Strange Hadrons Research Articles

Observation of prompt J/ψ meson elliptic flow in high-multiplicity pPb collisions at [formula omitted] TeV

A measurement of the elliptic flow (v2) of prompt J/ψ mesons in high-multiplicity pPbcollisions is reported using data collected by the CMS experiment at a nucleon-nucleon center-of-mass energy sNN=8.16TeV. Prompt J/ψ mesons decaying into two muons are reconstructed in the rapidity region in the nucleon-nucleon center-of-mass frame (ycm), corresponding to either −2.86<ycm<−1.86 or 0.94<ycm<1.94. The average v2 result from the two rapidity ranges is reported over the transverse momentum (pT ) range from 0.2 to 10 GeV. Positive v2 values are observed for the prompt J/ψ meson, as extracted from long-range two-particle correlations with charged hadrons, for 2<pT<8 GeV. The prompt J/ψ results are compared with previous CMS measurements of elliptic flow for open charm mesons (D0) and strange hadrons. From these measurements, constraints can be obtained on the collective dynamics of charm quarks produced in high-multiplicity events arising from small systems.

Multiplicity dependence of light-flavor hadron production in pp collisions at s=7TeV

Comprehensive results on the production of unidentified charged particles, $\pi^{\pm}$, $\rm{K}^{\pm}$, $\rm{K}^{0}_{S}$, $\rm{K}$*(892)$^{0}$, $\rm{p}$, $\overline{\rm{p}}$, $\phi$(1020), $\Lambda$, $\overline{\Lambda}$, $\Xi^{-}$, $\overline{\Xi}^{+}$, $\Omega^{-}$ and $\overline{\Omega}^{+}$ hadrons in proton-proton (pp) collisions at $\sqrt{s}$ = 7 TeV at midrapidity ($|y| < 0.5$) as a function of charged-particle multiplicity density are presented. In order to avoid auto-correlation biases, the actual transverse momentum ($p_{\rm{T}}$) spectra of the particles under study and the event activity are measured in different rapidity windows. In the highest multiplicity class, the charged-particle density reaches about 3.5 times the value measured in inelastic collisions. While the yield of protons normalized to pions remains approximately constant as a function of multiplicity, the corresponding ratios of strange hadrons to pions show a significant enhancement that increases with increasing strangeness content. Furthermore, all identified particle to pion ratios are shown to depend solely on charged-particle multiplicity density, regardless of system type and collision energy. The evolution of the spectral shapes with multiplicity and hadron mass shows patterns that are similar to those observed in p-Pb and Pb-Pb collisions at LHC energies. The obtained $p_{\rm{T}}$ distributions and yields are compared to expectations from QCD-based pp event generators as well as to predictions from thermal and hydrodynamic models. These comparisons indicate that traces of a collective, equilibrated system are already present in high-multiplicity pp collisions.

Freeze-out conditions from strangeness observables at RHIC

We determine chemical freeze-out conditions from strangeness observables measured at RHIC beam energies. Based on a combined analysis of lowest-order net-kaon fluctuations and strange anti-baryon over baryon yield ratios we obtain visibly enhanced freeze-out conditions at high beam energies compared to previous studies which analyzed net-proton and net-charge fluctuations. Our findings are in qualitative agreement with the recent study (Bellwied et al. in arXiv:1805.00088 [hep-ph], 2018) which utilizes the net-kaon fluctuation data in combination with information from lattice QCD. Our complementary approach shows that also strange hadron yield ratios are described by such enhanced freeze-out conditions.

Multiplicity dependence of strangeness and hadronic resonance production in pp and p-Pb collisions with ALICE at the LHC

One of the key results of the LHC Run 1 was the observation of an enhanced production of strange particles in high multiplicity pp and p–Pb collisions at sNN=7 and 5.02 TeV, respectively. The strangeness enhancement is investigated by measuring the evolution with multiplicity of single-strange and multi-strange baryon production relative to non-strange particles. A smooth increase of strange particle yields relative to the non-strange ones with event multiplicity has been observed in such systems. We report the latest results on multiplicity dependence of strange and multi-strange hadron production in pp collisions at s=13TeV with ALICE. We also presented recent measurements of mesonic and baryonic resonances in small collision systems like pp and p–Pb at sNN=13 and 8.16 TeV, respectively. The multiplicity dependent studies in pp and p-Pb collisions have been used to investigate how the hadronic scattering processes affect measured resonance yields and to better understand the interplay between canonical suppression and strangeness enhancement. The measurement of the ϕ(1020) meson as a function of multiplicity provides crucial constraints in this context.

