arXiv subjects
Publications and source records attributed to E. Sauvan.
This document summarises the talks and discussions happened during the VBSCan Split17 workshop, the first general meeting of the VBSCan COST Action network. This collaboration is aiming at a consistent and coordinated study of vector-boson scattering from the phenomenological and experimental point of view, for the best exploitation of the data that will be delivered by existing and future particle colliders.
Recent experimental results of searches for new phenomena performed at high energy colliders are reviewed. The results reported are based on data samples of up to 1 fb^-1 and 4 fb^-1 collected at HERA and at the Tevatron, respectively. No significant evidence for physics beyond the Standard Model has been found and limits at the 95% confidence level have been set on the mass and couplings of several possible new particles.
The high energy program of the HERA collider ended in March 2007. In total the H1 and ZEUS experiments collected an integrated luminosity of about 1 fb$^{-1}$. Recent results of model independent searches for new physics from both experiments are presented. Specifically, studies of the events with an isolated lepton and missing transverse momentum and multi-lepton topologies, where H1 and ZEUS data are combined, and a general signature based search are discussed.
The low-lying level structure of the unbound system $^{16}$B has been investigated via single-proton removal from a 35 MeV/nucleon $^{17}$C beam. The coincident detection of the beam velocity $^{15}$B fragment and neutron allowed the relative energy of the in-flight decay of $^{16}$B to be reconstructed. The resulting spectrum exhibited a narrow peak some 85 keV above threshold. It is argued that this feature corresponds to a very narrow ($Γ\ll $100 keV) resonance, or an unresolved multiplet, with a dominant $π(p_{3/2})^{-1} \otimes ν(d_{5/2}^3)_{J=3/2^+}$ + $π(p_{3/2})^{-1} \otimes ν(d_{5/2}^2,s_{1/2})_{J=3/2^+}$ configuration which decays by d-wave neutron emission.
We present a search for excited neutrinos and electrons using all data collected by the H1 experiment at HERA at a center-of-mass energy of 320 GeV with an integrated luminosity of up to 435 pb$^{-1}$. No evidence for excited neutrino or electron production is found. Mass dependent exclusion limits are determined for the ratio of the coupling to the compositeness scale, $f/Λ$. These limits greatly extend the excluded region to higher masses than has been possible in previous searches.
A model-independent search for deviations from the Standard Model prediction is performed in $e^+ p$ and $e^- p$ collisions at HERA II using all high energy data recorded by the H1 experiment. This corresponds to a total integrated luminosity of 337 pb$^{-1}$. All event topologies involving isolated electrons, photons, muons, neutrinos and jets with high transverse momenta are investigated in a single analysis. Events are assigned to exclusive classes according to their final state. A statistical algorithm is used to search for deviations from the Standard Model in distributions of the scalar sum of transverse momenta or invariant mass of final state particles and to quantify their significance. A good agreement with the Standard Model prediction is observed in most of the event classes. The most siginificant deviation is found in the \mujnp channel in $e^+p$ collisions.
The high energy programme of the HERA collider ended in March 2007. During the whole HERA programme, a combined total integrated luminosity of 1 fb$^{-1}$ was collected by the H1 and ZEUS experiments. In this context, an overview of the most recent results of both experiments concerning searches for new physics is presented. The topics covered are searches for contact interactions, leptoquarks and excited leptons, as well as studies of the isolated lepton and multi-lepton topologies, and a general signature based search.
We describe the most recent data on the diffractive structure functions from the H1 and ZEUS Collaborations at HERA using four models. First, a Pomeron Structure Function (PSF) model, in which the Pomeron is considered as an object with parton distribution functions. Then, the Bartels Ellis Kowalski Wusthoff (BEKW) approach is discussed, assuming the simplest perturbative description of the Pomeron using a two-gluon ladder. A third approach, the Bialas Peschanski (BP) model, based on the dipole formalism is then described. Finally, we discuss the Golec-Biernat-Wüsthoff (GBW) saturation model which takes into account saturation effects. The best description of all avaible measurements can be achieved with either the PSF based model or the BEKW approach. In particular, the BEKW prediction allows to include the highest $β$ measurements, which are dominated by higher twists effects and provide an efficient and compact parametrisation of the diffractive cross section. The two other models also give a good description of cross section measurements at small $x$ with a small number of parameters. The comparison of all predictions allows us to identify interesting differences in the behaviour of the effective pomeron intercept and in the shape of the longitudinal component of the diffractive structure functions. In this last part, we present some features that can be discriminated by new experimental measurements, completing the HERA program.
The proton diffractive structure function $F_2^{D(3)}$ measured in the H1 and ZEUS experiments at HERA are analysed in terms of perturbative QCD in the perspective of the QCD extrapolation to the Tevatron and the LHC. It is shown that both data sets can be well described by a QCD analysis in which point-like parton distributions, evolving according to the next-leading DGLAP equations, are assigned to the leading and sub-leading Regge exchanges. For present data from H1 and ZEUS the gluon distributions are found to be quite different and we give the corresponding sets of quark and gluon parton distributions for the Pomeron, extracted from the two experiments. An extrapolation to the Tevatron range is compared with CDF data on single diffraction. Conclusions on factorization breaking between HERA and Tevatron critically depend on whether H1 (strong violation) or ZEUS (compatibility at low $β$) fits are taken into account. Using the double Pomeron formulation in central diffractive dijet production we show that the Tevatron mass fraction is much sensitive to the high $β$ tail of the gluon in the Pomeron, suggesting a new way of handling the otherwise badly known gluon distribution in the Pomeron. Extrapolation of the fits to very high $Q^2$ are given since they will be relevant for QCD and diffraction studies at the LHC.
