Optimization of Signal Significance by Bagging Decision Trees

An algorithm for optimization of signal significance or any other classification figure of merit suited for analysis of high energy physics (HEP) data is described. This algorithm trains decision trees on many bootstrap replicas of training data with each tree required to optimize the signal significance or any other chosen figure of merit. New data are then classified by a simple majority vote of the built trees. The performance of this algorithm has been studied using a search for the radiative leptonic decay B->gamma l nu at BaBar and shown to be superior to that of all other attempted classifiers including such powerful methods as boosted decision trees. In the B->gamma e nu channel, the described algorithm increases the expected signal significance from 2.4 sigma obtained by an original method designed for the B->gamma l nu analysis to 3.0 sigma.Comment: 8 pages, 2 figures, 1 tabl

A multivariate approach to heavy flavour tagging with cascade training

This paper compares the performance of artificial neural networks and boosted decision trees, with and without cascade training, for tagging b-jets in a collider experiment. It is shown, using a Monte Carlo simulation of $WH \to l\nu q\bar{q}$ events, that for a b-tagging efficiency of 50%, the light jet rejection power given by boosted decision trees without cascade training is about 55% higher than that given by artificial neural networks. The cascade training technique can improve the performance of boosted decision trees and artificial neural networks at this b-tagging efficiency level by about 35% and 80% respectively. We conclude that the cascade trained boosted decision trees method is the most promising technique for tagging heavy flavours at collider experiments.Comment: 14 pages, 12 figures, revised versio

The Civil War, Migration, and Humanitarian Disaster in Russia Between 1917 and 1922

Поступила в редакцию 25.06.2018. Принята к печати 09.07.2018.Submitted on 25 June, 2018. Accepted on 09 July, 2018.Движение народонаселения России в годы революции и Г ражданской войны было отмечено беспрецедентной динамикой и имело формативный характер. В статье анализируются факторы, воздействовавшие на движение населения в 1917–1922 гг. Они условно разделены на связанные с рождаемостью и (естественной и насильственной) смертностью и с (вынужденными) передвижениями внутри страны и за ее пределы. Хотя статистика движения населения весьма приблизительна и неполна, фрагментарна и ненадежна, количественные данные о состоянии страны и протекании различных социальных процессов, собранные и обработанные сотрудниками статистических служб на территории России в годы революции и Г ражданской войны, позволяют создать ориентировочное представление о демографических аспектах русской революции. Методологически статья ориентируется на «пространственный подход», а именно на различение географически фиксируемой территории и социально конструируемого пространства. К ведущим формам миграции населения внутри страны в годы революции и Г ражданской войны отнесены передвижения армий и сопровождавшее их беженство, а также перемещения населения между городом и деревней, включая мешочничество и бегство из деревни в город ради спасения от голода, а также межрегиональные движения горожан и особенно крестьян в поисках урожайных, «сытых» земель. Миграционные практики широких слоев российского населения в значительной степени опирались на богатый прежний опыт и позволяли ему, таким образом, и в экстраординарных условиях революции и Г ражданской войны оставаться в рамках собственной культуры. Вместе с тем разразившаяся в революционной России демографическая катастрофа и рост удельного веса населения, выброшенного на обочину, свидетельствуют об ограниченном успехе миграционных практик населения в 1917–1922 гг.The movement of the Russian population in the years of the Revolution and the Civil War was characterised by an unprecedented dynamic and had a formative character. The article analyses factors that influenced the movement of the population between 1917 and 1922. They are roughly divided into factors connected with birth rates and death rates (either natural or violent) or linked to (forced) migrations inside and outside the country. Despite the fact that the statistics on the population movement are very inaccurate, incomplete, and unreliable, the quantitative data on the state of the country and the course of various social processes that employees of statistical services collected during the Revolution and the Civil War help draw an approximate idea of the demographic aspects of the Russian Revolution. Methodologically, the paper is based on the “spatial” approach, i.e. the distinction between geographical territories and social spaces. Among the main forms of migration of the population within the country in the years of the Revolution and the Civil War, the author singles out the first movements of armies and the concurrent waves of refugees, and secondly, population movements between rural and urban areas, including profiteering in grain and scarce merchandise and peasants’ flight from the countryside to the city to save themselves from hunger; and, thirdly, the interregional movements of citizens, and especially of peasants, in search of fertile lands. The migratory practices of the population were largely based on the rich experience of the past and, consequently, allowed it to remain in the framework of its own culture under the extraordinary conditions of the Revolution and the Civil War. However, the onset of a demographic catastrophe and the growing proportion of marginalised population point to the fact that the migration processes in Russia between 1917 and 1922 did not prove entirely successful.Статья написана на основе выступлений на международном научном семинаре «Перекрестки трансконтинентальной и транснациональной миграции в Р оссийской империи / СССР середины XIX – XX вв.», Челябинск, 9–10 сентября 2016 г. и на научном коллоквиуме, посвященном 100-летию российской Революции, организованном Совместной комиссией по изучению новейшей истории российско-германских отношений, 6–7 июля 2017 г

Measurement of branching fractions and CP-violating charge asymmetries for B-meson decays to D^(*)D^(*), and implications for the Cabibbo-Kobayashi-Maskawa angle γ

