Kaon Spectra Research Articles

Jet Fragmentation via Recombination of Parton Showers

We study hadron production in jets by applying quark recombination to jet shower partons. With the jet showers obtained from PYTHIA and augmented by additional non-perturbative effects, we compute hadron spectra in e+ + e−− collisions at GeV. Including contributions from resonance decays, we find that the resulting transverse momentum spectra for pions, kaons, and protons reproduce reasonably those from the string fragmentation as implemented in PYTHIA.

Strange particle production in proton-carbon interactions at 31 GeV/c

Spectra of positively charged kaons in p+C interactions at 31 GeV/c have been measured with the NA61/SHINE spectrometer at CERN SPS. The analysis is performed on the dataset collected during the 2007 pilot run (about 678×103 events). The target is a 2 cm long graphite specimen (4% of a nuclear interaction length λI). Charged pion spectra have been already measured with the same dataset [1]. Pion and kaon differential production cross sections are required to improve predictions of the neutrino flux for the T2K long baseline neutrino oscillation experiment in Japan. The knowledge of kaon production is especially important for the precise prediction of the intrinsic electron neutrino component of the T2K beam. The results are presented as a function of laboratory momentum in 2 intervals of the laboratory polar angle covering the range from 20 up to 240 mrad. Kaon spectra as well as K+/π+ ratios are compared with predictions of several hadron production models. In addition, first results from the analysis of the high statistics 2009 data taking are shown.

Scaling relations for hadron continuum scattering from carbon

Five scaling relations familiar from analyses of inclusive electron scattering spectra on complex nuclei are applied to 65 inclusive continuum spectra of protons, positive kaons, and pions incident upon carbon. Beam energies range from 300 MeV to 18.3 GeV with momentum transfers such that the conditions for quasifree scattering are met, similar to those for many electron scattering analyses. Several very strong assumptions need to be made to apply these scaling analyses to hadrons, and so the requirement that these spectra come into agreement under a scaling analysis is a severe test of these assumptions. Scaling is found in the sense that the responses of four of the five systems considered do agree over a significant range of momentum transfers for the three hadron species over a wide range of beam energies. Responses other than those for quasifree scattering destroy the validity of scaling systems for hadrons at large angles or momentum transfers or high beam energies.

Measurement of production properties of positively charged kaons in proton-carbon interactions at 31 GeV/c

Spectra of positively charged kaons in p+C interactions at 31 GeV/c were measured with the NA61/SHINE spectrometer at the CERN SPS. The analysis is based on the full set of data collected in 2007 with a graphite target with a thickness of 4% of a nuclear interaction length. Interaction cross sections and charged pion spectra were already measured using the same set of data. These new measurements in combination with the published ones are required to improve predictions of the neutrino flux for the T2K long baseline neutrino oscillation experiment in Japan. In particular, the knowledge of kaon production is crucial for precisely predicting the intrinsic electron neutrino component and the high energy tail of the T2K beam. The results are presented as a function of laboratory momentum in 2 intervals of the laboratory polar angle covering the range from 20 up to 240 mrad. The kaon spectra are compared with predictions of several hadron production models. Using the published pion results and the new kaon data, the K+/\pi+ ratios are computed.

Population of the X(2265) resonance in the p + p→X + K + reaction at T p = 2.5 GeV

DISTO data of p + p→p + Λ + K + reactions at several beam energies were studied. We found in the missing-mass ΔM(K + ) spectrum and the Λp invariant-mass spectrum at 2.85 GeV a broad resonance with M = 2267 MeV/c 2 and Γ = 118 MeV, associated with a mono energetic kaon spectrum, indicating that a dibaryonic state (X) with strangeness − 1 is produced in the p + p→X + K + reaction with X decaying into p + Λ. The energy dependence of the X production rate and the preliminary result of the recently analyzed p + p→p + Λ + K + data at T p = 2.5 GeV is presented.

