共查询到20条相似文献,搜索用时 15 毫秒
1.
I. P. Ivanov N. N. Nikolaev W. Schäfer B. G. Zakharov V. R. Zoller 《The European Physical Journal A - Hadrons and Nuclei》2003,18(2-3):437-440
We review the recent finding of the two-plateau momentum distribution of sea quarks in deep inelastic scattering off nuclei in the saturation regime. The diffractive plateau which dominates for small p measures precisely the momentum distribution of quarks in the beam photon, the rôle of the nucleus is simply to provide an opacity. The plateau for truly inelastic DIS exhibits a substantial nuclear broadening of the momentum distribution. Despite this nuclear broadening, the observed final-state and initial-state sea quark densities do coincide exactly. We emphasize how the saturated sea is generated from the nuclear-diluted Weizsäcker-Williams because of the anti-collinear splitting of gluons into sea quarks.Received: 30 September 2002, Published online: 22 October 2003PACS:
11.80.La Multiple scattering - 13.87.-a Jets in large-Q
2 scattering - 24.85. + p Quarks, gluons, and QCD in nuclei and nuclear processe 相似文献
2.
Z. Liu Y.H. Zhang X.H. Zhou M.L. Liu W.J. Luo Q.Y. Pan Z.G. Gan T. Hayakawa M. Oshima Y. Toh T. Shizima Y. Hatsukawa A. Osa T. Ishii M. Sugawara 《The European Physical Journal A - Hadrons and Nuclei》2002,13(3):277-280
Excited states of 142Ce, populated in deep inelastic reactions of 82Se projectiles bombarding 139La target, have been studied up to medium spins using in-beam γ spectroscopy techniques. Three new levels have been identified
at 2625, 2995, 3834 keV, and assigned as 8+, 9(-) and 11(-), respectively. These new yrast states follow closely the level systematics of the even mass N = 84 isotones. Their strctures have been discussed with the help of empirical shell model calculations.
Received: 2 November 2001 / Accepted: 15 January 2002 相似文献
3.
The ZEUS Collaboration S. Chekanov et al. 《The European Physical Journal C - Particles and Fields》2003,28(2):175-201
Cross sections for e-p neutral current deep inelastic scattering have been measured at a centre-of-mass energy of 318 GeV using an integrated luminosity
of 15.9 pb-1 collected with the ZEUS detector at HERA. Results on the double-differential cross-section in the range 185 < Q
2
< 50 000 GeV2 and 0.0037 < x < 0.75, as well as the single-differential cross-sections , and for Q
2
> 200 GeV2, are presented. To study the effect of Z-boson exchange, has also been measured for Q
2
> 10 000 GeV2. The structure function xF3 has been extracted by combining the e-p results presented here with the recent ZEUS measurements of e+p neutral current deep inelastic scattering. All results agree well with the predictions of the Standard Model.
Received: 2 August 2002 / Revised version: 30 January 2003 / Published online: 24 March 2003 相似文献
4.
S. Descotes-Genon L. Girlanda J. Stern 《The European Physical Journal C - Particles and Fields》2003,27(1):115-134
Multi-flavour chiral perturbation theory (PT) may exhibit instabilities due to vacuum fluctuations of sea pairs. Keeping the fluctuations small would require a very precise fine tuning of the low-energy constants and to , . A small deviation from these critical values - like the one suggested by the phenomenology of OZI-rule violation in the
scalar channel - is amplified by huge numerical factors inducing large effects of vacuum fluctuations. This would lead in
particular to a strong Nf dependence of chiral symmetry breaking (SB) and a suppression of the multi-flavour chiral order parameters. A simple resummation is shown to cure the instability
of PT, but it modifies the standard expressions of some O(p
2
) and O(p
4
) low-energy parameters in terms of observables. On the other hand, for r= m
s
/m > 15, the two-flavour condensate is not suppressed, due to the contribution induced by massive vacuum pairs. Thanks to the latter, the standard two-flavour PT is protected from multi-flavour instabilities and could provide a well-defined expansion scheme in powers of non-strange
quark masses.
