Search for QCD instanton-induced processes at HERA in the high-Q2{Q^2} domain

Signals of QCD instanton-induced processes are searched for in neutral current deep-inelastic scattering at the electron-proton collider HERA in the kinematic region defined by the Bjorken-scaling variable x > 10−3, the inelasticity 0.2 < y < 0.7 and the photon virtuality 150 < Q2 < 15000 GeV2. The search is performed using H1 data corresponding to an integrated luminosity of 351 pb−1. No evidence for the production of QCD instanton-induced events is observed. Upper limits on the cross section for instanton-induced processes between 1.5 pb and 6 pb, at 95% confidence level, are obtained depending on the kinematic domain in which instantons could be produced. Compared to earlier publications, the limits are improved by an order of magnitude and for the first time are challenging predictions

Unbinned deep learning jet substructure measurement in high Q2Q^2 ep collisions at HERA

The radiation pattern within high energy quark- and gluon-initiated jets (jet substructure) is used extensively as a precision probe of the strong force as well as an environment for optimizing event generators with numerous applications in high energy particle and nuclear physics. Looking at electron-proton collisions is of particular interest as many of the complications present at hadron colliders are absent. A detailed study of modern jet substructure observables, jet angularities, in electron-proton collisions is presented using data recorded using the H1 detector at HERA. The measurement is unbinned and multi-dimensional, using machine learning to correct for detector effects. All of the available reconstructed object information of the respective jets is interpreted by a graph neural network, achieving superior precision on a selected set of jet angularities. Training these networks was enabled by the use of a large number of GPUs in the Perlmutter supercomputer at Berkeley Lab. The particle jets are reconstructed in the laboratory frame, using the kt jet clustering algorithm. Results are reported at high transverse momentum transfer $Q^2$>150 GeV$^2$ , and inelasticity 0.2<y<0.7 . The analysis is also performed in sub-regions of Q$^2$, thus probing scale dependencies of the substructure variables. The data are compared with a variety of predictions and point towards possible improvements of such models

Study of η ′ → π + π − l + l − decays at BESIII

With a sample of (10087 ± 44) × 106J/ψ events accumulated with the BESIII detector, we analyze the decays η′ → π+π−l+l−(l = e, μ) via the process J/ψ → γη′. The branching fractions are measured to be B(η′ → π+π−e+e−) = (2.45 ± 0.02(stat.) ± 0.08(syst.)) × 10−3 and B(η′ → π+π−μ+μ−) = (2.16 ± 0.12(stat.) ± 0.06(syst.)) × 10−5, and the ratio is Bη′→π+π−e+e−Bη′→π+π−μ+μ−=113.4±0.9stat.±3.7syst.. In addition, by combining the η′ → π+π−e+e− and η′ → π+π−μ+μ− decays, the slope parameter of the electromagnetic transition form factor is measured to be bη′ = 1.30 ± 0.19 (GeV/c2)−2, which is consistent with previous measurements from BESIII and theoretical predictions from the VMD model. The asymmetry in the angle between the π+π− and l+l− decay planes, which has the potential to reveal the CP-violation originating from an unconventional electric dipole transition, is also investigated. The asymmetry parameters are determined to be ACPη′→π+π−e+e−=−0.21±0.73stat.±0.01syst.% and ACPη′→π+π−μ+μ−=0.62±4.71stat.±0.08syst.%, implying that no evidence of CP-violation is observed at the present statistics. Finally, an axion-like particle is searched for via the decay η′ → π+π−a, a → e+e−, and upper limits of the branching fractions are presented for the mass assumptions of the axion-like particle in the range of 0 − 500 MeV/c2

