On the Dipole Swing and the Search for Frame Independence in the Dipole Model

Small-x evolution in QCD is conveniently described by Mueller's dipole model which, however, does not include saturation effects in a way consistent with boost invariance. In this paper we first show that the recently studied zero and one dimensional toy models exhibiting saturation and explicit boost invariance can be interpreted in terms positive definite k-> k+1 dipole vertices. Such k-> k+1 vertices can in the full model be generated by combining the usual dipole splitting with k-1 simultaneous dipole swings. We show that, for a system consisting of N dipoles, one needs to combine the dipole splitting with at most N-1 simultaneous swings in order to generate all colour correlations induced by the multiple dipole interactions

Diffractive Excitation in DIS and pp Collisions

We have in earlier papers presented an extension of Mueller's dipole cascade model, which includes subleading effects from energy conservation and running coupling as well as colour suppressed effects from pomeron loops via a ``dipole swing''. The model was applied to describe the total cross sections in pp and gamma*p collisions. In this paper we present a number of improvements of the model, in particular related to the confinement mechanism. A consistent treatment of dipole evolution and dipole--dipole interactions is achieved by replacing the infinite range Coulomb potential by a screened potential, which further improves the frame-independence of the model. We then apply the model to elastic scattering and diffractive excitation, where we specifically study the effects of different sources for fluctuations. In our formalism we can take into account contributions from all different sources, from the dipole cascade evolution, the dipole--dipole scattering, from the impact-parameter dependence, and from the initial photon and proton wavefunctions. Good agreement is obtained with data from the Tevatron and from HERA, and we also present some predictions for the LHC.Comment: correction of titl

Geometric Scaling and QCD Dynamics in DIS

DIS data from HERA show a striking regularity as \sigma^{\gamma^* p} is a function of the ratio \tau=Q^2/Q_s^2(x) only. The scaling function shows a break at \tau ~ 1, which has been taken as an indication for saturation. However, besides saturation also the transition between dominance of k_t-ordered (DGLAP) and k_t-non-ordered (BFKL) evolution contributes to a break around this value of \tau, as well as the suppression for small Q^2 due to finite quark masses and confinement. In this paper we use a dipole cascade model based on Mueller's dipole model, which also includes energy conservation and pomeron mergins, to investigate the contributions of these different effects to the scaling behaviour. As a result we predict that the scaling function for \tau 1 GeV^2 become available. We also investigate the scaling properties of the charm contribution and the impact parameter dependence of the saturation scale.Comment: references added, figures 2, 7 and 8 updated v3: reference added, some misprints correcte

Small-x Dipole Evolution Beyond the Large-N_c Limit

We present a method to include colour-suppressed effects in the Mueller dipole picture. The model consistently includes saturation effects both in the evolution of dipoles and in the interactions of dipoles with a target in a frame-independent way. When implemented in a Monte Carlo simulation together with our previous model of energy--momentum conservation and a simple dipole description of initial state protons and virtual photons, the model is able to reproduce to a satisfactory degree both the gamma*-p cross sections as measured at HERA as well as the total p-p cross section all the way from ISR energies to the Tevatron and beyond

Numerical solution of the nonlinear evolution equation at small x with impact parameter and beyond the LL approximation

Nonlinear evolution equation at small x with impact parameter dependence is analyzed numerically. Saturation scales and the radius of expansion in impact parameter are extracted as functions of rapidity. Running coupling is included in this evolution, and it is found that the solution is sensitive to the infrared regularization. Kinematical effects beyond leading logarithmic approximation are taken partially into account by modifying the kernel which includes the rapidity dependent cuts. While the local nonlinear evolution is not very sensitive to these effects, the kinematical constraints cannot be neglected in the evolution with impact parameter.Comment: 22 pages, 37 figures, RevTe

