Browsing by Subject "SCATTERING"

Sort by: Order: Results:

Now showing items 21-40 of 65
  • Antchev, G.; Aspell, P.; Atanassov, I.; Avati, V.; Baechler, J.; Barrera, C. Baldenegro; Berardi, V.; Berretti, M.; Bossini, E.; Bottigli, U.; Bozzo, M.; Burkhardt, H.; Cafagna, F. S.; Catanesi, M. G.; Csanad, M.; Csorgo, T.; Deile, M.; De Leonardis, F.; Doubek, M.; Druzhkin, D.; Eggert, K.; Eremin, V.; Ferro, F.; Fiergolski, A.; Garcia, F.; Georgiev, V.; Giani, S.; Grzanka, L.; Hammerbauer, J.; Ivanchenko, V.; Kaspar, J.; Kopal, J.; Kundrat, V.; Lami, S.; Latino, G.; Lauhakangas, R.; Lindsey, C.; Lokajicek, M. V.; Losurdo, L.; Lo Vetere, M.; Rodriguez, F. Lucas; Macri, M.; Malawski, M.; Minafra, N.; Minutoli, S.; Naaranoja, T.; Nemes, F.; Niewiadomski, H.; Novak, T.; Oliveri, E.; Oljemark, F.; Oriunno, M.; Österberg, K.; Palazzi, P.; Passaro, V.; Peroutka, Z.; Prochazka, J.; Quinto, M.; Radermacher, E.; Radicioni, E.; Ravotti, F.; Robutti, E.; Royon, C.; Ruggiero, G.; Saarikko, H.; Scribano, A.; Smajek, J.; Snoeys, W.; Sziklai, J.; Taylor, C.; Tcherniaev, E.; Turini, N.; Vacek, V.; Welti, J.; Williams, J. (2020)
    The proton-proton elastic differential cross sectvion d sigma/dt has been measured by the TOTEM experiment at root s = 2.76 TeV energy with beta* = 11 m beam optics. The Roman Pots were inserted to 13 times the transverse beam size from the beam, which allowed tomeasure the differential cross-section of elastic scattering in a range of the squared four-momentum transfer (vertical bar t vertical bar) from 0.36 to 0.74 GeV2. The differential cross-section can be described with an exponential in the vertical bar t vertical bar-range between 0.36 and 0.54 GeV2, followed by a diffractive minimum (dip) at vertical bar t(dip)vertical bar = (0.61 +/- 0.03) GeV2 and a subsequent maximum (bump). The ratio of the ds/dt at the bump and at the dip is 1.7 +/- 0.2. When compared to proton-antiproton measurement of the D0 experiment at root s = 1.96 TeV, a significant difference can be observed. Under the condition that the effects due to the energy difference between TOTEM and D0 can be neglected, the result provides evidence for the exchange of a colourless C-odd three-gluon compound state in the t-channel of the proton-proton and proton-antiproton elastic scattering.
