Multi-parton correlations and "exclusive" cross sections

In addition to the inclusive cross sections discussed within the QCD-parton model, in the regime of multiple parton interactions, different and more exclusive cross sections become experimentally viable and may be suitably measured. Indeed, in its study of double parton collisions, the quantity measured by CDF was an "exclusive" rather than an inclusive cross section. The non perturbative input to the "exclusive" cross sections is different with respect to the non perturbative input of the inclusive cross sections and involves correlation terms of the hadron structure already at the level of single parton collisions. The matter is discussed in details keeping explicitly into account the effects of double and of triple parton collisions.Comment: 18 pages, no figures, corrected typo

A proposed DAQ system for a calorimeter at the International Linear Collider

This note describes R&D to be carried out on the data acquisition system for a calorimeter at the future International Linear Collider. A generic calorimeter and data acquisition system is described. Within this framework modified designs and potential bottlenecks within the current system are described. Solutions leading up to a technical design report will to be carried out within CALICE-UK groups.Comment: 13 pages, 4 figure

Jet Trimming

Initial state radiation, multiple interactions, and event pileup can contaminate jets and degrade event reconstruction. Here we introduce a procedure, jet trimming, designed to mitigate these sources of contamination in jets initiated by light partons. This procedure is complimentary to existing methods developed for boosted heavy particles. We find that jet trimming can achieve significant improvements in event reconstruction, especially at high energy/luminosity hadron colliders like the LHC.Comment: 20 pages, 11 figures, 3 tables - Minor changes to text/figure

CONSIDERATION OF MULTISPECIES INTERACTIONS IN THE ANTARCTIC: A PRELIMINARY MODEL OF THE MINKE WHALE – BLUE WHALE – KRILL INTERACTION

As a first step in investigating the major predator–prey interactions in the Antarctic, a model describing blue whales Balaenoptera musculus, minke whales Balaenoptera acutorostrata and krill Euphausia superba is developed. Blue and minke whales feed mainly on krill, and they share a similar feeding area near the Antarctic ice edge. In the early 20th century, the large baleen whales in the Antarctic were heavily harvested, some to near extinction. Blue whales were taken for almost 60 years, before being officially protected in 1964. Harvesting of the smaller minke whales commenced only in the 1970s, and the population probably increased during the mid 20th century, likely in response to increased krill abundance following the depletion of the large baleen whales. Recent studies show recoveries of some of these large baleen whale species in response to protection, and also a possible recent decrease in the stock of minke whales as the larger whales recover. This work investigates whether the abundance trends indicated by surveys and other information for these species can be explained by considering only harvesting and the predator–prey interactions between the two whale species and krill. Using historical catch data for blue and minke whales, a simple age-aggregated model including species interactions is fitted to survey abundance estimates. Uncertainties in the abundance estimates and the biological parameters are taken into account in the process by considering plausible ranges for their alues. Abundance trends for the species can broadly be replicated by the model, provided the parameter values show certain features, including (i) that blue whales are able to maintain their birth and krill consumption rates until krill abundance drops to relatively low levels, and (ii) that both minke and blue whales show relatively fast rates of growth if krill is abundant, but that minke growth rate falls more rapidly as krill abundance drops. The model suggests two interesting features of the dynamics of these species. First, a substantial decrease in krill biomass from the 1970s to the 1990s as a result of the preceding rapid increase in minke whale abundance, and hence krill consumption, following the depletion of the larger baleen whales. Second, a recovery of blue whales despite the impact of minke whales on krill abundance and its resultant decrease, because blue whales are better able to tolerate decreased krill abundance. Future projections show a gradual increasing trend in blue whale abundance and a gradual decrease in minke abundance, with large amplitude oscillations superimposed. Long-term monitoring of biological parameters and abundance are essential to provide a basis for verification or otherwise of such predictions. Results presented here should be viewed qualitatively rather than quantitatively. However, for the future, refinement of the model structure and incorporation of age structure, data on some other major predator species that feed on krill and some spatial structure, is under consideration.Afr. J. mar. Sci. 26: 245–25

