Bestimmung der fehlenden transversalen Energie auf der ersten Triggerstufe beim ATLAS-Experiment und Optimierung der Triggerselektion von supersymmetrischen Ereignissen

Das Standardmodell der Teilchenphysik, das drei der vier fundamentalen Wechselwirkungen beschreibt, stimmt bisher sehr gut mit den Messergebnissen der Experimente am CERN, dem Fermilab und anderen Forschungseinrichtungen überein. rnAllerdings können im Rahmen dieses Modells nicht alle Fragen der Teilchenphysik beantwortet werden. So lässt sich z.B. die vierte fundamentale Kraft, die Gravitation, nicht in das Standardmodell einbauen.rnDarüber hinaus hat das Standardmodell auch keinen Kandidaten für dunkle Materie, die nach kosmologischen Messungen etwa 25 % unseres Universum ausmacht.rnAls eine der vielversprechendsten Lösungen für diese offenen Fragen wird die Supersymmetrie angesehen, die eine Symmetrie zwischen Fermionen und Bosonen einführt. rnAus diesem Modell ergeben sich sogenannte supersymmetrische Teilchen, denen jeweils ein Standardmodell-Teilchen als Partner zugeordnet sind.rnEin mögliches Modell dieser Symmetrie ist das R-Paritätserhaltende mSUGRA-Modell, falls Supersymmetrie in der Natur realisiert ist.rnIn diesem Modell ist das leichteste supersymmetrische Teilchen (LSP) neutral und schwach wechselwirkend, sodass es nicht direkt im Detektor nachgewiesen werden kann, sondern indirekt über die vom LSP fortgetragene Energie, die fehlende transversale Energie (etmiss), nachgewiesen werden muss.rnrnDas ATLAS-Experiment wird 2010 mit Hilfe des pp-Beschleunigers LHC mit einer Schwerpunktenergie von sqrt(s)=7-10 TeV mit einer Luminosität von 10^32 #/(cm^2*s) mit der Suche nach neuer Physik starten.rnDurch die sehr hohe Datenrate, resultierend aus den etwa 10^8 Auslesekanälen des ATLAS-Detektors bei einer Bunchcrossingrate von 40 MHz, wird ein Triggersystem benötigt, um die zu speichernde Datenmenge zu reduzieren.rnDabei muss ein Kompromiss zwischen der verfügbaren Triggerrate und einer sehr hohen Triggereffizienz für die interessanten Ereignisse geschlossen werden, da etwa nur jedes 10^8-te Ereignisse für die Suche nach neuer Physik interessant ist.rnZur Erfüllung der Anforderungen an das Triggersystem wird im Experiment ein dreistufiges System verwendet, bei dem auf der ersten Triggerstufe mit Abstand die höchste Datenreduktion stattfindet.rnrnIm Rahmen dieser Arbeit rn%, die vollständig auf Monte-Carlo-Simulationen basiert, rnist zum einen ein wesentlicher Beitrag zum grundlegenden Verständnis der Eigenschaft der fehlenden transversalen Energie auf der ersten Triggerstufe geleistet worden.rnZum anderen werden Methoden vorgestellt, mit denen es möglich ist, die etmiss-Triggereffizienz für Standardmodellprozesse und mögliche mSUGRA-Szenarien aus Daten zu bestimmen. rnBei der Optimierung der etmiss-Triggerschwellen für die erste Triggerstufe ist die Triggerrate bei einer Luminosität von 10^33 #/(cm^2*s) auf 100 Hz festgelegt worden.rnFür die Triggeroptimierung wurden verschiedene Simulationen benötigt, bei denen eigene Entwicklungsarbeit eingeflossen ist.rnMit Hilfe dieser Simulationen und den entwickelten Optimierungsalgorithmen wird gezeigt, dass trotz der niedrigen Triggerrate das Entdeckungspotential (für eine Signalsignifikanz von mindestens 5 sigma) durch Kombinationen der etmiss-Schwelle mit Lepton bzw. Jet-Triggerschwellen gegenüber dem bestehenden ATLAS-Triggermenü auf der ersten Triggerstufe um bis zu 66 % erhöht wird.

