Bartels, H.W.
Two-Photon
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A Measurement of $\pi^0 \pi^0$ Production in Two Photon Collisions

The Crystal Ball collaboration Marsiske, H. ; Antreasyan, D. ; Bartels, H.W. ; et al.
Phys.Rev.D 41 (1990) 3324, 1990.
Inspire Record 294492 DOI 10.17182/hepdata.22923

The reaction e+e−→e+e−π0π0 has been analyzed using 97 pb−1 of data taken with the Crystal Ball detector at the DESY e−e+ storage ring DORIS II at beam energies around 5.3 GeV. For the first time we have measured the cross section for γγ→π0π0 for π0π0 mvariant masses ranging from threshold to about 2 GeV. We measure an approximately flat cross section of about 10 nb for W=mπ0π0<0.8 GeV, which is below 0.6 GeV, in good agreement with a theoretical prediction based on an unitarized Born-term model. At higher invariant masses we observe formation of the f2(1270) resonance and a hint of the f0(975). We deduce the following two-photon widths: Γγγ(f2(1270))=3.19±0.16±0.280.29 keV and Γγγ(f0(975))<0.53 keV at 90% C.L. The decay-angular distributions show the π0π0 system to be dominantly spin 0 for W<0.7 GeV and spin 2, helicity 2 in the f2(1270) region, with helicity 0 contributing at most 22% (90% C.L.).

2 data tables
Table 1

Statistical errors only.

Table 2

Statistical errors only.


A Measurement of the photon structure function F2

The AMY collaboration Sasaki, T. ; Yamagishi, Y. ; Tanaka, R. ; et al.
Phys.Lett.B 252 (1990) 491-498, 1990.
Inspire Record 299056 DOI 10.17182/hepdata.29524

The photon structure function F 2 has been measured at average Q 2 values of 73,160 and 390 ( GeV c ) 2 . We compare the x dependence of the Q 2 = 73 ( GeV c ) 2 data with theoretical expectations based on QCD. In addition we present results on the Q 2 evolution of the structure function for the intermediate x range (0.3⩽ x ⩽0.8). The results are consistent with QCD.

4 data tables
Table 1

X dependence at Q**2 = 73 GeV**2 for light quark data.

Table 2

X dependence at Q**2 = 73 GeV**2 for total data.

Table 3

Photon structure function F2 for total data.

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First observation of the reaction gamma gamma ---> pi (2) ---> pi0 pi0 pi0

The Crystal Ball collaboration Antreasyan, D. ; Bartels, H.W. ; Besset, D. ; et al.
Z.Phys.C 48 (1990) 561-568, 1990.
Inspire Record 296523 DOI 10.17182/hepdata.15136

The Crystal Ball detector has been used at the DORIS II storage ring at DESY to study the reactionγγ→π0π0π0 in theπ0π0π0 invariant mass range from 850 MeV/c2 to 2600 MeV/c2. An enhancement around 1750 MeV/c2 is attributed to theπ2(1670) resonance. The observedπ0π0 invariant mass distribution and theπ0 angular distributions are consistent with those expected for the decay chainπ2→π0f2(1270)→π0π0π0. From our measurements we find the following resonance parameters: two photon partial width\(\Gamma _{\pi _2 }^{\gamma \gamma }= (1.41 \pm 0.23 \pm 0.28)keV\), massM(π2)=(1742±31±49)MeV/c2. and total width\(\Gamma _{\pi _2 }^{tot}= (236 \pm 49 \pm 36)MeV\).

2 data tables
Table 1

Data read from graph.

Table 2

Cross section times branching ratio to 3pi0 assuming the decay chain pi2 --> pi0f2 --> 3pi0.


rivet Analysis
Measurement of $Z\gamma\gamma$ production in $pp$ collisions at $\sqrt{s}= 13$ TeV with the ATLAS detector

The ATLAS collaboration Aad, Georges ; Abbott, Braden Keim ; Abbott, D.C. ; et al.
Eur.Phys.J.C 83 (2023) 539, 2023.
Inspire Record 2593322 DOI 10.17182/hepdata.132903

Cross-sections for the production of a $Z$ boson in association with two photons are measured in proton$-$proton collisions at a centre-of-mass energy of 13 TeV. The data used correspond to an integrated luminosity of 139 fb$^{-1}$ recorded by the ATLAS experiment during Run 2 of the LHC. The measurements use the electron and muon decay channels of the $Z$ boson, and a fiducial phase-space region where the photons are not radiated from the leptons. The integrated $Z(\rightarrow\ell\ell)\gamma\gamma$ cross-section is measured with a precision of 12% and differential cross-sections are measured as a function of six kinematic variables of the $Z\gamma\gamma$ system. The data are compared with predictions from MC event generators which are accurate to up to next-to-leading order in QCD. The cross-section measurements are used to set limits on the coupling strengths of dimension-8 operators in the framework of an effective field theory.

16 data tables
Table 1

Measured fiducial-level integrated cross-section. NLO predictions from Sherpa 2.2.10 and MadGraph5_aMC@NLO 2.7.3 are also shown. The uncertainty in the predictions is divided into statistical and theoretical uncertainties (scale and PDF+$\alpha_{s}$).

Table 2

Measured unfolded differential cross-section as a function of the leading photon transverse energy $E^{\gamma1}_{\mathrm{T}}$. NLO predictions from Sherpa 2.2.10 and MadGraph5_aMC@NLO 2.7.3 are also shown. The uncertainty in the predictions is divided into statistical and theoretical uncertainties (scale and PDF+$\alpha_{s}$).

Table 3

Measured unfolded differential cross-section as a function of the subleading photon transverse energy $E^{\gamma2}_{\mathrm{T}}$. NLO predictions from Sherpa 2.2.10 and MadGraph5_aMC@NLO 2.7.3 are also shown. The uncertainty in the predictions is divided into statistical and theoretical uncertainties (scale and PDF+$\alpha_{s}$).

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