Search

On the statistics of ~1.7 × 108 interactions of positively charged kaons on copper nuclei, coherent events of the K+π0 system production are selected. The cross sections for the Coulomb and coherent strong components and their interference in the region of the K*(892) meson are measured. The partial width for the decay K*(892) → K+γ is determined. When studying the mass spectrum of the K+π0 system, an effect which can be interpreted as the interference of the chiral anomaly and the K*(892) s-channel amplitudes is found. This gives an estimate for the ratio of the observed amplitude of the chiral anomaly to the theoretical one: Aexp/Ath = 0.9 ± 0.24(stat.) ± 0.3(syst.).

A high statistics data sample of the $$K^{+}\rightarrow \mu ^{+}\nu _{\mu }$$ decay was accumulated by the OKA experiment in 2012. The missing mass analysis was performed to search for the decay channel $$K^{+}\rightarrow \mu ^{+}\nu _{H}$$ with a hypothetic stable heavy neutrino in the final state. The obtained missing mass spectrum does not show peaks that could be attributed to existence of stable heavy neutrinos in the mass range $$(270< m_{\nu _{H}} < 375)$$ MeV $$/c^{2}$$ . As a result, upper limits on the branching ratio and on the value of the mixing element $$|U_{\mu H}|^{2}$$ are obtained.

Recent results from OKA setup concerning form factor studies in Ke3 decay are presented. About 5.25 M events obtained for decays of 17.7 GeV/cK+ are selected for the analysis. The linear and quadratic slopes for the decay form factor f+(t) are measured: λ'+ = 2.95 ± 0.022 ± 0.018 × 10 -2 for the linear slope fit and λ+ = 2.611 ± 0.035 ± 0.028 × 10 -2, λ"+ = 1.91 ± 0.19 ± 0.14 × 10 -3 for the quadratic one. The scalar and tensor contributions are compatible with zero. Several alternative parametrizations are tried: the Pole fit parameter is found to be M V = 891 ± 3 MeV; the parameter of the dispersive parametrization is measured to be Λ+ = 2.458 ± 0.018 × 10-2.

A high statistics data sample of the decays of $$K^+$$ mesons to three charged particles was accumulated by the OKA experiment in 2012 and 2013. This allowed to select a clean sample of about 450 events with $$K^{+}\rightarrow \pi ^{+}\pi ^{-}\pi ^{+}\gamma $$ decays with the energy of the photon in the kaon rest frame greater than 30 MeV. The measured branching fraction of the $$K^{+}\rightarrow \pi ^{+}\pi ^{-}\pi ^{+}\gamma $$ , with $$E_{\gamma }^{*} > 30\ \hbox {MeV}$$ is equal to $$(0.71 \pm 0.05) \times 10^{-5}$$ . The measured differential branching fraction over photon energy is compared with the prediction of the chiral perturbation theory to $${\mathcal {O}}(p^{4})$$ . A search for an up-down asymmetry of the photon with respect to the hadronic system decay plane is also performed.

The ratio of branching fractions for \(K^ - \to e^ - \bar \nu _e \pi ^0\) andK− → π−π0 decays has been measured using the ISTRA+ spectrometer. The result of our measurement is the following: $$\mathcal{R}_{Ke_3 /K_{2\pi } } = 0.2423 \pm 0.0015(stat.) \pm 0.0037(syst.).$$ Using the current PDG value for the K2π branching fraction, this result leads to the measured Ke3 branching fraction of Br(Ke3) = 0.0501 ± 0.0009 and to the value of |Vus|f+(0) = 0.2115 ± 0.0021.

Heavy neutrino ν h with m h ≲ 300 MeV / c 2 can be effectively searched for in kaon decays. We put upper limits on a mixing matrix element | U μ h | 2 for radiatively decaying ν h from K − → μ − ν h ( ν h → ν γ ) decay chain in the following parameter region: 30 MeV / c 2 ⩽ m h ⩽ 80 MeV / c 2 ; 10 − 11 s ⩽ τ h ⩽ 10 − 9 s . For the whole region | U μ h | 2 ≲ 5 ⋅ 10 − 5 for Majorana type of ν h and | U μ h | 2 ≲ 8 ⋅ 10 − 5 for the Dirac case.

The radiative decay K − → μ − ν μ γ has been studied at ISTRA+ setup in a new kinematic region. About 22K events of K − → μ − ν μ γ have been observed. The sign and value of F V − F A have been measured for the first time. The result is F V − F A = 0.21 ± 0.04 ( stat ) ± 0.04 ( syst ) .

