Kaon Research Articles

Measurement of K⁎(892)± production in inelastic pp collisions at the LHC

The first results on K⁎(892)± resonance production in inelastic pp collisions at LHC energies of s=5.02, 8, and 13 TeV are presented. The K⁎(892)± has been reconstructed via its hadronic decay channel K⁎(892)→±KS0+π± with the ALICE detector. Measurements of transverse momentum distributions, pT-integrated yields, and mean transverse momenta for charged K⁎(892) are found to be consistent with previous ALICE measurements for neutral K⁎(892) within uncertainties. For pT>1 GeV/c the K⁎(892)± transverse momentum spectra become harder with increasing centre-of-mass energy from 5.02 to 13 TeV, similar to what previously observed for charged kaons and pions. For pT<1 GeV/c the K⁎(892)± yield does not evolve significantly and the abundance of K⁎(892)± relative to K is rather independent of the collision energy. The transverse momentum spectra, measured for K⁎(892)± at midrapidity in the interval 0 <pT<15 GeV/c, are not well described by predictions of different versions of PYTHIA 6, PYTHIA 8 and EPOS-LHC event generators. These generators reproduce the measured pT-integrated K⁎±/K ratios and describe well the momentum dependence for pT<2 GeV/c.

Multiplicity Dependencies of Midrapidity Transverse Momentum Distributions of Identified Charged Particles in Proton-Proton Collisions at (s)1/2 = 7 TeV at the LHC

Dependencies of midrapidity pt distributions of the charged pions and kaons, protons and antiprotons on charged-particle multiplicity density (&lt;dNch/dη&gt;) in inelastic proton-proton collisions at (s)1/2 = 7 TeV at the LHC, measured by ALICE Collaboration, are investigated. The simultaneous minimum χ2 fits with the Tsallis function with thermodynamical consistence and the Hagedorn function with included transverse flow have well-described the pt spectra of the particle species in the ten studied groups of charged-particle multiplicity density. The effective temperatures, T, of the Tsallis function with thermodynamical consistence have shown a steady rise with increasing the charged-particle multiplicity in proton-proton collisions at (s)1/2 = 7 TeV, in agreement with the similar result obtained recently in proton-proton collisions at (s)1/2 = 13 TeV at the LHC. The respective T versus &lt;dNch/dη&gt; dependence in proton-proton collisions at (s)1/2 = 7 TeV is reproduced quite well by the simple power function with the same value (≈ 1/3) of the exponent parameter as that extracted in proton-proton collisions at (s)1/2 = 13 TeV. The identical power dependence T~ε1/3 between the initial energy density and effective temperature of the system has been observed in proton-proton collisions at (s)1/2 = 7 and 13 TeV. We have observed that the transverse radial flow emerges at &lt;dNch/dη&gt; ≈ 6 and then increases, becoming substantial at larger multiplicity events in proton-proton collisions at (s)1/2 = 7 TeV. We have estimated, analyzing T0 and ⟨βt⟩ versus &lt;dNch/dη&gt; dependencies, that the possible onset of deconfinement phase transition in proton-proton collisions at (s)1/2 = 7 TeV occurs at &lt;dNch/dη&gt; ≈ 6.1 ± 0.3, which is close to the corresponding recent estimate (&lt;dNch/dη&gt; ≈ 7.1 ± 0.2) in proton-proton collisions at (s)1/2 = 13 TeV. The corresponding critical energy densities for probable onset of deconfinement phase transition in proton-proton collisions at (s)1/2 = 7 and 13 TeV at the LHC have been estimated to be 0.67 ± 0.03 and 0.76 ± 0.02 GeV/fm3, respectively.

Effects of thermal string fragmentation in inelastic pp collisions at the CERN Super Proton Synchrotron with beam momenta from 20 to 158 GeV/ c

The proton stopping behavior in proton-proton ($\mathit{pp}$) collisions at beam momentum of 20, 31, 40, 80, 158 GeV/$c$ suggests that more physics mechanisms are at play than traditionally assumed in Monte Carlo event generators. It is shown that the thermal string fragmentation model of pythia 8.303 is able to provide a good description of the observables in inelastic $\mathit{pp}$ collisions such as the rapidity and transverse momentum spectra of protons, charged pions, and charged kaons at the whole CERN SPS energies.