  • Antchev, G.; Aspell, P.; Atanassov, I.; Avati, V.; Baechler, J.; Berardi, V.; Berretti, M.; Bossini, E.; Bottigli, U.; Bozzo, M.; Broulim, P.; Buzzo, A.; Cafagna, F. S.; Campanella, C. E.; Catanesi, M. G.; Csanad, M.; Csoergo, T.; Deile, M.; De Leonardis, F.; D'Orazio, A.; Doubek, M.; Eggert, K.; Eremin, V.; Ferro, F.; Fiergolski, A.; Garcia, F.; Georgiev, V.; Giani, S.; Grzanka, L.; Guaragnella, C.; Hammerbauer, J.; Heino, J.; Karev, A.; Kaspar, J.; Kopal, J.; Kundrat, V.; Lami, S.; Latino, G.; Lauhakangas, R.; Linhart, R.; Lippmaa, E.; Lippmaa, J.; Lokajicek, M. V.; Losurdo, L.; Lo Vetere, M.; Lucas Rodriguez, F.; Macri, M.; Mercadante, A.; Minafra, N.; Minutoli, S.; Naaranoja, T.; Nemes, F.; Niewiadomski, H.; Oliveri, E.; Oljemark, F.; Orava, R.; Oriunno, M.; Österberg, K.; Palazzi, P.; Palocko, L.; Passaro, V.; Peroutka, Z.; Petruzzelli, V.; Politi, T.; Prochazka, J.; Prudenzano, F.; Quinto, M.; Radermacher, E.; Radicioni, E.; Ravotti, F.; Robutti, E.; Ropelewski, L.; Ruggiero, G.; Saarikko, H.; Scribano, A.; Smajek, J.; Snoeys, W.; Sodzawiczny, T.; Sziklai, J.; Taylor, C.; Turini, N.; Vacek, V.; Welti, J.; Wyszkowski, P.; Zielinski, K. (2015)
    The TOTEM experiment has made a precise measurement of the elastic proton proton differential cross-section at the centre-of-mass energy root s = 8 TeV based on a high-statistics data sample obtained with the beta* = 90 m optics. Both the statistical and systematic uncertainties remain below 1%, except for the t-independent contribution from the overall normalisation. This unprecedented precision allows to exclude a purely exponential differential cross-section in the range of four-momentum transfer squared 0.027 <vertical bar t vertical bar <0.2 GeV2 with a significance greater than 7 sigma. Two extended parametrisations, with quadratic and cubic polynomials in the exponent, are shown to be well compatible with the data. Using them for the differential cross-section extrapolation to t = 0, and further applying the optical theorem, yields total cross-section estimates of (101.5 +/- 2.1) mb and (101.9 +/- 2.1) mb, respectively, in agreement with previous TOTEM measurements. (C) 2015 The Authors. Published by Elsevier B.V.
  • The CMS collaboration; Sirunyan, A. M.; Eerola, P.; Forthomme, L.; Kirschenmann, H.; Österberg, K.; Voutilainen, M.; Garcia, F.; Havukainen, J.; Heikkilä, J. K.; Järvinen, T.; Karimäki, V.; Kinnunen, R.; Lampen, T.; Lassila-Perini, K.; Laurila, S.; Lehti, S.; Linden, T.; Luukka, P.; Mäenpää, T.; Siikonen, H.; Tuominen, E.; Tuominiemi, J.; Tuuva, T. (2020)
    A search forWWproduction from double-parton scattering processes using same-charge electron-muon and dimuon events is reported, based on proton-proton collision data collected at a center-of-mass energy of 13 TeV. The analyzed data set corresponds to an integrated luminosity of 77.4 fb-1, collected using the CMS detector at the LHC in 2016 and 2017. Multivariate classifiers are used to discriminate between the signal and the dominant background processes. A maximum likelihood fit is performed to extract the signal cross section. This leads to the first evidence for WW production via double-parton scattering, with a significance of 3.9 standard deviations. The measured inclusive cross section is 1.41 +/- 0.28 (stat) +/- 0.28 (syst) pb.
