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Öğe Measurements of Born cross sections of e+e- ? Ds* + DsJ- + c.c.(Amer Physical Soc, 2021) Ablikim, M.; Achasov, M. N.; Adlarson, P.; Ahmed, S.; Albrecht, M.; Aliberti, R.; Çetin, Serkant AliThe Born cross sections are measured for the first time for the processes e(+)e(-) -> D-s* + D-sJ(-) + c.c. and e(+)e(-) -> D-s* + D-s1(2460)(-) + c:c: at the center-of-mass energy root p = 4.600 GeV, 4.612 GeV, 4.626 GeV, 4.640 GeV, 4.660 GeV, 4.68 GeV, and 4.700 GeV, and for e(+)e(-) -> D-s* + D(s1()2536)(-) +c.c. at root s = 4.660 GeV, 4.680 GeV, and 4.700 GeV, using data samples collected with the BESIII detector at the BEPCII collider. No structures are observed in cross-section distributions for any of the processes.Öğe Polarization and entanglement in baryon-antibaryon pair production in electron-positron annihilation(Nature Portfolio, 2019) Ablikim, M.; Achasov, M. N.; Ahmed, S.; Albrecht, M.; Alekseev, M.; Amoroso, A.; Çetin, Serkant AliParticles directly produced at electron-positron colliders, such as the J/psi meson, decay with relatively high probability into a baryon-antibaryon pair(1). For spin-1/2 baryons, the pair can have the same or opposite helicites. A non-vanishing phase Delta Phi between the transition amplitudes to these helicity states results in a transverse polarization of the baryons(2-4). From the joint angular distribution of the decay products of the bary-ons, this phase as well as the parameters characterizing the baryon and the antibaryon decays can be determined. Here, we report the measurement of Delta Phi = 42.4 +/- 0.6 +/- 0.5 degrees using Lambda -> p pi(-) and (Lambda) over bar -> (p) over bar pi(+), (n ) over bar pi(0) decays at BESIII. We find a value for the Lambda -> p pi(-) decay parameter of alpha(-) = 0.750 +/- 0.009 +/- 0.004, 17 +/- 3% higher than the current world average, which has been used as input for all Lambda polarization measurements since 1978(5,6). For (Lambda) over bar -> (p) over bar pi(+) we find alpha(+) = -0.758 +/- 0.010 +/- 0.007, giving A(CP) = (alpha(-) + alpha(+))/(alpha(-) - alpha(+)) = -0.006 +/- 0.012 +/- 0.007, a precise direct test of charge-parity symmetry (CP) violation in Lambda decays.Öğe Oscillating features in the electromagnetic structure of the neutron(Nature Portfolio, 2021) Ablikim, M.; Achasov, M. N.; Adlarson, P.; Ahmed, S.; Albrecht, M.; Aliberti, R.; Çetin, Serkant Ali[Abstract Not Available]Öğe Test of the universality of ? and ? lepton couplings in W-boson decays with the ATLAS detector(Nature Portfolio, 2021) Aad, G.; Abbott, B.; Abbott, D. C.; Abud, A. Abed; Abeling, K.; Abhayasinghe, D. K.; Çetin, Serkant AliThe standard model of particle physics encapsulates our best current understanding of physics at the smallest scales. A fundamental axiom of this theory is the universality of the couplings of the different generations of leptons to the electroweak gauge bosons. The measurement of the ratio of the decay rate of W bosons to t leptons and muons, R(tau/mu), constitutes an important test of this axiom. Using 139 fb(-1) of proton-proton collisions recorded with the ATLAS detector at a centre-of-mass energy of 13 TeV, we report a measurement of this quantity from di-leptonic tt events where the top quarks decay into a W boson and a bottom quark. We can distinguish muons originating from W bosons and those originating from an intermediate t lepton through the muon transverse impact parameter and differences in the muon transverse momentum spectra. The measured value of R(tau/mu) is 0.992 +/- 0.013 [+/- 0.007(stat) +/- 0.011(syst)] and is in agreement with the hypothesis of universal lepton couplings as postulated in the standard model. This is the only such measurement from the Large Hadron Collider, so far, and obtains twice the precision of previous measurements.