Determination of the average lifetime of bottom hadrons

We have determined the average lifetime of hadrons containing b quarks produced in e⁺e^? annihilation to be

$\text{τ}\text{B}\text{=}\text{1.83}\text{+0.83}\text{+0.37}\text{?}\text{?0.34}\text{×10}{}^{\mathrm{?12}}\text{s}$

. Our method uses charged decay products from both non-leptonic and semileptonic decay modes.     

A measurement of the average bottom hadron lifetime

The average b hadron lifetime, т_b, has been measured using approximately 3.5 million hadronic events collected with the OPAL detector at LEP between 1991 and 1994. A lifetime tag based_ on a neural network algorithm was used to select Z⁰ → bb events. A secondary vertex reconstructed on the opposite side from the b-tag was used to measure the b hadron decay length. This was combined with an estimate of the b hadron momentum, allowing the b hadron decay time to be evaluated. The lifetime, т_b = 1.611 ± 0.010 (stat) ± 0.027 (syst) ps, was extracted from a fit involving the distribution of the 95620 decay times reconstructed in the data and the corresponding distribution in Monte Carlo.     

A precision measurement of the neutral Pion lifetime via the Primakoff effect

The main parameters and technical features of the PrimEx experiment conducting in Jefferson Lab (USA) are presented. One of the main parts of the PrimEx setup-electromagnetic calorimeter is described in details. Value of π⁰ meson decay width into two γ-quanta, obtained from PrimEx 2004 year data is Γ(π^o → 2γ) = 7.82 eV 2.2% (stat.) 2.1% (syst.)     

Improving the precision of fluorescence lifetime measurement using a streak camera

Streak camera has high temporal resolution and high sensitivity, and is a powerful tool in biomedical study to measure fluorescence lifetime and perform fluorescence lifetime imaging. However, nonuniformity of the gain in the streak tube and nonlinearity of the sweeping speed limit the precision of fluorescence lifetime measurement, particularly when fluorescence lifetimes are short. We have constructed a two-photon excitation fluorescence lifetime measurement system that is based on a synchroscan streak camera and have developed accordingly a method to correct the effect of gain nonuniformity and nonlinearity of sweeping speed on the measurement precision. A continuous-wave laser of high stability is used to calibrate the gain of the streak camera, and a Fabry-Perot etalon is used to calibrate the nonlinearity of the sweeping speed. Fitting algorithms are used to correct the gain of the streak camera and nonlinearity of the sweeping speed respectively, which significantly improves the measurement precision of the system, as characterized through the fluorescence lifetime of the short-lived fluorescence dye, Rose Bengal. Experimental results show that the measurement fluctuation of the lifetime has been improved from more than 10% to 2% after correcting the effects of gain nonuniformity and sweeping speed nonlinearity.     

Measurement of the lifetime of hadrons containing the b-quark

Data collected with the High Resolution Spectrometer at PEP, corresponding to an integrated luminosity of 200 pb⁻¹ of e⁺e⁻ annihilation at 29 GeV, were used to measure the mean lifetime of hadrons containing the bottom quark. The lifetime was determined using the impact parameter method on events containing a high-transverse-momentum electron. The result, based on a sample of 301 events, is τ_B = 1.02 ±_0.39^0.42 ps, where the indicated errors include both statistics and systematics.     

A high precision beam-foil meanlife measurement of the 1s 3p1P level in He I

A beam-foil measurement of the meanlife of the 1s 3p ¹ P level in He I has been made and yields the value 1.7225±0.0046 ns. The measurement was made with standard beam-foil techniques and equipment, but special attention was devoted to minimizing sources of uncertainty. The precision far exceeds that of previous beam-foil meanlife measurements and demonstrates that the beam-foil technique is capable of high precision and is competitive with and more flexible than methods such as resonant laser excitation.     

A measurement of the Ω− lifetime

In an experiment at the CERN-SPS charged-hyperon beam, a sample of $\text{2500 Ω}{}^{\mathrm{?}}\text{→ ΛK}{}^{\mathrm{?}}$ decays has been collected at Ω^? momenta of 98.5 and 115 GeV/c. The Ω^? lifetime is found to be $\text{τ}{}_{\mathrm{\Omega }}\text{= (0.822 ± 0.028) × 10}{}^{\mathrm{?10}}\text{s}$.     