We present measurements of the branching fractions and charge asymmetries of B decays to all D^(*)D^(*) modes. Using 232×10^6 BB pairs recorded on the Υ(4S) resonance by the BABAR detector at the e^+e^- asymmetric B factory PEP-II at the Stanford Linear Accelerator Center, we measure the branching fractions B(B^0→D^(*+)D^(*-))=(8.1±0.6±1.0)×10^(-4), B(B^0→D^(*±)D^∓)=(5.7±0.7±0.7)×10^(-4), B(B^0→D^+D^-)=(2.8±0.4±0.5)×10^(-4), B(B^+→D^(*+)D^(*0))=(8.1±1.2±1.2)×10^(-4), B(B^+→D^*+D^0)=(3.6±0.5±0.4)×10^(-4), B(B^+→D^+D^(*0))=(6.3±1.4±1.0)×10^(-4), and B(B^+→D^+D^(0))=(3.8±0.6±0.5)×10^(-4), where in each case the first uncertainty is statistical and the second systematic. We also determine the limits B(B^0→D^(*0)D^(*0))<0.9×10^(-4), B(B^0→D^(*0)D^0)<2.9×10^(-4), and B(B^0→D^0D^0)<0.6×10^(-4), each at 90% confidence level. All decays above denote either member of a charge-conjugate pair. We also determine the CP-violating charge asymmetries A(B^0→D^(*±)D^∓)=0.03±0.10±0.02, A(B^+→D^(*+)D^(*0))=-0.15±0.11±0.02, A(B^+→D^(*+)D^0)=-0.06±0.13±0.02, A(B^+→D^+D^(*0))=0.13±0.18±0.04, and A(B^+→D^+D^0)=-0.13±0.14±0.02. Additionally, when we combine these results with information from time-dependent CP asymmetries in B^0→D^((*)+)D^((*)-) decays and world-averaged branching fractions of B decays to D_s^(*)D^(*) modes, we find the Cabibbo-Kobayashi-Maskawa phase γ is favored to lie in the range (0.07–2.77) radians (with a +0 or +π radians ambiguity) at 68% confidence level

Search for the decay τ-→3π^-2π^+2π^0ν_τ

A search for the decay of the τ lepton to five charged and two neutral pions is performed using data collected by the BABAR detector at the PEP-II asymmetric-energy e^+e^- collider. The analysis uses 232  fb^(-1) of data at center-of-mass energies on or near the Υ(4S) resonance. We observe 10 events with an expected background of 6.5_(-1.4)^(+2.0) events. In the absence of a signal, we set the limit on the branching ratio B(τ-→3π^-2π^+2π^0ν_τ)<3.4×10^(-6) at the 90% confidence level. This is a significant improvement over the previously established limit. In addition, we search for the decay mode τ-→2ωπ-ν_τ. We observe 1 event with an expected background of 0.4+1.0/-0.4 events and calculate the upper limit B(τ-→2ωπ-ν_τ)<5.4×10^(-7) at the 90% confidence level. This is the first upper limit for this mode

Search for the charmed pentaquark candidate Θ_c(3100)^0 in e^+e^- annihilations at √s=10.58 GeV

We search for the charmed pentaquark candidate reported by the H1 collaboration, the Θ_c(3100)^0, in e^+e^- interactions at a center-of-mass (c.m.) energy of 10.58 GeV, using 124  fb^(-1) of data recorded with the BABAR detector at the PEP-II e^+e^- facility at SLAC. We find no evidence for such a state in the same pD^(*-) decay mode reported by H1, and we set limits on its production cross section times branching fraction into pD^(*-) as a function of c.m. momentum. The corresponding limit on its total rate per e^+e^-→qq event, times branching fraction, is about 3 orders of magnitude lower than rates measured for the charmed Λ_c and Σ_c baryons in such events

Observation of B^0 Meson Decay to a_1^±(1260)π^∓

We present a measurement of the branching fraction of the decay B^0→a_1^±(1260)π^∓ with a_1^±(1260)→π^∓π^±π^±. The data sample corresponds to 218×10^6 BB pairs produced in e^+e^- annihilation through the Υ(4S) resonance. We measure the branching fraction B(B^0→a_1^±(1260)π^∓)B(a_1^±(1260)→π^∓π^±π^±)=(16.6±1.9±1.5)×10^(-6), where the first error quoted is statistical and the second is systematic

Measurements of the semileptonic decays B[overbar]→Dℓν[overbar] and B[overbar]→D^*ℓν[overbar] using a global fit to DXℓν[overbar] final states

Semileptonic B[overbar] decays to DXℓν[overbar](ℓ=e or μ) are selected by reconstructing D^0ℓ and D^+ℓ combinations from a sample of 230×10^6 Υ(4S)→BB[overbar] decays recorded with the BABAR detector at the PEP-II e^+e^- collider at SLAC. A global fit to these samples in a three-dimensional space of kinematic variables is used to determine the branching fractions B(B^-→D^0ℓν[overbar])=(2.34±0.03±0.13)% and B(B^-→D^(*0)ℓν[overbar])=(5.40±0.02±0.21)% where the errors are statistical and systematic, respectively. The fit also determines form-factor parameters in a parametrization based on heavy quark effective theory, resulting in ρ_D^2=1.20±0.04±0.07 for B[overbar]→Dℓν[overbar] and ρ_(D*)^2=1.22±0.02±0.07 for B[overbar]→D^*ℓν[overbar]. These values are used to obtain the product of the Cabibbo-Kobayashi-Maskawa matrix element |V_(cb)| times the form factor at the zero recoil point for both B[overbar]→Dℓν[overbar] decays, G(1)|V_(cb)|=(43.1±0.8±2.3)×10^(-3), and for B[overbar]→D^*ℓν[overbar] decays, F(1)|V_(cb)|=(35.9±0.2±1.2)×10^(-3)