共查询到20条相似文献,搜索用时 359 毫秒
1.
A. Kondrat J. E. Hamann-Borrero N. Leps M. Kosmala O. Schumann A. K?hler J. Werner G. Behr M. Braden R. Klingeler B. Büchner C. Hess 《The European Physical Journal B - Condensed Matter and Complex Systems》2009,70(4):461-468
We have prepared the newly discovered Fe-based superconducting material LaO1-xFxFeAs (0 ≤ x ≤ 0.2) in polycrystalline form and have investigated the samples by means of structural, thermodynamic and transport
measurements. Our investigations reveal a non superconducting phase at 0 ≤ x 0.04 which for x = 0 is characterized by a structural transition towards an orthorhombic distortion at Ts ≈ 160 K and antiferromagnetic spin order at TN ≈ 138 K. Both transitions lead to strong anomalies in various transport properties as well as in magnetization and in specific
heat. Remarkably, the transition temperatures are only weakly doping dependent up to x ≈ 0.04. However, the transitions are
abruptly suppressed at x ≥ 0.05 in favour of a superconducting phase with a critical temperature Tc
20 K. Upon further increasing the F-doping Tc increases up to a maximum of Tc = 26.8 K at x = 0.1 which is followed by a decrease down to Tc ≈ 10 K at x ≥ 0.15. 相似文献
2.
Yichun Xu 《The European Physical Journal C - Particles and Fields》2009,62(1):187-190
We report the transverse momentum (p
T
) distributions for identified charged pions, protons and anti-protons using events triggered by high deposit energy in the
Barrel Electro-Magnetic Calorimeter (BEMC) from p+p collisions at
GeV. The spectra are measured around mid-rapidity (|y|<0.5) over the range of 3<p
T
<15 GeV/c with particle identification (PID) by the relativistic ionization energy loss (rdE/dx) in the Time Projection Chamber (TPC) of the Solenoidal Tracker at RHIC (STAR). The charged pion, proton and anti-proton
spectra at high p
T
are compared with published results from minimum bias triggered events and the Next-Leading-Order perturbative quantum chromodynamic
(NLO pQCD) calculations (DSS, KKP and AKK 2008). In addition, we present the particle ratios of π
−/π
+,
, p/π
+ and
in p+p collisions. 相似文献
3.
Zhi-Gang Wang 《The European Physical Journal C - Particles and Fields》2008,57(4):711-718
We calculate the strong coupling constant g
ΔN
π
and study the strong decay Δ++→p
π with light-cone QCD sum rules. The numerical value of the strong coupling constant g
ΔN
π
is consistent with the experimental data. The small discrepancy may be due to the failure to take into account perturbative
corrections. 相似文献
4.
X.-H. Guo Gang Lü Z.-H. Zhang 《The European Physical Journal C - Particles and Fields》2008,58(2):223-244
In the framework of factorization we study direct CP violation in the decays of bottom hadrons containing a strange quark or a charm quark, H
b
→f
ρ
0(ω)→f
π
+
π
− (H
b
is the bottom hadron and f is the product hadron) including the effect of ρ–ω mixing. We find that the CP violating asymmetry can be enhanced greatly via the ρ–ω mixing mechanism when the invariant mass of the π
+
π
− pair is in the vicinity of the ω resonance. For the processes associated with b→d transitions, e.g.
,
, B
c
−→D
−
π
+
π
−, B
c
−→D
*−
π
+
π
−, Ξ
b
0→Λ
π
+
π
−, and Ω
b
−→Ξ
−
π
+
π
−, the maximum CP violating asymmetries can reach about −84%, while for the processes associated with b→s transitions, e.g.
,
, B
c
−→D
s
−
π
+
π
−, B
c
−→D
s
*−
π
+
π
−, Ξ
b
−→Ξ
−
π
+
π
−, and Ω
b
−→Ω
−
π
+
π
−, the CP violating asymmetries can be enhanced to about 95%. Furthermore, taking ρ–ω mixing into account we calculate the b-hadron decay branching ratios. We also discuss the possibility to observe the predicted CP violating asymmetries at the LHC. 相似文献
5.
Junfeng Sun Dongsheng Du Yueling Yang 《The European Physical Journal C - Particles and Fields》2009,60(1):107-117
The B
c
→J/ψ
π, η
c
π decays are studied with the perturbative QCD approach. It is found that the form factors
and
for the B
c
→J/ψ, η
c
transitions and the branching ratios are sensitive to the parameters ω, v, f
J/ψ
and
, where ω and v are the parameters of the charmonium wave functions for a Coulomb potential and the harmonic-oscillator potential, respectively,
and f
J/ψ
and
are the decay constants of the J/ψ and η
c
mesons, respectively. The large branching ratios and the clear signals of the final states make the B
c
→J/ψ
π, η
c
π decays the prospective channels for measurements at the hadron colliders. 相似文献
6.
