Muon Pairs Research Articles

Search for a heavy pseudoscalar boson decaying to a Z and a Higgs boson at sqrt{s}=13,text {Te}text {V}

A search is presented for a heavy pseudoscalar boson text {A} decaying to a Z boson and a Higgs boson with mass of 125,text {GeV}. In the final state considered, the Higgs boson decays to a bottom quark and antiquark, and the Z boson decays either into a pair of electrons, muons, or neutrinos. The analysis is performed using a data sample corresponding to an integrated luminosity of 35.9,text {fb}^{-1} collected in 2016 by the CMS experiment at the LHC from proton–proton collisions at a center-of-mass energy of 13,text {Te}text {V}. The data are found to be consistent with the background expectations. Exclusion limits are set in the context of two-Higgs-doublet models in the text {A} boson mass range between 225 and 1000,text {GeV}.

Search for scalar resonances decaying into \u03bc+\u03bc\u2212 in events with and without b-tagged jets produced in proton-proton collisions at sqrt{s}=13 TeV with the ATLAS detector

A search for a narrow scalar resonance decaying into an opposite-sign muon pair produced in events with and without b-tagged jets is presented in this paper. The search uses 36.1 fb−1 of sqrt{s}=13 TeV proton-proton collision data recorded by the ATLAS experiment at the LHC. No significant excess of events above the expected Standard Model background is observed in the investigated mass range of 0.2 to 1.0 TeV. The observed upper limits at 95% confidence level on the cross section times branching ratio for b-quark associated production and gluon-gluon fusion are between 1.9 and 41 fb and 1.6 and 44 fb respectively, which is consistent with expectations.

Search for an exotic decay of the Higgs boson to a pair of light pseudoscalars in the final state with two muons and two b quarks in pp collisions at 13 TeV

A search for exotic decays of the Higgs boson to a pair of light pseudoscalar particles a1 is performed under the hypothesis that one of the pseudoscalars decays to a pair of opposite sign muons and the other decays to bb‾. Such signatures are predicted in a number of extensions of the standard model (SM), including next-to-minimal supersymmetry and two-Higgs-doublet models with an additional scalar singlet. The results are based on a data set of proton-proton collisions corresponding to an integrated luminosity of 35.9 fb−1, accumulated with the CMS experiment at the CERN LHC in 2016 at a centre-of-mass energy of 13 TeV. No statistically significant excess is observed with respect to the SM backgrounds in the search region for pseudoscalar masses from 20 GeV to half of the Higgs boson mass. Upper limits at 95% confidence level are set on the product of the production cross section and branching fraction, σhB(h→a1a1→μ+μ−bb‾), ranging from 5 to 33 fb, depending on the pseudoscalar mass. Corresponding limits on the branching fraction, assuming the SM prediction for σh, are (1–7)×10−4.

Nuclear dependence of light neutral meson production in p\u2013A collisions at 400\xa0GeV with NA60

The NA60 experiment has studied low-mass muon pair production in proton–nucleus collisions with a system of Be, Cu, In, W, Pb and U targets, using a 400 GeV proton beam at the CERN SPS. The transverse momentum spectra of the rho /omega and phi mesons are measured in the full p_{mathrm {T}} range accessible, from p_{mathrm {T}}= 0 up to 2 , {hbox {GeV/c}}. The nuclear dependence of the production cross sections of the eta , omega and phi mesons has been found to be consistent with the power law sigma _{mathrm {pA}} propto {mathrm {A}}^alpha , with the alpha parameter increasing as a function of p_{mathrm {T}} for all the particles, and an approximate hierarchy alpha _eta approx alpha _phi > alpha _omega . The cross section ratios sigma _eta /sigma _omega , sigma _rho /sigma _omega and sigma _phi /sigma _omega have been studied as a function of the size A of the production target, and an increase of the eta and phi yields relative to the omega is observed from p–Be to p–U collisions.

