Lattice worldline representation of correlators in a background field

We use a discrete worldline representation in order to study the continuum limit of the one-loop expectation value of dimension two and four local operators in a background field. We illustrate this technique in the case of a scalar field coupled to a non-Abelian background gauge field. The first two coefficients of the expansion in powers of the lattice spacing can be expressed as sums over random walks on a d -dimensional cubic lattice. Using combinatorial identities for the distribution of the areas of closed random walks on a lattice, these coefficients can be turned into simple integrals. Our results are valid for an anisotropic lattice, with arbitrary lattice spacings in each direction

Kinetic theory of a longitudinally expanding system of scalar particles

A simple kinematical argument suggests that the classical approximation may be inadequate to describe the evolution of a system with an anisotropic particle distribution. In order to verify this quantitatively, we study the Boltzmann equation for a longitudinally expanding system of scalar particles interacting with a ϕ 4 coupling, that mimics the kinematics of a heavy ion collision at very high energy. We consider only elastic 2 → 2 scatterings, and we allow the formation of a Bose-Einstein condensate in overpopulated situations by solving the coupled equations for the particle distribution and the particle density in the zero mode. For generic CGC-like initial conditions with a large occupation number, the solutions of the full Boltzmann equation cease to display the classical attractor behavior sooner than expected; for moderate coupling, the solutions appear never to follow a classical attractor solution

Small-radius jets to all orders in QCD

As hadron collider physics continues to push the boundaries of precision, it becomes increasingly important to have methods for predicting properties of jets across a broad range of jet radius values R , and in particular for small R . In this paper we resum all leading logarithmic terms, α s n  ln n R 2 , in the limit of small R , for a wide variety of observables. These include the inclusive jet spectrum, jet vetoes for Higgs physics and jet substructure tools. Some of the quantities that we consider are relevant also for heavy-ion collisions. Furthermore, we examine and comment on the underlying order-by-order convergence of the perturbative series for different R values. Our results indicate that small- R effects can be substantial. Phenomenological studies will appear in a forthcoming companion paper

The mass-hierarchy and CP-violation discovery reach of the LBNO long-baseline neutrino experiment

The next generation neutrino observatory proposed by the LBNO collaboration will address fundamental questions in particle and astroparticle physics. The experiment consists of a far detector, in its first stage a 20 kt LAr double phase TPC and a magnetised iron calorimeter, situated at 2300 km from CERN and a near detector based on a high-pressure argon gas TPC. The long baseline provides a unique opportunity to study neutrino flavour oscillations over their 1st and 2nd oscillation maxima exploring the $L/E$ behaviour, and distinguishing effects arising from $\delta_{CP}$ and matter. In this paper we have reevaluated the physics potential of this setup for determining the mass hierarchy (MH) and discovering CP-violation (CPV), using a conventional neutrino beam from the CERN SPS with a power of 750 kW. We use conservative assumptions on the knowledge of oscillation parameter priors and systematic uncertainties. The impact of each systematic error and the precision of oscillation prior is shown. We demonstrate that the first stage of LBNO can determine unambiguously the MH to $>5\sigma$C.L. over the whole phase space. We show that the statistical treatment of the experiment is of very high importance, resulting in the conclusion that LBNO has $\sim$ 100% probability to determine the MH in at most 4-5 years of running. Since the knowledge of MH is indispensable to extract $\delta_{CP}$ from the data, the first LBNO phase can convincingly give evidence for CPV on the $3\sigma$C.L. using today's knowledge on oscillation parameters and realistic assumptions on the systematic uncertainties

Prospects for Studies of the Free Fall and Gravitational Quantum States of Antimatter

Different experiments are ongoing to measure the effect of gravity on cold neutral antimatter atoms such as positronium, muonium, and antihydrogen. Among those, the project GBAR at CERN aims to measure precisely the gravitational fall of ultracold antihydrogen atoms. In the ultracold regime, the interaction of antihydrogen atoms with a surface is governed by the phenomenon of quantum reflection which results in bouncing of antihydrogen atoms on matter surfaces. This allows the application of a filtering scheme to increase the precision of the free fall measurement. In the ultimate limit of smallest vertical velocities, antihydrogen atoms are settled in gravitational quantum states in close analogy to ultracold neutrons (UCNs). Positronium is another neutral system involving antimatter for which free fall under gravity is currently being investigated at UCL. Building on the experimental techniques under development for the free fall measurement, gravitational quantum states could also be observed in positronium. In this contribution, we report on the status of the ongoing experiments and discuss the prospects of observing gravitational quantum states of antimatter and their implications