Measurement of the elastic electron-proton cross section and separation of the electric and magnetic form factor in the Q 2 range from 0.004 to 1 (GeV/c) 2

The electromagnetic form factors of the proton are fundamental quantities sensitive to the distribution of charge and magnetization inside the proton. Precise knowledge of the form factors, in particular of the charge and magnetization radii provide strong tests for theory in the non-perturbative regime of QCD. However, the existing data at Q^2 below 1 (GeV/c)^2 are not precise enough for a hard test of theoretical predictions.rnrnFor a more precise determination of the form factors, within this work more than 1400 cross sections of the reaction H(e,e′)p were measured at the Mainz Microtron MAMI using the 3-spectrometer-facility of the A1-collaboration. The data were taken in three periods in the years 2006 and 2007 using beam energies of 180, 315, 450, 585, 720 and 855 MeV. They cover the Q^2 region from 0.004 to 1 (GeV/c)^2 with counting rate uncertainties below 0.2% for most of the data points. The relative luminosity of the measurements was determined using one of the spectrometers as a luminosity monitor. The overlapping acceptances of the measurements maximize the internal redundancy of the data and allow, together with several additions to the standard experimental setup, for tight control of systematic uncertainties.rnTo account for the radiative processes, an event generator was developed and implemented in the simulation package of the analysis software which works without peaking approximation by explicitly calculating the Bethe-Heitler and Born Feynman diagrams for each event.rnTo separate the form factors and to determine the radii, the data were analyzed by fitting a wide selection of form factor models directly to the measured cross sections. These fits also determined the absolute normalization of the different data subsets. The validity of this method was tested with extensive simulations. The results were compared to an extraction via the standard Rosenbluth technique.rnrnThe dip structure in G_E that was seen in the analysis of the previous world data shows up in a modified form. When compared to the standard-dipole form factor as a smooth curve, the extracted G_E exhibits a strong change of the slope around 0.1 (GeV/c)^2, and in the magnetic form factor a dip around 0.2 (GeV/c)^2 is found. This may be taken as indications for a pion cloud. For higher Q^2, the fits yield larger values for G_M than previous measurements, in agreement with form factor ratios from recent precise polarized measurements in the Q2 region up to 0.6 (GeV/c)^2.rnrnThe charge and magnetic rms radii are determined as rn⟨r_e⟩=0.879 ± 0.005(stat.) ± 0.004(syst.) ± 0.002(model) ± 0.004(group) fm,rn⟨r_m⟩=0.777 ± 0.013(stat.) ± 0.009(syst.) ± 0.005(model) ± 0.002(group) fm.rnThis charge radius is significantly larger than theoretical predictions and than the radius of the standard dipole. However, it is in agreement with earlier results measured at the Mainz linear accelerator and with determinations from Hydrogen Lamb shift measurements. The extracted magnetic radius is smaller than previous determinations and than the standard-dipole value.

Hydrodynamical simulations of early-type galaxies: effects of galaxy shape and stellar dynamics on hot coronae

Early-Type galaxies (ETGs) are embedded in hot (10^6-10^7 K), X-ray emitting gaseous haloes, produced mainly by stellar winds and heated by Type Ia supernovae explosions, by the thermalization of stellar motions and occasionally by the central super-massive black hole (SMBH). In particular, the thermalization of the stellar motions is due to the interaction between the stellar and the SNIa ejecta and the hot interstellar medium (ISM) already residing in the ETG. A number of different astrophysical phenomena determine the X-ray properties of the hot ISM, such as stellar population formation and evolution, galaxy structure and internal kinematics, Active Galactic Nuclei (AGN) presence, and environmental effects. With the aid of high-resolution hydrodynamical simulations performed on state-of-the-art galaxy models, in this Thesis we focus on the effects of galaxy shape, stellar kinematics and star formation on the evolution of the X-ray coronae of ETGs. Numerical simulations show that the relative importance of flattening and rotation are functions of the galaxy mass: at low galaxy masses, adding flattening and rotation induces a galactic wind, thus lowering the X-ray luminosity; at high galaxy masses the angular momentum conservation keeps the central regions of rotating galaxies at low density, whereas in non-rotating models a denser and brighter atmosphere is formed. The same dependence from the galaxy mass is present in the effects of star formation (SF): in light galaxies SF contributes to increase the spread in Lx, while at high galaxy masses the halo X-ray properties are marginally sensitive to SF effects. In every case, the star formation rate at the present epoch quite agrees with observations, and the massive, cold gaseous discs are partially or completely consumed by SF on a time-scale of few Gyr, excluding the presence of young stellar discs at the present epoch.

