Neutral Strange Particle Production Research Articles

Measurement of K_S^0 and Lambda ^0 production in t bar{t} dileptonic events in pp collisions at sqrt{s} = 7 TeV with the ATLAS detector

Measurements of K_S^0 and Lambda ^0 production in tbar{t} final states have been performed. They are based on a data sample with integrated luminosity of 4.6 mathrm {fb}^{-1} from proton–proton collisions at a centre-of-mass energy of 7 TeV, collected in 2011 with the ATLAS detector at the Large Hadron Collider. Neutral strange particles are separated into three classes, depending on whether they are contained in a jet, with or without a b-tag, or not associated with a selected jet. The aim is to look for differences in their main kinematic distributions. A comparison of data with several Monte Carlo simulations using different hadronisation and fragmentation schemes, colour reconnection models and different tunes for the underlying event has been made. The production of neutral strange particles in tbar{t} dileptonic events is found to be well described by current Monte Carlo models for K_S^0 and Lambda ^0 production within jets, but not for those produced outside jets.

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

K0and Λ production in Ni+Ni collisions near threshold

New results concerning the production of neutral strange particles, K{sup 0} and {lambda} in Ni+Ni collisions at 1.93A GeV, measured with the FOPI detector at GSI Darmstadt, are presented. Rapidity density distributions and Boltzmann slope parameter distributions are measured in nearly the full phase space of the reaction. The observables are compared to existing K{sup +} and proton data. While the K{sup 0} data agree with previously reported K{sup +} measurements, the {lambda} distributions show a different behavior relative to that of protons. The strangeness balance and the production yield per participating nucleon as a function of the centrality of the reaction are discussed, for the first time at GSI Schwerionen Synchrotron (SIS) energies.

A study of the nuclear-medium influence on neutral-strange-particle production in deep-inelastic neutrino scattering

The influence of nuclear effects on the production of neutral strange particles (V 0) is investigated using the data obtained with SKAT propane-freon bubble chamber irradiated in the neutrino beam (with E v =3−30 GeV) at the Serpukhov accelerator. The mean multiplicity of V 0 particles in nuclear interactions, $$\langle n_{V^0 } \rangle _A = 0.092 \pm 0.010$$ , is found to exceed significantly that in “quasideuteron” interactions, $$\langle n_{V^0 } \rangle _D = 0.063 \pm 0.013$$ . The ratio of $$\rho _{V^0 } = \langle n_{V^0 } \rangle A/\langle n_{V^0 } \rangle _D = 1.46 \pm 0.23$$ is larger than that for π− mesons, $$\rho _{\pi ^ - } = 1.10 \pm 0.03$$ . It is shown that the multiplicity gain of V 0 particles can be explained by intranuclear interactions of produced pions.

A study of the nuclear-medium influence on transverse momentum of hadrons produced in deep-inelastic neutrino scattering

The influence of nuclear effects on the production of neutral strange particles ($V^{\circ}$) is investigated using the data obtained with SKAT propane-freon bubble chamber irradiated in the neutrino beam (with $E_{\nu}$ = 3-30 GeV) at Serpukhov accelerator. The measured mean multiplicity of $V^{\circ}$ particles in nuclear interactions, ${<n_{V^{\circ}}>}_A$ = 0.096$\pm$0.011, is found to exceed significantly that in 'quasinucleon' interactions, ${<n_{V^{\circ}}>}_N$ = 0.059$\pm$0.012. The ratio of ${\rho}_{V^{\circ}}$ =${<n_{V^{\circ}}>}_A/{<n_{V^{\circ}}>}_N$ =1.61$\pm$0.23 is larger than that for $\pi^{-}$ mesons, ${\rho}_{\pi^-}$ = 1.10$\pm$0.03. It is shown that a dominant part of the multiplicity gain of $V^{\circ}$ particles can be explained by intranuclear interactions of produced pions.

Strangeness measurements in NA49 experiment with Pb projectiles

Charged and neutral strange particle production was studied by the NA49 experiment at CERN. Preliminary inclusive spectra are presented for , , , , and particles, measured in a region close to mid-rapidity, for central Pb+Pb collisions at 158 GeV per nucleon. An enhanced strange particle production relative to properly scaled elementary nucleon-nucleon collisions is observed, but its strength is similar to lighter S + nucleus systems. The enhancement is stronger for multistrange particles.

