Publications
391 results found
Abi B, Acciarri R, Acero MA, et al., 2020, Volume IV The DUNE far detector single-phase technology, Journal of Instrumentation, Vol: 15, Pages: 1-619, ISSN: 1748-0221
The preponderance of matter over antimatter in the early universe, the dynamics of the supernovae that produced the heavy elements necessary for life, and whether protons eventually decay—these mysteries at the forefront of particle physics and astrophysics are key to understanding the early evolution of our universe, its current state, and its eventual fate. DUNE is an international world-class experiment dedicated to addressing these questions as it searches for leptonic charge-parity symmetry violation, stands ready to capture supernova neutrino bursts, and seeks to observe nucleon decay as a signature of a grand unified theory underlying the standard model. Central to achieving DUNE's physics program is a far detector that combines the many tens-of-kiloton fiducial mass necessary for rare event searches with sub-centimeter spatial resolution in its ability to image those events, allowing identification of the physics signatures among the numerous backgrounds. In the single-phase liquid argon time-projection chamber (LArTPC) technology, ionization charges drift horizontally in the liquid argon under the influence of an electric field towards a vertical anode, where they are read out with fine granularity. A photon detection system supplements the TPC, directly enhancing physics capabilities for all three DUNE physics drivers and opening up prospects for further physics explorations. The DUNE far detector technical design report (TDR) describes the DUNE physics program and the technical designs of the single- and dual-phase DUNE liquid argon TPC far detector modules. Volume IV presents an overview of the basic operating principles of a single-phase LArTPC, followed by a description of the DUNE implementation. Each of the subsystems is described in detail, connecting the high-level design requirements and decisions to the overriding physics goals of DUNE.
Abi B, Acciarri R, Acero MA, et al., 2020, Executive summary, JOURNAL OF INSTRUMENTATION, Vol: 15, ISSN: 1748-0221
Jones SB, Nonnenmacher TS, Atkin E, et al., 2020, Off-axis characterisation of the CERN T10 beam for low momentum proton measurements with a high pressure gas time projection chamber, Instruments, Vol: 4, Pages: 21-21, ISSN: 2410-390X
We present studies of proton fluxes in the T10 beamline at CERN. A prototype high pressure gas time projection chamber (TPC) was exposed to the beam of protons and other particles, using the 0.8 GeV/c momentum setting in T10, in order to make cross section measurements of low energy protons in argon. To explore the energy region comparable to hadrons produced by GeV-scale neutrino interactions at oscillation experiments, i.e., near 0.1 GeV of kinetic energy, methods of moderating the T10 beam were employed: the dual technique of moderating the beam with acrylic blocks and measuring scattered protons off the beam axis was used to decrease the kinetic energy of incident protons, as well as change the proton/minimum ionising particle (MIP) composition of the incident flux. Measurements of the beam properties were made using time of flight systems upstream and downstream of the TPC. The kinetic energy of protons reaching the TPC was successfully changed from ∼0.3 GeV without moderator blocks to less than 0.1 GeV with four moderator blocks (40 cm path length). The flux of both protons and MIPs off the beam axis was increased. The ratio of protons to MIPs vary as a function of the off-axis angle allowing for possible optimisation of the detector to select the type of required particles. Simulation informed by the time of flight measurements show that with four moderator blocks placed in the beamline, (5.6 ± 0.1) protons with energies below 0.1 GeV per spill traversed the active TPC region. Measurements of the beam composition and energy are presented.
Abe K, Akutsu R, Ali A, et al., 2020, First measurement of the charged current (nu)over-bar(mu) double differential cross section on a water target without( )pions in the final state, Physical Review D: Particles, Fields, Gravitation and Cosmology, Vol: 102, Pages: 1-16, ISSN: 1550-2368
This paper reports the first differential measurement of the charged-current ¯νμ interaction cross section on water with no pions in the final state. The unfolded flux-averaged measurement using the T2K off-axis near detector is given in double-differential bins of μ+ momentum and angle. The integrated cross section in a restricted phase space is σ=(1.11±0.18)×10−38 cm2 per water molecule. Comparisons with several nuclear models are also presented.
