The Experts below are selected from a list of 219624 Experts worldwide ranked by ideXlab platform
A M Sirunyan - One of the best experts on this subject based on the ideXlab platform.
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search for top squark pair production using dilepton final states in pp collision data collected at sqrt s 13 tev
European Physical Journal C, 2021Co-Authors: A M Sirunyan, Robin Erbacher, C Carrillo A Montoya, Wagner Carvalho, Maciej Gorski, Danek Kotlinski, C Lindsey, S Muthumuni, A Polatoz, Shaaban KhalilAbstract:A search is presented for supersymmetric partners of the top quark (top sQuarks) in final states with two oppositely charged leptons (electrons or muons), jets identified as originating from $${\text {b}}$$ Quarks, and missing transverse momentum. The search uses data from proton-proton collisions at $$\sqrt{s}=13\,\text {TeV} $$ collected with the CMS detector, corresponding to an integrated luminosity of 137 $$\,{\text {fb}}^{-1}$$ . Hypothetical signal events are efficiently separated from the dominant top quark pair production background with requirements on the significance of the missing transverse momentum and on transverse mass variables. No significant deviation is observed from the expected background. Exclusion limits are set in the context of simplified supersymmetric models with pair-produced lightest top sQuarks. For top sQuarks decaying exclusively to a top quark and a lightest neutralino, lower limits are placed at $$95\%$$ confidence level on the masses of the top squark and the neutralino up to 925 and 450 $$\,\text {GeV}$$ , respectively. If the decay proceeds via an intermediate chargino, the corresponding lower limits on the mass of the lightest top squark are set up to 850 $$\,\text {GeV}$$ for neutralino masses below 420 $$\,\text {GeV}$$ . For top sQuarks undergoing a cascade decay through charginos and sleptons, the mass limits reach up to 1.4 $$\,\text {TeV}$$ and 900 $$\,\text {GeV}$$ respectively for the top squark and the lightest neutralino.
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search for top squark pair production using dilepton final states in pp collision data collected at s 13tev
European Physical Journal C, 2021Co-Authors: A M Sirunyan, A Tumasyan, T Bergauer, M Dragicevic, J Ero, R Fruhwirth, F Ambrogi, Wolfgang Adam, Escalante A Del Valle, M JeitlerAbstract:A search is presented for supersymmetric partners of the top quark (top sQuarks) in final states with two oppositely charged leptons (electrons or muons), jets identified as originating from b Quarks, and missing transverse momentum. The search uses data from proton-proton collisions at s=13TeV collected with the CMS detector, corresponding to an integrated luminosity of 137 fb-1 . Hypothetical signal events are efficiently separated from the dominant top quark pair production background with requirements on the significance of the missing transverse momentum and on transverse mass variables. No significant deviation is observed from the expected background. Exclusion limits are set in the context of simplified supersymmetric models with pair-produced lightest top sQuarks. For top sQuarks decaying exclusively to a top quark and a lightest neutralino, lower limits are placed at 95% confidence level on the masses of the top squark and the neutralino up to 925 and 450 GeV , respectively. If the decay proceeds via an intermediate chargino, the corresponding lower limits on the mass of the lightest top squark are set up to 850 GeV for neutralino masses below 420 GeV . For top sQuarks undergoing a cascade decay through charginos and sleptons, the mass limits reach up to 1.4 TeV and 900 GeV respectively for the top squark and the lightest neutralino.
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search for the flavor changing neutral current interactions of the top quark and the higgs boson which decays into a pair of b Quarks at s 13 tev
Journal of High Energy Physics, 2018Co-Authors: A M Sirunyan, Robin Erbacher, C Carrillo A Montoya, Wagner Carvalho, S Muthumuni, B Ujvari, M Gorski, D Kotlinski, Richard Lander, N SmithAbstract:A search for flavor-changing neutral currents (FCNC) in events with the top quark and the Higgs boson is presented. The Higgs boson decay to a pair of b Quarks is considered. The data sample corresponds to an integrated luminosity of 35.9 fb−1 recorded by the CMS experiment at the LHC in proton-proton collisions at s√=13 TeV. Two channels are considered: single top quark FCNC production in association with the Higgs boson (pp → tH), and top quark pair production with FCNC decay of the top quark (t → qH). Final states with one isolated lepton and at least three reconstructed jets, among which at least two are associated with b Quarks, are studied. No significant deviation is observed from the predicted background. Observed (expected) upper limits at 95% confidence level are set on the branching fractions of top quark decays, ℬ(t → uH) < 0.47% (0.34%) and ℬ(t → cH) < 0.47% (0.44%), assuming a single nonzero FCNC coupling.
