Kaon Spectra Research Articles

Production of identified charged hadrons in Pb–Pb collisions at [formula omitted

In late 2015, the ALICE collaboration recorded data from Pb–Pb collisions at the unprecedented energy of sNN=5.02 TeV. The transverse-momentum (pT) spectra of pions, kaons and protons are presented. The evolution of the particle ratios as a function of collision energy and centrality is discussed. The ratio between pT-integrated particle yields are measured and compared to different collision energies as well as smaller collision systems. For the study of energy loss mechanisms in the QCD medium at high transverse momenta, the nuclear modification factors (RAA) are computed and compared with results obtained at lower energy.

Production of π0, K± and η mesons in Pb-Pb and pp collisions at = 2.76 TeV measured with the ALICE detector at the LHC

One of the key signatures of the Quark-Gluon Plasma (QGP) is the modification of hadron transverse momentum differential cross-sections in heavy-ion collisions (HIC) as compared to proton-proton (pp) collisions. Suppression of hadron production at high transverse momenta (pT) in HIC has been explained by the energy loss of the partons produced in the hard scattering processes which traverse the deconfined quantum chromodynamic (QCD) matter. The dependence of the observed suppression on the pT of the measured hadron towards higher pT is an important input for the theoretical understanding of jet quenching effects in the QGP and the nature of the energy loss, while suppression towards lower pT gives information about collective behaviour. The ALICE experiment at the Large Hadron Collider (LHC) performs a variety of measurements including the spectra of neutral mesons and kaons at mid-rapidity in a wide pT range in pp, p-Pb and Pb-Pb collisions. An overview of ALICE results in HIC and pp collisions at = 2.76 TeV of neutral pions, kaons and eta mesons as a function of transverse momentum (pT) and centrality will be presented. Ratios η/π0, K±/π± as well as comparisons to model calculations will also be discussed.

A New Two-Component Model for Hadron Production in Heavy-Ion Collisions

Using the experimental data from the ALICE program on the centrality dependence of the transverse momentum (pT) spectra in Pb+Pb collisions at sNN=2.76 TeV, we show that the double-Tsallis distribution and the generalized Fokker-Planck (FP) solution cannot describe the spectra of pions, kaons, and protons from central to peripheral collisions in the entire pT region, simultaneously. Hence, a new two-component distribution, which is a hydrodynamic extension of the generalized FP solution accounting for the collective motion effect in heavy-ion collisions, is proposed in order to reproduce all the identified particle spectra. Our results suggest that the particle production dynamics may be different for different particles, especially at very low pT region.

Rapidity and centrality dependence of particle production for identified hadrons in Cu + Cu collisions atsNN=200GeV

The BRAHMS collaboration has measured transverse momentum spectra of pions, kaons, protons, and antiprotons at rapidities 0 and 3 for Cu+Cu collisions at sNN=200 GeV. As the collisions become more central the collective radial flow increases while the temperature of kinetic freeze-out decreases. The temperature is lower and the radial flow weaker at forward rapidity. Pion and kaon yields with transverse momenta between 1.5 and 2.5 GeV/c are suppressed for central collisions relative to scaled p+p collisions. This suppression, which increases as the collisions become more central, is consistent with jet quenching models and is also present with comparable magnitude at forward rapidity. At such rapidities, initial state effects may also be present and persistence of the meson suppression to high rapidity may reflect a combination of jet quenching and nuclear shadowing. The ratio of protons to mesons increases as the collisions become more central and is largest at forward rapidities.

Centrality dependence of the nuclear modification factor of charged pions, kaons, and protons in Pb-Pb collisions atsNN=2.76TeV

Transverse momentum ($p_{\rm{T}}$) spectra of pions, kaons, and protons up to $p_{\rm{T}} = 20$ GeV/$c$ have been measured in Pb-Pb collisions at $\sqrt{s_{\rm NN}} = 2.76$ TeV using the ALICE detector for six different centrality classes covering 0-80%. The proton-to-pion and the kaon-to-pion ratios both show a distinct peak at $p_{\rm{T}} \approx 3$ GeV/$c$ in central Pb-Pb collisions that decreases towards more peripheral collisions. For $p_{\rm{T}} > 10$ GeV/$c$, the nuclear modification factor is found to be the same for all three particle species in each centrality interval within systematic uncertainties of 10-20%. This suggests there is no direct interplay between the energy loss in the medium and the particle species composition in the hard core of the quenched jet. For $p_{\rm{T}} < 10$ GeV/$c$, the data provide important constraints for models aimed at describing the transition from soft to hard physics.

