Un cross-over entre la matière nucléaire ordinaire et le plasma de quarks et gluons (PQG) est prédit par la QCD sur réseau à bas PB et haute température. Expérimentalement les collisions d'ions lourds ultrarelativistes sont utilisées pour étudier cet état dense et chaud. Produits lors d'un processus dur en début de collision, un parton de grande énergie en perd dans le milieu avant de fragmenter en une gerbe de hadrons appelée jet. Une étude de la modification de la structure et de la fragmentation du jet dans le milieu par rapport au vide permet d'améliorer notre connaissance du PQG. Les fonctions de fragmentation (FF) d'un jet décrivent les distributions en impulsion des hadrons dans ce dernier. Dans les collisions proton-proton (pp), leur mesure est importante pour comprendre les mécanismes de fragmentation de partons. Dans les collisions noyau-noyau, elle permet d'étudier les mécanismes de perte d'énergie. Cependant, la présence d'un important bruit de fond qui fluctue rend la mesure complexe. Il a alors été suggéré de mesurer les moments des FF qui y seraient moins sensibles. Le détecteur ALICE au LHC a des capacités de trajectométrie uniques permettant la mesure des particules chargées jusqu'à des impulsions de 150 MeV/c rendant possible une étude fine de la structure du jet et de ses FF. Les calorimètres électromagnétiques (EMCal et DCal) peuvent aussi être utilisés pour améliorer la mesure de l'énergie du jet. Nous présentons les mesures des FF des jets chargés et les premières études des moments des FF dans les collisions pp à .s=2.76 TeV dans ALICE. Une partie du travail est aussi dédiée à l'implémentation de la géométrie de DCal dans le logiciel d'analyse. / A cross-over between ordinary nuclear matter and a state of deconfined quarks and gluons, the Quark Gluon Plasma (QGP), is predicted by lattice QCD at low PB and high temperature. Experimentally, ultra-relativistic heavy ion collisions are used to produce and to study the hot and dense QGP medium. Produced in a hard scattering at the early stage of the collision a highly energetic parton is expected to lose energy in the medium before fragmenting into a spray of hadrons called jet. A study of the modification of the jet structure and of its fragmentation pattern in medium compared to the vacuum case should provide insights into the QGP properties. The jet fragmentation functions (FF) describe the momentum distribution of hadrons inside a jet. In proton-proton (pp) collisions their measurement is important for understanding the mechanisms of parton fragmentation while it can shed light on the energy loss mechanisms in nucleus-nucleus (AA) collisions. However, the presence of a large fluctuating background in AA makes the measurement a challenging task. The use of FF moments has been proposed to overcome this difficulty. The ALICE detector at the LHC has unique tracking capabilities enabling to measure charged particles down to transverse momenta of 150 MeV/c. This allows assessing possible modifications of the jet structure and FF. The electromagnetic calorimeters (EMCal and DCal) can also be used to improve the measurement of the jet energy. We present the measurements of charged-jet FF and the first studies of FF moments in pp collisions at .s=2.76 TeV in ALICE. Part of the work is also dedicated to the implementation of the DCal geometry in the ALICE offline software.

No description available.

京都大学 / 0048 / 新制・課程博士 / 博士(理学) / 甲第22626号 / 理博第4615号 / 新制||理||1663(附属図書館) / 京都大学大学院理学研究科物理学・宇宙物理学専攻 / (主査)教授 中家 剛, 准教授 WENDELL Roger, 教授 田中 貴浩 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DFAM

No description available.