Measurements of ttbar Differential Cross Section at the ATLAS Experiment in pp Collisions at sqrt(s)=7TeV and sqrt(s)=8TeV

This PhD thesis presents two measurements of differential production cross section of top and anti-top pairs tt ̅ decaying in a lepton+jets final state. The normalize cross section is measured as a function of the top transverse momentum and the tt ̅ mass, transverse momentum and rapidity using the full 2011 proton-proton (pp) ATLAS data taking at a center of mass energy of √s=7 TeV and corresponding to an integrated luminosity of L=4.6 〖fb〗^(-1). The cross section is also measured at the particle level as a function of the hadronic top transverse momentum for highly energetic events using the full 2012 data taking at √s=8 TeV and with L=20 〖fb〗^(-1). The measured spectra are fully corrected for detector efficiency and resolution effects and are compared to several theoretical predictions showing a quite good agreement, depending on different spectra.

Production of Z bosons in proton-proton collisions at root out s = 10 TeV: Expectations for early measurements at the ATLAS experiment

The production of the Z boson in proton-proton collisions at the LHC serves as a standard candle at the ATLAS experiment during early data-taking. The decay of the Z into an electron-positron pair gives a clean signature in the detector that allows for calibration and performance studies. The cross-section of ~ 1 nb allows first LHC measurements of parton density functions. In this thesis, simulations of 10 TeV collisions at the ATLAS detector are studied. The challenges for an experimental measurement of the cross-section with an integrated luminositiy of 100 pb−1 are discussed. In preparation for the cross-section determination, the single-electron efficiencies are determined via a simulation based method and in a test of a data-driven ansatz. The two methods show a very good agreement and differ by ~ 3% at most. The ingredients of an inclusive and a differential Z production cross-section measurement at ATLAS are discussed and their possible contributions to systematic uncertainties are presented. For a combined sample of signal and background the expected uncertainty on the inclusive cross-section for an integrated luminosity of 100 pb−1 is determined to 1.5% (stat) +/- 4.2% (syst) +/- 10% (lumi). The possibilities for single-differential cross-section measurements in rapidity and transverse momentum of the Z boson, which are important quantities because of the impact on parton density functions and the capability to check for non-pertubative effects in pQCD, are outlined. The issues of an efficiency correction based on electron efficiencies as function of the electron’s transverse momentum and pseudorapidity are studied. A possible alternative is demonstrated by expanding the two-dimensional efficiencies with the additional dimension of the invariant mass of the two leptons of the Z decay.

Search for time-integrated cp violation in $d^0 \rightarrow k^+k^-$ and $d^0 \rightarrow \pi^+\pi^-$ decays at lhcb.

The LHCb experiment at the LHC, by exploiting the high production cross section for $c\overline{c}$ quark pairs, offers the possibility to investigate $\mathcal{CP}$ violation in the charm sector with a very high precision.\\ In this thesis a measurement of time-integrated \(\mathcal{CP}\) violation using $D^0\rightarrow~K^+K^-$ and $D^0\rightarrow \pi^+\pi^-$ decays at LHCb is presented. The measured quantity is the difference ($\Delta$) of \(\mathcal{CP}\) asymmetry ($\mathcal{A}_{\mathcal{CP}}$) between the decay rates of $D^0$ and $\overline{D}^0$ mesons into $K^+K^–$ and $\pi^+\pi^-$ pairs.\\ The analysis is performed on 2011 data, collected at \(\sqrt{s}=7\) TeV and corresponding to an integrated luminosity of 1 fb\(^{-1}\), and 2012 data, collected at \(\sqrt{s}=8\) TeV and corresponding to an integrated luminosity of 2 fb\(^{-1}\).\\ A complete study of systematic uncertainties is beyond the aim of this thesis. However the most important systematic of the previous analysis has been studied. We find that this systematic uncertainty was due to a statistical fluctuation and then we demonstrate that it is no longer necessary to take into account.\\ By combining the 2011 and 2012 results, the final statistical precision is 0.08\%. When this analysis will be completed and published, this will be the most precise single measurement in the search for $\mathcal{CP}$ violation in the charm sector.