A. M. Hamed 《The European Physical Journal C - Particles and Fields》2009,61(4):597-601
The presented results are the first measurements at RHIC for direct γ-charged hadron azimuthal correlations in heavy ion collisions. We use these correlations to study the color charge density
of the medium through the medium-induced modification of high-p
T
parton fragmentation. Azimuthal correlations of direct photons at high transverse energy (8<p
T
<16 GeV) with away-side charged hadrons of transverse momentum (3<p
T
<6 GeV/c) have been measured over a broad range of centrality for Au+Au collisions and p+p collisions at
GeV in the STAR experiment. A transverse shower shape analysis in the STAR Barrel Electromagnetic Calorimeter Shower Maximum
Detector is used to discriminate between the direct photons and photons from the decays of high p
T
π
0. The per-trigger away-side yield of direct γ is smaller than from π
0 trigger at the same centrality class. Within the current uncertainty the I
CP
of direct γ and π
0 are similar. 相似文献
7.
We examine by molecular dynamics simulations the relaxation of polymer-solvent mixtures close to the glass transition. The
simulations employ a coarse-grained model in which polymers are represented by bead-spring chains and solvent particles by
monomers. The interaction parameters between polymer and solvent are adjusted such that mixing is favored. We find that the
mixtures have one glass transition temperature T
g or critical temperature T
c of mode-coupling theory (MCT). Both T
g and T
c (> T
g decrease with increasing solvent concentration . The decrease is linear for the concentrations studied (up to = 25%. Above T
c we explore the structure and relaxation of the polymer-solvent mixtures on cooling. We find that, if the polymer solution
is compared to the pure polymer melt at the same T, local spatial correlations on the length scale of the first peak of the static structure factor S(q) are reduced. This difference between melt and solution is largely removed when comparing the S(q) of both systems at similar distance to the respective T
c. Near T
c we investigate dynamic correlation functions, such as the incoherent intermediate scattering function (t), mean-square displacements of the monomers and solvent particles, two non-Gaussian parameters, and the probability distribution
P(ln r;t) of the logarithm of single-particle displacements. In accordance with MCT we find, for instance, that (t) obeys the time-temperature superposition principle and has relaxation times which are compatible with a power law increase close (but not too close) to T
c. In divergence to MCT, however, the increase of depends on the wavelength q, small q values having weaker increase than large ones. This decoupling of local and large-length scale relaxation could be related
to the emergence of dynamic heterogeneity at low T. In the time window of the relaxation an analysis of P(ln r;t) reveals a double-peak structure close to T
c. The first peak correponds to “slow” particles (monomer or solvent) which have not moved much farther than 10% of their diameter
in time t, whereas the second occurs at distances of the order of the particle diameter. These “fast” particles have succeeded in leaving
their nearest-neighbor cage in time t. The simulation thus demonstrates that large fluctuations in particle mobility accompany the final structural relaxation
of the cold polymer solution in the vicinity of the extrapolated T
c. 相似文献
8.
Zhi-Gang Wang 《The European Physical Journal C - Particles and Fields》2009,61(2):321-329
We calculate the masses and the pole residues of the
heavy baryons Ω
c
0(css) and Ω
b
−(bss) with the QCD sum rules. The numerical values
GeV (or
GeV) and
GeV (or
GeV) are in good agreement with the experimental data. 相似文献
9.
A. K. Chaudhuri 《The European Physical Journal C - Particles and Fields》2009,61(2):331-338
In a hydrodynamic model, we have studied J/ψ production in Au+Au/Cu+Cu collisions at RHIC energy,
GeV. At the initial time, J/ψ’s are randomly distributed in the fluid. As the fluid evolves in time, the free streaming J/ψ’s are dissolved if the local fluid temperature exceeds a threshold temperature T
J/ψ
. Sequential melting of charmonium states (χ
c
, ψ
′ and J/ψ), with melting temperatures
, T
J/ψ
≈2T
c
and feed-down fraction F≈0.3, explains the PHENIX data on the centrality dependence of J/ψ suppression in Au+Au collisions. J/ψ
p
T
spectra and the nuclear modification factor in Au+Au collisions are also well explained in the model. The model however overpredicts
the centrality dependence of J/ψ suppression in Cu+Cu collisions by 20–30%. The J/ψ
p
T
spectra are underpredicted by 20–30%. The model predicts that in central Pb+Pb collisions at LHC energy,
GeV, J/ψ’s are suppressed by a factor of ∼10. The model predicted a J/ψ
p
T
distribution in Pb+Pb collisions at LHC is similar to that in Au+Au collisions at RHIC. 相似文献
10.
