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ATLAS Collaboration (Aad, G. et al); Alvarez Piqueras, D.; Cabrera Urban, S.; Castillo Gimenez, V.; Cerda Alberich, L.; Costa, M.J.; Fernandez Martinez, P.; Ferrer, A.; Fiorini, L.; Fuster, J.; Garcia, C.; Garcia Navarro, J.E.; Gonzalez de la Hoz, S.; Hernandez Jimenez, Y.; Higon-Rodriguez, E.; Irles Quiles, A.; Jimenez Pena, J.; Kaci, M.; King, M.; Lacasta, C.; Lacuesta, V.R.; Marti-Garcia, S.; Mitsou, V.A.; Pedraza Lopez, S.; Perez Garcia-Estañ, M.T.; Romero Adam, E.; Ros, E.; Salt, J.; Sanchez Martinez, V.; Soldevila, U.; Sanchez, J.; Valero, A.; Valls Ferrer, J.A.; Vos, M. |
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Title |
Search for flavour-changing neutral current top quark decays t -> Hq in pp collisions at root s=8 TeV with the ATLAS detector |
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Journal Article |
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Year |
2015 |
Publication |
Journal of High Energy Physics |
Abbreviated Journal |
J. High Energy Phys. |
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Volume |
12 |
Issue |
12 |
Pages |
061 - 65pp |
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Keywords |
Hadron-Hadron Scattering; Top Physics; Higgs Physics; FCNC Interactions |
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Abstract |
A search for flavour-changing neutral current decays of a top quark to an up-type quark (q = u; c) and the Standard Model Higgs boson, where the Higgs boson decays to b (b) over bar, is presented. The analysis searches for top quark pair events in which one top quark decays to W b, with the W boson decaying leptonically, and the other top quark decays to Hq. The search is based on pp collisions at root s = 8TeV recorded in 2012 with the ATLAS detector at the CERN Large Hadron Collider and uses an integrated luminosity of 20.3 fb(-1). Data are analysed in the lepton-plus-jets final state, characterised by an isolated electron or muon and at least four jets. The search exploits the high multiplicity of b quark jets characteristic of signal events, and employs a likelihood discriminant that uses the kinematic differences between the signal and the background, which is dominated by t (t) over bar -> WbWb decays. No significant excess of events above the background expectation is found, and observed (expected) 95% CL upper limits of 0.56% (0.42%) and 0.61% (0.64%) are derived for the t -> Hc and t -> Hu branching ratios respectively. The combination of this search with other ATLAS searches in the H -> gamma gamma and H -> WW*, tau tau decay modes significantly improves the sensitivity, yielding observed (expected) 95% CL upper limits on the t -> Hc and t -> Hu branching ratios of 0.46% (0.25%) and 0.45% (0.29%) respectively. The corresponding combined observed (expected) upper limits on the vertical bar lambda(tcH)vertical bar and vertical bar lambda(tuH)vertical bar couplings are 0.13 (0.10) and 0.13 (0.10) respectively. These are the most restrictive direct bounds on t q H interactions measured so far. |
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[Jackson, P.; Lee, L.; Petridis, A.; Soni, N.; White, M. J.] Univ Adelaide, Dept Phys, Adelaide, SA, Australia |
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Springer |
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English |
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1029-8479 |
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Notes |
WOS:000366831600001 |
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no |
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Is ISI |
yes |
International Collaboration |
yes |
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Call Number |
IFIC @ pastor @ |
Serial |
2505 |
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Author |
ATLAS Collaboration (Aad, G. et al); Alvarez Piqueras, D.; Cabrera Urban, S.; Castillo Gimenez, V.; Costa, M.J.; Fernandez Martinez, P.; Ferrer, A.; Fiorini, L.; Fuster, J.; Garcia, C.; Garcia Navarro, J.E.; Gonzalez de la Hoz, S.; Hernandez Jimenez, Y.; Higon-Rodriguez, E.; Irles Quiles, A.; Jimenez Pena, J.; Kaci, M.; King, M.; Lacasta, C.; Lacuesta, V.R.; Marti-Garcia, S.; Mitsou, V.A.; Pedraza Lopez, S.; Perez Garcia-Estañ, M.T.; Romero Adam, E.; Ros, E.; Salt, J.; Sanchez Martinez, V.; Soldevila, U.; Sanchez, J.; Valero, A.; Valls Ferrer, J.A.; Vos, M. |
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Title |
Measurement of the t(t)over-barW and t(t)over-barZ production cross sections in pp collisions at root s=8 TeV with the ATLAS detector |
Type |
Journal Article |
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Year |
2015 |
Publication |
Journal of High Energy Physics |
Abbreviated Journal |
J. High Energy Phys. |
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Volume |
11 |
Issue |
11 |
Pages |
172 - 48pp |
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Keywords |
Electroweak interaction; Hadron-Hadron scattering; Top physics |
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Abstract |