Measurement of the inclusive jet cross section in proton-proton collisions at root out s = 7 TeV with the ATLAS detector

The dominant process in hard proton-proton collisions is the production of hadronic jets.rnThese sprays of particles are produced by colored partons, which are struck out of their confinement within the proton.rnPrevious measurements of inclusive jet cross sections have provided valuable information for the determination of parton density functions and allow for stringent tests of perturbative QCD at the highest accessible energies.rnrnThis thesis will present a measurement of inclusive jet cross sections in proton-proton collisions using the ATLAS detector at the LHC at a center-of-mass energy of 7 TeV.rnJets are identified using the anti-kt algorithm and jet radii of R=0.6 and R=0.4.rnThey are calibrated using a dedicated pT and eta dependent jet calibration scheme.rnThe cross sections are measured for 40 GeV < pT <= 1 TeV and |y| < 2.8 in four bins of absolute rapidity, using data recorded in 2010 corresponding to an integrated luminosity of 3 pb^-1.rnThe data is fully corrected for detector effects and compared to theoretical predictions calculated at next-to-leading order including non-perturbative effects.rnThe theoretical predictions are found to agree with data within the experimental and theoretic uncertainties.rnrnThe ratio of cross sections for R=0.4 and R=0.6 is measured, exploiting the significant correlations of the systematic uncertainties, and is compared to recently developed theoretical predictions.rnThe underlying event can be characterized by the amount of transverse momentum per unit rapidity and azimuth, called rhoue.rnUsing analytical approaches to the calculation of non-perturbative corrections to jets, rhoue at the LHC is estimated using the ratio measurement.rnA feasibility study of a combined measurement of rhoue and the average strong coupling in the non-perturbative regime alpha_0 is presented and proposals for future jet measurements at the LHC are made.

Messung der Charmonium-Produktion und Energiekalibration für Elektronen mit dem Atlas-Experiment

Der Wirkungsquerschnitt der Charmoniumproduktion wurde unter Nutzung der Daten aus pp-Kollisionen bei s^{1/2}=7TeV, die im Jahr 2010 vom Atlas-Experiment am LHC aufgezeichnet wurden, gemessen. Um das notwendige Detektorverständnis zu verbessern, wurde eine Energiekalibration durchgeführt.rnrnrnUnter Nutzung von Elektronen aus Zerfällen des Charmoniums wurde die Energieskala der elektromagnetischen Kalorimeter bei niedrigen Energien untersucht. Nach Anwendung der Kalibration wurden für die Energiemessung im Vergleich mit in Monte-Carlo-Simulationen gemessenen Energien Abweichungen von weniger als 0,5% gefunden.rnrnrnMit einer integrierten Luminosität von 2,2pb^{-1} wurde eine erste Messung des inklusiven Wirkungsquerschnittes für den Prozess pp->J/psi(e^{+}e^{-})+X bei s^{1/2}=7TeV vorgenommen. Das geschah im zugänglichen Bereich für Transversalimpulse p_{T,ee}>7GeV und Rapiditäten |y_{ee}|<2,4. Es wurden differentielle Wirkungsquerschnitte für den Transversalimpuls p_{T,ee} und für die Rapidität |y_{ee}| bestimmt. Integration beider Verteilungen lieferte für den inklusiven Wirkungsquerschnitt sigma(pp-> J/psi X)BR(J/psi->e^{+}e^{-}) die Werte (85,1+/-1,9_{stat}+/-11,2_{syst}+/-2,9_{Lum})nb und (75,4+/-1,6_{stat}+/-11,9_{syst}+/-2,6_{Lum})nb, die innerhalb der Systematik kompatibel sind.rnrnrnVergleiche mit Messungen von Atlas und CMS für den Prozess pp->J/psi(mu^{+}mu^{-})+X zeigten gute Übereinstimmung. Zum Vergleich mit der Theorie wurden Vorhersagen mit verschiedenen Modellen in nächst-zu-führender und mit Anteilen in nächst-zu-nächst-zu-führender Ordnung kombiniert. Der Vergleich zeigt eine gute Übereinstimmung bei Berücksichtigung von Anteilen in nächst-zu-nächst-zu-führender Ordnung.

