Hidden Strangeness Research Articles

Open and Hidden Strangeness with Kaons and φ-Mesons in Bjorken Energy Density Approach for Central Collisions from SPS to LHC

Open and Hidden Strangeness with Kaons and φ-Mesons in Bjorken Energy Density Approach for Central Collisions from SPS to LHC

Two-gluon production of ϕ and η′ mesons in proton-proton collisions at high energies

We discuss gluon-gluon mechanisms for production of mesons with hidden strangeness, such as $\eta'$ and $\phi$ meson, in proton-proton collisions at large energies. The $g^* g^* \to \eta'$ and $g^* g^* \to \phi g$ mechanisms are considered only and the corresponding cross sections are calculated in the $k_t$-factorization approach. The $F_{\gamma^* \gamma^* \to \eta'}$ and $F_{g^* g^* \to \eta'}$ form factors are calculated from quark-antiquark $\eta'$ light-cone wave function including quark/antiquark transverse momenta. The result for two-photon transition form factor demonstrates that higher twists may survive even to large photon virtualities. The result is compared with the result of a recent leading-twist NLO analysis which uses phenomenological distribution amplitudes fitted to exclusive production of $\eta'$ in $e^+ e^- \to e^+ e^- \eta'$ reaction. We calculate transverse momentum distributions of both $\eta'$ and $\phi$ mesons in proton-proton collisions for RHIC and LHC energies. The results are compared to experimental data whenever available. The results of the Lund string model are shown for comparison for $\eta'$ production at LHC energies. It seems that the two-gluon fusion is not the dominant mechanism for both $\phi$ and $\eta'$ production, although the situation for $\eta'$, especially at larger energies, is less clear due to lack of experimental data.

Exotic double-charm molecular states with hidden or open strangeness and around 4.5∼4.7 GeV

In this work, we investigate the interactions between the charmed-strange meson ($D_s, D_s^{*}$) in $H$-doublet and the (anti-)charmed-strange meson ($D_{s1}, D_{s2}^{*}$) in $T$-doublet, where the one boson exchange model is adopted by considering the $S$-$D$ wave mixing and the coupled-channel effects. By extracting the effective potentials for the discussed $H_s\bar{T}_s$ and $H_s{T}_s$ systems, we try to find the bound state solutions for the corresponding systems. We predict the possible hidden-charm hadronic molecular states with hidden strangeness, i.e., the $D_s^{*}\bar D_{s1}+c.c.$ states with $J^{PC}$=$0^{--}, 0^{-+}$ and the $D_s^{*}\bar D_{s2}^{*}+c.c.$ states with $J^{PC}$=$1^{--}, 1^{-+}$. Applying the same theoretical framework, we also discuss the $H_s T_s$ systems. Unfortunately, the existence of the open-charm and open-strange molecular states corresponding to the $H_s T_s$ systems can be excluded.

S wave hidden charm–hidden strangeness production in e+e− annihilation

It is suggested that the recently observed enhancement of the relative yield in e+e− annihilation of states with hidden charm and hidden strangeness above 4.43 GeV is associated with the S wave production of the charmed strange meson pairs Ds0(2317)D¯s⁎+c.c. and Ds1⁎(2460)D¯s+c.c. This mechanism implies a pattern of breaking of the Heavy Quark Spin Symmetry (HQSS) that can be tested in the final channels such as ηc(1S)ϕ, hc(1P)η, hc(1P)η′ produced in the same energy range.

Highlights from PHENIX at RHIC

Hadrons conveying strange quarks or heavy quarks are essential probes of the hot and dense medium created in relativistic heavy-ion collisions. With hidden strangeness, ϕ meson production and its transport in the nuclear medium have attracted high interest since its discovery. Heavy quark-antiquark pairs, like charmonium and bottomonium mesons, are mainly produced in initial hard scattering processes of partons. While some of the produced pairs form bound quarkonia, the vast majority hadronize into particles carrying open heavy flavor. In this context, the PHENIX collaboration carries out a comprehensive physics program which studies the ϕ meson production, and heavy flavor production in relativistic heavy-ion collisions at RHIC. In recent years, the PHENIX experiment upgraded the detector in installing silicon vertex tracker (VTX) at mid-rapidity region and forward silicon vertex tracker (FVTX) at the forward rapidity region. With these new upgrades, the experiment has collected large data samples, and enhanced the capability of heavy flavor measurements via precision tracking. This paper summarizes the latest PHENIX results concerning ϕ meson, open and closed charm and beauty heavy quark production in relativistic heavy-ion collisions. These results are presented as a function of rapidity, energy and system size, and their interpretation with respect to the current theoretical understanding.