Öğe Search for charged-lepton-flavour violation in Z-boson decays with the ATLAS detector(Nature Portfolio, 2021) Aad, G.; Abbott, B.; Abbott, D. C.; Abud, A. Abed; Abeling, K.; Abhayasinghe, D. K.; Çetin, Serkant AliLeptons with essentially the same properties apart from their mass are grouped into three families (or flavours). The number of leptons of each flavour is conserved in interactions, but this is not imposed by fundamental principles. Since the formulation of the standard model of particle physics, the observation of flavour oscillations among neutrinos has shown that lepton flavour is not conserved in neutrino weak interactions. So far, there has been no experimental evidence that this also occurs in interactions between charged leptons. Such an observation would be a sign of undiscovered particles or a yet unknown type of interaction. Here the ATLAS experiment at the Large Hadron Collider at CERN reports a constraint on lepton-flavour-violating effects in weak interactions, searching for Z-boson decays into a tau lepton and another lepton of different flavour with opposite electric charge. The branching fractions for these decays are measured to be less than 8.1 x 10(-6) (e tau) and 9.5 x 10(-6) (mu tau) at the 95% confidence level using 139 fb(-1) of proton-proton collision data at a centre-of-mass energy of root s = 13 TeV and 20.3 fb(-1) at root s = 8 TeV. These results supersede the limits from the Large Electron-Positron Collider experiments conducted more than two decades ago.Öğe Measurement of cross section for e+e- ? ?0(?)over-bar0 near threshold(Elsevier, 2021) Ablikim, M.; Achasov, M. N.; Adlarson, P.; Ahmed, S.; Albrecht, M.; Aliberti, R.; Çetin, Serkant AliUsing e(+)e(-) collision data at ten center-of-mass energies between 2.644 and 3.080 GeV collected with the BESIII detector at BEPCII and corresponding to an integrated luminosity of about 500 pb(-1), we measure the cross sections and effective form factors for the process e(+)e(-) -> Xi(0)(Xi) over bar (0) utilizing a single-tag method. A fit to the cross section of e(+)e(-) -> Xi(0)(Xi) over bar (0) with a pQCD-driven power function is performed, from which no significant resonance or threshold enhancement is observed. In addition, the ratio of cross sections for the processes e(+)e(-) -> Xi(0)(Xi) over bar (0) and Xi(0)(Xi) over bar (0) is calculated using recent BESIII measurement and is found to be compatible with expectation from isospin symmetry. (C) 2021 The Author(s). Published by Elsevier B.V.Öğe Measurement of the associated production of a Higgs boson decaying into b-quarks with a vector boson at high transverse momentum in pp collisions at ?s=13 TeV with the ATLAS detector(Elsevier, 2021) Aaboud, M.; Aad, G.; Abbott, B.; Abdinov, O.; Abeloos, B.; Abhayasinghe, D. K.; Çetin, Serkant AliThe associated production of a Higgs boson with a W or Z boson decaying into leptons and where the Higgs boson decays to a b (b) over bar pair is measured in the high vector-boson transverse momentum regime, above 250 GeV, with the ATLAS detector. The analysed data, corresponding to an integrated luminosity of 139 fb(-1), were collected in proton-proton collisions at the Large Hadron Collider between 2015 and 2018 at a centre-of-mass energy of root s = 13 TeV. The measured signal strength, defined as the ratio of the measured signal yield to that predicted by the Standard Model, is 0.72(-0.36)(+0.39) corresponding to an observed (expected) significance of 2.1 (2.7) standard deviations. Cross-sections of associated production of a Higgs boson decaying into b quark pairs with a W or Z gauge boson, decaying into leptons, are measured in two exclusive vector boson transverse momentum regions, 250-400 GeV and above 400 GeV, and interpreted as constraints on anomalous couplings in the framework of a Standard Model effective field theory. (C) 2021 The Author. Published by Elsevier B.V.