Trigger efficiency measurement in the charged Higgs boson H+ → τν analysis

Hiukkasfysiikan standardimalli on yksi nykypäivän tarkimmista teorioista. Vuonna 2012 tapahtuneen Higgsin bosonin havaitsemisen myötä olemme havainneet kaikki alkeishiukkaset ja niiden väliset vuorovaikutukset, jotka standardimalli ennustaa. Tarkkuudestaan huolimatta hiukkasfysiikassa on kuitenkin edelleen ilmiöitä, joita standardimalli ei kykene selittämään. Standardimallin laajennuksiksi kutsutut teoriat pyrkivät selittämään standardimallin avoimia kysymyksiä ja useat laajennukset ennustavat myös uusia hiukkasia. Tämä opinnäytetyö keskittyy kahden-Higgsin-dubletin malleihin joka kuuluu standardimallin laajennuksiin. Nämä mallit ennustavat yhden sijasta yhteensä viisi Higgsin bosonia, joista kaksi on sähköisesti varattuja. Analyysi, joka on myös esitelty tässä opinnäytetyössä, pyrkii havitsemaan nämä kaksi sähköisesti varattua Higgsin bosonia. Tähän käytetään dataa, joka on kerätty suurella hadronitörmäyttimellä (eng. Large Hadron Collider) käyttäen kompaktia myonisolenoidi-hiukkasilmaisinta (eng. Compact Muon Solenoid). Data kerätään törmäyttämällä protoneita yhteen suurella energialla. Suuri energia mahdollistaa uusien hiukkasten syntymisen ja näitä lopputuotteita tutkimalla voidaan selvittää syntyikö törmäyksessä mahdollisesti eksoottisia, jopa standardimallin ulkopuolisia hiukkasia, kuten sähköisesti varattuja Higgsin bosoneja. Protonisuihkut törmäävät jopa 40 000 000 kertaa sekunnissa, minkä takia dataa syntyy nopeammin kuin sitä ehditään tallentaa. Tästä syystä tapahtumien lukumäärää on leikattava, mikä tapahtuu käyttämällä liipaisua (eng. trigger system). Liipaisu koostuu hiukkasilmaisimen laitteistoon asennetuista komponenteista sekä laitteiston ulkopuolisista tietokoneohjelmistoista, jotka päättävät mitä osia kerätystä datasta on syytä tallentaa. Liipaisu on suunniteltu niin, että valinnan läpäisevät esimerkiksi hyvin energeettiset hiukkaset, jotka saattavat olla lähtöisin mielenkiintoisista kohteista. Liipaisun jälkeen datan määrä on vähentynyt niin että se on mahdollista kirjoittaa levylle tallennusta varten. Tässä opinnäytetyössä esitän uuden menetelmän mitata liipaisun tehokkuutta. Tehokkuus määritellään liipaisun valintaan sisään tulevien hiukkasten ja valinnan läpäisseiden hiukkasten lukumäärien suhteena. Uusi menetelmä sovittaa mitattuun ja simuloituun liipaisun tehokkuuteen funktion ja näin vähentää tehokkuuden mittauksen systemaattista epävarmuutta. Tämä pienentää koko analyysin systemaattisia virhelähteitä ja parantaa lopullisia tuloksia

Search for Charged Higgs Bosons in the Neutral Higgs Boson and W Boson Decay Channel with the CMS Experiment