  • Äystö, J.; Behr, K. -H.; Benlliure, J.; Bracco, A.; Egelhof, P.; Fomichev, A.; Gales, S.; Geissel, H.; Grahn, T.; Grigorenko, L. V.; Harakeh, M. N.; Hayano, R.; Heinz, S.; Itahashi, K.; Jokinen, A.; Kalantar-Nayestanaki, N.; Kanungo, R.; Lenske, H.; Mukha, I.; Muenzenberg, G.; Nociforo, C.; Ong, H. J.; Pietri, S.; Pfutzner, M.; Plass, W.; Prochazka, A.; Purushothaman, S.; Saito, T.; Scheidenberger, C.; Simon, H.; Tanihata, I.; Terashima, S.; Toki, H.; Trache, L.; Weick, H.; Winfield, J. S.; Winkler, M.; Zamfir, V.; Super-FRS Collaboration NUSTAR (2016)
    The physics program at the super-conducting fragment separator (Super-FRS) at FAIR, being operated in a multiple-stage, high-resolution spectrometer mode, is discussed. The Super-FRS will produce, separate and transport radioactive beams at high energies up to 1.5 AGeV, and it can be also used as a stand-alone experimental device together with ancillary detectors. Various combinations of the magnetic sections of the Super-FRS can be operated in dispersive, achromatic or dispersion-matched spectrometer ion-optical modes, which allow measurements of momentum distributions of secondary-reaction products with high resolution and precision. A number of unique experiments in atomic, nuclear and hadron physics are suggested with the Super-FRS as a stand-alone device, in particular searches for new isotopes, studies of hyper-nuclei, delta-resonances in exotic nuclei and spectroscopy of atoms characterized by bound mesons. Rare decay modes like multiple-proton or neutron emission and the nuclear tensor force observed in high momentum regime can be also addressed. The in-flight radioactivity measurements as well as fusion, transfer and deep-inelastic reaction mechanisms with the slowed-down and energy-bunched fragment beams are proposed for the high-resolution and energy buncher modes at the Super-FRS. (C) 2016 Elsevier B.V. All rights reserved.
  • TOTEM Collaboration; Antchev, G.; Berretti, M.; Garcia, F.; Heino, J.; Helander, P.; Lauhakangas, R.; Naaranoja, T.; Oljemark, F.; Österberg, K.; Saarikko, H.; Welti, J. (2019)
    The TOTEM collaboration has measured the proton- proton total cross section at v s = 13 TeV with a luminosity- independent method. Using dedicated ss * = 90m beam optics, the Roman Pots were inserted very close to the beam. The inelastic scattering rate has been measured by the T1 and T2 telescopes during the same LHC fill. After applying the optical theorem the total proton- proton cross section is stot = (110.6 +/- 3.4) mb, well in agreement with the extrapolation from lower energies. This method also allows one to derive the luminosity- independent elastic and inelastic cross sections: sel = (31.0 +/- 1.7) mband sinel = (79.5 +/- 1.8) mb.
  • The CMS collaboration; Sirunyan, A. M.; Tumasyan, A.; Eerola, P.; Forthomme, Laurent; Kirschenmann, H.; Saarikko, Heimo; Voutilainen, M.; Österberg, K.; Berretti, Mirko; Brücken, Erik; Garcia, F.; Havukainen, J.; Heikkilä, Jaana; Karimäki, V.; Kim, Minsuk; Kinnunen, R.; Lampén, T.; Lassila-Perini, K.; Laurila, S.; Lehti, S.; Lindén, T.; Luukka, P.; Naaranoja, Tiina; Oljemark, Fredrik Robert; Pekkanen, Juska; Siikonen, H.; Tuominen, E.; Tuominiemi, J.; Welti, Jan Sebastian; Viinikainen, Jussi; Tuuva, T. (2021)
    Events where the two leading jets are separated by a pseudorapidity interval devoid of particle activity, known as jet-gap-jet events, are studied in proton-proton collisions at root s = 13 TeV. The signature is expected from hard color-singlet exchange. Each of the highest transverse momentum (p(T)) jets must have p(T)(jet) > 40 GeV and pseudorapidity 1.4 < vertical bar eta(jet)vertical bar < 4.7, with eta(jet1)eta(jet2) < 0, where jet1 and jet2 are the leading and subleading jets in p(T), respectively. The analysis is based on data collected by the CMS and TOTEM experiments during a low luminosity, high-beta* run at the CERN LHC in 2015, with an integrated luminosity of 0.66 pb(-1). Events with a low number of charged particles with p(T) > 0.2 GeV in the interval vertical bar eta vertical bar < 1 between the jets are observed in excess of calculations that assume only color-exchange. The fraction of events produced via color-singlet exchange, f(CSE), is measured as a function of p(T)(jet2), the pseudorapidity difference between the two leading jets, and the azimuthal angular separation between the two leading jets. The fraction f(CSE) has values of 0.4-1.0%. The results are compared with previous measurements and with predictions from perturbative quantum chromodynamics. In addition, the first study of jet-gap-jet events detected in association with an intact proton using a subsample of events with an integrated luminosity of 0.40 pb(-1) is presented. The intact protons are detected with the Roman pot detectors of the TOTEM experiment. The f(CSE) in this sample is 2.91 +/- 0.70(stat)(-1.01)(+1.08)(syst) times larger than that for inclusive dijet production in dijets with similar kinematics.