Öğe Observation of photon-induced W+ W- production in pp collisions at ?s=13 TeV using the ATLAS detector(Elsevier, 2021) Aaboud, M.; Aad, G.; Abbott, B.; Abdinov, O.; Abeloos, B.; Abhayasinghe, D. K.; Çetin, Serkant AliThis letter reports the observation of photon-induced production of W-boson pairs, gamma gamma -> WW. The analysis uses 139 fb(-1) of LHC proton-proton collision data taken at root s = 13 TeV recorded by the ATLAS experiment during the years 2015-2018. The measurement is performed selecting one electron and one muon, corresponding to the decay of the diboson system as WW -> e(+/-)nu mu(-/+)nu final state. The background-only hypothesis is rejected with a significance of well above 5 standard deviations consistent with the expectation from Monte Carlo simulation. A cross section for the gamma gamma -> WW process of 3.13 +/- 0.31(stat.) +/- 0.28(syst.) fb is measured in a fiducial volume close to the acceptance of the detector, by requiring an electron and a muon of opposite signs with large dilepton transverse momentum and exactly zero additional charged particles. This is found to be in agreement with the Standard Model prediction. (C) 2021 The Author(s). Published by Elsevier B.V.Öğe Measurement of proton electromagnetic form factors in the time-like region using initial state radiation at BESIII(Elsevier, 2021) Ablikim, M.; Achasov, M. N.; Adlarson, P.; Ahmed, S.; Albrecht, M.; Alekseev, M.; Çetin, Serkant AliThe electromagnetic process e(+)e(-) -> p (p) over bar over bar is studied with the initial-state-radiation technique using 7.5 fb(-1) of data collected by the BESIII experiment at seven energy points from 3.773 to 4.600 GeV. The Born cross section and the effective form factor of the proton are measured from the production threshold to 3.0 GeV/c(2) using the p (p) over bar over bar invariant-mass spectrum. The ratio of electric and magnetic form factors of the proton is determined from the analysis of the proton-helicity angular distribution. (C) 2021 The Author. Published by Elsevier B.V.Öğe Measurement of the absolute branching fraction of ?c+ ? pKS0? decays(Elsevier, 2021) Ablikim, M.; Achasov, M. N.; Adlarson, P.; Ahmed, S.; Albrecht, M.; Alekseev, M.; Çetin, Serkant AliBased on 586 pb(-1) of e(+) e(-) annihilation data collected at a center-of-mass energy of root s = 4.6 GeV with the BESIII detector at the BEPCII collider, the absolute branching fraction of Lambda(+)(c) -> pK(S)(0)eta decays is measured for the first time to be B(Lambda(+)(c) -> pK(S)(0)eta) = (0.414 +/- 0.084 +/- 0.028)%, where the first uncertainty is statistical and the second is systematic. The result is compatible with a previous CLEO result on the relative branching fraction B(Lambda(+)(c) -> pK(S)(eta)(0))/B(Lambda(+)(c) -> pK(-)pi(+)), and consistent with theoretical predictions of SU(3) flavor symmetry. (C) 2021 The Author. Published by Elsevier B.V.Öğe Measurement of the inclusive branching fraction for ? (3686) ? KS0 + anything(Elsevier, 2021) Ablikim, M.; Achasov, M. N.; Adlarson, P.; Ahmed, S.; Albrecht, M.; Aliberti, R.; Çetin, Serkant AliUsing 5.9 pb(-1) of e(+)e(-) annihilation data collected at center-of-mass energies from 3.640 to 3.701 GeV with the BESIII detector at the BEPCII Collider, we measure the observed cross sections of e(+)e(-) -> (KSX)-X-0 (where X = anything). From a fit to these observed cross sections with the sum of continuum and psi(3686) and J/psi Breit-Wigner functions and considering initial state radiation and the BEPCII beam energy spread, we obtain for the first time the product of psi(3686) leptonic width and inclusive decay Physics Letters 820 (2021) 136576 branching fraction Gamma B-ee(psi)(3686)(psi(3686) -> (KSX)-X-0) = (373.8 +/- 6.7 +/- 20.0) eV, and assuming Gamma(ee)(psi)((3686)) is (2.33 +/- 0.04) keV from PDG value, we measure B(psi(3686) ->(KSX)-X-0) = (16.04 +/- 0.29 +/- 0.90)%, where the first uncertainty is statistical and the second is systematic. (C) 2021 The Author(s). Published by Elsevier B.V.