Forward pi^0 Production and Associated Transverse Energy Flow in Deep-Inelastic Scattering at HERA

Deep-inelastic positron-proton interactions at low values of Bjorken-x down to x \approx 4.10^-5 which give rise to high transverse momentum pi^0 mesons are studied with the H1 experiment at HERA. The inclusive cross section for pi^0 mesons produced at small angles with respect to the proton remnant (the forward region) is presented as a function of the transverse momentum and energy of the pi^0 and of the four-momentum transfer Q^2 and Bjorken-x. Measurements are also presented of the transverse energy flow in events containing a forward pi^0 meson. Hadronic final state calculations based on QCD models implementing different parton evolution schemes are confronted with the data.Comment: 27 pages, 8 figures and 3 table

Searches at HERA for Squarks in R-Parity Violating Supersymmetry

A search for squarks in R-parity violating supersymmetry is performed in e^+p collisions at HERA at a centre of mass energy of 300 GeV, using H1 data corresponding to an integrated luminosity of 37 pb^(-1). The direct production of single squarks of any generation in positron-quark fusion via a Yukawa coupling lambda' is considered, taking into account R-parity violating and conserving decays of the squarks. No significant deviation from the Standard Model expectation is found. The results are interpreted in terms of constraints within the Minimal Supersymmetric Standard Model (MSSM), the constrained MSSM and the minimal Supergravity model, and their sensitivity to the model parameters is studied in detail. For a Yukawa coupling of electromagnetic strength, squark masses below 260 GeV are excluded at 95% confidence level in a large part of the parameter space. For a 100 times smaller coupling strength masses up to 182 GeV are excluded.Comment: 32 pages, 14 figures, 3 table

Deep-Inelastic Inclusive ep Scattering at Low x and a Determination of alpha_s

A precise measurement of the inclusive deep-inelastic e^+p scattering cross section is reported in the kinematic range 1.5<= Q^2 <=150 GeV^2 and 3*10^(-5)<= x <=0.2. The data were recorded with the H1 detector at HERA in 1996 and 1997, and correspond to an integrated luminosity of 20 pb^(-1). The double differential cross section, from which the proton structure function F_2(x,Q^2) and the longitudinal structure function F_L(x,Q^2) are extracted, is measured with typically 1% statistical and 3% systematic uncertainties. The measured partial derivative (dF_2(x,Q^2)/dln Q^2)_x is observed to rise continuously towards small x for fixed Q^2. The cross section data are combined with published H1 measurements at high Q^2 for a next-to-leading order DGLAP QCD analysis.The H1 data determine the gluon momentum distribution in the range 3*10^(-4)<= x <=0.1 to within an experimental accuracy of about 3% for Q^2 =20 GeV^2. A fit of the H1 measurements and the mu p data of the BCDMS collaboration allows the strong coupling constant alpha_s and the gluon distribution to be simultaneously determined. A value of alpha _s(M_Z^2)=0.1150+-0.0017 (exp) +0.0009-0.0005 (model) is obtained in NLO, with an additional theoretical uncertainty of about +-0.005, mainly due to the uncertainty of the renormalisation scale.Comment: 68 pages, 24 figures and 18 table

Inelastic photoproduction of J/Psi mesons at HERA

An analysis of inelastic photoproduction of J/Psi mesons is presented using data collected at the ep collider HERA corresponding to an integrated luminosity of above 80pb-1. Differential and double differential cross sections are measured in a wide kinematic region: 6

Inelastic Photoproduction of J/Psi Mesons at HERA

An analysis of inelastic photoproduction of J/Psi mesons is presented using data collected at the ep collider HERA corresponding to an integrated luminosity of above 80pb-1. Differential and double differential cross sections are measured in a wide kinematic region: 60<W_gammap<260 GeV, 1<p_t^2< 60 GeV^2 and 0.05<z<0.9, where z is the fraction of the energy of the exchanged photon transferred to the J/Psi meson in the rest frame of the target proton. Cross sections at z<0.3 are presented for the first time. Theoretical calculations within the Colour Singlet Model at NLO for direct photon processes are shown to give a good description of the data in the medium z region (0.3<z<0.9) up to the highest p_t^2 values. A calculation using a k_t factorisation approach in LO in the Colour Singlet Model is also able to describe these data. The data in the full z range are also compared to LO calculations within a non-relativistic QCD framework including color octet and colour singlet contributions for direct and resolved photons. It seems possible to reconcile data and theory with modest contributions from colour octet processes. The polarisation of the J/Psi meson is measured as a function of z and p_t,psi and is reasonably described by the theoretical predictions.Comment: 30 pages, 11 figures, 11 table

Inelastic Leptoproduction of J/Psi Mesons at HERA

The leptoproduction of J/psi mesons is studied in inelastic reactions for four momentum transfers 2<Q^2<100GeV^2. The data were taken with the H1 detector at the electron proton collider HERA and correspond to an integrated luminosity of 77 pb-1. Single differential and double differential cross sections are measured with increased precision compared with previous analyses. New leading order calculations within the non-relativistic QCD factorisation approach including colour octet and colour singlet contributions are compared with the data and are found to give a reasonable description of most distributions. An exception is the shape of the distribution in the J/psi fractional energy, z, which deviates significantly from that of the data. Comparisons with photoproduction are made and the polarisation of the produced J/psi meson is analysed.Comment: 27 pages, 7 figures and 7 table

