The Experts below are selected from a list of 360 Experts worldwide ranked by ideXlab platform
A I Milstein - One of the best experts on this subject based on the ideXlab platform.
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electron positron Pair Production in ion collisions at low velocity beyond born approximation
Physics Letters B, 2016Co-Authors: R N Lee, A I MilsteinAbstract:Abstract We derive the spectrum and the total cross section of electromagnetic e + e − Pair Production in the collisions of two nuclei at low relative velocity β . Both free–free and bound-free e + e − Pair Production is considered. The parameters η A , B = Z A , B α are assumed to be small compared to unity but arbitrary compared to β ( Z A , B are the charge numbers of the nuclei and α is the fine structure constant). Due to a suppression of the Born term by high power of β , the first Coulomb correction to the amplitude appears to be important at η A , B ≳ β . The effect of a finite nuclear mass is discussed. In contrast to the result obtained in the infinite nuclear mass limit, the terms ∝ M − 2 are not suppressed by the high power of β and may easily dominate at sufficiently small velocities.
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strong suppression of coulomb corrections to the e e Pair Production cross section in ultrarelativistic nuclear collisions
Journal of Experimental and Theoretical Physics, 2009Co-Authors: R N Lee, A I MilsteinAbstract:The Coulomb corrections to the e+e− Pair Production cross section in ultrarelativistic nuclear collisions are calculated in the next-to-leading approximation with respect to the parameter L = lnγAγB, where γA, B are the Lorentz factors of colliding nuclei. We find considerable reduction of the Coulomb corrections even for large γAγB due to the suppression of the e+e− Pair Production with the total energy of the order of a few electron masses in the rest frame of one of the nuclei. Our result explains why the deviation from the Born result was not observed in the SPS experiment [1, 2].
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structure of the coulomb and unitarity corrections to the cross section of e e Pair Production in ultrarelativistic nuclear collisions
Physical Review A, 2002Co-Authors: R N Lee, A I Milstein, V G SerboAbstract:We analyze the structure of the Coulomb and unitarity corrections to the single e + e - Pair Production, as well as the cross section σ n for the multiple Pair Production in collision of ultra-relativistic nuclei. In the external field approximation, we consider the probability of one Pair Production at a fixed impact parameter p between colliding nuclei. We obtain the analytical result for this probability at large p as compared to the electron Compton wavelength. The energy dependence of this probability, as well as that of σ n , differ essentially from widely cited but incorrect results. We estimate also the unitary corrections to the total cross section of the process.
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coulomb corrections to thee e Pair Production in ultrarelativistic heavy ion collisions
Physical Review A, 2000Co-Authors: R N Lee, A I MilsteinAbstract:We manifest the origin of the wrong conclusion made by several groups of authors on the absence of Coulomb corrections to the cross section of the e + e − Pair Production in ultrarelativistic heavy-ion collisions. The source of the mistake is connected with an incorrect passage to the limit in the expression for the cross section. When this error is eliminated, the Coulomb corrections do not vanish and agree with the results
R N Lee - One of the best experts on this subject based on the ideXlab platform.
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electron positron Pair Production in ion collisions at low velocity beyond born approximation
Physics Letters B, 2016Co-Authors: R N Lee, A I MilsteinAbstract:Abstract We derive the spectrum and the total cross section of electromagnetic e + e − Pair Production in the collisions of two nuclei at low relative velocity β . Both free–free and bound-free e + e − Pair Production is considered. The parameters η A , B = Z A , B α are assumed to be small compared to unity but arbitrary compared to β ( Z A , B are the charge numbers of the nuclei and α is the fine structure constant). Due to a suppression of the Born term by high power of β , the first Coulomb correction to the amplitude appears to be important at η A , B ≳ β . The effect of a finite nuclear mass is discussed. In contrast to the result obtained in the infinite nuclear mass limit, the terms ∝ M − 2 are not suppressed by the high power of β and may easily dominate at sufficiently small velocities.
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strong suppression of coulomb corrections to the e e Pair Production cross section in ultrarelativistic nuclear collisions
Journal of Experimental and Theoretical Physics, 2009Co-Authors: R N Lee, A I MilsteinAbstract:The Coulomb corrections to the e+e− Pair Production cross section in ultrarelativistic nuclear collisions are calculated in the next-to-leading approximation with respect to the parameter L = lnγAγB, where γA, B are the Lorentz factors of colliding nuclei. We find considerable reduction of the Coulomb corrections even for large γAγB due to the suppression of the e+e− Pair Production with the total energy of the order of a few electron masses in the rest frame of one of the nuclei. Our result explains why the deviation from the Born result was not observed in the SPS experiment [1, 2].