Predicted new class of hadrons and the average parton charge

A semiempirical mass formula of a particular parton model, in which it is assumed that partons are highly charged, requires the existence of a new class of hadrons, at least one of which must be absolutely stable and whose masses are of the order of a few GeV. Several experiments (with accelerators and cosmic rays) appear to support the notions that partons are highly charged and that a new class of hadrons exists. The recently reported particle of Niu et al., with an apparent lifetime ～10^?13 sec, may be a member of the new predicted class.     

A precise measurement of the tau lifetime

The tau lepton lifetime has been measured with the events collected by the DELPHI detector at LEP in the years 1991-1995. Three different methods have been exploited, using both one-prong and three-prong decay channels. Two measurements have been made using events in which both taus decay to a single charged particle. Combining these measurements gave . A third measurement using taus which decayed to three charged particles yielded These were combined with previous DELPHI results to measure the tau lifetime, using the full LEP1 data sample, to be .Received: 12 November 2003, Revised: 1 June 2004, Published online: 20 July 2004     

Compositional dependences of average positron lifetime in binary As-S/Se glasses

Compositional dependence of average positron lifetime is studied systematically in typical representatives of binary As-S and As-Se glasses. This dependence is shown to be in opposite with molar volume evolution. The origin of this anomaly is discussed in terms of bond free solid angle concept applied to different types of structurally-intrinsic nanovoids in a glass.     

Study of baryon production mechanism in ee annihilation into hadrons

The mechanism of baryon-anti-baryon pair production in e⁺e⁻ annihilation into hadrons has been studied using the TOPAZ detector at the TRISTAN e⁺e⁻ collider at an average center-of-mass energy of 58 GeV. The distributions of various correlations were compared with two prominent models: the cluster-fragmentation model and the string-fragmentation model. We rejected the cluster-fragmentation model at the 90% C.L. Furthermore, in the context of the string-fragmentation model, we favor the “popcorn” model, rejecting the “diquark” model, where a diquark is considered to be a fundamental entity, at the 95% C.L.     

A measurement of the lifetime of the Λ3 H hypernucleus

The mean lifetime of the hypernucleus _Λ³H has been measured in a helium bubble chamber with the result, τ(_Λ³H)=(2.46_?0.41^+0.62)×10^?10 sec, based on 16 examples of the decay mode _Λ³H→π^?+³He and 24 examples of the decay mode _Λ³H→π^?+p+d. The decay branching ratio R₃ = Γ(_Λ³H → π^?+^{3He)/Γ(_Λ3H → all π? modes}) has been estimated to be 0.30 ± 0.07.     

New measurement of the Λ lifetime

A new measurement of the Λ lifetime has been performed using three different K^?p experiments in three different hydrogen bubble chambers. The final result based on 36 000 Λ decays leads to a lifetime of (2.626 +- 0.020) × 10^?10 s which is definitely larger than the present accepted value of (2.521 +- 0.021) × 10^?10 s.     

A measurement of the photon structure function F 2γ at an average Q 2 of 12 GeV2/ c 4

The hadronic photon structure functionF ₂ ^γ has been measured in theQ ² range from 4 to 30 GeV²/c ⁴ and down tox values of order 0.001, using data taken with the DELPHI detector at LEP between 1991 and 1993. A comparison is made with severalF ₂ ^γ parameterizations with special emphasis on their lowx behaviour. A result on theQ ² evolution ofF ₂ ^γ is presented.     

A high statistics measurement of the Lambda(+)(c) lifetime

A high statistics measurement of the Lambda(+)(c) lifetime from the Fermilab fixed-target FOCUS photoproduction experiment is presented. We describe the analysis technique with particular attention to the determination of the systematic uncertainty. The measured value of 204.6 +/- 3.4 (stat) +/- 2.5 (syst) fs from 8034 +/- 122 Lambda(+)(c)-->pK(-)pi(+) decays represents a significant improvement over the present world average.     

The particle emitter size dependence on energy in ee annihilations into hadrons

The nearly energy independent hadron emitter dimension r, measured in e⁺e⁻ annihilation in the energy range 10 to 91 GeV via the Bose–Einstein correlation of two identical charged pions, is shown to be well accounted for by choosing the hadron jets as independent pion sources. To this end the known normalised factorial cumulant moments dependence on particle sources is adapted to the Bose–Einstein correlation formalism to yield a relation between r and these sources. This approach is also able to account for the measured r values obtained for the Z⁰ decays into two and three hadron jets. Finally the estimated r value of the hadronic (9.46) decay via three gluons is expected to be higher by about 6 to 11% over that predicted for its one photon hadronic decay mode.