Machine learning for event selection in high energy physics

The field of high energy physics aims to discover the underlying structure of matter by searching for and studying exotic particles, such as the top quark and Higgs boson, produced in collisions at modern accelerators. Since such accelerators are extraordinarily expensive, extracting maximal information from the resulting data is essential. However, most accelerator events do not produce particles of interest, so making effective measurements requires event selection, in which events producing particles of interest (signal) are separated from events producing other particles (background). This article studies the use of machine learning to aid event selection. First, we apply supervised learning methods, which have succeeded previously in similar tasks. However, they are suboptimal in this case because they assume that the selector with the highest classification accuracy will yield the best final analysis; this is not true in practice, as such analyses are more sensitive to some backgrounds than others. Second, we present a new approach that uses stochastic optimization techniques to directly search for selectors that maximize either the precision of top quark mass measurements or the sensitivity to the presence of the Higgs boson. Empirical results confirm that stochastically optimized selectors result in substantially better analyses. We also describe a case study in which the best selector is applied to real data from the Fermilab Tevatron accelerator, resulting in the most precise top quark mass measurement of this type to date. Hence, this new approach to event selection has already contributed to our knowledge of the top quark's mass and our understanding of the larger questions upon which it sheds light.     

What Are Quantum States?

We present three strong arguments against the ontic interpretation of quantum states. We then show that the appropriate alternative is not an epistemic interpretation, but viewing quantum states as representing the available knowledge about the potentialities of a quantum system from the perspective a of a particular point in space. Unlike ordinary knowledge, which requires a knower, available knowledge can be assumed to be present regardless of a knower. The relationship between “perspectives on potentialities” and “the potentialities themselves” is clarified.     

A bacteriophage reagent for Salmonella: molecular studies on Felix 01

Felix 01 (F01) is a bacteriophage originally isolated by Felix and Callow which lyses almost all Salmonella strains and has been widely used as a diagnostic test for this genus. Molecular information about this phage is entirely lacking. In the present study, the DNA of the phage was found to be a double-stranded linear molecule of about 80 kb. 11.5 kb has been sequenced and in this region A + T content is 60%. There are relatively few restriction endonuclease cleavage sites in the native genome and clones show this is due to their absence rather than modification. A restriction map of the genome has been constructed. The ends of the molecule cannot be ligated although they contain 5' phosphates. At least 60% of the genome must encode proteins. In the sequenced portion, many open reading frames exist and these are tightly packed together. These have been examined for homology to published proteins but only 1 to 17 shows similarity to known proteins. F01 is therefore the prototype of a new phage family. On the basis of restriction sites, codon usage and the distribution of nonsense codons in the unused reading frames, a strong case can be made for natural selection that reacts to mRNA structure and function.     

Morbidity of DSM-IV Axis I disorders in patients with noncardiac chest pain: Psychiatric morbidity linked with increased pain and health care utilization.

The present study examined current and lifetime psychiatric morbidity, chest pain, and health care utilization in 229 patients with noncardiac chest pain (NCCP), angina-like pain in the absence of cardiac etiology. Diagnostic interview findings based on the Diagnostic and Statistical Manual of Mental Disorders (4th ed.; DSM-IV; American Psychiatric Association, 1994) revealed a psychiatrically heterogeneous sample of whom 44% had a current Axis I psychiatric disorder. A total of 41% were diagnosed with a current anxiety disorder, and 13% were diagnosed with a mood disorder. Overall, 75% of patients had an Axis I clinical or subclinical disorder. Lifetime diagnoses of anxiety (55%) and mood disorders (44%) were also prevalent, including major depressive disorder (41%), social phobia (25%), and panic disorder (22%). Patients with an Axis I disorder reported more frequent and more painful chest pain compared with those without an Axis I disorder. Presence of an Axis I disorder was associated with increased life interference and health care utilization. Findings reveal that varied DSM-IV Axis I psychiatric disorders are prevalent among patients with NCCP, and this psychiatric morbidity is associated with a less favorable NCCP presentation. Implications for early identification of psychiatric disorders are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Characteristics of transverse volume discharge in Cf2Cl2 and in Ar/Cf2Cl2 mixture

