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Model independent search for new physics at the Tevatron

Choudalakis, Georgios
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 242 p.
ENG
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The Standard Model of elementary particles can not be the final theory. There are theoretical reasons to expect the appearance of new physics, possibly at the energy scale of few TeV. Several possible theories of new physics have been proposed, each with unknown probability to be confirmed. Instead of arbitrarily choosing to examine one of those theories, this thesis is about searching for any sign of new physics in a model-independent way. This search is performed at the Collider Detector at Fermilab (CDF). The Standard Model prediction is implemented in all final states simultaneously, and an array of statistical probes is employed to search for significant discrepancies between data and prediction. The probes are sensitive to overall population discrepancies, shape disagreements in distributions of kinematic quantities of final particles, excesses of events of large total transverse momentum, and local excesses of data expected from resonances due to new massive particles. The result of this search, first in 1 fb-1 and then in 2 fb-1, is null, namely no considerable evidence of new physics was found.; by Georgios Choudalakis.; Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Physics, 2008.; Includes bibliographical references (p. 235-242).

Global Search for New Physics with 2.0/fb at CDF

CDF Collaboration; Aaltonen, T.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
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55.7%
Data collected in Run II of the Fermilab Tevatron are searched for indications of new electroweak-scale physics. Rather than focusing on particular new physics scenarios, CDF data are analyzed for discrepancies with the standard model prediction. A model-independent approach (Vista) considers gross features of the data, and is sensitive to new large cross-section physics. Further sensitivity to new physics is provided by two additional algorithms: a Bump Hunter searches invariant mass distributions for "bumps" that could indicate resonant production of new particles; and the Sleuth procedure scans for data excesses at large summed transverse momentum. This combined global search for new physics in 2.0/fb of ppbar collisions at sqrt(s)=1.96 TeV reveals no indication of physics beyond the standard model.; Comment: 8 pages, 7 figures. Final version which appeared in Physical Review D Rapid Communications

Interplay of energy dependent astrophysical neutrino flavor ratios and new physics effects

Mehta, Poonam; Winter, Walter
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
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55.72%
We discuss the importance of flavor ratio measurements in neutrino telescopes, such as by measuring the ratio between muon tracks to cascades, for the purpose of extracting new physics signals encountered by astrophysical neutrinos during propagation from the source to the detector. The detected flavor ratios not only carry the energy information of specific new physics scenarios which alter the transition probabilities in distinctive ways, but also the energy dependent flavor composition at the source. In the present work, we discuss the interplay of these two energy dependent effects and identify which new physics scenarios can be distinguished from the detected flavor ratios as a function of astrophysical parameters. We use a recently developed self-consistent neutrino production model as our toy model to generate energy dependent source flavor ratios and discuss (invisible) neutrino decay and quantum decoherence as specific new physics examples. Furthermore, we identify potentially interesting classes of sources on the Hillas plot for the purpose of new physics searches. We find that sources with substantial magnetic fields 10^3 Gauss <= B <= 10^6 Gauss, such as Active Galactic Nuclei (AGN) cores, white dwarfs, or maybe gamma-ray bursts...

New Physics Effects and Hadronic Form Factor Uncertainties in B -> K^* l^+ l^-

Das, Diganta; Sinha, Rahul
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
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It is well known that New Physics can contribute to weak decays of heavy mesons via virtual processes during its decays. The discovery of New Physics, using such decays is made difficult due to intractable strong interaction effects needed to describe it. Modes such as B -> K^* l^+ l^- offer an advantage as they provide a multitude of observables via angular analysis. We show how the multitude of "related observables" obtained from B -> K^* l^+ l^-, can provide many new "clean tests" of the Standard Model. The hallmark of these tests is that several of them are independent of the unknown universal form factors in heavy quark effective theory. We derive a relation between observables that is free of form factors and Wilson coefficients, the violation of which will be an unambiguous signal of New Physics. We also derive relations between observables and form factors that are independent of Wilson coefficients and enable verification of hadronic estimates. We show how form factor ratios can be measured directly from helicity fraction with out any assumptions what so ever. We find that the allowed parameter space for observables is very tightly constrained in Standard Model, thereby providing clean signals of New Physics. We examine both the large-recoil and low-recoil regions of the K^* meson and point out special features and derive relations between observables valid in the two limits. In the large-recoil regions several of the relations are unaffected by corrections to all orders in \alpha_s. We present yet another new relation involving only observables that would verify the validity of the relations between form-factors assumed in the low-recoil region. The several relations and constraints derived will provide unambiguous signals of New Physics if it contributes to these decays.; Comment: 26 pages...

