J.Phys.Conf.Ser.

Level structure of 8He has been studied in the reaction of stopped pion absorption by 11B nuclei 11B(π−,pd)X. The experiment was carried out at the LANL with a two-arm semiconductor spectrometer. The missing mass spectrum in the range 0 MeV < MM < 50 MeV has been described by the superposition of phase-space distributions and the six states of 8He. Parameters of these states have been compared with data of other experimental and theoretical works.

J.Phys.Conf.Ser.

The production of the 7He states was studied in the reactions of stopped pion absorption by carbon isotopes: 12C(π−, p4He)7He, 12C(π−, d3He)7He and 14C(π−, t4He)7He. Measurements were performed using two-arm multilayer semiconductor spectrometer. The ground and excited states were observed in all three reactions. Narrow (Γ < 2 M∍B) state with the high excitation energy ≈ 16 MeV was observed in the 14C(π−, t4He)7He reaction.

J. Phys. Conf. Ser.

Tau neutrino properties are not so well known in comparison to those of muon or electron neutrinos. The tau neutrino interaction cross-section was directly measured by the DONUT experiment in 2008 on a basis of 9 registered tau neutrinos, and with a large systematical error of 50% due to a poor knowledge of the tau neutrino flux in this beam dump experiment. However, more accurate measurement of the cross section is needed for future neutrino experiments. It would also allow testing the Lepton Universality (LU) of Standard Model in neutrino interactions. Recently several results for B-meson decays (LHCb, Babar) demonstrated hints of possible LU violation. The tau neutrinos are produced in the Ds meson decays to tau, Ds → τ v T, and the cascade decay of the tau τ → v T X. DsTau experiment has been proposed to study the tau neutrino production at CERN SPS. It will measure the Ds production differential cross-section in the proton-tungsten interactions. This will allow reducing of the uncertainty due to the tau neutrino flux in the DONUT result from 50% to 10%. The peculiar Ds cascade decay topology ("double kink") in a few mm range will be detected by nuclear emulsion tracker thanks to its excellent spatial resolution (∼50nm). In 2016 and 2017, we made test beam exposures of nuclear emulsion modules at CERN SPS 400GeV/c proton beam followed by the pilot run in August 2018. A physics run in 2021 is scheduled. The status and prospects of the DsTau project as well as a review of the modern nuclear emulsion technique and the methods of its data analysis are presented.

J. Phys. Conf. Ser.

We report Neutrino-4 experiment results of measurements of reactor antineutrinos flux and spectrum dependence on the distance in range 6-12 meters from the center of the reactor core. Using experimental spectrum, we performed the model independent analysis of restrictions on oscillation parameters and sin2 2θ 14. The results of this analysis exclude area of reactor and gallium anomaly at C.L more than 99.7% (> 3σ) for values and sin2 2θ14 > 0.1. However, we observed an oscillation effect at C.L 2.8σ in vicinity of and sin2 2θ 14 ≈ 0.39. The method of coherent addition of results of measurements, which allows us to directly observe the effect of oscillations, is proposed. The analysis of that effect is presented. In general, it seems that the effect predicted in gallium and reactor experiments is being confirmed but at sufficiently large value of . An additional analysis of the measurements was performed taking into account inhomogenei ty of the detector and background instability.

J. Phys. Conf. Ser.

In the coming years, the compact monoenergetic neutron generators (CNG) producing up to 104 n/s may become an alternative to the standard neutron sources based on radioactive isotopes for the calibrations of neutrino and dark matter detectors. Such neutron generators have a typical size of about several centimetres, they may be manufactured using low-background materials and may require only low voltage power supply for operation. We discuss the advantages and disadvantages of two main types of the compact neutron generators, namely a pyroelectric neutron source and a high voltage neutron generator. Also the results of the technical analysis of the possibilities to apply such sources for the calibration of low-background experiments are given, the variant of the internal device design is shown and the full-size compact neutron generator prototype are presented.

