Formfaktor-Bestimmung des semileptonischen K +- pi 0 my +- ny-Zerfalls mit dem NA48/2-Experiment

Der semileptonische Zerfall K^±→π^0 μ^± υ ist ein geeigneter Kanal zur Be-stimmung des CKM-Matrixelementes 〖|V〗_us |. Das hadronische Matrixelement dieses Zerfalls wird durch zwei dimensionslose Formfaktoren f_± (t) beschrieben. Diese sind abhängig vom Impulsübertrag t=〖(p_K-p_π)〗^2 auf das Leptonpaar. Zur Bestimmung von 〖|V〗_us | dienen die Formfaktoren als wichtige Parameter zur Berechnung des Phasenraumintegrals dieses Zerfalls. Eine präzise Messung der Formfaktoren ist zusätzlich dadurch motiviert, dass das Resultat des NA48-Experimentes von den übrigen Messungen der Experimente KLOE, KTeV und ISTRA+ abweicht. Die Daten einer Messperiode des NA48/2 -Experimentes mit offenem Trigger aus dem Jahre 2004 wurden analysiert. Daraus wählte ich 1.8 Millionen K_μ3^±-Zerfallskandidaten mit einem Untergrundanteil von weniger als 0.1% aus. Zur Bestimmung der Formfaktoren diente die zweidimensionale Dalitz-Verteilung der Daten, nachdem sie auf Akzeptanz des Detektors und auf radiative Effekte korrigiert war. An diese Verteilung wurde die theoretische Parameter-abhängige Funktion mit einer Chiquadrat-Methode angepasst. Es ergeben sich für quadratische, Pol- und dispersive Parametrisierung folgende Formfaktoren: λ_0=(14.82±〖1.67〗_stat±〖0.62〗_sys )×〖10〗^(-3) λ_+^'=(25.53±〖3.51〗_stat±〖1.90〗_sys )×〖10〗^(-3) λ_+^''=( 1.40±〖1.30〗_stat±〖0.48〗_sys )×〖10〗^(-3) m_S=1204.8±〖32.0〗_stat±〖11.4〗_(sys ) MeV/c^2 m_V=(877.4±〖11.1〗_stat±〖11.2〗_(sys ) MeV/c^2 LnC=0.1871±〖0.0088〗_stat±〖0.0031〗_(sys )±=〖0.0056〗_ext Λ_+=(25.42±〖0.73〗_stat±〖0.73〗_(sys )±=〖1.52〗_ext )×〖10〗^(-3) Die Resultate stimmen mit den Messungen der Experimente KLOE, KTeV und ISTRA+ gut überein, und ermöglichen eine Verbesserung des globalen Fits der Formfaktoren. Mit Hilfe der dispersiven Parametrisierung der Formfaktoren, unter Verwendung des Callan-Treiman-Theorems, ist es möglich, einen Wert für f_± (0) zu bestimmen. Das Resultat lautet: f_+ (0)=0.987±〖0.011〗_(NA48/2)±〖0.008〗_(ext ) Der für f_+ (0) berechnete Wert stimmt im Fehler gut mit den vorherigen Messungen von KTeV, KLOE und ISTRA+ überein, weicht jedoch um knapp zwei Standardabweichungen von der theoretischen Vorhersage ab.

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.

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.

Supersymmetry searches in dilepton final states with the ATLAS experiment

One of the main goals of the ATLAS experiment at the Large Hadron Collider (LHC) at CERN in Geneva is the search for new physics beyond the Standard Model. In 2011, proton-proton collisions were performed at the LHC at a center of mass energy of 7 TeV and an integrated luminosity of 4.7 fb^{-1} was recorded. This dataset can be tested for one of the most promising theories beyond limits achieved thus far: supersymmetry. Final states in supersymmetry events at the LHC contain highly energetic jets and sizeable missing transverse energy. The additional requirement of events with highly energetic leptons simplifies the control of the backgrounds. This work presents results of a search for supersymmetry in the inclusive dilepton channel. Special emphasis is put on the search within the Gauge-Mediated Symmetry Breaking (GMSB) scenario in which the supersymmetry breaking is mediated via gauge fields. Statistically independent Control Regionsrnfor the dominant Standard Model backgrounds as well as Signal Regions for a discovery of a possible supersymmetry signal are defined and optimized. A simultaneous fit of the background normalizations in the Control Regions via the profile likelihood method allows for a precise prediction of the backgrounds in the Signal Regions and thus increases the sensitivity to several supersymmetry models. Systematic uncertainties on the background prediction are constrained via the jet multiplicity distribution in the Control Regions driven by data. The observed data are consistent with the Standard Model expectation. New limits within the GMSB and the minimal Supergravity (mSUGRA) scenario as well as for several simplified supersymmetry models are set or extended.

