Division of Natural Science

In modern terms, quantum statistics differs from classical statistics for the indistinguishability of its elementary entities. An historical investigation of the emergence of Bose-Einstein statistics, however, shows that quantum statistics was initially interpreted as a statistics of non-independence, for it extended to gas particles the statistical correlation that was a long-recognized characteristic of light quanta. At the same time, the development of a quantum-statistical theory of the ideal gas was riddled with the question of the statistical significance of the exchange symmetry of a system of equal particles. Indistinguishability combines exchange symmetry and statistical correlation, and relates them to the loss of identity of particles in quantum mechanics. It is instructive, however, not to conflate these properties when analysing the historical emergence of quantum statistics. The statistical correlation of light quanta and the exchange symmetry of gas molecules remained two separate problems even though quantum gas theory and Bose-Einstein statistics were born from gas-radiation analogies in statistical theory.

This paper is a preliminary exploration of the connections between the statistical style of reasoning and the research practices of statistical mechanics in the early period of the long quantum revolution. It suggests that before 1925 the instantiations of the statistical style in physics went through two phases. The first phase consisted of the formulation of the Maxwell-Boltzmann statistics on the basis of the population-gas analogy. The second phase was characterized by the generalization of the Maxwell-Boltzmann statistics through analogies between ideal gas molecules and other microphysical entities, analogies that shaped and were shaped by the rise of quantum theory. Einstein's invention of the Bose-Einstein statistics started a third phase and created the conditions of possibility for a new classification of microphysical entities according to their different statistics.

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In deep inelastic, neutral current scattering of electrons and protons at ~/~ = 296 GeV, we observe in the ZEUS detector events with a large rapidity gap in the hadronic final state. They occur in the region of small Bjorken x and are observed up to Q2 of 100 GeV 2. They account for about 5% of the events with Q2 /> 10 GeV 2. Their general properties are inconsistent with the dominant mechanism of deep inelastic scattering, where color is transferred between the scattered quark and the proton remnant, and suggest that the underlying production mechanism is the diffractive dissociation of the virtual photon. l Supported by Worldlab,

This paper presents our first measurement of the F 2 structure function in neutral-current, deep inelastic scattering using the ZEUS detector at HERA, the ep colliding beam facility at DESY. The data correspond to an integrated luminosity of 24.7 nb-1. Results are presented for data in a range of Q2 from 10 GeV 2 to 4700 GeV 2 and Bjorken x down to 3.0 x 10-4. The F2 structure function increases rapidly as x decreases.

An outline models are current electron-proton deep-inelastic scattering at a centre o f mass energy o f 296 G eV are presented. Comparisons o f the results with the models show that Q C D radiation has a strong influence on the characteristics o f the hadronic final state. The data is reasonably well produced by the Lund model based on a matrix element calculation in first order o f the strong coupling, followed by appropriate parton showers. The colour dipole model also gives a reasonable representation of the data. Neither the first order matrix elements alone nor the Lund parton shower model, without the matrix element calculation, reproduce the data. The H E R W IG parton shower model is also deficient. The data was taken with the ZEUS detector at the H E R A accelerator in Hamburg, Germany. A genera! description of the detector design and principles of operation is provided. A three level trigger system is required to handle the high luminosity delivered by H E R A . The first two levels involve the local processing of component data. The third level makes a decision based on the global information from an event. It accepts events at 100 Hz, or 20 MBytes/sec, at the design luminosity and reduces this to around 5 Hz. The architecture and implementation o f the third level trigger system is discussed. of Q C D , the theory of strong interactions, is given and several Q C D Monte Carlo described in detail. Energy distributions o f the hadronic system produced in neutral Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Without a doubt, the first person I would like to thank is my supervisor, Robert S. Orr til the University o f Toronto. He offered me a wonderful opportunity anil provided constant enthusiasm, acumen, and humour. I also would like to thank John F. Martin of the University of Toronto who presented the Canadian students in Hambuig with a fine example of fair leadership and dedication to one's profession. In an experiment as large as ZEU S, one inevitably encounters a large and diverse group of individuals in the course o f work on the detector and analysis. I am particularly indebted to the members of the third level trigger group: Bob, David. Dinu. Sampa, Cicrd. Frank. Frederic.

This paper reports a search for excited electrons at the HERA electron-proton collider. In a sample corresponding to an integrated luminosity of 26 nb-I , no evidence was found for any resonant state decaying into e-y, uW-or e-Z °. Limits on the coupling strength of an excited electron have been determined for masses between 45 and 225 GeV. This study also reports the observation of the wide-angle ey Compton scattering process.

A sample of events with two distinct jets, in addition to the proton remnant, has been identified in deep inelastic, neutral current ep interactions recorded at HERA by the ZEUS experiment. For these events, the mass of the hadronic system ranges from 40 to 260 GeV. The salient features of the observed jet production agree with the predictions of higher order QCD.