Measurements of μμ pairs from open heavy flavor and Drell-Yan in p+p collisions at s=200 GeV

PHENIX reports differential cross sections of $\mu\mu$ pairs from semileptonic heavy-flavor decays and the Drell-Yan production mechanism measured in $p$$+$$p$ collisions at $\sqrt{s}=200$ GeV at forward and backward rapidity ($1.2<|\eta|<2.2$). The $\mu\mu$ pairs from $c\bar{c}$, $b\bar{b}$, and Drell-Yan are separated using a template fit to unlike- and like-sign muon pair spectra in mass and $p_T$. The azimuthal opening angle correlation between the muons from $c\bar{c}$ and $b\bar{b}$ decays and the pair-$p_T$ distributions are compared to distributions generated using {\sc pythia} and {\sc powheg} models, which both include next-to-leading order processes. The measured distributions for pairs from $c\bar{c}$ are consistent with {\sc pythia} calculations. The $c\bar{c}$ data presents narrower azimuthal correlations and softer $p_T$ distributions compared to distributions generated from {\sc powheg}. The $b\bar{b}$ data are well described by both models. The extrapolated total cross section for bottom production is $3.75{\pm}0.24({\rm stat}){\pm}^{0.35}_{0.50}({\rm syst}){\pm}0.45({\rm global})$[$\mu$b], which is consistent with previous measurements at the Relativistic Heavy Ion Collider in the same system at the same collision energy, and is approximately a factor of two higher than the central value calculated with theoretical models. The measured Drell-Yan cross section is in good agreement with next-to-leading-order quantum-chromodynamics calculations.

Search for contact interactions and large extra dimensions in the dilepton mass spectra from proton-proton collisions at sqrt{s}=13 TeV

A search for nonresonant excesses in the invariant mass spectra of electron and muon pairs is presented. The analysis is based on data from proton-proton collisions at a center-of-mass energy of 13 TeV recorded by the CMS experiment in 2016, corresponding to a total integrated luminosity of 36 fb−1. No significant deviation from the standard model is observed. Limits are set at 95% confidence level on energy scales for two general classes of nonresonant models. For a class of fermion contact interaction models, lower limits ranging from 20 to 32 TeV are set on the characteristic compositeness scale Λ. For the Arkani-Hamed, Dimopoulos, and Dvali model of large extra dimensions, the first results in the dilepton final state at 13 TeV are reported, and values of the ultraviolet cutoff parameter ΛT below 6.9 TeV are excluded. A combination with recent CMS diphoton results improves this exclusion to ΛT below 7.7 TeV, providing the most sensitive limits to date in nonhadronic final states.

Study of the rare decays of Bs0 and B0 mesons into muon pairs using data collected during 2015 and 2016 with the ATLAS detector

A study of the decays Bs0 → μ+μ− and B0 → μ+μ− has been performed using 26.3 fb−1 of 13 TeV LHC proton-proton collision data collected with the ATLAS detector in 2015 and 2016. Since the detector resolution in μ+μ− invariant mass is comparable to the Bs0-B0 mass difference, a single fit determines the signal yields for both decay modes. This results in a measurement of the branching fraction mathrm{mathcal{B}}left({B}_s^0to {mu}^{+}{mu}^{-}right)=left({3.2}_{-1.0}^{+1.1}right)times {10}^{-9} and an upper limit mathrm{mathcal{B}}left({B}^0to {mu}^{+}{mu}^{-}right)<4.3times {10}^{-10} at 95% confidence level. The result is combined with the Run 1 ATLAS result, yielding mathrm{mathcal{B}}left({B}_s^0to {mu}^{+}{mu}^{-}right)=left({2.8}_{-0.7}^{+0.8}right)times {10}^{-9} and mathrm{mathcal{B}}left({B}^0to {mu}^{+}{mu}^{-}right)<2.1times {10}^{-10} at 95% confidence level. The combined result is consistent with the Standard Model prediction within 2.4 standard deviations in the mathrm{mathcal{B}}left({B}^0to {mu}^{+}{mu}^{-}right)-mathrm{mathcal{B}}left({B}_s^0to {mu}^{+}{mu}^{-}right) plane.