Particles multiplicity based on rapidity in Landau and artificial neural network (ANN) models

In this paper, artificial neural network (ANN) model is used to estimate the multiplicity per rapidity for charged pions and kaons observed in various high-energy experiments from central [Formula: see text] heavy-ion collisions with energies ranging from 2–200 GeV, and then compared to available experimental data, including RHIC-BRAHMS experiment, and covering the energy range of the future accelerator facilities at NICA and FAIR. We also used Landau hydrodynamical approach, which has a better description for the evolution of hot and dense matter produced in ultra-relativistic heavy-ion collisions. The approach is fitted to both results estimated from experiment and ANN simulation. We noted that the Landau model accurately reproduces the entire range of multiplicity per rapidity for all created particles at all energies. Also ANN model can reproduce the multiplicity per rapidity very well for all the considered particles. This encourages us to use ANN model to predict the multiplicity per rapidity for [Formula: see text] particles at energies [Formula: see text] and [Formula: see text] GeV.

Analyzing Transverse Momentum Spectra by a New Method in High-Energy Collisions

We analyzed the transverse momentum spectra of positively and negatively charged pions (π+ and π−), positively and negatively charged kaons (K+ and K−), protons and antiprotons (p and p¯), as well as ϕ produced in mid-(pseudo)rapidity region in central nucleus–nucleus (AA) collisions over a center-of-mass energy range from 2.16 to 2760 GeV per nucleon pair. The transverse momentum of the considered particle is regarded as the joint contribution of two participant partons which obey the modified Tsallis-like transverse momentum distribution and have random azimuths in superposition. The calculation of transverse momentum distribution of particles is performed by the Monte Carlo method and compared with the experimental data measured by international collaborations. The excitation functions of effective temperature and other parameters are obtained in the considered energy range. With the increase of collision energy, the effective temperature parameter increases quickly and then slowly. The boundary appears at around 5 GeV, which means the change of reaction mechanism and/or generated matter.

Study of {mathrm{B}}_{mathrm{c}}^{+} decays to charmonia and three light hadrons

Using proton-proton collision data, corresponding to an integrated luminosity of 9 fb−1 collected with the LHCb detector, seven decay modes of the {mathrm{B}}_{mathrm{c}}^{+} meson into a J/ψ or ψ(2S) meson and three charged hadrons, kaons or pions, are studied. The decays {mathrm{B}}_{mathrm{c}}^{+} → (ψ(2S) → J/ψπ+π−)π+, {mathrm{B}}_{mathrm{c}}^{+} → ψ(2S)π+π−π+, {mathrm{B}}_{mathrm{c}}^{+} → J/ψK+π−π+ and {mathrm{B}}_{mathrm{c}}^{+} → J/ψK+K−K+ are observed for the first time, and evidence for the {mathrm{B}}_{mathrm{c}}^{+} → ψ(2S)K+K−π+, decay is found, where J/ψ and ψ(2S) mesons are reconstructed in their dimuon decay modes. The ratios of branching fractions between the different {mathrm{B}}_{mathrm{c}}^{+} decays are reported as well as the fractions of the decays proceeding via intermediate resonances. The results largely support the factorisation approach used for a theoretical description of the studied decays.

The NICA Complex and the MPD experiment at JINR: status and physics potential

The Multi-Purpose Detector is under construction at the Joint Institute for Nuclear Research in Dubna, as part of the NICA Accelerator Complex. The MPD Collaboration aims to study the phase diagram of QCD matter at maximum baryonic density, determine the nature of the phase transition between the deconfined and hadronic matter and search for the critical point. The combination of significant luminosity at NICA, collider geometry of the experiment and collision energies √SNN spanning the range of 4 to 11 GeV, where the transition from baryon to meson dominated matter is expected will allow MPD to provide unique insight into these questions. The status of the assembly of the detector in MPD Hall, as well as the progress in the production of MPD subdetectors will be reported on. The design physics performance of the detector will be discussed with the emphasis on the measurements in the strangeness sector. Tracking and particle identification procedures will enable precise determination of spectra of identified hadrons, including hyperons and hypernuclei, with the possibility of differential measurements and total yield extraction. The quality of directed and elliptic flow determination will be discussed, with comparison to model expectations. The sensitivity of event-by-event fluctuations to the nature of the phase transition and the presence of a critical point will be given. The femtoscopic analysis for charged pions and kaons has shown sensitivity to first order and cross-over phase transitions in EoS seen for the vHLLE model. All those studies will be put in context of addressing outstanding questions on the properties of the region of the QCD phase diagram probed by heavy-ion collisions in the NICA energy range.