Data for Polarization in Charmless B -> phi K^*: A Signal for New Physics?

Das, Prasanta Kumar; Yang, Kwei-Chou
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
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The recent observations of sizable transverse fractions of B-> phi K* are strongly contrary to the Standard Model expectation. We analyze all possible new-physics four-quark operators. We find that two classes of new-physics operators could offer resolutions to the B-> phi K* polarization anomaly. The (1-\gamma_5)\otimes (1-\gamma_5) and \sigma(1-\gamma_5)\otimes \sigma(1-\gamma_5) operators in the first class contribute to different helicity amplitudes as H{00}: H{--}: H{++} ~ O(1/mb):O(1):O(1/mb^2), while the contributions arising from (1+\gamma_5)\otimes (1+\gamma_5) and \sigma(1+\gamma_5)\otimes \sigma(1+\gamma_5) operators in the second class to various helicity amplitudes are given as H{00}: H{--}: H{++} ~ O(1/mb):O(1/mb^2):O(1). For each class of new physics, we find that all new physics effects can be lumped into a single parameter. Two possible experimental results of polarization phases, \arg(A_\perp)- \arg(A_\parallel) ~ \pi or 0, originating from the phase ambiguity in data, could be separately accounted for by our two new-physics scenarios: (i) the first scenario with the first class new-physics operators, and (ii) the second scenario with the second class new-physics operators. The consistency between the data and the new physics analysis...

B-Decay CP Asymmetries, Discrete Ambiguities and New Physics

Kayser, B.; London, D.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
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The first measurements of CP violation in the $B$ system will likely probe $\sin 2\alpha$, $\sin 2\beta$ and $\cos 2\gamma$. Assuming that the CP angles $\alpha$, $\beta$ and $\gamma$ are the interior angles of the unitarity triangle, these measurements determine the angle set $(\alpha,\beta,\gamma)$ except for a twofold discrete ambiguity. If one allows for the possibility of new physics, the presence of this discrete ambiguity can make its discovery difficult: if only one of the two candidate solutions is consistent with constraints from other measurements in the $B$ and $K$ systems, one is not sure whether new physics is present or not. We review the methods used to resolve the discrete ambiguity and show that, even in the presence of new physics, they can usually be used to uncover this new physics. There are some exceptions, which we describe in detail. We systematically scan the parameter space and present examples of values of $(\alpha,\beta,\gamma)$ and the new-physics parameters which correspond to all possibilities. Finally, we show that if one relaxes the assumption that the bag parameters $\BBd$ and $\BK$ are positive, one can no longer definitively establish the presence of new physics.; Comment: 29 pages, LaTeX, 1 figures...

Generalized top-spin analysis and new physics in $e^{+} e^{-}$ collisions with beam polarization

Ananthanarayan, B.; Lahiri, Jayita; Patra, Monalisa; Rindani, Saurabh D.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 04/10/2012
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A generalized top-spin analysis proposed some time ago in the context of Standard Model and subsequently studied in varying contexts is now applied primarily to the case of $e^+e^-\rightarrow t\bar{t}$ with transversely polarized beams. This extends our recent work with new physics couplings of scalar ($S$) and tensor ($T$) types. We carry out a comprehensive analysis assuming only the electron beam to be transversely polarized, which is sufficient to probe these interactions, and also eliminates any azimuthal angular dependence due to standard model or new physics of vector ($V$) and axial-vector ($A$) type interactions. We then consider new physics of general four-Fermi type of $V$ and $A$ type with both beams transversely polarized and discuss implications with longitudinal polarization as well. The generalized spin bases are all investigated in the presence of either longitudinal or transverse beam polarization to look for appreciable deviation from the SM prediction in case of the new physics. 90% confidence level limits are obtained on the interactions for the generalized spin bases with realistic integrated luminosity. In order to achieve this we present a general discussion based on helicity amplitudes and derive a general transformation matrix that enables us to treat the spin basis. We find that beamline basis combined with transverse polarization provides an excellent window of opportunity both for $S$...