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structure of the coulomb and unitarity corrections to the cross section of e e Pair Production in ultrarelativistic nuclear collisions
Physical Review A, 2002Co-Authors: R N Lee, A I Milstein, V G SerboAbstract:We analyze the structure of the Coulomb and unitarity corrections to the single e + e - Pair Production, as well as the cross section σ n for the multiple Pair Production in collision of ultra-relativistic nuclei. In the external field approximation, we consider the probability of one Pair Production at a fixed impact parameter p between colliding nuclei. We obtain the analytical result for this probability at large p as compared to the electron Compton wavelength. The energy dependence of this probability, as well as that of σ n , differ essentially from widely cited but incorrect results. We estimate also the unitary corrections to the total cross section of the process.
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coulomb corrections to thee e Pair Production in ultrarelativistic heavy ion collisions
Physical Review A, 2000Co-Authors: R N Lee, A I MilsteinAbstract:We manifest the origin of the wrong conclusion made by several groups of authors on the absence of Coulomb corrections to the cross section of the e + e − Pair Production in ultrarelativistic heavy-ion collisions. The source of the mistake is connected with an incorrect passage to the limit in the expression for the cross section. When this error is eliminated, the Coulomb corrections do not vanish and agree with the results
M Dragicevic - One of the best experts on this subject based on the ideXlab platform.
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study of the underlying event in top quark Pair Production in pp collisions at 13 tev
European Physical Journal C, 2019Co-Authors: A M Sirunyan, A Tumasyan, W Adam, T Bergauer, M Dragicevic, F Ambrogi, E Asilar, J Brandstetter, E Brondolin, J EroAbstract:Measurements of normalized differential cross sections as functions of the multiplicity and kinematic variables of charged-particle tracks from the underlying event in top quark and antiquark Pair Production are presented. The measurements are performed in proton-proton collisions at a center-of-mass energy of 13 Te , and are based on data collected by the CMS experiment at the LHC in 2016 corresponding to an integrated luminosity of 35.9 fb-1 . Events containing one electron, one muon, and two jets from the hadronization and fragmentation of b quarks are used. These measurements characterize, for the first time, properties of the underlying event in top quark Pair Production and show no deviation from the universality hypothesis at energy scales typically above twice the top quark mass.
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search for top squark Pair Production in pp collisions at sqrt s 13 tev using single lepton events
Journal of High Energy Physics, 2017Co-Authors: A M Sirunyan, A Tumasyan, W Adam, T Bergauer, M Dragicevic, F Ambrogi, E Asilar, J Brandstetter, E Brondolin, J EroAbstract:A search for top squark Pair Production in pp collisions at root s = 13 TeV is performed using events with a single isolated electron or muon, jets, and a large transverse momentum imbalance. The results are based on data collected in 2016 with the CMS detector at the LHC, corresponding to an integrated luminosity of 35.9 fb(-1). No significant excess of events is observed above the expectation from standard model processes. Exclusion limits are set in the context of supersymmetric models of Pair Production of top squarks that decay either to a top quark and a neutralino or to a bottom quark and a chargino. Depending on the details of the model, we exclude top squarks with masses as high as 1120 GeV. Detailed information is also provided to facilitate theoretical interpretations in other scenarios of physics beyond the standard model.
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search for Pair Production of first and second generation leptoquarks in proton proton collisions at s 8 tev
Physical Review D, 2016Co-Authors: V Khachatryan, A Tumasyan, W Adam, T Bergauer, M Dragicevic, E Asilar, J Brandstetter, E Brondolin, Albert M Sirunyan, J EroeAbstract:A search for Pair Production of first and second generation leptoquarks is performed in final states containing either two charged leptons and two jets, or one charged lepton, one neutrino and two jets, using proton-proton collision data at √s = 8 TeV. The data, corresponding to an integrated luminosity of 19.7 fb^(−1), were recorded with the CMS detector at the LHC. First-generation scalar leptoquarks with masses less than 1010 (850) GeV are excluded for β=1.0 (0.5), where β is the branching fraction of a leptoquark decaying to a charged lepton and a quark. Similarly, second-generation scalar leptoquarks with masses less than 1080 (760) GeV are excluded for β=1.0 (0.5). Mass limits are also set for vector leptoquark Production scenarios with anomalous vector couplings, and for R-parity violating supersymmetric scenarios of top squark Pair Production resulting in similar final-state signatures. These are the most stringent limits placed on the masses of vector leptoquarks and RPV top squarks to date.