Abe K, Akhlaq N, Akutsu R, et al., 2020, Simultaneous measurement of the muon neutrino charged-current cross section on oxygen and carbon without pions in the final state at T2K, Physical Review D: Particles, Fields, Gravitation and Cosmology, Vol: 101, Pages: 112004 – 1-112004 – 32, ISSN: 1550-2368
This paper reports the first simultaneous measurement of the double differential muon neutrino charged-current cross section on oxygen and carbon without pions in the final state as a function of the outgoing muon kinematics, made at the ND280 off-axis near detector of the T2K experiment. The ratio of the oxygen and carbon cross sections is also provided to help validate various models’ ability to extrapolate between carbon and oxygen nuclear targets, as is required in T2K oscillation analyses. The data are taken using a neutrino beam with an energy spectrum peaked at 0.6 GeV. The extracted measurement is compared with the prediction from different Monte Carlo neutrino-nucleus interaction event generators, showing particular model separation for very forward-going muons. Overall, of the models tested, the result is best described using local Fermi gas descriptions of the nuclear ground state with RPA suppression.
Abe K, Akhlaq N, Akutsu R, et al., 2020, First combined measurement of the muon neutrino and antineutrino charged-current cross section without pions in the final state at T2K, Physical Review D: Particles, Fields, Gravitation and Cosmology, Vol: 101, Pages: 112001 – 1-112001 – 44, ISSN: 1550-2368
This paper presents the first combined measurement of the double-differential muon neutrino and antineutrino charged-current cross sections with no pions in the final state on hydrocarbon at the off-axis near detector of the T2K experiment. The data analyzed in this work comprise 5.8×1020 and 6.3×1020 protons on target in neutrino and antineutrino mode respectively, at a beam energy peak of 0.6 GeV. Using the two measured cross sections, the sum, difference, and asymmetry were calculated with the aim of better understanding the nuclear effects involved in such interactions. The extracted measurements have been compared with the prediction from different Monte Carlo generators and theoretical models showing that the difference between the two cross sections have interesting sensitivity to nuclear effects.
Sirunyan AM, Tumasyan A, Adam W, et al., 2020, Study of dijet events with a large rapidity gap between the two leading jets in pp collisions at root s = 7TeV (vol 78, 242, 2018), European Physical Journal C: Particles and Fields, Vol: 80, Pages: 1-15, ISSN: 1124-1861
Events with no charged particles produced between the two leading jets are studied in proton–proton collisions at s√=7 TeV. The jets were required to have transverse momentum pjetT>40 GeV and pseudorapidity 1.5<|ηjet|<4.7, and to have values of ηjet with opposite signs. The data used for this study were collected with the CMS detector during low-luminosity running at the LHC, and correspond to an integrated luminosity of 8pb−1. Events with no charged particles with pT>0.2 GeV in the interval −1<η<1 between the jets are observed in excess of calculations that assume no color-singlet exchange. The fraction of events with such a rapidity gap, amounting to 0.5–1% of the selected dijet sample, is measured as a function of the pT of the second-leading jet and of the rapidity separation between the jets. The data are compared to previous measurements at the Tevatron, and to perturbative quantum chromodynamics calculations based on the Balitsky–Fadin–Kuraev–Lipatov evolution equations, including different models of the non-perturbative gap survival probability.
Abe K, Akutsu R, Ali A, et al., 2020, Search for electron antineutrino appearance in a long-baseline muon antineutrino beam, Physical Review Letters, Vol: 124, Pages: 161802-1-161802-8, ISSN: 0031-9007
Electron antineutrino appearance is measured by the T2K experiment in an accelerator-produced antineutrino beam, using additional neutrino beam operation to constrain parameters of the Pontecorvo-Maki-Nakagawa-Sakata (PMNS) mixing matrix. T2K observes 15 candidate electron antineutrino events with a background expectation of 9.3 events. Including information from the kinematic distribution of observed events, the hypothesis of no electron antineutrino appearance is disfavored with a significance of 2.40σ and no discrepancy between data and PMNS predictions is found. A complementary analysis that introduces an additional free parameter which allows non-PMNS values of electron neutrino and antineutrino appearance also finds no discrepancy between data and PMNS predictions.