Study of a new method for high energy top tagging at the ATLAS experiment

Since its discovery, top quark has represented one of the most investigated field in particle physics. The aim of this thesis is the reconstruction of hadronic top with high transverse momentum (boosted) with the Template Overlap Method (TOM). Because of the high energy, the decay products of boosted tops are partially or totally overlapped and thus they are contained in a single large radius jet (fat-jet). TOM compares the internal energy distributions of the candidate fat-jet to a sample of tops obtained by a MC simulation (template). The algorithm is based on the definition of an overlap function, which quantifies the level of agreement between the fat-jet and the template, allowing an efficient discrimination of signal from the background contributions. A working point has been decided in order to obtain a signal efficiency close to 90% and a corresponding background rejection at 70%. TOM performances have been tested on MC samples in the muon channel and compared with the previous methods present in literature. All the methods will be merged in a multivariate analysis to give a global top tagging which will be included in ttbar production differential cross section performed on the data acquired in 2012 at sqrt(s)=8 TeV in high phase space region, where new physics processes could be possible. Due to its peculiarity to increase the pT, the Template Overlap Method will play a crucial role in the next data taking at sqrt(s)=13 TeV, where the almost totality of the tops will be produced at high energy, making the standard reconstruction methods inefficient.

Multivariate analysis methods in the search for the Higgs boson produced in association with top pairs at the ATLAS experiment at LHC.

The Large Hadron Collider, located at the CERN laboratories in Geneva, is the largest particle accelerator in the world. One of the main research fields at LHC is the study of the Higgs boson, the latest particle discovered at the ATLAS and CMS experiments. Due to the small production cross section for the Higgs boson, only a substantial statistics can offer the chance to study this particle properties. In order to perform these searches it is desirable to avoid the contamination of the signal signature by the number and variety of the background processes produced in pp collisions at LHC. Much account assumes the study of multivariate methods which, compared to the standard cut-based analysis, can enhance the signal selection of a Higgs boson produced in association with a top quark pair through a dileptonic final state (ttH channel). The statistics collected up to 2012 is not sufficient to supply a significant number of ttH events; however, the methods applied in this thesis will provide a powerful tool for the increasing statistics that will be collected during the next LHC data taking.

Measurement of the top quark mass in multijet events with the CMS experiment at LHC

La massa del quark top è qui misurata per mezzo dei dati raccolti dall’esperimento CMS in collisioni protone-protone ad LHC, con energia nel centro di massa pari ad 8 TeV. Il campione di dati raccolto corrisponde ad una luminosità integrata pari a 18.2 /fb. La misura è effettuata su eventi con un numero di jet almeno pari a 6, di cui almeno due b-taggati (ovvero identificati come prodotto dell’adronizzazione di due quark bottom). Il valore di massa trovato è di (173.95 +- 0.43 (stat)) GeV/c2, in accordo con la media mondiale. The top quark mass is here measured by using the data that have been collected with the CMS experiment in proton-proton collisions at the LHC, at a center-of-mass energy of 8 TeV. The dataset which was used, corresponds to an integrated luminosiy of 18.2 /fb. The mass measurement is carried out by using events characterized by six or more jets, two of which identified as being originated by the hadronization of bottom quarks. The result of the measurement of the top quark mass performed here is: (173.95 +- 0.43 (stat)) GeV/c2, in accordance with the recently published world average.