Results of study of the K{sup -}{yields}{pi}{sup 0}e{sup -}{nu}-bar{gamma} decay at the ISTRA+ setup are presented. We observed 4476 events of this decay. The branching ratio is found to be R=(Br(K{sup -}{yields}{pi}{sup 0}e{sup -}{nu}-bar{sub e}{gamma}))/(Br(K{sup -}{yields}{pi}{sup 0}e{sup -}{nu}-bar{sub e})) (1.81{+-}0.03(stat.){+-}0.07(syst.)) x 10{sup -2} for E*{sub {gamma}} > 10 MeV and {theta}*{sub e{gamma}} > 10{sup o}. For comparison with the previous experiment the branching ratio with cuts E*{sub {gamma}} > 10 MeV, 0.6 30 MeV and {theta}*{sub e{gamma}} > 20{sup o}, used in most theoretical papers, Br (3.06 {+-} 0.09(stat.) {+-} 0.14(syst.)) x 10{sup -4}. For the asymmetry we get A{sub {xi}} = -0.015 {+-} 0.021. At present it is the best estimate of this asymmetry.

Using data collected with the ISTRA+ spectrometer during the 2001 run of the U-70 proton synchrotron in Protvino, we report the first observation of the radiative kaon decay K- -->mu-pi0gammanu. We find Br(Kmu3g)/Br(Kmu3) for two regions 5

The branching ratio in the charged-pion kinetic energy region of 55 to 90 MeV for the direct photon emission in the K- --> pi- pi0 gamma decay has been measured using in-flight decays detected with the ISTRA+ setup operating in the 25 GeV/c negative secondary beam of the U-70 PS. The value Br(DE)=[0.37+-0.39(stat)+-0.10(syst)]*10^(-5) obtained from the analysis of 930 completely reconstructed events is consistent with the average value of two stopped-kaon experiments, but it differs by 2.5 standard deviations from the average value of three in-flight-kaon experiments. The result is also compared with recent theoretical predictions., Comment: 13 pages, 8 figures

The decay K- -> pi0 e- nu is studied using in-flight decays detected with the ISTRA+ spectrometer. About 920K events are collected for the analysis. The lambda+ slope parameter of the decay form-factor f+(t) in the linear approximation (average slope) is measured: lambda+(lin)= 0.02774 +- 0.00047(stat) +- 0.00032(syst). The quadratic contribution to the form-factor was estimated to be lambda'+ = 0.00084 +- 0.00027(stat) +- 0.00031(syst). The linear slope, which has a meaning of df+(t)/dt|_{t=0} for this fit, is lambda+ = 0.02324 +- 0.00152(stat) +- 0.00032(syst). The limits on possible tensor and scalar couplings are derived: f_{T}/f_{+}(0)=-0.012 +- 0.021(stat) +- 0.011$(syst), f_{S}/f_{+}(0)=-0.0037^{+0.0066}_{-0.0056}(stat) +- 0.0041(syst)., Comment: 11 pages, 8 figures. Accepted by Phys.Lett. B

The decay K−→π0μ−ν has been studied using in-flight decays detected with the “STRA+” spectrometer. About 540K events were collected for the analysis. The λ+ and λ0 slope parameters of the decay form-factors f+(t), f0(t) have been measured: λ+=0.0277±0.0013(stat)±0.0009(syst), λ0=0.0183±0.0011(stat)±0.0006(syst), and dλ0/dλ+=−0.348. The limits on the possible tensor and scalar couplings have been derived: fT/f+(0)=−0.0007±0.0071, fS/f+(0)=0.0017±0.0014. No visible non-linearity in the form-factors have been observed.

The decay K − → μ − νπ 0 has been studied using in-flight decays detected with the ISTRA+ setup operating in the 25-GeV negative secondary beam of the U-70 PS. About 112K events were used for the analysis. The λ + and λ 0 slope parameters of the decay form factors f +(t) and f 0(t) have been measured: λ +=0.0321±0.004(stat.)±0.002(syst.), λ 0=0.0209±0.004(stat.)±0.002(syst.); the correlation dλ 0/dλ +=−0.46. The limits on the possible tensor and scalar couplings have been derived: f T/f +(0)=−0.021±0.028(stat.)±0.014(theor.), f S/f +(0)=0.004±0.005(stat.)±0.005(theor.).