A consistent parametrisation for the production rates of negatively charged hadrons and neutral strange particles in nucleon-nucleon, nucleon-nucleus and nucleus-nucleus collisions

A parametrisation of negative hadron and neutral strange particle production was developed which consistently describes presently available data from nucleon-nucleon, nucleon-nucleus and nucleus-nucleus collisions at a beam energy of 200 GeV per nucleon. Average multiplicities of negative hadrons are found to be proportional to the number of wounded nucleons, averageKs0 multiplicities proportional to the number of wounded quarks, and average Λ and\(\bar \Lambda \) multiplicities proportional to the number of wounded quarks plus an additional contribution proportional to the number of interactions of secondary produced particles. Predictions are given for lead-lead collisions.

Further development of a model for the production of strange particles in nucleus-nucleus collisions

A previously proposed model for the production of neutral strange particles in nucleus-nucleus collisions, based on the Additive Quark Model and nuclear cascading, is further developed. The model predictions on neutral strange particle multiplicities, transverse momentum and rapidity distributions are compared with the existing oxygen- and sulphur-nucleus data at 200 GeV per nucleon. The predictions for central PbPb collisions are presented and discussed in some detail.

Neutral strange particle production in deep inelastic scattering at HERA

This paper presents measurements ofK 0 and Λ production in neutral current, deep inelastic scattering of 26.7 GeV electrons and 820 GeV protons in the kinematic range 10<Q 2<640 GeV2, 0.0003<x<0.01, andy>0.04. Average multiplicities forK 0 and Λ production are determined for transverse momentap T>0.5 GeV and pseudorapidities |η|<1.3. The multiplicities favour a stronger strange to light quark suppression in the fragmentation chain than found ine + e − experiments. The production properties ofK 0' s in events with and without a large rapidity gap with respect to the proton direction are compared. The ratio of neutralK 0' s to charged particles per event in the measured kinematic range is, within the present statistics, the same in both samples.

Neutral strange particle production in neutrino and antineutrino charged-current interactions on neon.

The production of the neutral strange particlesK0, Λ and\(\bar \Lambda \) invp and\(\bar vp\) charged current interactions is studied in an experiment with the Big European Bubble Chamber. Mean multiplicities are measured as a function of the event variablesEv,W2 andQ2 and of the hadron variablesxF,z andp T 2 .K*± (892) and∑*± (1385) signals are observed, whereas there is no evidence for∑*- (1385) production invp scattering. Forward, backward and total mean multiplicities are found to compare well with the predictions of an empirical model for deep-inelastic reactions in the case of the strange mesonsK0 andK*± (892) but less so for the strange baryons Λ,\(\bar \Lambda \) and∑*± (1385). The strange baryon multiplicities are used to obtain the decuplet to octet baryon production ratio and to assess the probabilities of auu orud system to break up.

Neutral strange particle production in neutrino and antineutrino charged current interactions on protons

The production of the neutral strange particlesK 0, Λ and $$\bar \Lambda $$ invp and $$\bar vp$$ charged current interactions is studied in an experiment with the Big European Bubble Chamber. Mean multiplicities are measured as a function of the event variablesE v,W 2 andQ 2 and of the hadron variablesx F,z andp T 2 .K *± (892) and∑ *± (1385) signals are observed, whereas there is no evidence for∑ *- (1385) production invp scattering. Forward, backward and total mean multiplicities are found to compare well with the predictions of an empirical model for deep-inelastic reactions in the case of the strange mesonsK 0 andK *± (892) but less so for the strange baryons Λ, $$\bar \Lambda $$ and∑ *± (1385). The strange baryon multiplicities are used to obtain the decuplet to octet baryon production ratio and to assess the probabilities of auu orud system to break up.

NEW RESULTS ON HADRON PRODUCTION IN DEEP-INELASTIC LEPTON SCATTERING

New experimental results on the production of hadrons in deep-inelastic lepton–nucleon and lepton–nucleus collisions are reviewed. The following topics are covered: multiplicities, nuclear effects, intermittency, Bose–Einstein correlations, and production of neutral strange particles.

Neutral strange particle production inK + andπ + collisions with Al and Au nuclei at 250 GeV/c

Data are presented on inclusiveK 0 s and Λ production inK + and π+ collisions with Al and Au nuclei at 250 GeV/c. Results are given on total inclusive cross sections and theA dependence, as well as on distributions in Feynman-x F , rapidityy and transverse momentum. Ratios ofK 0 S and of Λ to π+ production are presented. The data are compared with predictions of the quark-parton model FRITIOF.