Search for supersymmetry in final states with jets, missing transverse energy and one charged lepton with the ATLAS-experiment

Im Jahr 2011 wurde am Large Hadron Collider mit dem ATLAS Experiment ein Datensatz von 4.7 inversen Femtobarn bei einer Schwerpunktsenergie von 7 TeV aufgezeichnet. Teil des umfangreichen Physikprogrammes des ATLAS Experiments ist die Suche nach Physik jenseits des Standardmodells. Supersymmetrie - eine neue Symmetrie zwischen Bosonen und Fermionen - wird als aussichtsreichester Kandidat für neue Physik angesehen, und zahlreiche direkte und indirekte Suchen nach Supersymmetrie wurden in den letzten Jahrzehnten bereits durchgeführt. In der folgenden Arbeit wird eine direkte Suche nach Supersymmetrie in Endzuständen mit Jets, fehlender Transversalenergie und genau einem Elektron oder Myon durchgeführt. Der analysierte Datensatz von 4.7 inversen Femtobarn umfasst die gesamte Datenmenge, welche am ATLAS Experiment bei einer Schwerpunktsenergie von 7 TeV aufgezeichnet wurde. Die Ergebnisse der Analyse werden mit verschiedenen anderen leptonischen Suchkanälen kombiniert, um die Sensitivität auf diversen supersymmetrischen Produktions- und Zerfallsmodi zu maximieren. Die gemessenen Daten sind kompatibel mit der Standardmodellerwartung, und neue Ausschlussgrenzen in verschiedenen supersymmetrischen Modellen werden berechnet.

Exclusive vector meson production in pp collisions at the COMPASS experiment

Produktionsmechanismen für Teilchenproduktion im mittleren Energiebereich wurden in Proton-Proton Kollisionen innerhalb der COMPASS-Kollaboration mit Hilfe des COMPASS-Spektrometers am SPS Beschleuniger am CERN untersucht. Die verschiedenen Produktionsmechanismen werden mittels Produktion der Vektormesonen omega und phi studiert und können die diffraktive Anregung des Strahlteilchens mit anschliessendem Zerfall der Resonanz, zentrale Produktion und den damit verwandten “Shake-off” Mechanismus enthalten. Die für diese Arbeit verwendeten Daten wurden in den Jahren 2008 und 2009 mit 190 GeV/c-Protonen aufgenommen, die auf ein Flüssigwasserstofftarget trafen. Das Target war von einem Rückstoßprotonendetektor umgeben, der ein integraler Bestandteil des neuentwickelten Hadrontriggersystems ist. Für dieses System wurden außerdem einige neue Detektoren gebaut. Die Leistungsfähigkeit des Rückstoßprotonendetektors und des Triggersystems wird untersucht und Effizienzen extrahiert. Außerdem wird sowohl eine Methode zur Rekonstruktion von Rückstoßprotonen als auch eine Methode zur Kalibration des Rückstoßprotonendetektors entwickelt und beschrieben. Die Produktion von omega-Mesonen wurde in der Reaktion pp -> p omega p, omega -> pi+pi-pi0 und die Produktion von phi-Mesonen in der Reaktion pp -> p phi p, phi -> K+K- bei einem Impulsübertrag zwischen 0.1 (GeV/c)^2 und 1 (GeV/c)^2 gemessen. Das Produktionsverhältnis s(pp -> p phi p)/s(pp -> p omega p) wird als Funktion des longitudinalen Impulsanteils xF bestimmt und mit der Vorhersage durch die Zweigregel verglichen. Es ergibt sich eine signifikante Verletzung der Zweigregel, die abhängig von xF ist. Die Verletzung wird in Verbindung zu resonanten Strukturen im pomega-Massenspektrum diskutiert. Die xF-Abhängigkeit verschwindet, wenn man die Region niedriger pomega- und pphi-Masse entfernt, die solche resonanten Strukturen aufweist. Zusätzlich wird die Spinausrichtung bzw. das Spindichtematrixelement rho00 für omega- und phi-Mesonen untersucht. Die Spinausrichtung wird im Helizitätssystemrnanalysiert, welches für eine Abgrenzung von resonanten, diffraktiven Anregungen geeignet ist. Außerdem wird die Spinausrichtung in einem Referenzsystem mit Bezug auf die Richtung des Impulsübertrags untersucht, mit dessen Hilfe zentrale Prozesse wie zentrale Produktion oder “shake-off” abgegrenzt werden. Auch hier wird eine Abhängigkeit von xF und der invarianten Masse des pomega-Systems beobachtet. Diese Abhängigkeit kann wieder auf die resonanten Strukturen in der Produktion von omega-Mesonen zurückgeführt werden. Die Ergebnisse werden abschließend im Hinblick auf die verschiedenen Produktionsmechanismen diskutiert.

