D. Horváth

["Measurement of the Λ→n+γ branching ratio"]

The branching ratio for the {Lambda} weak radiative decay has been measured to be {ital B}({Lambda}{r arrow}{ital n}+{gamma})/({Lambda}{r arrow}anything) =(1.78{plus minus}0.24(stat){plus minus}{sub 0.16}{sup 0.14}(syst)){times}10{sup {minus}3}. A low-energy kaon beam was used to produce the {Lambda} hyperons via the reaction {ital K}{sup {minus}}+{ital p}{r arrow}{Lambda}+{pi}{sup 0} at rest. Photons from the signal channel and {pi}{sup 0} decay were detected with a NaI(Tl) array. The final spectrum contains 287 events after background subtraction, an order of magnitude more events than from the only previous measurement.

Measurement of the. Lambda. r arrow n +. gamma. branching ratio

The branching ratio for the {Lambda} weak radiative decay has been measured to be {ital B}({Lambda}{r arrow}{ital n}+{gamma})/({Lambda}{r arrow}anything) =(1.78{plus minus}0.24(stat){plus minus}{sub 0.16}{sup 0.14}(syst)){times}10{sup {minus}3}. A low-energy kaon beam was used to produce the {Lambda} hyperons via the reaction {ital K}{sup {minus}}+{ital p}{r arrow}{Lambda}+{pi}{sup 0} at rest. Photons from the signal channel and {pi}{sup 0} decay were detected with a NaI(Tl) array. The final spectrum contains 287 events after background subtraction, an order of magnitude more events than from the only previous measurement.

Radiative hyperon processes

SummaryWeak as well as pure electromagnetic radiative decays of hyperons are discussed. The radiative decays of excited hyperon states can provide information on the quark wave functions inside the hyperons. The weak (strangeness-changing) decays represent the last low-q2 frontier of weak-interaction physics. The theoretical motivation of these studies is reviewed, as well as the existing experiments. Special emphasis is placed on recent experiments at the Brookhaven AGS and at Fermilab. Radiative K− at rest on the deuteron is also discussed, and new results from Brookhaven are presented.RiassuntoSi discutono i decadimenti radiativi elettromagnetici puri nonché quelli deboli. I decadimenti radiativi degli stati eccitati degli iperoni possono fornire informazioni sulle funzioni di onda dei quark all’interno degli iperoni. I decadimenti deboli (che cambiano la stranezza) rappresentano l’ultima frontiera a bassoq2 della fisica delle interazioni deboli. Si passano in rassegna la motivazione teorica di questi studi e gli esperimenti esistenti. Si pone particolare enfasi sui recenti esperimenti all’AGS di Brookhaven e a Fermilab. Si discute anche la cattura di K− radiativa a riposo sul deuterone e si presentano nuovi risultati di Brookhaven.РеэюмеОбсуждаются слабые и чисто злектромагнитные радиационные распады гиперонов. Радиационные распады воэбужденных гиперонных состояний могут дать информацию о волновых функциях кварков внутри гиперонов. Слабые (с иэменением странности) распады представляют последнюю нижнююq2 границу для фиэики слабых вэаимодействий. Предлагается теоретическая мотивация зтих исследований и сушествуюших зкспериментов. Особое внимание уделяется последним зкспериментам в Брукхейвене AGS и в лаборатории Ферми. Также обсуждается радиационный K−-эахват в покое на дейтроне и приводятся новые реэультаты, полученные в Брукхейвене.

Weak radiative hyperon decays

New measurements of the Σ+ and Λ weak radiative decays are discussed. The hyperons were produced at rest by the reaction K−p → Yπ where Y = Σ+ or Λ. The monoenergetic pion was used to tag the hyperon production, and the branching ratios were determined from the relative amplitudes of Σ+ → pγ to Σ+ → pπ0 and Λ → nγ to Λ → nπ0. The photons from weak radiative decays and from π0 decays were detected with modular NaI arrays.

Status of E811: Hyperon weak radiative decay

We report the status of branching ratio measurements of Σ+→p+γ and Λ→n+γ. For the Σ+ decay a preliminary result is presented.

Radiative kaon capture

Negative kaons were stopped in liquid hydrogen and liquid deuterium targets to study radiative capture rates. Branching ratios for the radiative kaon capture reactions K−p→Λγ and K−p→Σ0γ provide information about the quark structure of the Λ(1405). In the reaction K−d→Λnγ, the shape of the photon spectrum in the endpoint region provides information on the final state Λ‐n interaction. Superior photon resolution is needed to distinguish the signal photons from the background of π0 decay photons. Such resolution is provided by the B.U. NaI detector, which has a resolution of 1.3% (FWHM) near 300 MeV. A description of the experimental technique and data reduction is presented, along with preliminary branching ratio results.