On the muon neutrino mass Angelov, N.; Balestra, F.; Batusov, Yu ...
Nuclear physics. A,
12/2006, Letnik:
780, Številka:
1
Journal Article
Recenzirano
Odprti dostop
During the runs of the PS 179 experiment at LEAR of CERN, we photographed an event of antiproton–Ne absorption, with a complete
π
+
→
μ
+
→
e
+
chain. From the vertex of the reaction a very slow ...energy
π
+
was emitted. The
π
+
decays into a
μ
+
and subsequently the
μ
+
decays into a positron. At the first decay vertex a muon neutrino was emitted and at the second decay vertex an electron neutrino and a muon antineutrino. Measuring the pion and muon tracks and applying the momentum and energy conservation and using a classical statistical interval estimator, we obtained an experimental upper limit for the muon neutrino mass:
m
ν
<
2.2
MeV
at a 90% confidence level. A statistical analysis has been performed of the factors contributing to the square value of the neutrino mass, to deduce the possibility to reach experimentally the lowest muon neutrino mass limit from the
π
→
μ
ν
decays.
A current peak has been observed and measured in ionic electrolytic current of a glutamic acid aqueous solution, placed in a static magnetic field of flux density of 40 microT, with a superimposed ...low-frequency alternating magnetic field of flux density of 40 nT. The peak occurs at the frequency of the cyclotronic resonance of the molecular mass of a single charged glutamic acid ion, placed in a magnetic flux density equal to that of the static field. The amplitude of the current peak is about 30% of the background electrolytic current. Qualitative considerations and a listing of unsolved problems related to the phenomenology are given. The result is the first contribution to the study we have undertaken on the effects of low-frequency alternating electromagnetic fields on the ionic current of amino acid aqueous solutions which are the basic structural units of the proteins.
The Collins and Sivers asymmetries for charged hadrons produced in deeply inelastic scattering on transversely polarised protons have been extracted from the data collected in 2007 with the CERN SPS ...muon beam tuned at 160 GeV/c. At large values of the Bjorken x variable non-zero Collins asymmetries are observed both for positive and negative hadrons while the Sivers asymmetry for positive hadrons is slightly positive over almost all the measured x range. These results strongly support the present theoretical interpretation of these asymmetries, in terms of leading-twist quark distribution and fragmentation functions.
Multiplicities of charged hadrons produced in deep inelastic muon scattering off a
6
LiD target have been measured as a function of the DIS variables
x
Bj
,
Q
2
,
W
2
and the final state hadron ...variables
p
T
and
z
. The
distributions are fitted with a single exponential function at low values of
to determine the dependence of
on
x
Bj
,
Q
2
,
W
2
and
z
. The
z
-dependence of
is shown to be a potential tool to extract the average intrinsic transverse momentum squared of partons,
, as a function of
x
Bj
and
Q
2
in a leading order QCD parton model.
The ratio of the total exclusive production cross sections for
η' and
η mesons has been measured in the
pp reaction at
p
beam=3.67 GeV/
c. The observed
η
′/
η ratio is (0.83±0.11
+0.23
−0.18)×10
−2 ...from which the exclusive
η
′ meson production cross section is determined to be (1.12±0.15
+0.42
−0.31) μb. Differential cross section distributions have been measured. Their shape is consistent with isotropic
η
′ meson production.
The COMPASS experiment at the CERN SPS has studied the diffractive dissociation of negative pions into the π- π- π+ final state using a 190 GeV/c pion beam hitting a lead target. A partial wave ...analysis has been performed on a sample of 420,000 events taken at values of the squared 4-momentum transfer t' between 0.1 and 1 GeV2/c2. The well-known resonances a1(1260), a2(1320), and π2(1670) are clearly observed. In addition, the data show a significant natural-parity exchange production of a resonance with spin-exotic quantum numbers J(PC)=1-+ at 1.66 GeV/c2 decaying to ρπ. The resonant nature of this wave is evident from the mass-dependent phase differences to the J(PC)=2-+ and 1++ waves. From a mass-dependent fit a resonance mass of (1660±10(-64)(+0)) MeV/c2 and a width of (269±21(-64)(+42)) MeV/c2 are deduced, with an intensity of (1.7±0.2)% of the total intensity.
We present a LO evaluation of helicity densities of valence, Δuv+Δdv, non-strange sea, Δu¯+Δd¯, and strange quarks, Δs (assumed to be equal to Δs¯). They have been obtained from the inclusive ...asymmetry A1,d and the semi-inclusive asymmetries A1,dπ+, A1,dπ−, A1,dK+, A1,dK− measured in polarised deep inelastic muon–deuteron scattering. The full deuteron statistics of COMPASS (years 2002–2004 and 2006) has been used. The data cover the range Q2>1 (GeV/c)2 and 0.004<x<0.3. Both non-strange densities are found to be in a good agreement with previous measurements. The distribution of Δs(x) is compatible with zero in the whole measured range, in contrast to the shape of the strange quark helicity distribution obtained in most LO and NLO QCD fits. The sensitivity of the values of Δs(x) upon the choice of fragmentation functions used in the derivation is discussed.
The semi-inclusive difference asymmetry Ah+−h− for hadrons of opposite charge has been measured by the COMPASS experiment at CERN. The data were collected in the years 2002–2004 using a 160 GeV ...polarised muon beam scattered off a large polarised 6LiD target in the kinematic range 0.006<x<0.7 and 1<Q2<100 (GeV/c)2. In leading order QCD (LO) the deuteron asymmetry Ah+−h− measures the valence quark polarisation and provides an evaluation of the first moment of Δuv+Δdv which is found to be equal to 0.40±0.07(stat.)±0.06(syst.) over the measured range of x at Q2=10 (GeV/c)2. When combined with the first moment of g1d previously measured on the same data, this result favours a non-symmetric polarisation of light quarks Δu¯=−Δd¯ at a confidence level of two standard deviations, in contrast to the often assumed symmetric scenario Δu¯=Δd¯=Δs¯=Δs.
We present a determination of the gluon polarization ΔG/G in the nucleon, based on the helicity asymmetry of quasi-real photoproduction events, Q2<1 (GeV/c)2, with a pair of large transverse-momentum ...hadrons in the final state. The data were obtained by the COMPASS experiment at CERN using a 160 GeV polarized muon beam scattered on a polarized 6LiD target. The helicity asymmetry for the selected events is 〈A∥/D〉=0.002±0.019(stat)±0.003(syst). From this value, we obtain in a leading-order QCD analysis ΔG/G=0.024±0.089(stat)±0.057(syst) at xg=0.095 and μ2≃3 (GeV/c)2.
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