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a search for Pair Production of new light bosons decaying into muons
Physics Letters B, 2016Co-Authors: V Khachatryan, A Tumasyan, W Adam, T Bergauer, M Dragicevic, E Asilar, J Brandstetter, E Brondolin, Albert M Sirunyan, M FlechlAbstract:A search for the Pair Production of new light bosons, each decaying into a Pair of muons, is performed with the CMS experiment at the LHC, using a dataset corresponding to an integrated luminosity of 20.7 inverse femtobarns collected in proton-proton collisions at center-of-mass energy of sqrt(s) = 8 TeV. No excess is observed in the data relative to standard model background expectation and a model independent upper limit on the product of the cross section, branching fraction, and acceptance is derived. The results are compared with two benchmark models, the first one in the context of the next-to-minimal supersymmetric standard model, and the second one in scenarios containing a hidden sector, including those predicting a nonnegligible light boson lifetime.
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measurement of prompt j ψ Pair Production in pp collisions at s 7 tev
Journal of High Energy Physics, 2014Co-Authors: V Khachatryan, A M Sirunyan, A Tumasyan, W Adam, T Bergauer, M Dragicevic, J Ero, C Fabjan, M FriedlAbstract:Production of prompt J/psi meson Pairs in proton-proton collisions at sqrt(s)=7 TeV is measured with the CMS experiment at the LHC in a data sample corresponding to an integrated luminosity of about 4.7 inverse femtobarns. The two J/psi mesons are fully reconstructed via their decays into muon Pairs. This observation provides for the first time access to the high-transverse-momentum region of J/psi Pair Production where model predictions are not yet established. The total and differential cross sections are measured in a phase space defined by the individual J/psi transverse momentum pt[J/psi] and rapidity abs(y[J/psi]): abs(y[J/psi]) 6.5 GeV; 1.2 4.5 GeV. The total cross section, assuming unpolarized prompt J/psi Pair Production is 1.49 +/- 0.07 (stat.) +/- 0.13 (syst.) nb. Different assumptions about the J/psi polarization imply modifications to the cross section ranging from -31% to +27%.
T Bergauer - One of the best experts on this subject based on the ideXlab platform.
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study of the underlying event in top quark Pair Production in pp collisions at 13 tev
European Physical Journal C, 2019Co-Authors: A M Sirunyan, A Tumasyan, W Adam, T Bergauer, M Dragicevic, F Ambrogi, E Asilar, J Brandstetter, E Brondolin, J EroAbstract:Measurements of normalized differential cross sections as functions of the multiplicity and kinematic variables of charged-particle tracks from the underlying event in top quark and antiquark Pair Production are presented. The measurements are performed in proton-proton collisions at a center-of-mass energy of 13 Te , and are based on data collected by the CMS experiment at the LHC in 2016 corresponding to an integrated luminosity of 35.9 fb-1 . Events containing one electron, one muon, and two jets from the hadronization and fragmentation of b quarks are used. These measurements characterize, for the first time, properties of the underlying event in top quark Pair Production and show no deviation from the universality hypothesis at energy scales typically above twice the top quark mass.
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search for top squark Pair Production in pp collisions at sqrt s 13 tev using single lepton events
Journal of High Energy Physics, 2017Co-Authors: A M Sirunyan, A Tumasyan, W Adam, T Bergauer, M Dragicevic, F Ambrogi, E Asilar, J Brandstetter, E Brondolin, J EroAbstract:A search for top squark Pair Production in pp collisions at root s = 13 TeV is performed using events with a single isolated electron or muon, jets, and a large transverse momentum imbalance. The results are based on data collected in 2016 with the CMS detector at the LHC, corresponding to an integrated luminosity of 35.9 fb(-1). No significant excess of events is observed above the expectation from standard model processes. Exclusion limits are set in the context of supersymmetric models of Pair Production of top squarks that decay either to a top quark and a neutralino or to a bottom quark and a chargino. Depending on the details of the model, we exclude top squarks with masses as high as 1120 GeV. Detailed information is also provided to facilitate theoretical interpretations in other scenarios of physics beyond the standard model.