Abe K, Akutsu R, Ali A, et al., 2020, Constraint on the matter-antimatter symmetry-violating phase in neutrino oscillations, Nature, Vol: 580, Pages: 339-344, ISSN: 0028-0836
The charge-conjugation and parity-reversal (CP) symmetry of fundamental particles is a symmetry between matter and antimatter. Violation of this CP symmetry was first observed in 19641, and CP violation in the weak interactions of quarks was soon established2. Sakharov proposed3 that CP violation is necessary to explain the observed imbalance of matter and antimatter abundance in the Universe. However, CP violation in quarks is too small to support this explanation. So far, CP violation has not been observed in non-quark elementary particle systems. It has been shown that CP violation in leptons could generate the matter–antimatter disparity through a process called leptogenesis4. Leptonic mixing, which appears in the standard model’s charged current interactions5,6, provides a potential source of CP violation through a complex phase δCP, which is required by some theoretical models of leptogenesis7,8,9. This CP violation can be measured in muon neutrino to electron neutrino oscillations and the corresponding antineutrino oscillations, which are experimentally accessible using accelerator-produced beams as established by the Tokai-to-Kamioka (T2K) and NOvA experiments10,11. Until now, the value of δCP has not been substantially constrained by neutrino oscillation experiments. Here we report a measurement using long-baseline neutrino and antineutrino oscillations observed by the T2K experiment that shows a large increase in the neutrino oscillation probability, excluding values of δCP that result in a large increase in the observed antineutrino oscillation probability at three standard deviations (3σ). The 3σ confidence interval for δCP, which is cyclic and repeats every 2π, is [−3.41, −0.03] for the so-called normal mass ordering and [−2.54, −0.32] for the inverted mass ordering. Our results indicate CP violation in leptons and our method enables sensitive searches for matter–antimatter
Abe K, Akutsu R, Ali A, et al., 2020, Measurement of the muon neutrino charged-current single pi(+) production on hydrocarbon using the T2K off-axis near detector ND280, Physical Review D: Particles, Fields, Gravitation and Cosmology, Vol: 101, ISSN: 1550-2368
We report the measurements of the single and double differential cross section of muon neutrino charged-current interactions on carbon with a single positively charged pion in the final state at the T2K off-axis near detector using 5.56×1020 protons on target. The analysis uses data control samples for the background subtraction and the cross section signal, defined as a single negatively charged muon and a single positively charged pion exiting from the target nucleus, is extracted using an unfolding method. The model-dependent cross section, integrated over the T2K off-axis neutrino beam spectrum peaking at 0.6 GeV, is measured to be σ=(11.76±0.44(stat)±2.39(syst))×10−40 cm2 nucleon−1. Various differential cross sections are measured, including the first measurement of the Adler angles for single charged pion production in neutrino interactions with heavy nuclei target.
Abe K, Akutsu R, Ali A, et al., 2019, Measurement of neutrino and antineutrino neutral-current quasielasticlike interactions on oxygen by detecting nuclear deexcitation gamma rays, Physical Review D: Particles, Fields, Gravitation and Cosmology, Vol: 100, Pages: 1-19, ISSN: 1550-2368
Neutrino- and antineutrino-oxygen neutral-current quasielasticlike interactions are measured at Super-Kamiokande using nuclear deexcitation γ rays to identify signal-like interactions in data from a 14.94(16.35)×1020 protons-on-target exposure of the T2K neutrino (antineutrino) beam. The measured flux-averaged cross sections on oxygen nuclei are ⟨σν−NCQE⟩=1.70±0.17(stat.)+0.51−0.38(syst.)×10−38 cm2/oxygen with a flux-averaged energy of 0.82 GeV and ⟨σ¯ν−NCQE⟩=0.98±0.16(stat.)+0.26−0.19(syst.)×10−38 cm2/oxygen with a flux-averaged energy of 0.68 GeV, for neutrinos and antineutrinos, respectively. These results are the most precise to date, and the antineutrino result is the first cross section measurement of this channel. They are compared with various theoretical predictions. The impact on evaluation of backgrounds to searches for supernova relic neutrinos at present and future water Cherenkov detectors is also discussed.