Received: 31 July 2002 / Revised version: 6 November 2002 / Published online: 15 January 2003
RID="a"
ID="a" e-mail: sdg@hep.phys.soton.ac.uk
RID="b"
ID="b" e-mail: luca.girlanda@pd.infn.it * Present address: ECT*, Villa Tambosi, Strada delle Tabarelle 286, 38050 Trento, Italy
RID="c"
ID="c" e-mail: stern@ipno.in2p3.fr 相似文献
5.
O. Nachtmann 《The European Physical Journal C - Particles and Fields》2003,26(4):579-596
We relate the structure functions of deep inelastic lepton-nucleon scattering to current-current correlation functions in
a Euclidean field theory depending on a parameter r. The r-dependent Hamiltonian of the theory is P
0
-(1-r)P
3
, with P0 the usual Hamiltonian and P3 the third component of the momentum operator. We show that a small in the structure functions corresponds to the small r limit of the effective theory. We argue that for there is a critical regime of the theory where simple scaling relations should hold. We show that in this framework Regge
behaviour of the structure functions obtained with the hard pomeron ansatz corresponds to a scaling behaviour of the matrix
elements in the effective theory where the intercept of the hard pomeron appears as a critical index. Explicit expressions
for various analytic continuations of the structure functions and matrix elements are given as well as path integral representations
for the matrix elements in the effective theory. Our aim is to provide a framework for truly non-perturbative calculations
of the structure functions at small for arbitrary Q2.
Received: 16 July 2002 / Published online: 9 December 2002
RID="a"
ID="a" e-mail: O.Nachtmann@thphys.uni-heidelberg.de 相似文献
6.
K. Blaum G. Bollen F. Herfurth A. Kellerbauer H.-J. Kluge M. Kuckein E. Sauvan C. Scheidenberger L. Schweikhard 《The European Physical Journal A - Hadrons and Nuclei》2002,15(1-2):245-248
The cyclotron frequencies of singly charged carbon clusters Cn
+ (n ≥ 2) were measured with the Penning-trap mass spectrometer ISOLTRAP at ISOLDE/CERN. The present limit of mass accuracy δm/m = 1.2 . 10-8 and the extent of the mass-dependent systematic shift (δm/m)sys = 1.7(0.6) . 10-10/u
. (m - m
ref) of the setup were investigated for the first time. In addition, absolute mass measurements by use of pure clusters of the
most abundant carbon isotope 12C are now possible at ISOLTRAP.
Received: 21 March 2002 / Accepted: 16 May 2002 / Published online: 31 October 2002
RID="a"
ID="a"Present address: CERN, CH-1211 Geneva 23, Switzerland; e-mail: klaus.blaum@cern.ch 相似文献
7.
The HERA - B Collaboration I. Abt et al. 《The European Physical Journal C - Particles and Fields》2003,26(3):345-355
Using the HERA - B detector, the production cross section has been measured in 920 GeV proton collisions on carbon and titanium targets. The production was tagged via inclusive bottom quark decays into by exploiting the longitudinal separation of decay vertices from the primary proton-nucleus interaction. Both e
+
e
-
and channels have been reconstructed and the combined analysis yields the cross section .
Received: 6 June 2002 / Revised version: 2 September 2002 / Published online: 8 November 2002 相似文献
8.
A.V. Kisselev V.A. Petrov R.A. Ryutin 《The European Physical Journal C - Particles and Fields》2003,26(4):597-600
Quark mass effects are analyzed at high Q2 in the current fragmentation region of DIS. It is found that the linear combination F
2
-2.75F
c
2 scales at large Q2 and small x. We obtained a lower bound for the ratio F
c
2/F
2
which lies very close to the data from HERA.
Received: 14 January 2002 / Revised version: 9 October 2002 Published online: 9 December 2002
RID="a"
ID="a" e-mail: ryutin@th1.ihep.su 相似文献
9.
