| 1. |
- Singh, B. P., et al.
(författare)
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Experimental access to Transition Distribution Amplitudes with the PANDA experiment at FAIR
- 2015
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Ingår i: European Physical Journal A. Hadrons and Nuclei. - : Springer Science and Business Media LLC. - 1434-6001 .- 1434-601X. ; 51:8
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Tidskriftsartikel (refereegranskat)abstract
- Baryon-to-meson Transition Distribution Amplitudes (TDAs) encoding valuable new information on hadron structure appear as building blocks in the collinear factorized description for several types of hard exclusive reactions. In this paper, we address the possibility of accessing nucleon-to-pion (pi N) TDAs from (p) over barp -> e(+)e(-)pi(0) reaction with the future PANDA detector at the FAIR facility. At high center-of-mass energy and high invariant mass squared of the lepton pair q(2), the amplitude of the signal channel (p) over barp -> e(+)e(-)pi(0) admits a QCD factorized description in terms of pi N TDAs and nucleon Distribution Amplitudes (DAs) in the forward aid backward kinematic regimes. Assuming the validity of this factorized description, we perform feasibility studies for measuring (p) over barp -> e(+)e(-)pi(0) with the PANDA detector. Detailed simulations on signal reconstruction efficiency as well as on rejection of the most severe background channel, i.e. (p) over barp -> pi(+)pi(-)pi(0) were performed for the center-of-mass energy squared s = 5 GeV2 and s = 10 GeV2, in the kinematic regions 3.0 < q(2) < 4.3 GeV2 and 5 < q(2) < 9 GeV2, respectively, with a neutral pion scattered in the forward or backward cone vertical bar cos theta(pi 0)vertical bar > 0.5 in the proton-antiproton center-of-mass frame. Results of the simulation show that the particle identification capabilities of the PANDA detector will allow to achieve a background rejection factor of 5 . 10(7) (1 . 10(7)) at low (high) q(2) for s = 5 GeV2, and of 1 . 10(8) (6 . 10(6)) at low (high) q(2) for s = 10 GeV2, while keeping the signal reconstruction efficiency at around 40%. At both energies, a clean lepton signal can be reconstructed with the expected statistics corresponding to 2 of integrated luminosity. The cross sections obtained from the simulations are used to show that a test of QCD collinear factorization can be done at the lowest order by measuring scaling laws and angular distributions. The future measurement of the signal channel cross section with PANDA will provide a new test of the perturbative QCD description of a novel class of hard exclusive reactions and will open the possibility of experimentally accessing pi N TDAs.
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| 2. |
- Singh, B., et al.
(författare)
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Feasibility study for the measurement of pi N transition distribution amplitudes at (P)over-barANDA in (P)over-barp -> J/psi pi(0)
- 2017
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Ingår i: Physical Review D. - : AMER PHYSICAL SOC. - 2470-0010 .- 2470-0029. ; 95:3
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Tidskriftsartikel (refereegranskat)abstract
- The exclusive charmonium production process in (P) over barp annihilation with an associated pi 0 meson (p) over barp -> J/psi pi(0) is studied in the framework of QCD collinear factorization. The feasibility of measuring this reaction through the J/psi -> e(+) e(-) decay channel with the AntiProton ANnihilation at DArmstadt ((P) over bar ANDA) experiment is investigated. Simulations on signal reconstruction efficiency as well as the background rejection from various sources including the (P) over barp -> pi(+)pi(-)pi(0) and (p) over barp -> J/psi pi(0)pi(0) reactions are performed with PANDAROOT, the simulation and analysis software framework of the (P) over bar ANDA experiment. It is shown that the measurement can be done at (P) over bar ANDA with significant constraining power under the assumption of an integrated luminosity attainable in four to five months of data taking at the maximum design luminosity.
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| 3. |
- Aaltonen, T., et al.