Multi-leptons with High Transverse Momentum at HERA

Events with at least two high transverse momentum leptons (electrons or muons) are studied using the H1 and ZEUS detectors at HERA with an integrated luminosity of 0.94 fb-1. The observed numbers of events are in general agreement with the Standard Model predictions. Seven di- and tri-lepton events are observed in e+p collision data with a scalar sum of the lepton transverse momenta above 100GeV while 1.94 ± 0.17 events are expected. Such events are not observed in e-p collisions for which 1.19 ± 0.12 are predicted. Total visible and differential di-electron and di-muon photoproduction cross sections are extracted in a restricted phase space dominated by photon-photon collisions. © SISSA 2009

Measurement of e + e − → ωη ′ cross sections at s = 2. 000 to 3. 080 GeV

We measured the Born cross sections for the process e+e− → ωη′ at 22 center-of-mass energies from 2.000 to 3.080 GeV with the BESIII detector at the BEPCII collider. We observed a resonant structure with a statistical significance of 9.6σ. A Breit-Wigner fit determines its mass to be MR = (2153 ± 30 ± 31) MeV/c2 and its width to be ΓR = (167 ± 77 ± 7) MeV, where the first uncertainties are statistical and the second are systematic

Measurement of the e + e − → K S 0 K L 0 π 0 cross sections from s = 2. 000 to 3. 080 GeV

Based on e+e− collision data collected at center-of-mass energies from 2.000 to 3.080 GeV by the BESIII detector at the BEPCII collider, a partial wave analysis is performed for the process e+e− → KS0KL0π0. The results allow the Born cross sections of the process e+e− → KS0KL0π0, as well as its subprocesses e+e− → K∗(892)0K¯0 and K2∗(1430)0K¯0 to be measured. The Born cross sections for e+e− → KS0KL0π0 are consistent with previous measurements by BaBar, but with substantially improved precision. The Born cross section lineshape of the process e+e−K∗(892)0K¯0 is consistent with a vector meson state around 2.2 GeV with a significance of 3.2σ. A Breit-Wigner fit determines its mass as MY = (2164.7 ± 9.1 ± 3.1) MeV/c2 and its width as ΓY = (32.4 ± 21.0 ± 1.8) MeV

Search for the semi-muonic charmonium decay J/ψ → D − μ + ν μ + c. c

Using (10087 ± 44) × 106J/ψ events collected with the BESIII detector at the BEPCII e+e− storage ring at the center-of-mass energy of s = 3.097 GeV, we present a search for the rare semi-muonic charmonium decay J/ψ → D−μ+νμ + c.c.. Since no significant signal is observed, we set an upper limit of the branching fraction to be B (J/ψ → D−μ+νμ + c.c.) < 5.6 × 10−7 at 90% confidence level. This is the first search for the weak decay of charmonium with a muon in the final state

Search for ∆S = 2 nonleptonic hyperon decays Ω − → Σ 0 π − and Ω − → nK −

Using (27.12 ± 0.14) × 108ψ(3686) events collected by the BESIII detector at the center-of-mass energy of s = 3.686 GeV, we search for the first time for two nonleptonic hyperon decays that change strangeness by two units, Ω− → Σ0π− and Ω− → nK−. No significant signal is observed. The upper limits on their decay branching fractions are determined to be B(Ω− → Σ0π−) < 5.4 × 10−4 and B(Ω− → nK−) < 2.4 × 10−4 at the 90% confidence level

Events with an Isolated Lepton and Missing Transverse Momentum and Measurement of W Production at HERA

A search for events containing an isolated electron or muon and missing transverse momentum produced in e±p collisions is performed with the H1 and ZEUS detectors at HERA. The data were taken in the period 1994-2007 and correspond to an integrated luminosity of 0.98 fb-1. The observed event yields are in good overall agreement with the Standard Model prediction, which is dominated by single W production. In the e+p data, at large hadronic transverse momentum PTX \u3c 25GeV, a total of 23 events are observed compared to a prediction of 14.0 ±1.9. The total single W boson production cross section is measured as 1.06 ± 0.16 (stat.) ± 0.07 (sys.) pb, in agreement with an Standard Model (SM) expectation of 1.26 ± 0.19 pb