Phi Meson Research Articles

Determination of phi meson nuclear modification factors in the proton–lead nucleus interactions in the ALICE experiment at the LHC

Hadronic resonances are among the most interesting probes of the hot and dense matter created in Pb + Pb collisions. Due to their short lifetime, they are sensitive to the anticipated chiral symmetry restoration as well as to suppression and regeneration due to hadronic interactions in the final state. At intermediate and high transverse momenta (pT) resonances which cover the range of masses between the light pions and heavier protons contribute in systematic study of the baryon puzzle and parton energy loss in the dense medium. Studies in p + Pb collisions are important for the interpretation of heavy ion results as they allow to decouple and understand the cold nuclear matter effects from final state effects.The systematic study of the phi (1020) meson production at mid-rapidity in p + Pb collisions at LHC energies has been performed. In this article the most recent results of these studies including pT spectra and nuclear modification factor distributions in p + Pb collisions at an energy of 5.02 TeV are presented.

Highlights of Resonance Measurements With HADES

This contribution aims to give a basic overview of the latest results regarding the production of resonances in different collision systems. The results were extracted from experimental data collected with HADES that is a multipurpose detector located at the GSI Helmholtzzentrum, Darmstadt. The main points discussed here are: the properties of the strange resonances Lambda(1405) and Sigma(1385), the role of Delta's as a source of pions in the final state, the production dynamics reflected in form of differential cross sections, and the role of the phi meson as a source for K^- particles.

Commissioning of the New Taggers of the KLOE-2 Experiment

In order to fully reconstruct the gamma gamma processes (e+e- -> e+e- gamma gamma) in the energy region of the phi meson production, new detectors along the DAFNE beam line have been installed in order to detect the scattered e+e-.

Search for CP violation in D ± → K S 0 K ± and D s ± → K S 0 π ± decays

A search for C P violation in D+ -> phi pi(+) decays is performed using data collected in 2011 by the LHCb experiment corresponding to an integrated luminosity of 1.0 fb(-1) at a centre of mass energy of 7 TeV. The CP-violating asymmetry is measured to be (-0.04 +/- 0.14 +/- 0.14)% for candidates with K-K+ mass within 20 MeV/c(2) of the phi meson mass. A search for a CP-violating asymmetry that varies across the phi mass region of the D+ -> K-K+pi(+) Dalitz plot is also performed, and no evidence for CP violation is found. In addition, the CP asymmetry in the D-s(+) -> K-S(0)pi(+) decay is measured to be (0.61 +/- 0.83 +/- 0.14)%.

QCD sum rules on the complex Borel plane

Borel transformed QCD sum rules conventionally use a real valued parameter (the Borel mass) for specifying the exponential weight over which hadronic spectral functions are averaged. In this paper, it is shown that the Borel mass can be generalized to have complex values and that new classes of sum rules can be derived from the resulting averages over the spectral functions. The real and imaginary parts of these novel sum rules turn out to have damped oscillating kernels and potentially contain a larger amount of information on the hadronic spectrum than the real valued QCD sum rules. As a first practical test, we have formulated the complex Borel sum rules for the phi meson channel and have analyzed them using the maximum entropy method, by which we can extract the most probable spectral function from the sum rules without strong assumptions on its functional form. As a result, it is demonstrated that, compared to earlier studies, the complex valued sum rules allow us to extract the spectral function with a significantly improved resolution and thus to study more detailed structures of the hadronic spectrum than previously possible.

The differential production cross section of the [Formula: see text](1020) meson in [Formula: see text] = 7TeV [Formula: see text] collisions measured with the ATLAS detector.

A measurement is presented of the phi times mathcal {BR}(phi rightarrow K^{+}K^{-}) production cross section at sqrt{s} = 7 TeV using pp collision data corresponding to an integrated luminosity of 383 mathrm {upmu b^{-1}}, collected with the ATLAS experiment at the LHC. Selection of phi (1020) mesons is based on the identification of charged kaons by their energy loss in the pixel detector. The differential cross section is measured as a function of the transverse momentum, p_{mathrm {T,phi }}, and rapidity, y_{phi }, of the phi (1020) meson in the fiducial region 500 <p_{mathrm {T,phi }}< 1200 MeV, |y_{phi }|< 0.8, kaon p_{mathrm {T},K}> 230 MeV and kaon momentum p_{K}< 800 MeV. The integrated phi (1020)-meson production cross section in this fiducial range is measured to be sigma _{phi } times mathcal {BR}(phi rightarrow K^{+}K^{-}) = 570 pm 8 (stat) pm 66 (syst) pm 20 (lumi) mathrm {upmu b}.

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.