LHC searches for Dark Matter in compressed mass scenarios: challenges in the forward proton mode

We analyze in detail the LHC prospects at the center-of-mass enery of sqrt{s} = 14 TeV for charged electroweakino searches, decaying to leptons, in compressed supersymmetry scenarios, via exclusive photon-initiated pair production. This provides a potentially increased sensitivity in comparison to inclusive channels, where the background is often overwhelming. We pay particular attention to the challenges that such searches would face in the hostile high pile-up environment of the LHC, giving close consideration to the backgrounds that will be present. The signal we focus on is the exclusive production of same-flavour muon and electron pairs, with missing energy in the final state, and with two outgoing intact protons registered by the dedicated forward proton detectors installed in association with ATLAS and CMS. We present results for slepton masses of 120–300 GeV and slepton-neutralino mass splitting of 10–20 GeV, and find that the relevant backgrounds can be controlled to the level of the expected signal yields. The most significant such backgrounds are due to semi-exclusive lepton pair production at lower masses, with a proton produced in the initial proton dissociation system registering in the forward detectors, and from the coincidence of forward protons produced in pile-up events with an inclusive central event that mimics the signal. We also outline a range of potential methods to further suppress these backgrounds as well as to enlarge the signal yields.

Search for resonant production of second-generation sleptons with same-sign dimuon events in proton\u2013proton collisions at sqrt{s} = 13,text {TeV}

A search is presented for resonant production of second-generation sleptons (widetilde{mu } _{mathrm {L}}, widetilde{nu }_{mu }) via the R-parity-violating coupling {lambda ^{prime }_{211}} to quarks, in events with two same-sign muons and at least two jets in the final state. The smuon (muon sneutrino) is expected to decay into a muon and a neutralino (chargino), which will then decay into a second muon and at least two jets. The analysis is based on the 2016 data set of proton-proton collisions at sqrt{s}=13,text {TeV} recorded with the CMS detector at the LHC, corresponding to an integrated luminosity of 35.9,text {fb}^{-1}. No significant deviation is observed with respect to standard model expectations. Upper limits on cross sections, ranging from 0.24 to 730,text {fb}, are derived in the context of two simplified models representing the dominant signal contributions leading to a same-sign muon pair. The cross section limits are translated into coupling limits for a modified constrained minimal supersymmetric model with {lambda ^{prime }_{211}} as the only nonzero R-parity violating coupling. The results significantly extend restrictions of the parameter space compared with previous searches for similar models.

The SeaQuest spectrometer at Fermilab

The SeaQuest spectrometer at Fermilab was designed to detect oppositely-charged pairs of muons (dimuons) produced by interactions between a 120 GeV proton beam and liquid hydrogen, liquid deuterium and solid nuclear targets. The primary physics program uses the Drell-Yan process to probe antiquark distributions in the target nucleon. The spectrometer consists of a target system, two dipole magnets and four detector stations. The upstream magnet is a closed-aperture solid iron magnet which also serves as the beam dump, while the second magnet is an open aperture magnet. Each of the detector stations consists of scintillator hodoscopes and a high-resolution tracking device. The FPGA-based trigger compares the hodoscope signals to a set of pre-programmed roads to determine if the event contains oppositely-signed, high-mass muon pairs.

Search for the Higgs Boson Decaying to Two Muons in Proton-Proton Collisions at sqrt[s]=13 TeV.

A search for the Higgs boson decaying to two oppositely charged muons is presented using data recorded by the CMS experiment at the CERN LHC in 2016 at a center-of-mass energy sqrt[s]=13 TeV, corresponding to an integrated luminosity of 35.9 fb^{-1}. Data are found to be compatible with the predicted background. For a Higgs boson with a mass of 125.09GeV, the 95%confidence level observed (background-only expected) upper limit on the production cross section times the branching fraction to a pair of muons is found to be 3.0 (2.5) times the standard model expectation. In combination with data recorded at center-of-mass energies sqrt[s]=7 and 8TeV, the background-only expected upper limit improves to 2.2 times the standard model value with a standard model expected significance of 1.0 standard deviation. The corresponding observed upper limit is 2.9 with an observed significance of 0.9 standard deviation. This corresponds to an observed upper limit on the standard model Higgs boson branching fraction to muons of 6.4×10^{-4} and to an observed signal strength of 1.0±1.0(stat)±0.1(syst).