Abe K, Akutsu R, Ali A, et al., 2019, Search for heavy neutrinos with the T2K near detector ND280, Physical Review D: Particles, Fields, Gravitation and Cosmology, Vol: 100, ISSN: 1550-2368
This paper reports on the search for heavy neutrinos with masses in the range 140<MN<493 MeV/c2 using the off-axis near detector ND280 of the T2K experiment. These particles can be produced from kaon decays in the standard neutrino beam and then subsequently decay in ND280. The decay modes under consideration are N→ℓ±απ∓ and N→ℓ+αℓ−β(−)ν(α,β=e,μ). A search for such events has been made using the Time Projection Chambers of ND280, where the background has been reduced to less than two events in the current dataset in all channels. No excess has been observed in the signal region. A combined Bayesian statistical approach has been applied to extract upper limits on the mixing elements of heavy neutrinos to electron-, muon- and tau- flavored currents (U2e, U2μ, U2τ) as a function of the heavy neutrino mass, e.g., U2e<10−9 at 90% C.L. for a mass of 390 MeV/c2. These constraints are competitive with previous experiments.
Abe K, Akutsu R, Ali A, et al., 2019, Measurement of the muon neutrino charged-current cross sections on water, hydrocarbon and iron, and their ratios, with the T2K on-axis detectors, Progress of Theoretical and Experimental Physics, Vol: 2019, Pages: 1-30, ISSN: 0033-068X
We report a measurement of the flux-integrated νμ charged-current cross sections on water, hydrocarbon, and iron in the T2K on-axis neutrino beam with a mean neutrino energy of 1.5 GeV. The measured cross sections on water, hydrocarbon, and iron are σH2OCC=(0.840±0.010(stat.)+0.10−0.08(syst.))×10−38cm2/nucleon, σCHCC=(0.817±0.007(stat.)+0.11−0.08(syst.))×10−38cm2/nucleon, and σFeCC=(0.859±0.003(stat.)+0.12−0.10(syst.))×10−38cm2/nucleon, respectively, for a restricted phase space of induced muons: θμ<45∘ and pμ>0.4 GeV/c in the laboratory frame. The measured cross section ratios are σH2OCC/σCHCC=1.028±0.016(stat.)±0.053(syst.), σFeCC/σH2OCC=1.023±0.012(stat.)±0.058(syst.), and σFeCC/σCHCC=1.049±0.010(stat.)±0.043(syst.). These results, with an unprecedented precision for the measurements of neutrino cross sections on water in the studied energy region, show good agreement with the current neutrino interaction models used in the T2K oscillation analyses.
Abe K, Akutsu R, Ali A, et al., 2019, Search for neutral-current induced single photon production at the ND280 near detector in T2K, Journal of Physics G: Nuclear and Particle Physics, Vol: 46, ISSN: 0954-3899
Neutrino neutral-current (NC) induced single photon production is a sub-leading order process for accelerator-based neutrino beam experiments including T2K. It is, however, an important process to understand because it is a background for electron (anti)neutrino appearance oscillation experiments. Here, we performed the first search of this process below 1 GeV using the fine-grained detector at the T2K ND280 off-axis near detector. By reconstructing single photon kinematics from electron–positron pairs, we achieved 95% pure gamma ray sample from $5.738\times {10}^{20}$ protons-on-targets neutrino mode data. We do not find positive evidence of NC induced single photon production in this sample. We set the model-dependent upper limit on the cross-section for this process, at $0.114\times {10}^{-38}$ cm2 (90% C.L.) per nucleon, using the J-PARC off-axis neutrino beam with an average energy of $\left\langle {E}_{\nu }\right\rangle \sim 0.6$ GeV. This is the first limit on this process below 1 GeV which is important for current and future oscillation experiments looking for electron neutrino appearance oscillation signals.
Abe K, Akutsu R, Ali A, et al., 2019, Search for light sterile neutrinos with the T2K far detector Super-Kamiokande at a baseline of 295 km, Physical Review D: Particles, Fields, Gravitation and Cosmology, Vol: 99, ISSN: 1550-2368
We perform a search for light sterile neutrinos using the data from the T2K far detector at a baseline of 295 km, with an exposure of 14.7(7.6)×1020 protons on target in neutrino (antineutrino) mode. A selection of neutral-current interaction samples is also used to enhance the sensitivity to sterile mixing. No evidence of sterile neutrino mixing in the 3+1 model was found from a simultaneous fit to the charged-current muon, electron and neutral-current neutrino samples. We set the most stringent limit on the sterile oscillation amplitude sin2θ24 for the sterile neutrino mass splitting Δm241<3×10−3 eV2/c4.
