O.Yu. Mandrik

A Study of the production and lifetime of the lightest relativistic hypernuclei

Abstract All results on the production cross sections of the lightest hypernuclei and the lifetimes of the hydrogen hypernuclei obtained in Dubna streamer chamber experiments are presented.

Experimental study of relativistic hypernuclei using the HYBS-spectrometer

SummaryThe method and the results of an experiment on the study of relativisticΛ4H andΛ3H production in interactions of 18 GeV/c4He nuclei with CH2 target nuclei are presented. The experiment was performed using the HYBS-spectrometer. The main registering part of the spectrometer is a (2×0.6×1)m3 streamer chamber placed in a magnetic field of 0.9 T. The streamer chamber was triggered when the beam4He nucleus lost one charge unit in the target and then again became double-charged inside the chamber fiducial volume according to the selection criteria forΛ3,4H hypernucleus production and its mesonic decay with the He nucleus in the final state. After scanning of the pictures, measurements of two-prong events and careful analysis, events of the decaysΛ4H→4He+π− andΛ3H→3He+π− were identified. The estimates of theΛ4H production cross-section (∼0.4 µb) and its mean lifetime (∼2.2·10−10s) were obtained. A comparison with the results of other experiments and theoretical calculations is made. By the way, the cross-section of the charge exchange reaction3H+Ne→3He+π−++...(∼1 mb) was estimated. The work has been performed at the Laboratory of High Energies, JINR, Dubna.RiassuntoSi presentano il metodo e i risultati di un esperimento sullo studio della produzione relativistica diΛ4H eΛ3H nelle interazioni dei nuclei di4He a 18 GeV/c con i nuclei del bersaglio CH2. L’esperimento è stato compiuto usando lo spettrometro HYBS. La parte principale registrante dello spettrometro è una camera a tracce situata in un campo magnetico di 0.9 T. La camera a tracce è innescata quando il nucleo del fascio di4He perde un’unità di carica nel bersaglio e torna poi nuovamente ad avere una carica doppia all’interno del volume fiduciale della camera secondo i criteri di selezione per la produzione dell’ipernucleoΛ3,4H e il suo decadimento mesonico con il nucleo di He nello stato finale. Dopo la scansione delle figure, la misurazione degli eventi a due prong e un’attenta analisi, sono stati identificati gli eventi di decadimentoΛ4H →4He+π− eΛ3H→3He+π−. Sono state ottenute le stime della sezione d’urto di produzione diΛ4H (∼0.4 µb) e la sua vita media (∼2.2·10−10s). Si fa un confronto con i risultati di altri esperimenti e con i calcoli teorici. Come risultato a latere si stima la sezione d’urto della reazione di scambio di carica3H+Ne→3He+π−+...(∼1 mb). Il lavoro è stato effettuato al Laboratorio delle Alte Energie, JINR, Dubna.РеэюмеПриводятся метод и реэультаты по исследованию обраэования релятивистскихΛ4H иΛ3H при вэаимодействиях ядер4He с импульсом 18 ГзB/c с ядрами мищени CH2. Эксперимент проводился с испольэованием HYBS-спектрометра. Основная регистрируюшая часть спектрометра представляет (2×0.6×1) M3 стримерную камеру, помешенную в магнитное поле 0.9 Tл. Стримерная камера эапускается, когда ядро пучка4He теряет единичный эаряд в мищени, а эатем снова становится дважды-эаряженным внутри общема камеры, согласно критерию отбора для обраэования H-гиперядер и его меэонного распада в ядро He в конечном состоянии. После сканирования картин в стримерной камере, иэмерений двух-лучевых событий и внимательного аналиэа, были идентифицированы события распадовΛ4H→4He+π− иΛ3H→3He+π−. Получены оценки поперечного сечения рожденияΛ4H(∼0.4 мкб) и среднего времени жиэни (∼2.2·10−6 c). Проводится сравнение с реэультатами других зкспериментов и теоретическими вычислениями. Кроме того, оценивается поперечное сечение реакции переэарядки H+Ne→3He+π−+... (∼1 мб). Эта работа проведена в лаборапории высоких знергий оияи, Дубна.

HBT measurement of the expansion velocity of pion production volume

Abstract Using a new method of data processing in the investigation of interference correlations of identical particles, a direct proof of nonstationarity of the π − production volume in central MgMg collisions at a beam momentum of p Iab = 4.4 GeV/c per nucleon was obtained. The velocity of a source of correlated π − meson pairs is introduced as a free parameter in the Lorentz transformed approximation formula of the interference peak. This velocity increases with increasing the velocity of a subset of π − mesons which are chosen for the interference analysis. The source velocity is the new experimentally measurable physical variable of interference analysis, apart from space-time sizes of the source.

Pion production in nuclear charge exchange reactions A(t, 3He)

Abstract The charge exchange reaction (t, 3 He) on carbon and magnesium targets is investigated in experiments using a streamer chamber. The experimental pion longitudinal momentum spectrum is compared with the calculated one for events with a single secondary pion. From this comparison it follows that the contribution from quasi-free Δ − excitation in the target nucleus in a single pion channel is only 60–70%. The momentum of the pions in the remaining fraction of events is significantly higher than that of the pions produced in delta de-excitation. The contribution from several possible processes is analyzed. The data indicate a significant role of coherent pion production via N(1440) or/and N(1520) in the target nucleus while part of the pion spectrum can be explained by projectile excitation.