(författare)
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Combination of CDF and D0 measurements of the W boson helicity in top quark decays
- 2012
-
Ingår i: Physical Review D. - 1550-7998 .- 1550-2368. ; 85:7, s. 071106-
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Tidskriftsartikel (refereegranskat)abstract
- We report the combination of recent measurements of the helicity of the W boson from top quark decay by the CDF and D0 collaborations, based on data samples corresponding to integrated luminosities of 2.7-5.4 fb(-1) of p (p) over bar collisions collected during Run II of the Fermilab Tevatron collider. Combining measurements that simultaneously determine the fractions of W bosons with longitudinal (f(0)) and right-handed (f(+)) helicities, we find f(0) = 0.722 +/- 0.081[+/- 0.062(stat) +/- 0.052(syst)] and f(+) = -0.033 +/- 0.046[+/- 0.034(stat) +/- 0.031(syst)]. Combining measurements where one of the helicity fractions is fixed to the value expected in the standard model, we find f(0) = 0.682 +/- 0.057[+/- 0.035(stat) +/- 0.046(syst)] for fixed f(+) and f(+) = -0.015 +/- 0.035[+/- 0.018(stat) +/- 0.030(syst)] for fixed f(0). The results are consistent with standard model expectations.
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| 4. |
- Aaltonen, T., et al.
(författare)
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Combination of CDF and D0 W-Boson mass measurements
- 2013
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Ingår i: Physical Review D. - 1550-7998 .- 1550-2368. ; 88:5, s. 052018-
-
Tidskriftsartikel (refereegranskat)abstract
- We summarize and combine direct measurements of the mass of the W boson in root s = 1.96 TeV proton-antiproton collision data collected by CDF and D0 experiments at the Fermilab Tevatron Collider. Earlier measurements from CDF and D0 are combined with the two latest, more precise measurements: a CDF measurement in the electron and muon channels using data corresponding to 2.2 fb(-1) of integrated luminosity, and a D0 measurement in the electron channel using data corresponding to 4.3 fb(-1) of integrated luminosity. The resulting Tevatron average for the mass of the W boson is M-W = 80387 +/- 16 MeV. Including measurements obtained in electron-positron collisions at LEP yields the most precise value of M-W = 80385 +/- 15 MeV.
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| 5. |
- Aaltonen, T., et al.
(författare)
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Combination of measurements of the top-quark pair production cross section from the Tevatron Collider
- 2014
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Ingår i: Physical Review D. - 1550-7998 .- 1550-2368. ; 89:7
-
Tidskriftsartikel (refereegranskat)abstract
- We combine six measurements of the inclusive top-quark pair (t(sic)) production cross section (sigma(t)(sic)) from data collected with the CDF and D0 detectors at the Fermilab Tevatron with proton-antiproton collisions at root s = 1.96 TeV. The data correspond to integrated luminosities of up to 8.8 fb(-1). We obtain a value of sigma tt = 7.60 +/- 0.41 pb for a top-quark mass of m(t) = 172.5 GeV. The contributions to the uncertainty are 0.20 pb from statistical sources, 0.29 pb from systematic sources, and 0.21 pb from the uncertainty on the integrated luminosity. The result is in good agreement with the standard model expectation of 7.35(-0.33)(+0.28) pb at next-to-next-to-leading order and next-to-next-to leading logarithms in perturbative QCD.
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| 6. |
- Aaltonen, T., et al.
(författare)
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Combination of Tevatron Searches for the Standard Model Higgs Boson in the W+W- Decay Mode
- 2010
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Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 104:6, s. 061802-
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Tidskriftsartikel (refereegranskat)abstract
- We combine searches by the CDF and D0 Collaborations for a Higgs boson decaying to W+W-. The data correspond to an integrated total luminosity of 4.8 (CDF) and 5.4 (D0) fb(-1) of p (p) over bar collisions at root s = 1.96 TeV at the Fermilab Tevatron collider. No excess is observed above background expectation, and resulting limits on Higgs boson production exclude a standard model Higgs boson in the mass range 162-166 GeV at the 95% C.L.
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| 7. |
- Aaltonen, T., et al.
(författare)
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Combined Forward-Backward Asymmetry Measurements in Top-Antitop Quark Production at the Tevatron
- 2018
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Ingår i: Physical Review Letters. - : AMER PHYSICAL SOC. - 0031-9007 .- 1079-7114. ; 120:4
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Tidskriftsartikel (refereegranskat)abstract
- The CDF and D0 experiments at the Fermilab Tevatron have measured the asymmetry between yields of forward- and backward-produced top and antitop quarks based on their rapidity difference and the asymmetry between their decay leptons. These measurements use the full data sets collected in proton-antiproton collisions at a center-of-mass energy of root s = 1.96 TeV. We report the results of combinations of the inclusive asymmetries and their differential dependencies on relevant kinematic quantities. The combined inclusive asymmetry is A(FB)(t (t) over bar) = 0.128 +/- 0.025. The combined inclusive and differential asymmetries are consistent with recent standard model predictions.
