Improved extrapolation methods of data-driven background estimations in high energy physics

Data-driven methods of background estimations are often used to obtain more reliable descriptions of backgrounds. In hadron collider experiments, data-driven techniques are used to estimate backgrounds due to multi-jet events, which are difficult to model accurately. In this article, we propose an improvement on one of the most widely used data-driven methods in the hadron collision environment, the “ABCD” method of extrapolation. We describe the mathematical background behind the data-driven methods and extend the idea to propose improved general methods.

Top Quark Pair-Production in Noncommutative Standard Model

The differential cross-section of the top quark pair production via the quark-antiquark annihilation subprocess in hadron collision is calculated within the noncommutative standard model. A pure NC analytical expression for the forward-backward asymmetry at the tree level is obtained. Moreover, using recent Tevatron results from the full RUN2 data, a new lower bound on the noncommutative geometry parameter is deduced.

Extraction and validation of a new set of CMS pythia8 tunes from underlying-event measurements

New sets of CMS underlying-event parameters (“tunes”) are presented for the pythia8 event generator. These tunes use the NNPDF3.1 parton distribution functions (PDFs) at leading (LO), next-to-leading (NLO), or next-to-next-to-leading (NNLO) orders in perturbative quantum chromodynamics, and the strong coupling evolution at LO or NLO. Measurements of charged-particle multiplicity and transverse momentum densities at various hadron collision energies are fit simultaneously to determine the parameters of the tunes. Comparisons of the predictions of the new tunes are provided for observables sensitive to the event shapes at LEP, global underlying event, soft multiparton interactions, and double-parton scattering contributions. In addition, comparisons are made for observables measured in various specific processes, such as multijet, Drell–Yan, and top quark-antiquark pair production including jet substructure observables. The simulation of the underlying event provided by the new tunes is interfaced to a higher-order matrix-element calculation. For the first time, predictions from pythia8 obtained with tunes based on NLO or NNLO PDFs are shown to reliably describe minimum-bias and underlying-event data with a similar level of agreement to predictions from tunes using LO PDF sets.

CHOU-YANG MULTIPLICITY CORRELATIONS IN HIGH ENERGY MULTIPARTICLE PRODUCTION AND LHC PREDICTION

A Chou-Yang Type multiplicity distribution which consists of a stochastic (binomial) component for z = nf - nb and a nonstochastic (Generalized Multiplicity Distribution) component for n = nf + nb, is used to analyze the forward-backward multipicity distributions for hadron hadron collision over a wide range of cms energy. The results are compared with the multiplicity distribution using the Negative Binomial Distribution. Finally, cluster size r = 3.30±0.14 and the correlation parameter b = 0.98 are predicted for 14 TeV.

SINGLE SPIN ASYMMETRIES IN INCLUSIVE HIGH ENERGY HADRON–HADRON COLLISION PROCESSES

It has been realized for quite a long time that single-spin experiments, in which one of the colliding objects is transversely polarized, can be helpful in studying the properties of strong interaction in general and in testing quantum chromodynamics (QCD) in particular. Striking effects have been observed in the past few years which deviate drastically from the expectation of the perturbative QCD parton model. These effects have received much attention. New experiments of the similar type are underway and/or planned. Different theoretical attempts have been made to understand these effects. In this review, the special role played by singly polarized high-energy hadron–hadron collisions in high energy spin physics is emphasized. Characteristics of the available data for inclusive hadron productions are briefly summarized. Different theoretical approaches for such processes are reviewed with special attention to a nonperturbative model which explicitly takes the orbital motion of the valence quarks and hadronic surface effects into account. The connection between such asymmetries and hyperon polarization in unpolarized reactions is discussed. An example of the possible application of such experimental results in other processes is given.

INTERMITTENCY IN MULTIPARTICLE PRODUCTION — A BRIEF EXPERIMENTAL SURVEY

Intermittency patterns of fluctuations in particle production are observed in heavy ion collision experiments, hadron-hadron collision experiments and in e+e− experiments establishing the existence of this phenomenon. Some regularities are reviewed.

1/Nc EXPANSION, QUARK MODEL AND HADRON COLLISIONS AT HIGH ENERGIES

Soft hadron-collision processes at high energies are considered, under the assumption that gluon interactions are short-ranged and that the rules of the 1/Nc expansion are fulfilled. It is shown, that these considerations lead to the scheme of the additive quark model with some relatively large additional effects of colour screening. This colour screening is responsible for the unnatural breaking of the Levin-Frankfurt condition1 and also for the effective increase of cross sections for hadron-nucleus interactions2 if quark bags in nuclei exist, The formation mechanism of fragmentational particles is considered in multiple hadron-production processes.