Single freeze-out, statistics and pion, kaon and proton production in central Pb–Pb collisions at TeV

Many data in the high energy physics are, in fact, sample means. It is shown that when this exact meaning of the data is taken into account and the most weakly bound states are removed from the hadron resonance gas, the acceptable fit to the whole spectra of pions, kaons and protons measured at midrapidity in central Pb–Pb collisions at TeV (2012 Phys. Rev. Lett. 109 252301) is obtained. The invariant distributions are predicted with the help of the single-freeze-out model in the chemical equilibrium framework. Low pT pions and protons are reproduced simultaneously as well as the ratio. Additionally, correct predictions extend over lower parts of large pT data. Some more general, possible implications of this approach are pointed out.

Scaling behaviours of the pT spectra for identified hadrons in pp collisions

We extend the scaling behaviour observed in the inclusive charged hadron transverse momentum (pT) distributions to the pT spectra of pions, kaons and protons produced in proton–proton (pp) collisions with center of mass energies () at 0.9, 2.76 and 7 TeV. This scaling behaviour arises when a linear transformation, is applied on the pion, kaon or proton pT spectra. The scaling parameter K depends on and is determined by a new method, the quality factor method, which does not rely on the shape of the scaling function. We argue that the pions, kaons and protons originate from different distributions of clusters which are formed by strings overlapping, and the scaling behaviours of these identified particles pT spectra could be understood with the colour string percolation model in a quantitative way simultaneously.

Medium-induced flavor conversion and kaon spectra in electron-ion collisions

Multiple scattering and induced parton splitting lead to a medium modification of the QCD evolution for jet fragmentation functions and the final hadron spectra. Medium-induced parton splittings not only lead to energy loss of leading partons and suppression of leading hadron spectra, but also modify the flavor composition of a jet due to induced flavor conversion via gluon emission, quark pair production and annihilation. Through a numerical study of the medium-modified QCD evolution, leading $K^-$ strange meson spectra are found to be particularly sensitive to the induced flavor conversion in semi-inclusive deeply inelastic scatterings (SIDIS) off a large nucleus. The induced flavor conversion can lead to increased number of gluons and sea quarks in a jet and, as a consequence, enhance the leading $K^-$ spectra to counter the effect of parton energy loss in SIDIS with large momentum fractions $x_B$ where the struck quarks are mostly valence quarks of the nucleus.

Transverse-momentum spectra of strange particles produced in Pb + Pb collisions atsNN=2.76TeV in the chemical nonequilibrium model

We analyze the transverse-momentum spectra of strange hadrons produced in Pb + Pb collisions at the collision energy $\sqrt{{s}_{\mathrm{NN}}}=2.76$ TeV for different centrality bins. Our approach combines the concept of chemical nonequilibrium with the single-freeze-out scenario. The two ideas are realized in the framework of the Cracow model, whose thermodynamic parameters have been established in earlier studies of the ratios of hadron multiplicities. The geometric parameters of the model are obtained from the fit to the spectra of pions and kaons, only. Using these parameters, we obtain an excellent description of the spectra of protons and the ${K}_{S}^{0},{K}^{*}{(892)}^{0}$, and $\ensuremath{\phi}(1020)$ mesons. A satisfactory description is obtained for the $\ensuremath{\Lambda},\ensuremath{\Xi}$, and $\ensuremath{\Omega}$ hyperons.

Impact of secondary acceleration on the neutrino spectra in gamma-ray bursts

We discuss the acceleration of secondary muons, pions, and kaons in gamma-ray bursts within the internal shock scenario, and their impact on the neutrino fluxes. We introduce a two-zone model consisting of an acceleration zone (the shocks) and a radiation zone (the plasma downstream the shocks). The acceleration in the shocks, which is an unavoidable consequence of the efficient proton acceleration, requires efficient transport from the radiation back to the acceleration zone. On the other hand, stochastic acceleration in the radiation zone can enhance the secondary spectra of muons and kaons significantly if there is a sufficiently large turbulent region. Overall, it is plausible that neutrino spectra can be enhanced by up to a factor of two at the peak by stochastic acceleration, that an additional spectral peaks appears from shock acceleration of the secondary muons and pions, and that the neutrino production from kaon decays is enhanced. Depending on the GRB parameters, the general conclusions concerning the limits to the internal shock scenario obtained by recent IceCube and ANTARES analyses may be affected by up to a factor of two by secondary acceleration. Most of the changes occur at energies above 10^7 GeV, so the effects for next-generation radio-detection experiments will be more pronounced. In the future, however, if GRBs are detected as high-energy neutrino sources, the detection of one or several pronounced peaks around 10^6 GeV or higher energies could help to derive the basic properties of the magnetic field strength in the GRB.