Standard Model of particle physics is considered the most accurate description of elementary par- ticles and their interactions. Experimental observations, however, point clearly that the Standard Model doesn’t explain all phenomena in nature, such as the origin of dark matter and the matter- antimatter asymmetry in the universe. Therefore, beyond the Standard Model theories try to give explanations to the open questions by hypothesising the existence of new elementary particles. Many extensions of the Standard Model introduce five Higgs bosons, two of which are electrically charged. The Compact Muon Solenoid experiment at the Large Hadron Collider is designed to study the predictions of the Standard Model and search for new particles predicted by beyond the Standard Model theories. In this thesis, a search for charged Higgs bosons is presented in the neutral Higgs boson and W boson decay channel. This is the first time an experimental search is conducted in this decay channel. The neutral Higgs boson decays to two tau leptons are studied while the W boson decays to a muon or an electron and a neutrino. This thesis focuses on two channels, where both tau leptons decay hadronically. The data has been collected using the Compact Muon Solenoid detector during the years 2016, 2017 and 2018. The analysis uses a data-driven background measurement to estimate the dominating Standard Model background processes, where a jet is misidentified as a hadronically decaying tau lepton. Other minor background processes are estimated using simulation. The analysis is optimised to search for charged Higgs bosons in the mass range of 300 GeV and 700 GeV. Finally, the transverse mass distribution of the charged Higgs boson is reconstructed. Since no deviation from the Standard Model prediction is found, upper exclusion limits are extracted on the production cross section and branching fraction of the charged Higgs boson. To increase the signal sensitivity, the results are combined with two additional channels with one hadronically decaying tau lepton.Hiukkasfysiikan Standardimalli on tarkin tunnettu kuvaus alkeishiukkasista ja niiden välisistä vuorovaikutuksista. Siitä huolimatta kokeelliset havainnot osoittavat, että Standardimalli ei selitä kaikkia luonnon ilmiöitä, kuten pimeän aineen alkuperää tai maailmankaikkeudessa vallitsevaa materian ja antimaterian epätasapainoa. Standardimallin laajennukset pyrkivät vastaamaan näihin avoimiin kysymyksiin ennustamalla uusia alkeishiukkasia. Monet Standardimallin laajennukset ennustavat viisi Higgsin bosonia joista kaksi on sähköisesti varattuja. Kompakti Myonisolenoidi koejärjestely, joka on kytketty Suureen Hadronitörmyttimeen on suunniteltu tutkimaan Standardimallin ennustuksia ja etsimään Standardimallin laajennuksien ennustamia uusia alkeishiukkasia. Tässä väitöskirjassa esitän sähkövarattujen Higgsin bosonien etsinnän neutraalin Higgsin bosonin ja W bosonin hajoamiskanavassa. Väitöskirjassa esitetty tutkimus on ensimmäinen kokeellinen tutkimus, joka on suoritettu tässä hajoamiskanavassa. Analyysissä tutkin hajoamisketjua, jossa neutraali Higgsin bosoni hajoaa kahteen tau leptoniin ja W bosoni hajoaa myoniin tai elektroniin ja neutriinoon. Tämä väitöskirja keskittyy kahteen hajoamisketjuun, jossa molemmat tau leptonit hajoavat hadroneihin. Väitöskirjassa käytetty data on kerätty Kompaktilla Myonisolenoidilla vuosien 2016, 2017 ja 2018 aikana. Analyysi hyödyntää suurimpien Standardimallin taustojen mittauksissa dataan pohjautuvia menetelmiä. Standardimallin taustaprosessit, joissa hiukkasryöppy näyttäytyy tau leptonina mitataan datasta. Muut pienemmät taustaprosessit mallinnetaan käyttämällä simulaatiota. Analyysi on optimoitu etsimään sähkövarauksellisia Higgsin bosoneita massojen 300 GeV ja 700 GeV väliltä. Analyysi rakentaa sähkövarauksellisen Higgsin bosoneiden transverssimassan. Koska kerätyn datan ja Standardimallin ennusteen välillä ei löydetty eroavaisuuksia, lopullisia tuloksia käytetään asettamaan kokeellinen yläraja sähkövarauksellisten Higgsin bosonien vaikutusalalle protoni-protoni törmäyksissä. Lopuksi, väitöskirjassa esitetyt kaksi hajoamisketjua yhdistetään kahden hajoamisketjun kanssa, jotka tutkivat yhden tau leptonin hajoamista hadroneihin. Näin lopullisten tulosten merkittävyyttä voidaan kasvattaa

Observation of a New Excited Beauty Strange Baryon Decaying to Xi(-)(b)pi(+)pi(-)

