High Energy Photon-photon Collisions Research Articles

Hard Pomeron-odderon interference effects in the production ofπ+π−pairs in high energyγγcollisions at the LHC

We estimate the production of two meson pairs in high energy photon-photon collisions produced in ultraperipheral collisions at LHC. We show that the study of charge asymmetries may reveal the existence of the perturbative Odderon and discuss the concrete event rates expected at the LHC. Sizable rates and asymmetries are expected in the case of proton-proton collisions and medium values of {gamma}{gamma} energies {radical}(s{sub {gamma}}{sub {gamma}}){approx_equal}20 GeV. Proton-proton collisions will benefit from a high rate due to a large effective {gamma}{gamma} luminosity and ion-ion collisions with a somewhat lower rate from the possibility to trigger on ultraperipheral collisions and a reduced background from strong interactions.

Perspectives for inclusive quarkonium production in photon-photon collisions at the LHC

We report on the current status of knowledge on inclusive quarkonium production in high-energy photon-photon collisions. As a perspective for the LHC, we compute various production cross sections via direct photon-photon fusion in ultra-peripheral pp , pA and AA collisions at the LHC using the tree-level quarkonium amplitude generator MadOnia .

HIGH ENERGY PHOTON–PHOTON COLLISIONS AT A LINEAR COLLIDER

High intensity back-scattered laser beams will allow the efficient conversion of a substantial fraction of the incident lepton energy into high energy photons, thus significantly extending the physics capabilities of an e-e± linear collider. The annihilation of two photons produces C = + final states in virtually all angular momentum states. An important physics measurement is the measurement of the Higgs coupling to two photons. The annihilation of polarized photons into the Higgs boson determines its fundamental H0γγ coupling as well as determining its parity. Other novel two-photon processes include the two-photon production of charged pairs τ+τ-, W+W-, [Formula: see text], and supersymmetric squark and slepton pairs. The one-loop box diagram leads to the production of pairs of neutral particles such as γγ → Z0Z0, γZ0, and γγ. At the next order one can study Higgstrahlung processes, such as γγ → W+W-W-H. Since each photon can be resolved into a W+W- pair, high energy photon-photon collisions can also provide a remarkably background-free laboratory for studying possibly anomalous WW collisions and annihilation. In the case of QCD, each photon can materialize as a quark anti-quark pair which interact via multiple gluon exchange. The diffractive channels in photon-photon collisions allow a novel look at the QCD pomeron and odderon. The C = - odderon exchange contribution can be identified by looking at the heavy quark asymmetry. In the case of eγ → e′ collisions, one can measure the photon structure functions and its various components. Exclusive hadron production processes in photon-photon collisions provide important tests of QCD at the amplitude level, particularly as measures of hadron distribution amplitudes which are also important for the analysis of exclusive semi-leptonic and two-body hadronic B-decays.

Physics Opportunities at a Photon–Photon Collider

The advent of back-scattered laser beams for e±e-colliders will allow detailed studies of a large array of high energy γγ and γe collision processes with polarized beams. These include tests of electroweak theory in photon-photon annihilation such as γγ → W+W-, γγ → Higgs bosons, and higher-order loop processes, such as γγ → γγ, Zγ, H0Z0and ZZ. Methods for measuring the anomalous magnetic and quadrupole moments of the W and Z gauge bosons to high precision in polarized electron-photon and photon-photon collisions are discussed. Since each photon can be resolved into a W+W-pair, high energy photon-photon collisions can also provide a remarkably background-free laboratory for studying WW collisions and annihilation. I also review high energy γγ and eγ tests of quantum chromodynamics, including the production of two gluon jets in photon-photon collisions, deeply virtual Compton scattering on a photon target, and leading-twist single-spin asymmetries for a photon polarized normal to a production plane. Exclusive hadron production processes in photon-photon collisions provide important tests of QCD at the amplitude level, particularly as measures of hadron distribution amplitudes which are also important for the analysis of exclusive semi-leptonic and two-body hadronic B-decays.

High energy photon-photon collisions

The collisions of high energy photons produced at an electron-positron collider provide a comprehensive laboratory for testing QCD, electroweak interactions, and extensions of the standard model. The luminosity and energy of the colliding photons produced by backscattering laser beams is expected to be comparable to that of the primary e +e − collisions. In this overview, we shall focus on tests of electroweak theory in photon-photon annihilation, particularly γγ → W +W −, γγ → Higgs bosons, and higher-order loop processes, such as γγ → γγ, Zγ and ZZ. Since each photon can be resolved into a W +W − pair, high energy photon-photon collisions can also provide a remarkably background-free laboratory for studying WW collisions and annihilation. We also review high energy γγ tests of quantum chromodynamics, such as the scaling of the photon structure function, t t production, mini-jet processes, and diffractive reactions.

Higgs boson pair production in high energy photon-photon collisions

We study pair production of Higgs bosons at the Photon Linear Collider in the reaction γγ → HH. At large Higgs mass the cross section grows with increasing Higgs mass almost up to threshold. The mechanism is shown to be the dominant one for the double heavy Higgs boson production at future linear colliders. We find the cross section in the range of 1–10 fb, for Higgs boson masses of 450–950 GeV in monochromatic γγ collisions at s of 1–2 TeV. For the real photon spectrum the cross section is an order of magnitude smaller. The size of the cross section is sensitive to the presence of the triple Higgs self-coupling, but for a precise measurement of this coupling a very high integrated luminosity of 1000 fb −1 is needed.

Z boson pair production in high energy photon-photon collisions and the Higgs signal

The complete standard model calculation for the reaction γγ→ ZZ has been done. The W boson loop contribution is found to be substantial. It leads to a large value of the transversely polarized Z TZ T pair production cross section of 200 fb at S γγ = 500 GeV for unpolarized initial photons. The Z TZ T pair production would represent a severe irreducible background for the observation of the longitudinal Z LZ L pair production. So, the observation of the Higgs signal for M H⩾500 GeV at the Photon Linear Collider seems to be a problem unless discrimination between transverse and longitudinal Z polarization is possible.

Reduced cross-sections for high-energy photon-photon collisions

We demonstrate that, by an appropriate choice of the polarization vectors of the virtual photons, the photon-photon collisions cross-section may be written as a sum of four positive-definite sub-cross-sections.

Diffractive production of vector mesons in high-energy photon-photon collisions

We examine here the energy dependence of the production of vector mesons in photon-photon collisions based on a model applied earlier to the calculation of diffractive photoproduction cross sections with a derived form of the vector-dominance model. We observe here that production of heavy vector mesons is considerably suppressed.