  • Ducloué, B.; Szymanowski, L.; Wallon, S. (2016)
    We study the production of two forward jets with a large interval of rapidity at hadron colliders, which was proposed by Mueller and Navelet as a possible test of the high energy dynamics of QCD, within a complete next-to-leading logarithm framework. We show that using the Brodsky-Lepage-Mackenzie procedure to fix the renormalization scale leads to a very good description of the recent CMS data at the LHC for the azimuthal correlations of the jets. We show that the inclusion of next-to-leading order corrections to the jet vertex significantly reduces the importance of energy-momentum non-conservation which is inherent to the BFKL approach, for an asymmetric jet configuration. Finally, we argue that the double parton scattering contribution is negligible in the kinematics of actual CMS measurements.
  • Sinclair, Victoria A.; Moisseev, Dmitri; von Lerber, Annakaisa (2016)
    In this paper it is discussed how dual-polarization radar observations can be used to verify model representations of secondary ice production. An event where enhanced specific differential phase, K-dp, signatures in snow occur at the altitudes where temperatures lie in the range between -8 and -3 degrees C is investigated. By combining radar and surface-based precipitation observations it is shown that these dual-polarization radar signatures are most likely caused by ice with concentrations exceeding those expected from primary ice parameterizations. It is also shown that the newly formed ice particles readily aggregate, which may explain why K-dp values seem to be capped at 0.2-0.3 degrees/km for a Cband radar. For the event of interest, multiple high-resolution (1km) Weather Research and Forecasting (WRF) model simulations are conducted. When the default versions of the Morrison microphysics schemes were used, the simulated number concentration of frozen hydrometeors is much lower than observed and the simulated ice particle concentrations are comparable with values expected from primary ice parameterizations. Higher ice concentrations, which exceed values expected from primary ice parameterizations, were simulated when adhoc thresholds for rain and cloud water mixing ratio in the Hallett-Mossop part of the Morrison scheme were removed. These results suggest that the parameterization of secondary ice production in operational weather prediction models needs to be revisited and that dual-polarization radar observations, in conjunction with ancillary observations, can be used to verify them.
  • Kurylev, Yaroslav; Lassas, Matti; Uhlmann, Gunther (2018)
    We study two inverse problems on a globally hyperbolic Lorentzian manifold (M, g). The problems are: Passive observations in spacetime: consider observations in an open set . The light observation set corresponding to a point source at is the intersection of V and the light-cone emanating from the point q. Let be an unknown open, relatively compact set. We show that under natural causality conditions, the family of light observation sets corresponding to point sources at points determine uniquely the conformal type of W. Active measurements in spacetime: we develop a new method for inverse problems for non-linear hyperbolic equations that utilizes the non-linearity as a tool. This enables us to solve inverse problems for non-linear equations for which the corresponding problems for linear equations are still unsolved. To illustrate this method, we solve an inverse problem for semilinear wave equations with quadratic non-linearities. We assume that we are given the neighborhood V of the time-like path and the source-to-solution operator that maps the source supported on V to the restriction of the solution of the wave equation to V. When M is 4-dimensional, we show that these data determine the topological, differentiable, and conformal structures of the spacetime in the maximal set where waves can propagate from and return back to mu.
