KS Mesons Research Articles

Fractal Entropy of Nuclear Medium Probed by KS0 Mesons Produced in AuAu Collisions at RHIC

In this paper, we review our findings concerning fractal entropy of microscopic configurations corresponding to the production of KS0 mesons in AuAu collisions in the z-scaling approach. The entropy is expressed via structural and fragmentation fractal dimensions, and model parameter cAuAu is interpreted as a specific heat of produced medium. These parameters are related to the respective momentum fractions of the colliding nuclei, the momentum fractions of the scattered constituents that fragment into the produced hadrons, and the multiplicity density of negative particles in the central interaction region. The dependence of the entropy on the collision energy over the range of 7.7–200 GeV for most central and most peripheral events is studied as a function of the transverse momentum of the produced KS0 mesons. A non-trivial dependence of the entropy on the collision energy with decreasing transverse momentum is found. This reflects the irregularity of the behavior of the specific heat, cAuAu, and can point to a manifestation of phase transition in nuclear matter.

Measurement of the KS→ πeν branching fraction with the KLOE experiment

The ratio mathcal{R} = Γ(KS→ πeν)/Γ(KS→ π+π−) has been measured with a sample of 300 million KS mesons produced in ϕ → KLKS decays recorded by the KLOE experiment at the DAΦNE e+e− collider. KS→ πeν events are selected by a boosted decision tree built with kinematic variables and time-of-flight measurements. Data control samples of KL→ πeν decays are used to evaluate signal selection efficiencies. With 49647±316 signal events we measure mathcal{R} = (1.0421 ± 0.0066stat± 0.0075syst) × 10−3. The combination with our previous measurement gives mathcal{R} = (1.0338 ± 0.0054stat± 0.0064syst) × 10−3. From this value we derive the branching fraction mathcal{B} (KS→ πeν) = (7.153 ± 0.037stat± 0.044syst) × 10−4 and f+(0)|Vus| = 0.2170 ± 0.009.

Production of Λ and [formula omitted] in jets in p–Pb collisions at [formula omitted] TeV and pp collisions at [formula omitted] TeV

The production of Λ baryons and KS0 mesons (V0 particles) was measured in p–Pb collisions at sNN=5.02 TeV and pp collisions at s=7 TeV with ALICE at the LHC. The production of these strange particles is studied separately for particles associated with hard scatterings and the underlying event to shed light on the baryon-to-meson ratio enhancement observed at intermediate transverse momentum (pT) in high multiplicity pp and p–Pb collisions. Hard scatterings are selected on an event-by-event basis with jets reconstructed with the anti-kT algorithm using charged particles. The production of strange particles associated with jets pT,jetch>10 and pT,jetch>20 GeV/c in p–Pb collisions, and with jet pT,jetch>10 GeV/c in pp collisions is reported as a function of pT. Its dependence on angular distance from the jet axis, R(V0,jet), for jets with pT,jetch>10 GeV/c in p–Pb collisions is reported as well. The pT-differential production spectra of strange particles associated with jets are found to be harder compared to that in the underlying event and both differ from the inclusive measurements. In events containing a jet, the density of the V0 particles in the underlying event is found to be larger than the density in the minimum bias events. The Λ/KS0 ratio associated with jets in p–Pb collisions is consistent with the ratio in pp collisions and follows the expectation of jets fragmenting in vacuum. On the other hand, this ratio within jets is consistently lower than the one obtained in the underlying event and it does not show the characteristic enhancement of baryons at intermediate pT often referred to as “baryon anomaly” in the inclusive measurements.

Measurement of the branching fraction for the decay KS → πμν with the KLOE detector

Based on a sample of 300 million KS mesons produced in ϕ→KLKS decays recorded by the KLOE experiment at the DAΦNE e+e− collider we have measured the branching fraction for the decay KS→πμν. The KS mesons are identified by the interaction of KL mesons in the detector. The KS→πμν decays are selected by a boosted decision tree built with kinematic variables and by a time-of-flight measurement. Signal efficiencies are evaluated with data control samples of KL→πμν decays. A fit to the reconstructed muon mass distribution finds 7223±180 signal events. Normalising to the KS→π+π− decay events the result for the branching fraction is B(KS→πμν)=(4.56±0.11stat±0.17syst)×10−4. It is the first measurement of this decay mode and the result allows an independent determination of |Vus| and a test of the lepton-flavour universality.