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search for physics beyond the standard model in events with two leptons of same sign missing transverse momentum and jets in proton proton collisions at s 13tev
European Physical Journal C, 2017Co-Authors: A M Sirunyan, A Tumasyan, W Adam, T Bergauer, M Dragicevic, F Ambrogi, E Asilar, J Brandstetter, E Brondolin, J EroAbstract:A data sample of events from proton-proton collisions with two isolated same-sign leptons, missing transverse momentum, and jets is studied in a search for signatures of new physics phenomena by the CMS Collaboration at the LHC. The data correspond to an integrated luminosity of 35.9 inverse femtobarns, and a center-of-mass energy of 13 TeV. The properties of the events are consistent with expectations from standard model processes, and no excess yield is observed. Exclusion limits at 95% confidence level are set on cross sections for the pair production of gluinos, sQuarks, and same-sign top Quarks, as well as top-quark associated production of a heavy scalar or pseudoscalar boson decaying to top Quarks, and on the standard model production of events with four top Quarks. The observed lower mass limits are as high as 1500 GeV for gluinos, 830 GeV for bottom sQuarks. The excluded mass range for heavy (pseudo)scalar bosons is 350-360 (350-410) GeV. Additionally, model-independent limits in several topological regions are provided, allowing for further interpretations of the results.
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search for pair production of third generation scalar leptoQuarks and top sQuarks in proton proton collisions at s 8 tev
Physics Letters B, 2014Co-Authors: V Khachatryan, A M Sirunyan, A Tumasyan, W Adam, T Bergauer, M Dragicevic, C Fabjan, M Friedl, J Ero, R FruhwirthAbstract:A search for pair production of third-generation scalar leptoQuarks and supersymmetric top quark partners, top sQuarks, in final states involving tau leptons and bottom Quarks is presented. The search uses events from a data sample of proton-proton collisions corresponding to an integrated luminosity of 19.7 inverse femtobarns, collected with the CMS detector at the LHC with sqrt(s) = 8 TeV. The number of observed events is found to be in agreement with the expected standard model background. Third-generation scalar leptoQuarks with masses below 740 GeV are excluded at 95% confidence level, assuming a 100% branching fraction for the leptoquark decay to a tau lepton and a bottom quark. In addition, this mass limit applies directly to top sQuarks decaying via an R-parity violating coupling lambda'[333]. The search also considers a similar signature from top sQuarks undergoing a chargino-mediated decay involving the R-parity violating coupling lambda'[3jk]. Each top squark decays to a tau lepton, a bottom quark, and two light Quarks. Top sQuarks in this model with masses below 580 GeV are excluded at 95% confidence level. The constraint on the leptoquark mass is the most stringent to date, and this is the first search for top sQuarks decaying via lambda'[3jk].
Shuai Y F Liu - One of the best experts on this subject based on the ideXlab platform.
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spin polarizations in a covariant angular momentum conserved chiral transport model
Physical Review Letters, 2020Co-Authors: Shuai Y F Liu, Yifeng SunAbstract:Using a covariant and angular-momentum-conserved chiral transport model, which takes into account the spin-orbit interactions of chiral fermions in their scatterings via the side jumps, we study the quark spin polarization in quark matter. For a system of rotating and unpolarized massless Quarks in an expanding box, we find that side jumps can dynamically polarize the quark spin and result in a final quark spin polarization consistent with that of thermally equilibrated massless Quarks in a self-consistent vorticity field. For the quark matter produced in noncentral relativistic heavy ion collisions, we find that in the medium rest frame both the quark local spin polarizations in the direction perpendicular to the reaction plane and along the longitudinal beam direction show an azimuthal angle dependence in the transverse plane similar to those observed in experiments for the Lambda hyperon.
Moritz Preisser - One of the best experts on this subject based on the ideXlab platform.