Exclusive vector meson production at HERMES

Exclusive electroproduction of vector mesons has been measured on hydrogen and deuterium targets at HERMES using the 27.6 GeV electron/positron beam of HERA. From this process, more information can be obtained about generalized parton distributions (GPDs), which provide a unified description of the structure of hadrons embedding longitudinal-momentum distributions (ordinary PDFs) and transverse-position information (form factors). The study of the azimuthal distribution of the decay products via spin-density matrix elements provide constraints on helicity-amplitudes used to describe exclusive vector-meson production. Recent results from the HERMES experiment on the production of rho, omega and phi mesons will be presented.

PHOTOPRODUCTION OF PHI MESON NEAR THE THRESHOLD

Photoproduction of ϕ, γp → ϕ + p, is revisited in a model with Pomeron and hadron degrees of freedom. The scattering equation is written such that the final state interaction is included at the one-loop level of hadrons. We find a parameter set to reproduce the bump-like structure near the threshold in a way consistent with other meson production data.

Production ofKS0,K*±(892)andϕ0(1020)in minimum bias events andKS0andΛ0in jets inpp¯collisions ats=1.96 TeV

We report measurements of the inclusive transverse momentum pT distribution of centrally produced kshort, kstar(892), and phi(1020) mesons up to pT = 10 GeV/c in minimum-bias events, and kshort and lambda particles up to pT = 20 GeV/c in jets with transverse energy between 25 GeV and 160 GeV in pbar p collisions. The data were taken with the CDF II detector at the Fermilab Tevatron at sqrt(s) = 1.96 TeV. We find that as pT increases, the pT slopes of the three mesons (kshort, kstar, and phi) are similar, and the ratio of lambda to kshort as a function of pT in minimum-bias events becomes similar to the fairly constant ratio in jets at pT ~ 5 GeV/c. This suggests that the particles with pT >~ 5 GeV/c in minimum-bias events are from soft jets, and that the pT slope of particles in jets is insensitive to light quark flavor (u, d, or s) and to the number of valence quarks. We also find that for pT <~ 4 GeV relatively more lambda baryons are produced in minimum-bias events than in jets.

Measurability of , , and mesons via di-electron decays in high-temperature states produced in heavy-ion collisions

We discuss measurability of phi, omega and rho mesons via di-electron decays in high-temperature states produced in heavy-ion collisions, equivalently at different pion multiplicities per heavy-ion collision dN_{pi^{0} + pi^{+-}}/dy = 1000 and 2700 intended for the most central Au+Au collisions at sqrt(s_{NN}) = 200 GeV (RHIC) and the most central Pb+Pb collisions at sqrt(s_{NN}) = 5.5 TeV (LHC), by evaluating the signal-to-background ratios and the statistical significance for the idealized detection system in the numerical simulation. The simulation study provides a guideline to be applicable to a concrete detector design by focusing on only the key experimental issues relevant to the measurement of di-electrons. The results suggest that there are realizable parameter ranges to measure light vector mesons via di-electrons with the reasonable significance level, even in the highest multiplicity case.

Polarization inχcJ→ϕϕdecays

To understand the enhanced partial decay width for the decay of chi(c1) to the vector-meson pair phi phi recently observed by the BESIII collaboration, we suggest measuring the polarization parameter of the phi meson by analyzing the jointed angular distribution in the cascade decay e(+)e(-) -> psi(2S) -> gamma chi(cJ) -> gamma phi phi -> gamma 2(K+K-). The formulas to measure polarization parameters are presented, and they are estimated in the framework of perturbative QCD (pQCD) and the quark-pair-creation model. In pQCD we obtain results consistent with the expectation of the helicity selection rule. In the quark-pair-creation model, the parameter associated with the violation of the helicity selection rule is enhanced relative to that estimated in pQCD.

Formation ofη′(958)-mesic nuclei by the (p,d) reaction

We calculate theoretically the formation spectra of eta'(958)-nucleus systems in the (p,d) reaction for the investigation of the in-medium modification of the eta' mass. We show the comprehensive numerical calculations based on a simple form of the eta' optical potential in nuclei with various potential depths. We conclude that one finds an evidence of possible attractive interaction between eta' and nucleus as peak structure appearing around the eta' threshold in light nuclei such as 11C when the attractive potential is stronger than 100 MeV and the absorption width is of order of 40 MeV or less. Spectroscopy of the (p,d) reaction is expected to be performed experimentally at existing facilities, such as GSI. We also estimate the contributions from the omega and phi mesons, which have masses close to the eta' meson, concluding that the observation of the peak structure of the eta'-mesic nuclei is not disturbed although their contributions may not be small.