Studying the mechanisms of the hadron jets production in U+U collisions at GeV

Studying the properties and evolution of the quark-gluon plasma (QGP) is one of the main directions in modern nuclear physics. The leading direction in the QGP studies is the research of the particle production originating from hard scattering of partons produced in the ultra-relativistic heavy nuclei collision. Light mesons (π0, η and KS) invariant spectra and nuclear modification factors measurements at high transverse momenta are used for the parton energy loss models free parameters estimate in large systems and to examine various scaling behaviours. Spherically asymmetric uranium nuclei at GeV are used to determine the influence of geometrical parameters of the colliding system on the fragmentation of hard partons produced in high energy collision of heavy nuclei. This paper presents differential transverse momentum spectra and nuclear modification factors of KS mesons in U+U collisions at GeV measured in a wide transverse momentum range and different centrality intervals with PHENIX experiment at RHIC.

Sub-threshold production of K[formula omitted] mesons and Λ hyperons in Au+Au collisions at [formula omitted] GeV

We present first data on sub-threshold production of Ks0 mesons and Λ hyperons in Au+Au collisions at sNN=2.4 GeV. We observe an universal 〈Apart〉 scaling of hadrons containing strangeness, independent of their corresponding production thresholds. Comparing the yields, their 〈Apart〉 scaling, and the shapes of the rapidity and the pt spectra to state-of-the-art transport model (UrQMD, HSD, IQMD) predictions, we find that none of them can simultaneously describe these observables with reasonable χ2 values.

Measurement of the neutral and charged K* (892) mesons in the MPD experiment at NICA

Measurements of K*(892) meson production provide the means to study properties of relativistic heavy-ion collisions. Because of their short lifetimes, the charged and neutral K*(892) mesons provide information about the properties of the late hadronic phase due to the presence of rescattering and regeneration effects that can modify resonance yields. The K*(892) mesons can also be used to study the various mechanisms that shape particle transverse momentum (pT) spectra, including the collective flow, in-medium parton energy loss and recombination. Measurement of neutral K*(892) mesons requires reconstruction of the charged pions and kaons originating from the primary vertex. At the same time, the measurement of charged K*(892) mesons involves reconstruction of the weakly decaying Ks mesons. Simultaneous measurement of the two particles is a way to minimize systematic uncertainties of the corresponding physical studies. We present results of feasibility studies for measurement of the charged and neutral K*(892) mesons in the MPD experimental setup in heavy-ion collisions at NICA energies. Results are obtained using full-scale Monte Carlo simulations of the experimental setup.

Decay of K0 to $${K^ + }{e^ - }{\bar \nu _e}$$ K + e − ν ¯ e

The width of the neutral kaon with respect to its decay to a positively charged kaon, an electron, and an antineutrino is calculated. The branching ratios for the decay of KL and KS mesons to $${K^ + }{e^ - }{\bar \nu _e}$$ are found to be about 4 × 10−9 and 10−11 respectively. The calculations presented in this article are also valid for neutral antikaons decaying to a negatively charged kaon, a positron, and a neutrino.

Nuclear modification factors of KS and ω mesons in Cu+Au collisions at p

Jet quenching is an important evidence of the quark-gluon plasma (QGP) formation. The effect of jet quenching is emerged in ultra-relativistic heavy-ion collisions (A+A) by suppressed production of hadron yields at high transverse momenta (pT > 5 GeV/c) when compared to one measured in elementary proton-proton collisions (p+p). Cu+Au collisions are characterised by the unique asymmetric nuclei overlap geometry different from one presented in symmetric collisions (Au+Au, Cu+Cu). It makes the Cu+Au collision system especially interesting for jet quenching studies. In this paper we present results of the KS meson production measurement in Cu+Au collisions at with respect to the meson pT and collision centrality obtained using the electromagnetic calorimeter of PHENIX experiment. KS mesons are reconstructed via the KS →π0(→ γγ) π0(→ γγ) decay channel. Obtained KSmeson nuclear modification factors are consistent with ones measured for π0 and η mesons and reconstructed jets in the same collision system and ones measured in Cu+Cu and Au+Au collisions at the same collision energy.