Search for long-lived particles in final states with displaced dimuon vertices in pp collisions at s=13 TeV with the ATLAS detector

A search is performed for a long-lived particle decaying into a final state that includes a pair of muons of opposite-sign electric charge, using proton-proton collision data collected at $\sqrt{s}=$ 13 TeV by the ATLAS detector at the Large Hadron Collider corresponding to an integrated luminosity of 32.9 fb$^{-1}$. No significant excess over the Standard Model expectation is observed. Limits at 95% confidence level on the lifetime of the long-lived particle are presented in models of new phenomena including gauge-mediated supersymmetry or decay of the Higgs boson, $H$, to a pair of dark photons, $Z_D$. Lifetimes in the range c$\tau$ = 1-2400 cm are excluded, depending on the parameters of the model. In the supersymmetric model, the lightest neutralino is the next-to-lightest supersymmetric particle, with a relatively long lifetime due to its weak coupling to the gravitino, the lightest supersymmetric particle. The lifetime limits are determined for very light gravitino mass and various assumptions for the neutralino mass in the range 300 GeV to 1000 GeV. In the dark photon model, the lifetime limits are interpreted as exclusion contours in the plane of the coupling between the $Z_D$ and the Standard Model $Z$ boson versus the $Z_D$ mass (in the range 20-60 GeV), for various assumptions for the $H\rightarrow Z_D Z_D$ branching fraction.

CMS quarkonium Production at 13 TeV

A wide range of studies of quarkonium production and spectroscopy are performed by the CMS experiment. The quarkonium system is interesting and can be used mainly to probe the underlying Quantum Cromo Dynamics (QCD) processes but also to tune MC generators at new energies, since heavy flavour (HF) states are background to many searches, and can be used to obtain calibration and understanding of the detectors. Events are selected from muon pairs, and the final state includes hadrons and photons. The identification of secondary vertices allows for the separation of prompt (P) and non prompt (NP) production.In the conference talk I presented the many recent results obtained with 13 TeV data at the Large Hadron Collider (LHC) but in this paper I focus on the most recent result: the first observation of resolved χb1(3P) and χb2(3P) states and their mass splitting measurement through the decay channel χb(3P) → Υ(3S)γ.

Recent results of quarkonium and heavy flavour physics at ATLAS

Heavy quark spectroscopy and exotic states are studied with the ATLAS detector, mainly through final states containing muon pairs from J/ψ decays. This proceedings will summarise recent results from ATLAS on these topics, including production of quarkonium and heavy flavour, searches for exotic states and measurements of decay properties in open beauty production.

Search for heavy Majorana or Dirac neutrinos and right-handed W gauge bosons in final states with two charged leptons and two jets at sqrt{s}=13 TeV with the ATLAS detector

A search for heavy right-handed Majorana or Dirac neutrinos NR and heavy right-handed gauge bosons WR is performed in events with a pair of energetic electrons or muons, with the same or opposite electric charge, and two energetic jets. The events are selected from pp collision data with an integrated luminosity of 36.1 fb−1 collected by the ATLAS detector at sqrt{s}=13 TeV. No significant deviations from the Standard Model are observed. The results are interpreted within the theoretical framework of a left-right symmetric model and lower limits are set on masses in the heavy right-handed W boson and neutrino mass plane. The excluded region extends to {m}_{R_R}=4.7 TeV for both Majorana and Dirac NR neutrinos.

Higgs physics at CMS

The most recent results of a Higgs boson production and properties from the CMS Collaboration using the LHC Run 1 and Run 2 data are reported. These include analyses of a Higgs boson decaying to a pair of photons, four leptons via Z boson pair decays and the associated production of a Higgs boson with top quark pair, predicted by the Standard Model (SM). The studies of a Higgs boson decays to a pair of bottom quarks, a pair of tau leptons and a charm quark pair are also presented. The Higgs boson production via vector boson fusion (VBF) and decaying to invisible particles is reported here as well. The analysis of a Higgs boson decay to a pair of muons is also presented. The study of a Higgs boson pair production at 13 TeV is performed as well and projections of a Higgs boson self couplings together with the couplings to other particles at the HL-LHC are made.