Optimal jet radius in kinematic dijet reconstruction

Obtaining a good momentum reconstruction of a jet is a compromise between taking it large enough to catch the perturbative final-state radiation and small enough to avoid too much contamination from the underlying event and initial-state radiation. In this paper, we compute analytically the optimal jet radius for dijet reconstructions and study its scale dependence. We also compare our results with previous Monte-Carlo studies.Comment: 30 pages, 11 figures; minor corrections; published in JHE

The mass area of jets

We introduce a new characteristic of jets called mass area. It is defined so as to measure the susceptibility of the jet's mass to contamination from soft background. The mass area is a close relative of the recently introduced catchment area of jets. We define it also in two variants: passive and active. As a preparatory step, we generalise the results for passive and active areas of two-particle jets to the case where the two constituent particles have arbitrary transverse momenta. As a main part of our study, we use the mass area to analyse a range of modern jet algorithms acting on simple one and two-particle systems. We find a whole variety of behaviours of passive and active mass areas depending on the algorithm, relative hardness of particles or their separation. We also study mass areas of jets from Monte Carlo simulations as well as give an example of how the concept of mass area can be used to correct jets for contamination from pileup. Our results show that the information provided by the mass area can be very useful in a range of jet-based analyses.Comment: 36 pages, 12 figures; v2: improved quality of two plots, added entry in acknowledgments, nicer form of formulae in appendix A; v3: added section with MC study and pileup correction, version accepted by JHE

Inclusive and "exclusive" cross sections in the regime of multiple parton collisions

The large luminosity and the increased kinematical domain accessible at the LHC will allow to isolate large numbers of events with multiple parton collisions. Interestingly, the hadron is probed in different points contemporarily in the process, which allows to obtain information on the correlations between partons in the hadron structure. The whole experimentally accessible information on multiple parton collisions consists in the probability distribution of the elementary interactions, while the inclusive cross sections, usually considered in large p_t processes, acquire a precise statistical meaning as moments of the multiplicity distribution. Conversely different and more "exclusive" cross sections become experimentally viable, providing complementary information on the interaction dynamics. The matter is discussed in details in the case of hadron-hadron collisions and the role of parton correlations is outlined both in the inclusive and in the "exclusive" cross sections.Comment: 18 pages, no figures, corrected typo

TIM (TTC Interface Module) for ATLAS SCT & PIXEL Read Out Electronics

The design, functionality, description of hardware and firmware and preliminary results of the ROD ( Read Out Driver) System Tests of the TIM (TTC Interface Module) are described.The TIM is the standard SCT and PIXEL detector interface module to the ATLAS Level-1 Trigger, using the LHC-standard TTC (Timing, Trigger and Control) system.TIM designed and built during 1999 and 2000 and two prototypes have been in use since then (Fig. 1). More modules are being built this year to allow for more tests of the ROD system at different sites around the world

Quasars: a supermassive rotating toroidal black hole interpretation

A supermassive rotating toroidal black hole (TBH) is proposed as the fundamental structure of quasars and other jet-producing active galactic nuclei. Rotating protogalaxies gather matter from the central gaseous region leading to the birth of massive toroidal stars whose internal nuclear reactions proceed very rapidly. Once the nuclear fuel is spent, gravitational collapse produces a slender ring-shaped TBH remnant. These events are typically the first supernovae of the host galaxies. Given time the TBH mass increases through continued accretion by several orders of magnitude, the event horizon swells whilst the central aperture shrinks. The difference in angular velocities between the accreting matter and the TBH induces a magnetic field that is strongest in the region of the central aperture and innermost ergoregion. Due to the presence of negative energy states when such a gravitational vortex is immersed in an electromagnetic field, circumstances are near ideal for energy extraction via non-thermal radiation including the Penrose process and superradiant scattering. This establishes a self-sustaining mechanism whereby the transport of angular momentum away from the quasar by relativistic bi-directional jets reinforces both the modulating magnetic field and the TBH/accretion disk angular velocity differential. Quasar behaviour is extinguished once the BH topology becomes spheroidal. Similar mechanisms may be operating in microquasars, SNe and GRBs when neutron density or BH tori arise. In certain circumstances, long-term TBH stability can be maintained by a negative cosmological constant, otherwise the classical topology theorems must somehow be circumvented. Preliminary evidence is presented that Planck-scale quantum effects may be responsible.Comment: 26 pages, 14 figs, various corrections and enhancements, final versio