In this work, we examine how neutrino and collider experiments can each and together put constraints on new physics more stringently than ever. Constraints arise in three ways. First, possible new theoretical frameworks are reviewed and analyzed for the compatibility with collider experiments. We study alternate theories such as the superconnection formalism and non-commutative geometry (NCG) and show how these can be put to test, if any collider excess were to show up. In this case, we use the previous diboson and diphoton statistical excess as examples to do the analysis. Second, we parametrize low energy new physics in the neutrino sector in terms of non-standard interactions (NSI), which are constrained by past and proposed future neutrino experiments. As an example, we show the capability of resolving such NSI with the OscSNS, a detector proposed for Oak Ridge National Lab and derive interesting new constraints on NSI at very low energy (≲ 50 MeV). Apart from this, in order to better understand the NSI matter effect in long baseline experiments such as the future DUNE experiment, we derive a new compact formula to describe the effect analytically, which provides a clear physical picture of our understanding of the NSI matter effect compared to numerical computations. Last, we discuss the possibility of combining neutrino and collider data to get a better understanding of where the new physics is hidden. In particular, we study a model that produces sizable NSI to show how they can be constrained by past collider data, which covers a distinct region of the model parameter space from the DUNE experiment. In combining the two, we show that neutrino experiments are complementary to collider searches in ruling out models such as the ones that utilize a light mediator particle. More general procedures in constructing such models relevant to neutrino experiments are also described. / Ph. D.

