The Gamma Factory path to high-luminosity LHC with isoscalar beams
There are two main ways to increase LHC luminosity without upgrading CERN injectors: (1) modification of beam-collision optics and (2) reduction of beam transverse emittance. The former is followed in the ongoing high-luminosity upgrade of the LHC (HL-LHC), while the latter, applicable only to ion beams, is described in this contribution. The reduction of the beam emittance can be achieved by employing a laser-cooling technique to bunches of partially stripped ions at the SPS flat-top energy. In the case the isoscalar calcium beams fulfilling the presentbeam-operation constrains, the transverse beam emittance can be reduced in this way by a factor of 5 during the 8 second long cooling phase. This would allow to reach the nucleon–nucleon luminosity L_NN = 4.2 x 10^34 s^(-1)cm^(-2), which is comparable to the levelled luminosity for the HL-LHC proton–proton collisions, but with reduced pile-up background. The calcium–calcium collisions have several advantages over the proton–proton collisions for the electroweak physics, such as precision measurements of the W-boson mass and sin^2_W, clean observation of the Higgs boson decay into bbar in its photoproduction channel. If this scheme is confirmed by the future Gamma Factory proof-of-principle experiment, it could be implemented at CERN with minor infrastructure investments.
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