Physics - Bachelor's degree
http://hdl.handle.net/1721.1/7696
2017-10-20T11:31:08ZCalculation of the axial charge of a heavy nucleon in Lattice QCD
http://hdl.handle.net/1721.1/111890
Calculation of the axial charge of a heavy nucleon in Lattice QCD
Pefkou, Dimitra Anastasia
In this thesis, we aim to calculate the non-renormalized axial charge gA of a heavy nucleon made out of quarks at the physical mass of the strange quark. We present the framework of Lattice QCD which makes the calculation of such observables attainable from first principles. The data used for the estimation of gA were obtained on a 243 x64 hypercubic lattice with lattice spacing a ~ 0.12 fm and pion mass m[pi] = 0.450 GeV. Three different source-sink seperations were used, tsink = [12a, 14a, 16a]. For each timeslice seperation signal we perform a correlated x2 fit and obtain the following values for gA: 0.551, 0.564 and 0.556. The unrenormalized value value for gA is extracted taking the limit as tsink --> [infinity] and is shown to be gA = 0.558. We discuss how the accuracy of this result is compromised by the small number of tsink values, by excited state contamination and by the increase of statistical noise with time.
Thesis: S.B., Massachusetts Institute of Technology, Department of Physics, 2016.; Cataloged from PDF version of thesis.; Includes bibliographical references (pages 55-57).
2016-01-01T00:00:00ZStudy of a short distance top mass with a cross-section at NNLL + NNLO
http://hdl.handle.net/1721.1/111889
Study of a short distance top mass with a cross-section at NNLL + NNLO
Bachu, Brad
We consider top-quarks produced at large energy in e+e- collisions and address the question of what top-mass can be measured from reconstruction. The production process is characterized by the center-of-mass energy, Q, the top mass, m, the top decay width, It, and also AQCD. These scales are well separated and can be disentangled with effective theory methods such as the Heavy-Quark Effective Theory and Soft-Collinear Effective Theory. We compute a top mass observable for future e+e- colliders to next-to-next-to-leading-logarithmic order + [Omicron] [alpha] 2/[sigma](NNLL+NNLO), which goes beyond previous next-to-leading-logarithmic + [Omicron] [alpha] 2/[sigma] (NLL+NLO) analysis. We use the two-loop heavy quark jet-function, [Omicron] [alpha] 2/[sigma] corrections to the partonic hemisphere soft function, and hard matching for boosted tops at two loops. We find that the higher order corrections exhibit good convergence and reduced uncertainty in this cross section.
Thesis: S.B., Massachusetts Institute of Technology, Department of Physics, 2017.; Cataloged from PDF version of thesis.; Includes bibliographical references (pages 49-51).
2017-01-01T00:00:00ZSpin-orbit coupled Bose-Einstein condensates with observation of a stripe phase
http://hdl.handle.net/1721.1/111888
Spin-orbit coupled Bose-Einstein condensates with observation of a stripe phase
Burchesky, Sean
In this work we build a new spin-orbit coupling experiment to observe the supersolidlike stripe phase. The phase diagram of a 1-dimensional spin-orbit coupled Bose- Einstein condensate shows several interesting phases including the stripe phase. We find the stripe phase particularly interesting because the condensate develops a density modulation in free space while remaining superfluid, which are the signature of supersolidity. In order to observe the stripe phase, we develop a novel spin-j basis which uses the orbital bands of an optical superlattice. Our choice of pseudo-spin basis allows the condensate components to remain miscible at high enough spin-orbit coupling strengths to observe the stripe phase. The superlattice constitutes a chain of spins which develop an antiferromagnetic spin texture and a density modulation at twice the lattice spacing. Breaking the discrete translational symmetry of the lattice while maintaining superfluidity indicates the formation of a lattice supersolid which we detected with Bragg scattering. Finally, the density modulation of the stripe phase is measured with a Bragg reflected beam and a camera setup to resolve the angular spread of the beam. An angle resolved, coherent Bragg beam is direct evidence of the stripe phase density modulation in free space. The formation of a free space density modulation in a superfluid Bose-Einstein condensate breaks the continuous spatial translation symmetry of space; fulfilling the definition of supersolidity. My primary contributions to the work include: controlling the superlattice, designing and building the Bragg detection scheme, some data collection and analysis.
Thesis: S.B., Massachusetts Institute of Technology, Department of Physics, 2017.; Cataloged from PDF version of thesis.; Includes bibliographical references.
2017-01-01T00:00:00ZResolution effects in the hybrid strong/weak coupling model
http://hdl.handle.net/1721.1/111887
Resolution effects in the hybrid strong/weak coupling model
Hulcher, Zachary R
Within the context of a hybrid strong/weak coupling model of jet quenching, we study the consequences of the fact that the plasma produced in a heavy ion collision cannot resolve the substructure of a collimated parton shower within it to arbitrary resolution. We introduce a screening length parameter, LRes, proportional to the inverse of the local temperature in the plasma, estimating the value of the proportionality constant from both weakly coupled QCD calculations and holographic calculations appropriate in strongly coupled plasma. We then modify the hybrid model so that when a parton in a jet shower splits, its two offspring are initially treated as unresolved, and are only treated as two separate partons losing energy independently after they are separated by a distance LRes. This modification delays the quenching of partons with intermediate energy, resulting in the survival of more hadrons in the final state with PT in the several GeV range. We demonstrate that this effect modifies the jet shapes and jet fragmentations functions, as it makes it more probable for particles carrying a small fraction of the jet energy at larger angles from the jet axis to survive their passage through the quark-gluon plasma. We analyze the consequences of different choices for the value of the resolution length LRes on both partonic and hadronic jet shapes and fragmentation functions, as well as on missing-PT observables. More generally, we discuss the qualitative consequences, and importance, of including the effects of finite resolution.
Thesis: S.B., Massachusetts Institute of Technology, Department of Physics, 2017.; Cataloged from PDF version of thesis.; Includes bibliographical references (pages 33-34).
2017-01-01T00:00:00Z