636 research outputs found
Evolution of the nucleon structure in the lightest nuclei
The evolution of the nucleon structure as a function of atomic mass A is
considered for the first time for the lightest nuclei, D, 3H, 3He and 4He, with
an approach based on the Bethe-Salpeter formalism. We show that the pattern of
the oscillation of the structure functions ratio r^A(x) = F_2^A/F_2^N(D) varies
with A by changing the position of the cross-over point x_3 in which r^A(x) =
1, unlike the pattern for nuclei with masses A larger than 4, where only the
amplitude of the oscillation changes. In particular we find that the pattern of
F_2(x) modifications is controlled with the values (1 - x_3) = 0.32 (D/N), 0.16
(3He/D) and 0.08 (4He/D). The obtained results follow from the relativistic
consideration of the nuclear structure and allow us to define a whole class of
modifications of the partonic distributions in the nucleon bound in a nucleus.
The EMC effect is explained as a particular case of the considered class.Comment: Preprint of the publication submitted to Physics Letters B. 12 pages
(LaTeX) including 3 encapsulated figure
Relating the proton, neutron and deuteron structure functions in the covariant Bethe-Salpeter formalism
The neutron structure function F2n(x) is evaluated within the kinematic range
10**(-3)<x<1 from the deuteron and proton data by employing relativistic
theoretical description of F2D(x) and several assumptions on the hihg-x
asymptotics of F2n(x)/F2p(x). It is shown that new measurements of F2D(x) in
the range 0.6<x<0.8 would substantially improve understanding of the relation
between d and u valence quarks in the limit x -> 1.Comment: Revised on January 20, 2004: Modified Figs. 2 and 3 and the reference
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On the universality of the and dependence of the EMC effect and its relation to parton distributions in nuclei
It is shown that the latest results from the NMC (CERN) and E665 (Fermilab)
groups on obtained in the shadowing region bring new
evidence of the universal dependence of distortions made in a free-nucleon
structure function by a nuclear medium.
The observed universality implies that one can consider separately hard
( 4) and soft ( 4) parton distribution distortions. Soft
distortions, which result in differencies between the deep-inelastic scattering
cross-sections for nuclei with masses , 4, can be explained as
a consequence of the nuclear density variation, independent of in the range
0.001 0.7.
It is found that nuclear shadowing begins at = 0.0615
0.0024, independent of , which is consistent with models that allow for
three-parton recombination processes.Comment: 11 pages (LaTeX) and 4 Postscript figures in uuencoded compressed
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Search for light pseudoscalar sgoldstino in K- decays
A search for the light pseudoscalar sgoldstino production in the three body
K- decay K-->pipi0P has been performed with the ISTRA+ detector exposed to the
25 GeV negative secondary beam of the U70 proton synchrotron. No signal is
seen. An upper limit for the branching ratio Br(K->pipi0P), at 90% confidence
level, is found to be around 9*10**-6 in the effective mass m(P) range from 0
till 200 MeV, excluding the region near m(pi0) where it degrades to 3.5*10**-5.Comment: 10 pages, LATEX, 8 EPS figures, revised version, to be published in
Phys.Lett.
High statistic measurement of the K- -> pi0 e- nu decay form-factors
The decay K- -> pi0 e- nu is studied using in-flight decays detected with the
ISTRA+ spectrometer. About 920K events are collected for the analysis. The
lambda+ slope parameter of the decay form-factor f+(t) in the linear
approximation (average slope) is measured: lambda+(lin)= 0.02774 +-
0.00047(stat) +- 0.00032(syst). The quadratic contribution to the form-factor
was estimated to be lambda'+ = 0.00084 +- 0.00027(stat) +- 0.00031(syst). The
linear slope, which has a meaning of df+(t)/dt|_{t=0} for this fit, is lambda+
= 0.02324 +- 0.00152(stat) +- 0.00032(syst). The limits on possible tensor and
scalar couplings are derived: f_{T}/f_{+}(0)=-0.012 +- 0.021(stat) +-
0.011$(syst), f_{S}/f_{+}(0)=-0.0037^{+0.0066}_{-0.0056}(stat) +- 0.0041(syst).Comment: 11 pages, 8 figures. Accepted by Phys.Lett.
Measurement of the Dalitz plot slope parameters for K- -> pi0 pi0 pi- decay using ISTRA+ detector
The Dalitz plot slope parameters g, h and k for the K- -> pi0 pi0 pi- decay
have been measured using in-flight decays detected with the ISTRA+ setup
operating in the 25 GeV negative secondary beam of the U-70 PS. About 252 K
events with four-momenta measured for the pi- and four involved photons were
used for the analysis. The values obtained g=0.627+/-0.004(stat)+/-0.010(syst),
h=0.046+/-0.004(stat)+/-0.012(syst), k=0.001+/-0.001(stat)+/-0.002(syst) are
consistent with the world averages dominated by K+ data, but have significantly
smaller errors.Comment: LaTeX, 10 pages, 8 eps-figures, update of IHEP 2002-1
High statistic study of the K- -> pi0 mu- nu decay
The decay K- -> pi0 mu- nu has been studied using in-flight decays detected
with the "ISTRA+" spectrometer. About 540K events were collected for the
analysis. The lambda+ and lambda0 slope parameters of the decay form-factors
f+(t), f0(t) have been measured : lambda+ = 0.0277+-0.0013 (stat)+-0.0009
(syst), lambda0 = 0.0183+-0.0011(stat)+-0.0006(syst), and
d(lambda0)/d(lambda+)=-0.348. The limits on the possible tensor and scalar
couplings have been derived: fT/f+(0)=-0.0007 +- 0.0071, fS/f+(0)=0.0017 +-
0.0014. No visible non-linearity in the form-factors have been observed.Comment: 11 pages, 8 EPS figures, accepted by Physics Letters
High statistics study of the K- -> pi0 e- nu decay
The decay K- -> pi0 e- nu has been studied using in-flight decays detected
with the "ISTRA+" spectrometer working at the 25 GeV negative secondary beam of
the U-70 PS. About 550K events were used for the analysis. The lambda+
parameter of the vector form-factor has been measured: lambda+ = 0.0286 +-
0.0008 (stat) +- 0.0006(syst). The limits on the possible tensor and scalar
couplings have been obtained: f(T)/f+(0)=0.021 +0.064 -0.075 (stat) +-
0.026(syst) ; f(S)/f+(0)=0.002 +0.020 -0.022 (stat) +- 0.003(syst)Comment: LaTeX-2e, epsfig.sty, 10 pages, 7 figures in EPS forma
Spin asymmetry A_1^d and the spin-dependent structure function g_1^d of the deuteron at low values of x and Q^2
We present a precise measurement of the deuteron longitudinal spin asymmetry
A_1^d and of the deuteron spin-dependent structure function g_1^d at Q^2 < 1
GeV^2 and 4*10^-5 < x < 2.5*10^-2 based on the data collected by the COMPASS
experiment at CERN during the years 2002 and 2003. The statistical precision is
tenfold better than that of the previous measurement in this region. The
measured A_1^d and g_1^d are found to be consistent with zero in the whole
range of x.Comment: 17 pages, 10 figure
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