We perform a theoretical study based on dispersion relations of the reaction γγ → π
0
π
0 emphasizing the low-energy region. We discuss how the ƒ
0(980) signal emerges in γγ → ππ within the dispersive approach and how this fixes to a large extent the phase of the isoscalar S-wave γγ → ππ amplitude above the threshold. This allows us to make sharper predictions for the cross-section at lower energies and our results could then
be used to distinguish between different ππ isoscalar S-wave parameterizations with the advent of new precise data on ππ → π
0
π
0. We compare our dispersive approach with an updated calculation employing the unitary chiral perturbation theory (U
gC
PT). We also pay special attention to the role played by the σ-resonance in γγ → ππ and calculate its coupling and width to γγ, for which we obtain Γ(σ → γγ) = (1.68 ± 0.15) keV. 相似文献
11.
Song Mao Ma Wen-Gan Zhang Ren-You Guo Lei Wang Shao-Ming 《The European Physical Journal C - Particles and Fields》2009,59(4):761-768
Higgs-boson production in association with a W-boson pair at e
+
e
− linear colliders is one of the important processes in probing the coupling between the Higgs boson and vector gauge bosons
and discovering the signature of new physics. We describe the impact of the complete electroweak (EW) radiative corrections
of
to this process in the standard model (SM) at the International Linear Collider (ILC), and investigate the dependence of the
lowest-order (LO) and EW next-to-leading order (NLO) corrected cross sections on the colliding energy
and the Higgs-boson mass. The LO and NLO EW corrected distributions of the invariant mass of the W-boson pair and the transverse
momenta of the final W-boson and Higgs boson are presented. Our numerical results show that the relative EW radiative correction
(δ
ew) varies from −19.4% to 0.2% when m
H=120 GeV and
grows from 300 GeV to 1.2 TeV. 相似文献
12.
Xiang Liu Zhi-Gang Luo Yan-Rui Liu Shi-Lin Zhu 《The European Physical Journal C - Particles and Fields》2009,61(3):411-428
We perform a systematic study of the possible molecular states composed of a pair of heavy mesons such as
,
,
in the framework of the meson exchange model. The exchanged mesons include the pseudoscalar, scalar and vector mesons. Through
our investigation, we find the following results. (1) The structure X(3764) is not a molecular state. (2) There exists strong attraction in the range r<1 fm for the
system with J=0,1. If future experiments confirm Z
+(4051) as a loosely bound molecular state, its quantum number is probably J
P
=0+. Its partner state Φ
**0 may be searched for in the π
0
χ
c1 channel. (3) Vector meson exchange provides strong attraction in the
channel together with pion exchange. A bound state solution may exist with a reasonable cutoff parameter Λ∼1.4 GeV. X(3872) may be accommodated as a molecular state dynamically although drawing a very definite conclusion needs further investigation.
(4) The
molecular state may exist. 相似文献
13.
C. Wheldon Tz. Kokalova W. von Oertzen S. Thummerer H. G. Bohlen B. Gebauer A. Tumino T. N. Massey G. de Angelis M. Axiotis A. Gadea Th. Kröll N. Mărginean D. R. Napoli M. De Poli C. Ur D. Bazzacco S. M. Lenzi C. Rossi Alvarez S. Lunardi R. Menegazzo P. G. Bizzeti A. M. Bizzeti-Sona 《The European Physical Journal A - Hadrons and Nuclei》2005,26(3):321-326
Cluster states up to 12 MeV in the stable light nucleus 21Ne, based on the 16O + n + α molecular configurations, have been populated in the incomplete-fusion reaction 16 8O(73Li, np)2110Ne at 29.4 MeV. The observation of both intra- and inter-band transitions leads to a re-interpretation of some levels in the
Kπ =
- and Kπ =
- bands. The implications of this re-ordering on the octupole doublet bands are examined. The data allow a more accurate determination
of some previously uncertain level energies. The “missing” Iπ =
- level is also discussed. 相似文献
14.
T. Branz T. Gutsche V. Lyubovitskij 《The European Physical Journal A - Hadrons and Nuclei》2008,37(3):303-317
We discuss a possible interpretation of the f
0(980)-meson as a hadronic molecule —a bound state of K and mesons. Using a phenomenological Lagrangian approach we calculate the strong f
0(980) → ππ and electromagnetic f
0(980) → γγ decays. The compositeness condition provides a self-consistent method to determine the coupling constant between
f
0 and its constituents, K and . Form factors governing the decays of the f
0(980) are calculated by evaluating the kaon loop integrals. The predicted f
0(980) → ππ and f
0(980) → γγ decay widths are in good agreement with available data and results of other theoretical approaches. 相似文献
15.
