Study of the rare hyperon decay (original) (raw)

Search for CP Violation in Charged-Ξ and Λ Hyperon Decays

Physical Review Letters, 2004

We have compared the p and p angular distributions in 117 million Ξ − → Λπ − → pπ − π − and 41 million Ξ + → Λπ + → pπ + π + decays using a subset of the data from the HyperCP experiment (E871) at Fermilab. We find no evidence of CP violation, with the direct-CP-violating parameter AΞΛ ≡ (αΞαΛ − αΞαΛ)/(αΞαΛ + αΞαΛ) = [0.0±5.1(stat)±4.4(syst)]×10 −4 .

Search for direct CP violation in Λ and Ξ hyperon decays

Nuclear Physics B-proceedings Supplements, 1999

A sensitive search for direct CP violation in E-(E+) and A (3,) decays is underway at FNAL. Experiment E871 (HyperCP) intends to perform a precision measurement of the angular distribution of protons (anti-protons) with respect to the helicity axis in the rest frame of the A (/k). The slopes of these distributions give the decay parameters ~-=~h and c~c~,~. An asymmetry parameter ,4 in terms of these decay parameters has been defined for which a non-zero value would be unambiguous evidence for direct CP violation. Theoretical predictions for ,4 range from no asymmetry up to ,,~ 10 -3. HyperCP expects to measure ,4 with an uncertainty of ,,~ 2 x 10 -4.

Search for direct CP violation in Lambda and Xi hyperon decays

Nuclear Physics B-proceedings Supplements, 1999

A sensitive search for direct CP violation in Ξ - ( overlineΞ+) and Λ ( overlineΛ) decays is underway at FNAL. Experiment E871 (HyperCP) intends to perform a precision measurement of the angular distribution of protons (anti-protons) with respect to the helicity axis in the rest frame of the Λ ( overlineΛ). The slopes of these distributions give the decay parameters αΞαΛ and α overlineΞα overlineΛ. An asymmetry parameter A in terms of these decay parameters has been defined for which a non-zero value would be unambiguous evidence for direct CP violation. Theoretical predictions for A range from no asymmetry up to ˜ 10 -3. HyperCP expects to measure A with an uncertainty of ˜ 2 × 10 -4.

Search for CP violation in hyperon decays

Nuclear Physics B - Proceedings Supplements, 2003

Searches for experimental manifestations of CP violation have born much fruit in recent years with the discovery of direct CP violation and the first evidence of CP violation outside of the neutral kaon system. Nevertheless we still know little about CP violation: its origin remains a mystery and there is little hard evidence that it is the sole province of the standard model. Searches for CP violation in hyperon decays offer promising possibilities as they are sensitive to certain beyondthe-standard-model sources that are not probed in other systems. We report on the status of such searches, in particular a new result from the Fermilab Hyper C P experiment which has greatly increased the sensitivity over previous measurements and is confronting some beyond-the-standard-model theory predictions.

New physics andCPviolation in hyperon nonleptonic decays

Physical Review D, 2004

The sum of the CP-violating asymmetries A(Λ 0 −) and A(Ξ − −) in hyperon nonleptonic decays is presently being measured by the E871 experiment. We evaluate contributions to the asymmetries induced by chromomagnetic-penguin operators, whose coefficients can be enhanced in certain models of new physics. Incorporating recent information on the strong phases in Ξ → Λπ decay, we show that new-physics contributions to the two asymmetries can be comparable. We explore how the upcoming results of E871 may constrain the coefficients of the operators. We find that its preliminary measurement is already better than the ǫ parameter of K-K mixing in bounding the parity-conserving contributions.

Search for ΔS=2 Nonleptonic Hyperon Decays

Physical Review Letters, 2005

A sensitive search for the rare decays Ω − → Λπ − and Ξ 0 → pπ − has been performed using data from the 1997 run of the HyperCP (Fermilab E871) experiment. Limits on other such processes do not exclude the possibility of observable rates for |∆S| = 2 nonleptonic hyperon decays, provided the decays occur through parity-odd operators. We obtain the branching-fraction limits B(Ω − → Λπ − ) < 2.9 × 10 −6 and B(Ξ 0 → pπ − ) < 8.2 × 10 −6 , both at 90% confidence level.

New Results in Rare Allowed Muon and Pion Decays

International Journal of Modern Physics: Conference Series, 2014

Simple dynamics, few available decay channels, and highly controlled radiative and loop corrections, make pion and muon decays a sensitive means of exploring details of the underlying symmetries. We review the current status of the rare decays: π+ → e+ν (πe2), π+ → e+νγ (πe2γ), π+ → π0e+ν (πe3), and [Formula: see text]. For the latter we report new preliminary values for the branching ratio B(Eγ > 10 MeV , θeγ > 30°) = 4.365 (9) stat (42) syst × 10-3, and the decay parameter [Formula: see text], both in excellent agreement with standard model predictions. We review recent measurements, particularly by the PIBETA and PEN experiments, and near-term prospects for improvement. These and other similar precise low energy studies complement modern collider results materially.

Search for Direct CP Violation in Nonleptonic Decays of Charged Ξ and Λ Hyperons

Physical Review Letters, 2000

A search for direct CP violation in the non-leptonic decays of hyperons has been performed. In comparing the product of the decay parameters, α Ξ α Λ , in terms of an asymmetry parameter, A ΞΛ , between hyperons and anti-hyperons in the charged Ξ → Λπ and Λ → pπ decay sequence, we found no evidence of direct CP violations. The parameter A ΞΛ was measured to be 0.012 ± 0.014.

HyperCP (E871) experiment at Fermilab: search for direct CP violation in hyperon decays

Nuclear Physics B - Proceedings Supplements, 2001

The Fermilab HyperCP experiment has accumulated the world's largest sample of E-and ? hyperon decays within two running periods in 1997 and 1999. The primary goal of the experiment is to search for direct CP =_+ violation in the decay sequences 8-+ A ?r-+ p sr-Tand c + K n' + jj rr+ ?r+. A violation of CP would manifest itself as a difference between the angular distribution of the proton and the antiproton in the A and 7;i helicity frame. The amount of data is enough to reach a statistical sensitivity of 1.4 x 10m4 in the CP violating asymmetry dE* = (as CYA -CYH czr)/(aa QA + '~2 ax). We present an analysis method used to take into account the slight differences in the production of the E-and E' samples. A preliminary result on d=A at the level of a few 10m3 and based on a few percent of the 1997 data will be presented. 0920-5632/O]/% -see front matter 0 2001 Elsevier Science B.v All rights reserved.