-from- 𝑏,13 TeV)=0.426±0.002 (stat)±0.030 (syst)μb.

A new measurement of 𝜓(2𝑆)

production cross-sections in pp collisions at 𝑠√=7 TeV is also performed using data collected in 2011, corresponding to an integrated luminosity of 614 pb−1. The integrated production cross-sections in the kinematic range 3.5<𝑝T<14 GeV/𝑐 and 2.0<𝑦<4.5

are

𝜎( prompt 𝜓(2𝑆),7 TeV)=0.471±0.001 (stat)±0.025 (syst)μb,𝜎(𝜓(2𝑆)-from- 𝑏,7 TeV)=0.126±0.001 (stat)±0.008 (syst)μb.

All results show reasonable agreement with theoretical calculations.

An angular analysis of the B0→K∗0(→K+π−)μ+μ− decay is presented using a data set corresponding to an integrated luminosity of 4.7 fb−1 of pp collision data collected with the LHCb experiment. The full set of CP-averaged observables are determined in bins of the invariant mass squared of the dimuon system. Contamination from decays with the K+π− system in an S-wave configuration is taken into account. The tension seen between the previous LHCb results and the Standard Model predictions persists with the new data. The precise value of the significance of this tension depends on the choice of theory nuisance parameters.

Measurements of CP observables in B±→DK± and B±→Dπ± decays are presented, where D represents a superposition of D0 and D¯0 states. The D meson is reconstructed in the three-body final state K0SK±π∓. The analysis uses samples of B mesons produced in proton-proton collisions, corresponding to an integrated luminosity of 1.0, 2.0, and 6.0 fb−1 collected with the LHCb detector at centre-of-mass energies of s√= 7, 8, and 13 TeV, respectively. These measurements are the most precise to date, and provide important input for the determination of the CKM angle γ.

The decay-time-dependent CP asymmetry in B0→D∗±D∓ decays is measured using a data set corresponding to an integrated luminosity of 9fb−1 recorded by the LHCb detector in proton-proton collisions at centre-of-mass energies of 7, 8 and 13 TeV. The CP parameters are measured as SD∗D=−0.861±0.077(stat)±0.019(syst), ΔSD∗D=0.019±0.075(stat)±0.012(syst), CD∗D=−0.059±0.092(stat)±0.020(syst), ΔCD∗D=−0.031±0.092(stat)±0.016(syst), D∗D=0.008±0.014(stat)±0.006(syst). The analysis provides the most precise single measurement of CP violation in this decay channel to date. All parameters are consistent with their current world average values.

A measurement of the branching fraction of the decay B0s→K0SK0S is performed using proton–proton collision data corresponding to an integrated luminosity of 5  fb−1 collected by the LHCb experiment between 2011 and 2016. The branching fraction is determined to be B(B0s→K0SK0S)=[8.3±1.6(stat)±0.9(syst)±0.8(norm)±0.3(fs/fd)]×10−6, where the first uncertainty is statistical, the second is systematic, and the third and fourth are due to uncertainties on the branching fraction of the normalization mode B0→ϕK0S and the ratio of hadronization fractions fs/fd. This is the most precise measurement of this branching fraction to date. Furthermore, a measurement of the branching fraction of the decay B0→K0SK0S is performed relative to that of the B0s→K0SK0S channel, and is found to be B(B0→K0SK0S)B(B0s→K0SK0S)=[7.5±3.1(stat)±0.5(syst)±0.3(fs/fd)]×10−2.

This paper presents an analysis of the Λ0𝑏Λb0→ J/ψΛ angular distribution and the transverse production polarisation of Λ0𝑏Λb0 baryons in proton-proton collisions at centre-of-mass energies of 7, 8 and 13 TeV. The measurements are performed using data corresponding to an integrated luminosity of 4.9 fb−1, collected with the LHCb experiment. The polarisation is determined in a fiducial region of Λ0𝑏Λb0 transverse momentum and pseudorapidity of 1 < pT< 20 GeV/c and 2 < η < 5, respectively. The data are consistent with Λ0𝑏Λb0 baryons being produced unpolarised in this region. The parity-violating asymmetry parameter of the Λ → pπ− decay is also determined from the data and its value is found to be consistent with a recent measurement by the BES III collaboration.

The element |Vcb| of the Cabibbo-Kobayashi-Maskawa matrix is measured using semileptonic B0s decays produced in proton-proton collision data collected with the LHCb detector at center-of-mass energies of 7 and 8 TeV, corresponding to an integrated luminosity of 3 fb−1. Rates of B0s→D−sμ+νμ and B0s→D∗−sμ+νμ decays are analyzed using hadronic form-factor parametrizations derived either by Caprini, Lellouch and Neubert (CLN) or by Boyd, Grinstein and Lebed (BGL). The measured values of |Vcb| are (41.4±0.6±0.9±1.2)×10−3 and (42.3±0.8±0.9±1.2)×10−3 in the CLN and BGL parametrization, respectively. The first uncertainty is statistical, the second systematic, and the third is due to the external inputs used in the measurement. These results are in agreement with those obtained from decays of B+ and B0 mesons. They are the first determinations of |Vcb| at a hadron-collider experiment and the first using B0s meson decays.

The production of Ξ++cc baryons in proton-proton collisions at a centre-of-mass energy of s√=13 TeV is measured in the transverse-momentum range 4<pT<15 GeV/c and the rapidity range 2.0<y<4.5. The data used in this measurement correspond to an integrated luminosity of 1.7 fb−1, recorded by the LHCb experiment during 2016. The ratio of the Ξ++cc production cross-section times the branching fraction of the Ξ++cc→Λ+cK−π+π+ decay relative to the prompt Λ+c production cross-section is found to be (2.22±0.27±0.29)×10−4, assuming the central value of the measured Ξ++cc lifetime, where the first uncertainty is statistical and the second systematic.