Öğe Search for resonances decaying into photon pairs in 139 fb-1 of pp collisions at ?s=13 TeV with the ATLAS detector(Elsevier, 2021) Aad, G.; Abbott, B.; Abbott, D. C.; Abud, A. Abed; Abeling, K.; Abhayasinghe, D. K.; Çetin, Serkant AliSearches for new resonances in the diphoton final state, with spin 0 as predicted by theories with an extended Higgs sector and with spin 2 using a warped extra-dimension benchmark model, are presented using 139 fb(-1) of root s = 13 TeV pp collision data collected by the ATLAS experiment at the LHC. No significant deviation from the Standard Model is observed and upper limits are placed on the production cross-section times branching ratio to two photons as a function of the resonance mass. (C) 2021 The Author(s). Published by Elsevier B.V.Öğe A search for an unexpected asymmetry in the production of e+?- and e-?+ pairs in proton-proton collisions recorded by the ATLAS detector at ?s=13 TeV(Elsevier, 2022) Aad, G.; Abbott, B.; Abbott, D. C.; Abud, A. Abed; Abeling, K.; Abhayasinghe, D. K.; Çetin, Serkant AliThis search, a type not previously performed at ATLAS, uses a comparison of the production cross sections for e(+)mu(-) and e(-)mu(+) pairs to constrain physics processes beyond the Standard Model. It uses 139 fb(-1) of proton-proton collision data recorded at root s = 13 TeV at the LHC. Targeting sources of new physics which prefer final states containing e(+)mu(-) and e(-)mu(+), the search contains two broad signal regions which are used to provide model-independent constraints on the ratio of cross sections at the 2% level. The search also has two special selections targeting supersymmetric models and leptoquark signatures. Observations using one of these selections are able to exclude, at 95% confidence level, singly produced smuons with masses up to 640 GeV in a model in which the only other light sparticle is a neutralino when the R-parity-violating coupling lambda(23)(1)' is close to unity. Observations using the other selection exclude scalar leptoquarks with masses below 1880 GeV when g(1R)(eu) = g(1R)(mu c) = 1, at 95% confidence level. The limit on the coupling reduces to g(1R)(eu) = g(1R)(mu c) = 0.46 for a mass of 1420 GeV. (C) 2022 The Author(s). Published by Elsevier B.V.Öğe Evidence for Higgs boson decays to a low-mass dilepton system and a photon in pp collisions at ?s=13 TeV with the ATLAS detector(Elsevier, 2021) Aad, G.; Abbott, B.; Abbott, D. C.; Abud, A. Abed; Abeling, K.; Abhayasinghe, D. K.; Çetin, Serkant AliA search for the Higgs boson decaying into a photon and a pair of electrons or muons with an invariant mass m(ll) < 30 GeV is presented. The analysis is performed using 139 fb(-1) of proton-proton collision data, produced by the LHC at a centre-of-mass energy of 13 TeV and collected by the ATLAS experiment. Evidence for the H -> ll(gamma) process is found with a significance of 3.2 over the background-only hypothesis, compared to an expected significance of 2.1 for the Standard Model prediction. The best-fit value of the signal-strength parameter, defined as the ratio of the observed signal yield to the one expected in the Standard Model, is mu = 1.5 +/- 0.5. The Higgs boson production cross-section times the H -> ll(gamma) branching ratio for m(ll) < 30 GeV is determined to be 8.7(-2.7)(+2.8) fb. (C) 2021 The Author. Published by Elsevier B.V.Öğe Measurements of ?+ and ?