QCD with two light dynamical chirally improved quarks: Mesons

We present results for the spectrum of light and strange mesons on configurations with two flavors of mass-degenerate Chirally Improved sea quarks. The calculations are performed on seven ensembles of lattice size ${16}^{3}\ifmmode\times\else\texttimes\fi{}32$ at three different gauge couplings and with pion masses ranging from 250 to 600 MeV. To reliably extract excited states, we use the variational method with an interpolator basis containing both Gaussian and derivative quark sources. Both conventional and exotic channels up to spin 2 are considered. Strange quarks are treated within the partially quenched approximation. For kaons we investigate the mixing of interpolating fields corresponding to definite $C$-parity in the SU(3) limit. This enlarged basis allows for an improved determination of the low-lying kaon spectrum. In addition to masses we also extract the ratio of the pseudoscalar decay constants of the kaon and pion and obtain ${F}_{K}/{F}_{\ensuremath{\pi}}=1.215(41)$. The results presented here include some ensembles from previous publications and the corresponding results supersede the previously published values.

Oscillating HBT radii and the time evolution of the source—√s NN = 200 GeV Au + Au data analyzed with azimuthally sensitive Buda-Lund hydro model

Identified particle spectra of pions, kaons and (anti)protons, and elliptic flow and azimuthal dependence of Bose-Einstein or HBT correlations of identified pions in sNN = 200 GeV Au + Au collisions is analyzed simultaneously using an ellipsoidally symmetric generalization of the Buda-Lund hydrodynamical model. The transverse flow is found to be faster in the reaction plane than out of plane, which results in a reaction zone that gets slightly more elongated in-plane than out of plane.

Transverse momentum spectra in high-energy nucleus-nucleus, proton-nucleus and proton-proton collisions

The transverse momentum distributions of final-state particles produced in nucleus-nucleus (AA), proton-nucleus (pA), and proton-proton (pp) collisions at high energies are investigated using a multisource ideal gas model. Our calculated results show that the contribution of hard emission can be neglected in the study of transverse momentum spectra of charged pions and kaons produced in Cu-Cu collisions at =22.5 GeV. And if we consider the contribution of hard emission, the transverse momentum spectra of p and p̄ produced in Cu-Cu collisions at =22.5 GeV, K0s produced in Pb-Pb collisions at 158 A GeV, J/ψ particles produced in p-Pb collisions at 400 GeV and π+, K+, p produced in proton-proton collisions at = 200 GeV, can be described by the model, especially in the tail part of spectra.

Measurement of identified charged hadron spectra with the ALICE experiment at the LHC

The ALICE experiment features multiple particle identification systems. The measurement of the identified charged hadron pt spectra in proton-proton collisions at √s = 900 GeV will be discussed. In the central rapidity region (|η| < 0.9) particle identification and tracking are performed using the Inner Tracking System (ITS), which is the closest detector to the beam axis, the Time Projection Chamber (TPC) and a dedicated time-of-flight system (TOF). Particles are mainly identified using the energy loss signal in the ITS and TPC. In addition, the information from TOF is used to identify hadrons at higher momenta. Finally, the kink topology of the weak decay of charged kaons provides an alternative method to extract the transverse momentum spectra of charged kaons. This combination allows to track and identify charged hadrons in the transverse momentum (pt) range from 100 MeV/c up to 2.5 GeV/c. Mesons containing strange quarks (K0S, (ϕ) and both singly and doubly strange baryons are identified by their decay topology inside the TPC detector. Results obtained with the various identification tools above described and a comparison with theoretical models and previously published data will be presented.

Charged kaon spectra from Au+Au collisions at $\sqrt {s_{NN} } $ = 200 GeV

The Time-of-Flight detector, based on MRPC technology, has greatly enhanced particle identification capability in STAR. By combining dE/dx measured by the TPC and velocity information from the TOF, we have extended the charged kaon transverse momentum spectra measurements up to ρ T − 5 GeV/c at mid-rapidity for Au+Au collisions at $\sqrt {s_{NN} } $ = 200 GeV. Estimation of charged kaon’s contribution factors from K* and ϕ is also made.