We present in this thesis a detailed analysis of Higgs boson interactions at future colliders. In particular we examine, in a model independent way, the sensitivity of an Linear Collider in probing the interaction of Higgs boson with a pair of vector bosons with/without the use of polarized initial beams and/or the information on final state fermion polarization. We devise several observables which have definite transformation properties under discrete symmetry operations to constrain the different anomalous parts of the Higgs boson interactions having the same transformation properties. We also investigate effects of initial state radiation (ISR) and beamstrahlung on probes of anomalous Higgs boson couplings at higher center of mass energies. We begin the first chapter with an introduction of the Standard Model (SM) of particle physics. We mainly focus on the Higgs sector of the SM. In this chapter we review the electroweak (EW) symmetry breaking mechanism, viz. the Higgs mechanism, responsible for generating masses of all the particles in the SM. We briefly summarize the high precision tests of the SM. We discuss constraints on the mass of the SM Higgs boson derived from theoretical considerations such as stability of the electroweak vacuum, unitarity in scattering amplitudes, perturbativity of the Higgs self-coupling and no fine-tuning in the radiative corrections in the Higgs sector. Next we present the experimental bounds on the mass of the SM Higgs boson obtained from the direct searches of the Higgs boson at LEP and from the electroweak high precision measurements. We then discuss the importance of a general model independent approach to study properties of the Higgs boson and to verify the uniqueness of the SM. In the context of low energy effective theory, this analysis can be made by using the effective Lagrangian that contains higher dimensional operators. We conclude this chapter giving examples of dimension-6 operators which can contribute to the anomalous Higgs boson interactions that we analyze in this thesis. Second chapter contains the dominant Higgs boson production processes at an collider.In a model independent analysis we consider the effects of the most general ¯ (V = W Z) vertex, consistent with Lorentz invariance, for the process where f is any light fermion. This vertex also includes the possibility of CP violation and can be written as: where ki denote the momenta of the two W’s (Z’s), ǫναβis the antisymmetric tensor with ǫ0123 = 1. Previous studies showed that the squared matrix element of the process e+e−ZH does not include all the anomalous parts of a general ZZH vertex. Also it is obvious that one cannot analyse anomalous WWH couplings using this process. Hence we consider the full process e+e−ffH to probe all the anomalous parts of the VVH vertex. We devise a general and very elegant procedure to probe these couplings at an e+e−collider. We construct various combinations by taking dot and scalar triple product of momenta of initial and final state particles. These combinations have definite transformation properties under CP and naive time reversal (T˜)transformations. Hence the corresponding observables constructed using expectation value of sign of these combinations can probe a specific part of the anomalous VVH couplings whose coefficient in the effective Lagrangian has same transformation properties. We investigate the possible sensitivity to which the anomalous VVH couplings can be probed at a Linear Collider using these observables in the process e+e−ffH for unpolarized beams [1, 2]. We consider the case of a Linear Collider, operating at center of mass energy of 500 GeV, with an integrated luminosityof 500 fb−1 and assume a Higgs boson of mass 120 GeV. We impose various kinematical cuts on different final state particles to reduce backgrounds ¯and consider the events where H decays into bb with branching ratio 0.68. We can enhance or suppress the effect of the s-channel, Z-exchange diagram by imposing cut on the ¯invariant mass of the ff system. We use b-tagging efficiency to be 70%; a value expected to be possible in the collider environment. We first consider asymmetries involving either the polar or azimuthal angular distributions. Then we combine these informations to construct combined polar-azimuthal asymmetries in order to enhance the sensitivity. We obtain strong constraints on most of the anomalous parts of the ZZH vertex using cross section and these asymmetries. The process e+eν¯ −νH has two missing ν’s in the final state. Hence their momenta are not available to construct any observables. Therefore, direct probes for T˜-odd WWH couplings viz. ℑ(bW), ℜ(˜bW), cannot be constructed and only weak, indirect bounds are possible. Further, without using polarized beams the contamination from the ZZH vertex cannot be eliminated in the determination of WWH couplings. In the third chapter we analyze use of linearly polarized e+/e−beams and/or information on final state lepton polarization in probingthe interaction of the Higgs boson with a pair of vector bosons[3, 4]. We make several combinations of different particle momenta and spins. We then define observables as expectation values of signs of these combinations for longitudinally polarized beams and/or for production of final state τ’s with a definite helicity state. Use of polarization allows us to devise more observables as compared to the unpolarized case. We list the observables for which use of polarization affords a distinct gain in sensitivity. In our analysis we divide the total luminosity of 500 fb−1 equally among different polarization states of initial state e−/e+ and take the values 80% and 60% for e−/e+ respectively, foreseen at the ILC. We construct numerical combinations of various linearly polarized cross sections to enhance the contribution of ℜ(bZ) while getting rid of ΔaZand vice versa. It is necessary to construct such combinations of cross section as ℜ(bZ), ΔaZhave same CP and T˜transformation properties and hence there are no asymmetries that can be constructed to probe them individually. With these combinations it is possible to probe both these CP-and T˜-even couplings cleanly, using linearly polarized beams. We find that longitudinal beam polarization can improve the sensitivity to CP-odd ZZH couplings viz. ℜ(˜bZ), ℑ(˜bZ), by a factor of about 6 −7. We also construct observables for final state τ’s with definite helicity. We make a plausible assumption that it should be possible to isolate events with τ’s in definite helicity state with an efficiency of 40%. With this assumption we demonstrate that the use of final state τ polarization can improve the sensitivity to the CP-even and T˜-odd ZZH coupling (ℑ(bZ)) by a factor of about 3. Moreover use of final state τ-polarization measurement along with linearly polarized beams can improve the sensitivity for one of the CP-odd ZZH couplings (ℜ(˜bZ))bya factor of about 2.Use of longitudinally polarized beams can also help to reduce the contamination in the measurement of the WWH couplings coming from the ZZH vertex contribution. We also perform χ2-analysis using the observables for different polarizations. The cross section of the t–channel diagram increases with increasing center of mass energy. Therefore, off hand it may look like that going to higher energy can increase the sensitivity to WWH couplings. Hence in this chapter we further investigate possible gain in sensitivity going to higher center of mass energies[3, 4]. We use the same observables constructed with unpolarized beams and consider various center of mass energies ranging from 300 GeV to 3 TeV. We find that it is possible to increase the bZ)byabouta factor 2 1 TeVas compared to the case of 500 GeV. In this analysis we include the effects of initial state radiation (ISR) and beamstrahlung. Both the ISR and beamstrahlung =500 GeV, the ISR can affect cross sections for s–channel processes by 10−15%.However, we observe that the effects of ISR and beamstrahlung change both the SM and anomalous contributions more beneficial for the study of anomalous V V H couplings. In the last chapter we investigate the role of transversely polarized beams to constrain the anomalous V V H couplings[5]. Using transverse spin direction of e±it is possible to devise observables which are nonzero only for transversely polarized beams. Use of transverse beam polarization allows construction of completely independent probes of both the CP-and T˜-even anomalous ZZH couplings (ΔaZ, ℜ(bZ)), leading to independent determination of all the anomalous parts of the ZZH vertex. In addition the use of transverse beam polarization can also add to the sensitivity for one of the CP-odd ZZH couplings viz. ℜ(˜bZ). Measurement of final state τ-polarization with transversely polarized beams can in fact also offer improvement on the sensitivity for ℑ(bZ) which is even under CP-and odd under T˜-transformation. Use of transverse beam polarization cannot improve the bounds on the anomalous WWH couplings as the squared matrix element of the t– channel WW–fusion diagram does not have any transverse beam polarization dependent term. A summary of the results obtained in this thesis is follows. We have developed a general procedure to construct observables with specific CP and T˜transformation properties to probe various anomalous couplings of the Higgs boson to a pair of vector bosons (V = W/Z) at an e+/e−Linear Collider. We investigate probes of these couplings in the process e+e−ffH. This process gives access to those anomalous couplings which cannot be probed using angular distribution of the Z boson in the process e+eZH. We showed that it would be possible to obtain stringent bounds on some of the parts of the anomalous ZZH vertex even without using polarized beams and/or information on polarization of final state particles. Use of longitudinal beam polarization and/or final state τ polarization can significantly enhance the sensitivity in probing most of the anomalous parts of a general ZZH vertex. Use of longitudinal beam polarization also reduces the contamination from the ZZH couplings in the determination of the ˜T-even anomalous WWH couplings (ℜ(bW), ℑ(˜bW)). However, two missing neutrinos in the final state do not allow any direct probe of the T˜-odd WWH couplings (ℑ(bW), ℜ(˜bW)).We find that use of transverse polarization of the beams is essential to construct independent probes of the two anomalous ZZH couplings, which are even under CP and T˜transformations, viz.ΔaZand ℜ(bZ).We observed that there will be no significant gain 500 GeV), but with polarized beams is preferable from the point of view of studying anomalous V V H coupling. (For mathematical equations pl see the pdf file.)