- time-like electromagnetic form factors for center-of-mass energies from 2.3864 to 3.0200 GeV(Elsevier, 2021) Ablikim, M.; Achasov, M. N.; Adlarson, P.; Ahmed, S.; Albrecht, M.; Amoroso, A.; Çetin, Serkant AliThe Born cross sections of the e(+)e(-) -> Sigma(+)(Sigma) over bar (-) and e(+)e(-)-> Sigma(-)(Sigma) over bar (+) processes are determined for centerof-mass energy from 2.3864 to 3.0200 GeV with the BESIII detector. The cross section lineshapes can be described properly by a pQCD function and the resulting ratio of effective form factors for the Sigma(+) and Sigma(-) is consistent with 3. In addition, ratios of the Sigma(+) electric and magnetic form factors, vertical bar G(E)/G(M)vertical bar. are obtained at three center-of-mass energies through an analysis of the angular distributions. These measurements, which are studied for the first time in the off-resonance region, provide precision experimental input for understanding baryonic structure. The observed new features of the Sigma(+/-) form factors require more theoretical discussions for the hyperons. (C) 2021 The Author(s). Published by Elsevier B.V.Öğe Observation of a resonant structure in e+e-? ?? and another in e+e-? ??0 at center-of-mass energies between 2.00 and 3.08 GeV(Elsevier, 2021) Ablikim, M.; Achasov, M. N.; Adlarson, P.; Ahmed, S.; Albrecht, M.; Amoroso, A.; Çetin, Serkant AliBorn cross sections for the processes e(+)e(-) -> omega eta and e(+)e(-) -> omega pi(0) have been determined for centerof-mass energies between 2.00 and 3.08GeVwith the BESIII detector at the BEPCII collider. The results obtained in this work are consistent with previous measurements but with improved precision. Two resonant structures are observed. In the e(+)e(-) -> omega eta cross sections, a resonance with a mass of (2176 +/- 24 +/- 3) MeV/c(2) and a width of (89 +/- 50 +/- 5) MeV is observed with a significance of 6.2 sigma. Its properties are consistent with the phi(2170). In the e(+)e(-) -> omega pi(0) cross sections, a resonance denoted Y (2040) is observed with a significance of more than 10 sigma. Its mass and width are determined to be (2034 +/- 13 +/- 9) MeV/c(2) and (234 +/- 30 +/- 25) MeV, respectively, where the first uncertainties are statistical and the second ones are systematic. (C) 2020 The Author(s). Published by Elsevier B.V. This is an open access article under the CC BY license.Öğe Measurement of the e+e- ? ?+?- cross section between 600 and 900 MeV using initial state radiation (vol 753, pg 629, 2016)(Elsevier, 2021) Ablikim, M.; Achasov, M. N.; Adlarson, P.; Ahmed, S.; Albrecht, M.; Alekseev, M.; Çetin, Serkant AliIn Ref.[1] the BESIII collaboration published a cross section measurement of the process e(+)e(-) -> pi(+)pi(-) in the energy range between 600 and 900 MeV. In this corrigendum, we report a corrected evaluation of the statistical errors in terms of a fully propagated covariance matrix. The correction also yields a reduced statistical uncertainty for the hadronic vacuum polarization contribution to the anomalous magnetic moment of the muon, which now reads as a(mu)(pi pi,LO) (600 - 900 MeV) = (368.2 +/- 1.5(stat) +/- 3.3(syst)) x 10(-10). The central values of the cross section measurement and of a(mu)(pi pi,LO) , as well as the systematic uncertainties remain unchanged. (C) 2015 The Author(s). Published by Elsevier B.V. All rights reserved.Öğe Measurement of the jet mass in high transverse momentum Z(? b(b)over-bar)? production at ?s=13 TeV using the ATLAS detector(Elsevier, 2021) Aaboud, M.; Aad, G.; Abbott, B.; Abdinov, O.; Abeloos, B.; Abhayasinghe, D. K.; Çetin, Serkant AliThe integrated fiducial cross-section and unfolded differential jet mass spectrum of high transverse momentum Z -> b (b) over bar decays are measured in Z gamma events in proton-proton collisions at root s = 13 TeV. The data analysed were collected between 2015 and 2016 with the ATLAS detector at the Large Hadron Collider and correspond to an integrated