The Xi(-)(b)pi(+)pi(-) invariant mass spectrum is investigated with an event sample of proton-proton collisions at root s = 13 TeV, collected by the CMS experiment at the LHC in 2016-2018 and corresponding to an integrated luminosity of 140 fb(-1). The ground state Xi(-)(b) is reconstructed via its decays to J/psi Xi(-) and J/psi Lambda K-. A narrow resonance, labeled Xi(b)(6100)(-), is observed at a Xi(-)(b)pi(+)pi(-) invariant mass of 6100.3 +/- 0.2(stat) +/- 0.1(syst) +/- 0.6(Xi(-)(b)) MeV, where the last uncertainty reflects the precision of the Xi(-)(b) baryon mass. The upper limit on the Xi(b)(6100)(-) natural width is determined to be 1.9 MeV at 95% confidence level. The low Xi(b)(6100)(-) signal yield observed in data does not allow a measurement of the quantum numbers of the new state. However, following analogies with the established excited Xi(c) baryon states, the new Xi(b)(6100)(-) resonance and its decay sequence are consistent with the orbitally excited Xi(- )(b)baryon, with spin and parity quantum numbers J(P) = 3/2(-).Peer reviewe

Search for Wγ resonances in proton-proton collisions at vs=13 TeV using hadronic decays of Lorentz-boosted W bosons

A search for W gamma resonances in the mass range between 0.7 and 6.0 TeV is presented. The W boson is reconstructed via its hadronic decays, with the final-state products forming a single large-radius jet, owing to a high Lorentz boost of the W boson. The search is based on proton-proton collision data at root s = 13 TeV, corresponding to an integrated luminosity of 137 fb(-1), collected with the CMS detector at the LHC in 2016-2018. The W gamma mass spectrum is parameterized with a smoothly falling background function and examined for the presence of resonance-like signals. No significant excess above the predicted background is observed. Model-specific upper limits at 95% confidence level on the product of the cross section and branching fraction to the W gamma channel are set. Limits for narrow resonances and for resonances with an intrinsic width equal to 5% of their mass, for spin-0 and spin-1 hypotheses, range between 0.17 fb at 6.0 TeV and 55 fb at 0.7 TeV. These are the most restrictive limits to date on the existence of such resonances over a large range of probed masses. In specific heavy scalar (vector) triplet benchmark models, narrow resonances with masses between 0.75 (1.15) and 1.40 (1.36) TeV are excluded for a range of model parameters. Model-independent limits on the product of the cross section, signal acceptance, and branching fraction to the W gamma channel are set for minimum W gamma mass thresholds between 1.5 and 8.0 TeV. (c) 2022 The Author(s). Published by Elsevier B.V.Peer reviewe

Measurement of double-parton scattering in inclusive production of four jets with low transverse momentum in proton-proton collisions at root s=13 TeV

A measurement of inclusive four-jet production in proton-proton collisions at a center-of-mass energy of 13 TeV is presented. The transverse momenta of jets within vertical bar eta vertical bar 4.7 are required to exceed 35, 30, 25, and 20 GeV for the first-, second-, third-, and fourth-leading jet, respectively. Differential cross sections are measured as functions of the jet transverse momentum, jet pseudorapidity, and several other observables that describe the angular correlations between the jets. The measured distributions show sensitivity to different aspects of the underlying event, parton shower modeling, and matrix element calculations. In particular, the interplay between angular correlations caused by parton shower and double-parton scattering contributions is shown to be important. The double-parton scattering contribution is extracted by means of a template fit to the data, using distributions for single-parton scattering obtained from Monte Carlo event generators and a double-parton scattering distribution constructed from inclusive single-jet events in data. The effective double-parton scattering cross section is calculated and discussed in view of previous measurements and of its dependence on the models used to describe the single-parton scattering background.Peer reviewe

Probing Charm Quark Dynamics via Multiparticle Correlations in Pb-Pb Collisions at root s(NN)=5.02 TeV

Multiparticle azimuthal correlations of prompt D-0 mesons arc measured in Pb-Pb collisions at a nucleon-nucleon center-of-mass energy of root s(NN) = 5.02 TeV. For the first time, a four-particle cumulant method is used to extract the second Fourier coefficient of the azimuthal distribution (v(2)) of D-0 mesons as a function of event centrality and the D-0 transverse momentum. The ratios of the four-particle v(2) values to previously measured two-particle cumulant results provide direct experimental access to event-by-event fluctuations of charm quark azimuthal anisotropies. These ratios are also found to be comparable to those of inclusive charged particles in the event. However, hints of deviations are seen in the most central and peripheral collisions. To investigate the origin of flow fluctuations in the charm sector, these measurements are compared to a model implementing fluctuations of charm quark energy loss via collisional or radiative processes in the quark-gluon plasma. These models cannot quantitatively describe the data over the full transverse momentum and centrality ranges, although the calculations with collisional energy loss provide a better description of the data.Peer reviewe