Charmless hadronic decays $B \to PP, PV, VV$ and new physics effects in the general two-Higgs doublet models

Xiao, Zhenjun; Li, Chong Sheng; Chao, Kuang-Ta
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
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55.73%
Based on the low-energy effective Hamiltonian with the generalized factorization, we calculate the new physics contributions to the branching ratios of the two-body charmless hadronic decays of $B_u$ and $B_d$ mesons induced by the new gluonic and electroweak charged-Higgs penguin diagrams in the general two-Higgs doublet models (models I, II and III). Within the considered parameter space, we find that: (a) the new physics effects from new gluonic penguin diagrams strongly dominate over those from the new $\gamma$- and $Z^0$- penguin diagrams; (b) in models I and II, new physics contributions to most studied B meson decay channels are rather small in size: from -15% to 20%; (c) in model III, however, the new physics enhancements to the penguin-dominated decay modes can be significant, $\sim (30 -200)%$, and therefore are measurable in forthcoming high precision B experiments; (d) the new physics enhancements to ratios ${\cal B}(B \to K \etap)$ are significant in model III, $\sim (35 -70)%$, and hence provide a simple and plausible new physics interpretation for the observed unexpectedly large $B \to K \etap $ decay rates; (e) the theoretical predictions for ${\cal B}(B \to K^+ \pi)$ and ${\cal B}(B \to K^0 \pi^+)$ in model III are still consistent with the data within $2\sigma$ errors; (f) the significant new physics enhancements to the branching ratios of $B \to K^0 \pi^0...

Les Houches 2013: Physics at TeV Colliders: New Physics Working Group Report

Brooijmans, G.; Contino, R.; Fuks, B.; Moortgat, F.; Richardson, P.; Sekmen, S.; Weiler, A.; Alloul, A.; Arbey, A.; Baglio, J.; Barducci, D.; Barr, A. J.; Basso, L.; Battaglia, M.; Bélanger, G.; Belyaev, A.; Bernon, J.; Bharucha, A.; Bondu, O.; Boudjema,
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 07/05/2014
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We present the activities of the "New Physics" working group for the "Physics at TeV Colliders" workshop (Les Houches, France, 3--21 June, 2013). Our report includes new computational tool developments, studies of the implications of the Higgs boson discovery on new physics, important signatures for searches for natural new physics at the LHC, new studies of flavour aspects of new physics, and assessments of the interplay between direct dark matter searches and the LHC.; Comment: Proceedings of the New Physics Working Group of the 2013 Les Houches Workshop, Physics at TeV Colliders, Les Houches 3-21 June 2013. 201 pages

New physics upper bound on the branching ratio of B_s--> l+ l- and B_s--> l+ l- gamma

Alok, Ashutosh Kumar; Sankar, S. Uma
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 12/08/2006
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We consider the most general new physics effective Lagrangian for b--> s l+ l-. We derive the upper limit on the branching ratio for the processes B_s--> l^+ l- where l=e, mu, subject to the current experimental bounds on related processes, B--> (K,K*) l+ l-. If the new physics interactions are of vector/axial-vector form, the present measured rates for B--> (K,K*) l+ l- constrain B_s--> l+ l to be of the same order of magnitude as their respective Standard Model (SM) predictions. On the other hand, if the new physics interactions are of scalar/pseudoscalar form, B--> (K,K*) l+ l- rates do not impose any useful constraint on B_s--> l+ l- and the branching ratios of these decays can be as large as present experimental upper bounds. If future experiments measure B_s--> l+ l- to be > 10^{-8} then the new physics giving rise to these decays has to be of the scalar/pseudoscalar form. We also consider the effect of new physics on B_s--> l+ l- gamma subject to the present experimental constraints on B--> (K,K*) l+ l- and B--> K* gamma. New physics in form scalar/pseudoscalar, which makes a very large contribution to B_s--> l+ l-, makes no contribution at all to B_s--> l+ l- gamma due to angular momentum conservation. New Physics in the form of vector/axial-vector operators is constrained by the data on B--> (K...

