Following the growing success of generative neural networks in LHC simulations, the crucial question is how to control the networks and assign uncertainties to their event output. We show how Bayesian normalizing flow or invertible networks capture uncertainties from the training and turn them into an uncertainty on the event weight. Fundamentally, the interplay between density and uncertainty estimates indicates that these networks learn functions in analogy to parameter fits rather than binned event counts.
The precision of measurements of the strong coupling constant using event-shape variables in e+e- annihilations is limited by theoretical systematic uncertainties. The uncertainties are related to missing higher orders in the perturbative predictions for the event-shape distributions. A new method is presented for the assessment of theoretical uncertainties in alpha_s. This method evaluates the systematic uncertainty of the parameter alpha_s from the uncertainty of the prediction for the distributions from which it is extracted. The perturbative uncertainties are calculated on a purely theoret…
Standard Model $ZZ$ production is an important background for many searches at the LHC, especially in final states with missing transverse momentum. In this article, boson substitution is applied to estimate $ZZ \rightarrow \ell^+ \ell^- ν\barν$ yields from $Zγ\rightarrow \ell^+ \ell^- γ$ events. The cross-section ratio of the two processes and its uncertainties are evaluated at NNLO with the MATRIX generator as a function of the transverse momentum of the substituted boson. Uncertainties due to higher-order QCD corrections, parton distribution functions, photon isolation criteria, and electro…
The dark matter direct detection rates are highly correlated with the phase space distribution of dark matter particles in our galactic neighbourhood. In this paper, we make a systematic study of the impact of astrophysical uncertainties on electron recoil events at the direct detection experiments with Xenon and semiconductor detectors. We find that within the standard halo model there can be up to $ \sim 50\%$ deviation from the fiducial choice in the exclusion bounds from these observational uncertainties. For non-standard halo models, we report a similar deviation from the fiducial standar…
We study the model uncertainties on limits for quantum black hole production in dijet events from ATLAS. For models that assume a hard-disk cross section, the model uncertainty on the threshold mass limits is about 5%. If the trapped surface calculation is used for the cross section, the ATLAS mass threshold limits are below 2 TeV for all number of dimensions. Using the ATLAS data in the context of the Randall-Sundrum type-1 model gives a threshold mass lower limit of 2.84 TeV.
To achieve appropriate interaction rates in recent neutrino oscillation studies, high atomic number nuclear targets were utilized. Because of the nuclear effects in the experimental observable, the utilization of these complicated targets produced systematic uncertainties that needed to be assessed accurately to constrain the discovery. We made an effort to calculate the nuclear effects in the Ar and H targets, which are intended to be employed at the DUNE distant and near detectors, respectively, through our simulation effort. The DUNE flux is peaking around 2.5 GeV and CCRES is the dominant …
A threshold anomaly refers to a theoretically expected energy threshold that is not observed experimentally. Here we offer an explanation of the threshold anomalies encountered in the ultra-high energy cosmic ray events and the TeV-gamma ray events, by arguing that energy-momentum uncertainties due to quantum gravity, too small to be detected in low-energy regime, can affect particle kinematics so as to raise or even eliminate the energy thresholds. A possible modification of the energy-momentum dispersion relation, giving rise to time-of-flight differences between photons of different energie…
We present an investigation of the dependence of searches for boosted Higgs bosons using jet substructure on the perturbative and non-perturbative parameters of the Herwig++ Monte Carlo event generator. Values are presented for a new tune of the parameters of the event generator, together with the an estimate of the uncertainties based on varying the parameters around the best-fit values.
