论文标题
分别的$π^{+}π^{ - } $的测量
Measurement of Exclusive $π^{+}π^{-}$ and $ρ^0$ Meson Photoproduction at HERA
论文作者
论文摘要
使用$ EP $ Collider Hera的H1检测器研究了$ρ^0（770）$ MESON的独家光生效。大约900000事件的样本用于测量反应$γp\toπ^{+}π^{ - } y $的单分和双分截面的样本。质子保持完整的反应（$ {m_y {=} m_p} $）与质子分离到低质量hAdronic系统（$ m_p {<} m_y {<} <} 10 $ gev）的反应在统计上与质子分离的反应。双分化横截面的测量是衰减亲的不变质量$ m_ {ππ} $的函数，而Proton顶点的平方$ 4 $ -Momentum Transfer $ t $。测量值以光子 - 普罗顿碰撞能量$ W_ {γp} $的各种垃圾箱表示。相位空间限制为$ 0.5 <m_ {ππ} <2.2 $ gev，$ {\ vert t \ vert <1.5} $ gev $ {}^2 $，和$ {20 <w_w_ {γp} <80} <80} $ gev。提出了针对弹性和质子分离散射的横截面测量。观察到的横截面依赖性通过分析函数描述。参数化$ m_ {ππ} $依赖性，并在振幅水平上添加谐振和非共振贡献导致$ρ^{0}（770）$梅森质量和宽度$ p.m_ρ= 770.8 \ {+2.6}^{+2.6}^{+2.6} _} 151.3 \ {}^{+2.7} _ { - 3.6} $（tot）Mev。该模型用于提取$ρ^0（770）$对$π^{+}π^{ - } $交叉部分的贡献，并将其作为$ t $和$ w_ {γp} $的函数进行测量。在一个重新渐近极限中，一个重新轨迹$α（t）$主导，拦截$α（t {=} 0）= 1.0654 \ {}^{+0.0098} _ { - 0.0067} $ { - 0.0067} $ } _ { - 0.074} $（tot）Gev $ {}^{ - 2} $的$ T $依赖项的$ M_Y {=} m_p $。
Exclusive photoproduction of $ρ^0(770)$ mesons is studied using the H1 detector at the $ep$ collider HERA. A sample of about 900000 events is used to measure single- and double-differential cross sections for the reaction $γp \to π^{+}π^{-}Y$. Reactions where the proton stays intact (${m_Y{=}m_p}$) are statistically separated from those where the proton dissociates to a low-mass hadronic system ($m_p{<}m_Y{<}10$ GeV). The double-differential cross sections are measured as a function of the invariant mass $m_{ππ}$ of the decay pions and the squared $4$-momentum transfer $t$ at the proton vertex. The measurements are presented in various bins of the photon-proton collision energy $W_{γp}$. The phase space restrictions are $0.5 < m_{ππ} < 2.2$ GeV, ${\vert t\vert < 1.5}$ GeV${}^2$, and ${20 < W_{γp} < 80}$ GeV. Cross section measurements are presented for both elastic and proton-dissociative scattering. The observed cross section dependencies are described by analytic functions. Parametrising the $m_{ππ}$ dependence with resonant and non-resonant contributions added at the amplitude level leads to a measurement of the $ρ^{0}(770)$ meson mass and width at $m_ρ= 770.8\ {}^{+2.6}_{-2.7}$ (tot) MeV and $Γ_ρ= 151.3\ {}^{+2.7}_{-3.6}$ (tot) MeV, respectively. The model is used to extract the $ρ^0(770)$ contribution to the $π^{+}π^{-}$ cross sections and measure it as a function of $t$ and $W_{γp}$. In a Regge asymptotic limit in which one Regge trajectory $α(t)$ dominates, the intercept $α(t{=}0) = 1.0654\ {}^{+0.0098}_{-0.0067}$ (tot) and the slope $α^\prime(t{=}0) = 0.233\ {}^{+0.067 }_{-0.074 }$ (tot) GeV${}^{-2}$ of the $t$ dependence are extracted for the case $m_Y{=}m_p$.
