XQCAT: eXtra Quark Combined Analysis Tool

Abstract

XQCAT (eXtra Quark Combined Analysis Tool) is a tool aimed at determining exclusion confidence levels for scenarios of new physics characterised by the presence of one or multiple heavy extra quarks which interact through Yukawa couplings with any of the Standard Model quarks. The code uses a database of efficiencies for pre-simulated processes of QCD-induced pair production of extra quarks and their subsequent on-shell decays. In the version 1.2 of XQCAT the efficiencies have been computed for a set of seven publicly available search results by the CMS experiment. The input for the code is a text file in which masses, branching ratios and dominant chirality of the couplings of the new quarks are provided. The output of the code is the exclusion confidence levels of the test point for each implemented experimental analysis considered individually and, when possible, in statistical combination. Program summaryProgram title: XQCATCatalogue identifier: AEXS_v1_0Program summary URL:http://cpc.cs.qub.ac.uk/summaries/AEXS_v1_0.htmlProgram obtainable from: CPC Program Library, Queen’s University, Belfast, N. IrelandLicensing provisions: Standard CPC licence, http://cpc.cs.qub.ac.uk/licence/licence.htmlNo. of lines in distributed program, including test data, etc.: 84420No. of bytes in distributed program, including test data, etc.: 1959913Distribution format: tar.gzProgramming language: Perl and C++.Computer: Personal Computer.Operating system: Any OS where Perl, C++ and ROOT are installed.RAM: Around 2.5 MbytesClassification: 11.1, 11.6.External routines: C++, Perl and ROOTSubprograms used:Cat IdTitleReferenceAEFA_v2_0ROOTCPC 182(2011)1384Nature of problem: Experimental searches of new heavy extra quarks (XQs) usually consider minimal extensions of the Standard Model (SM) with only one XQ representation which couples only to the third generation SM quarks or only to the SM light quark families. In contrast, various theoretically-motivated scenarios of new physics predict a new quark sector, i.e. more than one new quark, with general couplings to SM quarks. Notable examples are composite Higgs models or universal extra-dimensions. Hence, recasting experimental limits for these scenarios can be a challenging task. To avoid time-consuming simulations and dedicated searches for scenarios which can already be excluded by current data, we present a tool for reinterpretation of existing experimental analyses, including those not made for XQs searches, in terms of exclusion confidence levels (eCLs) for XQ models. Our tool should serve as a useful preliminary approach to understand in a quick way the regions of validity of scenarios of new physics.Solution method: The core of the tool consists in a database of pre-simulated efficiencies (ϵ), defined as the ratio of signal events which survive a given set of experimental cuts over the total number of signal events. These efficiencies have been computed simulating the process of pair production and decay of XQs with masses in the range 400–2000 GeV and implementing the selection and kinematics cuts of a set of experimental searches at 7 and 8 TeV. The tool uses the database to reconstruct any scenario where XQs couple to SM quarks through Yukawa interactions and gives as output the eCL of the test point, characterised by values of the XQ masses and their branching ratios (BRs) into specific final states, for all the implemented searches. It also provides eCLs for combinations of experimental searches when search bins are uncorrelated. The method has been validated against experimental analyses.Restrictions: The efficiency database has been built under the following hypotheses: QCD induced pair production of quarks with masses from 400 GeV to 2000 GeV with steps of 100 GeV; the electro-weak (EW) couplings of XQs with SM states have a dominant chirality, according to the hypothesis that new quarks are vector-like and that a new chiral generation is excluded with high confidence level (see main text for more details); in v1.2 the number of searches implemented is limited: four supersymmetric (SUSY) inspired CMS searches for final states with jets, missing transverse energy and variable number of leptons at 7 TeV [1-4], two SUSY-inspired CMS searches at 8 TeV (updates of two of the implemented 7 TeV searches) [5,6] and one CMS direct search at 8 TeV of a vector-like t′ (a top quark partner) coupling to third generation SM quarks [7]. The code also relies on the possibility of reproducing experimental results by using a cut-and-count analysis technique and applying a eCL procedure.Running time: Around 30 seconds with two XQs and with 100k toy Monte Carlo (MC) experiments yielding specific numbers of signal and background events to determine the eCL (tested on a DELL Precision M4700 laptop with a Kubuntu Linux 12.04 distribution).