Diffractive dijet production with a leading proton in ep collisions at HERA

The cross section of the diffractive process e + p → e + Xp is measured at a centre-of-mass energy of 318 GeV, where the system X contains at least two jets and the leading final state proton p is detected in the H1 Very Forward Proton Spectrometer. The measurement is performed in photoproduction with photon virtualities Q 2 < 2 GeV 2 and in deep-inelastic scattering with 4 GeV 2 < Q 2 < 80 GeV 2 . The results are compared to next- to-leading order QCD calculations based on diffractive parton distribution functions as extracted from measurements of inclusive cross sections in diffractive deep-inelastic scattering

Measurement of multijet production in ep collisions at high Q2 and determination of the strong coupling αs

Inclusive jet, dijet and trijet differential cross sections are measured in neutral current deep-inelastic scattering for exchanged boson virtualities 150<Q2<15000GeV2 using the H1 detector at HERA. The data were taken in the years 2003 to 2007 and correspond to an integrated luminosity of 351pb-1 . Double differential Jet cross sections are obtained using a regularised unfolding procedure. They are presented as a function of Q2 and the transverse momentum of the jet, PTjet , and as a function of Q2 and the proton’s longitudinal momentum fraction, ξ , carried by the parton participating in the hard interaction. In addition normalised double differential jet cross sections are measured as the ratio of the jet cross sections to the inclusive neutral current cross sections in the respective Q2 bins of the jet measurements. Compared to earlier work, the measurements benefit from an improved reconstruction and calibration of the hadronic final state. The cross sections are compared to perturbative QCD calculations in next-to-leading order and are used to determine the running coupling and the value of the strong coupling constant as αs(MZ)=0.1165(8)exp(38)pdf,theo

Measurement of dijet production in diffractive deep-inelastic ep scattering at HERA

A measurement is presented of single- and double-differential dijet cross sections in diffractive deep-inelastic ep scattering at HERA using data collected by the H1 experiment corresponding to an integrated luminosity of 290 pb −1 . The investigated phase space is spanned by the photon virtuality in the range of 4 < Q 2 < 100 GeV 2 and by the fractional proton longitudinal momentum loss x ℙ < 0 . 03. The resulting cross sections are compared with next-to-leading order QCD predictions based on diffractive parton distribution functions and the value of the strong coupling constant is extracted

Measurement of Feynman- x spectra of photons and neutrons in the very forward direction in deep-inelastic scattering at HERA

Measurements of normalised cross sections for the production of photons and neutrons at very small angles with respect to the proton beam direction in deep-inelastic <math><mrow><mi>e</mi><mi>p</mi></mrow></math> scattering at HERA are presented as a function of the Feynman variable <math><msub><mi>x</mi><mi>F</mi></msub></math> and of the centre-of-mass energy of the virtual photon-proton system <math><mi>W</mi></math> . The data are taken with the H1 detector in the years 2006 and 2007 and correspond to an integrated luminosity of <math><mrow><mn>131</mn><mspace width="3.33333pt"/><msup><mtext>pb</mtext><mrow><mo>-</mo><mn>1</mn></mrow></msup></mrow></math> . The measurement is restricted to photons and neutrons in the pseudorapidity range <math><mrow><mi mathvariant="italic">η</mi><mo>&gt;</mo><mn>7.9</mn></mrow></math> and covers the range of negative four momentum transfer squared at the positron vertex <math><mrow><mn>6</mn><mo>&lt;</mo><msup><mi>Q</mi><mn>2</mn></msup><mo>&lt;</mo><mn>100</mn></mrow></math>  GeV <math><msup><mrow/><mn>2</mn></msup></math> , of inelasticity <math><mrow><mn>0.05</mn><mo>&lt;</mo><mi>y</mi><mo>&lt;</mo><mn>0.6</mn></mrow></math> and of <math><mrow><mn>70</mn><mo>&lt;</mo><mi>W</mi><mo>&lt;</mo><mn>245</mn><mspace width="3.33333pt"/></mrow></math> GeV. To test the Feynman scaling hypothesis the <math><mi>W</mi></math> dependence of the <math><msub><mi>x</mi><mi>F</mi></msub></math> dependent cross sections is investigated. Predictions of deep-inelastic scattering models and of models for hadronic interactions of high energy cosmic rays are compared to the measured cross sections