Search for bottom-squark pair production in pp collision events at √s=13 TeV with hadronically decaying τ-leptons, b-jets, and missing transverse momentum using the ATLAS detector

A search for pair production of bottom squarks in events with hadronically decaying τ -leptons, b -tagged jets, and large missing transverse momentum is presented. The analyzed dataset is based on proton-proton collisions at √ s = 13     TeV delivered by the Large Hadron Collider and recorded by the ATLAS detector from 2015 to 2018, and corresponds to an integrated luminosity of 139     fb − 1 . The observed data are compatible with the expected Standard Model background. Results are interpreted in a simplified model where each bottom squark is assumed to decay into the second-lightest neutralino ˜ χ 0 2 and a bottom quark, with ˜ χ 0 2 decaying into a Higgs boson and the lightest neutralino ˜ χ 0 1 . The search focuses on final states where at least one Higgs boson decays into a pair of hadronically decaying τ -leptons. This allows the acceptance and thus the sensitivity to be significantly improved relative to the previous results at low masses of the ˜ χ 0 2 , where bottom-squark masses up to 850 GeV are excluded at the 95% confidence level, assuming a mass difference of 130 GeV between ˜ χ 0 2 and ˜ χ 0 1 . Model-independent upper limits are also set on the cross section of processes beyond the Standard Model

Measurements of differential cross-sections in four-lepton events in 13 TeV proton-proton collisions with the ATLAS detector

Measurements of four-lepton differential and integrated fiducial cross-sections in events with two same-flavour, opposite-charge electron or muon pairs are presented. The data correspond to 139 fb−1 of s√ = 13 TeV proton-proton collisions, collected by the ATLAS detector during Run 2 of the Large Hadron Collider (2015–2018). The final state has contributions from a number of interesting Standard Model processes that dominate in different four-lepton invariant mass regions, including single Z boson production, Higgs boson production and on-shell ZZ production, with a complex mix of interference terms, and possible contributions from physics beyond the Standard Model. The differential cross-sections include the four-lepton invariant mass inclusively, in slices of other kinematic variables, and in different lepton flavour categories. Also measured are dilepton invariant masses, transverse momenta, and angular correlation variables, in four regions of four-lepton invariant mass, each dominated by different processes. The measurements are corrected for detector effects and are compared with state-of-the-art Standard Model calculations, which are found to be consistent with the data. The Z → 4ℓ branching fraction is extracted, giving a value of (4.41 ± 0.30) × 10−6. Constraints on effective field theory parameters and a model based on a spontaneously broken B − L gauge symmetry are also evaluated. Further reinterpretations can be performed with the provided information

Medium-Induced Modification of Z-Tagged Charged Particle Yields in Pb+Pb Collisions at 5.02 TeV with the ATLAS Detector

The yield of charged particles opposite to a Z boson with large transverse momentum ( p T ) is measured in 260     pb − 1 of p p and 1.7     nb − 1 of Pb + Pb collision data at 5.02 TeV per nucleon pair recorded with the ATLAS detector at the Large Hadron Collider. The Z boson tag is used to select hard-scattered partons with specific kinematics, and to observe how their showers are modified as they propagate through the quark-gluon plasma created in Pb + Pb collisions. Compared with p p collisions, charged-particle yields in Pb + Pb collisions show significant modifications as a function of charged-particle p T in a way that depends on event centrality and Z boson p T . The data are compared with a variety of theoretical calculations and provide new information about the medium-induced energy loss of partons in a p T regime difficult to measure through other channels

Search for pair production of third-generation scalar leptoquarks decaying into a top quark and a τ-lepton in pp collisions at s√ = 13 TeV with the ATLAS detector