Elastic computing on Cloud resources for the CMS experiment

Nowadays, data handling and data analysis in High Energy Physics requires a vast amount of computational power and storage. In particular, the world-wide LHC Com- puting Grid (LCG), an infrastructure and pool of services developed and deployed by a ample community of physicists and computer scientists, has demonstrated to be a game changer in the efficiency of data analyses during Run-I at the LHC, playing a crucial role in the Higgs boson discovery. Recently, the Cloud computing paradigm is emerging and reaching a considerable adoption level by many different scientific organizations and not only. Cloud allows to access and utilize not-owned large computing resources shared among many scientific communities. Considering the challenging requirements of LHC physics in Run-II and beyond, the LHC computing community is interested in exploring Clouds and see whether they can provide a complementary approach - or even a valid alternative - to the existing technological solutions based on Grid. In the LHC community, several experiments have been adopting Cloud approaches, and in particular the experience of the CMS experiment is of relevance to this thesis. The LHC Run-II has just started, and Cloud-based solutions are already in production for CMS. However, other approaches of Cloud usage are being thought of and are at the prototype level, as the work done in this thesis. This effort is of paramount importance to be able to equip CMS with the capability to elastically and flexibly access and utilize the computing resources needed to face the challenges of Run-III and Run-IV. The main purpose of this thesis is to present forefront Cloud approaches that allow the CMS experiment to extend to on-demand resources dynamically allocated as needed. Moreover, a direct access to Cloud resources is presented as suitable use case to face up with the CMS experiment needs. Chapter 1 presents an overview of High Energy Physics at the LHC and of the CMS experience in Run-I, as well as preparation for Run-II. Chapter 2 describes the current CMS Computing Model, and Chapter 3 provides Cloud approaches pursued and used within the CMS Collaboration. Chapter 4 and Chapter 5 discuss the original and forefront work done in this thesis to develop and test working prototypes of elastic extensions of CMS computing resources on Clouds, and HEP Computing “as a Service”. The impact of such work on a benchmark CMS physics use-cases is also demonstrated.

Bottom-up effects of plant diversity on multitrophic interactions in a biodiversity experiment

Biodiversity is rapidly declining, and this may negatively affect ecosystem processes, including economically important ecosystem services. Previous studies have shown that biodiversity has positive effects on organisms and processes across trophic levels. However, only a few studies have so far incorporated an explicit food-web perspective. In an eight-year biodiversity experiment, we studied an unprecedented range of above- and below-ground organisms and multitrophic interactions. A multitrophic data set originating from a single long-term experiment allows mechanistic insights that would not be gained from meta-analysis of different experiments. Here we show that plant diversity effects dampen with increasing trophic level and degree of omnivory. This was true both for abundance and species richness of organisms. Furthermore, we present comprehensive above-ground/below-ground biodiversity food webs. Both above ground and below ground, herbivores responded more strongly to changes in plant diversity than did carnivores or omnivores. Density and richness of carnivorous taxa was independent of vegetation structure. Below-ground responses to plant diversity were consistently weaker than above-ground responses. Responses to increasing plant diversity were generally positive, but were negative for biological invasion, pathogen infestation and hyperparasitism. Our results suggest that plant diversity has strong bottom-up effects on multitrophic interaction networks, with particularly strong effects on lower trophic levels. Effects on higher trophic levels are indirectly mediated through bottom-up trophic cascades.