  • Ahonen, Lauri; Li, Chenxi; Kubecka, Jakub; Iyer, Siddharth; Vehkamäki, Hanna; Petäjä, Tuukka; Kulmala, Markku; Hogan, Christopher J. (2019)
    Nanometer-scale clusters form from vapor-phase precursors and can subsequently grow into nanoparticles during atmospheric nucleation events. A particularly interesting set of clusters relevant to nucleation is hybrid iodine pentoxide-iodic acid clusters of the form (I2O5)(x)(HIO3)(y) as these clusters have been observed in coastal region nucleation events in anomalously high concentrations. To better understand their properties, we utilized ion mobility-mass spectrometry to probe the structures of cluster anions of the form (I2O5)(x)(HIO3)(y)(IO alpha)(-) (x = 0-7,y = 0-1, alpha = 1-3), similar to those observed in coastal nucleation events. We show that (I2O5)(x)(HIO3)(y)(IO alpha)(-) clusters are relatively stable against dissociation during mass spectrometric measurement, as compared to other clusters observed in nucleation events over continental sites, and that at atmospherically relevant relative humidity levels (65% and less) clusters can become sufficiently hydrated to facilitate complete conversion of iodine pentoxide to iodic acid but that water sorption beyond this level is limited, indicating that the clusters do not persist as nanometer-scale droplets in the ambient.
  • Honkanen, Ari-Pekka; Ollikkala, Sami; Ahopelto, Taru; Kallio, Antti-Jussi; Blomberg, Merja; Huotari, Simo (2019)
    We present a low-cost laboratory X-ray absorption spectrometer that uses a conventional X-ray tube source and bent Johann-type crystal monochromators. The instrument is designed for X-ray absorption spectroscopy studies in the 4-20 keV range which covers most K edges of 3d transition metals and L edges of 5d transition metals and actinides. The energy resolution is typically in the range of 1-5 eV at 10 keV depending on the crystal analyser and the Bragg angle. Measurements can be performed in transmission, fluorescence, and imaging modes. Due to its simple and modular design, the spectrometer can be modified to accommodate additional equipment and complex sample environments required for in situ studies. A showcase of various applications is presented. Published under license by AIP Publishing.
  • The ALICE collaboration; Acharya, S.; Adamova, D.; Kim, D. J.; Krizek, F.; Novitzky, Norbert; Onnerstad, A.; Parkkila, J. E.; Rytkönen, Heidi Maria; Räsänen, Sami; Saarimäki, Oskari Antti Matti; Slupecki, M.; Trzaska, W. H. (2021)
    In quantum scattering processes between two particles, aspects characterizing the strong and Coulomb forces can be observed in kinematic distributions of the particle pairs. The sensitivity to the interaction potential reaches a maximum at low relative momentum and vanishing distance between the two particles. Ultrarelativistic heavy-ion collisions at the LHC provide an abundant source of many hadron species and can be employed as a measurement method of scattering parameters that is complementary to scattering experiments. This study confirms that momentum correlations of particles produced in Pb-Pb collisions at the LHC provide an accurate measurement of kaon-proton scattering parameters at low relative momentum, allowing precise access to the K- p -> K- p process. This work also validates the femtoscopic measurement in ultrarelativistic heavy-ion collisions as an alternative to scattering experiments and a complementary tool to the study of exotic atoms with comparable precision. In this work, the first femtoscopic measurement of momentum correlations of K- p (K+(p) over bar) and K+p (K-(p) over bar) pairs in Pb-Pb collisions at centre-of-mass energy per nucleon pair of root sNN = 5.02 TeV registered by the ALICE experiment is reported. The components of the K- p complex scattering length are extracted and found to be Rf(0) = -0.91 +/- 0.03(stat)(-0.03)(+0.17) (syst) and Sf(0) = 0.92 +/- 0.05(stat)(-0.33)(+0.12)(syst). The results are compared with chiral effective field theory predictions as well as with existing data from dedicated scattering and exotic kaonic atom experiments. (C) 2021 ALICE, European Organization for Nuclear Research. Published by Elsevier B.V.
