Search for heavy neutral resonances in the dielectron channel with the CMS detector at the LHC

A search for dielectron decays of heavy neutral resonances has been performed using proton-proton collision data collected at √s = 7 TeV by the Compact Muon Solenoid (CMS) experiment at the Large Hadron Collider (LHC) in 2011. The data sample corresponds to an integrated luminosity of 5 fb⁻¹. The dielectron mass distribution is consistent with Standard Model (SM) predictions. An upper limit on the ratio of the cross section times branching fraction of new bosons, normalized to the cross section times branching fraction of the Z boson, is set at the 95 % confidence level. This result is translated into limits on the mass of new neutral particles at the level of 2120 GeV for the Z′ in the Sequential Standard Model, 1810 GeV for the superstring-inspired Z′_ψ resonance, and 1940 (1640) GeV for Kaluza-Klein gravitons with the coupling parameter k/M_Pl of 0.10 (0.05).

High energy photoproduction of neutral mesons

Cross sections for the photoproduction of neutral pi, eta, rho and phi mesons on hydrogen have been measured at the Stanford Linear Accelerator Center using a missing mass spectrometer technique. The data cover photon energies between 5.0 and 17.8 GeV and four momentum transfer squared t between -.12 and -1.38 (GeV/c)².

Pion differential cross sections at lower energies show a peak at low momentum transfers, a distinctive dip and secondary maximum for t in the region -.4 to -.9 (GeV /c)², and a smooth decrease at higher momentum transfers. As photon energy increases, the dip becomes less pronounced, in contradiction to the expectations of simple Regge theories based on the exchange of omega and B trajectories only.

Eta photoproduction was measured only below 10 GeV. The cross section has about the same magnitude as the pion production cross section, but decreases exponentially with t, showing no dip.

Rho mesons appear to be diffractively produced. The differential cross section varies approximately as exp(8.5t + 2t²). It falls slowly with energy, decreasing about 35 percent from 6 GeV to 17.8 GeV. A simple quark model relation appears to describe the data well.

Phi meson cross sections are also consistent with diffraction production. The differential cross section varies approximately as exp(4t). The cross section tends to decrease slightly with photon energy.

Polymerization of functionalized olefins with neutral group ten catalysts

This thesis describes the preparation, characterization, and application of welldefined single-component group ten salicylaldimine complexes for the polymerization of ethylene to high molecular weight materials as well as the copolymerization of ethylene and functionalized olefins. After an initial introduction to the field, Chapter 2 describes the preparation of PPh₃ complexes that contain a series of modified salicylaldimine and naphthaldimine ligands. Such complexes were activated for polymerization by the addition of cocatalysts such as Ni(COD)₂ or B(C₆F₅)₃. As the steric demand of the ligand set increased-the molecular weight, polymerization activity, and lifetime of the catalyst was observed to increase. In fact, complexes containing "bulky" ligands, such as the [^Anthr,HSal] ligand (2.5), were found to be highly-active single component complexes for the polymerization of ethylene. Model hydrido compound were prepared-allowing for a better understanding of both the mechanism of polymerization and one mode of decomposition.

Chapter 3 describes the effect which additives play on neutral Ni^II polymerization catalysts such as 2.5. The addition of excess ethers, esters, ketones, anhydrides, alcohols, and water do not deactivate the catalysts for polymerization. However, the addition of excess acid, thiols, and phosphines was observed to shut-down catalysis. Since excess phosphine was found to inhibit catalysis, "phosphine-free" complexes, such as the acetonittile complex (3.26), were prepared. The acetonitrile complex was found to be the most active neutral polymerization catalyst prepared to date.

Chapter 4 outlines the use of catalyst 2.5 and 3.26 for the preparation of linear functionalized copolymers containing alcohols, esters, anhydrides, and ethers. Copolymers can be prepared with γ-functionalized-α-olefins, functionalized norbornenes, and functionalized tricyclononenes, with up to 30 mol% comonomer incorporation.

Chapter 5 outlines the preparation of a series of Pt^II alkyl/olefin salicylaldimine complexes which serve as models for the active species in the Ni^II-catalyzed polymerization process. Understanding the nature of the M-olefin interaction as a the electronic and steric properties of the salicylaldimine ligand is varied has allowed for a number of predictions about the design of future polymerization systems.