A search for any resonant state coupled to an electron and a proton constituent has been performed using collisions of electron and proton beams at HERA. In a sample with integrated luminosity of 26 nb-I, no evidence has been found for production of leptoquarks with decays to e-+ jet or v + jet. Limits on the coupling strength of scalar leptoquarks to electron and quark have been determined for masses above 25 GeV. For example, scalar isosinglet leptoquarks (So) with electroweak coupling strength to (e-u) states are ruled out at the 95% confidence level for masses below 168 GeV for left-handed couplings and below 176 GeV for right-handed couplings.

Results are presented on neutral current, deep inelastic scattering measured in collisions of 26.7 GeV electrons and 820 GeV protons. The events typically populate a range in Q2 from 10 to 100 GeV 2. The values of x extend down to x ~ 10-4 which is two orders of magnitude lower than previously measured at such Q2 values in fixed target experiments. The measured cross sections are in accord with the extrapolations of current parametrisations of parton distributions.

This paper is a preliminary exploration of the connections between the statistical style of reasoning and the research practices of statistical mechanics in the early period of the long quantum revolution. It suggests that before 1925 the instantiations of the statistical style in physics went through two phases. The first phase consisted of the formulation of the Maxwell-Boltzmann statistics on the basis of the population-gas analogy. The second phase was characterized by the generalization of the Maxwell-Boltzmann statistics through analogies between ideal gas molecules and other microphysical entities, analogies that shaped and were shaped by the rise of quantum theory. Einstein's invention of the Bose-Einstein statistics started a third phase and created the conditions of possibility for a new classification of microphysical entities according to their different statistics.

The change that quantum statistics produced in the concept of microphysical entities was not the result of an experimental discovery, a logical inference, nor a choice between preformed conceptual models. It was, rather, the result of uncoordinated e orts to reach a physical understanding of the evolving mathematical-theoretical apparatus by modifying and rearranging familiar ideas about particles. This chapter examines the history of early interpretations of quantum statistics, from Einstein's rst deciphering of Bose's formal procedure to the earliest attempts to make sense of the formalism that uni ed Bose-Einstein and Fermi-Dirac statistics with the quantum mechanics of multi-particle systems. The fragmentary and discordant views of this early period highlight the interpretive exibility of the formal apparatus. The rst extended articulations of a new, uni ed conception of particles emerged only after WWII, as signalled by Dirac's 1945 proposal of the two new foundational categories of "bosons" and "fermions". THE transition from classical to quantum physics has produced a profound change in the concept of elementary particles. In the quantum world, particles are no longer scaled-down versions of idealized mass-produced macroscopic objects, as for instance perfect bullets or monochrome billiard balls, which, although perfectly equal, are identi able by their spatio-temporal trajectories, but are so completely nonidenti able that all their imaginable permutations constitute one single physical state. In physicists' everyday language, classical particles are said to be 'distinguishable', quantum particles 'indistinguishable'. Indistinguishability is thus commonly taken to be the de ning attribute of quantum statistics, the theory that statistically describes and explains the behaviour of microphysical entities. It is indistinguishability that separates quantum statistics from its parent theory, the so-called classical statistical mechanics. But when and how, exactly, did this transition occur? When did particles become indistinguishable? The apparent simplicity of this question conceals several layers of complication. To begin with, the terminology of indistinguishability, though common, is neither unanimous nor unequivocal, for even classical particles, if they belong to the same particle species and are imagined at rest, are observationally indistinguishable. For this reason, some authors describe the conceptual transition as the change from the classical idea of indistinguishability to a quantum idea of indistinguishability. Others evade the ambiguity by stressing that quantum particles are 'absolutely' indistinguishable. Philosophers of physics have ner distinctions and a 1 2 p. 256

The Phoenix and Mars Reconnaissance Orbiter (MRO) missions collaborated in an unprecedented campaign to observe the northern polar region summer atmosphere throughout the Phoenix mission (25 May to 2 November 2008; L s = 76°-150°) and slightly beyond (∼L s = 158°). Five atmospherically related campaigns were defined a priori and were executed on 37 separate Martian days (sols). Phoenix and MRO observed the atmosphere nearly simultaneously. We describe the observation strategy and history, the participating experiments, and some initial results. We find that there is general agreement between measurements from different instruments and platforms and that complementary measurements provide a consistent picture of the atmosphere. Seasonal water abundance behavior matches with historical measurements. Winds aloft, as measured by cloud motions, showed the same seasonally consistent, diurnal rotation as the winds measured at the lander, during the first part of the mission (L s = 76°-118°). A diurnal cycle recorded from L s ∼ 108.3°-109.1°, in which a dust front was approaching the Phoenix Lander, is examined in detail. Cloud heights measured on subsequent orbits showed that in areas of active lifting, dust can be lofted quite high in the atmosphere, doubling in height over 2 h. The combination of experiments also revealed that there were discrete vertical layers of water ice and dust. Water vapor column abundances compared to near-surface water vapor pressure indicate that water is not well mixed from the surface to a cloud condensation height and that the depth of the layer that exchanges diurnally with the surface is 0.5-1 km.