News from the strong interactions program of NA61/SHINE

NA61/SHINE (SPS Heavy Ion and Neutrino Experiment) is a fixedtarget experiment operating at the CERN SPS accelerator. The main goal of the strong interactions program of NA61/SHINE is to study the properties of the phase transition between confined matter and quark-gluon plasma by performing a two-dimensional scan in beam momentum and size of collided nuclei. Within this program, collisions of different systems (p+p, p+Pb, Be+Be, Ar+Sc, Xe+La, Pb+Pb) over a wide range of beam momenta (13A-150(8)A GeV/c) have been recorded. This contribution discusses the latest results of hadron production in p+p, Be+Be, Ar+Sc and Pb+Pb reactions measured by the NA61/SHINE. In particular, the results include charged kaons and pions spectra and higher-order moments of multiplicity and net charge distributions. The presented data are compared with the predictions of different theoretical models as well as the results from other experiments. Finally, the motivation and plans for future NA61/SHINE measurements are discussed.

Two-loop electroweak corrections to the Top-Quark Contribution to \u03f5K

The parameter ϵK measures CP violation in the neutral kaon system. It is a sensitive probe of new physics and plays a prominent role in the global fit of the Cabibbo-Kobabyashi-Maskawa matrix. The perturbative theory uncertainty is currently dominated by the top-quark contribution. Here, we present the calculation of the full two-loop electroweak corrections to the top-quark contribution to ϵK, including the resummation of QED-QCD logarithms. We discuss different renormalization prescriptions for the electroweak input parameters. In the traditional normalization of the weak Hamiltonian with two powers of the Fermi constant GF, the top-quark contribution is shifted by −1%.

The D_s^+ rightarrow a_0(980) e^+ nu _e reaction and the a_0(980)-f_0(980) mixing

We perform a study of the D_s^+ rightarrow a_0(980)(f_0(980)) e^+ nu _e reactions investigating the different sources of isospin violation which make the production of the a_0(980) possible. We find that loops involving kaons in the production mechanism provide a source of isospin violation since they do not cancel due to the different mass of charged and neutral kaons, but we also find that the main source comes from the breaking of isospin in the meson-meson transition T matrices, which contain information on the nature of the low lying scalar mesons. The reaction is thus very sensitive to the nature of the a_0(980) and f_0(980) resonances. Our results are consistent with the present upper bound for a_0(980) production and only a factor three smaller, indicating that future runs with more statistics should find actual numbers for this reaction from where we can learn more about the origin of the scalar resonances and their nature.

Charged pion, kaon, proton and antiproton production in large collision systems

The main goal of PHENIX expirement, located at Relativistic Heavy-ion collider, is the investigation of quark-gluon plasma (QGP). One of the aspects of the QGP study is describing the process of its hadronization. Very important contribution to understanding of hadronization process was given by discovering of anomaly large ratio of protons production to pions production (ρ/π) in Au+Au collisions in comparison to the same ratio in proton-proton collisions. This effect was called baryon puzzle and was explained in a frame of recombination model of hadronization.Although charged hadrons production has been previously studied in elementary proton-proton collisions and symmetric Au+Au collisions, it has never been investigated before in the large asymmetric collisions systems (such as Cu+Au) or the collisions of large deformed nuclei (U+U). The study of such large collisions systems allows to study features of baryon and meson production versus collision geometry and system size.

Search for B^{+}→K^{+}νν[over ¯] Decays Using an Inclusive Tagging Method at Belle II.

A search for the flavor-changing neutral-current decay B^{+}→K^{+}νν[over ¯] is performed at the Belle II experiment at the SuperKEKB asymmetric energy electron-positron collider. The data sample corresponds to an integrated luminosity of 63 fb^{-1} collected at the ϒ(4S) resonance and a sample of 9 fb^{-1} collected at an energy 60MeV below the resonance. Because the measurable decay signature involves only a single charged kaon, a novel measurement approach is used that exploits not only the properties of the B^{+}→K^{+}νν[over ¯] decay, but also the inclusive properties of the other B meson in the ϒ(4S)→BB[over ¯] event, to suppress the background from other B meson decays and light-quark pair production. This inclusive tagging approach offers a higher signal efficiency compared to previous searches. No significant signal is observed. An upper limit on the branching fraction of B^{+}→K^{+}νν[over ¯] of 4.1×10^{-5} is set at the 90% confidence level.