The production cross sections of top-quark pairs in association with massive vector bosons have been measured using data from pp collisions at root s = 8 TeV. The dataset corresponds to an integrated luminosity of 20.3 fb(-1) collected by the ATLAS detector in 2012 at the LHC. Final states with two, three or four leptons are considered. A fit to the data considering the t (t) over barW and t (t) over barZ processes simultaneously yields a significance of 5.0 sigma (4.2 sigma) over the background-only hypothesis for t (t) over barW (t (t) over barZ) production. The measured cross sections are sigma(t (t) over barW) = 369(-91)(+100) fb and sigma(t (t) over barZ) = 176(-52)(+58) fb. The background-only hypothesis with neither t (t) over barW nor t (t) over barZ production is excluded at 7.1 sigma. All measurements are consistent with next-to-leading-order calculations for the t (t) over barW and t (t) over barZ processes. |
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[Jackson, P.; Lee, L.; Petridis, A.; Soni, N.; Whitel, M. J.] Univ Adelaide, Dept Phys, Adelaide, SA, Australia |
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Springer |
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English |
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1029-8479 |
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Conference |
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Notes |
WOS:000366139900001 |
Approved |
no |
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Is ISI |
yes |
International Collaboration |
yes |
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Call Number |
IFIC @ pastor @ |
Serial |
2488 |
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Author |
ATLAS Collaboration (Aad, G. et al); Alvarez Piqueras, D.; Cabrera Urban, S.; Castillo Gimenez, V.; Costa, M.J.; Fernandez Martinez, P.; Ferrer, A.; Fiorini, L.; Fuster, J.; Garcia, C.; Garcia Navarro, J.E.; Gonzalez de la Hoz, S.; Hernandez Jimenez, Y.; Higon-Rodriguez, E.; Irles Quiles, A.; Jimenez Pena, J.; Kaci, M.; King, M.; Lacasta, C.; Lacuesta, V.R.; Marti-Garcia, S.; Mitsou, V.A.; Oliver Garcia, E.; Pedraza Lopez, S.; Perez Garcia-Estañ, M.T.; Romero Adam, E.; Ros, E.; Salt, J.; Sanchez Martinez, V.; Soldevila, U.; Sanchez, J.; Valero, A.; Valladolid Gallego, E.; Valls Ferrer, J.A.; Vos, M. |
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Title |
Search for new phenomena in events with at least three photons collected in pp collisions at root s=8 TeV with the ATLAS detector |
Type |
Journal Article |
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Year |
2016 |
Publication |
European Physical Journal C |
Abbreviated Journal |
Eur. Phys. J. C |
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Volume |
76 |
Issue |
4 |
Pages |
210 - 26pp |
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Abstract |
Results of a search for new phenomena in events with at least three photons are reported. Data from proton-proton collisions at a centre-of-mass energy of 8 TeV, corresponding to an integrated luminosity of 20.3 fb(-1), were collected with the ATLAS detector at the LHC. The observed data are well described by the Standard Model. Limits at the 95 % confidence level on new phenomena are presented based on the rate of events in an inclusive signal region and a restricted signal region targeting the rare decay Z -> 3 gamma, as well as di-photon and tri-photon resonance searches. For a Standard Model Higgs boson decaying to four photons via a pair of intermediate pseudoscalar particles ( a), limits are found to be sigma xBR( h -> aa) xBR(a -> gamma gamma) 2 < 10(-3) sigma(SM) for 10 GeV < m(a) < 62 GeV. Limits are also presented for Higgs boson-like scalars (H) for m(H) > 125 GeV, and for a Z' decaying to three photons via Z' -> a + gamma -> 3 gamma. Additionally, the observed limit on the branching ratio of the Z boson decay to three photons is found to be BR( Z -> 3 gamma) < 2.2 x 10(-6), a result five times stronger than the previous result from LEP. |
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Address |
[Gonzalez, B. Alvarez; Armbruster, A. J.; Boveia, A.; Catinaccio, A.; Cattai, A.; Dell'Acqua, A.; Di Girolamo, A.; Di Girolamo, B.; Dudarev, A.; Gorini, B.; Correia, A. M. Henriques; Hoecker, A.; Jenni, P.; Krasznahorkay, A.; Lapoire, C.; Lenzi, B.; Mandelli, B.; Marzin, A.; Milic, A.; Nairz, A. M.; Nicquevert, B.; Petersen, B. A.; Poppleton, A.; Rembser, C.; Ruiz-Martinez, A.; Salzburger, A.; Serfon, C.; Sfyrla, A.; Tricoli, A.; ATLAS Collaboration] CERN, CH-1211 Geneva 23, Switzerland |
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Publisher |
Springer |
Place of Publication |
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Language |
English |
Summary Language |
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Series Editor |
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Series Title |
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Abbreviated Series Title |
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Series Volume |