Probing new physics with flavor physics (and probing flavor physics with new physics)

Nir, Yosef
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 14/08/2007
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This is a written version of a series of lectures aimed at graduate students and postdoctoral fellows in particle theory/string theory/particle experiment familiar with the basics of the Standard Model. We begin with an overview of flavor physics and its implications for new physics. We emphasize the "new physics flavor puzzle". Then, we give four specific examples of flavor measurements and the lessons that have been (or can be) drawn from them: (i) Charm physics: lessons for supersymmetry from the upper bound on $\Delta m_D$. (ii) Bottom physics: model independent lessons on the KM mechanism and on new physics in neutral B mixing from $S_{\psi K_S}$. (iii) Top physics and beyond: testing minimal flavor violation at the LHC. (iv) Neutrino physics: interpreting the data on neutrino masses and mixing within flavor models.; Comment: 50 pages, 5 figures; Lectures given at PiTP 2007, "Standard Model and Beyond", IAS, Princeton, USA, July 16-25 2007, and at the 2007 CERN-FERMILAB Hadron Collider Physics Summer School, CERN, Geneva, Switzerland, June 6-15 2007

New physics, the cosmic ray spectrum knee, and $pp$ cross section measurements

Dixit, Aparna; Jain, Pankaj; McKay, Douglas W.; Mukherjee, Parama
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
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55.71%
We explore the possibility that a new physics interaction can provide an explanation for the knee just above $10^6$ GeV in the cosmic ray spectrum. We model the new physics modifications to the total proton-proton cross section with an incoherent term that allows for missing energy above the scale of new physics. We add the constraint that the new physics must also be consistent with published $pp$ cross section measurements, using cosmic ray observations, an order of magnitude and more above the knee. We find that the rise in cross section required at energies above the knee is radical. The increase in cross section suggests that it may be more appropriate to treat the scattering process in the black disc limit at such high energies. In this case there may be no clean separation between the standard model and new physics contributions to the total cross section. We model the missing energy in this limit and find a good fit to the Tibet III cosmic ray flux data. We comment on testing the new physics proposal for the cosmic ray knee at the Large Hadron Collider.; Comment: 17 pages, 4 figures

Future sensitivity to new physics in B_d, B_s and K mixings

Charles, Jerome; Descotes-Genon, Sebastien; Ligeti, Zoltan; Monteil, Stephane; Papucci, Michele; Trabelsi, Karim
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
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We estimate, in a large class of scenarios, the sensitivity to new physics in B_d and B_s mixings achievable with 50 ab-1 of Belle II and 50 fb-1 of LHCb data. We find that current limits on new physics contributions in both B_{d,s} systems can be improved by a factor of ~5 for all values of the CP violating phases, corresponding to over a factor of 2 increase in the scale of new physics probed. Assuming the same suppressions by CKM matrix elements as those of the standard model box diagrams, the scale probed will be about 20 TeV for tree-level new physics contributions, and about 2 TeV for new physics arising at one-loop. We also explore the future sensitivity to new physics in K mixing. Implications for generic new physics and for various specific scenarios, such as minimal flavor violation, light third-generation dominated flavor violation, or U(2) flavor models are studied.; Comment: 12 pages; discussion of MFV extended; a fit for a hypothetical future new physics signal is added for illustration; first plot in figure 5 corrected; v3 is (essentially) identical to the published article

Testing new physics with the electron g-2

Giudice, G. F.; Paradisi, P.; Passera, M.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
55.71%
We argue that the anomalous magnetic moment of the electron (a_e) can be used to probe new physics. We show that the present bound on new-physics contributions to a_e is 8*10^-13, but the sensitivity can be improved by about an order of magnitude with new measurements of a_e and more refined determinations of alpha in atomic-physics experiments. Tests on new-physics effects in a_e can play a crucial role in the interpretation of the observed discrepancy in the anomalous magnetic moment of the muon (a_mu). In a large class of models, new contributions to magnetic moments scale with the square of lepton masses and thus the anomaly in a_mu suggests a new-physics effect in a_e of (0.7 +- 0.2)*10^-13. We also present examples of new-physics theories in which this scaling is violated and larger effects in a_e are expected. In such models the value of a_e is correlated with specific predictions for processes with violation of lepton number or lepton universality, and with the electric dipole moment of the electron.; Comment: 34 pages, 7 figures. Minor changes and references added

Searching for New Physics in $D^0\rightarrow \mu^+\mu^-,\; e^+e^-, \;\mu^{\pm}e^{\mp}$ at BES and/or Super Charm-Tau Factory