Abe K, Akutsu R, Amey J, et al., 2018, Search for CP violation in neutrino and antineutrino oscillations by the T2K experiment with 2.2 x 10(21) protons on target, Physical Review Letters, Vol: 121, ISSN: 0031-9007
The T2K experiment measures muon neutrino disappearance and electron neutrino appearance in accelerator-produced neutrino and antineutrino beams. With an exposure of 14.7(7.6)×1020 protons on target in the neutrino (antineutrino) mode, 89 νe candidates and seven anti-νe candidates are observed, while 67.5 and 9.0 are expected for δCP=0 and normal mass ordering. The obtained 2σconfidence interval for the CP-violating phase, δCP, does not include the CP-conserving cases (δCP=0, π). The best-fit values of other parameters are sin2θ23=0.526+0.032−0.036 and Δm232=2.463+0.071−0.070×10−3 eV2/c4.
Sirunyan AM, Tumasyan A, Adam W, et al., 2018, Pseudorapidity and transverse momentum dependence of flow harmonics in pPb and PbPb collisions, PHYSICAL REVIEW C, Vol: 98, ISSN: 2469-9985
Measurements of azimuthal angular correlations are presented for high-multiplicity pPb collisions at √sNN=5.02TeV and peripheral PbPb collisions at √sNN=2.76TeV. The data used in this work were collected with the Compact Muon Solenoid (CMS) detector at the European Organization for Nuclear Research (CERN) Large Hadron Collider (LHC). Fourier coefficients as functions of transverse momentum and pseudorapidity are studied using the scalar product method; four-, six-, and eight-particle cumulants; and the Lee-Yang zero technique. The influence of event plane decorrelation is evaluated using the scalar product method and found to account for most of the observed pseudorapidity dependence.
Abe K, Amey J, Andreopoulos C, et al., 2018, Characterization of nuclear effects in muon-neutrino scattering on hydrocarbon with a measurement of final-state kinematics and correlations in charged-current pionless interactions at T2K, PHYSICAL REVIEW D, Vol: 98, ISSN: 2470-0010
This paper reports measurements of final-state proton multiplicity, muon and proton kinematics, and their correlations in charged-current pionless neutrino interactions, measured by the T2K ND280 near detector in its plastic scintillator (C8H8) target. The data were taken between years 2010 and 2013, corresponding to approximately 6×1020 protons on target. Thanks to their exploration of the proton kinematics and of imbalances between the proton and muon kinematics, the results offer a novel probe of the nuclear-medium effects most pertinent to the (sub-)GeV neutrino-nucleus interactions that are used in accelerator-based long-baseline neutrino oscillation measurements. These results are compared to many neutrino-nucleus interaction models which all fail to describe at least part of the observed phase space. In case of events without a proton above a detection threshold in the final state, a fully consistent implementation of the local Fermi gas model with multinucleon interactions gives the best description of the data. In the case of at least one proton in the final state, the spectral function model agrees well with the data, most notably when measuring the kinematic imbalance between the muon and the proton in the plane transverse to the incoming neutrino. Within the models considered, only the existence of multinucleon interactions are able to describe the extracted cross section within regions of high transverse kinematic imbalance. The effect of final-state interactions is also discussed.
Abe K, Amey J, Andreopoulos C, et al., 2018, Measurement of inclusive double-differential nu(mu) charged-current cross section with improved acceptance in the T2K off-axis near detector, Physical Review D - Particles, Fields, Gravitation and Cosmology, Vol: 98, ISSN: 1550-2368
We report a measurement of the flux-integrated cross section for inclusive muon neutrino charged-current interactions on carbon. The double-differential measurements are given as a function of the muon momentum and angle. Relative to our previous publication on this topic, these results have an increased angular acceptance and higher statistics. The data sample presented here corresponds to 5.7×1020 protons on target. The total flux-integrated cross section is measured to be (6.950±0.662)×10−39 cm2 nucleon−1 and is consistent with our simulation.