On the Rise of the Proton Structure Function F2_2 Towards Low x

A measurement of the derivative (d ln F_2 / d lnx)_(Q^2)= -lambda(x,Q^2) of the proton structure function F_2 is presented in the low x domain of deeply inelastic positron-proton scattering. For 5*10^(-5)=1.5 GeV^2, lambda(x,Q^2) is found to be independent of x and to increase linearly with ln(Q^2)

Le rôle des connaissances historiques dans l'étude du comportement procréateur en U.R.S.S

The analysis of the children's role in the economy of a patriarchal peasant family, of the different elements of the non-economic value of children, of the attitude towards their birth or death and towards birth control in the traditional Russian society shows that if the fertility level in the past, right up to the twenties of the 20th cent., was very high, it was not a consequence of «rational» fertility behaviour of couples, their conscious interest in having as many children as possible. A new historical type of fertility behaviour based on free personal choice and presupposing a deliberate search of purposes and adequate means to achieve them, takes shape and spreads on a large scale only as a resuit of the demographic revolution (in USSR - in 20th cent.).L'analyse du rôle des enfants dans l'économie des familles paysannes patriarcales, de divers éléments de la valeur non économique des enfants, de l'attitude envers la naissance et la mort des enfants, de la régulation des naissances au sein de la famille propre à la société russe traditionnelle montre que si dans le passé jusqu'aux années 20 du XXe siècle, la fécondité en Russie était très élevée, ce n'était pas la conséquence du comportement procréateur «rationnel» des couples, de leur intérêt conscient d'avoir le plus grand nombre d'enfants. C'est seulement à l'issue de la révolution démographique (en URSS au XXe siècle) que se forme et se répand largement un type historique nouveau de comportement procréateur fondé sur un choix libre présumant l'assignation consciente d'un but et la recherche de moyens adéquats pour y parvenir.Vichnevski Anatoli. Le rôle des connaissances historiques dans l'étude du comportement procréateur en U.R.S.S. In: Annales de démographie historique, 1987. pp. 213-239

L'Asie centrale post-soviétique : entre le colonialisme et la modernité

Post-soviet Central Asia : between colonialism and modernity. This article is set within the context of the old, very narrow "soviet" view of Central Asia (Srednjaja Azija). The Russian conquest of the area, completed in 1885, marked a double turning-point in the destiny of Central Asia. Geographically speaking, it no longer belonged to the Turko-Persian Islamic world, whose Northern border it had formed for centuries, before becoming the Southern border of the Russian empire. At the end of the XlXth century, the expansion of Russia was taking place at a much more rapid rate than that of the flagging Turkish and Iranian societies which predominated in the south of the country. In addition, their entry into a new sphere of influence also meant for Central Asia a historical turning-point, their engagement with the processes of modernization which, even though they developed with difficulty, were taking root in Russia. 1985 was the centenary of the conquest of Central Asia, and it was also marked by the introduction of "perestroika", which heralded definitive changes. What should be to-day's assessment of a century's Russian influence in Central Asia ? What is its legacy, at a point where the region is entering upon a new phase in its history ? How are the five new states, born here from the collapse of the Soviet Union, likely to evolve within a context of uncompleted modernization and renascent traditionalism ?Cet article reste dans le cadre de l'ancienne conception "soviétique" très étroite de l'Asie centrale (Srednjaja Azija). La conquête russe du territoire, achevée en 1885, a marqué un double tournant dans la destinée de l'Asie centrale. Sur le plan géographique, elle n'appartenait désormais plus au monde islamique turco-perse dont elle avait constitué la périphérie nord pendant des siècles avant de devenir la périphérie sud de l'Empire russe. A la fin du XIXe siècle, le développement de la Russie s'effectuait à un rythme beaucoup plus rapide que celui des sociétés turque et iranienne, en perte de vitesse, qui prédominaient au sud du pays. Aussi l'entrée dans une nouvelle sphère d'influence signifiait-elle également pour l'Asie centrale un tournant historique, l'adhésion à des processus de modernisation qui, même s'ils se développaient avec difficulté, prenaient racine en Russie. 1985 est l'année du centenaire de la conquête de l'Asie centrale et elle est marquée, par ailleurs, par le début de la perestroïka en U.R.S.S., annonciatrice de changements déterminants. Quel bilan faire aujourd'hui d'un siècle d'influence russe en Asie centrale ? Quel en est l'héritage, au moment où la région amorce un nouveau tournant historique ? Comment les cinq nouveaux Etats nés ici de l'effondrement de l'Union soviétique vont-ils évoluer dans un contexte de modernité inachevée et de traditionalisme renaissant ?Vichnevski Anatoli, Visnevskaja Marina. L'Asie centrale post-soviétique : entre le colonialisme et la modernité. In: Revue d'études comparatives Est-Ouest, vol. 26, 1995, n°4. pp. 101-123