Jia, Lian-Bao; Zhao, Ming-Gang; Ke, Hong-Wei; Li, Xue-Qian
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
55.71%
In contrast with $B^0-\bar B^0$, $B_s-\bar B_s$ mixing where the standard model (SM) contributions overwhelm that of new physics beyond standard model (BSM), a measured relatively large $D^0-\bar D^0$ mixing where the SM contribution is negligible, definitely implies the existence of new physics BSM. It is natural to consider that the rare decays of D meson might be more sensitive to new physics, and the rare decay $D^0\to \mu^+\mu^-$ could be an ideal area to search for new physics because it is a flavor changing process. In this work we look for a trace of new physics BSM in the leptonic decays of $D^0$, concretely we discuss the contributions of unparticle or an extra gauge boson $Z'$ while imposing the constraints set by fitting the $D^0-\bar D^0$ mixing data. We find that the long-distance SM effects for $D^0\to l\bar l$ still exceed those contributions of the BSM under consideration, but for a double-flavor changing process such as $D^0\to \mu^{\pm}e^{\mp}$, the new physics contribution would be significant.; Comment: 14 pages, 1 figure, 2 tables

Anatomy of New Physics in B-Bbar mixing

Lenz, A.; Nierste, U.; Charles, J.; Descotes-Genon, S.; Jantsch, A.; Kaufhold, C.; Lacker, H.; Monteil, S.; Niess, V.; T'Jampens, S.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
55.71%
We analyse three different New Physics scenarios for Delta F=2 flavour-changing neutral currents in the quark sector in the light of recent data on neutral-meson mixing. We parametrise generic New Physics contributions to B_q-Bbar_q mixing (q=d,s), in terms of one complex quantity Delta_q, while three parameters Delta_K^tt, Delta_K^ct and Delta_K^cc are needed to describe K-Kbar mixing. In Scenario I, we consider uncorrelated New Physics contributions in the B_d, B_s, and K sectors. In this scenario, it is only possible to constrain the parameters Delta_d and Delta_s whereas there are no non-trivial constraints on the kaon parameters. In Scenario II, we study the case of Minimal Flavour Violation (MFV) and small bottom Yukawa coupling and Scenario III is the generic MFV case with large bottom Yukawa couplings. Our quantitative analyses consist of global CKM fits within the Rfit frequentist statistical approach, determining the Standard Model parameters and the new physics parameters of the studied scenarios simultaneously. We find that the recent measurements indicating discrepancies with the Standard Model are well accomodated in Scenarios I and III with new mixing phases, with a slight preference for Scenario I that permits different new CP phases in the B_d and B_s systems. Within our statistical framework...

CP violation and limits on New Physics including recent Bs measurements

Botella, Francisco J.; Branco, Gustavo C.; Nebot Gómez, Miguel
Fonte: Elsevier Publicador: Elsevier
Tipo: Artículo Formato: 2373 bytes; text/plain
ENG
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20 pages, 13 figures.-- ISI Article Identifier: 000245765000001.-- ArXiv pre-print available at: http://arxiv.org/abs/hep-ph/0608100; Printed version published on Apr 16, 2007.; We analyse present constraints on the SM parameter space and derive, in a model independent way, various bounds on New Physics contributions to Bd(0)-(B)over-bar(0)(d) and Bs(0)-(B)over-bar(0)(s) mixings. Our analyses include information on a large set of asymmetries, leading to the measurement of the CKM phases γ and (β)over-bar, as well as recent data from D0 and CDF related to the Bs(0)-(B)over-bar(0)(s) system such as the measurement of ΔMBs, A and ΔΓ(CP)(s). We examine in detail several observables such as the asymmetries A(sl)(d), A, the width differences ΔΓ(d) and ΔΓ(CP)(S) and discuss the role they play in establishing the limits on New Physics. The present data clearly favour the SM, with the New Physics favoured region placed around the SM solution. A New Physics solution significantly different from the SM is still allowed, albeit quite disfavoured (2.6% probability). We analyse the presently available indirect knowledge on the phase (Χ)over-bar entering in Bs(0)-Bs(0) mixing and study the impact of a future measurement of (Χ)over-bar to be achieved at LHC...