The conditions of ignition and the characteristics are given for a nanosecond transverse volume discharge in Freon-12 (CF₂C1₂) and in an Ar/CF₂C1₂ mixture. It is shown that, in the ultraviolet and visible ultraviolet spectral region, a plasma based on CF₂C1₂ molecules is a source of radiation of excited carbon atoms and Cl₂ molecules. The volumetric stage of the discharge exists atU _charge ≤ 12 kV and [CF₂C1₂] = 0.1–3 kPa, and the current and voltage oscillograms are similar to the respective characteristics of a transverse discharge with prior-to-prebreakdown electron multiplication in He(Ne)/SF6(F2) mixtures. A plasma of an Ar/CF2C12 mixture is a source of radiation of the λ = 258 nm bands for Cl ₂ ^* , 193 nm for ArF, and 175 nm for ArCl. Such sources may be used in short-wave pulse photometry, microelectronics, and photo- and biochemistry.     

On the limits of expert systems and engineering models in process control

The review is based on an analysis of current literature of expert systems and of system engineering models in dynamic process control. It starts with an analysis of the mental operations and cognitive requirements needed for supervisory control. Mental models are discussed as a function of situational requirements as well as of personal strategies. Systems engineering models and expert systems are briefly described and their function as decision support tools evaluated. Criteria are the overall functionality, similarity of knowledge bases and reasoning strategies of the human and the support system, adaptability to the operator's skill level and self-explanation of the support system in the interaction mode. As a result, system engineering models are only of limited value for knowledge-based process control. Expert systems seem to be very valuable tools for augmenting human decision making in process control, if the interaction problem can be solved.     

Stereochemical Discrimination at Organic Crystal Surfaces 1: The Systems Serine/Threonine and Serine/Allothreonine

The stereoselective interactions in aqueous solution between the crystal faces of centrosymmetric (R,S) serine 1 and additives resolved and racemic threonine 2 and allothreonine 3 were studied by four independent techniques: change in crystal habit on growth, anisotropic distribution of occluded additive during the crystal growth, etch pit formation on partial dissolution and atom-atom potential energy calculations. The effects of the two diastereomers 2 and 3 are radically different due to differences in adsorption: threonine is adsorbed on the {011} crystal faces; the (R) enantiomer is adsorbed at, and eventually occluded through the (011) and (011) crystal faces replacing an (R) serine molecule. By symmetry, (S) threonine is adsorbed and occluded through the enantiotopic (011) and (011) faces replacing (S) serine. In contrast, (R) and (S) allothreonine are both adsorbed primarily at the (100) and (100) faces. The results indicate that the serine moiety of adsorbed threonine and allothreonine assume the same conformation and position as the substrate molecule. The additive is adsorbed only at specific sites such that the C_β-CH₃ groups emerge from the crystal surface. The observed effects lead in the case of threonine, but not allothreonine, to the assignment of its absolute configuration.     

A water-vapor electric-discharge vacuum ultraviolet source

The optical emission from a longitudinal dc glow discharge in water vapors (P=0.05–2.5 kPa) was studied in a wavelength range of λ=130–350 nm. It is shown that the discharge in low-pressure water vapors can be used as a source of the vacuum UV (VUV) radiation in the 140–190 nm wavelength range. As the vapor pressure was increased to 2.5 kPa, the emission intensity decreased by one-two orders of magnitude and the main peaks shifted to λ=286 and 306–315 nm. The bands of optical emission from the products of water decomposition agree in position with the emission band edges of the hydroxyl molecule. The obtained results are important for the development of a simple water-vapor electric-discharge VUV source.