One-loop Factorization for Inclusive Hadron Production in pApA Collisions in the Saturation Formalism

We demonstrate the QCD factorization for inclusive hadron production in $pA$ collisions in the saturation formalism at one-loop order, with explicit calculation of both real and virtual gluon radiation diagrams. The collinear divergences associated with the incoming parton distribution of the nucleon and the outgoing fragmentation function of the final state hadron, as well as the rapidity divergence with small-$x$ dipole gluon distribution of the nucleus are factorized into the splittings of the associated parton distribution and fragmentation functions and the energy evolution of the dipole gluon distribution function. The hard coefficient function is evaluated at one-loop order, and contains no divergence.Comment: 8 pages, 1 figur

Inclusive Hadron Productions in pA Collisions

We calculate inclusive hadron productions in pA collisions in the small-x saturation formalism at one-loop order. The differential cross section is written into a factorization form in the coordinate space at the next-to-leading order, while the naive form of the convolution in the transverse momentum space does not hold. The rapidity divergence with small-x dipole gluon distribution of the nucleus is factorized into the energy evolution of the dipole gluon distribution function, which is known as the Balitsky-Kovchegov equation. Furthermore, the collinear divergences associated with the incoming parton distribution of the nucleon and the outgoing fragmentation function of the final state hadron are factorized into the splittings of the associated parton distribution and fragmentation functions, which allows us to reproduce the well-known DGLAP equation. The hard coefficient function, which is finite and free of divergence of any kind, is evaluated at one-loop order.Comment: 20 pages, 7 figures; v2 with minor updates and correction

Non-Universality of Transverse Momentum Dependent Parton Distributions at Small-x

We study the universality issue of the transverse momentum dependent parton distributions at small-x, by comparing the initial/final state interaction effects in dijet-correlation in pA collisions with those in deep inelastic lepton nucleus scattering. We demonstrate the non-universality by performing an explicit calculation in a particular model where the multiple gauge boson exchange contributions are summed up to all orders. We comment on the implications of our results on the theoretical interpretation of di-hadron correlation in dA collisions in terms of the saturation phenomena in deep inelastic lepton nucleus scattering.Comment: 11 pages, 3 figure

Similarity-aware Web Content Management and Document Pre-fetching

Web caching is intended to reduce network traffic, server load and user-perceived retrieval latency. Web pre-fetching, which can be considered as active caching, builds on regular Web caching, minimizing further a Web user\u27s access delay. To be effective, however, the pre-fetching techniques must be able to predict subsequent Web access with minimum computational overheads. This paper presents a similarity-based mechanism to support similarity-aware Web document pre-fetching between proxy caches and browsing clients. We first define a set of measures to assess similarities between Web documents, and then propose a multi-cache architecture to cache Web documents based on those similarities. A predictor is developed to support the similarity-aware document pre-fetching algorithm. Preliminary experiments have shown that our predictor offers superior performance when compared with some existing prediction algorithms

Initial and Final State Interaction Effects in Small-x Quark Distributions

We study the initial and final state interaction effects in the transverse momentum dependent parton distributions in the small-$x$ saturation region. In particular, we discuss the quark distributions in the semi-inclusive deep inelastic scattering, Drell-Yan lepton pair production and dijet-correlation processes in $pA$ collisions. We calculate the quark distributions in the scalar-QED model and then extend to the color glass condensate formalism in QCD. The quark distributions are found universal between the DIS and Drell-Yan processes. On the other hand, the quark distribution from the $qq'\to qq'$ channel contribution to the dijet-correlation process is not universal. However, we find that it can be related to the quark distribution in DIS process by a convolution with the normalized unintegrated gluon distribution in the color glass condensate formalism in the large $N_c$ limit.Comment: 20 pages, 6 figure