X-ray properties and evolution of high-redshift AGN, and the gas content of host galaxies

In this thesis, I have investigated the evolution of the high-redshift (z > 3) AGN population by collecting data from some of the major Chandra and XMM-Newton surveys. The final sample (141 sources) is one of the largest selected at z> 3 in the X- rays and it is characterised by a very high redshift completeness (98%). I derived the spectral slopes and obscurations through a spectral anaysis and I assessed the high-z evolution by deriving the luminosity function and the number counts of the sample. The best representation of the AGN evolution is a pure density evolution (PDE) model: the AGN space density is found to decrease by a factor of 10 from z=3 to z=5. I also found that about 50% of AGN are obscured by large column densities (logNH > 23). By comparing these data with those in the Local Universe, I found a positive evolution of the obscured AGN fraction with redshift, especially for luminous (logLx > 44) AGN. I also studied the gas content of z < 1 AGN-hosting galaxies and compared it with that of inactive galaxies. For the first time, I applied to AGN a method to derive the gas mass previously used for inactive galaxies only. AGN are found to live preferentially in gas-rich galaxies. This result on the one hand can help us in understanding the AGN triggering mechanisms, on the other hand explains why AGN are preferentially hosted by star-forming galaxies.

COSMIC-LAB: Terzan 5 as a fossil remnant of the Galactic bulge formation epoch

The formation and evolution of galaxy bulges is a greatly debated topic in modern astrophysics. An approach to address this issue is to look at the Galactic bulge, the closest to us. According to some theoretical models, our bulge built-up from the merger of substructures formed from the instability and fragmentation of a proto-disk in the early phases of Galactic evolution. We may have discovered the remnant of one of these substructures: the stellar system Terzan 5. Terzan 5 hosts two stellar populations with different iron abundances, thus suggesting it once was far more massive than today. Moreover, its peculiar chemistry resembles that observed only in the Galactic bulge. In this Thesis we perform a detailed photometric and spectroscopic analysis of this cluster to determine its formation and evolutionary histories. Form the photometric point of view we built a high-resolution differential reddening map in Terzan 5 direction and we measured relative proper motions to separate its member population from the contaminating field stars. This information represents the necessary work to measure the absolute ages of Terzan 5 populations via the Turn-off luminosity method. From the spectroscopic point of view we measured abundances for more than 600 stars belonging to Terzan 5 and its surroundings in order to build the largest field-decontaminated metallicity distribution for this system. We find that the metallicity distribution is extremely wide (more than 1 dex) and we discovered a third, metal-poor and alpha-enhanced population with average [Fe/H]=-0.8. The striking similarity between Terzan 5 and the bulge in terms of their chemical formation and evolution revealed by this Thesis suggests that Terzan 5 formed in situ with the bulge itself. In particular its metal-poor populations trace the early stages of the bulge formation, while its most metal-rich component contains crucial information on the bulge more recent evolution.

Tracing AGN accretion and star formation in Herschel galaxies

In this Thesis, we study the physical properties and the cosmic evolution of AGN and their host galaxies since z∼3. Our analysis exploits samples of star forming galaxies detected with Herschel at far-IR wavelengths (from 70 up to 500 micron) in different extragalactic surveys, such as COSMOS and the deep GOODS (South and North) fields. The broad-band ancillary data available in COSMOS and the GOODS fields, allows us to implement Herschel and Spitzer photometry with multi-wavelength ancillary data. We perform a multicomponent SED-fitting decomposition to decouple the emission due to star formation from that due to AGN accretion, and to estimate both host-galaxy parameters (such as stellar mass, M* and star formation rate, SFR), and nuclear intrinsic bolometric luminosities. We use the individual estimates of AGN bolometric luminosity obtained through SED-fitting decomposition to reconstruct the redshit evolution of the AGN bolometric luminosity function since z∼3. The resulting trends are used to estimate the overall AGN accretion rate density at different cosmic epochs and to trace the first ever estimate of the AGN accretion history from an IR survey. Later on, we focus our study on the connection between AGN accretion and integrated galaxy properties. We analyse the relationships of AGN accretion with galaxy properties in the SFR-M* plane and at different cosmic epochs. Finally, we infer what is the parameter that best correlates with AGN accretion, comparing our results with previous studies and discussing their physical implications in the context of current scenarios of AGN/galaxy evolution.