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| 8. |
- Aaltonen, T., et al.
(författare)
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Evidence for a Particle Produced in Association with Weak Bosons and Decaying to a Bottom-Antibottom Quark Pair in Higgs Boson Searches at the Tevatron
- 2012
-
Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 109:7, s. 071804-
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Tidskriftsartikel (refereegranskat)abstract
- We combine searches by the CDF and D0 Collaborations for the associated production of a Higgs boson with a W or Z boson and subsequent decay of the Higgs boson to a bottom-antibottom quark pair. The data, originating from Fermilab Tevatron p (p) over bar collisions at root s = 1.96 TeV, correspond to integrated luminosities of up to 9.7 fb(-1). The searches are conducted for a Higgs boson with mass in the range 100-150 GeV/c(2). We observe an excess of events in the data compared with the background predictions, which is most significant in the mass range between 120 and 135 GeV/c(2). The largest local significance is 3.3 standard deviations, corresponding to a global significance of 3.1 standard deviations. We interpret this as evidence for the presence of a new particle consistent with the standard model Higgs boson, which is produced in association with a weak vector boson and decays to a bottom-antibottom quark pair.
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| 9. |
- Aaltonen, T., et al.
(författare)
-
Higgs boson studies at the Tevatron
- 2013
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Ingår i: Physical Review D. - 1550-7998 .- 1550-2368. ; 88:5, s. 052014-
-
Tidskriftsartikel (refereegranskat)abstract
- We combine searches by the CDF and D0 Collaborations for the standard model Higgs boson with mass in the range 90-200 GeV/c(2) produced in the gluon-gluon fusion, WH, ZH, t (t) over barH, and vector boson fusion processes, and decaying in the H -> b (b) over bar, H -> W+W-, H -> ZZ, H -> tau(+)tau(-), and H -> gamma gamma modes. The data correspond to integrated luminosities of up to 10 fb(-1) and were collected at the Fermilab Tevatron in p (p) over bar collisions at root s = 1.96 TeV. The searches are also interpreted in the context of fermiophobic and fourth generation models. We observe a significant excess of events in the mass range between 115 and 140 GeV/c(2). The local significance corresponds to 3.0 standard deviations at m(H) = 125 GeV/c(2), consistent with the mass of the Higgs boson observed at the LHC, and we expect a local significance of 1.9 standard deviations. We separately combine searches for H -> b (b) over bar, H -> W+W-, H -> tau(+)tau(-), and H -> gamma gamma. The observed signal strengths in all channels are consistent with the presence of a standard model Higgs boson with a mass of 125 GeV/c(2).
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| 10. |
- Aaltonen, T., et al.
(författare)
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Observation of s-Channel Production of Single Top Quarks at the Tevatron
- 2014
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Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 112:23
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Tidskriftsartikel (refereegranskat)abstract
- We report the first observation of single-top-quark production in the s channel through the combination of the CDF and D0 measurements of the cross section in proton-antiproton collisions at a center-of-mass energy of 1.96 TeV. The data correspond to total integrated luminosities of up to 9.7 fb(-1) per experiment. The measured cross section is sigma(s) = 1.29(-0.24)(+0.26) pb. The probability of observing a statistical fluctuation of the background to a cross section of the observed size or larger is 1.8 x 10(-10), corresponding to a significance of 6.3 standard deviations for the presence of an s-channel contribution to the production of single-top quarks.
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| 11. |
- Aaltonen, T., et al.