Abe K, Abe K, Ahn SH, et al., 2018, Physics potentials with the second Hyper-Kamiokande detector in Korea, Progress of Theoretical and Experimental Physics, Vol: 2018, ISSN: 2050-3911
Hyper-Kamiokande consists of two identical water-Cherenkov detectors of total 520 kt, with the first one in Japan at 295 km from the J-PARC neutrino beam with 2.5∘ off-axis angles (OAAs), and the second one possibly in Korea at a later stage. Having the second detector in Korea would benefit almost all areas of neutrino oscillation physics, mainly due to longer baselines. There are several candidate sites in Korea with baselines of 1000–1300 km and OAAs of 1∘–3∘.We conducted sensitivity studies on neutrino oscillation physics for a second detector, either in Japan (JD ×2) or Korea (JD + KD), and compared the results with a single detector in Japan. Leptonic charge–parity (CP) symmetry violation sensitivity is improved, especially when the CP is non-maximally violated. The larger matter effect at Korean candidate sites significantly enhances sensitivities to non-standard interactions of neutrinos and mass ordering determination. Current studies indicate the best sensitivity is obtained at Mt. Bisul (1088 km baseline, 1.3∘ OAA). Thanks to a larger (1000 m) overburden than the first detector site, clear improvements to sensitivities for solar and supernova relic neutrino searches are expected.
Sirunyan AM, Tumasyan A, Adam W, et al., 2018, Search for vectorlike light-flavor quark partners in proton-proton collisions at root s=8 TeV, PHYSICAL REVIEW D, Vol: 97, ISSN: 2470-0010
A search is presented for heavy vectorlike quarks (VLQs) that couple only to light quarks in proton-proton collisions at √s=8 TeV at the LHC. The data were collected by the CMS experiment during 2012 and correspond to an integrated luminosity of 19.7 fb−1. Both single and pair production of VLQs are considered. The single-production search is performed for down-type VLQs (electric charge of magnitude 1/3), while the pair-production search is sensitive to up-type (charge of magnitude 2/3) and down-type VLQs. Final states with at least one muon or one electron are considered. No significant excess over standard model expectations is observed, and lower limits on the mass of VLQs are derived. The lower limits range from 400 to 1800 GeV, depending on the single-production cross section and the VLQ branching fractions B to W, Z, and Higgs bosons. When considering pair production alone, VLQs with masses below 845 GeV are excluded for B(W)=1.0, and below 685 GeV for B(W)=0.5, B(Z)=B(H)=0.25. The results are more stringent than those previously obtained for single and pair production of VLQs coupled to light quarks.
Sirunyan AM, Tumasyan A, Adam W, et al., 2018, Measurement of normalized differential t(t)over-bar cross sections in the dilepton channel from pp collisions at root s=13 TeV, Journal of High Energy Physics, Vol: 2018, ISSN: 1029-8479
Normalized differential cross sections for top quark pair production are measured in the dilepton (e+e−, μ+μ−, and μ∓e±) decay channels in proton-proton collisions at a center-of-mass energy of 13 TeV. The measurements are performed with data corresponding to an integrated luminosity of 2.1 fb−1 using the CMS detector at the LHC. The cross sections are measured differentially as a function of the kinematic properties of the leptons, jets from bottom quark hadronization, top quarks, and top quark pairs at the particle and parton levels. The results are compared to several Monte Carlo generators that implement calculations up to next-to-leading order in perturbative quantum chromodynamics interfaced with parton showering, and also to fixed-order theoretical calculations of top quark pair production up to next-to-next-to-leading order.