Multiplicity Dependence of Strangeness and Charged Particle Production in Proton--Proton Collisions

In this contribution, the production rates and the transverse momentum distributions of strange hadrons are reported as a function of charged particle multiplicity. In this analysis, the data collected in proton-proton collisions at $\sqrt{s}$ = 13 TeV with the ALICE detector at the LHC are used. It is found that the production rate of $K_{S}^{0}$, $\Lambda$, $\Xi^{\pm}$, and $\Omega$ increases with multiplicity faster than that for charged particles. The higher the strangeness content of the hadron, the more pronounced is the increase. Moreover, the energy and multiplicity dependence of charged particle production in pp collisions are presented and the results are compared to predictions from Monte Carlo (MC) event generators. It turns out that the average multiplicity density increases steeply with center-of-mass energy for high multiplicity classes.

Real-time alignment and reconstruction: performance and recent developments at the LHCb experiment

The LHCb detector is a single-arm forward spectrometer designed for the efficient reconstruction decays of c- and b-hadrons. LHCb has introduced a novel real-time detector alignment and calibration strategy for LHC Run II. Data collected at the start of the fill are processed in a few minutes and used to update the alignment, while the calibration constants are evaluated for each run. This is one of the key elements which allow the reconstruction quality of the software trigger in Run-II, which fully includes the particle identification selection criteria, to be as good as the offline quality of Run-I. This approach greatly increases the efficiency, in particular for the selection of charm and strange hadron decays. We discuss strategy and performance of this novel approach, followed by a presentation of the recent developments implemented for the 2017 run of data taking, and with the performance and reconstruction quality achieved by the LHCb experiment in LHC Run-II.

Elliptic Flow of Charm and Strange Hadrons in High-Multiplicity p+Pb Collisions at sqrt[s_{NN}]=8.16 TeV.

The elliptic azimuthal anisotropy coefficient (v_{2}) is measured for charm (D^{0}) and strange (K_{S}^{0}, Λ, Ξ^{-}, and Ω^{-}) hadrons, using a data sample of p+Pb collisions collected by the CMS experiment, at a nucleon-nucleon center-of-mass energy of sqrt[s_{NN}]=8.16 TeV. A significant positive v_{2} signal from long-range azimuthal correlations is observed for all particle species in high-multiplicity p+Pb collisions. The measurement represents the first observation of possible long-range collectivity for open heavy flavor hadrons in small systems. The results suggest that charm quarks have a smaller v_{2} than the lighter quarks, probably reflecting a weaker collective behavior. This effect is not seen in the larger PbPb collision system at sqrt[s_{NN}]=5.02 TeV, also presented.

Spectra of strange hadrons and their role in neutrinos flux prediction

Hadron production measurements are important for the long baseline neutrino oscillation experiment as well as for the study of extensive air shower produced by cosmic rays. For precise measurements of the neutrinos flux prediction, and Λ need to be considered. To this aim, the study of and Λ in polar angle intervals of 0 to 300 mrad and 0 to 420 mrad, respectively, is carried out. Hadron production models, EPOS 1.99, EPOS-LHC and QGSJETII-04, are used to simulate the particles with proton-carbon interactions at 31 GeV/c. The models predictions are compared with the measurements of the NA61/SHINE experiment based on the analysis of data collected in 2009 with a carbon target. None of the models completely describe the experimental data over the entire range of momentum and angular intervals. EPOS 1.99 and EPOS-LHC give a good description of the data for both strange particles except at for Λ, where the models overestimate. The QGSJETII-04 model overestimates the yield of the strange hadrons around the peak of the distribution, primarily at low angular intervals. Generally, all models are in excellent agreement at high momentum values of the distributions.

Measurements and understanding of fundamental properties of hot and dense nuclear matter with HADES

Heavy ion collisions at few GeV per nucleon energy range according to microscopic transport model calculations, create matter with densities several times larger that the ground density and heated to temperatures of 90 MeV. At such conditions the fundamental properties of the particles might be modified. Promising observables are the rare (multi-) strange hadrons and dileptons. The High Acceptance DiElectron Spectrometer was designed to measure rare and penetrating probes. It is a fixed target experiment located at SIS18 accelerator at GSI, Darmstadt, Germany. Recent results on dileptons and strangeness production in Au+Au collisions at center of mass energy are presented. Moreover, future experiments and upgrades of the apparatus are discussed.