Motivated by the recent galactic center gamma-ray excess identified in the Fermi-LAT data, we perform a detailed study of QCD fragmentation uncertainties in the modeling of the energy spectra of gamma-rays from Dark-Matter (DM) annihilation. When Dark-Matter particles annihilate to coloured final states, either directly or via decays such as $W^{(*)}\to q\bar{q}'$, photons are produced from a complex sequence of shower, hadronisation and hadron decays. In phenomenological studies, their energy spectra are typically computed using Monte Carlo event generators. These results have however intrins…
Machine Learning is a powerful tool to reveal and exploit correlations in a multi-dimensional parameter space. Making predictions from such correlations is a highly non-trivial task, in particular when the details of the underlying dynamics of a theoretical model are not fully understood. Using adversarial networks, we include a priori known sources of systematic and theoretical uncertainties during the training. This paves the way to a more reliable event classification on an event-by-event basis, as well as novel approaches to perform parameter fits of particle physics data. We demonstrate t…
We discuss theoretical uncertainties of the distribution in the cosine of the W polar angle projected into a measurement of the anomalous triple gauge-boson coupling λ=λ_γ=λ_Z at LEP2 energies for the tandem of the Monte Carlo event generators KoralW and YFSWW3 and for the Monte Carlo event generator RacoonWW. Exploiting numerical results of these programs and cross-checks with experimental fitting procedures, we estimate that the theoretical uncertainty of the value of λdue to electroweak corrections, as obtained at LEP2 with the help of these programs, is ~0.005, about half of the expected e…
Precision electroweak tests are a powerful probe of physics beyond the Standard Model, but the sensitivity is limited by the precision with which the $W$ boson mass ($M_W$) has been measured. The Parton Distribution Function (PDF) uncertainties are a potential limitation for measurements of $M_W$ with LHC data. It has recently been pointed out that, thanks to LHCb's unique forward rapidity acceptance, a new measurement of $M_W$ by LHCb can improve this situation. Here we report on a detailed study on the mechanism driving the PDF uncertainty in the LHCb measurement of $M_W$, and propose an app…
We study the influence of measured high cumulants of conserved charges on their associated statistical uncertainties in relativistic heavy-ion collisions. With a given number of events, the measured cumulants randomly fluctuate with an approximately normal distribution, while the estimated statistical uncertainties are found to be correlated with corresponding values of the obtained cumulants. Generally, with a given number of events, the larger the cumulants we measure, the larger the statistical uncertainties that are estimated. The error-weighted averaged cumulants are dependent on statisti…
The MC@NLO and MEPS@NLO methods, as implemented in the Monte-Carlo event generator framework Sherpa, are used to estimate the perturbative and non-perturbative uncertainties in various processes such as dijet production and the production of a W boson in association with (multiple) jets.
We study the process pp -> t tbar H at sqrt(s)=14 TeV where H -> WW. We focus on final states that include three or four leptons. Signal and background samples are generated at leading order (LO) and normalized to next-to-leading order (NLO) calculations. We employ the "Snowmass" detector simulation and event reconstruction. Cuts are selected which provide a substantial signal yield while suppressing the main backgrounds. Systematic uncertainties are estimated for the overall normalization of signal and background processes. With no improvement in the current theoretical uncertainties on sigma…
We predict geoneutrino fluxes in a reference model based on a detailed description of Earth's crust and mantle and using the best available information on the abundances of uranium, thorium, and potassium inside Earth's layers. We estimate the uncertainties of fluxes corresponding to the uncertainties of the element abundances. In addition to distance integrated fluxes, we also provide the differential fluxes as a function of distance from several sites of experimental interest. Event yields at several locations are estimated and their dependence on the neutrino oscillation parameters is discu…
Institut für Theoretische Physik, Universität Heidelberg（海德堡大学理论物理研究所）；Interdisciplinary Center for Scientific Computing (IWR), Universität Heidelberg（海德堡大学跨学科科学计算中心）；TIFLab, Università degli Studi di Milano & INFN Sezione di Milano（米兰大学物理理论实验室与意大利国家核物理研究所米兰分部）
A strategy to determine the luminosity at Hadron Colliders is discussed using the simultaneous W-boson and Z-boson event counts. The emphasis of the study will be on the uncertainty induced by the parton density functions. Understanding this source of uncertainties is crucial for a reliable luminosity determination using the W-boson and Z-boson events. As an example we will use the D0 run 1 results to extract the luminosity using the vector boson events and compare the result with the traditional method. Subsequently we will look at the implications for the top cross section uncertainties usin…
We quantify uncertainties in the Monte-Carlo simulation of inclusive and dijet final states, which arise from using the MC@NLO technique for matching next-to-leading order parton level calculations and parton showers. We analyse a large variety of data from early measurements at the LHC. In regions of phase space where Sudakov logarithms dominate over high-energy effects, we observe that the main uncertainty can be ascribed to the free parameters of the parton shower. In complementary regions, the main uncertainty stems from the considerable freedom in the simulation of underlying events.
In the era of precision physics measurements at the LHC, efficient and exhaustive estimations of theoretical uncertainties play an increasingly crucial role. In the context of Monte Carlo (MC) event generators, the estimation of such uncertainties traditionally requires independent MC runs for each variation, for a linear increase in total run time. In this work, we report on an automated evaluation of the dominant (renormalization-scale and non-singular) perturbative uncertainties in the PYTHIA 8 event generator, with only a modest computational overhead. Each generated event is accompanied b…
CP-violation or Nuclear Excitation: Reviewing the Role of Neutrino Interaction Model Uncertainties on Accelerator-Based Neutrino Oscillation Measurements
Monte Carlo event generators are an essential tool for data analysis in collider physics. To include subleading quantum corrections, these generators often need to produce negative weight events, which leads to statistical dilution of the datasets and downstream computational costs for detector simulation. Building on the recent proposal of a positive resampler method to rebalance weights within histogram bins, we introduce neural resampling: an unbinned approach to Monte Carlo reweighting based on neural networks that scales well to high-dimensional and variable-dimensional phase space. We pa…
We study the QCD sources of systematic uncertainties in the experimental extraction of the W cross section at hadron colliders. The uncertainties appear in the evaluation of the detector acceptances used to convert the number of observed events into a total production cross section. We consider the effect of NLO corrections, as well as of the inclusion of parton showers, and evaluate the impact of spin correlations and of PDF and scale uncertainties.