A search for pair production of third-generation scalar leptoquarks decaying into a top quark and a τ-lepton is presented. The search is based on a dataset of pp collisions at s√ = 13 TeV recorded with the ATLAS detector during Run 2 of the Large Hadron Collider, corresponding to an integrated luminosity of 139 fb−1. Events are selected if they have one light lepton (electron or muon) and at least one hadronically decaying τ -lepton, or at least two light leptons. In addition, two or more jets, at least one of which must be identified as containing b-hadrons, are required. Six final states, defined by the multiplicity and flavour of lepton candidates, are considered in the analysis. Each of them is split into multiple event categories to simultaneously search for the signal and constrain several leading backgrounds. The signal-rich event categories require at least one hadronically decaying τ-lepton candidate and exploit the presence of energetic final-state objects, which is characteristic of signal events. No significant excess above the Standard Model expectation is observed in any of the considered event categories, and 95% CL upper limits are set on the production cross section as a function of the leptoquark mass, for different assumptions about the branching fractions into tτ and bν. Scalar leptoquarks decaying exclusively into tτ are excluded up to masses of 1.43 TeV while, for a branching fraction of 50% into tτ, the lower mass limit is 1.22 TeV

Muon reconstruction and identification efficiency in ATLAS using the full Run 2 pp collision data set at \sqrt{s}=13 TeV

This article documents the muon reconstruction and identification efficiency obtained by the ATLAS experiment for 139 \hbox {fb}^{-1} of pp collision data at \sqrt{s}=13 TeV collected between 2015 and 2018 during Run 2 of the LHC. The increased instantaneous luminosity delivered by the LHC over this period required a reoptimisation of the criteria for the identification of prompt muons. Improved and newly developed algorithms were deployed to preserve high muon identification efficiency with a low misidentification rate and good momentum resolution. The availability of large samples of Z\rightarrow \mu \mu and J/\psi \rightarrow \mu \mu decays, and the minimisation of systematic uncertainties, allows the efficiencies of criteria for muon identification, primary vertex association, and isolation to be measured with an accuracy at the per-mille level in the bulk of the phase space, and up to the percent level in complex kinematic configurations. Excellent performance is achieved over a range of transverse momenta from 3 GeV to several hundred GeV, and across the full muon detector acceptance of |\eta |<2.7

Search for dark matter in events with missing transverse momentum and a Higgs boson decaying into two photons in pp collisions at root s=13 TeV with the ATLAS detector

A search for dark-matter particles in events with large missing transverse momentum and a Higgs boson candidate decaying into two photons is reported. The search uses 139 fb−1 of proton-proton collision data collected at s√ = 13 TeV with the ATLAS detector at the CERN LHC between 2015 and 2018. No significant excess of events over the Standard Model predictions is observed. The results are interpreted by extracting limits on three simplified models that include either vector or pseudoscalar mediators and predict a final state with a pair of dark-matter candidates and a Higgs boson decaying into two photons

Two-particle azimuthal correlations in photonuclear ultraperipheral Pb plus Pb collisions at 5.02 TeV with ATLAS

Two-particle long-range azimuthal correlations are measured in photonuclear collisions using 1.7 nb − 1 of 5.02 TeV Pb + Pb collision data collected by the ATLAS experiment at the CERN Large Hadron Collider. Candidate events are selected using a dedicated high-multiplicity photonuclear event trigger, a combination of information from the zero-degree calorimeters and forward calorimeters, and from pseudorapidity gaps constructed using calorimeter energy clusters and charged-particle tracks. Distributions of event properties are compared between data and Monte Carlo simulations of photonuclear processes. Two-particle correlation functions are formed using charged-particle tracks in the selected events, and a template-fitting method is employed to subtract the nonflow contribution to the correlation. Significant nonzero values of the second- and third-order flow coefficients are observed and presented as a function of charged-particle multiplicity and transverse momentum. The results are compared with flow coefficients obtained in proton-proton and proton-lead collisions in similar multiplicity ranges, and with theoretical expectations. The unique initial conditions present in this measurement provide a new way to probe the origin of the collective signatures previously observed only in hadronic collision

