Γγ Production Research Articles

Observation of Wγγ triboson production in proton-proton collisions at [formula omitted] TeV with the ATLAS detector

This letter reports the observation of W(ℓν)γγ production in proton-proton collisions. This measurement uses the full Run 2 sample of events recorded at a center-of-mass energy of s=13 TeV by the ATLAS detector at the LHC, corresponding to an integrated luminosity of 140 fb−1. Events with a leptonically-decaying W boson and at least two photons are considered. The background-only hypothesis is rejected with an observed and expected significance of 5.6 standard deviations. The inclusive fiducial production cross section of W(eν)γγ and W(μν)γγ events is measured to be σfid=13.8±1.1(stat)+2.1−2.0(syst)±0.1(lumi) fb, in agreement with the Standard Model prediction.

Single- and double-scattering production of four muons in ultraperipheral PbPb collisions at the Large Hadron Collider

We discuss production of two μ+μ− pairs in ultraperipheral ultrarelativistic heavy ion collisions at the LHC. We take into account electromagnetic (two-photon) double-scattering production and for a first time direct γγ production of four muons in one scattering. We study the unexplored process γγ→μ+μ−μ+μ−. We present predictions for total and differential cross sections. Measurable nuclear cross sections are obtained and corresponding differential distributions and counting rates are presented.

ROSE: A numerical tool for the study of scattering events between photons and charged particles

We present the dimensioning of a photon–photon collider based on conventional Compton gamma sources for the observation of secondary γγ production. Two symmetric electron beams in collision with two high energy lasers produce two primary gamma rays pulses through Compton back scattering. Tuning the energy of the system to the energy of the photon–photon cross section maximum, a flux of secondary gamma photons is generated. The Monte Carlo code ‘Rate Of Scattering Events’ (ROSE) has been developed adhoc for the counting of the QED events. The benchmark of the code for the Compton scattering process is presented. Realistic numbers of the secondary gamma yield, referring to existing or approved set-ups are presented.

Study of photon–photon scattering events

We present the design of a photon–photon collider based on conventional Compton gamma sources for the observation of secondary γγ production. Two symmetric electron beams, generated by photocathodes and accelerated in linacs, produce two primary gamma rays through Compton back scattering with two high energy lasers. Tuning the system energy to the energy of the photon–photon cross section maximum, a flux of secondary gamma photons is generated. The process is analyzed by start-to-end simulations from the photocathodes to the propagation of the QED photons towards the detector. The new Monte Carlo code ‘Rate Of Scattering Events’ (ROSE) has been developed ad hoc for the counting of the QED events. Realistic numbers of the secondary gamma yield, referring to existing or approved set-ups and a discussion of the feasibility of the experiment are presented.

Advantages of exclusive γγ production to probe high mass systems

We recall that the exclusive production of high mass objects via γγ fusion at the LHC is not strongly suppressed in comparison with inclusive γγ fusion. Therefore it may be promising to study new objects, X, produced by the γγ subprocess in experiments with exclusive kinematics. We list the main advantages of exclusive experiments. We discuss the special advantage of observing exclusive events.

An analytical expression of the asymptotic QED cross-section of four lepton two pair production in γγ collisions

For the first time we have obtained an analytical QED asymptotic formula for the γγ production of two lepton pair with equal or unequal masses.

Search for exclusive or semi-exclusive γγ production and observation of exclusive and semi-exclusive e+e− production in pp collisions at $ \sqrt{s}=7 $ TeV