The event mixing method is analyzed for the study of the event-by-event $K/π$ ratio distribution. It is shown that there exists some correlation between the kaon and pion multiplicities in the mixed events. The $K/π$ ratio distributions in the mixed events for different sets of real events are shown. The dependence of the distributions on the mean $K/π$ ratio, mean and variance of multiplicity distribution in the real events is investigated systematically. The effect of imperfect particle identification on the $K/π$ ratio distribution in the mixed event is also considered.
We do not understand light. I argue that a terascale photon collider is necessary to determine the structure of the photon at 100 GeV. Uncertainties in photon parton distribution functions lead to cross section predictions that vary by a factor of 5. This limits our ability to predict how well we can perform precision measurements, e.g., extracting the width of Higgs into two photons. These uncertainties will only be resolved by measuring the gluonic structure of the photon in situ.
We present the implementation and validation of the techniques used to efficiently evaluate parametric and perturbative theoretical uncertainties in matrix-element plus parton-shower simulations within the Sherpa event-generator framework. By tracing the full $α_s$ and PDF dependences, including the parton-shower component, as well as the fixed-order scale uncertainties, we compute variational event weights on-the-fly, thereby greatly reducing the computational costs to obtain theoretical-uncertainty estimates.
We report an analysis of charmless hadronic decays of neutral B mesons to the final state KsK+/-pi-/+, using a data sample of (465 +/- 5) x 10^6 BB-bar events collected with the BABAR detector at the Y(4S) resonance. We observe an excess of signal events with a significance of 5.2 standard deviations including systematic uncertainties and measure the branching fraction to be BF(B0 --> KsK+/-pi-/+) = (3.2 +/- 0.5 +/- 0.3) x 10^-6, where the uncertainties are statistical and systematic, respectively.
We critically examine a number of theoretical uncertainties affecting the MiniBooNE short-baseline neutrino oscillation experiment in an attempt to better understand the observed excess of electron-like events. We re-examine the impact of fake charged current quasi-elastic (CCQE) events, the background due to neutral current $π^0$ production, and the single-photon background. For all processes, we compare the predictions of different event generators (GENIE, GiBUU, NUANCE, and NuWro) and, for GENIE, of different tunes. Where MiniBooNE uses data-driven background predictions, we discuss the unc…
Analyses in high energy physics aim to put the Standard Model---the commonly accepted theory---to test. For convincing conclusions, analysis methods are needed which offer an unambiguous comparison between data and theory while allowing reliable estimates of uncertainties. The Matrix Element Method (MEM) is a Maximum Likelihood method which is especially tailored for signal searches and parameter estimation at colliders. The MEM has proven to be beneficial due to optimal use of the available information and a clean statistical interpretation of the results. But it has a big drawback: In its or…
The FCC-ee physics program will deliver two complementary top-notch precision determinations of the W boson mass, and width. The first and main measurement relies on the rapid rise of the W-pair production cross section near its kinematic threshold. This method is extremely simple and clean, involving only the selection and counting of events, in all different decay channels. An optimal threshold-scan strategy with a total integrated luminosity of $12\,{\rm ab}^{-1}$ shared on energy points between 157 and 163 GeV will provide a statistical uncertainty on the W mass of 0.5 MeV and on the W wid…
We propose a new method to resolve combinatorial ambiguities in hadron collider events involving two invisible particles in the final state. This method is based on the kinematic variable MT2 and on the MT2-assisted-on-shell reconstruction of invisible momenta, that are reformulated as `test' variables Ti of the correct combination against the incorrect ones. We show how the efficiency of the single Ti in providing the correct answer can be systematically improved by combining the different Ti and/or by introducing cuts on suitable, combination-insensitive kinematic variables. We illustrate ou…
Machine learning methods incorporating deep neural networks have been the subject of recent proposals for new hadronic resonance taggers. These methods require training on a dataset produced by an event generator where the true class labels are known. However, training a network on a specific event generator may bias the network towards learning features associated with the approximations to QCD used in that generator which are not present in real data. We therefore investigate the effects of variations in the modelling of the parton shower on the performance of deep neural network taggers usi…