Study of dijet events with large rapidity separation in proton-proton collisions at root s=2.76 TeV

The cross sections for inclusive and Mueller-Navelet dijet production are measured as a function of the rapidity separation between the jets in proton-proton collisions at root s = 2.76 TeV for jets with transverse momentum p(T) > 35 GeV and rapidity vertical bar y vertical bar 20 GeV is introduced to improve the sensitivity to the effects of the Balitsky-Fadin-Kuraev-Lipatov (BFKL) evolution. The measurement is compared with the predictions of various Monte Carlo models based on leading-order and next-to-leading-order calculations including the Dokshitzer-Gribov-Lipatov-Altarelli-Parisi leading-logarithm (LL) parton shower as well as the LL BFKL resummation.Peer reviewe

Search for electroweak production of charginos and neutralinos in proton-proton collisions at root s=13 TeV

A direct search for electroweak production of charginos and neutralinos is presented. Events with three or four leptons, with up to two hadronically decaying tau leptons, or two same-sign light leptons are analyzed. The data sample consists of 137 fb(-1) of proton-proton collisions with a center of mass energy of 13 TeV, recorded with the CMS detector at the LHC. The results are interpreted in terms of several simplified models. These represent a broad range of production and decay scenarios for charginos and neutralinos. A parametric neural network is used to target several of the models with large backgrounds. In addition, results using orthogonal search regions are provided for all the models, simplifying alternative theoretical interpretations of the results. Depending on the model hypotheses, charginos and neutralinos with masses up to values between 300 and 1450 GeV are excluded at 95% confidence level.Peer reviewe

Observation of B-0 ->psi(2S)K-S(0)pi(+)pi(-) and B-s(0)->psi(2S)K-S(0) decays

Using a data sample of root s = 13 TeV protonproton collisions collected by the CMS experiment at the LHC in 2017 and 2018 with an integrated luminosity of 103 fb(-1), the B-s(0) -> psi(2S)K-S(0) and B-0 -> psi(2S)K-S(0) pi(+) pi(-) decays are observed with significances exceeding 5 standard deviations. The resulting branching fraction ratios, measured for the first time, correspond to B(B-s(0) -> psi(2S)K-S(0))/B(B-0 Zeta -> psi(2S)K-S(0)) = (3.33 +/- 0.69(stat) +/- 0.11 (syst) +/- 0.34 (f(s)/f(d))) x 10(-2) and B(B-0 -> psi(2S)K-S(0) pi(+) pi(-))/B(B-0 -> psi(2S)K-S(0)) = 0.480 +/- 0.013 (stat) +/- 0.032 (syst), where the last uncertainty in the first ratio is related to the uncertainty in the ratio of production cross sections of B-s(0) and B-0 mesons, f(s)/f(d).Peer reviewe

Search for new particles in an extended Higgs sector with four b quarks in the final state at s=13TeV

Publisher Copyright: © 2022 The Author(s)A search for a massive resonance X decaying to a pair of spin-0 bosons ϕ that themselves decay to pairs of bottom quarks, is presented. The analysis is restricted to the mass ranges mϕ from 25 to 100 GeV and mX from 1 to 3 TeV. For these mass ranges, the decay products of each ϕ boson are expected to merge into a single large-radius jet. Jet substructure and flavor identification techniques are used to identify these jets. The search is based on CERN LHC proton-proton collision data at s=13TeV, collected with the CMS detector in 2016–2018, corresponding to an integrated luminosity of 138fb−1. Model-specific limits, where the two new particles arise from an extended Higgs sector, are set on the product of the production cross section and branching fraction for X→ϕϕ→(bb‾)(bb‾) as a function of the resonances' masses, where both the X→ϕϕ and ϕ→bb‾ branching fractions are assumed to be 100%. These limits are the first of their kind on this process, ranging between 30 and 1 fb at 95% confidence level for the considered mass ranges.Peer reviewe