(författare)
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Tevatron Combination of Single-Top-Quark Cross Sections and Determination of the Magnitude of the Cabibbo-Kobayashi-Maskawa Matrix Element V-tb
- 2015
-
Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 115:15
-
Tidskriftsartikel (refereegranskat)abstract
- We present the final combination of CDF and D0 measurements of cross sections for single-top-quark production in proton-antiproton collisions at a center-of-mass energy of 1.96 TeV. The data correspond to total integrated luminosities of up to 9.7 fb(-1) per experiment. The t-channel cross section is measured to be sigma(t) = 2.25(-0.31)(+0.29) pb. We also present the combinations of the two-dimensional measurements of the s- vs t-channel cross section. In addition, we give the combination of the s + t channel cross section measurement resulting in sigma(s+t) = 3.30(-0.40)(+0.52) pb, without assuming the standard model value for the ratio sigma(s)/sigma(t). The resulting value of the magnitude of the top-to-bottom quark coupling is vertical bar V-tb vertical bar = 1.02(-0.05)(+0.06), corresponding to vertical bar V-tb vertical bar > 0.92 at the 95% C. L.
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| 12. |
- Aaltonen, T., et al.
(författare)
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Tevatron Constraints on Models of the Higgs Boson with Exotic Spin and Parity Using Decays to Bottom-Antibottom Quark Pairs
- 2015
-
Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 114:15
-
Tidskriftsartikel (refereegranskat)abstract
- Combined constraints from the CDF and D0 Collaborations on models of the Higgs boson with exotic spin J and parity P are presented and compared with results obtained assuming the standard model value J(P) = 0(+). Both collaborations analyzed approximately 10 fb(-1) of proton-antiproton collisions with a center-of-mass energy of 1.96 TeV collected at the Fermilab Tevatron. Two models predicting exotic Higgs bosons with J(P) = 0(-) and J(P) = 2(+) are tested. The kinematic properties of exotic Higgs boson production in association with a vector boson differ from those predicted for the standard model Higgs boson. Upper limits at the 95% credibility level on the production rates of the exotic Higgs bosons, expressed as fractions of the standard model Higgs boson production rate, are set at 0.36 for both the J(P) = 0(-) hypothesis and the J(P) = 2(+) hypothesis. If the production rate times the branching ratio to a bottom-antibottom pair is the same as that predicted for the standard model Higgs boson, then the exotic bosons are excluded with significances of 5.0 standard deviations and 4.9 standard deviations for the J(P) = 0(-) and J(P) = 2(+) hypotheses, respectively.
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| 13. |
- Aaltonen, T., et al.
(författare)
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Tevatron Run II combination of the effective leptonic electroweak mixing angle
- 2018
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Ingår i: Physical Review D. - : AMER PHYSICAL SOC. - 2470-0010 .- 2470-0029. ; 97:11
-
Tidskriftsartikel (refereegranskat)abstract
- Drell-Yan lepton pairs produced in the process p (p) over bar -> l(+)l(-) + X through an intermediate gamma*/Z boson have an asymmetry in their angular distribution related to the spontaneous symmetry breaking of the electroweak force and the associated mixing of its neutral gauge bosons. The CDF and D0 experiments have measured the effective-leptonic electroweak mixing parameter sin(2) theta(lept)(eff) using electron and muon pairs selected from the full Tevatron proton-antiproton data sets collected in 2001-2011, corresponding to 9-10 fb(-1) of integrated luminosity. The combination of these measurements yields the most precise result from hadron colliders, sin(2)theta(lept)(eff) = 0.23148 +/- 0.00033. This result is consistent with, and approaches in precision, the best measurements from electron-positron colliders. The standard model inference of the on-shell electroweak mixing parameter sin(2) theta(W), or equivalently the W-boson mass M-W, using the ZFITTER software package yields sin(2) theta(W) = 0.22324 +/- 0.00033 or equivalently, M-W = 80.367 +/- 0.017 GeV/c(2).
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| 14. |
- Anderson, Dan, 1943, et al.
(författare)
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Interaction between two partially incoherent soliton stripes
- 2008
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Ingår i: Optics Communications. - : Elsevier BV. - 0030-4018. ; 281:14, s. 3919-3923
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Tidskriftsartikel (refereegranskat)abstract
- A detailed analysis is made of the mutual interaction of two, initially well separated, partially incoherent solitons in a nonlinear Kerr medium. Explicit expressions are obtained describing the influence of partial incoherence on the subsequent dynamics of the solitons. In particular it is shown that as the degree of incoherence increases, the character of the interaction may change between attractive and repulsive behavior (or vice versa). Furthermore, it is found that this dependence is not always monotonous. © 2008 Elsevier B.V. All rights reserved.