Enhancement of cyanobacterial control by fungi degraded palm oil trunk

The elliptic azimuthal anisotropy coefficient (v2) is measured for charm (D0) and strange (K0 S, Λ, Ξ−, and Ω−) hadrons, using a data sample of p þ Pb collisions collected by the CMS experiment, at a nucleonnucleon center-of-mass energy of ffiffiffiffiffiffiffi sNN p ¼ 8.16 TeV. A significant positive v2 signal from long-range azimuthal correlations is observed for all particle species in high-multiplicity p þ Pb collisions. The measurement represents the first observation of possible long-range collectivity for open heavy flavor hadrons in small systems. The results suggest that charm quarks have a smaller v2 than the lighter quarks, probably reflecting a weaker collective behavior. This effect is not seen in the larger PbPb collision system at ffiffiffiffiffiffiffi sNN p ¼ 5.02 TeV, also presented.

Performance Studies for Strange Hadron Flow Measurements in CBM at FAIR

Measurements of the directed and elliptic flow of strange and multi-strange hadrons are an important part of the physics program of the Compressed Baryonic Matter experiment (CBM) at the future accelerator complex FAIR in Darmstadt, Germany. We present recent results from the CBM performance studies for measurements of the directed (

Flavor-dependent eigenvolume interactions in a hadron resonance gas

Eigenvolume effects in the hadron resonance gas (HRG) model are studied for experimental hadronic yields in nucleus–nucleus collisions. If particle eigenvolumes are different for different hadron species, the excluded volume HRG (EV-HRG) improves fits to multiplicity data. In particular, using different mass–volume relations for strange and non-strange hadrons we observe a remarkable improvement in the quality of the fits. This effect appears to be rather insensitive to other details in the schemes employed in the EV-HRG. We show that the parameters found from fitting the data of the ALICE Collaboration in central Pb+Pb collisions at the collision energy sNN=2.76 TeV entail the same improvement for all centralities at the same collision energy, and for the RHIC and SPS data at lower collision energies. Our findings are put in the context of recent fits of lattice QCD results.

Contribution of a kaon component in the viscosity and conductivity of a hadronic medium

The two-point correlation functions of kaonic viscous stress tensors and electro-magnetic currents have been calculated respectively to estimate the contributions of the strange sector in the shear viscosity and electrical conductivity of hadronic medium. In the one-loop correlators, kaon propagators contain a non-zero thermal width that leads to non-divergent values of transport coefficients. With the help of effective Lagrangian densities of strange hadrons, we have calculated in-medium self-energy of kaon for different possible mesonic loops, whose imaginary part provide the estimation of kaon thermal width. It is observed that near the quark-hadron transition temperature, the contribution of kaons to shear viscosity is larger and increases faster with temperature than pionic contribution. In case of electrical conductivity the trend due kaon component appears to be opposite in nature with respect to pion component.

Search for a Λnn bound state in Pb-Pb collisions with ALICE at the LHC

The extreme energy densities reached at the LHC lead to the production of a significant amount of baryons and strangeness. Such a regime allows for an increased production of potentially existing exotic QCD bound states containing nuclei and strange hadrons. An interesting measurement for the phenomenology of the nuclear interaction is the presence of a neutral bound state constituted by one Λ and two neutrons. The excellent particle identification, tracking and vertexing performance of the ALICE experiment allow for the search of this exotic bound state in the decay channel Λnn →3H+π- in Pb-Pb collisions. In order to improve detection of this state despite the presence of a huge combinatorial background, the extraction of the signal is performed by means of a multivariate approach with the TMVA (Toolkit for Multivariate Data Analysis with ROOT). So far the indication for the existence of the Λnn state was reported only by the HypHI Collaboration, so the observation by ALICE would crucially contribute to the study of such an exotic state.