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Series Issue |
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Edition |
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ISSN |
1434-6044 |
ISBN |
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Area |
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Conference |
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Notes |
WOS:000375307600001 |
Approved |
no |
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Is ISI |
yes |
International Collaboration |
yes |
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Call Number |
IFIC @ pastor @ |
Serial |
2651 |
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Author |
ATLAS Collaboration (Aad, G. et al); Alvarez Piqueras, D.; Cabrera Urban, S.; Castillo Gimenez, V.; Costa, M.J.; Fernandez Martinez, P.; Ferrer, A.; Fiorini, L.; Fuster, J.; Garcia, C.; Garcia Navarro, J.E.; Gonzalez de la Hoz, S.; Hernandez Jimenez, Y.; Higon-Rodriguez, E.; Irles Quiles, A.; Jimenez Pena, J.; Kaci, M.; King, M.; Lacasta, C.; Lacuesta, V.R.; Marti-Garcia, S.; Mitsou, V.A.; Oliver Garcia, E.; Pedraza Lopez, S.; Perez Garcia-Estañ, M.T.; Romero Adam, E.; Ros, E.; Salt, J.; Sanchez Martinez, V.; Soldevila, U.; Sanchez, J.; Valero, A.; Valladolid Gallego, E.; Valls Ferrer, J.A.; Vos, M. |
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Title |
Search for direct top squark pair production in final states with two tau leptons in pp collisions at root s=8 TeV with the ATLAS detector |
Type |
Journal Article |
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Year |
2016 |
Publication |
European Physical Journal C |
Abbreviated Journal |
Eur. Phys. J. C |
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Volume |
76 |
Issue |
2 |
Pages |
81 - 30pp |
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Abstract |
A search for direct pair production of the supersymmetric partner of the top quark, decaying via a scalar tau to a nearly massless gravitino, has been performed using 20 fb(-1) of proton-proton collision data at root s = 8 TeV. The data were collected by the ATLAS experiment at the LHC in 2012. Top squark candidates are searched for in events with either two hadronically decaying tau leptons, one hadronically decaying tau and one light lepton, or two light leptons. No significant excess over the Standard Model expectation is found. Exclusion limits at 95 % confidence level are set as a function of the top squark and scalar tau masses. Depending on the scalar tau mass, ranging from the 87 GeV LEP limit to the top squark mass, lower limits between 490 and 650 GeV are placed on the top squark mass within the model considered. |
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Address |
[Aleksa, M.; Gonzalez, B. Alvarez; Anders, G.; Anghinolfi, F.; Armbruster, A. J.; Arnaez, O.; Avolio, G.; Baak, M. A.; Backes, M.; Backhaus, M.; Barak, L.; Beltramello, O.; Bianco, M.; Bogaerts, J. A.; Boveia, A.; Boyd, J.; Burckhart, H.; Campana, S.; Garrido, M. D. M. Capeans; Carli, T.; Carrillo-Montoya, G. D.; Catinaccio, A.; Cattai, A.; Cerv, M.; Chromek-Burckhart, D.; Conti, G.; Dell'Acqua, A.; Deviveiros, P. O.; Di Girolamo, A.; Di Girolamo, B.; Dittus, F.; Dobos, D.; Dudarev, A.; Duehrssen, M.; Eifert, T.; Ellis, N.; Elsing, M.; Farthouat, P.; Fassnacht, P.; Feigl, S.; Perez, S. Fernandez; Francis, D.; Froidevaux, D.; Gadatsch, S.; Gillberg, D.; Glatzer, J.; Goossens, L.; Gorini, B.; Gray, H. M.; Hawkings, R. J.; Correia, A. M. Henriques; Hervas, L.; Hoecker, A.; Huhtinen, M.; Iengo, P.; Jaekel, M. R.; Jakobsen, S.; Jenni, P.; Klioutchnikova, T.; Krasznahorkay, A.; Lapoire, C.; Lassnig, M.; Miotto, G. Lehmann; Lenzi, B.; Lichard, P.; Macina, D.; Malyukov, S.; Mandelli, B.; Mapelli, L.; Marzin, A.; Milic, A.; Mornacchi, G.; Nairz, A. M.; Nakahama, Y.; Nessi, M.; Nicquevert, B.; Nordberg, M.; Oide, H.; Palestini, S.; Pauly, T.; Pernegger, H.; Peters, K.; Petersen, B. A.; Pommes, K.; Poppleton, A.; Poulard, G.; Poveda, J.; Prasad, S.; Rammensee, M.; Raymond, M.; Rembser, C.; Ritsch, E.; Roe, S.; Ruiz-Martinez, A.; Salzburger, A.; Schaefer, D.; Schlenker, S.; Schmieden, K.; Serfon, C.; Sforza, F.; Sfyrla, A.; Solans, C. A.; Spigo, G.; Stelzer, H. J.; Teischinger, F. A.; TenKate, H.; Tremblet, L.; Tricoli, A.; Tsarouchas, C.; Unal, G.; van Woerden, M. C.; Vandelli, W.; Voss, R.; Vuillermet, R.; Wells, P. S.; Wengler, T.; Wenig, S.; Werner, P.; Wilkens, H. G.; Wotschack, J.; Young, C. J. S.; Zwalinski, L.; ATLAS Collaboration] CERN, CH-1211 Geneva 23, Switzerland |
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Publisher |
Springer |
Place of Publication |
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Editor |
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Language |
English |
Summary Language |
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Original Title |
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Series Editor |
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Series Title |
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Abbreviated Series Title |
