Results on Diffraction at HERA and Tevatron

Recent results on diffraction at HERA, from the H1 and ZEUS Collaborations, and at Tevatron, from the CDF and D0 Collaborations, are reviewed. The measurement of the diffractive structure function at HERA is presented, and the pomeron structure function is extracted from QCD fits. Diffractive dijet production is given as an example analysis of the diffractive final state. These analysis are consistent with a leading gluon partonic structure for the pomeron. Hard single diffraction, double diffraction and double pomeron exchange processes are studied at the Tevatron and complement the studies performed at HERA. Finally, HERA results on the diffractive (exclusive) production of a vector particle, either a vector meson or a photon, are presented and compared to models based on perturbative QCD.Comment: Results presented at "La Thuile" conference, feb/mar 2000, Italy. To appear in the proceedings. 12 pages, 10 figure

Elastic production of Vector Mesons at HERA: study of the scale of the interaction and measurement of the helicity amplitudes

A compilation of H1 and ZEUS cross section measurements for elastic vector meson production is presented as a function of the scale $K^2 = (Q^2+M_V^2)/4$, where Q^2 is the exchanged photon virtuality and M_V is the mass of the vector meson. The ratio of longitudinal to transverse cross sections R = $\sigma_L/\sigma_T$ is presented as a function of Q^2/M^2_V. The cross sections are separated in a transverse and a longitudinal component, and are presented as a function of K^2. The intercept $\alpha(0)$ -- 1 governing the energy dependence of the vector meson cross sections is compared with the $\lambda$ parameter measured in inclusive F_2 analysis. For $\rho$ meson production, the helicity amplitude ratios $|T_{ij}|/|T_{00}|$, extracted from the H1 and ZEUS measurements of the spin density matrix elements are presented as a function of Q^2 and W and are compared to recent predictions.Comment: The note includes plots presented in the vector meson discussion session of the Workshop of Low-x Physics (june 1999), Tel-Aviv, Israel. 12 pages, 7 figures, 1 table. New version with new model predictio

A study of the time evolution of GERB shortwave calibration by comparison with CERES Edition-3A data

This study examines the evolution of the GERB-2 and GERB-1 Edition 1 shortwave radiance calibration between 2004-2007 and 2007-2012 respectively, through comparison with CERES instrument FM1 Edition 3A SSF instantaneous radiances. Two periods when simultaneous observations from both GERB-2 and GERB-1 were available, January 13th to February 11th 2007 and May 1st to May 10th 2007, are also compared. For these two overlap periods respectively, averaged over all CERES ‘unfiltered-to-filtered radiance ratio’ subsets, the GERB-1/CERES unfiltered radiance ratio is on average found to be 1.6% and 1.9% lower than the associated GERB-2/CERES unfiltered radiance ratio. Over the two longer time series the GERB/CERES unfiltered radiance ratio shows a general decrease with time for both GERB-2 and GERB-1. The rate of decrease varies through time but no significant seasonal dependence is seen. Averaged over all subsets the GERB-2/CERES unfiltered radiance ratio showed a decrease of 1.9% between June 2004 and June 2006. Between June 2007 and June 2012, the corresponding decrease in the GERB-1/CERES unfiltered radiance ratio was 6.5%. The evolution of the GERB/CERES unfiltered radiance ratio for both GERB-2 and GERB-1 shows a strong dependence on the CERES unfiltered-to-filtered radiance ratio, indicating that it is spectrally dependent. Further time-series analysis and theoretical work using simulated spectral radiance curves suggests that for GERB-1 the evolution is consistent with a darkening in the GERB shortwave spectral response function which is most pronounced at the shortest wavelengths. For GERB-2, no single spectral cause can be identified, suggesting that the evolution is likely due to a combination of several different effects

Search for scalar leptons in e+e- collisions

Search for pair production of sleptons have been performed using the data collected by the ALEPH detector at LEP in the year 2000. The centre-of-mass energy ranges from 204 to 209 GeV, corresponding to an integrated luminosity of 207.3 pb-1. No evidence for the production of these particles was found. The number of candidates observed is consistent with the background expected from four-fermion processes and gamma-gamma interactions. Improved mass limits at 95% C.L. are reported