JINST

This paper presents a fast approach to simulating muons produced in interactions of the SPS proton beams with the target of the SHiP experiment. The SHiP experiment will be able to search for new long-lived particles produced in a 400 GeV/c SPS proton beam dump and which travel distances between fifty metres and tens of kilometers. The SHiP detector needs to operate under ultra-low background conditions and requires large simulated samples of muon induced background processes. Through the use of Generative Adversarial Networks it is possible to emulate the simulation of the interaction of 400GeV/c proton beams with the SHiP target, an otherwise computationally intensive process. For the simulation requirements of the SHiP experiment, generative networks are capable of approximating the full simulation of the dense fixed target, offering a speed increase by a factor of O(106). To evaluate the performance of such an approach, comparisons of the distributions of reconstructed muon momenta in SHiP’s spectrometer between samples using the full simulation and samples produced through generative models are presented. The methods discussed in this paper can be generalised and applied to modelling any non-discrete multi-dimensional distribution.

Eur. Phys. J. C

The GERmanium Detector Array (Gerda) is a low background experiment located at the Laboratori Nazionali del Gran Sasso in Italy, which searches for neutrinoless double-beta decay of$^{76}$Ge into$^{76}$Se+2e$^-$. Gerda has been conceived in two phases. Phase II, which started in December 2015, features several novelties including 30 new$^{76}$Ge enriched detectors. These were manufactured according to the Broad Energy Germanium (BEGe) detector design that has a better background discrimination capability and energy resolution compared to formerly widely-used types. Prior to their installation, the new BEGe detectors were mounted in vacuum cryostats and characterized in detail in the Hades underground laboratory in Belgium. This paper describes the properties and the overall performance of these detectors during operation in vacuum. The characterization campaign provided not only direct input for Gerda Phase II data collection and analyses, but also allowed to study detector phenomena, detector correlations as well as to test the accuracy of pulse shape simulation codes.

JHEP

A determination of the top-quark mass is presented using 20.2 fb$^{−1}$ of 8 TeV proton-proton collision data produced by the Large Hadron Collider and collected by the ATLAS experiment. The normalised differential cross section of top-quark pair production in association with an energetic jet is measured in the lepton+jets final state and unfolded to parton and particle levels. The unfolded distribution at parton level can be described using next-to-leading-order QCD predictions in terms of either the top-quark pole mass or the running mass as defined in the (modified) minimal subtraction scheme. A comparison between the experimental distribution and the theoretical prediction allows the top-quark mass to be extracted in the two schemes. The value obtained for the pole-mass scheme is:

Eur.Phys.J.C

The algorithms used by the ATLAS Collaboration during Run 2 of the Large Hadron Collider to identify jets containing b-hadrons are presented. The performance of the algorithms is evaluated in the simulation and the efficiency with which these algorithms identify jets containing b-hadrons is measured in collision data. The measurement uses a likelihood-based method in a sample highly enriched in $t{\bar{t}}$ events. The topology of the $t \rightarrow W b$ decays is exploited to simultaneously measure both the jet flavour composition of the sample and the efficiency in a transverse momentum range from 20 to 600 GeV. The efficiency measurement is subsequently compared with that predicted by the simulation. The data used in this measurement, corresponding to a total integrated luminosity of 80.5 $\hbox {fb}^{-1}$, were collected in proton–proton collisions during the years 2015–2017 at a centre-of-mass energy $\sqrt{s}=$ 13 TeV. By simultaneously extracting both the efficiency and jet flavour composition, this measurement significantly improves the precision compared to previous results, with uncertainties ranging from 1 to 8% depending on the jet transverse momentum.

Eur.Phys.J.C

Measurements are presented of the triple-differential cross section for inclusive isolated-photon+jet events in pp collisions at $\sqrt{s} =$ 8 TeV as a function of photon transverse momentum ($p_\mathrm{T}^\gamma$), photon pseudorapidity ($\eta^\gamma$), and jet pseudorapidity ($\eta^\text{jet}$). The data correspond to an integrated luminosity of 19.7 fb$^{-1}$ that probe a broad range of the available phase space, for $|\eta^\gamma|$ $<$ 1.44 and 1.57 $<$ $|\eta^\gamma|$ $<$ 2.50, $|\eta^\text{jet}|$ $<$ 2.5, 40 $<$ $p_\mathrm{T}^\gamma$ $<$ 1000 GeV, and jet transverse momentum, $p_\mathrm{T}^\text{jet}$, $>$ 25 GeV. The measurements are compared to next-to-leading order perturbative quantum chromodynamics calculations, which reproduce the data within uncertainties.