S. D. Bass 《The European Physical Journal A - Hadrons and Nuclei》2003,18(2-3):327-329
The light-mass exotics with J
PC
= 1- + observed at BNL and CERN may have a simple explanation as dynamically generated resonances in
rescattering in the final-state interaction. This dynamics is mediated by the same anomalous glue which also generates the large mass of the
. OZI-violating processes are also potentially important to
production in proton-proton collisions close to threshold.Received: 30 September 2002, Published online: 22 October 2003PACS:
12.39.Mk Glueball and nonstandard multi-quark/gluon states - 13.75.Lb Meson-meson interactions - 13.75.Cs Nucleon-nucleon interactions (including antinucleons, deuterons, etc.) 相似文献
10.
We present an experimental study of non-linear selective reflection (SR) at a quartz–Cs-vapor interface in a V-type three-level
scheme. The non-linear selective reflection at the Cs D2 resonance line (6
S
1/2F=4→6
P
3/2) is monitored with and without pumping. The sub-Doppler reflection spectrum is observed and the effect of pumping on the
signal of the selective reflection is investigated. The experimental result is in agreement with the theoretical calculation.
Received: 16 April 2002 / Revised version: 12 June 2002 / Published online: 25 September 2002
RID="*"
ID="*"Corresponding author. Fax: +86-351/701-1500, E-mail: zhaojm@sxu.edu.cn 相似文献
11.
The use of mid-infrared polarization spectroscopy (PS) for the detection of CO2 has been demonstrated. The P(13) and P(14) resonances of the (0 00 0)→(1 00 1) transition of CO2 were probed using a single-mode optical parametric generator system to produce a high-intensity laser beam at approximately
2.7 μm. The experiments were performed in an atmospheric pressure CO2 jet and also in a sub-atmospheric pressure gas cell. The experimental results were compared with the results of the time-dependent
density-matrix equations using direct numerical integration. The Zeeman-state structure of the upper and lower energy levels
was included in the multi-state formulation of the density-matrix equations. Fifty-eight Zeeman states and two bath levels
were included in the numerical analysis of the P(14) transition. The measured and calculated PS line shapes were in good agreement,
and the absolute experimental signal level agreed with the theoretical calculation to within a factor of five.
Received: 20 March 2002 / Revised version: 16 August 2002 / Published online: 11 December 2002
RID="*"
ID="*"Present address: Innovative Scientific Solutions Inc., 2766 Indian Ripple Road, Dayton, OH 45 440, USA
RID="**"
ID="**"Corresponding author. Fax: +1-765/494-0539, E-mail: Lucht@purdue.edu
RID="***"
ID="***"Present address: School of Mechanical Engineering, Purdue University, W. Lafayette, IN 47807-2040 USA 相似文献
12.
B. Ananthanarayan S.D. Rindani A. Stahl 《The European Physical Journal C - Particles and Fields》2003,27(1):33-41
We study the prospects of discovering CP-violation in the production of leptons in the reaction at TESLA, an e
+
e
-
linear collider with center-of-mass energies of 500 or even 800 GeV. Non-vanishing expectation values of certain correlations
between the momenta of the decay products of the two leptons would signal the presence of CP-violation beyond the standard model. We study how longitudinal beam polarization
of the electron and positron beams will enhance these correlations. We find that T-odd and T-even vector correlations are well suited for the measurements of the real and imaginary parts of the electric dipole form
factors. We expect measurements of the real part with a precision of roughly 10-20 e cm and of the imaginary part of 10-17
Received: 13 June 2002 / Revised version: 17 October 2002 / Published online: 20 December 2002 相似文献
13.
