M. Beneventano

Single direct photon production in pp collisions at √s = 53.2 GeV in the pt interval 2.3 to 5.7 GeV/c

Abstract We report the results of an experiment made at the CERN ISR to investigate the possible diret production of single photons in pp collisions at √ s = 53.2 GeV at 90° and in the p t interval 2.3 to 5.7 GeV/ c . The value of the ratio R = n γ / n π 0 is compatible with zero for low p t ⪅ 3 GeV/ c but, in spite of the large error, shows a trend to increase for larger p t .

Search for single photon direct production in p + p collisions at s=53.2 GeV

Abstract From measurements at the ISR of CERN with a lead glass counter matrix we establish an upper limit of 6% (at 95% C.L.) for the ratio of the directly produced photons to the produced π0 at 90° and s = 53.2 GeV in the p ∗ T region 2.3–3.7 GeV/c.

COMPARISON OF DIRECT PHOTON PRODUCTION IN P P COLLISIONS AT S**(1/2) = 30.6-GEV AND 53.2-GEV

Abstract We present data obtained at the ISR, on the determination of the ratio R = γ π 0 at s = 30.6 GeV and we compare the results with our previous measurement at s = 53.2 GeV. The ratio R = γ π 0 integrated over the interval 0.1 ⩽ χ T ⩽ 0.2 is (1.6 ± 0.5) × 10 −2 and we obtain an indication of a universal χ T dependence.

Comparison of direct photon production in pp collisions at s= 30.6 GeV and 53.2 GeV

Abstract We present data obtained at the ISR, on the determination of the ratio R = γ π 0 at s = 30.6 GeV and we compare the results with our previous measurement at s = 53.2 GeV. The ratio R = γ π 0 integrated over the interval 0.1 ⩽ χ T ⩽ 0.2 is (1.6 ± 0.5) × 10 −2 and we obtain an indication of a universal χ T dependence.

Multigamma-ray events at the CERN ISR

Abstract Results of a search for multigamma-ray events at √s = 52 GeV in pp collision are reported. The results are compared with a Monte Carlo simulation of the decay of pairs of heavy mass particles by gamma-ray emission, and upper limits for the production cross section are determined.

Inclusive η production in p + p collision at ISR energies

Abstract We report on the experimental results obtained at the ISR for the η particle production at 90° and √s = 30.6 and 53.2 GeV. We determine the invariant cross section and the pt distribution in the interval 1 ⩽ pt ⩽ 5 GeV/c. We find that the pt distribution has the same shape of the π0 production and differ from it by a constant factor R90° = 0.5 ± 0.07.

Two-photon mass spectra produced in p-p collision at √s = 52 GeV

In this paper we repor t on the resul ts obta ined at t i le ISR for ~Js--52 GeV on the react ion p-p -+ 2 y + a n y t h i n g , where the two photons are emi t t ed on opposite sides a round 90 ~ wi th respect to the c i rcula t ing beams. The lay-out of the exper imenta l set up, main ly consist ing of two matr ices of lead glasses (SP, S X ) , has been described in a previous paper (1) on the produc t ion cross-section of the J / ~ observed in the e+e decay mode. The da ta repor ted here correspond to an in tegra ted luminos i ty of 1.15.1037 em 2 and have been obta ined wi th the same t r igger described in ref. (~), i.e. at least one lead glass in each of the two matr ices wi th a deposi ted energy ~ 600 MeV. In the analysis, we look for lead glasses showing re la t ive m a x i m a of the deposi ted energy > 100 MeV, and define as ( the sum of the energies deposi ted in this counter and in the ad jacent lead glasses. A (~ y-ray ,) is defined as an energy cluster wi thou t signal in the scint i l la tor counter in f ront of it. 0 n l y those events have been analyses tha t show in the S P as well as in the S X units at least one (, y-ray ,) wi th energy larger t han 900 MeV. A single cluster somet imes is due to unresolved ~0. Fo r reducing this cont r ibut ion we have in t roduced the following selection requ i rements :

Measurement of π+π− and π0π0 photoproduction differential cross-sections for incident γ-ray energies from 600 to 900 MeV

SummaryCross-sections of the reactions γ+p→p+π++π− and γ+p→p+π0+π0 have been measured at the 1.1 Gev Frascati electrosynchrotron for photon energiesEγ between 600 and 900 MeV, for five proton momenta and at fixed proton laboratory angleθp=32°. The cross-sections of π+π− photoproduction exhibit behaviours in agreement with the Δ++ production; no immediate evidence is found of contribution of ππ interactions. The mean value of the ratio π+π−/π0π0 is 2.7±0.3.RiassuntoPresso l’elettrosincrotrone da 1.1 GeV di Frascati sono state misurate le sezioni d’urto dei processi γ+p→p+π++π− e γ+p→p+π0+π0 nell’intervallo di energia del gamma incidente (600÷900) MeV per cinque valori dell’impulso del protone e ad angolo fisso del protone nel laboratorio (θp=32°). Le sezioni d’urto della fotoproduzione di π+π− mostrano andamenti in buon accordo con l’ipotesi che questo processo sia dominato dal canale γ+p→Δ+++π−; non si hanno prove immediate di contributi dovuti a interazioni ππ. Il valor medio determinato sperimentalmente del rapporto π+π−/π0π0 è 2.7±0.3.РеэюмеБыли иэмерены поперечные сечения реакций γ+p→p+π++π− и γ+p→p+π0+π0 на 1.1 ГзВ злектросинхротроне Фраскати для знергий фотона Eг от 600 до 900 МзВ, для пяти импульсов протона и при фиксированном лабораторном угле протона θp=32°. Поперечные сечения фоторождения π+π− обнаруживают поведение, согласуюшееся с рождением Δ++. Не обнаружено непосредственного подтверждения вклада лл вэаимодействий. Средняя величина отнощения π+π−/π0π0 равна 2.7±0.3.

Charged and neutral double pion photoproduction cross-sections in the γ-ray energy range (600÷900) MeV

in hydrogen have been investigated at the Frascati electronsynehrotron for incident v-ray energies from 600 to 900 MeV, at fixed proton laboratory emission angle 0p~ = 32 ~ and for five proton laboratory momenta p = 410, 440, 475, 510, 550MeV/c. Reaction 2) has been investigated by detecting and analysing the protons by means of a weakfocusing magnetic spectrometer and a plastic scintillation counter system and a Cerenkov counter. Reaction 1) has been investigated by detecting in coincidence with the proton at least one charged particle by means of a plastic scintillation counter system placed around the target. The results have been corrected for the following effects: I) empty-target contributions (~ 20~o), II) accidental coincidences (~ 10%), I I I ) losses due to mnltiple scattering in the proton counters (~ 30%). The contribution from single-= ~ photoproduction (V_[_p__ > p__~:o) to the reaction 2) and the contribution to the proton-charged-particle coincidences due to the conversion of v-rays from the r~ ~ decays (~ 15%) have been evaluated with measurements below the double pion photoproduction threshold. Five yields Y ( E ) have been measured, corresponding to the five above-mentioned momenta, for reactions 1) and 2); as is known Y ( E ) is the number of events revealed by the apparatus per equivalent quantum as a function of the maximum energy of the bremsstrablung spectrum. All the corrections on each yield are practically constant in the measured energy range. The single-~ ~ photoproduction contributions have been subtracted from the yields of reaction 2). In conclusion the measured yields are