Search for Higgs boson decays into a pair of light bosons in the bbμμ final state in pp collision at [formula omitted] with the ATLAS detector

A search for decays of the Higgs boson into a pair of new spin-zero particles, H→aa, where the a-bosons decay into a b-quark pair and a muon pair, is presented. The search uses 36.1 fb−1 of proton–proton collision data at s=13 TeV recorded by the ATLAS experiment at the LHC in 2015 and 2016. No significant deviation from the Standard Model prediction is observed. Upper limits at 95% confidence level are placed on the branching ratio (σH/σSM)×B(H→aa→bbμμ), ranging from 1.2×10−4 to 8.4×10−4 in the a-boson mass range of 20–60 GeV. Model-independent limits are set on the visible production cross-section times the branching ratio to the bbμμ final state for new physics, σvis(X)×B(X→bbμμ), ranging from 0.1 fb to 0.73 fb for mμμ between 18 and 62 GeV.

Mixed electroweak-QCD corrections to e+e−.→μ+μ−H at CEPC with finite-width effect**The work of W. C. and Y. J. is Supported in part by the National Natural Science Foundation of China (11475188, 1187051300, 11261130311) (CRC110 by DGF and NSFC). The work of F. F. is Supported by the National Natural Science Foundation of China (11505285, 11875318) and by the Fundamental Research Funds

The associated production of Higgs boson with a muon pair, e+e− → μ+μ−H,is one of the golden channels to pin down the properties of the Higgs boson in the prospective Higgs factories exemplified by CEPC. The projected accuracy of the corresponding cross section measurement is about per cent level at CEPC. In this work, we investigate both weak correction and the mixed electroweak-QCD corrections for this channel, appropriately taking into account the effect of finite Z0 width. The μ+μ− invariant mass spectrum is also predicted. The mixed electroweak-QCD correction turns out to reach 1.5% of the Born-order result, and thereby must be included in future confrontation with the data. We also observe that, after including higher-order corrections, the simplified prediction for the integrated cross section employing the narrow-width-approximation may deviate from our full result by a few per cents.

Observation of Centrality-Dependent Acoplanarity for Muon Pairs Produced via Two-Photon Scattering in Pb+Pb Collisions at sqrt[s_{NN}]=5.02 TeV with the ATLAS Detector.

This Letter presents a measurement of γγ→μ^{+}μ^{-} production in Pb+Pb collisions recorded by the ATLAS detector at the Large Hadron Collider at sqrt[s_{NN}]=5.02 TeV with an integrated luminosity of 0.49 nb^{-1}. The azimuthal angle and transverse momentum correlations between the muons are measured as a function of collision centrality. The muon pairs are produced from γγ through the interaction of the large electromagnetic fields of the nuclei. The contribution from background sources of muon pairs is removed using a template fit method. In peripheral collisions, the muons exhibit a strong back-to-back correlation consistent with previous measurements of muon pair production in ultraperipheral collisions. The angular correlations are observed to broaden significantly in central collisions. The modifications are qualitatively consistent with rescattering of the muons while passing through the hot matter produced in the collision.

Search for the decay of a Higgs boson in the \u2113\u2113\u03b3 channel in proton-proton collisions at sqrt{s}=13 TeV

A search for a Higgs boson decaying into a pair of electrons or muons and a photon is described. Higgs boson decays to a Z boson and a photon (H → Zγ → ℓℓγ, ℓ = e or μ), or to two photons, one of which has an internal conversion into a muon pair (H → γ*γ → μμγ) were considered. The analysis is performed using a data set recorded by the CMS experiment at the LHC from proton-proton collisions at a center-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 35.9 fb−1. No significant excess above the background prediction has been found. Limits are set on the cross section for a standard model Higgs boson decaying to opposite-sign electron or muon pairs and a photon. The observed limits on cross section times the corresponding branching fractions vary between 1.4 and 4.0 (6.1 and 11.4) times the standard model cross section for H → γ*γ → μμγ (H → Zγ → ℓℓγ) in the 120–130 GeV mass range of the ℓℓγ system. The H → γ*γ → μμγ and H → Zγ →ℓℓγ analyses are combined for mH =125GeV, obtaining an observed (expected) 95% confidence level upper limit of 3.9 (2.0) times the standard model cross section.