The new Beam Halo Monitor for the CMS experiment at the LHC

In the context of increasing beam energy and luminosity of the LHC accelerator at CERN, it will be important to accurately measure the Machine Induced Background. A new monitoring system will be installed in the CMS cavern for measuring the beam background at high radius. This detector, called the Beam Halo Monitor, will provide an online, bunch-by-bunch measurement of background induced by beam halo interactions, separately for each beam. The detector is composed of synthetic quartz Cherenkov radiators, coupled to fast UV sensitive photomultiplier tubes. The directional and fast response of the system allows the discrimination of the background particles from the dominant flux in the cavern induced by pp collision debris, produced within the 25 ns bunch spacing. The readout electronics of this detector will make use of many components developed for the upgrade of the CMS Hadron Calorimeter electronics, with a dedicated firmware and readout adapted to the beam monitoring requirements. The PMT signal will be digitized by a charge integrating ASIC, providing both the signal rise time and the charge integrated over one bunch crossing. The backend electronics will record bunch-by-bunch histograms, which will be published to CMS and the LHC using the newly designed CMS beam instrumentation specific DAQ. A calibration and monitoring system has been designed to generate triggered pulses of UV light to monitor the efficiency of the system. The experimental results validating the design of the detector, the calibration system and the electronics will be presented.

Measurement of the $B^0$ - $\bar{B}^0$ and $B^0_s$ - $\bar{B}^0_s$ production asymmetries in pp collisions at $\sqrt{s}=7$ TeV and $\sqrt{s}=8$ TeV with the LHCb experiment

The production rate of $b$ and $\bar{b}$ hadrons in $pp$ collisions are not expected to be strictly identical, due to imbalance between quarks and anti-quarks in the initial state. This phenomenon can be naively related to the fact that the $\bar{b}$ quark produced in the hard scattering might combine with a $u$ or $d$ valence quark from the colliding protons, whereas the same cannot happen for a $b$ quark. This thesis presents the analysis performed to determine the production asymmetries of $B^0$ and $B^0_s$. The analysis relies on data samples collected by the LHCb detector at the Large Hadron Collider (LHC) during the 2011 and 2012 data takings at two different values of the centre of mass energy $\sqrt{s}=7$ TeV and at $\sqrt{s}=8$ TeV, corresponding respectively to an integrated luminosity of 1 fb$^{-1}$ and of 2 fb$^{-1}$. The production asymmetry is one of the key ingredients to perform measurements of $CP$ violation in b-hadron decays at the LHC, since $CP$ asymmetries must be disentangled from other sources. The measurements of the production asymmetries are performed in bins of $p_\mathrm{T}$ and $\eta$ of the $B$-meson. The values of the production asymmetries, integrated in the ranges $4 < p_\mathrm{T} < 30$ GeV/c and $2.5<\eta<4.5$, are determined to be: \begin{equation} A_\mathrm{P}(\B^0)= (-1.00\pm0.48\pm0.29)\%,\nonumber \end{equation} \begin{equation} A_\mathrm{P}(\B^0_s)= (\phantom{-}1.09\pm2.61\pm0.61)\%,\nonumber \end{equation} where the first uncertainty is statistical and the second is systematic. The measurement of $A_\mathrm{P}(B^0)$ is performed using the full statistics collected by LHCb so far, corresponding to an integrated luminosity of 3 fb$^{-1}$, while the measurement of $A_\mathrm{P}(B^0_s)$ is realized with the first 1 fb$^{-1}$, leaving room for improvement. No clear evidence of dependences on the values of $p_\mathrm{T}$ and $\eta$ is observed. The results presented in this thesis are the most precise measurements available up to date.

Measurement of CP asymmetries in $\lambda^0_b \to pk^-$ and $\lambda^0_b \to p \pi^-$ decays at LHCb

The LHCb experiment has been designed to perform precision measurements in the flavour physics sector at the Large Hadron Collider (LHC) located at CERN. After the recent observation of CP violation in the decay of the Bs0 meson to a charged pion-kaon pair at LHCb, it is interesting to see whether the same quark-level transition in Λ0b baryon decays gives rise to large CP-violating effects. Such decay processes involve both tree and penguin Feynman diagrams and could be sensitive probes for physics beyond the Standard Model. The measurement of the CP-violating observable defined as ∆ACP = ACP(Λ0b → pK−)−ACP(Λ0b →pπ−),where ACP(Λ0b →pK−) and ACP(Λ0b →pπ−) are the direct CP asymmetries in Λ0b → pK− and Λ0b → pπ− decays, is presented for the first time using LHCb data. The procedure followed to optimize the event selection, to calibrate particle identification, to parametrise the various components of the invariant mass spectra, and to compute corrections due to the production asymmetry of the initial state and the detection asymmetries of the final states, is discussed in detail. Using the full 2011 and 2012 data sets of pp collisions collected with the LHCb detector, corresponding to an integrated luminosity of about 3 fb−1, the value ∆ACP = (0.8 ± 2.1 ± 0.2)% is obtained. The first uncertainty is statistical and the second corresponds to one of the dominant systematic effects. As the result is compatible with zero, no evidence of CP violation is found. This is the most precise measurement of CP violation in the decays of baryons containing the b quark to date. Once the analysis will be completed with an exhaustive study of systematic uncertainties, the results will be published by the LHCb Collaboration.