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on the light massive flavor dependence of the large order asymptotic behavior and the ambiguity of the pole mass
Journal of High Energy Physics, 2017Co-Authors: Andre H Hoang, Christopher Lepenik, Moritz PreisserAbstract:We provide a systematic renormalization group formalism for the mass effects in the relation of the pole mass m pole and short-distance masses such as the $$ \overline{\mathrm{MS}} $$ mass $$ {\overline{m}}_Q $$ of a heavy quark Q, coming from virtual loop insertions of massive Quarks lighter than Q. The formalism reflects the constraints from heavy quark symmetry and entails a combined matching and evolution procedure that allows to disentangle and successively integrate out the corrections coming from the lighter massive Quarks and the momentum regions between them and to precisely control the large order asymptotic behavior. With the formalism we systematically sum logarithms of ratios of the lighter quark masses and m Q , relate the QCD corrections for different external heavy Quarks to each other, predict the $$ \mathcal{O}\left({\alpha}_s^4\right) $$ virtual quark mass corrections in the pole- $$ \overline{\mathrm{MS}} $$ mass relation, calculate the pole mass differences for the top, bottom and charm Quarks with a precision of around 20 MeV and analyze the decoupling of the lighter massive quark flavors at large orders. The summation of logarithms is most relevant for the top quark pole mass m pole , where the hierarchy to the bottom and charm Quarks is large. We determine the ambiguity of the pole mass for top, bottom and charm Quarks in different scenarios with massive or massless bottom and charm Quarks in a way consistent with heavy quark symmetry, and we find that it is 250 MeV. The ambiguity is larger than current projections for the precision of top quark mass measurements in the high-luminosity phase of the LHC.
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on the light massive flavor dependence of the large order asymptotic behavior and the ambiguity of the pole mass
arXiv: High Energy Physics - Phenomenology, 2017Co-Authors: Andre H Hoang, Christopher Lepenik, Moritz PreisserAbstract:We provide a systematic renormalization group formalism for the mass effects in the relation of the pole mass $m_Q^{\rm pole}$ and short-distance masses such as the $\overline{\rm MS}$ mass $\overline{m}_Q$ of a heavy quark $Q$, coming from virtual loop insertions of massive Quarks lighter than $Q$. The formalism reflects the constraints from heavy quark symmetry and entails a combined matching and evolution procedure that allows to disentangle and successively integrate out the corrections coming from the lighter massive Quarks and the momentum regions between them and to precisely control the large order asymptotic behavior. With the formalism we systematically sum logarithms of ratios of the lighter quark masses and $m_Q$, relate the QCD corrections for different external heavy Quarks to each other, predict the ${\cal O}(\alpha_s^4)$ virtual quark mass corrections in the pole-$\overline{\rm MS}$ mass relation, calculate the pole mass differences for the top, bottom and charm Quarks with a precision of around $20$ MeV and analyze the decoupling of the lighter massive quark flavors at large orders. The summation of logarithms is most relevant for the top quark pole mass $m_t^{\rm pole}$, where the hierarchy to the bottom and charm Quarks is large. We determine the ambiguity of the pole mass for top, bottom and charm Quarks in different scenarios with massive or massless bottom and charm Quarks in a way consistent with heavy quark symmetry, and we find that it is $250$ MeV. The ambiguity is larger than current projections for the precision of top quark mass measurements in the high-luminosity phase of the LHC.
Yifeng Sun - One of the best experts on this subject based on the ideXlab platform.
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spin polarizations in a covariant angular momentum conserved chiral transport model
Physical Review Letters, 2020Co-Authors: Shuai Y F Liu, Yifeng SunAbstract:Using a covariant and angular-momentum-conserved chiral transport model, which takes into account the spin-orbit interactions of chiral fermions in their scatterings via the side jumps, we study the quark spin polarization in quark matter. For a system of rotating and unpolarized massless Quarks in an expanding box, we find that side jumps can dynamically polarize the quark spin and result in a final quark spin polarization consistent with that of thermally equilibrated massless Quarks in a self-consistent vorticity field. For the quark matter produced in noncentral relativistic heavy ion collisions, we find that in the medium rest frame both the quark local spin polarizations in the direction perpendicular to the reaction plane and along the longitudinal beam direction show an azimuthal angle dependence in the transverse plane similar to those observed in experiments for the Lambda hyperon.