Momentum dependence of theφ-meson nuclear transparency

The production of phi mesons in proton collisions with C, Cu, Ag, and Au targets has been studied via the phi -> K+K- decay at an incident beam energy of 2.83 GeV using the ANKE detector system at COSY. For the first time, the momentum dependence of the nuclear transparency ratio, the in-medium phi width, and the differential cross section for phi meson production at forward angles have been determined for these targets over the momentum range of 0.6 - 1.6 GeV/c. There are indications of a significant momentum dependence in the value of the extracted phi width, which corresponds to an effective phi-N absorption cross section in the range of 14 - 21 mb.

Measurement of the semileptonic branching fraction of theBsmeson

We report a measurement of the inclusive semileptonic branching fraction of the B_s meson using data collected with the BaBar detector in the center-of-mass (CM) energy region above the Upsilon(4S) resonance. We use the inclusive yield of phi mesons and the phi yield in association with a high-momentum lepton to perform a simultaneous measurement of the semileptonic branching fraction and the production rate of B_s mesons relative to all B mesons as a function of CM energy. The inclusive semileptonic branching fraction of the B_s meson is determined to be B(B_s to l nu X)=9.5 (+2.5/-2.0)(stat)(+1.1/-1.9)(syst)%, where l indicates the average of e and mu.

Resonances from AMPT

A multiphase transport (AMPT) model that includes both initial partonic and final hadron rescattering effects in relativistic heavy ion collisions is briefly reviewed. Particular attention is given to the scattering processes in the hadronic phase in order to address resonances production in these collisions. As an example, phi meson production is discussed in detail through both its dikaon and dilepton decay channels. Results from the AMPT model for heavy ion collisions at both SPS and RHIC are compared to the experimental data to extract information on the production mechanism and in-medium properties of the phi meson.

Measurements of Particle Production in pp Collisions in the Forward Region at the LHC

The phase space coverage of the LHCb detector allows a unique insight into the particle production in the forward region at the LHC. Due to its unique pseudorapidity range and to the possibility of extending the measurements to low transverse momenta, the LHCb data provide important input to the understanding of particle production in a kinematical range where QCD models have large uncertainties. Measurements of the production of charged particles and of the strange phi mesons are presented. In addition the ratio of (Lambda) over bar/Lambda is studied as a function of rapidity and transverse momentum for centre-of-mass energies root s = 0.9 TeV and root s = 7.0 TeV, probing baryon number transport from the beam. Baryon strangeness suppression is evaluated through the measurement of (Lambda) over bar /K-S(0). The LHCb results are compared with lower energy measurements, phenomenological models and Monte Carlo event generators.

Dielectron production in Ar + KCl collisions at 1.76AGeV

We present results on dielectron production in Ar+KCl collisions at 1.76A GeV. For the first time $\omega$ mesons could be reconstructed in a heavy-ion reaction at a bombarding energy which is well below the production threshold in free nucleon-nucleon collisions. The omega multiplicity has been extracted and compared to the yields of other particles, in particular of the phi meson. At intermediate e+e- invariant masses, we find a strong enhancement of the pair yield over a reference spectrum from elementary nucleon-nucleon reactions suggesting the onset of non-trivial effects of the nuclear medium. Transverse-mass spectra and angular distributions have been reconstructed in three invariant mass bins. In the former unexpectedly large slopes are found for high-mass pairs. The latter, in particular the helicity-angle distributions, are largely consistent with expectations for a pair cocktail dominated at intermediate masses by delta Dalitz decays.

Properties of the ϕ meson at high temperatures and densities

We calculate the spectral density of the phi meson in a hot bath of nucleons and pions using a general formalism relating self-energy to the forward scattering amplitude (FSA). In order to describe the low energy FSA, we use experimental data along with a background term. For the high energy FSA, a Regge parameterization is employed. We verify the resulting FSA using dispersion techniques. We find that the position of the peak of the spectral density is slightly shifted from its vacuum position and that its width is considerably increased. The width of the spectral density at a temperature of 150 MeV and at normal nuclear density is more than 90 MeV.

Measurement of neutral mesons inp+pcollisions ats=200 GeVand scaling properties of hadron production

The PHENIX experiment at the Relativistic Heavy Ion Collider has measured the invariant differential cross section for production of K^0_S , \omega, \eta prime, and \phi mesons in p + p collisions at = 200 GeV. Measurements \omega and \phi production in different decay channels give consistent results. New results for the \phi are in agreement with previously published data and extend the measured pT coverage. The spectral shapes of all hadron transverse momentum distributions measured by PHENIX are well described by a Tsallis distribution functional form with only two parameters, n and T, determining the high-pT and characterizing the low-pT regions of the spectra, respectively. The values of these parameters are very similar for all analyzed meson spectra, but with a lower parameter T extracted for protons. The integrated invariant cross sections calculated from the fitted distributions are found to be consistent with existing measurements and with statistical model predictions.