Rescaling of quantized skyrmions: From nucleon to heavy flavored baryons

The role of rescaling (expansion or squeezing) of quantized skyrmions is studied for the spectrum of baryons beginning with nucleon and $\Delta(1232)$, and with flavors strangeness, charm or beauty. The expansion of skyrmions due to the centrifugal forces has influence on the masses of baryons without flavor ($N$ and especially $\Delta$). The rescaling of skyrmions has smaller influence on the spectrum of strange baryons, it is more important for the case of charm, and is crucial for baryons with beauty quantum number, where strong squeezing takes place. Two competing tendencies are clearly observed: expansion of skyrmions when isospin (or spin) increases, and squeezing with increasing mass of the flavor. For the case of beauty baryon $\Lambda_b$ satisfactory agreement with data can be reached for the value $r_b= F_B/F_\pi \simeq 2.6 $, for the case of $\Sigma_b$ there should be $r_b\sim 2$, so for the beauty flavor the method seems to be not quite satisfactory because of certain intrinsic discrepances. Some pentaquark states with hidden strangeness, charm or beauty are considered as well.

Some properties of the states at the hidden-strangeness mixed 12++12− heavy meson pair threshold in e+e− annihilation

The threshold behavior of $e^+ e^-$ annihilation is considered in the channels $B_{s0} \bar B_s^* + c.c.$, $B_{s1} \bar B_s + c.c.$, and $B_{s1} \bar B_s^* +c.c.$, where $B_{s0}$ and $B_{s1}$ are the excited bottom-strange $J^P=0^+$ and $J^P = 1^+$ mesons. It is argued that due to the heavy quark spin symmetry (HQSS) only one coherent combination of the first two channels is produced in the $S$ wave as well as the third channel. Thus, if there exist threshold molecular peaks in the considered channels, only two of such peaks can be formed in the annihilation. The properties of such threshold states are discussed, including the heavy-light spin structure and the related transitions to bottomonium plus light mesons, as well as mixing with the channels with and without hidden strangeness.

η − η′ mixing and decays of mesons with heavy quarks

The inclusion of elastic rescattering and annihilation of quark–antiquarks pairs in final state can explain the [Formula: see text]-dependency for cross-section ratio of [Formula: see text] and [Formula: see text] mesons in charge exchange reaction. The estimation for mixing angle [Formula: see text] with isoscalar states [Formula: see text] and hidden strangeness [Formula: see text] has been obtained. The consistent description of [Formula: see text] and [Formula: see text] meson outputs in [Formula: see text], [Formula: see text] and [Formula: see text] decays was also considered.

Simple estimates of the masses of pentaquarks with hidden beauty or strangeness

The masses of cryptoexotic pentaquarks with hidden beauty are estimated phenomenologically using the results by the LHCb collaboration which discovered recently the cryptoexotic pentaquarks with hidden charm. The expected masses of the hidden beauty pentaquarks are about $10.8$ GeV and $10.7$ GeV in the limit of some kind of heavy quark symmetry. The states with hidden strangeness considered in similar way have masses about $2.37$ Gev and $2.30$ GeV, by several hundreds of MeV higher than states discussed previously in connection with the relatively light positive strangeness pentaquark $\theta^+$. Empirical data on spectra of pentaquarks can be used to get information about quarkonia interaction with nucleons. The results obtained for the case of heavy flavors are in fair agreement with model of isospin (pion) exchange between flavored baryons and anti-flavored vector mesons, proposed by Karliner and Rosner, and in qualitative agreement with the bound state version of the chiral soliton model.

