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Laurent Schoeffel

Publications and source records attributed to Laurent Schoeffel.

36 records · Page 2Linked to original sources

About the non-random Content of Financial Markets

For the pedestrian observer, financial markets look completely random with erratic and uncontrollable behavior. To a large extend, this is correct. At first approximation the difference between real price changes and the random walk model is too small to be detected using traditional time series analysis. However, we show in the following that this difference between real financial time series and random walks, as small as it is, is detectable using modern statistical multivariate analysis, with several triggers encoded in trading systems. This kind of analysis are based on methods widely used in nuclear physics, with large samples of data and advanced statistical inference. Considering the movements of the Euro future contract at high frequency, we show that a part of the non-random content of this series can be inferred, namely the trend-following content depending on volatility ranges. Of course, this is not a general proof of statistical inference, as we focus on one particular example and the generality of the process can not be claimed. Therefore, we produce other examples on a completely different markets, largely uncorrelated to the Euro future, namely the DAX and Cacao future contracts. The same procedure is followed using a trading system, based on the same ingredients. We show that similar results can be obtained and we conclude that this is an evidence that some invariants, as encoded in our system, have been identified. They provide a kind of quantification of the non-random content of the financial markets explored over a 10 years period of time.

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Diffraction at HERA

Between 1992 and 2007, the HERA accelerator provided $ep$ collisions at center of mass energies beyond $300 \ {\rm GeV}$ at the interaction points of the H1 and ZEUS experiments. Interesting results to emerge relate to the newly accessed field of perturbative strong interaction physics at low Bjorken-$x$, where parton densities become extremely large. Questions arise as to how and where non-linear dynamics tame the parton density growth and challenging features such as geometric scaling are observed. Central to this low $x$ physics landscape is a high rate of diffractive processes, in which a colorless exchange takes place and the proton remains intact. A review is given for main results obtained by H1 and ZEUS experiments in this field.

hep-ph↗

Experimental aspects of diffraction in hadronic physics

The most important results on subnuclear diffractive phenomena obtained at HERA and Tevtaron are reviewed and new issues in nucleon tomography are discussed. Some challenges for understanding diffraction at the LHC, including the discovering of the Higgs boson, are outlined.

hep-ph↗

Diffraction and its QCD interpretation

The most important results on hadronic diffractive phenomena obtained at HERA and Tevtaron are reviewed and new issues in nucleon tomography are discussed. Some challenges for understanding diffraction at the LHC, including the discovering of the Higgs boson, are outlined.

hep-ph↗

Advances in diffraction of subnuclear waves

In this review, we present and discuss the most recent results on inclusive and exclusive diffractive processes at HERA and Tevatron colliders. Measurements from fixed target experiments at HERMES and Jefferson laboratory are also reviewed. The complementarity of all these results is analysed in the context of perturbative QCD and new challenging issues in nucleon tomography are studied. A first understanding of how partons are localised in the nucleon to build orbital momenta can be addressed with these experimental results. Some prospects are outlined for new measurements in fixed target kinematic, at Jefferson laboratory and CERN, at COMPASS, or at the LHC. Of special interest is the exclusive (coherent) production of Higgs boson and heavy objects at the LHC. Based on the present knowledge, some perspectives are presented in this direction.

hep-ph↗

DVCS at HERA and at CERN

Deeply Virtual Compton Scattering (DVCS) in $ep$ collisions has emerged in recent years as a an essential reaction to obtain information on the correlation of partons in the hadron (proton) or on the transverse distribution of these partons. In these proceedings, we examine the lattest data from HERA (at low $x_{Bj}<10^{-2}$) and their impact on models. We analyse in detail what these data imply on the spatial structure of the proton. In particular, the most recent measurements of the Beam Charge Asymmetry by the H1 experiment is discussed in this context. Perspectives are presented for further measurements of DVCS cross sections at CERN, within the COMPASS experiment.

hep-ph↗

Understanding the structure of the proton at the LHC

Understanding the fundamental structure of matter requires an understanding of how quarks and gluons are assembled to form hadrons and of the structure of the protons which are the colliding particles at LHC. The arrangement of quarks and gluons inside nucleons can be probed by accelerating electrons, hadrons or nuclei to precisely controlled energies, smashing them into a target nucleus and examining in detail the final products. The LHC physics program is rich and has been widely described. It encompasses the searches for new particles up to masses of several TeV, including the elucidation of electroweak symmetry breaking and the possible observation of new symmetries at higher scales, and precision measurements of fundamental parameters in the electroweak and strong gauge sectors. Obviously, this program requires a precise understanding of the structure of the proton in terms of quarks and gluons, obtained from HERA and Tevatron. However, the knowledge on parton distribution functions (PDFs) is still limited for many aspects of LHC physics and the discovery potential is thus reduced. In this proceeding, we show on one example that it is possible to find some observables less sensitive to PDF uncertainties to probe with a high efficency new physics beyond the standard model.