Advanced detector R&D for both new and ongoing experiments in HEP requires performing computationally intensive and detailed simulations as part of the detector-design optimisation process. We propose a versatile approach to this task that is based on machine learning and can substitute the most computationally intensive steps of the process while retaining the GEANT4 accuracy to details. The approach covers entire detector representation from the event generation to the evaluation of the physics performance. The approach allows the use of arbitrary modules arrangement, different signal and background conditions, tunable reconstruction algorithms, and desired physics performance metrics. While combined with properties of detector and electronics prototypes obtained from beam tests, the approach becomes even more versatile. We focus on the Phase II Upgrade of the LHCb Calorimeter under the requirements on operation at high luminosity. We discuss the general design of the approach and particular estimations, including spatial and energy resolution for the future LHCb Calorimeter setup at different pile-up conditions.

A new baryon state is observed in the Λ0bπ+π− mass spectrum with high significance using a data sample of pp collisions, collected with the LHCb detector at centre-of-mass energies s√=7,8 and 13TeV, corresponding to an integrated luminosity of 9fb−1. The mass and natural width of the new state are measured to be

m=6072.3±2.9±0.6±0.2MeV,Γ=72±11±2MeV,

where the first uncertainty is statistical and the second systematic. The third uncertainty for the mass is due to imprecise knowledge of the Λ0b baryon mass. The new state is consistent with the first radial excitation of the Λ0b baryon, the Λb(2S)0 resonance. Updated measurements of the masses and the upper limits on the natural widths of the previously observed Λb(5912)0 and Λb(5920)0 states are also reported.

The Λ+cK− mass spectrum is studied with a data sample of pp collisions at a centre-of-mass energy of 13 TeV corresponding to an integrated luminosity of 5.6 fb−1 collected by the LHCb experiment. Three Ξ0c states are observed with a large significance and their masses and natural widths are measured to be

m(Ξc(2923)0)=2923.04±0.25±0.20±0.14 MeV,Γ(Ξc(2923)0)=7.1±0.8±1.8 MeV,

m(Ξc(2939)0)=2938.55±0.21±0.17±0.14 MeV,Γ(Ξc(2939)0)=10.2±0.8±1.1 MeV,

m(Ξc(2965)0)=2964.88±0.26±0.14±0.14 MeV,Γ(Ξc(2965)0)=14.1±0.9±1.3 MeV,

where the uncertainties are statistical, systematic, and due to the limited knowledge of the Λ+c mass. The Ξc(2923)0 and Ξc(2939)0 baryons are new states. The Ξc(2965)0 state is in the vicinity of the known Ξc(2970)0 baryon; however, their masses and natural widths differ significantly.

Using proton-proton collision data at centre-of-mass energies of s=7,8 and 13TeV recorded by the LHCb experiment at the Large Hadron Collider, corresponding to an integrated luminosity of 9fb-1, the invariant mass spectrum of J/ψ pairs is studied. A narrow structure around 6.9GeV/c2 matching the lineshape of a resonance and a broad structure just above twice the J/ψ mass are observed. The deviation of the data from nonresonant J/ψ-pair production is above five standard deviations in the mass region between 6.2 and 7.4GeV/c2, covering predicted masses of states composed of four charm quarks. The mass and natural width of the narrow X(6900) structure are measured assuming a Breit–Wigner lineshape.

The Cabibbo-suppressed semileptonic decay B+→pp⎯⎯⎯μ+νμ is observed for the first time using a sample of pp collisions corresponding to an integrated luminosity of 1.0, 2.0 and 1.7fb−1 at centre-of-mass energies of 7, 8 and 13TeV, respectively. The differential branching fraction is measured as a function of the pp⎯⎯⎯ invariant mass using the decay mode B+→J/ψK+ for normalisation. The total branching fraction is measured to be

(B+→pp⎯⎯⎯μ+νμ)=(5.27+0.23−0.24±0.21±0.15)×10−6,

where the first uncertainty is statistical, the second systematic and the third is from the uncertainty on the branching fraction of the normalisation channel.

A precision measurement of the 𝐵+𝑐Bc+ meson mass is performed using proton- proton collision data collected with the LHCb experiment at centre-of-mass energies of 7, 8 and 13 TeV, corresponding to a total integrated luminosity of 9.0 fb−1. The 𝐵+𝑐Bc+ mesons are reconstructed via the decays 𝐵+𝑐Bc+→ J/ψπ+, 𝐵+𝑐Bc+→ J/ψπ+π−π+, 𝐵+𝑐→𝐽/𝜓𝑝𝑝⎯⎯⎯𝜋+Bc+→J/ψpp¯π+, 𝐵+𝑐→𝐽/𝜓𝐷+𝑠Bc+→J/ψDs+, 𝐵+𝑐Bc+→ J/ψ D0K+ and 𝐵+𝑐→𝐵0𝑠𝜋+Bc+→Bs0π+. Combining the results of the individual decay channels, the 𝐵+𝑐Bc+ mass is measured to be 6274.47 ± 0.27 (stat) ± 0.17 (syst) MeV/c2. This is the most precise measurement of the 𝐵+𝑐Bc+ mass to date. The difference between the 𝐵+𝑐Bc+ and 𝐵0𝑠Bs0 meson masses is measured to be 907.75 ± 0.37 (stat) ± 0.27 (syst) MeV/c.