Speaker
Ruchi Chudasama
(Bhabha Atomic Research Center, Mumba)
Description
Relativistic heavy ions are a copious source of virtual photons, which allow to study the gamma$-$proton and gamma$-$gamma interactions in ultraperipheral collisions (UPC). The exclusive photoproduction of heavy vector mesons provide a clean probe of the gluon distribution at very small values of parton fractional momenta (Bjorken x) x$ \approx$$10^{-2}$ $10^{-4}$ at central rapidities ($|y| < 2.5$) and search for saturation phenomena. We present the first measurement of exclusive photoproduction of $\Upsilon$ (1S,2S,3S) states in their dimuon decay channel in ultraperipheral collisions of protons and heavy ions (pPb) with the CMS experiment at $\sqrt{s_{NN}}=5.02$ TeV for an integrated luminosity $L_{int} = 33 $ nb$^{-1}$. The photoproduction cross$-$section of $\Upsilon$ (1S) is measured as a function of photon$-$proton center$-$of$-$mass energy $W_{\gamma p}$. The differential cross$-$section $d\sigma/dt$, where $t$ is the squared four$-$momentum transfer at the photon$-$proton vertex, is measured in the range $|t| < 1.0$ (GeV/c)$^2$ . The results are compared with other measurements and theoretical predictions.
Author
Ruchi Chudasama
(Bhabha Atomic Research Center, Mumba)