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| 15. |
- Anderson, Dan, 1943, et al.
(författare)
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Modulational instabilities of partially incoherent light
- 2004
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Ingår i: Proceedings of "Nonlinear Guided Waves and Their Applications", March 28-31 2004, Toronto, Canada. - 9781557528209 ; , s. paper TuC32-
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Konferensbidrag (refereegranskat)
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| 16. |
- Barucca, G., et al.
(författare)
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Study of excited Ξ baryons with the P¯ ANDA detector
- 2021
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Ingår i: European Physical Journal A. - : Springer Nature. - 1434-6001 .- 1434-601X. ; 57:4
-
Tidskriftsartikel (refereegranskat)abstract
- The study of baryon excitation spectra provides insight into the inner structure of baryons. So far, most of the world-wide efforts have been directed towards N∗ and Δ spectroscopy. Nevertheless, the study of the double and triple strange baryon spectrum provides independent information to the N∗ and Δ spectra. The future antiproton experiment P¯ANDA will provide direct access to final states containing a Ξ¯ Ξ pair, for which production cross sections up to μb are expected in p¯p reactions. With a luminosity of L= 10 31 cm- 2 s- 1 in the first phase of the experiment, the expected cross sections correspond to a production rate of ∼106events/day. With a nearly 4 π detector acceptance, P¯ANDA will thus be a hyperon factory. In this study, reactions of the type p¯p → Ξ¯ +Ξ∗ - as well as p¯p → Ξ¯ ∗ +Ξ- with various decay modes are investigated. For the exclusive reconstruction of the signal events a full decay tree fit is used, resulting in reconstruction efficiencies between 3 and 5%. This allows high statistics data to be collected within a few weeks of data taking.
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| 17. |
- Barucca, G., et al.
(författare)
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The potential of Λ and Ξ- studies with PANDA at FAIR
- 2021
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Ingår i: European Physical Journal A. - : Springer Nature. - 1434-6001 .- 1434-601X. ; 57:4
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Tidskriftsartikel (refereegranskat)abstract
- The antiproton experiment PANDA at FAIR is designed to bring hadron physics to a new level in terms of scope, precision and accuracy. In this work, its unique capability for studies of hyperons is outlined. We discuss ground-state hyperons as diagnostic tools to study non-perturbative aspects of the strong interaction, and fundamental symmetries. New simulation studies have been carried out for two benchmark hyperon-antihyperon production channels: p¯ p→ Λ¯ Λ and p¯ p→ Ξ¯ +Ξ-. The results, presented in detail in this paper, show that hyperon-antihyperon pairs from these reactions can be exclusively reconstructed with high efficiency and very low background contamination. In addition, the polarisation and spin correlations have been studied, exploiting the weak, self-analysing decay of hyperons and antihyperons. Two independent approaches to the finite efficiency have been applied and evaluated: one standard multidimensional efficiency correction approach, and one efficiency independent approach. The applicability of the latter was thoroughly evaluated for all channels, beam momenta and observables. The standard method yields good results in all cases, and shows that spin observables can be studied with high precision and accuracy already in the first phase of data taking with PANDA.
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| 18. |
- Buyanova, M., et al.
(författare)
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Influence of secondary emission yield on the saturation properties of multipactor discharges between two parallel metal plates
- 2010
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Ingår i: Physics of Plasmas. - : AIP Publishing. - 1089-7674 .- 1070-664X. ; 17:4, s. 043504 -
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Tidskriftsartikel (refereegranskat)abstract
- A detailed numerical simulation analysis is made of the saturation stage of multipactor discharges between two infinite parallel metal plates in vacuum exposed to a rf voltage. The main physical effect causing saturation of the multipactor discharge is increased space charge, as the electron density becomes large. It is found that the properties of the saturation stage depend crucially on the value of the secondary emission yield of the metal surfaces. Below a certain threshold value, the discharge has a two-sided character, but at this threshold the discharge makes an abrupt transition into two decoupled single-sided multipactor discharges containing significantly increased electron densities. The result of the numerical simulations gives a good picture of the saturation properties of the multipactor discharge and is also supplemented by an approximate analytical investigation that highlights and explains the characteristic properties of the observed saturation behavior.