Transverse mass distributions in central heavy-ion collisions at high energies

The transverse mass spectra of protons, pions, kaons, Lambda and Antilambda produced in central nucleus-nucleus collisions at high energies are described by using one-temperature and two-temperature emission pictures. The calculated results are compared and found to be in good agreement with the experimental data of the E895, E866 and E917 Collaborations measured in central Au-Au collisions at the Alternating Gradient Synchrotron (AGS) energies and the NA49 Collaboration measured in central Pb-Pb collisions at the Super Proton Synchrotron (SPS) energies. It is demonstrated that the transverse mass distributions of protons, kaons, Lambda and Antilambda, except for Lambda hyperons produced in central Pb-Pb collisions at 158 A GeV, can be described by using the one-temperature emission picture, and for pions, we need to use the two-temperature emission picture.

Spectra, elliptic flow and azimuthally sensitive HBT radii from the Buda-Lund model for $ \sqrt{{s_{NN}}}$ = 200 GeV Au + Au collisions

We present calculations of elliptic flow and azimuthal dependence of correlation radii in the ellipsoidally symmetric generalization of the Buda-Lund hydrodynamic model of hadron production in high-energy nuclear collisions. We compare them to data from RHIC by simultaneous fits to azimuthally integrated invariant spectra of pions, kaons and protons-antiprotons measured by PHENIX in Au+Au reactions at center of mass energy of 200 AGeV. STAR data were used for azimuthally sensitive two-particle correlation function radii and for the transverse momentum dependence of the elliptic flow parameter v2. We have found that the transverse flow is faster in the reaction plane then out of plane, which results in a reaction zone that gets slightly more elongated in-plane than out of plane. The model parameters extracted from the fits are shown and discussed.

Interplay of the emission from thermal and direct sources in relativistic heavy ion collisions

The separation of the source created in ultrarelativistic heavy ion collisions into a thermalized dense core and an outer mantle consisting of independent nucleon-nucleon collisions is discussed. Indications for such a two-component picture are found in the transverse mass spectra of kaons, protons, and antiprotons produced in Au-Au collisions at $\sqrt{s}=200$ GeV. Estimates of the sizes of the thermal and direct sources are compared with models separating the interaction zone into a core and a corona. New initial conditions corresponding to the dense core lead to a stronger azimuthal asymmetry of the fireball, and pressure gradients also increase. We find faster transverse hydrodynamic expansion and stronger elliptic flow for the dense core initial conditions.

Transverse-mass spectra in heavy-ion collisions at energiesElab=2−160GeV/nucleon

Transverse-mass spectra of protons, pions, and kaons produced in collisions of heavy nuclei are analyzed within the model of three-fluid dynamics. It was demonstrated that this model consistently reproduces these spectra in wide ranges of incident energies, 4A GeV < or approx. E{sub lab} < or approx.160A GeV, rapidity bins, and centralities of the collisions. In particular, the model describes the 'step-like' dependence of kaon inverse slopes on the incident energy. The key point of this explanation is interplay of hydrodynamic expansion of the system with its dynamical freeze-out.

The(π−,K+)reaction onSi28and theΣ-nucleus potential

We calculate in the impulse approximation the kaon spectrum from the ({pi}{sup -},K{sup +}) reaction on {sup 28}Si. The strength V{sub {sigma}} of the real part of the single particle potential of the {sigma} hyperons produced in the reaction is obtained from the Nijmegen model F of the baryon-baryon interaction, and the strength W{sub {sigma}} of the imaginary (absorptive) part is determined by the {sigma}N cross sections for the {sigma}{lambda} conversion and also for the elastic {sigma}N scattering (this elastic scattering introduces a strong dependence of W{sub {sigma}} on the {sigma} momentum). The momentum dependence of V{sub {sigma}} is also considered. Our calculated inclusive kaon spectrum agrees reasonably with the spectrum measured at KEK. The strengths of the real and absorptive {sigma} potentials used in the present calculation are compatible with these strengths determined in the analyses of {sigma} atoms and of the strangeness exchange reactions.

Pion and kaon spectra from distributed mass quark matter

After discussing some hints for possible masses of quasiparticles in quark matter on the basis of the lattice equation of state, we present pion and kaon transverse spectra obtained by recombining quarks with distributed mass and thermal cut power-law momenta as well as fragmenting by NLO pQCD with intrinsic kT and nuclear broadening.