Measurement ofKS0andK*0inp+p,d+Au, and Cu + Cu collisions atsNN=200 GeV

The PHENIX experiment at the Relativistic Heavy Ion Collider has performed a systematic study of $K_S^0$ and $K^{*0}$ meson production at midrapidity in $p$$+$$p$, $d$$+$Au, and Cu$+$Cu collisions at $\sqrt{s_{_{NN}}}=200$ GeV. The $K_S^0$ and $K^{*0}$ mesons are reconstructed via their $K_S^0 \rightarrow \pi^0(\rightarrow \gamma\gamma)\pi^0(\rightarrow\gamma\gamma)$ and $K^{*0} \rightarrow K^{\pm}\pi^{\mp}$ decay modes, respectively. The measured transverse-momentum spectra are used to determine the nuclear modification factor of $K_S^0$ and $K^{*0}$ mesons in $d$$+$Au and Cu$+$Cu collisions at different centralities. In the $d$$+$Au collisions, the nuclear modification factor of $K_S^0$ and $K^{*0}$ mesons is almost constant as a function of transverse momentum and is consistent with unity showing that cold-nuclear-matter effects do not play a significant role in the measured kinematic range. In Cu$+$Cu collisions, within the uncertainties no nuclear modification is registered in peripheral collisions. In central collisions, both mesons show suppression relative to the expectations from the $p$$+$$p$ yield scaled by the number of binary nucleon-nucleon collisions in the Cu$+$Cu system. In the $p_T$ range 2--5 GeV/$c$, the strange mesons ($K_S^0$, $K^{*0}$) similarly to the $\phi$ meson with hidden strangeness, show an intermediate suppression between the more suppressed light quark mesons ($\pi^0$) and the nonsuppressed baryons ($p$, $\bar{p}$). At higher transverse momentum, $p_T>5$ GeV/$c$, production of all particles is similarly suppressed by a factor of $\approx$ 2.

The ${\mit \Sigma }_{\pi N}$ Term, Chiral Multiplet Mixing and Hidden Strangeness in the Nucleon

The ${\mit \Sigma }_{\pi N}$ Term, Chiral Multiplet Mixing and Hidden Strangeness in the Nucleon

Investigating the microscopic properties of strongly interacting matter with HADES

Abstract In the energy domain of 1–2 GeV kinetic energy per nucleon, HADES has measured rare and penetrating probes in elementary and heavy ion collisions. Our results demonstrate that electron pair emission in C+C collisions can essentially be explained as a superposition of independent N+N collisions. HADES results on e+e− production in Ar+KCl collisions, however, show a strong enhancement of the dilepton yield relative to a reference spectrum obtained from elementary nucleon-nucleon reactions, signal the onset of medium effects beyond the superposition of individual N+N collisions. Intriguing results where also obtained from the reconstruction of hadrons with open and hidden strangeness. Analyses of the experimentally obtained hadronic yields measured in Ar+KCl allows to extract the chemical freeze-out conditions in the T -µB phase diagram of strongly interacting matter. While the measured abundance of all reconstructed particles are well described assuming thermalization, the also reconstructed double strange baryon ≡− appears about ten times more abundant than expected. This result will be discussed in the context of the exploration of the nuclear matter phase diagram in the region of finite density. Further investigations to search for significant medium effects, will be followed over the coming years with an upgraded HADES detector.

Dilepton and strangeness production probed with HADES

With the High Acceptance Di-Electron Spectrometer (HADES) at GSI we have studied dilepton production in the few-GeV energy regime in various collisions systems, from elementary NN, over pA, up to the medium-heavy Ar + KCl system. We have thus confirmed the puzzling results of the former DLS Collaboration at the Bevalac. While we have traced the origin of the excess pair yield in CC collisions to elementary pp and pn processes, in our Ar + KCl data a contribution from the dense phase of the collision has been identified. Together with the e+e− pairs, we have also obtained in the Ar + KCl system at 1.76 A GeV a high-statistics data set on open and hidden strangeness, i.e. K±, Ks0, Λ, ϕ, and Ξ−, allowing for a comprehensive discussion of strangeness production in this system.

Open and hidden strangeness in hadronic systems

DepartmentofPhysics,FNSPE,CzechTechnicalUniversityinPrague11519Prague1,CzechRepublic(Received January 11, 2012)We investigate production of ˚ mesons and baryons in nucleus–nucleuscollisions. Reactionsonstrangeparticlesactingasacatalyserareproposedtointerpretthehighobserved˚yieldsinHADESexperimentsaswellastheenergydependenceofthewidthsof˚rapidityspectraincolli-sionsattheSPSenergies. Itisarguedthattheenhancementof yieldobserved by HADES is even higher than originally reported, if effects oftheexperimentalcentralitytriggeraretakenintoaccount. Crosssectionsfornewhadronicprocessesthatcouldproduce arereviewed.

COMPASS HADRON SPECTROSCOPY — FINAL STATES INVOLVING NEUTRALS AND KAONS

The COMPASS experiment at CERN is well designed for light-hadron spectroscopy with emphasis on the detection of new states, in particular the search for JPC-exotic states and glueballs. We have collected data with 190 GeV/c charged hadron beams on a liquid hydrogen and nuclear targets in 2008/09. The spectrometer features good coverage by electromagnetic calorimetry and a RICH detector further provides π K separation, allowing for studying final states involving neutral particles like π0 or η as well as hidden strangeness, respectively. We discuss the status of ongoing analyses with specific focus on diffractively produced (π0π0π)- as well as [Formula: see text] final states.

Three Body Systems with Strangeness and Exotic Systems

We report on four Σ’s and three Λ’s, in the 1500–1800 MeV region, as two meson—one baryon S-wave (1/2)+ resonances found by solving the Faddeev equations in the coupled channel approach, which can be associated to the existing S = −1, J P = 1/2+ low lying baryon resonances. On the other hand we also report on a new, hidden strangeness N * state, mostly made of \({K \bar{K} N}\), with mass around 1920 MeV, which we think could be responsible for the peak seen in the γp → K + Λ around this energy. Finally we address a very novel topic in which we show how few body systems of several ρ mesons can be produced, with their spins aligned up to J = 6, and how these states found theoretically can be associated to several known mesons with spins J = 2, 3, 4, 5, 6.

η PHOTO-PRODUCTION ON THE DEUTERON AT LNS, TOHOKU UNIVERSITY

The differential and total cross sections were measured for the γp → ηp and γd → ηpn reactions at Eγ ≤ 1150 MeV by using an electro-magnetic (EM) calorimeter SCISSORS II at the Laboratory of Nuclear Science (LNS), Tohoku University. The total cross section on the deuteron shows a bump around Eγ = 1 GeV , while no bump is observed in the same energy region of that on the proton. This bump is attributed to be a nucleon resonance excited from the neutron, and it is a candidate of anti-decuplet penta-quark baryons with hidden strangeness. It was difficult, however, to detect all the γ's coming from η decay since the solid angle of SCISSORS II was only 12.6% in total. Statistics of the detected η produced events is poor and systematic uncertainty of the obtained cross section is not small due to low acceptance. A new EM calorimeter complex called FOREST with a solid angle of about 4π sr has been constructed. The spin and parity of the relevant resonance are expected to be determined by the experiments with FOREST.

ϕ meson measurements and flavor-dependent nuclear suppression at RHIC-PHENIX

Measurement of low mass vector mesons (ρ, ω, ϕ) provides important information to understand the properties of quark–gluon plasma (QGP) created in the central heavy-ion collision at RHIC. The mass and branching ratio of the ϕ meson decay into di-electron and di-kaon could be modified in the excited vacuum due to the effect of partial chiral symmetry restoration. In addition, ϕ meson contains hidden strangeness and hence its measurement can figure out the strangeness production. The suppression pattern of ϕ meson with high transverse momentum in heavy-ion collisions, compared to scaled p + p results, provides the information to understand the mechanism of production and energy loss of strange quark with the strongly coupled matter. The PHENIX experiment at RHIC has measured the ϕ meson production in p+p, d+Au and Au+Au collisions at up to 200 GeV at mid-rapidity. In this paper, we will present recent PHENIX results about the ϕ meson production. The mass peaks for ϕ have been observed in both di-electron and di-kaon invariant mass spectra. The extracted spectra, mass and width of ϕ in p+p, d+Au and Au+Au are reviewed. Moreover, we compare the nuclear modification factors of various hadrons and discuss flavor dependence of their suppression patterns.

Search for exotic baryons with hidden strangeness in proton diffractive production at the energy of 70 GeV

The first preliminary results from the upgraded SPHINX spectrometer, working in the proton beam with the energy of 70 GeV of the IHEP accelerator, are presented. The data for the reaction p + N ⊒ [Σ0 K +] + N based on new statistics are in good agreement with our previous data and strongly support the existence of the X (2000) state (with an increase in statistics for this state by a factor of ∼5). We also observed radiative decay of Λ(1520) → Λγ. The significant increase in statistics for many diffractive-production reactions will allow us to study them in great detail.

Resonances with hidden strangeness in [formula omitted] in flight

Resonances with hidden strangeness in [formula omitted] in flight