Phys.Rev.Lett.

We report the first observation of D+→τ+ντ with a significance of 5.1σ. We measure B(D+→τ+ντ)=(1.20±0.24stat±0.12syst)×10-3. Taking the world average B(D+→μ+νμ)=(3.74±0.17)×10-4, we obtain Rτ/μ=Γ(D+→τ+ντ)/Γ(D+→μ+νμ)=3.21±0.64stat±0.43syst., which is consistent with the standard model expectation of lepton flavor universality. Using external inputs, our results give values for the D+ decay constant fD+ and the Cabibbo-Kobayashi-Maskawa matrix element |Vcd| that are consistent with, but less precise than, other determinations.

Phys.Rev.Lett.

Results are reported from a search for the rare decays Bs0→τ±μ∓ and B0→τ±μ∓, where the τ lepton is reconstructed in the channel τ-→π-π+π-ντ. These processes are effectively forbidden in the standard model, but they can potentially occur at detectable rates in models of new physics that can induce lepton-flavor-violating decays. The search is based on a data sample corresponding to 3  fb-1 of proton-proton collisions recorded by the LHCb experiment in 2011 and 2012. The event yields observed in the signal regions for both processes are consistent with the expected standard model backgrounds. Because of the limited mass resolution arising from the undetected τ neutrino, the Bs0 and B0 signal regions are highly overlapping. Assuming no contribution from B0→τ±μ∓, the upper limit B(Bs0→τ±μ∓)<4.2×10-5 is obtained at 95% confidence level. If no contribution from Bs0→τ±μ∓ is assumed, a limit of B(B0→τ±μ∓)<1.4×10-5 is obtained at 95% confidence level. These results represent the first limit on B(Bs0→τ±μ∓) and the most stringent limit on B(B0→τ±μ∓).

J.Phys.Conf.Ser.

The J/ψ production is a powerful probe of hadron structure, which is complementary to other parts of the SPD physics program. In this work, the current experimental status and modern theoretical approaches to J/ψ and charmonia production are reviewed. In this context, the SPD performance and feasibility of key measurements are discussed.

Phys.Rev.D

Using E1 radiative transitions ψ(3686)→γχcJ from a sample of (448.1±2.9)×106  ψ(3686) events collected with the BESIII detector, the decays χcJ→Σ+p¯KS0+c.c.(J=0,1,2) are studied. The decay branching fractions are measured to be B(χc0→Σ+p¯KS0+c.c.)=(3.52±0.19±0.21)×10-4, B(χc1→Σ+p¯KS0+c.c.)=(1.53±0.10±0.08)×10-4, and B(χc2→Σ+p¯KS0+c.c.)=(8.25±0.83±0.49)×10-5, where the first and second uncertainties are the statistical and systematic ones, respectively. No evident intermediate resonances are observed in the studied processes.

Sci.China Phys.Mech.Astron.

A search for the doubly charmed baryon $\Xi_{cc}^+$ is performed through its decay to the $\Lambda_c^ + {K^ -}{\pi ^ +}$ final state, using proton-proton collision data collected with the LHCb detector at centre-of-mass energies of 7, 8 and 13 TeV. The data correspond to a total integrated luminosity of 9 fb$^{−1}$. No significant signal is observed in the mass range from 3.4 to 3.8 GeV/c$^{2}$. Upper limits are set at 95% credibility level on the ratio of the $\Xi_{cc}^+$ production cross-section times the branching fraction to that of $\Lambda_c^ +$ and $\Xi_{cc}^{+ +}$ baryons. The limits are determined as functions of the $\Xi_{cc}^+$ mass for different lifetime hypotheses, in the rapidity range from 2.0 to 4.5 and the transverse momentum range from 4 to 15 GeV/c.

