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arXiv 0907.5049hep-exnucl-ex
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PHENIX中低质量矢量介子在RHIC的介质内修正

In-Medium Modifications of Low-Mass Vector Mesons in PHENIX at RHIC

Yuji Tsuchimoto

备注：
4 pages, 4 figures
发表信息：
Nucl.Phys.A830:487c-490c,2009
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摘要：

在RHIC的测量已经建立了夸克胶子等离子体（QGP）在大多数中央重离子碰撞的创建。理解QGP性质的一个重要工具是研究低质量矢量介子（LVM）、$ρ$、$ω$和$ϕ$的谱形，它们可以在介质中通过部分恢复手征对称性而被修改。这种修改可以直接通过测量低动量的LVM的通过他们的衰变到轻子对内的热物质。由于轻子不受强相互作用的影响，它们在离开介质时不会再散射。RHIC的PHENIX实验测量了$\sqrt{s_{\rm NN}}$ = 200 GeV的$p$ + $p$、$d$ +Au和Au+Au碰撞中快度时的LVM产生。在分辨率为10 MeV/ $c^2$的双电子不变质谱中，在所有三个碰撞系统中观察到了质量峰。本文综述了$p$ + $p$、$d$ +Au和Au+Au中的$ω$和$ϕ$在轻子和强子衰变道中的提取光谱、质量和宽度。由于介子的宽度在介质中会受到影响，各种衰变模式的分支比也可以从真空中的值进行修改。比较了$ϕ\to e^+e^-$和$ϕ\to K^+K^-$之间的相对支化比，由于$ϕ\to K^+K^-$的Q值小，这可能对质量修饰敏感。

英文摘要：

Measurements at RHIC have established the creation of a Quark Gluon Plasma (QGP) in most central heavy-ion collisions. An important tool to understand properties of the QGP is study of the spectral shapes of low-mass vector mesons (LVM's), $ρ$, $ω$ and $ϕ$, which can be modified in the medium by partial restoration of chiral symmetry. This modification may be accessed directly by measuring low-momentum LVM's via their decays into lepton pairs inside the hot matter. Since leptons are not subject to the strong interaction, they do not rescatter on their way out of the medium. The PHENIX experiment at RHIC has measured LVM production at mid-rapidity in $p$ + $p$, $d$+Au and Au+Au collisions at $\sqrt{s_{\rm NN}}$ = 200 GeV\@. Mass peaks for the LVM's have been observed in the di-electron invariant mass spectra with a resolution of 10 MeV/$c^2$ in all of the three collision systems. The extracted spectra, mass and width of $ω$ and $ϕ$ in $p$ + $p$, $d$+Au and Au+Au, in the leptonic and hadronic decay channels are reviewed. As the widths of the mesons may be affected in the medium, the branching ratios of various decay modes may also be modified from the values in vacuum. The relative branching ratio is compared between $ϕ\to e^+e^-$ and $ϕ\to K^+K^-$, which may be sensitive to the mass modification due to the small Q-value of $ϕ\to K^+K^-$.

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