Sirunyan AM, Tumasyan A, Adam W, et al., 2018, Search for supersymmetry with Higgs boson to diphoton decays using the razor variables at root s=13 TeV, PHYSICS LETTERS B, Vol: 779, Pages: 166-190, ISSN: 0370-2693
An inclusive search for anomalous Higgs boson production in the diphoton decay channel and in association with at least one jet is presented, using LHC proton–proton collision data collected by the CMS experiment at a center-of-mass energy of 13 TeV and corresponding to an integrated luminosity of . The razor variables and , as well as the momentum and mass resolution of the diphoton system, are used to categorize events into different search regions. The search result is interpreted in the context of strong and electroweak production of supersymmetric particles. We exclude bottom squark pair-production with masses below 450 GeV for bottom squarks decaying to a bottom quark, a Higgs boson, and the lightest supersymmetric particle (LSP) for LSP masses below 250 GeV. For wino-like chargino–neutralino production, we exclude charginos with mass below 170 GeV for LSP masses below 25 GeV. In the GMSB scenario, we exclude charginos with mass below 205 GeV for neutralinos decaying to a Higgs boson and a goldstino LSP with 100% branching fraction.
Sirunyan AM, Tumasyan A, Adam W, et al., 2018, Measurement of associated Z plus charm production in proton-proton collisions at root s=8TeV, EUROPEAN PHYSICAL JOURNAL C, Vol: 78, ISSN: 1434-6044
A study of the associated production of a Z boson and a charm quark jet (Z+c), and a comparison to production with a b quark jet (Z+b), in pp collisions at a centre-of-mass energy of 8TeV are presented. The analysis uses a data sample corresponding to an integrated luminosity of 19.7fb−1, collected with the CMS detector at the CERN LHC. The Z boson candidates are identified through their decays into pairs of electrons or muons. Jets originating from heavy flavour quarks are identified using semileptonic decays of c or b flavoured hadrons and hadronic decays of charm hadrons. The measurements are performed in the kinematic region with two leptons with pℓT>20GeV, |ηℓ|<2.1, 71<mℓℓ<111GeV, and heavy flavour jets with pjetT>25GeV and |ηjet|<2.5. The Z+c production cross section is measured to be σ(pp→Z+c+X)B(Z→ℓ+ℓ−)=8.8±0.5(stat)±0.6(syst)pb. The ratio of the Z+c and Z+b production cross sections is measured to be σ(pp→Z+c+X)/σ(pp→Z+b+X)=2.0±0.2(stat)±0.2(syst). The Z+c production cross section and the cross section ratio are also measured as a function of the transverse momentum of the Z boson and of the heavy flavour jet. The measurements are compared with theoretical predictions.
Sirunyan AM, Tumasyan A, Adam W, et al., 2018, Suppression of Excited gamma States Relative to the Ground State in Pb-Pb Collisions at root s(NN)=5.02 TeV, PHYSICAL REVIEW LETTERS, Vol: 120, ISSN: 0031-9007
The relative yields of Υ mesons produced in pp and Pb-Pb collisions at √sNN=5.02 TeV and reconstructed via the dimuon decay channel are measured using data collected by the CMS experiment. Double ratios are formed by comparing the yields of the excited states, Υ(2S) and Υ(3S), to the ground state, Υ(1S), in both Pb-Pb and pp collisions at the same center-of-mass energy. The double ratios, [Υ(nS)/Υ(1S)]Pb−Pb/[Υ(nS)/Υ(1S)]pp, are measured to be 0.308±0.055(stat)±0.019(syst) for the Υ(2S) and less than 0.26 at 95% confidence level for the Υ(3S). No significant Υ(3S) signal is found in the Pb-Pb data. The double ratios are studied as a function of collision centrality, as well as Υ transverse momentum and rapidity. No significant dependencies are observed.
Sirunyan AM, Tumasyan A, Adam W, et al., 2018, Search for natural supersymmetry in events with top quark pairs and photons in pp collisions at root s=8 TeV, JOURNAL OF HIGH ENERGY PHYSICS, Vol: 2018, ISSN: 1029-8479
Results are presented from a search for natural gauge-mediated supersymmetry (SUSY) in a scenario in which the top squark is the lightest squark, the next-to-lightest SUSY particle is a bino-like neutralino, and the lightest SUSY particle is the gravitino. The strong production of top squark pairs can produce events with pairs of top quarks and neutralinos, with each bino-like neutralino decaying to a photon and a gravitino. The search is performed using a sample of pp collision data accumulated by the CMS experiment at s√=8 TeV, corresponding to an integrated luminosity of 19.7 fb−1. The final state consists of a lepton (electron or muon), jets, and one or two photons. The imbalance in transverse momentum in the events is compared with the expected spectrum from standard model processes. No excess event yield is observed beyond the expected background, and the result is interpreted in the context of a general model of gauge-mediated SUSY breaking that leads to exclusion of top squark masses below 650–730 GeV.
