Alignment procedure of the LHCb Vertex Detector

LHCb is one of the four main experiments of the Large Hadron Collider (LHC) project, which will start at CERN in 2008. The experiment is primarily dedicated to B-Physics and hence requires precise vertex reconstruction. The silicon vertex locator (VELO) has a single hit precision of better than 10 micron and is used both off-line and in the trigger. These requirements place strict constraints on its alignment. Additional challenges for the alignment arise from the detector being retracted between each fill of the LHC and from its unique circular disc r/phi strip geometry. This paper describes the track based software alignment procedure developed for the VELO. The procedure is primarily based on a non-iterative method using a matrix inversion technique. The procedure is demonstrated with simulated events to be fast, robust and to achieve a suitable alignment precision.Comment: accepted for publication in NIM

LHCb VELO software alignment, Part III: the alignment of the relative sensor positions

The LHCb Vertex Locator contains 42 silicon sensor modules. Each module has two silicon sensors. A method for determining the relative alignment of the silicon sensors within each module from data is presented. The software implementation details are discussed. Monte-Carlo simulation studies are described that demonstrate an alignment precision of 1.3 micron is obtained in the sensor plane

Isomeric effects in the gas-phase reactions of dichloroethene, C2H2Cl2, with a series of cations

A study of the reactions of a series of gas-phase cations (NH$_4^+$, H$_3$O$^+$, SF$_3^+$, CF$_3^+$, CF$^+$, SF5$^+$, SF$_2^+$, SF$^+$, CF$_2^+$, SF$_4^+$, O$_2^+$, Xe$^+$, N$_2$O$^+$, CO$_2^+$, Kr$^+$, CO$^+$, N$^+$, N$_2^+$, Ar$^+$, F$^+$ and Ne$^+$) with the three structural isomers of dichloroethene, i.e. 1,1-C$_2$H$_2$Cl$_2$, cis-1,2-C$_2$H$_2$Cl$_2$ and trans-1,2-C$_2$H$_2$Cl$_2$ is reported. The recombination energy of these ions spans the range 4.7-21.6 eV. Reaction rate coefficients and product branching ratios have been measured at 298 K in a selected ion flow tube. Collisional rate coefficients are calculated by modified average dipole orientation theory and compared with experimental data. Thermochemistry and mass balance have been used to predict the most feasible neutral products. Threshold photoelectron-photoion coincidence spectra have also been obtained for the three isomers of C$_2$H$_2$Cl$_2$ with photon energies in the range 10-23 eV. The fragment ion branching ratios have been compared with those of the flow tube study to determine the importance of long-range charge transfer. A strong influence of the isomeric structure of dichloroethene on the products of ion-molecule reactions has been observed for H$_3$O$^+$, CF$_3^+$, and CF$^+$. For 1,1-C$_2$H$_2$Cl$_2$ the reaction with H$_3$O$^+$ proceeds at the collisional rate with the only ionic product being 1,1-C$_2$H$_2$Cl$_2$H$^+$. However, the same reaction yields two more ionic products in the case of cis-1,2- and trans-1,2-C$_2$H$_2$Cl$_2$, but only proceeds with 14 % and 18 % efficiency, respectively. The CF$_3^+$ reaction proceeds with 56-80 % efficiency, the only ionic product for 1,1-C$_2$H$_2$Cl$_2$ being C$_2$H$_2$Cl$^+$ formed via Cl- abstraction, whereas the only ionic product for both 1,2-isomers is CHCl$_2^+$ corresponding to a breaking of the C=C double bond. Less profound isomeric effects, but still resulting in different products for 1,1- and 1,2-C$_2$H$_2$Cl$_2$ isomers, have been found in the reactions of SF$^+$, CO$_2^+$, CO$^+$, N$_2^+$, and Ar$^+$. Although these five ions have recombination energies above the ionization energy of any of the C$_2$H$_2$Cl$_2$ isomers and hence the threshold for long-range charge transfer, the results suggest that the formation of a collision complex at short range between these ions and C$_2$H$_2$Cl$_2$ is responsible for the observed effects

LHCb VELO software alignment - PART II: the alignment of the VELO detector-halves

The software alignment of the Vertex Locator (VELO) is a critical component of the LHCb alignment strategy. This note demonstrates a potential algorithm to perform the alignment of the VELO detector-halves. The approach described in this document, and the tools developed, are also applicable to the alignment of the other LHCb sub-systems and the global relative alignment of the sub-detectors

