Production In Two-photon Collisions Research Articles

High-statistics study of KFormula pair production in two-photon collisions

We report a high-statistics measurement of the differential cross section of the process gamma gamma --> K^0_S K^0_S in the range 1.05 GeV <= W <= 4.00 GeV, where W is the center-of-mass energy of the colliding photons, using 972 fb^{-1} of data collected with the Belle detector at the KEKB asymmetric-energy e^+ e^- collider operated at and near the Upsilon-resonance region. The differential cross section is fitted by parameterized S-, D_0-, D_2-, G_0- and G_2-wave amplitudes. In the D_2 wave, the f_2(1270), a_2(1320) and f_2'(1525) are dominant and a resonance, the f_2(2200), is also present. The f_0(1710) and possibly the f_0(2500) are seen in the S wave. The mass, total width and product of the two-photon partial decay width and decay branching fraction to the K bar{K} state Gamma_{gamma gamma}B(K bar{K}) are extracted for the f_2'(1525), f_0(1710), f_2(2200) and f_0(2500). The destructive interference between the f_2(1270) and a_2(1320) is confirmed by measuring their relative phase. The parameters of the charmonium states chi_{c0} and chi_{c2} are updated. Possible contributions from the chi_{c0}(2P) and chi_{c2}(2P) states are discussed. A new upper limit for the branching fraction of the P- and CP-violating decay channel eta_c --> K^0_S K^0_S is reported. The detailed behavior of the cross section is updated and compared with QCD-based calculations.

Measurement ofηηproduction in two-photon collisions

We report the first measurement of the differential cross section for the process gamma gamma --> eta eta in the kinematic range above the eta eta threshold, 1.096 GeV < W < 3.8 GeV over nearly the entire solid angle range, |cos theta*| <= 0.9 or <= 1.0 depending on W, where W and theta* are the energy and eta scattering angle, respectively, in the gamma gamma center-of-mass system. The results are based on a 393 fb^{-1} data sample collected with the Belle detector at the KEKB e^+ e^- collider. In the W range 1.1-2.0 GeV/c^2 we perform an analysis of resonance amplitudes for various partial waves, and at higher energy we compare the energy and the angular dependences of the cross section with predictions of theoretical models and extract contributions of the chi_{cJ} charmonia.

Inclusive single-particle production in two-photon collisions at LEP II with the DELPHI detector

A study of the inclusive charged hadron production in two-photon collisions is described. The data were collected with the DELPHI detector at LEP II. Results on the inclusive single-particle pT distribution and the differential charged hadrons dσ/dpT cross-section are presented and compared to the predictions of perturbative NLO QCD calculations and to published results.

High-statistics study of neutral-pion pair production in two-photon collisions

The differential cross sections for the process gamma gamma -> pi(0)pi(0) have been measured in the kinematic range 0.6 GeV < W < 4.1 GeV, vertical bar cos theta* vertical bar < 0.8 in energy and pion scattering angle, respectively, in the gamma gamma center-of-mass system. The results are based on a 223 fb(-1) data sample collected with the Belle detector at the KEKB e(+)e(-) collider. The differential cross sections are fitted in the energy region 1.7 GeV < W < 2.5 GeV to confirm the two-photon production of two pions in the G wave. In the higher-energy region, we observe production of the chi(c0) charmonium state and obtain the product of its two-photon decay width and branching fraction to pi(0)pi(0). We also compare the observed angular dependence and ratios of cross sections for neutral-pion and charged-pion pair production to QCD models. The energy and angular dependence above 3.1 GeV are compatible with those measured in the pi(+)pi(-) channel, and in addition we find that the cross section ratio, sigma(pi(0)pi(0))/sigma(pi(+)pi(-)), is 0.32 +/- 0.03 +/- 0.05 on average in the 3.1-4.1 GeV region.

Study of ππ Production in Two-Photon Collisions at Belle

We have measured the cross section for π + π − production in two-photon collisions using a data sample with an integrated luminosity of 85.9 fb −1 collected with the Belle detector. The f 0 (980) resonance is observed as a peak in the energy spectrum of the cross section. We also report preliminary results for γγ → π 0 π 0 with two-photon center-of-mass energies ranging from 0.6 to 4.0 GeV, based on a 95 fb −1 data sample.

Measurement of the Cross Section for open b-Quark Production in Two-Photon Interactions at LEP

Inclusive b-quark production in two-photon collisions has been measured at LEP using data collected by the ALEPH detector.