Strange hadron production in pp, pPb, and PbPb collisions at LHC energies

Identified particle spectra provide an important tool for understanding the particle production mechanism and the dynamical evolution of the medium created in relativistic heavy ion collisions. Studies involving strange and multi-strange hadrons, such as K0S, Λ, and Ξ−, carry additional information since there is no net strangeness content in the initial colliding system. Strangeness enhancement in AA collisions with respect to pp and pA collisions has long been considered as one of the signatures for quark-gluon plasma (QGP) formation. Recent observations of collective effects in high-multiplicity pp and pA collisions raise the question of whether QGP can also be formed in the smaller systems. Systematic studies of strange particle abundance, particle ratios, and nuclear modification factors can shed light on this issue. The CMS experiment has excellent strange-particle reconstruction capabilities over a broad kinematic range, and dedicated high-multiplicity triggers in pp and pPb collisions. The spectra of K0S, Λ, and Ξ− hadrons have been measured in various multiplicity and rapidity regions as a function of pT in pp, pPb, and PbPb collisions for several collision energies. The spectral shapes and particle ratios are compared in the different collision systems for events that have the same multiplicity and interpreted in the context of hydrodynamics models.

Theoretical perspective on strangeness production

A brief review of some highlights and puzzles on strangeness production in heavy ion collisions is given. These include strangeness production and the nuclear equation of state; deeply subthreshold strangeness production; mean-field potentials on strange hadrons; phi meson in dense matter; anomalous strange hadron to pion ratios; density fluctuations on particle production; A hyperon polarization and the vorticity field, and exotic hadrons.

Strangeness production in Pb-Pb collisions at LHC energies with ALICE

The results on the production of strange and multi-strange hadrons (K0S, Λ, Ξ and Ω) measured with ALICE in Pb-Pb collisions at the top LHC energy of [see formula in PDF] = 5.02 TeV are reported. Thanks to its excellent tracking and particle identification capabilities, ALICE is able to measure weakly decaying particles through the topological reconstruction of the identified hadronic decay products. Results are presented as a function of centrality and include transverse momentum spectra measured at central rapidity, pT-dependent Λ/K0S ratios and integrated yields. A systematic study of strangeness production is of fundamental importance for determining the thermal properties of the system created in ultrarelativistic heavy ion collisions. In order to study strangeness enhancement, the yields of studied particles are normalised to the corresponding measurement of pion production in the various centrality classes. The results are compared to measurements performed at lower energies, as well as to different systems and to predictions from statistical hadronization models.

The Dynamics of Beauty \&amp; Charm Hadrons and Top Quarks in the Era of the LHCb \&amp; Belle II and ATLAS \&amp; CMS --- Motto: Non-perturbative QCD \&amp; Many-body Final States

Our community has to apply {\em non}-perturbative QCD on different levels of flavor dynamics in strange, charm \& beauty hadrons and even for top quarks. We need {\em consistent} parameterization of the CKM matrix and describe weak decays of beauty hadrons with {\em many-body} final states. It is crucial to use the {\em Wilsonian} OPE as much as possible and discuss "duality" in the worlds of quarks and hadrons. The pole mass of heavy quarks is {\em not} well-defined on the {\em non}-perturbative level -- i.e., it is {\em not} Borel summable in total QCD. We need a novel team to combine the strengths of our tools from MEP and HEP.

Strange and heavy hadrons production from coalescence plus fragmentation in AA collisions at RHIC and LHC

In a coalescence plus fragmentation approach we study the pT spectra of charmed hadrons D0, Ds up to about 10 GeV and the Λ+c /D0 ratio from RHIC to LHC energies. In this study we have included the contribution from decays of heavy hadron resonances and also that due to fragmentation of heavy quarks that are left in the system after coalescence. The pT dependence of the heavy baryon/meson ratios is found to be sensitive to the heavy quark mass. In particular we found that the Λc/D0 is much flatter than the one for light baryon/meson ratio like p/π and Λ/K.

Separate freeze-out of strange particles and the quark-hadron phase transition

The scenario of the independent chemical freeze-outs for strange and nonstrange particles is discussed. Within such a scenario an apparent in-equilibrium of strangeness is naturally explained by a separation of chemical freeze-out of strange hadrons from the one of non-strange hadrons, which, nevertheless, are connected by the conservation laws of entropy, baryonic charge and third isospin projection. An interplay between the separate freeze-out of strangeness and its residual non-equilibrium is studied within an elaborate version of the hadron resonance gas model. The developed model enables us to perform a high-quality fit of the hadron multiplicity ratios measured at AGS, SPS and RHIC with an overall fit quality ϰ2/dof = 0:93. A special attention is paid to a description of the Strangeness Horn and to the well-known problem of selective suppression of Δ- and ж hyperons. It is remarkable that for all collision energies the strangeness suppression factor γs is about 1 within the error bars. The only exception is found in the vicinity of the center-of-mass collision energy 7.6 GeV, at which a residual enhancement of strangeness of about 20 % is observed.