Probing new physics at the LHC: searches for heavy top-like quarks with the ATLAS experiment

Succurro, Antonella; Casado Lechuga, María Pilar
Fonte: [Barcelona] : Universitat Autònoma de Barcelona, Publicador: [Barcelona] : Universitat Autònoma de Barcelona,
Tipo: Tesis i dissertacions electròniques; info:eu-repo/semantics/doctoralThesis; info:eu-repo/semantics/publishedVersion Formato: application/pdf
Publicado em //2014 ENG
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¿Es el Modelo Estándar (Standard Model o SM) de las partículas elementales completo? Al parecer, la respuesta es "no". Un gran número de teorías intentando dar respuestas a preguntas como por ejamplo cuál es la naturaleza de la materia oscura, o cuál es la razón por la que el bosón de Higgs es tan ligero, han sido propuestas. Ahora que el Large Hadron Collider (LHC) en el CERN está en pleno funcionamiento, experimentos como ATLAS son capaces de explorar regímenes de muy alta energía, donde se puede testear la presencia de nueva física. El trabajo presentado en esta tesis consta de dos análisis diseñados para descubrir (o excluir) la existencia de una nueva partícula: un quark similar al quark top (la partícula más pesada del SM), "top-like", pero con una masa mucho más alta. Este nuevo quark exótico podría ser una simple réplica del quark top del SM, sólo mas masivo, es decir, una cuarta generación quiral de up-type quark, o podría tener una naturalez aún más exótica. Esta última hipótesis es particularmente interesante ya que muchas extensiones del SM predicen nuevos quarks llamados "vectoriales". Ambas búsquedas están basadas en el análisis de una muestra parcial de los datos acumulados por el experimento ATLAS en colisiones protón-protón durante el año 2012. Estos resultados están documentados en dos notas públicas (ATLAS-CONF-2013-018 y ATLAS-CONF-2013-060) y en la actualidad se están actualizando con las estadísticas completas. Estos análisis también son parte de un esfuerzo combinado de diferentes equipos de investigación dentro del grupo de trabajo ATLAS Exóticos...

Estimation of the Z->vv background to New Physics searches in ATLAS

Sandoval, Tanya
Fonte: University of Cambridge; Department of Physics; Wolfson College; CERN; Cavendish Laboratory Publicador: University of Cambridge; Department of Physics; Wolfson College; CERN; Cavendish Laboratory
Tipo: Thesis; doctoral; PhD
EN
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This thesis describes a series of studies related to searches for new phenomena, beyond the Standard Model of particle physics, in high energy hadron collisions. In such searches, it becomes crucial to identify the Standard Model backgrounds in order to resolve a potential new signal. The thesis presents a method that uses photon events to determine one of such backgrounds, caused by the production of Z boson events. The studies performed to validate the method, both theoretically and experimentally, are presented and the method was shown to be successful as well as to provide reliable results. Theoretically, the method is found to be robust up to a ~10% uncertainty. Experimentally, the method is implemented to estimate the Z(vv) + jets background for the SUSY 0l + E_T^miss + jets search in the ATLAS experiment at the Large Hadron Collider, where this background is one of the most important components for the final sensitivity and is impossible to measure directly. The main experimental results presented are the latest from ATLAS at the time of writing, corresponding to the full dataset of proton-proton collisions delivered by the LHC in 2011 (4.7 fb^-1) at a centre of mass energy of 7 TeV. Given that this method has been mainstream since 2010...

Phenomenological aspects of new physics at high energy hadron colliders

Papaefstathiou, Andreas
Fonte: University of Cambridge; Department of Physics Publicador: University of Cambridge; Department of Physics
Tipo: Thesis; doctoral; PhD
EN
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This thesis contains studies of phenomenological aspects of new physics at hadron colliders, such as the Large Hadron Collider (LHC). After a general introduction in chap- ter 1, in chapter 2 we outline the main features of the Standard Model (SM) of particle physics and the theoretical motivations for going beyond it. We subsequently provide brief descriptions of a few popular models that aim to solve the issues that arise within the SM. In chapter 3 we describe the general Monte Carlo method for evaluating multidimen- sional integrals and show how it can be used to construct a class of computational tools called Monte Carlo event generators. We describe the main generic features of event generators and how these are implemented in the HERWIG++ event generator. By applying resummation techniques, we provide, in chapter 4, analytical calcula- tions of two types of hadron collider observables. The first, global inclusive variables, are observables that make use of all measured particle momenta and can provide useful information on the scale of new physics. The second observable is the transverse energy of the QCD initial state radiation (ET ), associated with the either Drell-Yan gauge boson production or Higgs boson production. In both cases we provide comparisons to results obtained from Monte Carlo event generators. In chapter 5 we examine two well-motivated models for new physics: one of new heavy charged vector bosons (W prime)...