Measurement of the pair production of b-jets in proton-proton collisions at root out s = 7 TeV with the ATLAS detector

In hadronischen Kollisionen entstehen bei einem Großteil der Ereignisse mit einem hohen Impulsübertrag Paare aus hochenergetischen Jets. Deren Produktion und Eigenschaften können mit hoher Genauigkeit durch die Störungstheorie in der Quantenchromodynamik (QCD) vorhergesagt werden. Die Produktion von \textit{bottom}-Quarks in solchen Kollisionen kann als Maßstab genutzt werden, um die Vorhersagen der QCD zu testen, da diese Quarks die Dynamik des Produktionsprozesses bei Skalen wieder spiegelt, in der eine Störungsrechnung ohne Einschränkungen möglich ist. Auf Grund der hohen Masse von Teilchen, die ein \textit{bottom}-Quark enthalten, erhält der gemessene, hadronische Zustand den größten Teil der Information von dem Produktionsprozess der Quarks. Weil sie eine große Produktionsrate besitzen, spielen sie und ihre Zerfallsprodukte eine wichtige Rolle als Untergrund in vielen Analysen, insbesondere in Suchen nach neuer Physik. In ihrer herausragenden Stellung in der dritten Quark-Generation könnten sich vermehrt Zeichen im Vergleich zu den leichteren Quarks für neue Phänomene zeigen. Daher ist die Untersuchung des Verhältnisses zwischen der Produktion von Jets, die solche \textit{bottom}-Quarks enthalten, auch bekannt als $b$-Jets, und aller nachgewiesener Jets ein wichtiger Indikator für neue massive Objekte. In dieser Arbeit werden die Produktionsrate und die Korrelationen von Paaren aus $b$-Jets bestimmt und nach ersten Hinweisen eines neuen massiven Teilchens, das bisher nicht im Standard-Modell enthalten ist, in dem invarianten Massenspektrum der $b$-Jets gesucht. Am Large Hadron Collider (LHC) kollidieren zwei Protonenstrahlen bei einer Schwerpunktsenergie von $\sqrt s = 7$ TeV, und es werden viele solcher Paare aus $b$-Jets produziert. Diese Analyse benutzt die aufgezeichneten Kollisionen des ATLAS-Detektors. Die integrierte Luminosität der verwendbaren Daten beläuft sich auf 34~pb$^{-1}$. $b$-Jets werden mit Hilfe ihrer langen Lebensdauer und den rekonstruierten, geladenen Zerfallsprodukten identifiziert. Für diese Analyse müssen insbesondere die Unterschiede im Verhalten von Jets, die aus leichten Objekten wie Gluonen und leichten Quarks hervorgehen, zu diesen $b$-Jets beachtet werden. Die Energieskala dieser $b$-Jets wird untersucht und die zusätzlichen Unsicherheit in der Energiemessung der Jets bestimmt. Effekte bei der Jet-Rekonstruktion im Detektor, die einzigartig für $b$-Jets sind, werden studiert, um letztlich diese Messung unabhängig vom Detektor und auf Niveau der Hadronen auswerten zu können. Hiernach wird die Messung zu Vorhersagen auf nächst-zu-führender Ordnung verglichen. Dabei stellt sich heraus, dass die Vorhersagen in Übereinstimmung zu den aufgenommenen Daten sind. Daraus lässt sich schließen, dass der zugrunde liegende Produktionsmechanismus auch in diesem neu erschlossenen Energiebereich am LHC gültig ist. Jedoch werden auch erste Hinweise auf Mängel in der Beschreibung der Eigenschaften dieser Ereignisse gefunden. Weiterhin können keine Anhaltspunkte für eine neue Resonanz, die in Paare aus $b$-Jets zerfällt, in dem invarianten Massenspektrum bis etwa 1.7~TeV gefunden werden. Für das Auftreten einer solchen Resonanz mit einer Gauß-förmigen Massenverteilung werden modell-unabhängige Grenzen berechnet.