Search for the weak decay of a lightly bound H0 dibaryon

We present results of a search for a new form of hadronic matter, a six-quark, dibaryon state called the H0, a state predicted to exist in several theoretical models. Analyzing data collected by experiment E799-II at Fermilab, we searched for the decay H0-->Lambdappi(-) and found no candidate events. We place an upper limit on [B(H0-->Lambdappi(-))dsigma(H)/dOmega]/(dsigma(Xi)/dOmega) and, in the context of published models, exclude the region of lightly bound mass states just below the LambdaLambda mass threshold, 2.194相似文献   

Search for weak transitions in the decay of125Sb and accurate gamma intensities

The weak transitions in the decay of¹²⁵Sb have been investigated through gamma ray measurements with high resolution X-ray and with large volume Ge(Li) detectors. The 172.6, 178.8 and 198.5 keV gamma rays are confirmed, while others previously reported were not. Accurate intensities were obtained for the stronger transitions. The weighted averages of these intensities which cover the range of 116 to 670 keV are useful for calibration of Ge(Li) systems.     

Search for narrow dibaryon resonances in neutral pion photoproduction from the deuteron

The reaction γd↦π⁰ X has been measured with TAPS at MAMI in the energy range E _γ = 140-300 MeV. Using the Glasgow tagging spectrometer a photon energy resolution of 0.8 MeV was achieved. The energy excitation functions of integral and differential total cross-sections show no structures of statistical significance > 2σ. Upper limits for the production of narrow isoscalar or isovector dibaryons with masses m? 2100 MeV/c² were deduced. They are in the range 2-5 μb averaged over the 0.8 MeV energy resolution. Received: 25 October 2000 / Accepted: 24 November 2000     

Search for dibaryon production in 4Hep interactions at intermediate energies

With the aid of the 2-m liquid-hydrogen bubble chamber constructed at the Institute of Theoretical and Experimental Physics (ITEP, Moscow), ⁴Hep interactions are studied at primary alpha-particle momenta of 2.7 and 5 GeV/c (the respective kinetic energies of primary protons in the ⁴He rest frame are T _p=220 and 620 MeV). The effective-mass spectra of two nucleons from the reactions ⁴Hep → dppn and ⁴Hep → pppnn are analyzed. The effective-mass spectrum of the two-proton system produced in the quasielastic-charge-exchange reaction p ⁴He → n _F(pp)d at T _p=620 MeV (here, n _F stands for the fast neutron in the ⁴He rest frame) shows a narrow peak, which is indicative of the existence of a dibaryon whose mass and width are M _2p =2008±13 MeV and Γ _2p =0±5 MeV, respectively. In the mass spectra of the two-proton system from the reactions p ⁴He → n _F(pp)d and p ⁴He → p _F(pp)(nn), narrow threshold peaks are also found at a mass of M _2p ?1878–1879 MeV.     

Evidence for a bound H dibaryon from lattice QCD

We present evidence for the existence of a bound H dibaryon, an I=0, J=0, s=-2 state with valence quark structure uuddss, at a pion mass of m(π)～389 MeV. Using the results of lattice QCD calculations performed on four ensembles of anisotropic clover gauge-field configurations, with spatial extents of L～2.0, 2.5, 3.0, and 3.9 fm at a spatial lattice spacing of b(s)～0.123 fm, we find an H dibaryon bound by B(∞)(H)=16.6±2.1±4.6 MeV at a pion mass of m(π)～389 MeV.     

Ultrahigh-energy cosmic rays and stable H dibaryon

It is shown that an instanton-induced interaction between quarks produces a very deeply bound H dibaryon with mass below 2M _N , viz., M _H =1718 MeV. Therefore the H dibaryon is predicted to be a stable particle. The reaction of photodisintegration of the H dibaryon to 2Λ in the course of its motion in the cosmic microwave background will result in a new possible cutoff in the cosmic-ray spectrum. This provides an explanation for the ultrahigh-energy cosmic ray events observed above the GZK cutoff as being the result of the strong interaction of high-energy H dibaryons from cosmic rays with nuclei in the Earth’s atmosphere. Pis’ma Zh. éksp. Teor. Fiz. 70, No. 8, 483–486 (25 October 1999) Published in English in the original Russian journal. Edited by Steve Torstveit.     