Production of strange particles in charged jets in Pb–Pb and p–Pb collisions measured with ALICE

Measurements of spectra of identified particles produced in jets represent an important tool for understanding the interplay of various hadronisation mechanisms which contribute to particle production in the hot and dense medium created in ultra-relativistic heavy-ion collisions. In this contribution, we present the measurements of the pT spectra of Λ baryons and KS0 mesons produced in charged jets in Pb–Pb collisions at sNN=2.76 TeV and in p–Pb collisions at sNN=5.02 TeV. The results are obtained with the ALICE detector at the LHC, exploiting the excellent particle identification capabilities of this experiment. Baryon-to-meson ratios of the spectra of strange particles associated with jets are studied in central collisions and are compared with the inclusive ratios.

CPLEAR data on semileptonic decay of K0, K̄0 and the mass difference of KL0 and KS0 mesons

It is demonstrated that for a determination of the mass difference of the [Formula: see text] and [Formula: see text] mesons an explicit theoretical formula to be derived by an assumption of the CP-conservation has been used by CPLEAR Collaboration in a fitting of the time-dependent CPLEAR data on ASYMMETRY. So, in such procedure the mass difference [Formula: see text] of the [Formula: see text] and [Formula: see text] mesons has been found and in no case [Formula: see text] one as in this case the CP-violation has to be considered.

RECENT τ LEPTON RESULTS FROM BABAR

We report recent measurements on τ leptons obtained by the BABAR collaboration using the entire recorded sample of electron-positron collisions at and around the Υ(4S) (about 470fb-1). The events were recorded at the PEP-II asymmetric collider at the SLAC National Accelerator Laboratory. The measurements include high multiplicity τ decay branching fractions with 3 or 5 charged particles in the final state, a search for the second class current the τ decay τ → πη′ν, τ branching fractions into final states containing two KS mesons, [Formula: see text], with h = π, K, and preliminary measurements of hadronic spectra of τ decays with three hadrons (τ- → h-h+h-ντ decays, where h = π, K). The results improve the experimental knowledge of the τ lepton properties and can be used to improve the precision tests of the Standard Model.

Measurement of neutral strange particle production in the underlying event in proton-proton collisions ats=7 TeV

Measurements are presented of the production of primary KS0 and Λ particles in proton-proton collisions at s=7 TeV in the region transverse to the leading charged-particle jet in each event. The average multiplicity and average scalar transverse momentum sum of KS0 and Λ particles measured at pseudorapidities |η|<2 rise with increasing charged-particle jet pT in the range 1–10 GeV/c and saturate in the region 10–50 GeV/c. The rise and saturation of the strange-particle yields and transverse momentum sums in the underlying event are similar to those observed for inclusive charged particles, which confirms the impact-parameter picture of multiple parton interactions. The results are compared to recent tunes of the pythia Monte Carlo event generator. The pythia simulations underestimate the data by 15%–30% for KS0 mesons and by about 50% for Λ baryons, a deficit similar to that observed for the inclusive strange-particle production in non-single-diffractive proton-proton collisions. The constant strange- to charged-particle activity ratios with respect to the leading jet pT and similar trends for mesons and baryons indicate that the multiparton-interaction dynamics is decoupled from parton hadronization, which occurs at a later stage.Received 26 May 2013DOI:https://doi.org/10.1103/PhysRevD.88.052001This article is available under the terms of the Creative Commons Attribution 3.0 License. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.© 2013 CERN, for the CMS Collaboration

Search for the CP violating KS → 3π° decay with the KLOE detector

We present a new search for the KS → 3π0 decay performed with the KLOE detector operating at the DAΦNE ϕ-factory. The KS mesons were tagged via registration of KL mesons which crossed the drift chamber without decaying and interacted with the KLOE electromagnetic calorimeter. The KS → 3π0 decay was then searched requiring six prompt photons. To suppress background, originating from fake KS tags and KS → 2π0 decays with additional two spurious clusters, we have performed a discriminant analysis based on kinematical fit, testing of the signal and background hypotheses and exploiting of the differences in kinematics of the KS decays into 2π0 and 3π0. In a sample of about 1.7·109 ϕ → KSKL events we have found no candidates in data and simulated background samples. Normalizing to the number of KS → 2π0 events in the same sample, we have set the upper limit on the KS → 3π0 branching ratio BR(KS → 3π0) < 2.6 · 10−8 at 90% C.L., five times lower than the previous limit. This upper limit can be translated into a limit on the modulus of the η000 parameter amounting to |η000| < 0.0088 at 90% C.L., improving by a factor two the latest direct measurement.

