Results and Future Prospects of Exclusive Vector Meson Production with pPb Collisions at CMS

摘要

127.1 Introduction Exclusive vector meson (VM) photoproduction is defined by the reaction Y + p→VM+p, with the characteristic features that, apart from the vector meson in the final state, no other particles are produced and the vector meson has a low transverse momentum. This process can be studied at the Large Hadron Collider in ultra-peripheral collisions (UPCs) of ions and protons occurring at impact parameters much larger than the sum of their radii. Recently, CMS [1], ALICE [2] and LHCb [3] presented their measurements of exclusive heavy vector meson photoproduction at the LHC. Since the process occurs through Yp or YPb interactions via the exchange of two-gluons with no net color transfer, the cross section at leading order (LO) is proportional to the square of the gluon density in the target proton or ion. It provides a valuable probe of the gluon density at a small momentum fraction x, which is kine-matically related to W-_(Yp) (x= (M_r/W_(Yp))~2).Theexclusivephotoproductionof Y(lS, 2S, 3S) has been measured in their dimuon decay channel in ultraperipheral collisions of protons and heavy ions (pPb) with the CMS experiment [5] at {formula}=5.02TeV for an integrated luminosity of L_(int)=33 nb~(-1). The photoproduction cross section for Y(nS) is measured as a function of W-_(Yp) in the range 91 < W-_(Yp) < 826 GeV, which corresponds to the rapidity of the Y meson in the range | y | < 2.2, and x values are of the order x~ 10~(-4) to x~ 1.3 ? 10~(-2). The differential cross section da/dt, has been measured in the range |t| < 1.0 (GeV/c)~2 and the b-slope parameter is estimated.