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search for Pair Production of first and second generation leptoquarks in proton proton collisions at s 8 tev
Physical Review D, 2016Co-Authors: V Khachatryan, A Tumasyan, W Adam, T Bergauer, M Dragicevic, E Asilar, J Brandstetter, E Brondolin, Albert M Sirunyan, J EroeAbstract:A search for Pair Production of first and second generation leptoquarks is performed in final states containing either two charged leptons and two jets, or one charged lepton, one neutrino and two jets, using proton-proton collision data at √s = 8 TeV. The data, corresponding to an integrated luminosity of 19.7 fb^(−1), were recorded with the CMS detector at the LHC. First-generation scalar leptoquarks with masses less than 1010 (850) GeV are excluded for β=1.0 (0.5), where β is the branching fraction of a leptoquark decaying to a charged lepton and a quark. Similarly, second-generation scalar leptoquarks with masses less than 1080 (760) GeV are excluded for β=1.0 (0.5). Mass limits are also set for vector leptoquark Production scenarios with anomalous vector couplings, and for R-parity violating supersymmetric scenarios of top squark Pair Production resulting in similar final-state signatures. These are the most stringent limits placed on the masses of vector leptoquarks and RPV top squarks to date.
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a search for Pair Production of new light bosons decaying into muons
Physics Letters B, 2016Co-Authors: V Khachatryan, A Tumasyan, W Adam, T Bergauer, M Dragicevic, E Asilar, J Brandstetter, E Brondolin, Albert M Sirunyan, M FlechlAbstract:A search for the Pair Production of new light bosons, each decaying into a Pair of muons, is performed with the CMS experiment at the LHC, using a dataset corresponding to an integrated luminosity of 20.7 inverse femtobarns collected in proton-proton collisions at center-of-mass energy of sqrt(s) = 8 TeV. No excess is observed in the data relative to standard model background expectation and a model independent upper limit on the product of the cross section, branching fraction, and acceptance is derived. The results are compared with two benchmark models, the first one in the context of the next-to-minimal supersymmetric standard model, and the second one in scenarios containing a hidden sector, including those predicting a nonnegligible light boson lifetime.
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measurement of prompt j ψ Pair Production in pp collisions at s 7 tev
Journal of High Energy Physics, 2014Co-Authors: V Khachatryan, A M Sirunyan, A Tumasyan, W Adam, T Bergauer, M Dragicevic, J Ero, C Fabjan, M FriedlAbstract:Production of prompt J/psi meson Pairs in proton-proton collisions at sqrt(s)=7 TeV is measured with the CMS experiment at the LHC in a data sample corresponding to an integrated luminosity of about 4.7 inverse femtobarns. The two J/psi mesons are fully reconstructed via their decays into muon Pairs. This observation provides for the first time access to the high-transverse-momentum region of J/psi Pair Production where model predictions are not yet established. The total and differential cross sections are measured in a phase space defined by the individual J/psi transverse momentum pt[J/psi] and rapidity abs(y[J/psi]): abs(y[J/psi]) 6.5 GeV; 1.2 4.5 GeV. The total cross section, assuming unpolarized prompt J/psi Pair Production is 1.49 +/- 0.07 (stat.) +/- 0.13 (syst.) nb. Different assumptions about the J/psi polarization imply modifications to the cross section ranging from -31% to +27%.
W Adam - One of the best experts on this subject based on the ideXlab platform.
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study of the underlying event in top quark Pair Production in pp collisions at 13 tev
European Physical Journal C, 2019Co-Authors: A M Sirunyan, A Tumasyan, W Adam, T Bergauer, M Dragicevic, F Ambrogi, E Asilar, J Brandstetter, E Brondolin, J EroAbstract:Measurements of normalized differential cross sections as functions of the multiplicity and kinematic variables of charged-particle tracks from the underlying event in top quark and antiquark Pair Production are presented. The measurements are performed in proton-proton collisions at a center-of-mass energy of 13 Te , and are based on data collected by the CMS experiment at the LHC in 2016 corresponding to an integrated luminosity of 35.9 fb-1 . Events containing one electron, one muon, and two jets from the hadronization and fragmentation of b quarks are used. These measurements characterize, for the first time, properties of the underlying event in top quark Pair Production and show no deviation from the universality hypothesis at energy scales typically above twice the top quark mass.