The STAR collaboration recorded s =200 GeV per nucleon d+Au and p+p collision events during the year 2003 RHIC run. In the p+p and the d+Au data samples, it is possible to reconstruct jets and make comparisons between them. This dissertation describes the reconstructed jet sample from the p+p events, the measurements of the jet jT distribution which quantifies the shape of the jet perpendicular to the jet direction, the jet fragmentation function (z), which quantifies the fraction of jet momentum carried by the jet particles, and the width of the parton momentum broadening distribution (kT). This dissertation also describes the comparison of these results to the reconstructed jet sample from d+Au events. Measurements of jet jT and jet fragmentation from p+p, d+Au, and PYTHIA are compared. The z and jT distributions from p+p and also d+Au are found to be consistent with PYTHIA event simulation version 6.205. RMS(jT) equals 612±12±30 MeV/c for p+p, and RMS(jT) equals 630±13±30 MeV/c for d+Au. The p+p kT Gaussian sigma (width) equals 2.08±0.12±0.13 GeV/c. This width is consistent with PYTHIA, kT literature surveys, and other RHIC measurements. A limit on nuclear kT broadening in the Au nucleus is also obtained, showing that nuclear kT is consistent with zero to within 0.5 GeV/c. The present status of the RdAu measurement from jets is also described. The nuclear kT broadening, in particular, is a measurement which has been done at this energy for the first time at RHIC. These measurements, while interesting by themselves, also will contribute ultimately to the understanding of Au+Au collisions at RHIC, and the properties of the high-density matter which results from them.