A selected sample of 59200 π+p andK+p nonsingle-diffrative interactions at\(\sqrt s \) =22 GeV is used to investigate one, two- and three-dimensional factorial moments, factorial cumulant moments, as well as correlation integrals. The rise of factorial moments and cumulants with decreasing phase-space volume is stronger when evaluated in three than in lower dimensions. Ratios of slopes are easier to obtain than the slopes themselves. Contrary to earlier findings, they turn out to depend on the dimension. The order dependence of the averaged ratios is better described by a Levy stable law solution with μ=1.6 than by Gaussian approximation of the α-model (μ=2) or a second order phase transition (μ=0), but values μ>2 inconsistent with Levy-type fluctuations are reached in a three-dimensional analysis. The multiparticle contributions to the factorial moments are calculated by means of factorial cumulant moments. A particular improvement of the method is that of correlation (or density) integrals. It leads to the conclusion that Bose-Einstein interference plays an important role in the intermittency effect, but indication is found for an interpretation alternative to the conventional view of Bose-Einstein correlations.

We report on a study of inclusiveπ0 and η meson production inπ+p andK+p interactions at 250 GeV/c beam momentum. The Feynman-x spectrum ofπ0 is very similar in shape and normalization to that of negatively charged particles produced in the same experiment. The results are compared with data at other energies and with FRITIOF model predictions. This model overestimates the η cross section by a factor of 2.5. It reproduces theπ0 cross section correctly, but predicts a too hardπ0x distribution.

Inclusive production of direct soft photons is studied inK + p andK + π interactions at 250 GeV/c. Total cross sections, Feynman-x and transverse momentum distributions of direct γ's are presented. The measured cross sections are several times larger than expected from QED inner bremsstrahlung, indicating the presence of an anomalous soft photon source. The model of Lichard and Van Hove, based on the “cold quark-gluon plasma” picture, agrees with the data.

Experimental data are presented on deuteron production in the target fragmentation region for 250 GeV/c π+ interactions with Al and Au nuclei, and compared with analogous data on proton production. Indications are observed for narrow structures in the (dπ-) effective mass system at ∼2.04 and ∼2.08 GeV.

A sample of 8000 interactions of 250 GeV/c π+ andK+ mesons on Al and Au nuclei, is used to search for intermittency effects by calculating the normalized factorial moments of order two to four. No significant effect is observed in the higher moments. Two-body rapidity correlations and Bose-Einstein correlations in these interactions are presented.

Two- and three-particle rapidity correlations are analyzed inK+p and π+p-interactions at 250 GeV/c. The main contribution to the two- and three-particle correlation functions comes from mixing of events of different multiplicity. The (short range) two-particle correlation remaining after exclusion of mixing is significantly larger for (+−) than for the equal charge combinations, and is positive for a wider range in rapidity difference. FRITIOF and a 2-string DPM are excluded by our data. A quark-gluon (multi-)string model can describe our inclusive correlation function, but needs to be tuned on the short range part. The multiplicity mixing part increases much faster with increasing energy than the short range part. In the central region, our correlation is similar to that observed ine+e− and μp collisions at similar energy.

The negative binomial distribution (NBD) is fitted to all charged and to negative particle multiplicity distributions in restricted rapidity intervals, both in the forward and backward c.m. hemispheres of positive meson interactions on Al and Au nuclei. For negative particle multiplicity distributions, the NBD parameters are also determined as a function ofng, the number of grey tracks, corresponding to varying number of intranuclear collisions. The data are interpreted in terms of the clan picture of Giovannini and Van Hove and compared to the MCMHA and Fritiof models. Both models reproduce quite well the global multiplicity distributions, but not when sub-samples are considered with fixed number of grey tracks. Regularities are better visible on the parton than on the particle level.

The inclusive production of neutral kaons is studied inK+p and π+p interactions at 250 GeV/c. Total and semi-inclusive cross sections and average kaon multiplicities are presented and compared with the data at lower energies. The longitudinal and transverse momentum distributions and their energy dependence are analyzed. The results are interpreted in the framework of recent parton models.

We report on a study of ρ0, ρ+, ω,\(\bar K^{*0} (892)\) andK*0 (892) inclusive production in π+p interactions at 250 GeV/c, for ρ+,\(\bar K^{*0} (892)\) for the first time in a π+p experiment. The data are compared withK+p data in the same experiment, with results of other experiments and with quark-parton models. Interesting differences are found between ρ+,0 and ω production.

Density fluctuations are studied in rapidity, pseudo-rapidity and azimuthal angle, as well as in two-dimensional distributions in rapidity and azimuthal angle. Evidence for intermittency, i.e. rise of factorial moments with increasing resolution, is found in all four distributions. Intermittency is stronger in two dimensions than in one, but the difference is smaller than would be expected from the production of “pencil jets”. Contrary to what would be expected from Bose-Einstein interference, no increase by a factor 2 is found in slope when the analysis is restricted to particles of identical charge.