Sirunyan AM, Tumasyan A, Adam W, et al., 2018, Study of dijet events with a large rapidity gap between the two leading jets in pp collisions at root s=7 TeV, EUROPEAN PHYSICAL JOURNAL C, Vol: 78, ISSN: 1434-6044
Events with no charged particles produced between the two leading jets are studied in proton-proton collisions at s√=7 TeV. The jets were required to have transverse momentum pjetT>40 GeV and pseudorapidity 1.5<|ηjet|<4.7, and to have values of ηjet with opposite signs. The data used for this study were collected with the CMS detector during low-luminosity running at the LHC, and correspond to an integrated luminosity of 8pb−1. Events with no charged particles with pT>0.2 GeV in the interval −1<η<1 between the jets are observed in excess of calculations that assume no color-singlet exchange. The fraction of events with such a rapidity gap, amounting to 0.5–1% of the selected dijet sample, is measured as a function of the pT of the second-leading jet and of the rapidity separation between the jets. The data are compared to previous measurements at the Tevatron, and to perturbative quantum chromodynamics calculations based on the Balitsky–Fadin–Kuraev–Lipatov evolution equations, including different models of the non-perturbative gap survival probability.
Abe K, Amey J, Andreopoulos C, et al., 2018, Measurement of the single pi(0) production rate in neutral current neutrino interactions on water, Physical Review D - Particles, Fields, Gravitation and Cosmology, Vol: 97, ISSN: 1550-2368
The single π0 production rate in neutral current neutrino interactions on water in a neutrino beam with a peak neutrino energy of 0.6 GeV has been measured using the PØD, one of the subdetectors of the T2K near detector. The production rate was measured for data taking periods when the PØD contained water (2.64 × 1020 protons-on-target) and also periods without water (3.49 × 1020 protons-on-target). A measurement of the neutral current single π0 production rate on water is made using appropriate subtraction of the production rate with water in from the rate with water out of the target region. The subtraction analysis yields 106 ± 41 ± 69 signal events where the uncertainties are statistical (stat.) and systematic (sys.) respectively. This is consistent with the prediction of 157 events from the nominal simulation. The measured to expected ratio is 0.68 ± 0.26 (stat) ± 0.44 (sys) ± 0.12 (flux). The nominal simulation uses a flux integrated cross section of 7.63 × 10−39cm2 per nucleon with an average neutrino interaction energy of 1.3 GeV.
Sirunyan AM, Tumasyan A, Adam W, et al., 2018, Search for dark matter and unparticles in events with a Z boson and missing transverse momentum in proton-proton collisions at root s = 13 TeV (vol 9, 106, 2017), Journal of High Energy Physics, Vol: 2018, ISSN: 1029-8479
Sirunyan AM, Tumasyan A, Adam W, et al., 2018, Azimuthal anisotropy of charged particles with transverse momentum up to 100GeV/c in PbPb collisions at root S-NN=5.02 TeV, Physics Letters B, Vol: 776, Pages: 195-216, ISSN: 0370-2693
The Fourier coefficients v2 and v3 characterizing the anisotropy of the azimuthal distribution of chargedparticles produced in PbPb collisions at √sNN = 5.02 TeV are measured with data collected by the CMSexperiment. The measurements cover a broad transverse momentum range, 1 < pT < 100 GeV/c. Theanalysis focuses on the pT > 10 GeV/c range, where anisotropic azimuthal distributions should reflect thepath-length dependence of parton energy loss in the created medium. Results are presented in severalbins of PbPb collision centrality, spanning the 60% most central events. The v2 coefficient is measuredwith the scalar product and the multiparticle cumulant methods, which have different sensitivities toinitial-state fluctuations. The values from both methods remain positive up to pT ∼ 60–80 GeV/c, in allexamined centrality classes. The v3 coefficient, only measured with the scalar product method, tends tozero for pT 20 GeV/c. Comparisons between theoretical calculations and data provide new constraintson the path-length dependence of parton energy loss in heavy ion collisions and highlight the importanceof the initial-state fluctuations
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