Editorial

Editorial

Controlling the process of muon formation for muon-catalyzed fusion: method of non-destructive average muon sign detection

The recent development of intense muon sources (Holmlid, Swedish Patent SE 539,684 C 2 (2017)) is crucial for the use of muon-catalyzed fusion reactors (L. Holmlid, Fusion Science and Technology 75, 208 (2019)) which are likely to be the first generation of practical fusion reactors. For this purpose, only negative muons are useful. For existing sources where negative muons can be ejected (if not formed) preferentially, it is necessary to know the amount of negative muons to determine and optimize the fusion reactor efficiency on-line. Here, a method is developed to measure the absolute muon flux and its average sign without collecting or deflecting the muons. The muons from the patented muon generator have an energy of 100 MeV and above and an intensity of 1013 muons per laser pulse. Here, the detection of the relativistic laser-induced muons from H(0) is reported with a standard particle beam method, using a wire coil on a ferrite toroid as detector for the relativistic particles. The coil detection method shows that these relativistic particles are charged, thus not photons, neutrinos or neutral kaons. This makes the coil method superior to scintillator methods and it is the only possible method due to the large muon intensity. If an equal number of positive and negative mouns passed the coil, no signal would be observed. The signal at the coil in the case shown here is due to relativistic positive muons as concluded from a signal charge sign verification in the coil.

Taming εK in little Randall-Sundrum models

The Randall Sundrum models receive significant constraints from the neutral kaon system. The $CP$ violating observable ${\ensuremath{\epsilon}}_{K}$, in the Randall Sundrum scenario, requires the lightest $KK$ gluon to be heavier than $\ensuremath{\sim}24\text{ }\text{ }\mathrm{TeV}$. The constraint is even stronger in the little Randall Sundrum (LRS) models, $\ensuremath{\gtrsim}32\text{ }\text{ }\mathrm{TeV}$. The LRS models are motivated for their possible visibility at the LHC. We show that the stringent constraints from $K$ physics can be relaxed in the LRS models, in the presence of the brane localized kinetic terms (BLKT). In particular, for a range of values, a UV BLKT could significantly modify the lightest $KK$ gluon wave function such that the limit can reduces to 5 TeV. We also show that such a relaxation of the constraints can also be achieved by imposing flavor symmetries \`a la minimal flavor protection.

Test of quantum nonlocality via vector meson decays to KSKS

In the system of a pair of quantum-entangled neutral kaons from meson decays, when one kaon collapses into the [Formula: see text] state, the other will collapse instantaneously into the [Formula: see text] state, due to entanglement and nonlocality. However, if the alternative hypothesis is correct and there is a time window during which one kaon is unaware that the other has decayed, some quantum mechanically prohibited [Formula: see text] decays may occur. We calculate the branching ratios of [Formula: see text] in vector meson decays under locality hypothesis and compare them with experimental results. We show that the branching ratio of [Formula: see text] under locality assumption is already excluded by the BESIII experimental upper limit. Additional experimental results are proposed to perform this test in the future.

Portal Effective Theories. A framework for the model independent description of light hidden sector interactions

We present a framework for the construction of portal effective theory (PETs) that couple effective field theories of the Standard Model (SM) to light hidden messenger fields. Using this framework we construct electroweak and strong scale PETs that couple the SM to messengers carrying spin zero, one half, or one. The electroweak scale PETs encompass all portal operators up to dimension five, while the strong scale PETs additionally contain all portal operators of dimension six and seven that contribute at leading order to quark-flavour violating transitions. Using the strong scale PETs, we define a set of portal currents that couple hidden sectors to QCD, and construct portal chiral perturbation theory (χPTs) that relate these currents to the light pseudoscalar mesons. We estimate the coefficients of the portal χPT Lagrangian that are not fixed by SM observations using non-perturbative matching techniques and give a complete list of the resulting one- and two-meson portal interactions. From those, we compute transition amplitudes for three golden channels that are used in hidden sector searches at fixed target experiments: i) charged kaon decay into a charged pion and a spin zero messenger, ii) charged kaon decay into a charged lepton and a spin one half messenger, and iii) neutral pion decay into a photon and a spin one messenger. Finally, we compare these amplitudes to specific expressions for models featuring light scalar particles, axion-like particles, heavy neutral leptons, and dark photons.