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Series Volume |
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Series Issue |
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Edition |
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ISSN |
1434-6044 |
ISBN |
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Expedition |
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Conference |
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Notes |
WOS:000375284100001 |
Approved |
no |
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Is ISI |
yes |
International Collaboration |
yes |
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Call Number |
IFIC @ pastor @ |
Serial |
2657 |
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| Permanent link to this record |
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Author |
ATLAS Collaboration (Aad, G. et al); Alvarez Piqueras, D.; Cabrera Urban, S.; Castillo Gimenez, V.; Costa, M.J.; Fernandez Martinez, P.; Ferrer, A.; Fiorini, L.; Fuster, J.; Garcia, C.; Garcia Navarro, J.E.; Gonzalez de la Hoz, S.; Hernandez Jimenez, Y.; Higon-Rodriguez, E.; Irles Quiles, A.; Jimenez Pena, J.; Kaci, M.; King, M.; Lacasta, C.; Lacuesta, V.R.; Marti-Garcia, S.; Mitsou, V.A.; Oliver Garcia, E.; Pedraza Lopez, S.; Perez Garcia-Estañ, M.T.; Romero Adam, E.; Ros, E.; Salt, J.; Sanchez Martinez, V.; Soldevila, U.; Sanchez, J.; Valero, A.; Valladolid Gallego, E.; Valls Ferrer, J.A.; Vos, M. |
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Title |
A new method to distinguish hadronically decaying boosted Z bosons from W bosons using the ATLAS detector |
Type |
Journal Article |
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Year |
2016 |
Publication |
European Physical Journal C |
Abbreviated Journal |
Eur. Phys. J. C |
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Volume |
76 |
Issue |
5 |
Pages |
238 - 33pp |
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Keywords |
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Abstract |
The distribution of particles inside hadronic jets produced in the decay of boosted W and Z bosons can be used to discriminate such jets from the continuum background. Given that a jet has been identified as likely resulting from the hadronic decay of a boosted W or Z boson, this paper presents a technique for further differentiating Z bosons from W bosons. The variables used are jet mass, jet charge, and a b-tagging discriminant. A likelihood tagger is constructed from these variables and tested in the simulation of W' -> WZ for bosons in the transverse momentum range 200 GeV < p(T) < 400 GeV in root s = 8 TeV pp collisions with the ATLAS detector at the LHC. For Z-boson tagging efficiencies of epsilon(Z) = 90, 50, and 10 %, one can achieve W+-boson tagging rejection factors (1/epsilon(W+)) of 1.7, 8.3 and 1000, respectively. It is not possible to measure these efficiencies in the data due to the lack of a pure sample of high p(T), hadronically decaying Z bosons. However, the modelling of the tagger inputs for boosted W bosons is studied in data using a t (t) over bar -enriched sample of events in 20.3 fb(-1) of data at root s = 8 TeV. The inputs are well modelled within uncertainties, which builds confidence in the expected tagger performance. |
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Address |
[Jackson, P.; Lee, L.; Petridis, A.; Soni, N.; White, M. J.] Univ Adelaide, Dept Phys, Adelaide, SA, Australia |
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Corporate Author |
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Thesis |
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Publisher |
Springer |
Place of Publication |
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Editor |
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Language |
English |
Summary Language |
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Original Title |
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Series Editor |
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Series Title |
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Abbreviated Series Title |
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Series Volume |
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Series Issue |
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Edition |
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ISSN |
1434-6044 |
ISBN |
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Medium |
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Area |
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Expedition |
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Conference |
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Notes |
WOS:000399466100001 |
Approved |
no |
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Is ISI |
yes |
International Collaboration |
yes |
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Call Number |
IFIC @ pastor @ |
Serial |
3087 |
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| Permanent link to this record |