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| 19. |
- Collaboration, The PANDA, et al.
(författare)
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Feasibility studies of time-like proton electromagnetic form factors at PANDA at FAIR
- 2016
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Ingår i: European Physical Journal A. - : Springer Publishing Company. - 1434-6001 .- 1434-601X. ; 52:10
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Tidskriftsartikel (refereegranskat)abstract
- Simulation results for future measurements of electromagnetic proton form factors at P ¯ ANDA (FAIR) within the PandaRoot software framework are reported. The statistical precision with which the proton form factors can be determined is estimated. The signal channel p¯ p→ e+e- is studied on the basis of two different but consistent procedures. The suppression of the main background channel, i.e.p¯ p→ π+π-, is studied. Furthermore, the background versus signal efficiency, statistical and systematical uncertainties on the extracted proton form factors are evaluated using two different procedures. The results are consistent with those of a previous simulation study using an older, simplified framework. However, a slightly better precision is achieved in the PandaRoot study in a large range of momentum transfer, assuming the nominal beam conditions and detector performance.
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| 20. |
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| 21. |
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| 22. |
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| 23. |
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| 24. |
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| 25. |
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| 26. |
- Kossyi, I.A., et al.
(författare)
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Electrical breakdown in space-borne microwave equipment
- 2010
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Ingår i: Europhysics News. - 1432-1092 .- 0531-7479. ; 41:6
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Tidskriftsartikel (refereegranskat)abstract
- An experimental and numerical investigation is made of multipactor discharges in a coaxial waveguide. Particular attention is given to the determination of the multipactor threshold and the distribution of the impact energy of the electrons. Simulations are carried out for different parameters of the secondary emission coefficient of the electrode surfaces. This makes it possible to determine these parameters through a comparison between the numerical and experimental results. The comparison also shows that the observed multipactor is mainly of polyphase (non-resonant) nature and represents a mixture of single- and double-surface multipactor discharges.
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| 27. |
- Kossyi, I.A., et al.
(författare)
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Experimental and numerical investigation of multipactor discharges in a coaxial waveguide
- 2010
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Ingår i: Journal of Physics D: Applied Physics. - : IOP Publishing. - 1361-6463 .- 0022-3727. ; 43:34
-
Tidskriftsartikel (refereegranskat)abstract
- An experimental and numerical investigation is made of multipactor discharges in a coaxial waveguide. Particular attention is given to the determination of the multipactor threshold and the distribution of the impact energy of the electrons. Simulations are carried out for different parameters of the secondary emission coefficient of the electrode surfaces. This makes it possible to determine these parameters through a comparison between the numerical and experimental results. The comparison also shows that the observed multipactor is mainly of polyphase (non-resonant) nature and represents a mixture of single- and double-surface multipactor discharges.
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| 28. |
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| 29. |
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| 30. |
- Kossyi, I.A., et al.
(författare)
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Polyphase (non-resonant) multipactor in rectangular waveguides
- 2008
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Ingår i: Journal of Physics D: Applied Physics. - : IOP Publishing. - 1361-6463 .- 0022-3727. ; 41:6, s. 065203 1-8
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Tidskriftsartikel (refereegranskat)abstract
- The polyphase multipactor, i.e. the non-resonant form of secondary electron emission rf discharges in vacuum, has been analysed and studied experimentally. The multipactor discharge was observed in an evacuated standard rectangular waveguide through which pulsed high-power microwave radiation in the decimeter wavelength range was transmitted. The power interval in which the two-sided (between the wide walls of the waveguide) multipactor appeared has been determined. It is found that there is a characteristic delay time for the onset of the multipactor breakdown as compared with the time at which the microwave power is applied. The dependence of this delay time on the microwave power has been established. The experimental results are compared with results of numerical simulations which make it possible to estimate the secondary emission properties of the waveguide walls. Reasons for some observed discrepancies between numerical results and experimental data are discussed as well as the nature of the observed multipactor delay.
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| 31. |
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| 32. |
- Mader, P., et al.