Prompt [formula omitted] production in pp collisions at [formula omitted

The production of KS0 mesons in pp collisions at a centre-of-mass energy of 0.9 TeV is studied with the LHCb detector at the Large Hadron Collider. The luminosity of the analysed sample is determined using a novel technique, involving measurements of the beam currents, sizes and positions, and is found to be 6.8±1.0 μb−1. The differential prompt KS0 production cross-section is measured as a function of the KS0 transverse momentum and rapidity in the region 0<pT<1.6 GeV/c and 2.5<y<4.0. The data are found to be in reasonable agreement with previous measurements and generator expectations.

Comparative analysis of the narrow resonances

Several narrow resonance features in the system of two KS mesons were found on the basis of experimental data obtained by using the 6-m spectrometer of the Institute of Theoretical and Experimental Physics (ITEP, Moscow). Three resonances, X(1070), X(1545), and fJ(2220), are considered in the present study. An interference with the background is observed for the X(1545) resonance. It is shown that X(1070) and fJ(2220) resonances are produced under nearly identical kinematical conditions characterized by high transverse momenta and the production of accompanying extra pions.

Discovery of a 1731-MeV narrow resonance

Results obtained by studying a previously unknown narrow meson of mass about 1731 MeV are presented. This state was found in a system of two K S mesons. The experimental-data set subjected to the present analysis was obtained with a 6-m spectrometer of the Institute of Theoretical and Experimental Physics (ITEP, Moscow). The statistical sample of event of double K S -meson production was accumulated in π− p interactions by using a beam of 40-GeV pions from the U-70 accelerator of the Institute of High Energy Physics (IHEP, Protvino). There are 58 events at the respective maximum, its statistical significance being close to six standard deviations. The parameters of the observed meson are the following; the mass is M = 1731 ± 2.5 MeV, the width is σ = 3.2 ± 2 MeV, and the product of the production cross section and the respective branching ratio is not less than 20 nb. The fact that the observed meson is extremely narrow does not have a satisfactory theoretical explanation.

Features of carbon-carbon interactions at a momentum of 4.2 GeV/c per nucleon that are accompanied by the production of Λ hyperons and K 0S mesons versus the degree of nuclei collision centrality

Experiemntal data obtained by using the 2-m propane bubble chamber of the Joint Institute for Nuclear Research (JINR, Dubna) are used to study the effect collision centrality on the spectra of Λ hyperons and KS0 mesons produced in carbon-carbon interactions at 4.2 A GeV/c. The multiplicity of participant protons having momenta in excess of 300 MeV/c is taken to be a measure of collision centrality. The features of pions and protons accompanying strange-particle production are also presented. The experimental data in question are compared with the prediction of a modified version of the FRITIOF model. It is shown that strange particles are predominantly produced in central and semicentral collisions. The average kinematical features of KS0 mesons are found to be indepedent of collision centrality. At the same time, the average transverse momentum of Λ hyperons and the average value of their emission angle increase slowly with increasing degree of collision centrality. The anisotropy of the angular distributions of both Λ hypersons and KS/0 mesons in the c.m. frame of nucleon-nucleon collisions decreases with increasing collision centrality. The average transverse momentum of KS0 mesons is approximately 1.6 times higher than the average transverse momentum of π− mesons.

Scaling of semi-inclusive events in pp interactions

The normalized single-particle semi-inclusive double-differential spectrum of πt- mesons from pp interactions at 6.6–400 GeV/c and the relative concentration of π0 and KS0 mesons in such events of fixed multiplicity of π− mesons are completely determined by specifying any feature of this spectrum—for example, 〈y2〉n or 〈E〉n. Therefore, a two-parameter sample of semi-inclusive events that depends on the energy and the multiplicity reduces to a one-parameter sample.

Search for neutrinolessτdecays involving theKS0meson

We have searched for lepton flavor violating decays of the tau lepton with one or two KS0 mesons in the final state. The data used in the search were collected with the CLEO II and II.V detectors at the Cornell Electron Storage Ring (CESR) and correspond to an integrated luminosity of 13.9 fb^-1 at the Upsilon(4S) resonance. No evidence for signals were found, therefore we have set 90% confidence level (C.L.) upper limits on the branching fractions B(tau -> e KS0) < 9.1e-7, B(tau -> mu KS0) < 9.5e-7, B(tau -> e 2KS0) < 2.2e-6, and B(tau -> mu 2KS0) < 3.4e-6. These represent significantly improved upper limits on the two-body decays and first upper limits on the three-body decays.