Chemical studies of viral entry mechanisms: I. Hydrophobic protein-lipid interactions during sendai virus membrane fusion. II. Kinetics of bacteriophage λ DNA injection.

Viruses possess very specific methods of targeting and entering cells. These methods would be extremely useful if they could also be applied to drug delivery, but little is known about the molecular mechanisms of the viral entry process. In order to gain further insight into mechanisms of viral entry, chemical and spectroscopic studies in two systems were conducted, examining hydrophobic protein-lipid interactions during Sendai virus membrane fusion, and the kinetics of bacteriophage λ DNA injection.

Sendai virus glycoprotein interactions with target membranes during the early stages of fusion were examined using time-resolved hydrophobic photoaffinity labeling with the lipid-soluble carbene generator3-(trifluoromethyl)-3-(m-^(125 )I] iodophenyl)diazirine (TID). The probe was incorporated in target membranes prior to virus addition and photolysis. During Sendai virus fusion with liposomes composed of cardiolipin (CL) or phosphatidylserine (PS), the viral fusion (F) protein is preferentially labeled at early time points, supporting the hypothesis that hydrophobic interaction of the fusion peptide at the N-terminus of the F_1 subunit with the target membrane is an initiating event in fusion. Correlation of the hydrophobic interactions with independently monitored fusion kinetics further supports this conclusion. Separation of proteins after labeling shows that the F_1 subunit, containing the putative hydrophobic fusion sequence, is exclusively labeled, and that the F_2 subunit does not participate in fusion. Labeling shows temperature and pH dependence consistent with a need for protein conformational mobility and fusion at neutral pH. Higher amounts of labeling during fusion with CL vesicles than during virus-PS vesicle fusion reflects membrane packing regulation of peptide insertion into target membranes. Labeling of the viral hemagglutinin/neuraminidase (HN) at low pH indicates that HN-mediated fusion is triggered by hydrophobic interactions, after titration of acidic amino acids. HN labeling under nonfusogenic conditions reveals that viral binding may involve hydrophobic as well as electrostatic interactions. Controls for diffusional labeling exclude a major contribution from this source. Labeling during reconstituted Sendai virus envelope-liposome fusion shows that functional reconstitution involves protein retention of the ability to undergo hydrophobic interactions.

Examination of Sendai virus fusion with erythrocyte membranes indicates that hydrophobic interactions also trigger fusion between biological membranes, and that HN binding may involve hydrophobic interactions as well. Labeling of the erythrocyte membranes revealed close membrane association of spectrin, which may play a role in regulating membrane fusion. The data show that hydrophobic fusion protein interaction with both artificial and biological membranes is a triggering event in fusion. Correlation of these results with earlier studies of membrane hydration and fusion kinetics provides a more detailed view of the mechanism of fusion.

The kinetics of DNA injection by bacteriophage λ. into liposomes bearing reconstituted receptors were measured using fluorescence spectroscopy. LamB, the bacteriophage receptor, was extracted from bacteria and reconstituted into liposomes by detergent removal dialysis. The DNA binding fluorophore ethidium bromide was encapsulated in the liposomes during dialysis. Enhanced fluorescence of ethidium bromide upon binding to injected DNA was monitored, and showed that injection is a rapid, one-step process. The bimolecular rate law, determined by the method of initial rates, revealed that injection occurs several times faster than indicated by earlier studies employing indirect assays.

It is hoped that these studies will increase the understanding of the mechanisms of virus entry into cells, and to facilitate the development of virus-mimetic drug delivery strategies.

Fiber-optic integration and efficient detection schemes for optomechanical resonators

With the advent of the laser in the year 1960, the field of optics experienced a renaissance from what was considered to be a dull, solved subject to an active area of development, with applications and discoveries which are yet to be exhausted 55 years later. Light is now nearly ubiquitous not only in cutting-edge research in physics, chemistry, and biology, but also in modern technology and infrastructure. One quality of light, that of the imparted radiation pressure force upon reflection from an object, has attracted intense interest from researchers seeking to precisely monitor and control the motional degrees of freedom of an object using light. These optomechanical interactions have inspired myriad proposals, ranging from quantum memories and transducers in quantum information networks to precision metrology of classical forces. Alongside advances in micro- and nano-fabrication, the burgeoning field of optomechanics has yielded a class of highly engineered systems designed to produce strong interactions between light and motion.