It is shown that at collider energies experimental multiplicity distributions are well parameterized by a sum of Gupta-Sarma distributions. This extends earlier description of the lower energy data by the two parameter sum of Poissonians. Implications of the proposed parametrization for LHC are discussed., 16 pages, Latex, 4 EPS figures

It is shown that charged hadron multiplicity distributions in lepton-nucleon scattering are fairly well described by the modified negative binomial distribution in the energy range from 3-4 to 220 GeV. The energy behaviour of the parameter k is similar to the dependence observed for e+e- annihilation., Comment: 12 pages, Latex, 2 Poscript figures, epsfig is used, to be published in Physics Letters B

It is shown that charged hadron multiplicity distributions in restricted (pseudo)rapidity intervals in e+e- annihilation and in e+p scattering at HERA are quite well described by the modified negative binomial distribution and its simple extension., Comment: 12 pages, Latex, to be published in Physics Letters B

An analysis is presented of the rapidity and transverse momentum distributions and of the nuclear stopping power in collisions ofπ + andK + mesons with Al and Au nuclei at 250 GeV/c. The experimental results are compared to predictions of the additive quark model and the dual parton model. The AQM offers an overall consistent description of the data in this experiment. The DPM reproduces reasonably well the rapidity spectra in the central and projectile fragmentation regions, but fails to describe the nuclear stopping power.

Density fluctuations are studied in rapidity, separately for low and intermediate transverse momentum particles. In our data, the effect of intermittency is increased when the analysis is restricted to low pT particles.

A triple Regge analysis is performedof inclusive Λ production in the proton fragmentation region ofK+→Λ+X and π+→Λ+X at 250 GeV/c. Slope and intercept of the leading strange meson trajectory are determined. The results obtained here are compared with those of other experiments.

Quasi-elastic scattering with central dipion cluster production is studied in π+p andK+p interactions at 250 GeV/c. The cross section of double pomeron exchange is obtained as σDPE(π+p →π+(π+π−)p)=24 ±5 µb and σDPE(K+p→K+(π+π−)p)=19 ±5 µb. The low energy pomeron-pomeron cross section is estimated for the first time.

Inclusive data are presented on ϱ 0 ,ϱ + and ω produced in k + p interactions at 250 GeV/ c , for ϱ + and ω for the first time in K + p experiment. In the forward CM hemisphere, the ϱ + , ϱ 0 and ω differential production rates are equal within errors, and remarkably similar to muon-inelastic scattering data on ϱ 0 and ω at 280 GeV/ c .

Inclusive charged pion production is studied in an exposure of BEBC, filled with hydrogen, to an incidentK + beam of 70 GeV/c. Total cross sections for pion production and inclusive longitudinal and transverse momentum distributions of π−'s and of positive particles are presented and compared with data at lower energies. Earlier evidence for scaling in the fragmentation regions is confirmed. The central region π− cross section increases proportionally top LAB −1/4 ; positive particles show almost no energy dependence atx=0. Particle ratios π+/π− are studied as a function ofx andy * and a comparison with 70 GeV/cK − p data is made. Analysis of structure functions for (ππ) pairs and of particle production associated with π± triggers at large |x| in the context of quark/parton models, provides qualitative evidence for the diquark-quark structure of the proton.

Multiplicity distributions, observed inK + interactions with Al and Au nuclei at 250 GeV/c incident momentum are presented. They are analyzed in the framework of multiple collisions of the incident particle inside a nucleus. The probability distribution of the number of grey tracks is well described by the model of Andersson et al., if a negative binomial distribution is assumed for the distribution of the number of grey protons produced per elementary collision instead of the usual geometrical distribution. The analysis of the average and dispersion of the charge multiplicity distribution supports the validity of the multiple collision model, including results on correlations between forward and backward multiplicities.

Production of Σ ∗− and Ξ ∗− antibaryon resonances in K+ fragmentation processes is observed by studying inclusive λ π + and λ K + invariant mass distributions in 32 GeV/c K+p interactions. A possible Ξ ∗− state is reported with a mass of 2137±4 MeV and width ≲20 MeV. Signals are observed at λ K + masses of 2240, 2380 and 2540 MeV, which correspond to previously observed Ξ ∗− states. Evidence is presented for a low-mass λ p enhancement around 2145 MeV.

Four- and six-body final states in K + p interactions at 32 GeV/ c are studied in terms of principal-axis variables. Evidence is found for considerable alignment of the final-state particles towards a preferred plane in momentum space. The experimental results are compared with an uncorrelated production model which, apart from the alignment effects, reproduces satisfactorily the main characteristics of the principal-axis variables. The slope of the “generalized scattering angle” distribution is found to provide information on the r.m.s. initial-state impact parameter of the reaction.