J Ero - One of the best experts on this subject based on the ideXlab platform.
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search for top squark pair production using dilepton final states in pp collision data collected at s 13tev
European Physical Journal C, 2021Co-Authors: A M Sirunyan, A Tumasyan, T Bergauer, M Dragicevic, J Ero, R Fruhwirth, F Ambrogi, Wolfgang Adam, Escalante A Del Valle, M JeitlerAbstract:A search is presented for supersymmetric partners of the top quark (top sQuarks) in final states with two oppositely charged leptons (electrons or muons), jets identified as originating from b Quarks, and missing transverse momentum. The search uses data from proton-proton collisions at s=13TeV collected with the CMS detector, corresponding to an integrated luminosity of 137 fb-1 . Hypothetical signal events are efficiently separated from the dominant top quark pair production background with requirements on the significance of the missing transverse momentum and on transverse mass variables. No significant deviation is observed from the expected background. Exclusion limits are set in the context of simplified supersymmetric models with pair-produced lightest top sQuarks. For top sQuarks decaying exclusively to a top quark and a lightest neutralino, lower limits are placed at 95% confidence level on the masses of the top squark and the neutralino up to 925 and 450 GeV , respectively. If the decay proceeds via an intermediate chargino, the corresponding lower limits on the mass of the lightest top squark are set up to 850 GeV for neutralino masses below 420 GeV . For top sQuarks undergoing a cascade decay through charginos and sleptons, the mass limits reach up to 1.4 TeV and 900 GeV respectively for the top squark and the lightest neutralino.
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search for physics beyond the standard model in events with two leptons of same sign missing transverse momentum and jets in proton proton collisions at s 13tev
European Physical Journal C, 2017Co-Authors: A M Sirunyan, A Tumasyan, W Adam, T Bergauer, M Dragicevic, F Ambrogi, E Asilar, J Brandstetter, E Brondolin, J EroAbstract:A data sample of events from proton-proton collisions with two isolated same-sign leptons, missing transverse momentum, and jets is studied in a search for signatures of new physics phenomena by the CMS Collaboration at the LHC. The data correspond to an integrated luminosity of 35.9 inverse femtobarns, and a center-of-mass energy of 13 TeV. The properties of the events are consistent with expectations from standard model processes, and no excess yield is observed. Exclusion limits at 95% confidence level are set on cross sections for the pair production of gluinos, sQuarks, and same-sign top Quarks, as well as top-quark associated production of a heavy scalar or pseudoscalar boson decaying to top Quarks, and on the standard model production of events with four top Quarks. The observed lower mass limits are as high as 1500 GeV for gluinos, 830 GeV for bottom sQuarks. The excluded mass range for heavy (pseudo)scalar bosons is 350-360 (350-410) GeV. Additionally, model-independent limits in several topological regions are provided, allowing for further interpretations of the results.
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search for pair production of third generation scalar leptoQuarks and top sQuarks in proton proton collisions at s 8 tev
Physics Letters B, 2014Co-Authors: V Khachatryan, A M Sirunyan, A Tumasyan, W Adam, T Bergauer, M Dragicevic, C Fabjan, M Friedl, J Ero, R FruhwirthAbstract:A search for pair production of third-generation scalar leptoQuarks and supersymmetric top quark partners, top sQuarks, in final states involving tau leptons and bottom Quarks is presented. The search uses events from a data sample of proton-proton collisions corresponding to an integrated luminosity of 19.7 inverse femtobarns, collected with the CMS detector at the LHC with sqrt(s) = 8 TeV. The number of observed events is found to be in agreement with the expected standard model background. Third-generation scalar leptoQuarks with masses below 740 GeV are excluded at 95% confidence level, assuming a 100% branching fraction for the leptoquark decay to a tau lepton and a bottom quark. In addition, this mass limit applies directly to top sQuarks decaying via an R-parity violating coupling lambda'[333]. The search also considers a similar signature from top sQuarks undergoing a chargino-mediated decay involving the R-parity violating coupling lambda'[3jk]. Each top squark decays to a tau lepton, a bottom quark, and two light Quarks. Top sQuarks in this model with masses below 580 GeV are excluded at 95% confidence level. The constraint on the leptoquark mass is the most stringent to date, and this is the first search for top sQuarks decaying via lambda'[3jk].