High-statistics measurement of neutral-pion pair production in two-photon collisions

We present a high-statistics measurement of differential cross sections and the total cross section for the process γγ→π0π0 in the kinematic range 0.6 GeV≤W≤4.0 GeV and |cosθ*|≤0.8, where W and θ* are the energy and pion scattering angle, respectively, in the γγ center-of-mass system. Differential cross sections are fitted to obtain information on S, D0, D2, G0, and G2 waves. The G waves are important above W≃1.6 GeV. The general behavior of partial waves is studied by fitting differential cross sections in a simple parametrization where amplitudes contain resonant contributions and smooth background. The D2 wave is dominated by the f2(1270) meson whose parameters are consistent with the current world averages. The D0 wave contains a f2(1270) component, whose fraction is fitted. For the S wave, the f0(980) parameters are found to be consistent with the values determined from our recent π+π− data. In addition to the f0(980), the S wave prefers to have another resonance-like contribution whose parameters are obtained.5 MoreReceived 22 May 2008DOI:https://doi.org/10.1103/PhysRevD.78.052004©2008 American Physical Society

Study of ππ production in two-photon collisions at Belle

We have measured the cross section for π+π− production in two-photon collisions using a data sample with an integrated luminosity of 85.9 fb−1 collected with the Belle detector. The f0(980) resonance is observed as a peak in the energy spectrum of the cross section. We also report preliminary results for γγ → π0π0 with two-photon center-of-mass energies ranging from 0.6 to 4.0 GeV, based on a 95 fb−1 data sample. We find at least four resonant structures including a peak from f0(980). In addition, there is evidence for χc0 production. We also make a preliminary discussion of the angular dependence and cross section ratio of γγ → π+π− and γγ → π0π0.

Measurement of the cross section for open b-quark production in two-photon interactions at LEP

Inclusive beauty-quark production in two-photon collisions has been measured at LEP using an integrated luminosity of 698 pb-1 collected by the ALEPH detector with sqrt(s) between 130 and 209 GeV. The b quarks were identified using lifetime information. The cross section is found to be sigma(e+ e- --> e+ e- b \bar{b} X) = (5.4 +/- 0.8 (stat) +/- 0.8 (syst)) pb which is consistent with Next-to-Leading Order QCD.

A study of [formula omitted] production at energies from 2.4 to 4.0 GeV at Belle

K S 0 K S 0 production in two-photon collisions has been studied using a 397.6 fb −1 data sample collected with the Belle detector at the KEKB e + e − collider. For the first time the cross sections are measured in the two-photon center-of-mass energy range between 2.4 GeV and 4.0 GeV and angular range | cos θ ∗ | < 0.6 . Combining the results with measurements of γ γ → K + K − from Belle, we observe that the cross section ratio σ ( K S 0 K S 0 ) / σ ( K + K − ) decreases from ∼0.13 to ∼0.01 with increasing energy. Signals for the χ c 0 and χ c 2 charmonium states are also observed.

Experimental studies of charmonia in two-photon collisions at Belle

We report on the measurements of charmonium production in two-photon collisions performed with the Belle detector at the KEKB e + e − collider with the integrated luminosity up to about 400 fb−1. A new resonant state decaying to D D ¯ has been observed in the vicinity of 3.93 GeV/c2. From the measured angular distribution we found that it could be a candidate for the not yet found χ c 2 ′ , a radial excitation state of 3P2 charmonium. We have observed production of the χ c 0 and χ c 2 in the two-meson final states, π + π − , K + K − and K S 0 K S 0 and production of η c decaying to proton pairs. The χ c 2 production was also measured in the γ J / ψ decay mode. These three charmonia were also observed in their decays to the four-meson final states, where the meson is a charged pion or kaon. The products of the two-photon partial decay width and branching ratio were determined.

Measurement of exclusive [formula omitted] production in mid-virtuality two-photon interactions and study of the [formula omitted] process at LEP

Exclusive ρ+ρ− production in two-photon collisions between a quasi-real photon, γ, and a mid-virtuality photon, γ∗, is studied with data collected at LEP at centre-of-mass energies 183 GeV⩽s⩽209 GeV with a total integrated luminosity of 684.8 pb−1. The cross section of the γγ∗→ρ+ρ− process is determined as a function of the photon virtuality, Q2, and the two-photon centre-of-mass energy, Wγγ, in the kinematic region: 0.2 GeV2⩽Q2⩽0.85 GeV2 and 1.1 GeV⩽Wγγ⩽3 GeV. These results, together with previous L3 measurements of ρ0ρ0 and ρ+ρ− production, allow a study of the γγ∗→ρρ process over the Q2-region 0.2 GeV2⩽Q2⩽30 GeV2.