Preliminary signs of the initiation of deep convection by GNSS

This study reports on the exploitation of GNSS (Global Navigation Satellite System) and a new potential application for weather forecasts and nowcasting. We focus on GPS observations (post-processing with a time resolution of 5 and 15 min and fast calculations with a time resolution of 5 min) and try to establish typical configurations of the water vapour field which characterise convective systems and particularly which supply precursors of their initiation are associated with deep convection. We show the critical role of GNSS horizontal gradients of the water vapour content to detect small scale structures of the troposphere (i. e. convective cells), and then we present our strategy to obtain typical water vapour configurations by GNSS called "H2O alert". These alerts are based on a dry/wet contrast taking place during a 30 min time window before the initiation of a convective system. GNSS observations have been assessed for the rainfall event of 28-29 June 2005 using data from the Belgian dense network (baseline from 5 to 30 km). To validate our GNSS H2O alerts, we use the detection of precipitation by C-band weather radar and thermal infrared radiance (cloud top temperature) of the 10.8-micrometers channel [Ch09] of SEVIRI instrument on Meteosat Second Generation. Using post-processed measurements, our H2O alerts obtain a score of about 80 %. Final and ultra-rapid IGS (International GNSS Service) orbits have been tested and show equivalent results. Fast calculations (less than 10 min) have been processed for 29 June 2005 with a time resolution of 5 min. The mean bias (and standard deviation) between fast and reference post-processed ZTD (zenith total delay) and gradients are, respectively, 0.002 (+/- 0.008) m and 0.001 (+/- 0.004) m. The score obtained for the H2O alerts generated by fast calculations is 65 %

Search with the CMS detector for heavy resonances decaying into an electron pair

This note presents the CMS experiment potential to discover heavy resonances decaying into an electron-positron pair, such as Kaluza-Klein excitations of a Z or graviton boson predicted in extra dimension models (the TeV^-1 model and the Randall-Sundrum model), or as neutral heavy Z' boson predicted by Grand Unified Theories. Full and fast simulation and reconstruction are used to investigate these productions, with the pileup condition corresponding to a luminosity equal to 2 times 10^ 33; mathrm cm ^ -2 mathrm s ^ -1 . For an integrated luminosity of 60 fbinv, a 5 sigma discovery limit has been obtained for a mass of 5.9 tevct in the case of Kaluza-Klein excitation Z boson production. For the Randall-Sundrum graviton production, the limit is found for graviton masses of 1.8 tevct with a coupling parameter constant c=0.01 and 4.1 tevct for c=0.1 . For the six Z' models considered here, the 5 sigma discovery limit ranges for masses from 3.6 tevct (rm Z_psi) to 4.6 tevct (rm Z_ALRM)

Rainfall retrieval using Spinning Enhanced Visible and Infrared Imager (SEVIRI-MSG) and Cloud Physical Properties (CPP) algorithm : validation over Belgium and applications

Precipitation is the main variable of the water cycle and the water resources availability. Despite numerous available methods, precipitation measurements are still insufficient to quantify with certainty ongoing changes and to provide data for numerical models validation. Roebeling & Holleman (2009) presented the Cloud Physical Properties algorithm using data from the SEVIRI instrument on board Meteosat Second Generation. The goal of present study is to extend previous validations and verify the algorithm performances throughout yearly and daily cycles in order to identify possible use and applications. A seven-years data set of parallax-shift corrected clouds and precipitation data over Western Europe have therefore been processed using CPP algorithm. Results are encouraging for both precipitation areas delimitation and rain rates assessment. However, rain rates estimation are strongly affected by sun zenith angle with increasing overestimation for sza above 60°. Systematic errors also affect the retrieval of cloud properties for very thick clouds with an overestimation of extreme precipitation events

Model-independent constraints on the CKM matrix elements ∣Vtb∣|V_{tb}|, ∣Vts∣|V_{ts}| and ∣Vtd∣|V_{td}|

Single top quark production cross sections at hadron colliders are traditionally used to extract the modulus of the $V_{tb}$ element of the Cabibbo-Kobayashi-Maskawa matrix under the following assumption: $|V_{tb}| \gg |V_{td}|, |V_{ts}|$. For the first time, direct limits on $|V_{td}|$ and $|V_{ts}|$ are obtained using experimental data without the assumption of the unitarity of the CKM matrix. Limits on the $|V_{td}|$, $|V_{ts}|$ and $|V_{tb}|$ are extracted from differential measurements of single top quark cross sections in $t$-channel as a function of the rapidity and transverse momentum of the top quark and the light jet recoiling against the top quark. We have shown that the pseudorapidity of the forward jet in the single top production is one of the most powerful observables for discriminating between the $|V_{td}|$ and $|V_{tb}|$ events. We perform a global fit of top quark related CKM elements to experimental data from the LHC Runs I and II and Tevatron. Experimental data include inclusive and differential single top cross sections in $t$-channel, inclusive tW production cross section, and top quark branching ratio to b quark and W boson. We present bounds on $|V_{tb}|$, $|V_{ts}|$ and $|V_{td}|$ using current data and project the results for future LHC data sets corresponding to luminosities of 300 and 3000 \fb