Eur.Phys.J.C

A measurement of $W^\pm$ boson production in Pb+Pb collisions at $\sqrt{s_\mathrm {NN}} = 5.02~\text {Te}\text {V}$ is reported using data recorded by the ATLAS experiment at the LHC in 2015, corresponding to a total integrated luminosity of $0.49\,\mathrm {nb^{-1}}$. The $W^\pm$ bosons are reconstructed in the electron or muon leptonic decay channels. Production yields of leptonically decaying $W^\pm$ bosons, normalised by the total number of minimum-bias events and the nuclear thickness function, are measured within a fiducial region defined by the detector acceptance and the main kinematic requirements. These normalised yields are measured separately for $W^+$ and $W^-$ bosons, and are presented as a function of the absolute value of pseudorapidity of the charged lepton and of the collision centrality. The lepton charge asymmetry is also measured as a function of the absolute value of lepton pseudorapidity. In addition, nuclear modification factors are calculated using the $W^\pm$ boson production cross-sections measured in pp collisions. The results are compared with predictions based on next-to-leading-order calculations with CT14 parton distribution functions as well as with predictions obtained with the EPPS16 and nCTEQ15 nuclear parton distribution functions. No dependence of normalised production yields on centrality and a good agreement with predictions are observed for mid-central and central collisions. For peripheral collisions, the data agree with predictions within 1.7 (0.9) standard deviations for $W^-$ ($W^+$) bosons.

Eur.Phys.J.A

This work measured $\mathrm{d}\sigma/\mathrm{d}\Omega$ for neutral kaon photoproduction reactions from threshold up to a c.m. energy of 1855MeV, focussing specifically on the $\gamma p\rightarrow K^0\Sigma^+$, $\gamma n\rightarrow K^0\Lambda$, and $\gamma n\rightarrow K^0 \Sigma^0$ reactions. Our results for $\gamma n\rightarrow K^0 \Sigma^0$ are the first-ever measurements for that reaction. These data will provide insight into the properties of $N^{\ast}$ resonances and, in particular, will lead to an improved knowledge about those states that couple only weakly to the $\pi N$ channel. Integrated cross sections were extracted by fitting the differential cross sections for each reaction as a series of Legendre polynomials and our results are compared with prior experimental results and theoretical predictions.

JINST

We report measurements of the charged daughter fraction of 218Po as a result of the 222Rn alpha decay, and the mobility of 218Po+ ions, using radon-polonium coincidences from the 238U chain identified in 532 live-days of DarkSide-50 WIMP-search data. The fraction of 218Po that is charged is found to be 0.37 ± 0.03 and the mobility of 218Po+ is (8.6 ± 0.1) × 10−4 cm2/Vs.

JHEP

A search for the standard model production of four top quarks (pp → $\mathrm{t}\overline{\mathrm{t}}\mathrm{t}\overline{\mathrm{t}}$) is reported using single-lepton plus jets and opposite-sign dilepton plus jets signatures. Proton-proton collisions are recorded with the CMS detector at the LHC at a center-of-mass energy of 13 TeV in a sample corresponding to an integrated luminosity of 35.8 fbParseError: KaTeX parse error: Double superscript at position 5: ^{−}^̲{1}. A multivariate analysis exploiting global event and jet properties is used to discriminate $\mathrm{t}\overline{\mathrm{t}}\mathrm{t}\overline{\mathrm{t}}$ from $\mathrm{t}\overline{\mathrm{t}}$ production. No significant deviation is observed from the predicted background. An upper limit is set on the cross section for $\mathrm{t}\overline{\mathrm{t}}\mathrm{t}\overline{\mathrm{t}}$ production in the standard model of 48 fb at 95% confidence level. When combined with a previous measurement by the CMS experiment from an analysis of other final states, the observed signal significance is 1.4 standard deviations, and the combined cross section measurement is ${13}_{-9}^{+11}$ fb. The result is also interpreted in the framework of effective field theory.

JETP Lett.

The pre-asymptotic analysis of the multichannel scattering problem for particles with an arbitrary spin and short-range interactions has been presented. The complete operator-valued dependence of the scattered differential flux on the distance to the target exactly consistent with the unitarity condition has been obtained.