Dilute Nitride GaInNAsSb for Next Generation Optical Communications

Current technology for the light detection in telecommunication revolves around InGaAs based on InP substrates. However, there is interest in switching to GaAs substrates to take advantage of the cheaper and larger substrates as well as the lattice-matched AlxGa1−xAs material system. Therefore, this thesis reports on the use of the dilute nitride alloy GaInNAsSb lattice matched to GaAs that can detect at wavelengths important to telecommunications such as 1.55µm. Molecular beam epitaxy (MBE) was used to grow GaInNAsSb p-i-n and n-i-p photodetectors on GaAs substrates with the lowest band gap reaching 0.64eV, far below the necessary band gap required for detection at 1.55µm (0.8eV) and that for InGaAs (0.74eV). However, due to the high defect concentration typically found in dilute nitride alloys, a post-growth thermal anneal was applied to the samples which has the effect of blueshifting the band gap by approximately 40meV. The effect of a post-growth anneal on the band gap, dark current, unintentional doping concentration and quantum efficiency is investigated in order to find the most optimal temperature. This temperature is found to be related to an intrinsic dopant type switch in the GaInNAsSb as one of the samples with the lowest dark current density (2.2mAcm −2 at −5V) is one that is annealed at 735◦C, just before a switch in intrinsic type from n-type to p-type. This is further investigated with a much narrower annealing range centred around 735◦C. While this narrow annealing range did not result in a consistent type switch temperature for all samples, admittance spectroscopy indicated a large increase in a p-type defect concentration demonstrating the potential for the anneal to worsen the performance of the photodiode at sufficiently high temperatures. Furthermore, it was found that annealing at temperatures close to 730◦C results in a much better photodetector than as-grown devices, which can be quantified by comparing the quantum efficiency at 1.55µm where the annealed sample reaches 38% as compared to the 3% in the as-grown device.The 3dB bandwidth was measured on the most optimally annealed photodetectors. In this measurement, the highest bandwidth reached is 9.2GHz at −18V which is limited by the resistance of the photodetector and can be further improved using Ohmic contacts with a lower resistance. Finally, a discussion on the integration of GaInNAsSb with AlGaAs in a separate absorption and multiplication avalanche photodiode (SAM APD) is held. Impact ionisation in GaInNAsSb and its effect on noise is discussed, as well as the design of a SAM APD with a very thin AlGaAs multiplication layer of 50nm. In this study, such SAM APDs are grown with a GaAs absorber instead of GaInNAsSb to allow for any corrections required in the important charge sheet layer, however in future studies GaInNAsSb can be used instead of GaAs as an absorber

A Cost-benefit analysis model for the retrofit of sustainable urban drainage systems towards improved flood risk mitigation

The Environment Agency estimates that one in six homes in England (approximately 5.2million properties) are at risk from flooding and 185,000 commercial properties are located in flood-prone areas. Further, an estimated 10,000 new homes are built on flood plains yearly. The UK has witnessed a significant increase in flood events over the past 10 years. During this period, there has been growing research attention into measures to mitigate the effects of flooding, including the benefits of deploying Sustainable Urban Drainage Systems (SuDs) in new developments or as a retrofit. This study presents the development of a cost-benefit analysis model for the retrofit of SuDs focusing on the potential for improved flood risk mitigation in the context of commercial properties. A synthesis of flood risk management and SuDs literature is used to inform the development of a conceptual cost-benefit analysis model for the retrofit of SuDs and focusing on the potential for improved flood risk mitigation in the context of commercial properties. Sustainable urban drainage systems have been applied successfully in different parts of the world, however, the uptake of SuDs, in particular, the retrofit of SuDs, has been restricted by a number of issues including a lack of experience and trust in their performance and a lack of understanding in their true benefits. In particular, there is the limited experience of retrofitting SuDs and there are no well-established procedures for evaluating the feasibility, value or cost-effectiveness of doing this. This offers the potential to support the UK government’s flood risk management policy by helping to increase the resilience of properties, whilst offering other benefits to communities such as improvements in air quality and biodiversity and also presenting a clearer understanding of the monetary and non-monetary implication to owners of commercial properties for a more informed and acceptable uptake of SuDs retrofit. The proposed model will allow a more comprehensive understanding of the costs and associated benefits associated with SuDs retrofit, highlighting the flood risk mitigation benefits that might accrue over a period of time for commercial property

An improved study of the kappa resonance and the non-exotic ss wave πK\pi K scatterings up to s=2.1\sqrt{s}=2.1GeV of LASS data

We point out that the dispersion relation for the left hand cut integral presented in one of our previous paper (Nucl. Phys. {\bf A}733(2004)235) is actually free of subtraction constant, even for unequal mass elastic scatterings. A new fit to the LASS data~\cite{Aston} is performed and firm evidence for the existence of $\kappa$ pole is found. The correct use of analyticity also put strong constraints on threshold parameters -- which are found to be in good agreement with those obtained from chiral theories. We also determined the pole parameters of $K_0^*(1430)$ on the second sheet, and reconfirm the existence of $K_0^*(1950)$ on the third sheet. We stress that the LASS data do not require them to have the twin pole structure of a typical Breit--Wigner resonance.Comment: 14 pages + 4 postscript figures; discussions largely expanded; references added; version to appear in NPA; title changed in the journa

Restoration of kTk_T factorization for low pTp_T hadron hadroproduction

We discuss the applicability of the $k_T$ factorization theorem to low-$p_T$ hadron production in hadron-hadron collision in a simple toy model, which involves only scalar particles and gluons. It has been shown that the $k_T$ factorization for high-$p_T$ hadron hadroproduction is broken by soft gluons in the Glauber region, which are exchanged among a transverse-momentum-dependent (TMD) parton density and other subprocesses of the collision. We explain that the contour of a loop momentum can be deformed away from the Glauber region at low $p_T$, so the above residual infrared divergence is factorized by means of the standard eikonal approximation. The $k_T$ factorization is then restored in the sense that a TMD parton density maintains its universality. Because the resultant Glauber factor is independent of hadron flavors, experimental constraints on its behavior are possible. The $k_T$ factorization can also be restored for the transverse single-spin asymmetry in hadron-hadron collision at low $p_T$ in a similar way, with the residual infrared divergence being factorized into the same Glauber factor.Comment: 12 pages, 2 figures, version to appear in EPJ