Neutral Current Production Research Articles

VH + jet production in hadron-hadron collisions up to order {alpha}_{mathrm{s}}^3 in perturbative QCD

We present precise predictions for the hadronic production of an on-shell Higgs boson in association with a leptonically decaying gauge boson and a jet up to order {alpha}_{mathrm{s}}^3 . We include the complete set of NNLO QCD corrections to both charged- and neutral-current Drell-Yan type contributions, as well as the previously known leading heavy quark loop induced contributions which involve a direct Higgs-quark coupling. As an application, we study a range of differential observables in proton-proton collisions at sqrt{s} = 13 TeV for both the charged- and neutral-current production modes. For each Higgs production process, we assess the improvement in the theoretical uncertainty for both the exclusive (njet = 1) and inclusive (njet ≥ 1) jet categories. We find that the inclusion of the NNLO corrections to the Drell-Yan type contributions is essential in stabilising the predictions and in reducing the theoretical uncertainty for both inclusive and exclusive jet production for all three modes. This is particularly true in the kinematical regimes associated with low to medium values of the transverse momentum of the produced vector boson and where the differential cross sections are the largest. For the neutral-current process, we find that the heavy quark loop induced contributions have their largest phenomenological impact (an increase in the size of the NNLO corrections, a distortion of the distribution shape and an enlargement of the left over remaining uncertainties) in kinematical regions associated to large values of pT,Z (typically above 150 GeV) where the cross sections are smaller.

Search for long-lived heavy neutrinos at the LHC with a VBF trigger

The charged current production of long-lived heavy neutrinos at the LHC can use a prompt charged lepton for triggering the measurement of the process. However, in order to fully characterize the heavy neutrino interactions, it is necessary to also probe Higgs or Z mediated neutral current production. In this case the charged lepton is not available, so other means of triggering are required. In this work, we explore the possibility of using a vector boson fusion trigger in the context of a GeV-scale Type I Seesaw model. We consider a minimal model, where both Higgs and Z-mediated contributions produce one heavy neutrino, as well as an extended model where the Higgs can decay into two heavy ones. Both scenarios are tested through displaced dilepton and displaced multitrack jet searches.

U(1) ′ mediated decays of heavy sterile neutrinos in MiniBooNE

The MiniBooNE low-energy excess is a longstanding problem which has received further confirmation recently with a reanalysis using newly collected data, with the anomaly now at the $4.8\sigma$ level. In this letter we propose a novel explanation which advocates a low-energy sector containing $Z^\prime$ bosons with GeV-scale masses and sterile neutrinos with masses around $100$-$500$ MeV. We show that this scenario can provide an excellent spectral agreement with the MiniBooNE low-energy excess in the form of $Z^\prime$-mediated neutral current production of heavy sterile states, a fraction of whose subsequent decay to $e^+e^-$ pairs are misidentified as single electron-like electromagnetic showers. Our model inscribes itself in the broad class of models in which sterile neutrinos are charged under novel interactions, allowing new couplings to hidden-sector physics. Alongside the electron-like MiniBooNE signature this model also predicts a novel, low-background, signal in LArTPC detectors such as MicroBooNE consisting of two distinguishable electron-like electromagnetic showers originating from a single vertex with no associated hadronic activity.

Measurement of Neutral-Current K^{+} Production by Neutrinos using MINERvA.

Neutral-current production of K^{+} by atmospheric neutrinos is a background in searches for the proton decay p→K^{+}ν[over ¯]. Reactions such as νp→νK^{+}Λ are indistinguishable from proton decays when the decay products of the Λ are below detection threshold. Events with K^{+} are identified in MINERvA by reconstructing the timing signature of a K^{+} decay at rest. A sample of 201 neutrino-induced neutral-current K^{+} events is used to measure differential cross sections with respect to the K^{+} kinetic energy, and the non-K^{+} hadronic visible energy. An excess of events at low hadronic visible energy is observed relative to the prediction of the neut event generator. Good agreement is observed with the cross section prediction of the genie generator. A search for photons from π^{0} decay, which would veto a neutral-current K^{+} event in a proton decay search, is performed, and a 2σ deficit of detached photons is observed relative to the genie prediction.

Search for associated production of a Z boson with a single top quark and for tZ flavour-changing interactions in pp collisions at sqrt{s}=8 TeV

A search for the production of a single top quark in association with a Z boson is presented, both to identify the expected standard model process and to search for flavour-changing neutral current interactions. The data sample corresponds to an integrated luminosity of 19.7 fb−1 recorded by the CMS experiment at the LHC in proton-proton collisions at sqrt{s}=8 TeV. Final states with three leptons (electrons or muons) and at least one jet are investigated. An events yield compatible with tZq standard model production is observed, and the corresponding cross section is measured to be σ(pp → tZq → ℓνbℓ+ℓ−q) = 10− 7+ 8 fb with a significance of 2.4 standard deviations. No presence of flavour-changing neutral current production of tZq is observed. Exclusion limits at 95% confidence level on the branching fractions of a top quark decaying to a Z boson and an up or a charm quark are found to be ℬ(t → Zu) < 0.022% and ℬ(t → Zc) < 0.049%.