D. Elsner A. Süle P. Barneo P. Bartsch D. Baumann J. Bermuth R. Böhm D. Bosnar M. Ding M. Distler D. Drechsel I. Ewald J. Friedrich J. M. Friedrich S. Grözinger P. Jennewein S. Kamalov F. H. Klein M. Kohl K. W. Krygier H. Merkel P. Merle U. Müller R. Neuhausen Th. Pospischil M. Potokar G. Rosner H. Schmieden M. Seimetz O. Strähle L. Tiator Th. Walcher M. Weis 《The European Physical Journal A - Hadrons and Nuclei》2006,27(1):91-97
The reaction p(e, e'p)π0 has been studied at Q2 = 0.2 (GeV/c)2 in the region of W = 1232MeV. From measurements left and right of
, cross-section asymmetries ρLT have been obtained in forward kinematics ρLT(
= 20°) = (- 11.68±2.36stat±2.36sys) and backward kinematics ρLT(
= 160°) = (12.18±0.27stat±0.82sys) π0. Multipole ratios
{S1+ * M1+}/| M1+|2 and
{S0+ * M1+}/| M1+|2 were determined in the framework of the MAID2003 model. The results are in agreement with older data. The unusally strong
negative
{S0+ * M1+}/| M1+|2 required to bring also the result of Kalleicher et al. in accordance with the rest of the data is almost excluded. 相似文献
16.
Omar Mustafa S. Habib Mazharimousavi 《International Journal of Theoretical Physics》2009,48(1):183-193
Non-Hermitian but
-symmetrized spherically-separable Dirac and Schr?dinger Hamiltonians are considered. It is observed that the descendant Hamiltonians
H
r
, H
θ
, and H
φ
play essential roles and offer some “user-feriendly” options as to which one (or ones) of them is (or are) non-Hermitian.
Considering a
-symmetrized H
φ
, we have shown that the conventional Dirac (relativistic) and Schr?dinger (non-relativistic) energy eigenvalues are recoverable.
We have also witnessed an unavoidable change in the azimuthal part of the general wavefunction. Moreover, setting a possible
interaction V(θ)≠0 in the descendant Hamiltonian H
θ
would manifest a change in the angular θ-dependent part of the general solution too. Whilst some
-symmetrized H
φ
Hamiltonians are considered, a recipe to keep the regular magnetic quantum number m, as defined in the regular traditional Hermitian settings, is suggested. Hamiltonians possess properties similar to the
-symmetric ones (here the non-Hermitian
-symmetric Hamiltonians) are nicknamed as pseudo-
-symmetric. 相似文献
17.
V. A. Schegelsky A. V. Sarantsev A. V. Anisovich M. P. Levchenko 《The European Physical Journal A - Hadrons and Nuclei》2006,27(2):199-205
The reaction γγ → π+π-π0 with quasi-real photons is studied with a total integrated luminosity of 663pb^-1, collected by the L3 detector at LEP at
center-of-mass energies from 183 to 209GeV. The results of an energy-dependent partial wave analysis in the mass region 1.1≤M(π+π-π0)≤2.2GeV are presented. The reaction is dominated by a2(1320) formation. A strong signal consistent with the first radial excitation of the isovector tensor state, a2(1700), is present and confirms the previous L3 observation. Its two-photon partial width is found to be
Br(3π) = 0.37+0.12-0.08keV, the relative branching ratio of ρ(770)π to f2(1270)π is 3.4±0.4. For all observed states the product of γγ partial width and 3π branching ratios is measured. 相似文献
18.
The decays η,
→ π+π-
l
+
l
- (with l = e,μ are investigated within a chiral unitary approach which combines the chiral effective Lagrangian with a coupled-channels
Bethe-Salpeter equation. Predictions for the decay widths and spectra are given. 相似文献
19.
J/ψ production at forward and midrapidity at the Relativistic Heavy-Ion Collider (RHIC) is calculated within a previously constructed
rate-equation approach accounting for both direct production and regeneration from c and
. The results are compared to the experimental data. The observed stronger suppression at forward rapidity can be qualitatively
explained by a smaller statistical regeneration component together with stronger cold nuclear matter induced suppression compared
to midrapidity. The χ
c
over J/ψ ratio and ψ′ over J/ψ ratio are also calculated. 相似文献
20.
Chih-Yuan Lu Patrick J. