Phi Meson Research Articles

Phi meson in nuclear medium

I will report on the progress in theoretical studies of the ϕ meson mass shift in a nuclear medium and provide an overview of the current experimental status for observing such an effect. Additionally, I will discuss how the distinct momentum dependencies of the transverse and longitudinal modes can be experimentally distinguished, particularly through the e+e− and K+K− decay modes of the ϕ meson as it decays within the medium.

Exclusive photo- and electroproduction of excited light vector mesons via holographic model

In this paper, we study total and differential observables of electro- and photoproduction of light rho , omega and phi mesons as functions of the center-of-mass energy of the gamma p collision and momentum transfer squared |t|. The corresponding vector mesons wave functions have been computed in the framework of relativistic AdS/QCD holographic approach. A satisfactory description of all available data on ground-state rho (1S), omega (1S) and phi (1S) mesons production cross sections has been achieved in the color dipole picture. Finally, the key observables of excited rho (2S), omega (2S) and phi (2S) states production in gamma ^{(*)} p collisions have been presented here using a common wave function formalism. This study reveals a large theoretical uncertainty coming from the modeling of the partial dipole amplitude in the nonperturbative kinematical domain. Hence, the latter could benefit from future measurements of photoproduction of the excited states.

Phi meson electroproduction at low transferred momentum

The electroproduction of phi meson is analyzed. The amplitude consist of two terms, the soft and the hard pomeron terms. it is assumed, that both pomerons are Regge poles. In the present approach, the two pomeron amplitude for the photoproduction processes is extended to construct an amplitude for the electroproduction processes by introducing the photon virtual mass ( . The residues of the two poles become functions of ( . These functions are extracted by fitting the differential cross section ( ) of the extended model at constant energy to the experimental data using the chi- square method. At each , the hard and the soft terms are multiplied by the factors and to match the data. The vertices of the pomeron coupling to the interacting particles are calculated by the dimensions of the vertices which are related to the masses of the interacting particles at each vertex.

Energy dependence of phi meson production at forward rapidity in pp collisions at the LHC

The production of phi mesons has been studied in pp collisions at LHC energies with the ALICE detector via the dimuon decay channel in the rapidity region 2.5< y < 4. Measurements of the differential cross section mathrm{d}^2sigma /mathrm{d}y mathrm{d}p_{mathrm {T}} are presented as a function of the transverse momentum (p_{mathrm {T}}) at the center-of-mass energies sqrt{s}=5.02, 8 and 13 TeV and compared with the ALICE results at midrapidity. The differential cross sections at sqrt{s}=5.02 and 13 TeV are also studied in several rapidity intervals as a function of p_{mathrm {T}}, and as a function of rapidity in three p_{mathrm {T}} intervals. A hardening of the p_{mathrm {T}}-differential cross section with the collision energy is observed, while, for a given energy, p_{mathrm {T}} spectra soften with increasing rapidity and, conversely, rapidity distributions get slightly narrower at increasing p_{mathrm {T}}. The new results, complementing the published measurements at sqrt{s}=2.76 and 7 TeV, allow one to establish the energy dependence of phi meson production and to compare the measured cross sections with phenomenological models. None of the considered models manages to describe the evolution of the cross section with p_{mathrm {T}} and rapidity at all the energies.

Studying the Phi Meson in Nuclear Matter by Simulating pA Reactions in a Transport Approach

Studying the Phi Meson in Nuclear Matter by Simulating pA Reactions in a Transport Approach

Production of pions, kaons, (anti-)protons and phi mesons in Xe\u2013Xe collisions at sqrt{s_{mathrm{NN}}}\xa0=\xa05.44 TeV

The first measurement of the production of pions, kaons, (anti-)protons and phi mesons at midrapidity in Xe–Xe collisions at sqrt{s_{mathrm{NN}}} = 5.44~text {TeV} is presented. Transverse momentum (p_{mathrm{T}}) spectra and p_{mathrm{T}}-integrated yields are extracted in several centrality intervals bridging from p–Pb to mid-central Pb–Pb collisions in terms of final-state multiplicity. The study of Xe–Xe and Pb–Pb collisions allows systems at similar charged-particle multiplicities but with different initial geometrical eccentricities to be investigated. A detailed comparison of the spectral shapes in the two systems reveals an opposite behaviour for radial and elliptic flow. In particular, this study shows that the radial flow does not depend on the colliding system when compared at similar charged-particle multiplicity. In terms of hadron chemistry, the previously observed smooth evolution of particle ratios with multiplicity from small to large collision systems is also found to hold in Xe–Xe. In addition, our results confirm that two remarkable features of particle production at LHC energies are also valid in the collision of medium-sized nuclei: the lower proton-to-pion ratio with respect to the thermal model expectations and the increase of the phi -to-pion ratio with increasing final-state multiplicity.

Measuring Phi Mesons in p + Au and He + Au Collisions at 200 GeV

Measuring Phi Mesons in p + Au and He + Au Collisions at 200 GeV

The scalar f_0(500), f_0(980), and a_0(980) resonances and vector mesons in the single Cabibbo-suppressed decays Lambda _c rightarrow p K^+K^- and ppi ^+pi ^-

In the chiral unitary approach, we have studied the single Cabibbo-suppressed decays Lambda _crightarrow pK^+K^- and Lambda _c rightarrow p pi ^+pi ^- by taking into account the s-wave meson–meson interaction as well as the contributions from the intermediate vectors phi and rho ^0. Our theoretical results for the ratios of the branching fractions of Lambda _crightarrow p {bar{K}}^{*0} and Lambda _crightarrow p omega with respect to the one of Lambda _crightarrow p phi are in agreement with the experimental data. Within the picture that the scalar resonances f_0(500), f_0(980), and a_0(980) are dynamically generated from the pseudoscalar-pseudoscalar interactions in s-wave, we have calculated the K^+K^- and pi ^+pi ^- invariant mass distributions respectively for the decays Lambda _crightarrow pK^+K^- and Lambda _crightarrow ppi ^+pi ^-. One can find a broad bump structure for the f_0(500) and a narrow peak for the f_0(980) in the pi ^+pi ^- invariant mass distribution of the decay Lambda _crightarrow ppi ^+pi ^-. For the K^+K^- invariant mass distribution, in addition to the narrow peak for the phi meson, there is an enhancement structure near the K^+K^- threshold mainly due to the contribution from the f_0(980). Both the pi ^+pi ^- and K^+K^- invariant mass distributions are compatible with the BESIII measurement. We encourage our experimental colleagues to measure these two decays, which would be helpful to understand the nature of the f_0(500), f_0(980), and a_0(980).

Measurement of phi meson production in p + p interactions at 40, 80 and 158 , hbox {GeV}/c with the NA61/SHINE spectrometer at the CERN SPS

Results on phi meson production in inelastic p + p collisions at CERN SPS energies are presented. They are derived from data collected by the NA61/SHINE fixed target experiment, by means of invariant mass spectra fits in the phi rightarrow K^+ K^- decay channel. They include the first ever measured double differential spectra of phi mesons as a function of rapidity y and transverse momentum p_{text {T}} for proton beam momenta of 80 , hbox {GeV}/c and 158 , hbox {GeV}/c, as well as single differential spectra of y or p_{text {T}} for beam momentum of 40 , hbox {GeV}/c. The corresponding total phi yields per inelastic p + p event are obtained. These results are compared with existing data on phi meson production in p + p collisions. The comparison shows consistency but superior accuracy of the present measurements. The emission of phi mesons in p + p reactions is confronted with that occurring in mathrm{Pb} + mathrm{Pb} collisions, and the experimental results are compared with model predictions. It appears that none of the considered models can properly describe all the experimental observations.

Nuclear dependence of light neutral meson production in p\u2013A collisions at 400\xa0GeV with NA60

The NA60 experiment has studied low-mass muon pair production in proton–nucleus collisions with a system of Be, Cu, In, W, Pb and U targets, using a 400 GeV proton beam at the CERN SPS. The transverse momentum spectra of the rho /omega and phi mesons are measured in the full p_{mathrm {T}} range accessible, from p_{mathrm {T}}= 0 up to 2 , {hbox {GeV/c}}. The nuclear dependence of the production cross sections of the eta , omega and phi mesons has been found to be consistent with the power law sigma _{mathrm {pA}} propto {mathrm {A}}^alpha , with the alpha parameter increasing as a function of p_{mathrm {T}} for all the particles, and an approximate hierarchy alpha _eta approx alpha _phi > alpha _omega . The cross section ratios sigma _eta /sigma _omega , sigma _rho /sigma _omega and sigma _phi /sigma _omega have been studied as a function of the size A of the production target, and an increase of the eta and phi yields relative to the omega is observed from p–Be to p–U collisions.

Near threshold kaon-kaon interaction in the reactions ${e^ + }{e^ - } \to {K^ + }{K^ - }\gamma$ and ${e^ + }{e^ - } \to {K^0}{\bar K^0}\gamma$

Strong interactions between pairs of the K+ K- and K0 K0bar mesons can be studied in radiative decays of phi(1020) mesons. We present a theoretical model of the reactions e+ e- --> phi --> K+ K- gamma and e+ e- --> phi --> K0 K0bar gamma. The K+ K- and K0 K0bar effective mass dependence of the differential cross sections is derived. The total cross sections and the branching fractions for the two radiative phi decays are calculated.

Phi meson measurements in Cu+Au collisions at 200 GeV and in U+U collisions at 192 GeV

A major objective in the field of high-energy nuclear physics is to quantify and characterize the quark-gluon plasma (QGP) formed in relativistic heavy-ion collisions, representing an ideal liquid with partonic degrees of freedom [1-4]. Due to the very short lifetime the ϕ-meson can decay in QGP, thereby providing a key information on the hot and dense medium properties created in the relativistic heavy ion collisions. In central Cu+Au collision, the smaller nucleus is fully enveloped in the larger one thus reducing the contribution of nucleon-nucleon collisions in the low-density nuclear corona region. The U+U collision system provides the largest energy density available at RHIC. Also, the uranium nucleus is highly asymmetric, which leads to different parametrizations of the U+U collision geometry. In this report we will present latest results on the ϕ-meson production in Cu+Au at and U+U collisions at using the PHENIX detector at the RHIC [5]. This report presents invariant transverse momentum spectra and nuclear modification factors of ϕ-meson.

Phi meson production at forward rapidity in Pb\u2013Pb collisions at sqrt{s_mathrm {NN}}=2.76\xa0TeV

phi meson measurements provide insight into strangeness production, which is one of the key observables for the hot medium formed in high-energy heavy-ion collisions. ALICE measured phi production through its decay in muon pairs in Pb–Pb collisions at sqrt{s_mathrm {NN}} = 2.76 TeV in the intermediate transverse momentum range 2< p_mathrm {T}< 5 GeV/c and in the rapidity interval 2.5<y<4. The phi yield was measured as a function of the transverse momentum and collision centrality. The nuclear modification factor was obtained as a function of the average number of participating nucleons. Results were compared with the ones obtained via the kaon decay channel in the same p_mathrm {T} range at midrapidity. The values of the nuclear modification factor in the two rapidity regions are in agreement within uncertainties.

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.

Nuclear suppression of the phi meson yields with large p_T at the RHIC and the LHC

We calculate phi meson transverse momentum spectra in mathrm{p}+mathrm{p} collisions as well as their nuclear suppressions in central mathrm{A}+mathrm{A} collisions both at the RHIC and the LHC in LO and NLO with the QCD-improved parton model. We have included the parton energy loss effect in a hot/dense QCD medium with the effectively medium-modified phi fragmentation functions in the higher-twist approach of jet quenching. The nuclear modification factors of the phi meson in central mathrm{Au}+mathrm{Au} collisions at the RHIC and central mathrm{Pb}+mathrm{Pb} collisions at the LHC are provided, and nice agreement of our numerical results at NLO with the ALICE measurement is observed. Predictions of the yield ratios of neutral mesons such as phi /pi ^0, phi /eta and phi /rho ^0 at large p_T in relativistic heavy-ion collisions are also presented for the first time.

Tests of Discrete Symmetries and Quantum Coherence with Neutral Kaons at the KLOE-2 Experiment

The KLOE-2 detector records decays of quantum-entangled pairs of neutral kaons produced in decays of phi mesons provided by the DAFNE accelerator at the Laboratori Nazionali di Frascati, Italy. This system allows for a broad range of studies of fundamental discrete symmetries including tests which are only feasible with entangled neutral mesons. This work reports on the Lorentz non-invariance and CPT violation searches with the KSKL->pi+pi-pi+pi- process in the framework of the Standard Model Extension. Moreover, status and results of quantum coherence tests with the same process are discussed. Finally, the status of ongoing direct tests of T and CPT in neutral kaon transitions is presented. For each of thereported studies, perspectives are discussed for the KLOE-2 experiment, which is presently taking data.

Excitation functions of parameters in Erlang distribution, Schwinger mechanism, and Tsallis statistics in RHIC BES program

Experimental results of the transverse momentum distributions of phi mesons and $\Omega$ hyperons produced in gold-gold (Au-Au) collisions with different centrality intervals, measured by the STAR Collaboration at different energies (7.7, 11.5, 19.6, 27, and 39 GeV) in the beam energy scan (BES) program at the relativistic heavy ion collider (RHIC), are approximately described by the single Erlang distribution and the two-component Schwinger mechanism. Meanwhile, the STAR experimental transverse momentum distributions of negatively charged particles, produced in Au-Au collisions at RHIC BES energies, are approximately described by the two-component Erlang distribution and the single Tsallis statistics. The excitation functions of free parameters are obtained from the fit to the experimental data. A weak softest point in the string tension in $\Omega$ hyperon spectra is observed at 7.7 GeV.

Phi meson spectral moments and QCD condensates in nuclear matter

A detailed analysis of the lowest two moments of the ϕ meson spectral function in vacuum and nuclear matter is performed. The consistency is examined between the constraints derived from finite energy QCD sum rules and the spectra computed within an improved vector dominance model, incorporating the coupling of kaonic degrees of freedom with the bare ϕ meson. In the vacuum, recent accurate measurements of the e+e−→K+K− cross section allow us to determine the spectral function with high precision. In nuclear matter, the modification of the spectral function can be described by the interactions of the kaons from ϕ→KK‾ with the surrounding nuclear medium. This leads primarily to a strong broadening and an asymmetric deformation of the ϕ meson peak structure. We confirm that, both in vacuum and nuclear matter, the zeroth and first moments of the corresponding spectral functions satisfy the requirements of the finite energy sum rules to a remarkable degree of accuracy. Limits on the strangeness sigma term of the nucleon are examined in this context. Applying our results to the second moment of the spectrum, we furthermore discuss constraints on four-quark condensates and the validity of the commonly used ground state saturation approximation.

Role of pentaquark components inϕmeson production proton-antiproton annihilation reactions

The pentaquark component is included in the proton wave functions to study phi meson production proton-antiproton annihilation reactions. With all possible configurations of the uuds subsystem proposed for describing the strangeness spin and magnetic moment of the proton, we estimate the branching ratios of the annihilation reactions at rest proton-antiproton to phi + X (X=pi, eta, rho, omega) from atomic proton-antiproton S- and P-wave states by using effective quark line diagrams incorporating the 3P0 model. The best agreement of theoretical prediction with the experimental data is found when the pentaquark configuration of the proton wave function takes the flavor-spin symmetry, [4]_FS [22]_F [22]_S.

Theoretical studies of the reactione+e−→K+K−γ

We present studies of the e+ e- --> K+ K- gamma reaction for the e+e- center-of-mass energies close to the phi(1020) meson mass. Different mechanisms leading to the final state are considered. The strong interaction amplitudes of the K+K- pairs in the S-wave are taken into account. In addition, the photon emission in the initial state, the final state radiation effects and all the possible interference terms are included in the transition matrix elements. The K+K- effective mass distributions and the angular dependence of the reaction cross-section are calculated.