We summarize the recent results on electroweak physics and physics beyond the Standard Model that have been presented at the XIV International Workshop on Deep Inelastic Scattering 2006.
New measurements of the reduced cross section $σ_r^{D(3)}$ for the diffractive process $ep \to eXY$ in the kinematic domain $12 \leq Q^2 \leq 90$ GeV$^2$, $0.01 \leq β\leq 0.65$ and $\xpom<0.1$ are presented. Data events recorded by the H1 detector during the years 1999--2000 and 2004 have been used, corresponding to a total integrated luminosity of 68 pb$^{-1}$. The measurements are derived in the same range as previous H1 data, namely $M_Y < 1.6$ GeV and $|t| < 1.0$ GeV$^2$. Two different analysis methods, rapidity gap and $M_X$, are used and similar results are obtained in the kinematic domain of overlap. Finally, together with previous data, the diffractive structure function measurements are analysed with a model based on the dipole formulation of diffractive scattering. It is found to give a very good description of the data over the whole kinematic range.
A model based on the sudden approximation has been developed to describe high energy single nucleon removal reactions. Within this approach, which takes as its starting point the formalism of Hansen \cite{Anne2}, the nucleon-removal cross section and the full 3-dimensional momentum distributions of the core fragments including absorption, diffraction, Coulomb and nuclear-Coulomb interference amplitudes, have been calculated. The Coulomb breakup has been treated to all orders for the dipole interaction. The model has been compared to experimental data for a range of light, neutron-rich psd-shell nuclei. Good agreement was found for both the inclusive cross sections and momentum distributions. In the case of $^{17}$C, comparison is also made with the results of calculations using the transfer-to-the-continuum model. The calculated 3-dimensional momentum distributions exhibit longitudinal and transverse momentum components that are strongly coupled by the reaction for s-wave states, whilst no such effect is apparent for d-waves. Incomplete detection of transverse momenta arising fromlimited experimental acceptances thus leads to a narrowing of the longitudinal distributions for nuclei with significant s-wave valence neutron configurations, as confirmed by the data. Asymmetries in the longitudinal momentum distributions attributed to diffractive dissociation are also explored.
A study of high energy (43--68 MeV/nucleon) one-neutron removal reactions on a range of neutron-rich psd-shell nuclei (Z = 5--9, A = 12--25) has been undertaken. The inclusive longitudinal and transverse momentum distributions for the core fragments, together with the cross sections have been measured for breakup on a carbon target. Momentum distributions for reactions on tantalum were also measured for a subset of nuclei. An extended version of the Glauber model incorporating second order noneikonal corrections to the JLM parametrisation of the optical potential has been used to describe the nuclear breakup, whilst the Coulomb dissociation is treated within first order perturbation theory. The projectile structure has been taken into account via shell model calculations employing the psd-interaction of Warburton and Brown. Both the longitudinal and transverse momentum distributions, together with the integrated cross sections were well reproduced by these calculations and spin-parity assignments are thus proposed for $^{15}$B, $^{17}$C, $^{19-21}$N, $^{21,23}$O, $^{23-25}$F. In addition to the large spectroscopic amplitudes for the $\nu2$s$_{1/2}$ intruder configuration in the N=9 isotones,$^{14}$B and $^{15}$C, significant $\nu2$s$_{1/2}^2$ admixtures appear to occur in the ground state of the neighbouring N=10 nuclei $^{15}$B and $^{16}$C. Similarly, crossing the N=14 subshell, the occupation of the $\nu2$s$_{1/2}$ orbital is observed for $^{23}$O, $^{24,25}$F. Analysis of the longitudinal and transverse momentum distributions reveals that both carry spectroscopic information, often of a complementary nature. The general utility of high energy nucleon removal reactions as a spectroscopic tool is also examined.
Radiative capture of protons is investigated as a probe of clustering in nuclei far from stability. The first such measurement on a halo nucleus is reported here for the reaction $^6$He(p,$γ$) at 40 MeV. Capture into $^7$Li is observed as the strongest channel. In addition, events have been recorded that may be described by quasi-free capture on a halo neutron, the $α$ core and $^5$He. The possibility of describing such events by capture into the continuum of $^7$Li is also discussed.
A systematic study of high energy, one-neutron removal reactions on 23 neutron-rich, psd--shell nuclei (Z=5-9, A=12-25) has been carried out. The longitudinal momentum distributions of the core fragments and corresponding single-neutron removal cross sections are reported for reactions on a carbon target. Extended Glauber model calculations, weighted by the spectroscopic factors obtained from shell model calculations, are compared to the experimental results. Conclusions are drawn regarding the use of such reactions as a spectroscopic tool and spin-parity assignments are proposed for 15B, 17C, 19-21N, 21,23O, 23-25F. The nature of the weakly bound systems 14B and 15,17C is discussed.