Search for tensor couplings in the weak interaction

The existence of exotic couplings in the weak interaction can be tested by a precise measurement of the β-ν angular correlation parameter a in nuclear beta decay. In the case of ⁶He, the ratio of tensor and axial-vector couplings can be determined. The goal of the LPC Trap experiment is to improve the limits on the existence of tensor currents. The LPCTrap setup is installed on the low energy beam line LIRAT of the SPIRAL/GANIL facility. The ⁶He⁺ ions are confined in a novel transparent Paul trap allowing the detection in coincidence of both the β-particle and the recoil ion. The detection setup enables to detect the position and energy of these two particles. The a parameter can then be extracted from the time of flight spectrum of the recoil ions. The first ⁶He⁺ decay events were observed in May 2005 during a commissioning run. Over 10⁵ coincidence events have been recorded during a second run in July 2006.     

Search for rare decay modes of Californium

The results ofmeasurements on the search for the cluster decay of ²⁵²Cfnucleus with the emission ofthe bound state of eight neutrons are presented. The value of an upper limit ofthe partial probabilities for this process is obtained, which contradicts to the results ofthe recently published work, in which the possible existence of octaneutron was declared. Based on the results of our measurements, the estimations for the upper limits ofpartial probabilities for the emission of ²⁰C, ²⁴O, ²⁸Ne, 32Mg, ³⁶Si, ⁴⁰S, ⁴⁰P, and ⁴⁰Si clusters are given. The estimation for the upper limit of the partial probability of ²⁵⁰Cf decay with the emission of the bound state of six neutrons is also obtained.     

Search for cluster decay of114Ba

A search for the¹²C decay of¹¹⁴Ba produced in the⁵⁸Ni(⁵⁸Ni,2n) reaction was performed by using polycarbonate track detectors. Assuming the total half-life of¹¹⁴Ba to be 0.1 s, the lower limit T _c ≥10³ s for the partial¹²C-decay half-life was established.     

Search for the invisible decay of neutrons with KamLAND

The Kamioka Liquid scintillator Anti-Neutrino Detector is used in a search for single neutron or two-neutron intranuclear disappearance that would produce holes in the -shell energy level of (12)C nuclei. Such holes could be created as a result of nucleon decay into invisible modes (inv), e.g., n--> 3v or nn--> 2v. The deexcitation of the corresponding daughter nucleus results in a sequence of space and time-correlated events observable in the liquid scintillator detector. We report on new limits for one- and two-neutron disappearance: tau(n--> inv) > 5.8 x 10(29) years and tau (nn--> inv) > 1.4 x 10(30) years at 90% C.L. These results represent an improvement of factors of approximately 3 and >10(4) and over previous experiments.     

Search for time dependence of the Cs decay constant

Starting from June 2011, the activity of a ¹³⁷Cs source has been measured by means of a HPGe detector installed deep underground in the Gran Sasso Laboratory. Over 5100 hourly recorded energy spectra have been collected in 217 days. These data allowed the search for time variations of the decay constant with periods from a few hours to 1 year. No signal with amplitude larger than 9.6⋅10⁻⁵$9.6\cdot {10}^{-5}$ at 95% C.L. has been detected. These limits are more than one order of magnitude lower than the values on the oscillation amplitude reported in literature. In particular, for 1 year period an oscillation amplitude larger than 8.5⋅10⁻⁵$8.5\cdot {10}^{-5}$ has been excluded at 95% C.L., independently of the phase. The same data give a value of 29.96±0.08$29.96\pm 0.08$ years for the ¹³⁷Cs half-life, in good agreement with the world mean value of 30.05±0.08$30.05\pm 0.08$ years.