Applying Learning Algorithms to Preference Elicitation

We consider the parallels between the preference elicitation problem in combinatorial auctions and the problem of learning an unknown function from learning theory. We show that learning algorithms can be used as a basis for preference elicitation algorithms. The resulting elicitation algorithms perform a polynomial number of queries. We also give conditions under which the resulting algorithms have polynomial communication. Our conversion procedure allows us to generate combinatorial auction protocols from learning algorithms for polynomials, monotone DNF, and linear-threshold functions. In particular, we obtain an algorithm that elicits XOR bids with polynomial communication.Engineering and Applied Science

Impact of a theoretically based sex education programme (SHARE) delivered by teachers on NHS registered conceptions and terminations: final results of cluster randomised trial

<b>Objective</b>: To assess the impact of a theoretically based sex education programme (SHARE) delivered by teachers compared with conventional education in terms of conceptions and terminations registered by the NHS. Design Follow-up of cluster randomised trial 4.5 years after intervention. <b>Setting</b>: NHS records of women who had attended 25 secondary schools in east Scotland. <b>Participants</b>: 4196 women (99.5% of those eligible). <b>Intervention</b>: SHARE programme (intervention group) v existing sex education (control group). <b>Main outcome measure</b>: NHS recorded conceptions and terminations for the achieved sample linked at age 20. <b>Results</b>: In an "intention to treat" analysis there were no significant differences between the groups in registered conceptions per 1000 pupils (300 SHARE v 274 control; difference 26, 95% confidence interval –33 to 86) and terminations per 1000 pupils (127 v 112; difference 15, –13 to 42) between ages 16 and 20. <b>Conclusions</b>: This specially designed sex education programme did not reduce conceptions or terminations by age 20 compared with conventional provision. The lack of effect was not due to quality of delivery. Enhancing teacher led school sex education beyond conventional provision in eastern Scotland is unlikely to reduce terminations in teenagers

Threshold photoelectron photoion coincidence spectroscopy and selected ion flow tube reactions of CHF3: comparison of product branching ratios

The threshold photoelectron and threshold photoelectron photoion coincidence spectra of CHF$_3$ in the range 13.5 – 24.5 eV have been recorded. Ion yields and branching ratios have been determined for the three fragments CF$_3^+$, CHF2$^+$ and CF$^+$. The mean kinetic energy releases into fragment ions involving either C-H or C-F bond cleavage have been measured, and compared with statistical and impulsive models. CHF$_3^+$ behaves in a non-statistical manner characteristic of the small-molecule limit, with the ground electronic state and low-lying excited states of CHF$_3^+$ being largely repulsive along the C-H and C-F coordinates, respectively. The rate coefficients and product ion branching ratios have been measured at 298 K in a selected ion flow tube for the reactions of CHF$_3$ with a large number of gas-phase cations whose recombination energies span the range 6.3 through 21.6 eV. A comparison between the branching ratios from the two experiments, together with an analysis of the threshold photoelectron spectrum of CHF$_3$, shows that long-range charge transfer probably occurs for the Ar$^+$ and F$^+$ atomic ions whose recombination energies lie above ca. 15 eV. Below this energy, the mechanism involves a combination of short-range charge transfer and chemical reactions involving a transition state intermediate

Computational Challenges in E-Commerce

Economic and social sciences will drive Internet protocols and services into the future.Engineering and Applied Science

A selected ion flow tube study of the ion-molecule reactions of monochloroethene, trichloroethene and tetrachloroethene

Data for the rate coefficients and product cations of the reactions of a large number of atomic and small molecular cations with monochloroethene, trichloroethene and tetrachloroethene in a selected ion flow tube at 298 K are reported. The recombination energy of the ions range from 6.27 eV (H$_3$O$^+$) through to 21.56 eV (Ne$^+$). Collisional rate coefficients are calculated by modified average dipole orientation theory and compared with experimental values. Thermochemistry and mass balance predict the most feasible neutral products. Together with previously reported results for the three isomers of dichloroethene (J. Phys. Chem. A., 2006, 110, 5760), the fragment ion branching ratios have been compared with those from threshold photoelectron photoion coincidence spectroscopy over the photon energy range 9-22 eV to determine the importance or otherwise of long-range charge transfer. For ions with recombination energy in excess of the ionisation energy of the chloroethene, charge transfer is energetically allowed. The similarity of the branching ratios from the two experiments suggest that long-range charge transfer is dominant. For ions with recombination energy less than the ionisation energy, charge transfer is not allowed; chemical reaction can only occur following formation of an ion-molecule complex, where steric effects are more significant. The products that are now formed and their percentage yield is a complex interplay between the number and position of the chlorine atoms with respect to the C=C bond, where inductive and conjugation effects can be important