Neutral strange particle production in antineutrino-neon charged current interactions

Neutral strange particle production in $$\bar v$$ Ne charged current interactions is studied using the bubble chamber BEBC, exposed to the CERN SPS antineutrino wide band beam. From a sample of 1191 neutral strange particles, the inclusive production rates are determined to be (15.7±0.8)% forK 0 mesons, (8.2±0.5)% for Λ, (0.4±0.2)% for $$\bar \Lambda $$ and (0.6±0.3)% for Σ0 hyperons. The inclusive production properties ofK 0 mesons and Λ hyperons are investigated. The Λ hyperons are found to be polarized in the production plane.

Production of neutral strange particles inpAr,pXe and $$\bar p$$ Xe collisions at 200 GeV

The production of neutral strange particles (K 0, Λ) inp Ar,pXe and $$\bar p$$ Xe collisions at 200 GeV is investigated in the NA5 experiment using a streamer chamber at the CERN SPS. Results are presented on inclusive cross sections, average multiplicities, and on rapidity and transverse momentum distributions of neutral strange particles.

Neutral strange particle production in sulphur-sulphur and proton-sulphur collisions at 200 GeV/nucleon

The production of Λ, $$\bar \Lambda$$ andK 0 has been studied in 200 GeV/nucleonp+S and S+S collisions in the streamer chamber of the NA35 experiment at the CERN SPS. Significant enhancement of the multiplicities of all observed strange particles relative to negative hadrons was observed in central S+S collisions, as compared top+p andp+S collisions. The latter collisions show no overall (relative) strangeness enhancement overp+p, but the rapidity distributions and hadron multiplicities indicate some secondary cascading production of Λ particles in thep+S andp+Au collisions. The Λ polarization in central S+S collisions was found to be compatible with zero up top T =2 GeV/c.

Neutral strange particle production in S-S collisions at 200 GEV/nucleon

Neutral strange particle production in S-S collisions at 200 GEV/nucleon

A study ofK s o , Λ and $$\bar \Lambda $$ production in 60 and 200 GeV per nucleon OAu and pAu collisions with a streamer chamber detector at the CERN SPSproduction in 60 and 200 GeV per nucleon OAu and pAu collisions with a streamer chamber detector at the CERN SPS

The production of neutral strange particlesK s o , Λ and % MathType!MTEF!2!1!+-% feaafiart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9% vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x% fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaacciGaf83MdW% Kbaebaaaa!3780! $$\bar \Lambda $$ has been studied in 60 and 200 GeV per nucleon OAu and pAu collisions with the streamer chamber vertex spectrometer of the NA35 experiment at the CERN-SPS accelerator. Ratios of neutral strange particle production to negatively charged particle production in selected regions of phase space were measured to be the same in OAu and pAu reactions. The rates of strange particle production in central OAu collisions are about a factor of 16 higher than in pAu collisions when compared in the same regions of phase space. If an enhancement of strange particle production in OAu collisions relative to pAu collisions is considered to be a signature for quark-gluon plasma formation, no evidence supporting it is observed. The experimental results are compared to the Lund FRITIOF model.

Neutral strange-particle production in p̄20Ne reactions at 607 MeV/c

The Λ 0 and K 0 s production cross sections have been measured at 607 MeV/ c for the reaction p ̄ + 20 Ne → V 0 + X ( V 0 =Λ, 0 , K 0 s ) . The Λ 0 /K 0 s production ratio is found to be (2.3±0.7). The data are consistent with an evaporative character of the emission mechanism from a multinucleon system for Λ 0 and from one nucleon for K 0 s . The rapidity distributions of negative tracks in K 0 x events are different from those in Λ 0 events without V 0 .

Neutral strange particle production in charged current νA-interactions in the energy range 3≦E ν≦30 GeV

For charged current neutrino nucleus interactions at energies below 30 GeV, resulting from an experiment with the freon filled bubble chamber SKAT,K0 and Λ production is investigated. An estimation of the total strange and charm production cross section is made.K0 and Λ production rates are given in dependence on different inclusive variables. The production properties forK0′s and Λ′s are discussed in terms of the Quark-Parton-Model. Comparisons with other ν-experiments at higher energies are performed.