Abstract
The production of the Higgs boson in photon-photon interactions with proton and nucleus beams at three planned or proposed future CERN colliders --- the high-luminosity Large Hadron Collider (HL-LHC), the high-energy LHC (HE-LHC), and the Future Circular Collider (FCC) --- is studied. The cross sections for the process AA$\xrightarrow{\gamma\gamma}$(A)H(A), with the ions A surviving the interaction and the Higgs scalar exclusively produced, are computed with MadGraph 5 modified to include the corresponding elastic $\gamma$ fluxes, for Pb-Pb, Xe-Xe, Kr-Kr, Ar-Ar, O-O, p-Pb, and p-p over the nucleon-nucleon collision energy range $\sqrt{s}\approx 3$--100 TeV. Simulations of the $\gamma\gamma\to H \to b\bar{b}$ decay mode --- including realistic (mis)tagging and reconstruction efficiencies for the final-state b-jets, as well as appropriate kinematical selection criteria to reduce the similarly computed $\gamma\gamma\to b\bar{b},c\bar{c},q\bar{q}$ continuum backgrounds --- have been carried out. Taking into account the expected luminosities for all systems, the yields and significances for observing the Higgs boson in ultraperipheral collisions (UPCs) are estimated. At the HL-LHC and HE-LHC, the colliding systems with larger Higgs significance are Ar-Ar(6.3 TeV) and Kr-Kr(12.5 TeV) respectively, but $3\sigma$ evidence for two-photon Higgs production would require 200 and 30 times larger integrated luminosities than those planned today at both machines. Factors of ten can be gained by running for a year, rather than the typical 1-month heavy-ion LHC operation, but the process will likely remain unobserved until a higher energy hadron collider, such as the FCC, is built. In the latter machine, the $5\sigma$ observation of Higgs production in UPCs is feasible in just the first nominal run of Pb-Pb and p-Pb collisions at $\sqrt{s} = 39$ and 63 TeV respectively.
Highlights
Heavy ions accelerated at high energies are surrounded by huge electromagnetic
fields generated by the collective action of their Z individual proton charges
such strong e.m. fields can be identified as quasireal photon beams with very low virtualities Q2
Summary
Heavy ions accelerated at high energies are surrounded by huge electromagnetic (e.m.) fields generated by the collective action of their Z individual proton charges. Proton (and lighter ions) features larger ωmax values thanks to their lower radii RA and larger beam γL factors and can thereby reach higher photon-photon center-of-mass (c.m.) energies. The beam luminosities for p-p are 7 orders of magnitude larger than those for Pb-Pb, the running conditions with multiple pileup p-p collisions per bunch crossing hinder the measurement of exclusive γγ interactions with central masses at 125 GeV (unless one installs, in the LHC case, very forward proton taggers at 420 m inside the tunnel, with 10-picosecond time resolution [7]). One can see that the maximum photon-photon c.m. energy reaches abovpe ffiffitffihffiffieffiffiffi kinematical threshold for Higgs boson production, smγγax ≳ mH 1⁄4 125 GeV, through the process depicted in Fig. 1 (left). Our new work includes higher luminosities than originally planned for the LHC, and collisions of lighter ions (Xe-Xe, Kr-Kr, Ar-Ar, O-O) never considered before
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