Kinematics

$\gamma+A$ kinematics for ultra peripheral collisions for SPS fixed-target experiments:

For an A+A collision, $K_\mathrm{beam} =$ 158 GeV and $m_1=m_2=$ 0.931 GeV:

g+A coherent collision with R(A=Indium) ~ 1.2*A^(1/3) ~ 5.8 fm (= 5.8 fm/[0.197 GeV fm] = 29.4 GeV$^{-1}$) as seen from the nucleus at rest: omega_max = gamma_beam/R = 170./29.4 = 5.78 GeV sqrt(s)_{g+A}_max = sqrt(m2.+2.*omega_max*m) = sqrt(0.9312+2*5.78*0.931) = 3.4 GeV

so an Indium beam (with R = 5.8 fm) with K_beam = 158 GeV seems to be very close to the kinematical limit to produce a J/Psi ... (e.g., for comparison, a SPS Pb-beam (R~7. fm) will produce an even softer gamma spectrum with omega_max~4.78 GeV and, correspondingly, sqrt(s)_{gA} = 3.12 GeV).

Related work

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