  • Ryan, A. M.; Gallagher, P. T.; Carley, E. P.; Brentjens, M. A.; Murphy, P. C.; Vocks, C.; Morosan, D. E.; Reid, H.; Magdalenic, J.; (AIP), Leibniz Institut fur Astrophysik; Zucca, P.; Fallows, R.; Mann, G.; Kerdraon, A.; Halfwerk, R. (2021)
    The solar corona is a highly-structured plasma which can reach temperatures of more than similar to 2 MK. At low frequencies (decimetric and metric wavelengths), scattering and refraction of electromagnetic waves are thought to considerably increase the imaged radio source sizes (up to a few arcminutes). However, exactly how source size relates to scattering due to turbulence is still subject to investigation. The theoretical predictions relating source broadening to propagation effects have not been fully confirmed by observations due to the rarity of high spatial resolution observations of the solar corona at low frequencies. Here, the LOw Frequency ARray (LOFAR) was used to observe the solar corona at 120-180 MHz using baselines of up to similar to 3.5 km (corresponding to a resolution of similar to 1-2 ') during the partial solar eclipse of 2015 March 20. A lunar de-occultation technique was used to achieve higher spatial resolution (similar to 0.6 ') than that attainable via standard interferometric imaging (similar to 2.4 '). This provides a means of studying the contribution of scattering to apparent source size broadening. It was found that the de-occultation technique reveals a more structured quiet corona that is not resolved from standard imaging, implying scattering may be overestimated in this region when using standard imaging techniques. However, an active region source was measured to be similar to 4 ' using both de-occultation and standard imaging. This may be explained by the increased scattering of radio waves by turbulent density fluctuations in active regions, which is more severe than in the quiet Sun.
  • Ramesh, R.; Kumari, A.; Kathiravan, C.; Ketaki, D.; Rajesh, M.; Vrunda, M. (2020)
    We carried out a statistical study of the "quiet" solar corona during the descending phase of the Sunspot Cycle 24 (i.e., January 2015 to May 2019) using data obtained with the Gauribidanur RAdioheliograPH (GRAPH) at 53 and 80 MHz simultaneously. Our results show that the equatorial (east-west) diameters of the solar corona at the above two frequencies shrunk steadily. The decrease was found to be due to a gradual reduction in the coronal electron density (N-e). Independent estimates ofN(e)in the equatorial region of the "background" corona using white-light coronagraph observations indicate a decline consistent with our findings.
  • Beuf, G.; Lappi, T.; Paatelainen, R. (2021)
    In this work, we will present the first complete calculation of the one-loop longitudinal photon-to-quark-antiquark light cone wave function, with massive quarks. The quark masses are renormalized in the pole mass scheme. The result is used to calculate the next-to-leading order correction to the high energy deep inelastic scattering longitudinal structure function on a dense target in the dipole factorization framework. For massless quarks the next-to-leading order correction was already known to be sizeable, and our result makes it possible to evaluate it also for massive quarks.
  • The CMS collaboration; Sirunyan, A. M.; Eerola, P.; Kirschenmann, H.; Pekkanen, J.; Voutilainen, M.; Havukainen, J.; Heikkilä, J. K.; Järvinen, T.; Karimäki, V.; Kinnunen, R.; Lampén, T.; Lassila-Perini, K.; Laurila, S.; Lehti, S.; Lindén, T.; Luukka, P.; Mäenpää, T.; Siikonen, H.; Tuominen, E.; Tuominiemi, J.; Tuuva, T. (2018)
    Pseudorapidity, transverse momentum, and multiplicity distributions are measured in the pseudorapidity range vertical bar eta vertical bar < 2.4 for charged particles with transverse momenta satisfying pT > 0.5 GeV in proton-proton collisions at a center-of-mass energy of root s = 13 TeV. Measurements are presented in three different event categories. The most inclusive of the categories corresponds to an inelastic pp data set, while the other two categories are exclusive subsets of the inelastic sample that are either enhanced or depleted in single diffractive dissociation events. The measurements are compared to predictions from Monte Carlo event generators used to describe high-energy hadronic interactions in collider and cosmic-ray physics.