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search for top squark Pair Production in pp collisions at sqrt s 13 tev using single lepton events
Journal of High Energy Physics, 2017Co-Authors: A M Sirunyan, A Tumasyan, W Adam, T Bergauer, M Dragicevic, F Ambrogi, E Asilar, J Brandstetter, E Brondolin, J EroAbstract:A search for top squark Pair Production in pp collisions at root s = 13 TeV is performed using events with a single isolated electron or muon, jets, and a large transverse momentum imbalance. The results are based on data collected in 2016 with the CMS detector at the LHC, corresponding to an integrated luminosity of 35.9 fb(-1). No significant excess of events is observed above the expectation from standard model processes. Exclusion limits are set in the context of supersymmetric models of Pair Production of top squarks that decay either to a top quark and a neutralino or to a bottom quark and a chargino. Depending on the details of the model, we exclude top squarks with masses as high as 1120 GeV. Detailed information is also provided to facilitate theoretical interpretations in other scenarios of physics beyond the standard model.
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search for Pair Production of first and second generation leptoquarks in proton proton collisions at s 8 tev
Physical Review D, 2016Co-Authors: V Khachatryan, A Tumasyan, W Adam, T Bergauer, M Dragicevic, E Asilar, J Brandstetter, E Brondolin, Albert M Sirunyan, J EroeAbstract:A search for Pair Production of first and second generation leptoquarks is performed in final states containing either two charged leptons and two jets, or one charged lepton, one neutrino and two jets, using proton-proton collision data at √s = 8 TeV. The data, corresponding to an integrated luminosity of 19.7 fb^(−1), were recorded with the CMS detector at the LHC. First-generation scalar leptoquarks with masses less than 1010 (850) GeV are excluded for β=1.0 (0.5), where β is the branching fraction of a leptoquark decaying to a charged lepton and a quark. Similarly, second-generation scalar leptoquarks with masses less than 1080 (760) GeV are excluded for β=1.0 (0.5). Mass limits are also set for vector leptoquark Production scenarios with anomalous vector couplings, and for R-parity violating supersymmetric scenarios of top squark Pair Production resulting in similar final-state signatures. These are the most stringent limits placed on the masses of vector leptoquarks and RPV top squarks to date.
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a search for Pair Production of new light bosons decaying into muons
Physics Letters B, 2016Co-Authors: V Khachatryan, A Tumasyan, W Adam, T Bergauer, M Dragicevic, E Asilar, J Brandstetter, E Brondolin, Albert M Sirunyan, M FlechlAbstract:A search for the Pair Production of new light bosons, each decaying into a Pair of muons, is performed with the CMS experiment at the LHC, using a dataset corresponding to an integrated luminosity of 20.7 inverse femtobarns collected in proton-proton collisions at center-of-mass energy of sqrt(s) = 8 TeV. No excess is observed in the data relative to standard model background expectation and a model independent upper limit on the product of the cross section, branching fraction, and acceptance is derived. The results are compared with two benchmark models, the first one in the context of the next-to-minimal supersymmetric standard model, and the second one in scenarios containing a hidden sector, including those predicting a nonnegligible light boson lifetime.
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measurement of prompt j ψ Pair Production in pp collisions at s 7 tev
Journal of High Energy Physics, 2014Co-Authors: V Khachatryan, A M Sirunyan, A Tumasyan, W Adam, T Bergauer, M Dragicevic, J Ero, C Fabjan, M FriedlAbstract:Production of prompt J/psi meson Pairs in proton-proton collisions at sqrt(s)=7 TeV is measured with the CMS experiment at the LHC in a data sample corresponding to an integrated luminosity of about 4.7 inverse femtobarns. The two J/psi mesons are fully reconstructed via their decays into muon Pairs. This observation provides for the first time access to the high-transverse-momentum region of J/psi Pair Production where model predictions are not yet established. The total and differential cross sections are measured in a phase space defined by the individual J/psi transverse momentum pt[J/psi] and rapidity abs(y[J/psi]): abs(y[J/psi]) 6.5 GeV; 1.2 4.5 GeV. The total cross section, assuming unpolarized prompt J/psi Pair Production is 1.49 +/- 0.07 (stat.) +/- 0.13 (syst.) nb. Different assumptions about the J/psi polarization imply modifications to the cross section ranging from -31% to +27%.