Nuorten päihteiden käyttö ja vanhempien saama tuki

Nuorten päihteiden käyttö on lisääntynyt viime vuosina. Nuoret eivät yleensä ole päihteistä riippuvaisia, mutta satunnainenkin kokeilu ja käyttö ovat haitallisia. Päihteiden käyttö voi olla yksittäinen ongelma, mutta myös osa suurempaa ongelmakokonaisuutta. Tämän vuoksi nuoren tilannetta tulee tarkastella kokonaisvaltaisesti. Päihteiden käyttöä ei aina huomata, ja sen ilmeneminen voi olla sokki läheisille. Päihteiden käyttö on ongelma käyttäjälle, mutta voi sairastuttaa myös läheiset. Läheiset, usein nuorten vanhemmat, tarvitsevat myös tukea ja neuvoa tilanteessa. Vanhempien oma asenne ja päihdekäyttäytyminen sekä nuoren asioista perillä oleminen ovat tärkeitä ehkäiseviä tekijöitä nuoren päihteiden käytölle. Myös nuoren oma asenne päihteisiin sekä sosiaaliset suhteet ja onnistumisen kokemukset ovat päihteiltä suojaavia tekijöitä. Tämä opinnäytetyö on tehty kokoamalla kattavasti teoriatietoa päihteistä, niiden käytöstä ja haitoista. Etelä-Karjalan sosiaali- ja terveyspiirin (Eksoten) internet-sivuilta selvitettiin, mistä ja miten voi hakea apua ja neuvoja läheisen päihteiden käytön ongelmiin. Lisäksi tehtiin kysely päihdenuorten vanhemmille. Kyselyllä selvitettiin päihdenuorten vanhempien omaa kokemusta saamastaan tuesta sosiaali- ja terveysalan ammattilaisilta. Tulokset analysoitiin empiirisesti. Tulosten mukaan osa vanhemmista on tyyty-väisiä saamaansa tukeen, osa taas kokee, ettei ole saanut tarpeeksi tukea ja tietoa. Päihdepalvelujen parempi ja määrällisesti laajempi saatavuus on kyse-lyyn vastanneiden vanhempien toiveissa. Tästä voidaan päätellä, että päih-denuorten vanhemmat otetaan huomioon ja tukea on tarjolla, mutta kaikkia tuki ei tavoita. Jatkotutkimuksessa voisi selvittää millaiseksi päihdenuoret kokevat saamansa hoidon. Lisäksi voisi selvittää miten sosiaali- ja terveysalan ammattilaiset koke-vat voivansa vaikuttaa nuorten päihdekäyttäytymiseen ja miten sosiaali- ja ter-veysalan ammattilaiset voisivat ottaa päihdenuorten vanhemmat paremmin huomioon. Kirjallisen nuorten päihdeasioita käsittelevän oppaan tekeminen ja jakaminen vanhemmille voisi olla hyödyllinen.Intoxicant use and abuse in young people has increased in recent years. Young people are generally not dependent on intoxicants, but occasional experimentation and use are harmful. Intoxicant use can be a single problem or part of a larger set of problems. Because of this, the situation of the young people should be considered from a broad perspective. Intoxicant use is not always noticed and its appearance may be a shock to those close to the user. Intoxicant use is a problem in the user, but can cause problems for families and friends, as well. Closely related, commonly parents, also need support and counsel in these situations. Parent's own attitudes and customs to use intoxicants, and knowing well issues about young people are important preventive factors for young people's intoxicant use. Also young people's attitude to intoxicant use and social affairs and experience of success are protective factors for intoxicant use. This thesis has been done by collecting comprehensive information on theory of intoxicant consumption and drawbacks of them. With the help of South Karelia District of Social and Health Service's websites, information about where and how to get help and advice for those close to young people with problems was found. In addition to this has been done an inquiry to parents of young people who use intoxicants. By the inquiry, the parents own experiences of having support from professionals in social and health care were examined. The results were analyzed empirically. According to the results, a proportion of parents are satisfied for support they have got, whereas part of parents find that they have not had enough support and information. The parents hope for better and wider availability of services for intoxicant users. Parents of young intoxicant abusers were taken into ac-count, and support services are available, but they do not reach all who need them. For further study, the opinions of the young people, and also of the health professionals about care of intoxicant abusers would be of interest