Neutrino cross section measurements with MiniBooNE

The MiniBooNE neutrino oscillation experiment has collected a large sample of charged- and neutral-current neutrino interaction events. These samples are important to understand the normalization and backgrounds in neutrino oscillation searches. They also reveal insight into the structure of the nucleus and nucleon. The MiniBooNE experiment is briefly described and neutrino interaction rates presented. Preliminary results are reported for neutral-current elastic scattering and neutral-current production of π 0 .

Flavor-Changing Neutral-Current Production of tc̄ in Association with a Neutral Top-Higgs at LHC in the Topcolor-Assisted Technicolor Model

In the framework of the topcolor-assisted technicolor (TC2) model we investigate the flavor-changing neutral-current production pp → tc̄h0t at the Large Hadron Collider (LHC), which proceeds through the parton-level processes gg → tc̄h0t, uū → tc̄h0t and dd → tc̄h0t. We calculate the production rate and present the distributions of the transverse momenta and the invarient mass of the neutral top-higgs. It is found that the cross section of pp → tc̄h0t can reach a few hundreds of fb in a large part of the allowed parameter space. Considering the main decay mode of top-higgs for mht < 2mt, we find that such a production may provide copious events. In the case of unobservation, the LHC can set meaningful constraints on the TC2 model.

Evidence for diffractive charm production inνμFeandν¯μFescattering at the Fermilab Tevatron

We present evidence for the diffractive processes nu_mu Fe -> mu^- D_s^+ (D_s^*+) Fe and nubar_mu Fe -> mu^+ D_s^- (D_s^*-) Fe using the Fermilab SSQT neutrino beam and the Lab E neutrino detector. We observe the neutrino trident reactions nu_mu Fe -> nu_mu mu^- mu^+ Fe and nubar_mu Fe -> nubar_mu mu^+ mu^- Fe at rates consistent with Standard Model expectations. We see no evidence for neutral-current production of J/psi via either diffractive or deep inelastic scattering mechanisms.

Leptoproduction of heavy quarks. I. General formalism and kinematics of charged current and neutral current production processes.

Existing calculations of heavy quark production in charged-current and neutral current lepton-hadron scattering are formulated differently because of the artificial distinction of ``light'' and ``heavy'' quarks made in the traditional approach. A proper QCD formalism valid for a wide kinematic range from near threshold to energies much higher then the quark mass should treat these processes in a uniform way. We formulate a unified approach to both types of leptoproduction processes based on the conventional factorization theorem. In this paper, we present the general framework with complete kinematics appropriate for arbitrary masses, emphasizing the simplifications provided by the helicity formalism. We illustrate this approach with an explicit calculation of the leading order contribution to the quark structure functions with general masses. This provides the basis for a complete QCD analysis of charged current and neutral current leptoproduction of charm and bottom quarks to be presented in subsequent papers.

Charged- and neutral-current production ofΔ(1236)

Based on a quark-model approach previously developed by us which employs a ${q}^{2}$ continuation in terms of generalized meson-dominance form factors we study the weak production of the isobar $\ensuremath{\Delta}(1236)$. First we demonstrate that our model is in agreement with the Argonne data on charged-current production of the $\ensuremath{\Delta}$. We then study neutral-current $\ensuremath{\Delta}$ production using four different gauge models, namely, the standard Weinberg-Salam model, a vectorlike model with six quarks, a five-quark model due to Achiman, Koller, and Walsh, and a variant of the G\"ursey-Sikivie model. We fine that the results for the differential cross section in the forward region ($|{q}^{2}|\ensuremath{\lesssim}0.1$ Ge${\mathrm{V}}^{2}$) are very sensitive to the structure of the weak neutral current and suggest that measurements in this region constitute a stringent test of weak-interaction models. We also calculate the density-matrix elements measurable from decay correllations. The density-matrix elements are not so sensitive to the models containing some axial-vector contribution, whereas the vectorlike model shows a behavior quite distinct from the others.

Single-pion production in antineutrino-induced neutral-current interactions

Results are presented on antineutrino-induced processes in which a single π 0or π − is produced. The raw data come from analysis of film from Gargamelle filled with a propane-freon mixture. Comparison of the neutral-current production rates for π 0and π −, after correction for nuclear effects, indicates that pure isoscalar or pure isovector transitions are not favoured. The ratio of the neutral-to-charged-current single- π 0 production rates is found to be compatible with the static model for Δ 33 resonance production in the framework of the Weinberg-Salam theory, yielding values for sin 2 θ W in the range 0.15–0.52.

Vector axial-vector ambiguity in neutral currents and polarization of Δ(1236)

Measurements of the polarization density matrix in neutral current production of Δ(1236) can eliminate the vector axial-vector ambiguity for the isovector neutral couplings.