Laser-assisted kaon decay and CPT symmetry violation

In this paper, we have investigated the charged kaons decay at the lowest order in the presence of a circularly polarized laser field. To be more precise, we have examined the leptonic decay of both positive (matter) and negative (antimatter) kaon which weakly decay via the exchange of W boson. Indeed, we have derived the expression of the leptonic decay width, the leptonic branching ratio, the leptonic ratio and the charged kaon lifetime by using the decay matrix approach. In addition, by using numerical computation, we have presented and discussed how the laser field influences these physical quantities. Moreover, we have analyzed the effect of the laser field on the parameter associated to the CPT symmetry. Then, we have concluded that, in the presence of an electromagnetic field and based on this CPT symmetry parameter, it is possible to control the dominance of matter over antimatter or vice-versa by applying an external field to either violate or conserve the CPT symmetry.

Mambillikalathil Govind Kumar Menon. 28 August 1928—22 November 2016

M. G. K. Menon, referred to as Goku, was an outstanding particle physicist and an extraordinary statesman of science. He made his major contributions to particle physics during the tortuous years of the unravelling of the full complexity of the families of elementary particles. It was an exciting but perplexing period, and the elucidation of the complexities of the world of elementary particles took the combined efforts of the experimentalists and the theorists. Goku's contributions were central to establishing what was eventually to become the standard picture of elementary particles. He will be remembered for his studies of the two- and three-body decay modes of the charged kaon that gave rise to the ‘τ–θ’ puzzle signalling non-conservation of parity. He coined the evocative phrase ‘associated production’ to describe the creation of kaons and hyperons together in high-energy interactions. He led a team that carried out experiments at great depths underground, and in 1965 they detected an event in which a cosmic-ray neutrino interacted with rock, producing an energetic muon. In the 1980s, with a large detector, also deployed underground, he set a lower bound on the lifetime for the decay of the proton. Menon was a great builder of academic and scientific institutions and a pre-eminent advocate for science. Accordingly, he stimulated and participated actively in building up the scientific and technological infrastructure in independent India, initially as the secretary of the Government of India and subsequently as the minister of state for science and technology. As the president of the International Council of Scientific Unions, he spearheaded its participation in the policymaking body of the United Nations. He was at various times the president of the three leading academies of sciences in India and a founding member and vice-president of the World Academy of Sciences. He was a gentle and loving family man and an energetic and engaged scientific colleague.

Chiral properties of ( 2+1 )-flavor QCD in strong magnetic fields at zero temperature

We present lattice QCD results for masses and magnetic polarizabilities of light and strange pseudoscalar mesons, chiral condensates, decay constants of neutral pion, and neutral kaon in the presence of background magnetic fields with $eB$ ranging up to around 3.35 GeV$^2$ ($\sim70~M_\pi^2$) in the vacuum. The computations were carried out in (2+1)-flavor QCD mostly on $32^3 \times 96$ lattices using the highly improved staggered quark action with $M_{\pi} \approx $ 220 MeV at zero temperature. We find that the masses of neutral pseudoscalar mesons monotonously decrease as the magnetic field strength grows and then saturate at a nonzero value, while there exists a nonmonotonous behavior of charged pion and kaon masses in the magnetic field. We observe a $qB$ scaling of the up and down quark flavor components of neutral pion mass, neutral pion decay constant as well as the quark chiral condensates at 0.05 $\lesssim eB\lesssim$ 3.35 GeV$^2$. We show that the correction to the Gell-Mann-Oakes-Renner relation involving the neutral pion is less than 6% and the correction for the relation involving neutral kaon is less than 30% at $eB\lesssim$ 3.35 GeV$^2$. We also derive the Ward-Takahashi identities for QCD in the magnetic field in the continuum formulation including the relation between integrated neutral pseudoscalar meson correlators and chiral condensates.