Explanation of hadron transverse-momentum spectra in heavy-ion collisions atsNN=2.76TeV within a chemical nonequilibrium statistical hadronization model

Chemical non-equilibrium version of the statistical hadronization model combined with a single-freeze-out scenario is used to analyze the transverse-momentum spectra of pions, kaons and protons produced in heavy-ion collisions at sqrt(sNN) = 2.76 TeV. With the statistical parameters found in earlier studies of hadronic ratios and two new geometric parameters determined by the absolute normalization and slopes of the spectra, we obtain a very good agreement between the data and the model predictions. In particular, the enhancement of pions observed at the very low transverse-momenta is very well reproduced. In the chemical non-equilibrium approach, this effect may be naturally interpreted as the onset of pion condensation in heavy-ion collisions. We further stress that the chemical non-equilibrium explains not only the proton yield but the proton spectra as well.

Transverse momentum spectra of the produced hadrons at SPS energy and a random walk model

The transverse momentum spectra of the produced hadrons have been compared to a model, which is based on the assumption that a nucleus–nucleus collision is a superposition of isotropically decaying thermal sources at a given freeze-out temperature. The freeze-out temperature in nucleus–nucleus collisions is fixed from the inverse slope of the transverse momentum spectra of hadrons in nucleon–nucleon collision. The successive collisions in thessss nuclear reactions leads to gain in transverse momentum, as the nucleons propagate in the nucleus following a random walk pattern. The average transverse rapidity shift per collision is determined from the nucleon–nucleus collision data. Using this information, we obtain parameter-free result for the transverse momentum distribution of produced hadrons in nucleus–nucleus collisions. It is observed that such a model is able to explain the transverse mass spectra of the produced pions at SPS energies. However, it fails to satisfactorily explain the transverse mass spectra of kaons and protons. This indicates the presence of collective effect which cannot be accounted for, by the initial state collision broadening of transverse momentum of produced hadrons, the basis of random walk model.

Non-extensive statistics and a systematic study of meson-spectra at LHC energy $\sqrt{s_{NN}} = 2.76$ TeV

The transverse momentum spectra of secondary pions and kaons, produced in $P+P$ and various central $Pb+Pb$ collisions at $\sqrt{s_{NN}}=2.76$ TeV at LHC, have been analyzed systematically with an approach based on Tsallis non-extensive statistics. The analytical results have been utilized to determine some of the very important thermodynamical parameters bearing characteristic signatures of the partonic medium produced in such collisions.

Spectra and elliptic flow for identified hadrons in2.76ATeV Pb + Pb collisions

Using the VISHNU hybrid model that couples (2+1)-dimensional viscous hydrodynamics to a microscopic hadronic transport model, we calculate the multiplicity, p_T spectra and elliptic flow for pions, kaons, and protons in 2.76 A TeV Pb+Pb collisions, using MC-KLN initializations with smoothed initial conditions, obtained by averaging over a large number of events. The results from our calculations are compared to data from the ALICE collaboration, showing nice agreement over several centrality bins. Using the same inputs, we predict the p_T spectra and elliptic flow for phi mesons and explore its flow development in the strong and weak coupling limits through hydrodynamic calculations with different decoupling temperatures. In addition we study the influence of baryon and anti-baryon annihilation processes on common observables and demonstrate that by including annihilation processes below a switching temperature of 165 MeV, VISHNU provides a good description of the multiplicity and p_T spectra for pions, kaons and protons measured by PHENIX and ALICE at both RHIC and the LHC.

Measurements of production properties ofKS0mesons andΛhyperons in proton-carbon interactions at 31 GeV/c

Spectra of K0S mesons and Lambda hyperons were measured in p+C interactions at 31 GeV/c with the large acceptance NA61/SHINE spectrometer at the CERN SPS. The data were collected with an isotropic graphite target with a thickness of 4% of a nuclear interaction length. Interaction cross sections, charged pion spectra, and charged kaon spectra were previously measured using the same data set. Results on K0S and Lambda production in p+C interactions serve as reference for the understanding of the enhancement of strangeness production in nucleus-nucleus collisions. Moreover, they provide important input for the improvement of neutrino flux predictions for the T2K long baseline neutrino oscillation experiment in Japan. Inclusive production cross sections for K0S and Lambda are presented as a function of laboratory momentum in intervals of the laboratory polar angle covering the range from 0 up to 240 mrad. The results are compared with predictions of several hadron production models. The K0S mean multiplicity in production processes <n_K0S> and the inclusive cross section for K0S production were measured and amount to 0.127 +- 0.005 (stat) +- 0.022 (sys) and 29.0 +- 1.6 (stat) +- 5.0 (sys) mb, respectively.

FRAGMENTATION FUNCTIONS AT BABAR

Inclusive hadron production cross section in e+e- annihilation shed light on fundamental questions of hadronization and fragmentation processes. We present measurements of inclusive spectra of charged pions, kaons, and protons (antiprotons) produced in e+e- collisions at the center-of-mass energy of 10.54 GeV, and tests of QCD predictions and hadronization models. We also report the results on the measurement of the azimuthal modulation induced by the Collins effect in inclusive production of charged pion pairs e+e- → ππX, where the two pions are produced in opposite hemispheres. These data allows the determination of the polarized Collins fragmentation functions.