The hierarchy problem of the electroweak scale is an intriguing puzzle which can conceivably be solved during upcoming runs of the Large Hadron Collider (LHC). Supersymmetry (SUSY) is an attractive potential solution to this problem, though the fact that no supersymmetric particles have been discovered thus far raises fine tuning of most models to &order;(1&percnt;). Extradimensional SUSY is especially interesting in light of this fact since certain models are easier to reconcile with LHC data. This thesis discusses two different extradimensional SUSY scenarios: auto-concealment and Maximally Natural SUSY (MNSUSY). The auto-concealment mechanism applies when the lightest ordinary superymmetric particle (LOSP), a brane localized state, promptly decays to the Kaluza-Klein (KK) tower of a bulk lightest supersymmetric particle (LSP). This dynamically realizes the compression mechanism for hiding SUSY as decays into the more numerous heavier KK LSP states are favored. LHC limits on LOSP squarks weaken to ≲ 450 GeV while limits on LOSP right-handed sleptons evaporate. Slepton searches perform poorly in this case because LHC analyses are blind to compressed slepton spectra. To help fill this gap, this thesis presents a monojet-like search sensitive to the very compressed range 3 GeV < m _&itilde; − m^&Tilde;<sub style='position: relative; left: -.7em;'>x</sub>⁰<sub style='position: relative; left: -.6em;'>1</sub> < 24 GeV. The analysis should allow LHC14 with 100 fb^−1 to search for degenerate left-handed selectrons and smuons in the compressed region up to m _{&itilde;_L} ≲ 150 GeV. In addition, it should be sensitive to m _{&itilde;_L} ≲ 110 GeV for auto-concealed SUSY. To expand the class of extradimensional SUSY models the LHC is able to test this thesis also describes the Lagrangian and mass matrices of MNSUSY, which are needed to implement this model in the Feynman rules generator program FeynRules for use in Monte Carlo programs for collider simulations. It also describes benchmark scenarios useful for the first collider phenomenology studies.

No description available.

Understanding the spin structure of the nucleon can be considered as one of the fundamental goals in nuclear physics. Following the introduction of the quark model in 1964, the spin of the proton was naively explained by the alignment of spins of the valence quarks. However, in our current understanding, the valence quarks, sea quarks, gluons, and their possible orbital angular momentum are all expected to contribute to the overall spin of the proton. Despite this significant progress, our understanding of the individual spin contributions of quarks and antiquarks to the proton is not yet complete. Measurements of W± single spin asymmetries in longitudinally polarized proton-proton collisions at RHIC provides unique and clean access to the individual helicity distributions of light quarks and antiquarks of the proton. W± boson are produced through the annihilation of up + anti-down (anti-up + down) quarks and can be detected through their leptonic decays to electrons and anti-electron neutrinos (positrons and electron neutrinos). Due to maximal violation of parity during the production, W bosons couple to left-handed quarks and right-handed anti-quarks and hence offer direct probes of their respective helicity distributions in the nucleon. The STAR experiment at RHIC is well equipped to measure W decay electrons and positrons in longitudinally polarized p+p collisions, where only the charged lepton is observed in the final state with a large missing transverse energy opposite in azimuth due to the undetected neutrino. In this dissertation, the details of the analysis and the results of the longitudinal single spin asymmetry, AL, for W boson production at RHIC are presented. The total integrated luminosity of the data analyzed is 246 pb-1 with an average beam polarization of ~54%. The data are collected during 2013 in longitudinally polarized proton-proton collisions at √S =510 GeV by the STAR experiment at RHIC. The analysis includes the procedure, the results and the evaluation of the systematic uncertainty of the calibration of the STAR Barrel Electromagnetic Calorimeter which was performed coincident with the primary W AL analysis. The W AL analysis is discussed in terms of data QA, the reconstruction of W bosons via decayed electrons and positrons, and the estimation of the electroweak and QCD type background contributions. The reconstruction of W decay events includes the use of the Time Projection Chamber for the tracking purposes and the Barrel Electromagnetic Calorimeter for the identification and isolation of electron and poistron candidates by measuring their transverse energies in the calorimeter towers. Finally the results of AL for W+ (W-) are reported as a function of decay positron (electron) pseudo-rapidity, η, between -1 and +1. The theoretical predictions for the spin asymmetries calculated using recent polarized and unpolarized parton distribution functions, are compared with the measured values. / Physics