luminosity of 36.1 fb(-1). Photons are required to have a transverse momentum p(T) > 175 GeV. The Z -> b (b) over bar decay is reconstructed using a jet with p(T) > 200 GeV, found with the anti-k(t) R = 1.0 jet algorithm, and groomed to remove soft and wide-angle radiation and to mitigate contributions from the underlying event and additional proton-proton collisions. Two different but related measurements are performed using two jet grooming definitions for reconstructing the Z -> b (b) over bar decay: trimming and soft drop. These algorithms differ in their experimental and phenomenological implications regarding jet mass reconstruction and theoretical precision. To identify Zbosons, b-tagged R = 0.2 track-jets matched to the groomed large-R calorimeter jet are used as a proxy for the b-quarks. The signal yield is determined from fits of the data-driven background templates to the different jet mass distributions for the two grooming methods. Integrated fiducial cross-sections and unfolded jet mass spectra for each grooming method are compared with leading-order theoretical predictions. The results are found to be in good agreement with Standard Model expectations within the current statistical and systematic uncertainties. (C) 2020 The Author. Published by Elsevier B.VÖğe A search for the dimuon decay of the Standard Model Higgs boson with the ATLAS detector(Elsevier, 2021) Aaboud, M.; Aad, G.; Abbott, B.; Abdinov, O.; Abeloos, B.; Abhayasinghe, D. K.; Çetin, Serkant AliA search for the dimuon decay of the Standard Model (SM) Higgs boson is performed using data corresponding to an integrated luminosity of 139 fb(-1) collected with the ATLAS detector in Run 2 pp collisions at root s = 13 TeV at the Large Hadron Collider. The observed (expected) significance over the background-only hypothesis for a Higgs boson with a mass of 125.09 GeV is 2.0 sigma (1.7 sigma). The observed upper limit on the cross section times branching ratio for pp -> H -> mu mu is 2.2 times the SM prediction at 95% confidence level, while the expected limit on a H -> mu mu signal assuming the absence (presence) of a SM signal is 1.1(2.0). The best-fit value of the signal strength parameter, defined as the ratio of the observed signal yield to the one expected in the SM, is mu = 1.2 +/- 0.6. (C) 2020 The Author(s). Published by Elsevier B.V.Öğe Search for R-parity-violating supersymmetry in a final state containing leptons and many jets with the ATLAS experiment using ?s=13 TeV proton-proton collision data(Springer, 2021) Aad, G.; Abbott, B.; Abbott, D. C.; Abud, A. Abed; Abeling, K.; Abhayasinghe, D. K.; Çetin, Serkant AliA search for R-parity-violating supersymmetry in final states characterized by high jet multiplicity, at least one isolated light lepton and either zero or at least three b-tagged jets is presented. The search uses 139 fb(-1) of root s = 13 TeV proton-proton collision data collected by the ATLAS experiment during Run 2 of the Large Hadron Collider. The results are interpreted in the context of R-parity-violating supersymmetry models that feature gluino production, top-squark production, or electroweakino production. The dominant sources of background are estimated using a data-driven model, based on observables at medium jet multiplicity, to predict the b-tagged jet multiplicity distribution at the higher jet multiplicities used in the search. Machine-learning techniques are used to reach sensitivity to electroweakino production, extending the data-driven background estimation to the shape of the machine-learning discriminant. No significant excess over the Standard Model expectation is observed and exclusion limits at the 95% confidence level are extracted, reaching as high as 2.4 TeV in gluino mass, 1.35 TeV in top-squark mass, and 320 (365) GeV in higgsino (wino) mass.