Phys.Rev.D

Using a sample of 448.1×106  ψ(3686) events collected with the BESIII detector, we perform a study of the decay ψ(3686)→ϕπ+π-η. The branching fraction of ψ(3686)→ϕη′ is determined to be (1.51±0.16±0.12)×10-5, which is consistent with the previous measurement but with significantly improved precision. The resonances f1(1285) and η(1405) are clearly observed in the π+π-η mass spectrum with statistical significances of 18σ and 9.7σ, respectively. The corresponding product branching fractions are measured to be B(ψ(3686)→ϕf1(1285), f1(1285)→π+π-η)=(1.03±0.10±0.09)×10-5 and B(ψ(3686)→ϕη(1405), η(1405)→π+π-η)=(8.46±1.37±0.92)×10-6. These results are used to test the perturbative QCD “12% rule.”

Phys. Lett. B

A search for a right-handed gauge boson WR , decaying into a boosted right-handed heavy neutrino NR , in the framework of Left-Right Symmetric Models is presented. It is based on data from proton–proton collisions with a centre-of-mass energy of 13 TeV collected by the ATLAS detector at the Large Hadron Collider during the years 2015, 2016 and 2017, corresponding to an integrated luminosity of 80 fb −1 . The search is performed separately for electrons and muons in the final state. A distinguishing feature of the search is the use of large-radius jets containing electrons. Selections based on the signal topology result in smaller background compared to the expected signal. No significant deviation from the Standard Model prediction is observed and lower limits are set in the WR and NR mass plane. Mass values of the WR smaller than 3.8–5 TeV are excluded for NR in the mass range 0.1–1.8 TeV.

PoS

A search for the production of three massive vector bosons in proton--proton collisions is performed using data at $\sqrt{s}=13\,TeV$ recorded with the ATLAS detector at the Large Hadron Collider in the years 2015--2017, corresponding to an integrated luminosity of $79.8\,\text{fb}^{-1}$. Events with two same-sign leptons $\ell$ (electrons or muons) and at least two reconstructed jets are selected to search for $WWW\to\ell\nu\ell\nu qq$. Events with three leptons without any same-flavour opposite-sign lepton pairs are used to search for $WWW\to\ell\nu\ell\nu\ell\nu$, while events with three leptons and at least one same-flavour opposite-sign lepton pair and one or more reconstructed jets are used to search for $WWZ\to\ell\nu qq \ell\ell$. Finally, events with four leptons are analysed to search for $WWZ\to\ell\nu\ell\nu\ell\ell$ and $WZZ\to qq \ell\ell\ell\ell$. Evidence for the joint production of three massive vector bosons is observed with a significance of 4.0 standard deviations, where the expectation is 3.1 standard deviations.

Phys.Lett.B

A search for the production of three massive vector bosons in proton–proton collisions is performed using data at s=13 TeV recorded with the ATLAS detector at the Large Hadron Collider in the years 2015–2017, corresponding to an integrated luminosity of 79.8 fb −1 . Events with two same-sign leptons ℓ (electrons or muons) and at least two reconstructed jets are selected to search for WWW→ℓνℓνqq . Events with three leptons without any same-flavour opposite-sign lepton pairs are used to search for WWW→ℓνℓνℓν , while events with three leptons and at least one same-flavour opposite-sign lepton pair and one or more reconstructed jets are used to search for WWZ→ℓνqqℓℓ . Finally, events with four leptons are analysed to search for WWZ→ℓνℓνℓℓ and WZZ→qqℓℓℓℓ . Evidence for the joint production of three massive vector bosons is observed with a significance of 4.1 standard deviations, where the expectation is 3.1 standard deviations.

Phys. Lett. B

A measurement of the Higgs boson production cross sections via associated WH and ZH production using H→WW⁎→ℓνℓν decays, where ℓ stands for either an electron or a muon, is presented. Results for combined WH and ZH production are also presented. The analysis uses events produced in proton–proton collisions collected with the ATLAS detector at the Large Hadron Collider in 2015 and 2016. The data correspond to an integrated luminosity of 36.1fb−1 recorded at a centre-of-mass energy of 13 TeV. The products of the H→WW⁎ branching fraction times the WH and ZH cross sections are measured to be 0.67−0.27+0.31 (stat.) −0.14+0.18 (syst.) pb and 0.54−0.24+0.31 (stat.) −0.07+0.15 (syst.) pb respectively, in agreement with the Standard Model predictions.