(författare)
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Experimental validation of fringing field effects for the multipactor phenomenon
- 2012
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Ingår i: 15th International Symposium on Antenna Technology and Applied Electromagnetics, ANTEM 2012, Toulouse, 25-28 June 2012. - 9781467302913
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Konferensbidrag (refereegranskat)abstract
- The multipactor effect is a constraining phenomenon in the design of RF components. Due to an increasing number of channels and power levels for multicarrier signals, specific requirements of design must be taken into account in order to prevent the multipactor effect. The current methods of analysis are based on the Hatch and Williams diagrams, which provide the multipaction threshold voltage for a parallel plate geometry as a function of the frequency gap product. However, whereas experimental results have shown good correlation with the theoretical charts for the parallel plate geometry, discrepancies have been found for complex geometries such as irises.
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| 33. |
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| 34. |
- Puech, J., et al.
(författare)
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CNES-Chalmers-IAP-ONERA-XLIM activities in the domain of high RF power breakdown phenomena
- 2017
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Ingår i: EPJ Web of Conferences. - : EDP Sciences. - 2101-6275 .- 2100-014X. ; 157
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Konferensbidrag (refereegranskat)abstract
- Multipactor breakdown is an important potential failure mechanism in many different microwave devices working under close to vacuum conditions. Applications range from space borne RF equipment to high-power microwave generators. The basic physics involved in the multipactor phenomenon is well known for the case of two infinite pallel plates made of metal. However, most realistic RF device geometries involve inhomogeneous RF electric fields and curved field lines and sometimes also dielectric material. The purpose of this paper is to set up methodologies to determine the Multipactor threshold in such situations.
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| 35. |
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| 36. |
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| 37. |
- Puech, J., et al.
(författare)
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Summary of Research Activities on Multipactor phenomenon with dielectric materials within INTAS project
- 2005
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Ingår i: Proc. 5th International Workshop on Multipactor, Corona and Passive Intermodulation, September 12 – 14, 2005, ESTEC, Noordwijk, The Netherlands, In: Space RF Hardware (MULCOPIM' 2005). ; , s. 161-167
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Konferensbidrag (refereegranskat)
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| 38. |
- Rasch, Joel, 1982, et al.
(författare)
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Gas breakdown in inhomogenous microwave electric fields
- 2009
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Ingår i: Journal of Physics D: Applied Physics. - 1361-6463 .- 0022-3727. ; 42:20, s. 205203-
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Tidskriftsartikel (refereegranskat)abstract
- The main physical properties of gas breakdown in inhomogeneous high frequency microwave electric fields are investigated using both analytical and numerical analysis. In particular, the interplay between diffusion and attachment in redistributing electrons from high field regions to low field regions and the concomitant effect on the breakdown threshold is studied using three different examples of ionization profiles. The results give a clear physical picture of the dependence of breakdown electric field on pressure showing a high pressure branch determined by conditions in the high field region, a low pressure branch determined by the properties of the low field region only, and a more or less smooth transition region for intermediate pressures. Simple estimates for the extension of the transition region are given in good agreement with the numerical simulations, and a comparison of the theoretical breakdown threshold with previous experimental results also shows good agreement.
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| 39. |
- Rasch, Joel, 1982, et al.
(författare)
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Microwave breakdown due to heating of an irradiated metal sphere
- 2012
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Ingår i: 39th EPS Conference on Plasma Physics 2012, EPS 2012 and the 16th International Congress on Plasma Physics; Stockholm; Sweden; 2 July 2012 through 6 July 2012; Code 96757. - 9781622769810 ; 3, s. 1907-1910
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Konferensbidrag (refereegranskat)
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| 40. |
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| 41. |
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| 42. |
- Rasch, Joel, 1982, et al.
(författare)
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Microwave Corona Breakdown in rf Devices
- 2009
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Ingår i: Progress in Electromagnetics Research Symposium (PIERS), August 18-21, 2009, Moscow, Russia, PIERS Proceedings, Moscow Russia, The Electromagnetics Academy, Cambridge, MA, USA. ; , s. 1228-1231
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Konferensbidrag (refereegranskat)
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| 43. |
- Rasch, Joel, 1982, et al.