B. Davids S.M. Austin D. Bazin H. Esbensen B.M. Sherrill I.J. Thompson J.A. Tostevin 《The European Physical Journal A - Hadrons and Nuclei》2002,15(1-2):65-68
A kinematically complete measurement was made of the Coulomb dissociation of 8B nuclei on a Pb target at 83 MeV/nucleon. The cross-section was measured at low relative energies in order to infer the astrophysical
S-factor for the 7Be(p,γ)8B reaction. A first-order perturbation theory analysis of the reaction dynamics including E1, E2, and M1 transitions was employed to extract the E1 strength relevant to neutrino-producing reactions in the solar interior. By fitting the measured cross-section from E
rel = 130 keV to 400 keV, we find S
17(0) = 17.8+1.4
-1.2 eV b. Semiclassical 1st-order perturbation theory and fully quantum-mechanical continuum-discretized coupled-channels analyses
yield nearly identical results for the E1 strength relevant to solar-neutrino flux calculations, suggesting that theoretical reaction mechanism uncertainties need
not limit the precision of Coulomb-breakup determinations of the 7Be(p,γ)8B S-factor. A recommended value of S
17(0) based on a weighted average of this and other measurements is presented. This recommendation implies a revised value for
the theoretical flux of 8B solar neutrinos, which is also given.-1
Received: 21 March 2002 / Accepted: 16 May 2002 / Published online: 31 October 2002
RID="a"
ID="a"Present address: Kernfysisch Versneller Instituut, Zernikelaan 25, 9747 AA Groningen, The Netherlands; e-mail: davids@kvi.nl 相似文献
14.
We present the first photoacoustic spectrometer for gas sensing employing both the fundamental and the frequency-doubled radiation
of a continuously tunable high-pressure CO2 laser with room temperature operation. A quasi-phase-matched diffusion-bonded GaAs crystal is used in the system for second-harmonic
generation. A pulsed photoacoustic detection scheme with a non-resonant cell, equipped with an 80-microphone array, is employed.
The wide continuous tuning range in the fundamental (9.2–10.7 μm) and the frequency-doubled (4.6–5.35 μm) regimes, together
with the narrow linewidth of 540 MHz (0.018 cm-1) for the 10-μm region and of 1050 MHz (0.0315 cm-1) for the 5-μm region, allow the measurement of gas mixtures, individual species and isotope discrimination. This is illustrated
with measurements on NO and CO2. The measured isotope ratio 15
NO/14
NO=(3.58±0.55)×10-3 agrees well with the literature (3.700×10-3) and demonstrates the good selectivity of the system.
Received: 30 April 2002 / Revised version: 10 June 2002 / Published online: 2 September 2002
RID="*"
ID="*"Corresponding author. Fax: +41-1/633-1077, E-mail: sigrist@iqe.phys.ethz.ch 相似文献
15.
In the resonance region we have precisely determined the electromagnetic properties of the
-resonance, in particular the E2/M1 ratio
. For pion electroproduction recent experimental data from Mainz, Bates, Bonn and JLab for Q2 up to 4.0 (GeV/c)2 have been analyzed with the isobar model MAID. The extracted E2/M1 ratio shows, starting from a small and negative value at the real photon point, a clear tendency to cross zero, and becomes positive with increasing Q2. This is a possible indication of a very slow approach toward the pQCD region. The C2/M1 ratio near the photon point is found as
. At high Q2, the absolute value of the ratio is strongly increasing, a further indication that pQCD is not yet reached. The electromagnetic-transition form factors of the
excitation are parameterized and fitted to the electroproduction data. This also shows a zero-crossing of the electric form factor GE* at
(GeV/c)2.Received: 1 November 2002, Published online: 15 July 2003PACS:
13.40.Gp Electromagnetic form factors - 13.60.Le Meson production - 14.20.Gk Baryon resonances with S=0 - 25.20.Lj Photoproduction reactions 相似文献
16.
V.K. Henner P.G. Frick T.S. Belozerova V.G. Solovyev 《The European Physical Journal C - Particles and Fields》2002,26(1):3-7
We demonstrate the advantages of the wavelet analysis (WA) for resolving the structures in experimental data on e
+
e
-
annihilation into hadron states with quantum numbers of meson. The WA yields a useful set of starting conditions for analysis of states with multiresonance unitary Breit-Wigner method. We also apply the WA for the ratio R
e+e-
.
Received: 4 February 2002 / Revised version: 28 August 2002 / Published online: 18 October 2002
RID="a"
ID="a" e-mail: vhenner@python.physics.louisville.edu and henner@psu.ru 相似文献
17.