Dynamics of strangeness and collective flows in heavy-ion collisions near threshold energies

Strangeness (K$^{0,+}$, $\Lambda$ and $\Sigma^{-,0,+}$) production in heavy-ion collisions near threshold energies has been investigated within the Lanzhou quantum molecular dynamics (LQMD) transport model. The kaon (anti-kaon)-nucleon and hyperon-nucleon potentials in dense nuclear matter are implemented in the model, which are computed from the chiral perturbation approach and the relativistic mean-field model, respectively. It is found that the in-medium potentials change the structure of transverse flow, and also affect the rapidity distributions and the inclusive spectra for strangeness production. The local temperature of the fire ball extracted from the kaon spectra of inclusive invariant cross sections is influenced by the kaon-nucleon potential. The stiffness of nuclear symmetry energy and the kaon-nucleon potential by distinguishing isospin effect play a significant role on the ratio of K$^{0}$/K$^{+}$, in particular at the subthreshold energies. The ratio of $\Sigma^{-}/\Sigma^{+}$ depends on the high-density symmetry energy, in which the $\Sigma$-nucleon potential has a neglectable contribution on the isospin ratio.

Meson Spectra in p + p Collisions at LHC

The p + p (proton + proton) collisions are important to understand particle production mechanism in partonic collisions and are also used as baseline for heavy ion collisions. We present systematic study of meson spectra in p + p collisions at LHC energies (√s = 0.9, 2.76 and 7.0 TeV). We also studied the transverse mass (mT) spectra of pion and kaon for p + p collisions at all above mentioned energies. In an earlier study [1], it was shown that all the mesons produced in p + p and d + Au collisions at √sNN = 200 GeV follow mT scaling while in Au + Au collisions at same energy the mesons with strange and charm quark contents do not follow mT scaling which can be attributed to medium modifications. Here we fit all pion spectra with Hagedorn distribution and extract all the output parameters from the fitting. Then we fit kaon spectra using mT scaling with the help of those extracted fitting parameters along with a normalizing factor. We observed that mT scaling in case of kaon is valid in p + p collisions at LHC energies. The normalizing factor of kaon with respect to pion (K/п) is almost constant in all energies . This study is important for the observation of strangeness enhancement in heavy ion collisions, which is an important probe of quark gluon plasma (QGP). It is also used as a baseline for the study of medium modifications in heavy ion collisions. Kaon spectra provides a unique opportunity to identify new flavor and CP violating interactions beyond the Standard Model (SM).Keywords: LHC, Hagedorn Function, Meson Spectra.

Meson Spectra in p + p Collisions at LHC

The p + p (proton + proton) collisions are important to understand particle production mechanism in partonic collisions and are also used as baseline for heavy ion collisions. We present systematic study of meson spectra in p + p collisions at LHC energies (√s = 0.9, 2.76 and 7.0 TeV). We also studied the transverse mass (m T ) spectra of pion and kaon for p + p collisions at all above mentioned energies. In an earlier study [1], it was shown that all the mesons produced in p + p and d + Au collisions at √s NN = 200 GeV follow m T scaling while in Au + Au collisions at same energy the mesons with strange and charm quark contents do not follow m T scaling which can be attributed to medium modifications. Here we fit all pion spectra with Hagedorn distribution and extract all the output parameters from the fitting. Then we fit kaon spectra using m T scaling with the help of those extracted fitting parameters along with a normalizing factor. We observed that m T scaling in case of kaon is valid in p + p collisions at LHC energies. The normalizing factor of kaon with respect to pion (K/π) is almost constant in all energies . This study is important for the observation of strangeness enhancement in heavy ion collisions, which is an important probe of quark gluon plasma (QGP). It is also used as a baseline for the study of medium modifications in heavy ion collisions. Kaon spectra provides a unique opportunity to identify new flavor and CP violating interactions beyond the Standard Model (SM).

Molecular dynamics description of an expandingq/q¯plasma with the Nambu–Jona-Lasinio model and applications to heavy ion collisions at energies available at the BNL Relativistic Heavy Ion Collider and the CERN Large Hadron Collider

We present a relativistic molecular dynamics approach based on the Nambu--Jona-Lasinio Lagrangian. We derive the relativistic time evolution equations for an expanding plasma, discuss the hadronization cross section, and explain how they act in such a scenario. We present in detail how one can transform the time evolution equation to a simulation program and apply this program to study the expansion of a plasma created in experiments at the Relativistic Heavy Ion Collider and the Large Hadron Collider. We present first results on the centrality dependence of ${v}_{2}$ and of the transverse momentum spectra of pions and kaons and discuss in detail the hadronization mechanism.