(författare)
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Microwave Corona Breakdown in Strongly Inhomogeneous Fields
- 2009
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Ingår i: 36th European Physical Society Conference on Plasma Physics 2009, EPS 2009; Sofia; Bulgaria; 29 June 2009 through 3 July 2009. - 9781622763368 ; 33E, s. 657-660
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Konferensbidrag (refereegranskat)abstract
- We investigate the main physical properties of microwave corona breakdown in strongly inhomogeneous electric fields. The focus is put on numerical and approximate analytical calculations of the breakdown threshold in an exponential ionization profile, which is the basic form of the ionization profile caused by the field enhancement around irregular and curved conducting objects. The breakdown threshold is a value associated with a certain plasma density profile. We explain the major characteristics of the density profile, its dependance on pressure and the interplay of diffusion and attachment. For lower pressures the diffusion distributes the electrons from regions of high ionization frequency to regions of weak ionization, where the attachment acts as a sink. For high pressures the diffusion becomes negligible and the breakdown threshold is set by the equality of the ionization and attachment frequencies in the high field region.
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| 44. |
- Rasch, Joel, 1982, et al.
(författare)
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Microwave multipactor breakdown between two cylinders
- 2010
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Ingår i: IEEE Transactions on Plasma Science. - 0093-3813 .- 1939-9375. ; 38:8, s. 1997 - 2005
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Tidskriftsartikel (refereegranskat)abstract
- An analysis has been made of the microwave breakdownthreshold for multipactor in an open structure comprisingtwo parallel cylinders, approximating, e.g., parts of a helix antenna. The electron motion in the corresponding electromagnetic field is analyzed by separating the motion into a slowly varying drift velocity (driven by the ponderomotive force due to the electric field inhomogeneity) and a rapidly oscillating part (driven bythe oscillating electric field). Furthermore, the curvature of the cylindrical surfaces of emission is shown to give rise to a new effect that implies a loss of electrons. This leads to a more stringent multipactor breakdown condition for the two-wire structure thanfor the classical situation corresponding to the case of two plane parallel infinite plates. The importance of this effect is determined by the ratio of the cylinder radii and the distance between the cylinders, and it is shown that when this ratio is small, multipactor can only occur for surfaces having very large secondary emissioncoefficients. A detailed analysis is also made to determine the lowest voltage between the cylinders at which multipactor becomes possible.
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| 45. |
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| 46. |
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| 47. |
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| 48. |
- Rasch, Joel, 1982, et al.
(författare)
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Multipactor breakdown in microwave pulses
- 2013
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Ingår i: Journal of Physics D: Applied Physics. - : IOP Publishing. - 1361-6463 .- 0022-3727. ; 46:50
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Tidskriftsartikel (refereegranskat)abstract
- A theoretical investigation is made of the effect of finite pulse length on the multipactor breakdown condition for microwave signals. The analysis considers the case of multipactor between two parallel metallic plates, using the classical resonance theory. It is found that decreasing pulse length tends to successively eliminate higher order resonance zones and lead to a 'pulse hardening' of lower order modes where the multipactor-prone resonance zones shrink and the lower boundary breakdown field of the zones smoothly increases as the pulse becomes shorter, eventually to completely eliminate the multipactor effect for sufficiently short pulses.
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| 49. |
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| 50. |
- Rasch, Joel, 1982, et al.
(författare)
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On the microwave breakdown stability of a spherical hot spot in air
- 2010
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Ingår i: Journal of Physics D: Applied Physics. - : IOP Publishing. - 1361-6463 .- 0022-3727. ; 43:32
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Tidskriftsartikel (refereegranskat)abstract
- An analysis is made of the basic physical conditions under which a small local microwave-induced breakdown region in a gas may develop to extended 'global' breakdown. The analysis describes the different nonlinear stages of the microwave breakdown process. In the first stage, the increasing breakdown plasma density suppresses the electric field in the breakdown region to reach a quasi-stationary state with constant electron density. The subsequent heating of the gas due to absorption of microwave power in the breakdown plasma is then analysed and the corresponding steady state for the thermal evolution is found including the temperature dependence of the breakdown electric field. The stability properties of the stationary state are examined and it is found that there exists a critical (unstable) radius of the initial breakdown plasma region such that initial regions smaller than this critical dimension will shrink to ultimately vanish whereas plasma regions larger than the critical dimension will grow indefinitely and transform the local breakdown region into full scale 'global' breakdown. The practical implication of this model is to give an order of magnitude estimate for the critical size of hot spots, regions of enhanced field and intensified heating in rf systems.
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