  • The ALICE collaboration; Acharya, S.; Brucken, E. J.; Chang, B.; Hilden, T. E.; Kim, D. J.; Litichevskyi, V.; Mieskolainen, M. M.; Orava, R.; Parkkila, J. E.; Rak, J.; Rytkonen, H.; Räsänen, Sami; Slupecki, M.; Snellman, T. W.; Trzaska, W. H.; Vargyas, M.; Viinikainen, J.; Zhou, Z. (2020)
    Two-particle correlation functions were measured for p (p) over bar, p (Lambda) over bar, (p) over bar Lambda, and Lambda(Lambda) over bar pairs in Pb-Pb collisions at root sNN = 2.76 TeV and root sNN = 5.02 TeV recorded by the ALICE detector. From a simultaneous fit to all obtained correlation functions, real and imaginary components of the scattering lengths, as well as the effective ranges, were extracted for combined p (Lambda) over bar and (p) over bar Lambda pairs and, for the first time, for Lambda(Lambda) over bar pairs. Effective averaged scattering parameters for heavier baryon-antibaryon pairs, not measured directly, are also provided. The results reveal similarly strong interaction between measured baryon-antibaryon pairs, suggesting that they all annihilate in the same manner at the same pair relative momentum k*. Moreover, the reported significant non-zero imaginary part and negative real part of the scattering length provide motivation for future baryon-antibaryon bound state searches. (C) 2020 The Author(s). Published by Elsevier B.V.
  • The CMS collaboration; Sirunyan, A. M.; Eerola, P.; Pekkanen, J.; Voutilainen, M.; Härkönen, J.; Järvinen, T.; Karimäki, V.; Kinnunen, R.; Lampén, T.; Lassila-Perini, K.; Lehti, S.; Lindén, T.; Luukka, P.; Tuominen, E.; Tuominiemi, J.; Tuovinen, E.; Talvitie, J.; Tuuva, T. (2018)
    The top quark pair production cross section (ad) is measured for the first time in pp collisions at a center-of-mass energy of 5.02 TeV. The data were collected by the CMS experiment at the LHC and correspond to an integrated luminosity of 27.4 pb(-1). The measurement is performed by analyzing events with at least one charged lepton. The measured cross section is sigma(tt) = 69.5 +/- 6.1 (stat) +/- 5.6 (syst) +/- 1.6 (lumi) pb, with a total relative uncertainty of 12%. The result is in agreement with the expectation from the standard model. The impact of the presented measurement on the determination of the gluon distribution function is investigated.
  • Lawson, John; Schultz, David M.; Vaughan, Geraint; Kirshbaum, Daniel J. (2013)
  • Jin, Xin; Crocombette, Jean-Paul; Djurabekova, Flyura; Zhang, Shuo; Nordlund, Kai; Garrido, Frederico; Debelle, Aurelien (2020)
    As Rutherford backscattering spectrometry in channeling mode (RBS/C) is an efficient technique for characterizing crystallographic defects, its computational simulation has drawn attention over the past several decades. Recently, a RBS/C simulation code based on the binary collision approximation called Rutherford backscattering simulation in arbitrary defective crystals has been suggested and successfully applied to predict the RBS/C spectra from different damaged materials, whose structures were generated in high-dose ion irradiation atomistic simulations. In the present paper, we introduce new developments improving the flexibility of the developed software and its applicability to different types of materials. More precisely, we modified the algorithm describing the slowdown process of backscattered ions, added fitting parameters in the collision partner search routine, modified the routine taking into account target atom thermal vibrations and provided new descriptions of the ion beam divergence. As an example, the effect of the modifications on simulated RBS/C spectra is shown for an <011 & rang;-oriented UO(2)crystal analyzed with a 3.085 MeV He(2+)ion beam. Some of these changes proved necessary to achieve satisfying agreement between simulations and experimental data. Similar observation was made for <001 & rang;-oriented Si and <001 & rang;-oriented GaAs crystals analyzed with a 1.4 MeV He(+)ion beam. In these simulations, the modifications have also resulted in good agreement with experiment.