J. P. Wessels 《The European Physical Journal A - Hadrons and Nuclei》2003,18(2-3):521-525
In this paper the latest results from the analysis of e
+
e
--pairs emitted in Pb + Au collisions at 40 AGeV/c and a combined analysis of all data available at 158 AGeV/c are presented. The enhancement of low-mass e
+
e
--pairs (m
ee
> 0.2 GeV/c
2) with respect to the expected yield from hadron decays first reported at 158 AGeV/c is also found at 40 AGeV/c and is even larger there. Comparing to various theoretical models based on
annihilation, the data can only be reproduced, if the properties of the intermediate
in the hot and dense medium are modified. Hadron data taken at the same beam energies sheds light on the dynamical evolution of the fireball and addresses the question whether the medium modification is linked to baryon density rather than temperature. In the future e
+
e
--pairs emitted in heavy-ion collisions will be measured at the LHC with the ALICE Transition Radiation Detector (TRD). Here, special emphasis will be put on the production of heavy vector mesons (
,
).Received: 30 September 2002, Published online: 22 October 2003PACS:
25.75.-q Relativistic heavy-ion collisions - 12.38.Mh Quark-gluon plasma - 13.85.Qk Inclusive production with identified leptons, photons, or other nonhadronic particles 相似文献
18.
F. Herfurth A. Kellerbauer F. Ames G. Audi D. Beck K. Blaum G. Bollen O. Engels H.-J. Kluge D. Lunney R.B. Moore M. Oinonen E. Sauvan C. Scheidenberger S. Schwarz G. Sikler C. Weber 《The European Physical Journal A - Hadrons and Nuclei》2002,15(1-2):17-20
Mass measurements of 34Ar, 73-78Kr, and 74,76Rb were performed with the Penning-trap mass spectrometer ISOLTRAP. Very accurate Q
EC-values are needed for the investigations of the
t-value of 0+ → 0+ nuclear β-decays used to test the standard model predictions for weak interactions. The necessary accuracy on the Q
EC-value requires the mass of mother and daughter nuclei to be measured with δm/m ⩽ 3 . 10-8. For most of the measured nuclides presented here this has been reached. The 34Ar mass has been measured with a relative accuracy of 1.1 . 10-8. The Q
EC-value of the 34Ar 0+ → 0+ decay can now be determined with an uncertainty of about 0.01%. Furthermore, 74Rb is the shortest-lived nuclide ever investigated in a Penning trap.
Received: 21 March 2002 / Accepted: 16 May 2002 / Published online: 31 October 2002
RID="a"
ID="a"e-mail: frank.herfurth@cern.ch 相似文献
19.
We consider the Navier-Stokes equation on a two dimensional torus with a random force which is white noise in time, and excites
only a finite number of modes. The number of excited modes depends on the viscosity ν, and grows like ν
-3
when ν goes to zero. We prove that this Markov process has a unique invariant measure and is exponentially mixing in time.
Received: 14 March 2002 / Accepted: 7 May 2002 Published online: 22 August 2002 相似文献
20.
T. Beier H. Häffner N. Hermanspahn S. Djekic H.-J. Kluge W. Quint S. Stahl T. Valenzuela J. Verdú G. Werth 《The European Physical Journal A - Hadrons and Nuclei》2002,15(1-2):41-44
We describe a double-Penning-trap experiment suitable for testing QED in strong fields by determining the electronic g-factor of a single hydrogen-like ion in its ground state. Our measurements on 12C5 + reach a relative accuracy of 2×10-9, where the largest uncertainty results from the mass of the electron. Together with equally precise theoretical predictions
therefore, it is possible to evaluate a new value for the electron's mass. The possibilities to obtain other fundamental constants
and nuclear parameters are lined out.
Received: 21 March 2002 / Accepted: 16 May 2002 / Published online: 31 October 2002
RID="a"
ID="a"e-mail: t.beier@gsi.de 相似文献