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.

Bestimmung thermischer Untergrundparameter in Erdwärmesondenfeldern und Evaluierung tiefenaufgelöster Thermal-Response-Tests durch thermohydraulische Modellierungen

Die oberflächennahe Geothermie leistet im Bereich der Nutzung regenerativer Wärme einen wichtigen Beitrag zum Klima- und Umweltschutz. Um die technische Nutzung oberflächennaher Geothermie zu optimieren, ist die Kenntnis der Beschaffenheit des geologischen Untergrundes ausschlaggebend. Die vorliegende Dissertation befasst sich mit der Bestimmung verschiedener Untergrundparameter an einem Erdwärmesondenfeld. Es wurden Untersuchungen zur Bestimmung der Wärmeleitfähigkeit wie der enhanced Thermal Response Test (eTRT), sowie eine Untergrund-Temperaturüberwachung im ersten Betriebsjahr durchgeführt. Die Überwachung zeigte keine gegenseitige Beeinflussung einzelner Sonden. Ein Vergleich zwischen dem geplanten und dem tatsächlichem Wärmebedarf des ersten Betriebsjahres ergab eine Abweichung von ca. 35%. Dies zeigt, dass die Nutzungsparameter der Anlage deren Effizienz maßgeblich beeinflussen können. Der am Beispielobjekt praktisch durchgeführte eTRT wurde mittels numerischer Modellierung auf seine Reproduzierbarkeit hin überprüft. Bei einem rein konduktiven Wärmetransport im Untergrund betrug die maximale Abweichung der Messung selbst unter ungünstigen Bedingungen lediglich ca. 6% vom zu erwartenden Wert. Die Detektion von grundwasserdurchflossenen Schichten ist in den Modellen ebenfalls gut abbildbar. Problematisch bleibt die hohe Abhängigkeit des Tests von einer konstanten Wärmezufuhr. Lediglich die Bestimmung der Wärmeleitfähigkeit über das Relaxationsverhalten des Untergrundes liefert bei Wärmeeintragsschwankungen hinreichend genaue Ergebnisse. Die mathematische Nachbearbeitung von fehlerhaften Temperaturkurven bietet einen Einstiegspunkt für weiterführende Forschung.

Measurement of the forward-backward asymmetry of Z boson decays in electron-positron pairs with the ATLAS detector in proton-proton collisions at root out s = 7TeV at the LHC

In this thesis the measurement of the effective weak mixing angle wma in proton-proton collisions is described. The results are extracted from the forward-backward asymmetry (AFB) in electron-positron final states at the ATLAS experiment at the LHC. The AFB is defined upon the distribution of the polar angle between the incoming quark and outgoing lepton. The signal process used in this study is the reaction pp to zgamma + X to ee + X taking a total integrated luminosity of 4.8\,fb^(-1) of data into account. The data was recorded at a proton-proton center-of-mass energy of sqrt(s)=7TeV. The weak mixing angle is a central parameter of the electroweak theory of the Standard Model (SM) and relates the neutral current interactions of electromagnetism and weak force. The higher order corrections on wma are related to other SM parameters like the mass of the Higgs boson.rnrnBecause of the symmetric initial state constellation of colliding protons, there is no favoured forward or backward direction in the experimental setup. The reference axis used in the definition of the polar angle is therefore chosen with respect to the longitudinal boost of the electron-positron final state. This leads to events with low absolute rapidity have a higher chance of being assigned to the opposite direction of the reference axis. This effect called dilution is reduced when events at higher rapidities are used. It can be studied including electrons and positrons in the forward regions of the ATLAS calorimeters. Electrons and positrons are further referred to as electrons. To include the electrons from the forward region, the energy calibration for the forward calorimeters had to be redone. This calibration is performed by inter-calibrating the forward electron energy scale using pairs of a central and a forward electron and the previously derived central electron energy calibration. The uncertainty is shown to be dominated by the systematic variations.rnrnThe extraction of wma is performed using chi^2 tests, comparing the measured distribution of AFB in data to a set of template distributions with varied values of wma. The templates are built in a forward folding technique using modified generator level samples and the official fully simulated signal sample with full detector simulation and particle reconstruction and identification. The analysis is performed in two different channels: pairs of central electrons or one central and one forward electron. The results of the two channels are in good agreement and are the first measurements of wma at the Z resonance using electron final states at proton-proton collisions at sqrt(s)=7TeV. The precision of the measurement is already systematically limited mostly by the uncertainties resulting from the knowledge of the parton distribution functions (PDF) and the systematic uncertainties of the energy calibration.rnrnThe extracted results of wma are combined and yield a value of wma_comb = 0.2288 +- 0.0004 (stat.) +- 0.0009 (syst.) = 0.2288 +- 0.0010 (tot.). The measurements are compared to the results of previous measurements at the Z boson resonance. The deviation with respect to the combined result provided by the LEP and SLC experiments is up to 2.7 standard deviations.