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تسجيل مستخدم جديدLeptonic decay of $phi$(1020) meson measured with the STAR experiment
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Masayuki Wada
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We present the measurement of the $phi$(1020)$rightarrow e^{+}e^{-}$ transverse momentum spectrum and yield for $0.3 < p_{T} < 2.5$ GeV at mid-rapidity ($|y| < 1$) from the STAR experiment in Au+Au collisions at $sqrt{s_{_{NN}}} = 200$ GeV and compare it to the yield and spectrum from the hadronic decays. We also compare the $phi$(1020) mass and width obtained by fitting Breit-Wigner function to simulated values. Particle identification based on the newly installed STAR Time-Of-Flight (TOF) detector in conjunction with energy-loss (dE/dx) based particle identification measurements from the Time Projection Chamber (TPC) are used for a clean electron and positron identification.
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We report the measurement of the leptonic ($e^{+}e^{-}$) decay channel of the $phi$(1020) meson in Au+Au collisions at $sqrt{s_{_{NN}}}$ = 200 GeV by the STAR experiment. The transverse momentum ($p_{rm T}$) spectrum is measured for 0.1 $le p_{rm T}
le 2.5$ GeV/$c$ at mid-rapidity ($|y|le1$). We obtain the $p_{rm T}$-integrated $phi$(1020) mass $M_{phi}=1017.7pm0.8 (rm {stat.}) pm0.9 (rm {sys.})$ MeV/$c^{2}$ and width $Gamma_{phi} = 8.0pm 2.5(rm {stat.}) pm 2.3(rm {sys.}) textrm{MeV/}c^{2}$, which are within 1.5,$sigma$ and 1.1,$sigma$ of the vacuum values, respectively. No significant difference is observed in the measured $p_{rm T}$ spectrum, $dN/dy$, or $left<p_{rm T}right>$ of the $phi$(1020) meson between the $e^{+}e^{-}$ and hadronic ($K^{+}K^{-}$) decay channels as measured by the same experiment. The experimental results are compared to a theoretical model including medium-modified $phi$(1020).
We report a measurement of $phi$ meson production in central Pb+Au collisions at E$_{lab}$/A=158 GeV. For the first time in heavy-ion collisions, $phi$ mesons were reconstructed in the same experiment both in the K$^+$K$^-$ and the dilepton decay cha
nnel. Near mid-rapidity, this yields rapidity densities, corrected for production at the same rapidity value, of 2.05 +- 0.14(stat) +- 0.25(syst) and 2.04 +- 0.49(stat)+-{0.32}(syst), respectively. The shape of the measured transverse momentum spectra is also in close agreement in both decay channels. The data rule out a possible enhancement of the $phi$ yield in the leptonic over the hadronic channel by a factor larger than 1.6 at 95% CL.
The $phi$(1020) meson leptonic width has been determined from the combined analysis of 4 major decay modes of the resonance ($phito K^+ K^-,K^0_LK^0_S,pi^+pi^-pi^0,etagamma$) studied with the CMD-2 detector at the VEPP-2M $e^+e^-$ collider. The follo
wing value has been obtained: $Gamma(phito e^+e^-) = 1.235pm 0.006pm 0.022$ keV. The $phi(1020)$ meson parameters in four main decay channels have been also recalculated: $B(phito K^+K^-) = 0.493pm 0.003pm 0.007$, $B(phito K_LK_S) = 0.336pm 0.002pm 0.006$, $B(phitopi^+pi^-pi^0) = 0.155pm 0.002pm 0.005$, $B(phitoetagamma) = 0.0138pm 0.0002pm 0.0002$.
The process e+e-->mu+mu- has been studied by SND detector at VEPP-2M e+e- collider in the phi(1020)-resonance energy region. The measured effective phi meson leptonic branching ratio: B(phi->l+l-)=sqrt{B(phi->e+e-)*B(phi->mu+mu-)}=(2.89+-0.10+-0.06)*
10^{-4} agrees well with the PDG value B(phi->e+e-)=(2.91+-0.07)*10^{-4} confirming mu-e universality. Without additional assumption of mu-e universality the branching ratio B(phi->mu+mu-)=(2.87+-0.20+-0.14)*10^{-4} was obtained.
In the SND experiment at VEPP-2M $e^+e^-$ collider the $phi(1020)topi^0pi^0gamma$ decay was studied and its branching ratio was measured: $B(phitopi^0pi^0gamma)=(1.221pm 0.098pm0.061)cdot10^{-4}$. It was shown, that $f_0(980)gamma$ intermediate state
dominates in this decay and the $f_0(980)$-meson parameters were obtained.
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