Optomechanical crystals are one such system in which the patterning of periodic holes in thin dielectric films traps both light and sound waves to a micro-scale volume. These devices feature strong radiation pressure coupling between high-quality optical cavity modes and internal nanomechanical resonances. Whether for applications in the quantum or classical domain, the utility of optomechanical crystals hinges on the degree to which light radiating from the device, having interacted with mechanical motion, can be collected and detected in an experimental apparatus consisting of conventional optical components such as lenses and optical fibers. While several efficient methods of optical coupling exist to meet this task, most are unsuitable for the cryogenic or vacuum integration required for many applications. The first portion of this dissertation will detail the development of robust and efficient methods of optically coupling optomechanical resonators to optical fibers, with an emphasis on fabrication processes and optical characterization.

I will then proceed to describe a few experiments enabled by the fiber couplers. The first studies the performance of an optomechanical resonator as a precise sensor for continuous position measurement. The sensitivity of the measurement, limited by the detection efficiency of intracavity photons, is compared to the standard quantum limit imposed by the quantum properties of the laser probe light. The added noise of the measurement is seen to fall within a factor of 3 of the standard quantum limit, representing an order of magnitude improvement over previous experiments utilizing optomechanical crystals, and matching the performance of similar measurements in the microwave domain.

The next experiment uses single photon counting to detect individual phonon emission and absorption events within the nanomechanical oscillator. The scattering of laser light from mechanical motion produces correlated photon-phonon pairs, and detection of the emitted photon corresponds to an effective phonon counting scheme. In the process of scattering, the coherence properties of the mechanical oscillation are mapped onto the reflected light. Intensity interferometry of the reflected light then allows measurement of the temporal coherence of the acoustic field. These correlations are measured for a range of experimental conditions, including the optomechanical amplification of the mechanics to a self-oscillation regime, and comparisons are drawn to a laser system for phonons. Finally, prospects for using phonon counting and intensity interferometry to produce non-classical mechanical states are detailed following recent proposals in literature.

Studies of bacteriophage T4 tail fibers and tail fiber genes

The distal half of the bacteriophage T4 tail fiber interacts with the surface of the bacterium during adsorption. The largest polypeptide in this half fiber is the product of gene 37 (P37). During assembly of the tail fiber, P37 interacts with the product of gene 38 (P38). These two gene products are incompatible with the corresponding gene products from the related phage T2. T2 P37 does not interact with T4 P38 and T2 P38 does not interact with T4 P37. Crosses between T2 and T4 phages mutant in genes 37 and 38 have shown that the carboxyl end of P37 interacts with P38 and with the bacterial surface. In the corresponding region of gene 37 and in gene 38 there is no recombination between T2 and T4. In the rest of gene 37 there are two small regions with relatively high recombination and a region of low recombination.

When T2/T4 heteroduplex DNA molecules are examined in the electron microscope four nonhomologous loops appear in the region of genes 37 and 38. Heteroduplexes between hybrid phages which have part of gene 37 from T4 and part from T2 have roughly located gene 37 mutations in the heteroduplex pattern. For a more precise location of the , mutations a physical map of gene 37 was constructed by determining the molecular weights of amber polypeptide fragments on polyacrylamide gels in the presence of sodium dodecyl sulfate. When the physical and heteroduplex maps are aligned, the regions of low recombination correspond to regions of nonhomology between T2 and T4. Regions with relatively high recombination are homologous.

The molecular weight of T2 P37 is about 13,000 greater than that of T4 P37. Analysis of hybrid phage has shown that this molecular weight difference is all at the carboxyl end of P37.

An antiserum has been prepared which is specific for the distal half fiber of T4. Tests of the ability of gene 37 hybrids to block this antiserum show that there are at least 4 subclasses of antigen specified by different parts of P37.

Observations in the electron microscope of the tailfiber - anti- body complexes formed by the gene 37 hybrids and the specific anti- serum have shown that P37 is oriented linearly in the distal half fiber with its N-terminus near the joint between the two half fibers and its C-terminus near the tip of the fiber. These observations lead to a simple model for the structure of the distal half fiber.

The high recombination in T4 gene 34 was also investigated. A comparison of genetic and physical maps of gene 34 showed that there is a gradient of increasing recombination near one end of the gene.