Abstract A search for exclusive or semi-exclusive γγ production, pp → p(*) + γγ + p(*) (where p* stands for a diffractively-dissociated proton), and the observation of exclusive and semi-exclusive e+e− production, pp → p(*) + e+e− + p(*), in proton-proton collisions at $ \sqrt{s}=7 $ TeV, are presented. The analysis is based on a data sample corresponding to an integrated luminosity of 36 pb−1 recorded by the CMS experiment at the LHC at low instantaneous luminosities. Candidate γγ or e+e− events are selected by requiring the presence of two photons or a positron and an electron, each with transverse energy E T > 5.5 GeV and pseudorapidity |η| < 2.5, and no other particles in the region |η| < 5.2. No exclusive or semi-exclusive diphoton candidates are found in the data. An upper limit on the cross section for the reaction pp → p(*) + γγ + p(*), within the above kinematic selections, is set at 1.18 pb at 95% confidence level. Seventeen exclusive or semi-exclusive dielectron candidates are observed, with an estimated background of 0.85 ± 0.28 (stat.) events, in agreement with the QED-based prediction of 16.3 ± 1.3 (syst.) events.

Observation of ExclusiveγγProduction inpp¯Collisions ats=1.96 TeV

We have observed exclusive γγ production in proton-antiproton collisions at √s=1.96 TeV, using data from 1.11±0.07 fb(-1) integrated luminosity taken by the Run II Collider Detector at Fermilab. We selected events with two electromagnetic showers, each with transverse energy E(T)>2.5 GeV and pseudorapidity |η|<1.0, with no other particles detected in -7.4<η<+7.4. The two showers have similar E(T) and azimuthal angle separation Δφ~π; 34 events have two charged particle tracks, consistent with the QED process pp¯→p+e(+)e(-)+p¯ by two-photon exchange, while 43 events have no charged tracks. The number of these events that are exclusive π(0)π(0) is consistent with zero and is <15 at 95% C.L. The cross section for pp¯→p+γγ+p¯ with |η(γ)|<1.0 and E(T)(γ)>2.5 GeV is 2.48(-0.35)(+0.40)(stat)(-0.51)(+0.40)(syst) pb.

Low-mass scalar production in γγ scattering

We estimate the I = 0 scalar meson σ / f 0 ( 600 ) γ γ widths, from ππ and γγ scattering data below 700 MeV using an improved analytic K-matrix model.

γγ Production of heavy flavour at LEP

The measurements of the experiments ALEPH, DELPHI, L3 and OPAL on heavy quark production in two-photon collisions are presented. The total and differential cross sections for inclusive charm production have been measured at LEP 2 energies. The gluon content of the photon is important to describe the data. The total cross section of inclusive bottom production is three times larger than the QCD prediction.

An experimentalist's highlights

A concise summary of recent experimental data presented at this conference illustrates the progress in our understanding of the photon interactions. The perturbative QCD domain of high Q 2 two-photon events and high p t jet production in both γγ and eγ interactions is well described by NLO calculations and parton density functions. Measurements of diffractive processes and resonance formation provide a detailed information on the difficult field of long range strong interaction forces.

Search for the glueball candidates f0(1500) and fJ(1710) in γγ collisions

Data taken with the ALEPH detector at LEP1 have been used to search for γγ production of the glueball candidates f 0(1500) and f J (1710) via their decay to π + π −. No signal is observed and upper limits to the product of γγ width and π + π − branching ratio of the f 0(1500) and the f J (1710) have been measured to be Γ(γγ→f 0(1500))· B R(f 0(1500)→π +π −)<0.31 keV and Γ(γγ→f J(1710))· B R(f J(1710)→π +π −)<0.55 keV at 95% confidence level.

Anomalous quartic couplings in [formula omitted] production via WW-fusion at LEP2

The production of ν ν ̄ γγ in high-energy e + e − collisions offers a window on anomalous quartic gauge boson couplings. We investigate the effect of two possible anomalous couplings on the cross section for ν ν ̄ γγ production via WW-fusion at LEP2 ( s =200 GeV).