Measurement of the [formula omitted] and [formula omitted] processes at energies of 2.4–4.1 GeV

We have measured π+π− and K+K− production in two-photon collisions using 87.7fb−1 of data collected with the Belle detector at the asymmetric energy e+e− collider KEKB. The cross sections are measured to high precision in the two-photon center-of-mass energy (W) range between 2.4GeV<W<4.1GeV and angular region |cosθ∗|<0.6. The cross section ratio σ(γγ→K+K−)/σ(γγ→π+π−) is measured to be 0.89±0.04(stat.)±0.15(syst.) in the range of 3.0GeV<W<4.1GeV, where the ratio is energy-independent. We observe a sin−4θ∗ behavior of the cross section in the same W range. Production of χc0 and χc2 mesons is observed in both γγ→π+π− and γγ→K+K− modes.

Formula omitted] plus jet associated production in two-photon collisions at next-to-leading order

We calculate the cross section of J / ψ plus jet inclusive production in γγ collisions at next-to-leading order within the factorization formalism of non-relativistic quantum chromodynamics (NRQCD) focusing on direct photoproduction. Apart from direct J / ψ production, we also include the feed-down from directly-produced χ c J and ψ ′ mesons. We discuss the analytical calculation, in particular, the treatment of the various types of singularities and the NRQCD operator renormalization, in some detail. We present theoretical predictions for the future e + e − linear collider TESLA, taking into account both brems- and beamstrahlung.

J/ψplus prompt-photon associated production in two-photon collisions at next-to-leading order

We calculate the cross section of $J/\ensuremath{\psi}$ plus prompt-photon inclusive production in $\ensuremath{\gamma}\ensuremath{\gamma}$ collisions at next-to-leading order within the factorization formalism of nonrelativistic quantum chromodynamics (NRQCD) focusing on direct photoproduction. Apart from direct $J/\ensuremath{\psi}$ production, we also include the feed-down from directly produced ${\ensuremath{\chi}}_{cJ}$ and ${\ensuremath{\psi}}^{\ensuremath{'}}$ mesons. We discuss the analytical calculation, in particular the treatment of the various types of singularities and the NRQCD operator renormalization, in some detail. We present theoretical predictions for the future ${e}^{+}{e}^{\ensuremath{-}}$ linear collider TESLA, taking into account both brems- and beamstrahlung.

Inclusive jet production in two-photon collisions at LEP

Inclusive jet production in two-photon collisions at LEP

Measurement of exclusive [formula omitted] production in mid-virtuality two-photon interactions at LEP

Exclusive ρ0ρ0 production in two-photon collisions between a quasi-real and a mid-virtuality photon is studied with data collected at LEP at centre-of-mass energies 183<s<209 GeV with a total integrated luminosity of 684.8 pb−1. The cross section of the process γγ*→ρ0ρ0 is determined as a function of the photon virtuality, Q2, and the two-photon centre-of-mass energy, Wγγ, in the kinematic region: 0.2<Q2<0.85 GeV2 and 1.1<Wγγ<3 GeV.

Inclusive jet production in two-photon collisions at LEP

Inclusive jet production, e+e−→e+e− jet X, is studied using 560 pb−1 of data collected at LEP with the L3 detector at centre-of-mass energies between 189 and 209 GeV. The inclusive differential cross section is measured using a kt jet algorithm as a function of the jet transverse momentum, pt, in the range 3<pt<50 GeV for a pseudorapidity, η, in the range −1<η<1. This cross section is well represented by a power law. For high pt, the measured cross section is significantly higher than the NLO QCD predictions, as already observed for inclusive π± and π0 production.

Production in two-photon collisions at next-to-leading order

In this paper, we report on the calculation of the cross section of J/\Psi plus jet inclusive production in direct two-photon collisions at next-to-leading order within the factorization formalism of nonrelativistic quantum chromodynamics (NRQCD). Theoretical predictions for the future e^+e^- linear collider TESLA are also presented.

Measurement of exclusive ρ+ρ−ρ+ρ− production in high-Q2Q2 two-photon collisions at LEP

Exclusive ρ + ρ − production in two-photon collisions involving a single highly-virtual photon is studied for the first time with data collected by the L3 experiment at LEP at centre-of-mass energies 89 < s < 209 GeV with a total integrated luminosity of 854.7 pb − 1 . The cross section of the process γ γ * → ρ + ρ − is determined as a function of the photon virtuality, Q 2 , and the two-photon centre-of-mass energy, W γ γ , in the kinematic region: 1.2 < Q 2 < 30 GeV 2 and 1.1 < W γ γ < 3 GeV . The ρ + ρ − production cross section is found to be of the same magnitude as the cross section of the process γ γ * → ρ 0 ρ 0 , measured in the same kinematic region by L3, and to have similar W γ γ and Q 2 dependences.