The inclusive inelastic processesK + p→pX + andK + p→Δ ++ X 0 are studied at an incident momentum of 70 GeV/c. The data comes from the Big European Bubble Chamber BEBC filled with hydrogen, exposed to an rf reparatedK + beam at the CERN SPS accelerator. The inclusive cross section for protons with laboratory momentump LAB≦1.2 GeV/c is equal to (6.1±0.1) mb. InclusiveΔ ++-production is studied for |t p, Δ

The production properties ofKs0,\(\bar \Lambda\) andK+p interactions at 32 GeV/c are investigated using the final statistics of the experiment. We present total and semi-inclusive cross sections and aver-age multiplicities. Estimates are given of the diffractive dissociation contributions to total and differential cross sections. Thex-,pT−, and transverse mass dependence of inclusive and semi-inclusive distributions is discussed as well as properties of “prompt”Ks0's. The ratio of “prompt”K890+ (K8900) to “prompt”K0 cross sections is measured to be 1.03±0.12 (0.98±0.17). From a comparison of\(\bar \Lambda\) production inK±p interactions at 32 GeV/c, we estimate a strange sea-quark suppression of 0.26 ±0.02. The double differential cross sections ofKs0's is studied as a function of Feynman-x andpT2, and a Triple-Regge fit performed. The data are compared in detail to versions of the Lund-model for low-pT hadronic collisions.

The charged particle multiplicity distribution is studied for non-single-diffractive π + p collisions at √ s =22 GeV, in central rapidity intervals separated from the outer regions by empty gaps. A priori unexpectedly, also these distributions yield good negative binomial fits. The variation of the parameter 1/ k as a function of the gap size can be understood in terms of cascading clans of limited rapidity range if events with a large number of clans preferably contribute to the central region. The Fritiof-3 model agrees quantitatively with the data.

Inclusive production of Δ ++ (1232) with >| t p, Δ ++>| c ) 2 is studied in 32 GeV/ c K + p interactions. A systematic comparison with the reaction K + p→pX for >| t p,p>| c ) 2 is made. The production properties of the Δ ++ (1232), of associated π + , π − and K 0 production and of the recoiling system X 0 are investigated in detail. The polarization of the Δ ++ and the energy dependence of the total K + π − cross sections, determined by a Chew-Low extrapolation, are presented and discussed.

The charged particle multiplicity distribution has been studied for non-single-diffractive π+ p andpp collisions at $$\sqrt s = 22$$ GeV, for full phase space as well as for intervals in rapidity, azimuthal angle and transverse momentum. In general, the multiplicity distribution is well described by a negative binomial. From comparison of the distribution for negative or positive particles to that of all charged particles, cascading is favoured as an interpretation over stimulated emission. Interesting consequences follow from a comparison of our results to those at collider energies and toe + e − data at comparable energy. Furthermore, evidence is given that the multiplicity distribution is not exactly of negative binomial type in every (connected or disconnected) phase space region.

Cross sections and charged multiplicity distributions for π+p,K+p andpp interactions at 250 GeV/c are presented and compared to each other as well as to earlier (for π+p andK+p lower energy) data. Consistently, the meson-proton (M+p) data have narrower multiplicity distributions and higher average multiplicity thanpp data. Up to our energy, generalized KNO functions describe the energy dependence of the shape of the multiplity distribution with one parameter forM+p and one forpp collisions. If interpreted in terms of negative binomials, the parameter 1/k tends to be slightly lower forM+p than forpp data. For both types of hadron-hadron collision, 1/k is larger than fore+e− andlp collisions.

Two-particle K0π+ and K0π− rapidity correlations in K+p interactions at 8.2 and 16 GeV/c are compared for different regions of (K0π±) effective mass. It is shown that at these energies the strong K∗(892) resonance production has a very small effect on the K0π+ rapidity behaviour.

The inclusive production of Ξ+ and Ξ− hyperons is investigated in K+ p interactions at 32 GeV/c. The production cross sections, 36.4±9 μb for the Ξ+ and 6.5±3 μb for the Ξ−, are rising strongly with energy similarly to Λ and Λ production in K+ p interactions. The Ξ+ are produced preferentially in the forward direction in the c.m.s., while the Ξ− are produced dominantly backwards. The average transverse momenta 〈pT〉Ξ+=0.73±0.09 GeV/c and 〈pT〉Ξ−=0.58±0.09 GeV/c.