Rapidity-dependent chemical potentials in a statistical approach**Research supported by the Polish Ministry of Education and Science, grants N202 034 32/0918 and 2 P03B 02828.

We present a single-freeze-out model with thermal and geometric parameters dependent on the position within the fireball and use it to describe the rapidity distribution and transverse-momentum spectra of pions, kaons, protons and antiprotons measured at RHIC at by BRAHMS. THERMINATOR is used to perform the necessary simulation, which includes all resonance decays. The result of the fit to the data is the expected growth of the baryon and strange chemical potentials with the spatial rapidity α∥. The value of the baryon chemical potential at α∥ ∼ 3 is about 200 MeV, i.e. it lies in the range of the highest SPS energies. The chosen geometry of the fireball has a decreasing transverse size as the magnitude of α∥ is increased, which also corresponds to decreasing transverse flow. The strange chemical potential obtained from the fit to the K+/K− ratio is such that the local strangeness density in the fireball is compatible with zero. The resulting rapidity distribution of net protons are described qualitatively within the statistical approach. As a result of our study, the knowledge of the ‘topography’ of the fireball is acquired, allowing for other analyses and predictions.

High-pT kaon spectra from Au+Au collisions at GeV at RHIC

The time-of-flight detector, based on MRPC technology, has greatly enhanced particle identification capability in STAR. We have developed a new method on particle identification by combining dE/dx measured by the TPC and velocity information from the TOF. Using this method, for the first time, the charged kaon transverse momentum spectra measurements are extended up to pT∼ 5 GeV/c at mid-rapidity for Au+Au collisions at GeV. We also present the K/π ratios as a function of transverse momentum and the implications of the results are discussed. Comparisons with the corresponding results from Au+Au collisions at GeV are also presented.

Response of Charged Hadrons to a Coulomb Potential in Heavy-Ion Collisions at the RHIC

Response of Charged Hadrons to a Coulomb Potential in Heavy-Ion Collisions at the RHIC Byungsik Hong Department of Physics, Korea University, Seoul 136-701 (Received 27 August 2007, in nal form 19 November 2007) We have analyzed the charged hadron spectra at the Relativistic Heavy Ion Collider (RHIC) in terms of the Coulomb interaction between the hadrons and the thermally expanding reball. Fitting the pion, kaon, and proton spectra simultaneously by using the boost-invariant thermal blast wave formula gives a common kinetic freeze-out temperature of 130 MeV and an expansion velocity of 0.67c, which are quite di erent from the previous estimates. Considering the Coulomb interaction, the yield ratios of negative to positive hadrons are expected to increase signi cantly in the low-momentum region. For the published hadron spectra at the RHIC, we determine the upper limit of the magnitude for the Coulomb potential as 10 MeV. Such a relatively small value of the Coulomb potential is consistent with the large nuclear transparency observed at the RHIC. PACS numbers: 25.75.Dw, 25.75.Ld

Antiparticle to particle ratios and identified hadron spectra in Cu+Cu and Au+Au collisions

New results on antiparticle to particle ratios in Cu+Cu and Au+Au collisions at = 62.4 and 200 GeV from the PHOBOS experiment at RHIC are presented. Transverse momentum spectra of pions, kaons, protons and antiprotons from Au+Au collisions at = 62.4 GeV close to mid-rapidity are also discussed. Antiparticle to particle ratios are found to be remarkably independent of the collision centrality in both colliding systems. The collision energy dependence of the ratios is very significant in Cu+Cu collisions. Baryons are found to have substantially harder transverse momentum spectra than mesons. The pT region in which the proton to pion ratio reaches unity in central Au+Au collisions at = 62.4 GeV fits into a smooth trend as a function of collision energy. The observed particle yields at very low pT are comparable to extrapolations from higher pT for kaons, protons and antiprotons. The net proton yield at mid-rapidity is found to be proportional to the number of participant nucleons in Au+Au collisions at 62.4 and 200 GeV energies.