Fluctuations, Saturation, and Diffractive Excitation in High Energy Collisions

Diffractive excitation is usually described by the Good--Walker formalism for low masses, and by the triple-Regge formalism for high masses. In the Good--Walker formalism the cross section is determined by the fluctuations in the interaction. In this paper we show that by taking the fluctuations in the BFKL ladder into account, it is possible to describe both low and high mass excitation by the Good--Walker mechanism. In high energy $pp$ collisions the fluctuations are strongly suppressed by saturation, which implies that pomeron exchange does not factorise between DIS and $pp$ collisions. The Dipole Cascade Model reproduces the expected triple-Regge form for the bare pomeron, and the triple-pomeron coupling is estimated.Comment: 20 pages, 12 figure

Designing touch screen user interfaces for future flight deck operations

Many interactional issues with Flight Management Systems (FMS) in modern flight decks have been reported. Avionics designers are seeking for ways to reduce cognitive load of pilots with the aim to reduce the potential for human error. Academic research showed that touch screen interfaces reduce cognitive effort and provide an intuitive way of interaction. A new way of interaction to manipulate radio frequencies of avionics systems is presented in this paper. A usability experiment simulating departures and approaches to airports was used to evaluate the interface and compare it with the current system (FMS). In addition, interviews with pilots were conducted to find out their personal impressions and to reveal problem areas of the interface. Analyses of task completion time and error rates showed that the touch interface is significantly faster and less prone to user input errors than the conventional input method (via physical or virtual keypad). Potential problem areas were identified and an improved interface is suggested

Target size guidelines for interactive displays on the flight deck

The avionics industry is seeking to understand the challenges and benefits of touchscreens on flight decks. This paper presents an investigation of interactive displays on the flight deck focusing on the impact of target size, placement and vibration on performance. A study was undertaken with search and rescue (SAR) crew members in an operational setting in helicopters. Results are essential to understand how to design effective touchscreen interfaces for the flight deck. Results show that device placement, vibration and target size have significant effects on targeting accuracy. However, increasing target size eliminates the negative effects of placement and vibration in most cases. The findings suggest that 15 mm targets are sufficiently large for non-safety critical Electronic Flight Bag (EFB) applications. For interaction with fixed displays where pilots have to extend their arms, and for safety critical tasks it is recommended to use interactive elements of about 20 mm size

Mixed method approach in designing flight decks with touch screens: a framework

Touch screen technology’s first public appearance was in the early 2000s. Touch screens became a part of the daily life with the invention of smartphones and tablets. Now, this technology has the potential to be the next big change in flight deck design. To date, mobile devices are deployed by several air carriers to perform a host of non-safety critical pre-flight and in-flight tasks. Due to high safety requirements requested by authorities, new technologies cannot be adopted as fast as in other settings. Flight deck evolution, which is briefly presented in this paper, is reflecting this natural time delay. Avionics manufacturers are exploring and working on future concepts with touch screen displays. This paper investigates the potential benefits and challenges of touch screen technology on flight decks by means of a variety of qualitative and quantitative research methods (mixed method approach). On the basis of this, a framework was constructed showing the relation between various aspects that could impact the usability of touch screens on the flight deck. This paper concludes with a preliminary questionnaire that can help avionic designers to evaluate whether a touch screen is an appropriate user interface for their system

Target size guidelines for interactive displays on the flight deck

The avionics industry is seeking to understand the challenges and benefits of touchscreens on flight decks. This paper presents an investigation of interactive displays on the flight deck focusing on the impact of target size, placement and vibration on performance. A study was undertaken with search and rescue (SAR) crew members in an operational setting in helicopters. Results are essential to understand how to design effective touchscreen interfaces for the flight deck. Results show that device placement, vibration and target size have significant effects on targeting accuracy. However, increasing target size eliminates the negative effects of placement and vibration in most cases. The findings suggest that 15 mm targets are sufficiently large for non-safety critical Electronic Flight Bag (EFB) applications. For interaction with fixed displays where pilots have to extend their arms, and for safety critical tasks it is recommended to use interactive elements of about 20 mm size