Two photons plus jet at LHC: the NNLO contribution from the gg initiated process

The production of the Standard Model Higgs boson of mass ≈100–140 GeV at the LHC likely gives clear signals in the γγ (1) and in the γγ jet (2) channels. The quantitative evaluation of the background to channel (1) is very hard since the next-to-leading order (NLO) and next-to-next-to-leading order (NNLO) QCD corrections are large. In particular, the contributions of the NNLO QCD subprocess gg→ γγ to inclusive γγ production is comparable to the contribution of the leading order subprocess q q ̄ →γγ . The quantitative description of the background to channel (1), therefore, requires to calculate all corrections up to the NNNLO level. In this letter we present results on the contribution of the NNLO QCD subprocess gg→ gγγ to the production rate of channel (2). We have found that in this case this NNLO contribution is less than 20% of the Born contribution. Since the NNLO contributions will likely be dominated by this subprocess one can argue that in the case of channel (2) – contrary to the case of channel (1) – a quantitative description of the background can be achieved already at next-to-leading order accuracy.

Suppression of heavy ion γγ production of the Higgs particle by Coulomb dissociation

Predicted two-photon Higgs production with heavy ions at LHC is shown to be reduced due to the large Coulomb dissociation cross section. Incorporating the effect of dissociation reduces the production of a 100 GeV Higgs by about a factor of three compared to rates in the literature calculated without this effect.

Inclusive two-jet production in γγ and γp collisions

The theory of jet production in low Q 2 e + e − and ep collisions including next-to-leading order corrections for the direct and resolved contributions is reviewed. Mainly inclusive two-jet production is considered. The theoretical results are compared with experimental data from the TRISTAN (γγ) and HERA ( γp ) colliders.

Inclusive two-jet production in γγ and γp collisions

The theory of jet production in low Q2 e+e− and ep collisions including next-to-leading order corrections for the direct and resolved contributions is reviewed. Mainly inclusive two-jet production is considered. The theoretical results are compared with experimental data from the TRISTAN (γγ) and HERA (γp) colliders.

The physics of hadrons

The next-to-leading-order (NLO) cross section for the production of heavy quarks at large transverse momenta ( p ⊥ in γγ collisions is calculated with perturbative fragmentation functions (PFFs). This approach allows for a resummation of terms ∝ α s ln( p 2 ⊥/ m 2) which arise in NLO from collinear emission of gluons by heavy quarks at large p ⊥ or from almost collinear branching of photons or gluons into heavy-quark pairs. We present single-inclusive distributions in p ⊥ and rapidity including direct and resolved photons for γγ production of heavy quarks at e + e − colliders and at high-energy γγ colliders. The results are compared with the fixed-order calculation for m finite including QCD radiative corrections. The two approaches differ in the definitions and relative contributions of the direct and resolved terms, but essentially agree in their sum. The resummation of the α s ln( p 2 ⊥/ m 2) terms in the PFF approach leads to a softer p ⊥ distribution and to a reduced sensitivity to the choice of the renormalization and factorization scales.

γγ production of non-strongly interacting SUSY particles at hadron colliders

Non-strongly interacting particles in supersymmetric theories — sleptons, charginos/neutralinos, and charged Higgs bosons — are difficult to detect at the Large Hadron Collider. We therefore examine the possibility of producing particles of this type in virtual γγ collisions at the LHC. Since photons can be emitted from protons which do not break up in the radiation process, very clean events can be generated, compensating to some extent for the small event numbers. Higher rates are expected, at the expense of stray hadrons, for events in which one or both protons break up.

Search for heavy neutral spinless particles using e+e− → e+e− and e+e− → γγ reactions in the CM energy range between 54 and 64 GeV

Heavy neutral spinless particles are searched for using e + e − collision data of CM energies between 54 and 64 GeV, collected with the VENUS detector at TRISTAN. The existence of such a particle might explain the anomalous e + e − → l + l − γγ reaction recently reported by a LEP experiment. Negative results lead to constraints on the partial decay width of such particles to electrons: in narrow resonance cases, Γ ee < 1MeV from Bhabha scattering data and Γ ee ΓB γγ < 3 keV from γγ production data at the 95% CL for masses around 59 GeV/ c 2.