G. Torelli

Precise measurement of the 2s12-2p32 splitting in the (μ−4He)+ muonic ion

Abstract The results of a new measurement of the 2 S 1 2 -2 P 3 2 splitting S 1 in the muonic ion (μ −4 He) + are presented. We found S e xp 1 = 1527.5 ± 0.3 meV. Using the new, recently determined, value of the rms charge radius for 4 He we obtain for the difference D , between S exp 1 and the corresponding theoretical prediction, the value D = 0.2 ± 4.2 meV: this value directly confirms, assuming μ-e universality, the QED vacuum polarization prediction to 0.25 %.

Observation of muonic X-rays in helium gas and measurement of the two-photon decay rate of the 2s metastable state

SummaryWe have measured the yield of theK andL lines of the muonic helium system stopping negative muons in a gaseous helium target (7 atm, 293 °K). We have also observed the two-photon decay of the ionie metastable 2s state and we found that this system is formed in (3.4 ± 0.7)% of the stopped muons.RiassuntoAbbiamo misurato le intensità delle lineeK edL del sistema muonico eccitato (μHe) fermando muoni negativi in elio gassoso (7 atm, 293 °K). Abbiamo anche osservato il decadimento, via due fotoni, del sistema ionico metastabile (μHe)2s+ ed è stato trovato che questo si forma nel (3.4 ± 0.7)% dei casi in cui un muone è fermato.РеэюмеМы иэмерили интенсивностьK- иL-линий системы меэоатомов гелия, обраэуюшихся при остановке отрицательных мюонов в мищени гаэообраэного гелия (при давлении 7 атмосферы и температуре 293 °К). Мы также наблюдали двух-фотонный распад метастабильного 2s состояния иона меэоатома гелия (μНе)+ и обнаружили, что зта система обраэуется в (3.4 ± 0.7)% случаев остановки мюонов.

Measurement of the 2S12−2P12 splitting in the (μ−4He)+ muonic ion

Abstract The measurement of the 2S 1 2 → 2P 1 2 energy transition in muonic helium is presented. The energy difference S1 is found to be Sexp1 = 1381.3±0.5 meV. This result agrees with the expected value S 1 = 1381.2±0.3 meV obtained assuming the previously measured value for the 2S 1 2 → 2P 3 2 energy difference.

Measurement of the 2P3/2−S1/2 energy difference in the (μ−4He)+ muonic ion by means of a tunable infrared dye-laser

Abstract Results of an experiment to measure the 2P 3/2 −2S 1/2 energy difference δ 1 in the muonic (μ −4 H e) + ion are presented; we found δ 1 exp = 1.5274 ± 0.0009 eV. Comparison with QED predictions shows that there is agreement between theory and experiment within 0.0087 eV; this limitation is mainly due to the uncertainty with which the r.m.s. charge radius of the 4 He nucleus is known.

Search for a resonant π-π interaction in the process π−1p → π+−n near threshold

SummaryThe π-π interaction in the final state of the process π−p → π+π−n has been investigated at an incoming kinetic energy of 276 MeV. No resonant behaviour has been found in the invariant-mass range examinated ((280÷350) MeV). The π-π mass distribution is discussed and compared with other experimental and theoretical results.RiassuntoAbbiamo studiato l’interazione π-π nello stato finale della reazione π−p → π−π+n ad una energia cinetica del pione incidente di 276 MeV. Nessun comportamento risonante è stato osservato nell’intervallo di massa esaminato ((280÷350) MeV). Le distribuzioni di massa π-π ottenute sono discusse e confrontate con altri risultati teorici e sperimentali.

Measurement of the 2S1/2–2P3/2 level splitting in muonic helium: A test of quantum electrodynamics predictions on electronic vacuum polarization

SummaryThe results of a measurement of the 2S1/2-2P3/2 energy difference in the (μ4He) muonic system are presented. Full account of the experimental method as well as an up-to-date review of the pertaining theoretical predictions are given. The obtained results show a good agreement with QED predictions; the electronic vacuum polarization term of order α is checked with a relative accuracy of 5·10−3.RiassuntoSi presenta il risultato di una misura della differenza di energia tra i livelli 2S1/2 e 2P3/2 nel sistema muonico (μ4He). Si discute in dettaglio il metodo sperimentale e si riporta una rassegna delle previsioni teoriche. Il risultato ottenuto è in buon accordo con le predizioni dell’elettrodinamica quantistica; in particolare esso permette di verificare con una precisione relativa del 5‰ il contributo della polarizzazione di vuoto elettronica all’ordine α.РезюмеПриводятся результаты измерения разности энергии для 2S1/2-2P3/2 в мюонной системе (μ4He). Подробно обсуждается экспериментальная методика и предлагается обзор теоретических предсказаний. Полученные результаты обнаруживают хорошее согласие с предсказаниqqjми квантовой электродинамики. В частности, проводится проверка вклада в поляризацию электронногоам вакуу от члена порядка α с относительной точностью 5·10−3.

Production of a positive pion in a collision of a 247 MeV negative pion with a proton

Abstract We have measured the total cross-section σ for the reaction π−p → π−π+n at 74 MeV over the threshold and we have found σ = (60 ± 15) μb. The observed differential distributions in the Dalitz plot have been analysed with Gribovs formula obtaining a2 − a0 = −(0.42 ± 0.10) mπ−1.