Comparison of CBS-QB3, CBS-APNO, and G3 predictions of gas phase deprotonation data

The G3, CBS-QB3, and CBS-APNO methods have been used to calculate ΔH and ΔG values for deprotonation of seventeen gas-phase reactions where the experimental values are reported to be accurate within one kcal/mol. For these reactions, the mean absolute deviation of these three methods from experiment is 0.84 to 1.26 kcal/mol, and the root-mean-square deviation for ΔG and ΔH is 1.43 and 1.49 kcal/mol for the CBS-QB3 method, 1.06 and 1.14 kcal/mol for the CBS-APNO method, and 1.16 and 1.28 for the G3 method. The high accuracy of these methods makes them reliable for calculating gas-phase deprotonation reactions, and allows them to serve as a valuable check on the accuracy of experimental data reported in the National Institutes of Standards and Technology database.

Comparison of CBS-QB3, CBS-APNO, G2, and G3 thermochemical predictions with experiment for formation of ionic clusters of hydronium and hydroxide ions complexed with water

The GAUSSIAN 2, GAUSSIAN 3, complete basis set-QB3, and complete basis set-APNO methods have been used to calculate ΔH∘ and ΔG∘ values for ionic clusters of hydronium and hydroxide ions complexed with water. Results for the clusters H3O+(H2O)n andOH−(H2O)n, where n=1–4 are reported in this paper, and compared against experimental values contained in the National Institutes of Standards and Technology (NIST) database. Agreement with experiment is excellent for the three ab initio methods for formation of these clusters. The high accuracy of these methods makes them reliable for calculating energetics for the formation of ionic clusters containing water. In addition this allows them to serve as a valuable check on the accuracy of experimental data reported in the NIST database, and makes them useful tools for addressing unresolved issues in atmospheric chemistry.

A Laboratory Experiment Using Nanoindentation to Demonstrate the Indentation Size Effect

A laboratory experiment using nanoindentation to demonstrate the indentation size effect is described. This laboratory introduces students to sophisticated instrumentation at low cost and low risk and utilizes recent research in the materials community as its foundation. The motivation, learning objectives, experimental details, data, and data analysis are presented. This experiment is intended for use in an upper-division materials science elective at the university level and has been successfully used in laboratory courses for senior undergraduates and first-year graduate students at Stanford University and Santa Clara University.

Tracing of 15N in a mountain spruce forest: comparison of experimental data with th TRACE model

Despite numerous studies about nitrogen-cycling in forest ecosystems, many uncertainties remain, especially regarding the longer-term nitrogen accumulation. To contribute to filling this gap, the dynamic process-based model TRACE, with the ability to simulate 15N tracer redistribution in forest ecosystems was used to study N cycling processes in a mountain spruce forest of the northern edge of the Alps in Switzerland (Alptal, SZ). Most modeling analyses of N-cycling and C-N interactions have very limited ability to determine whether the process interactions are captured correctly. Because the interactions in such a system are complex, it is possible to get the whole-system C and N cycling right in a model without really knowing if the way the model combines fine-scale interactions to derive whole-system cycling is correct. With the possibility to simulate 15N tracer redistribution in ecosystem compartments, TRACE features a very powerful tool for the validation of fine-scale processes captured by the model. We first adapted the model to the new site (Alptal, Switzerland; long-term low-dose N-amendment experiment) by including a new algorithm for preferential water flow and by parameterizing of differences in drivers such as climate, N deposition and initial site conditions. After the calibration of key rates such as NPP and SOM turnover, we simulated patterns of 15N redistribution to compare against 15N field observations from a large-scale labeling experiment. The comparison of 15N field data with the modeled redistribution of the tracer in the soil horizons and vegetation compartments shows that the majority of fine-scale processes are captured satisfactorily. Particularly, the model is able to reproduce the fact that the largest part of the N deposition is immobilized in the soil. The discrepancies of 15N recovery in the LF and M soil horizon can be explained by the application method of the tracer and by the retention of the applied tracer by the well developed moss layer, which is not considered in the model. Discrepancies in the dynamics of foliage and litterfall 15N recovery were also observed and are related to the longevity of the needles in our mountain forest. As a next step, we will use the final Alptal version of the model to calculate the effects of climate change (temperature, CO2) and N deposition on ecosystem C sequestration in this regionally representative Norway spruce (Picea abies) stand.