hep-ph↗

GPDs at HERA and perspectives at COMPASS

Measurements of the deep-inelastic scattering (DIS) of leptons and nucleons, $e+p\to e+X$, allow the extraction of Parton Distribution Functions (PDFs) which describe the longitudinal momentum carried by the quarks, anti-quarks and gluons that make up the fast-moving nucleons. While PDFs provide crucial input to perturbative Quantum Chromodynamic (QCD) calculations of processes involving hadrons, they do not provide a complete picture of the partonic structure of nucleons. In particular, PDFs contain neither information on the correlations between partons nor on their transverse motion. Hard exclusive processes, in which the nucleon remains intact, have emerged in recent years as prime candidates to complement this essentially one dimentional picture. The simplest exclusive process is the deeply virtual Compton scattering (DVCS) or exclusive production of real photon, $e + p \to e + γ+ p$. This process is of particular interest as it has both a clear experimental signature and is calculable in perturbative QCD. The DVCS reaction can be regarded as the elastic scattering of the virtual photon off the proton via a colourless exchange, producing a real photon in the final state. In the Bjorken scaling regime, QCD calculations assume that the exchange involves two partons, having different longitudinal and transverse momenta, in a colourless configuration. These unequal momenta or skewing are a consequence of the mass difference between the incoming virtual photon and the outgoing real photon. This skewedness effect can be interpreted in the context of generalised parton distributions (GPDs). In this proceeding, we examine typical measurements from HERA and prospects for COMPASS at CERN, that can bring new insights on the quarks/gluons imaging of the nucleon.

hep-ph↗

New developments in QCD analysis of inclusive diffraction at HERA

A large collection of results for the diffractive dissociation of virtual photons, $γ^{\star}p \to Xp$, have been obtained with the H1 and ZEUS detectors at HERA. Different experimental techniques have been used, by requiring a large rapidity gap between $X$ and the outgoing proton, by analysing the mass distribution, $M_X$, of the hadronic final state, as well as by directly tagging the proton. A reasonable compatibility between those techniques and between H1 and ZEUS results have been observed. Some common fundamental features in the measurements are also present in all data sets. Diffractive PDFs can give a good account of those features. Ideas and new developments are discussed in these proceedings.

hep-ph↗

Deeply virtual compton scattering at HERA and perspectives at CERN

Standard parton distribution functions contain neither information on the correlations between partons nor on their transverse motion, then a vital knowledge about the three dimensional structure of the nucleon is lost. Hard exclusive processes, in particular DVCS, are essential reactions to go beyond this standard picture. In the following, we examine the most recent data from HERA (at low $x_{Bj}<10^{-2}$) and their impact on GPD models. The most recent measurements of the Beam Charge Asymmetry by the H1 experiment is discussed. Perspectives are presented for further measurements of DVCS cross sections at CERN, within the COMPASS experiment.

hep-ph↗

New measurement of charge asymmetry $x{F}_3$ from HERA

After presenting the recent measurements of neutral current cross section in DIS at HERA, we explain the effect of the $γ-Z_0$ interference at the electro-weak scale, visible on these data. Then, the beam charge difference $x{F}_3$ is measured and the interference itself is extracted. Results are discussed in the context of perturbative QCD.

hep-ph↗

Diffractive cross sections at HERA and diffractive PDFs

A large collection of results for the diffractive dissociation of virtual photons, $γ^{\star}p \to Xp$, have been obtained with the H1 and ZEUS detectors at HERA. Different experimental techniques have been used, by requiring a large rapidity gap between $X$ and the outgoing proton, by analyzing the mass distribution, $M_X$, of the hadronic final state, as well as by directly tagging the proton. A reasonable compatibility between those techniques and between H1 and ZEUS results have been observed. Some common fundamental features in the measurements are also present in all data sets. They are detailed in this document. Diffractive PDFs can give a good account of those features. Ideas and results are discussed in the following.

hep-ph↗

Deeply Virtual Compton Scattering at HERA and perspectives at CERN

Standard parton distribution functions contain neither information on the correlations between partons nor on their transverse motion, then a vital knowledge about the three dimensional structure of the nucleon is lost. Hard exclusive processes, in particular DVCS, are essential reactions to go beyond this standard picture. In the following, we examine the most recent data in view of the dipole model predictions and their implication on the quarks/gluons imaging (tomography) of the nucleon.

hep-ph↗

Deeply Virtual Compton Scattering at HERA and Prospects on Nucleon Tomography

Standard parton distribution functions contain neither information on the correlations between partons nor on their transverse motion, then a vital knowledge about the three dimensional structure of the nucleon is lost. Hard exclusive processes, in particular DVCS, are essential reactions to go beyond this standard picture. In the following, we examine the most recent data and their implication on the quarks/gluons imaging (tomography) of the nucleon.

hep-ph↗

Deeply Virtual Compton Scattering at HERA II

A new measurement is presented of elastic deeply virtual Compton scattering (DVCS) based on data taken by the H1 detector during the complete HERA II period. The data are well described by QCD based calculations. For the first time, a beam charge asymmetry is obtained in a colliding mode, using data recorded in $e^-p$ and $e^+p$. A significant non zero value is measured, related to the interference of QCD and QED processes, namely the DVCS and Bethe-Heitler reactions.

hep-ph↗

Inclusive NC and CC diffraction

Recent diffractive structure function measurements in deep inelastic scattering (DIS) by the H1 and ZEUS experiments at HERA are reviewed. In neutral current (NC) DIS, precise measurements have been made of diffraction, $ep \to eXY$, the signature of which is a large rapidity gap (LRG) between the hadronic system $X$ and the proton or one of its low-mass excited states $Y$. New results on charged current (CC) DIS are also presented. They are identified in a CC DIS sample by a large rapidity gap, corresponding to a diffractive process $ep \to νXY$ with a $W$ boson exchange. Moreover, within the framework of QCD hard scattering factorisation in DIS, all these data provide constraints on the diffractive parton distribution functions of the proton and predict a large gluon content. For example, the resulting gluon distribution, extracted from the H1 measurements, carries an integrated fraction of about 70% of the exchanged momentum. Note that these functions are crucial inputs for the calculations of diffractive dijet or charm production in DIS. These parton distribution functions may also be applicable to hadron-hadron scattering provided that an additional rapidity gap survival probability is taken into account.

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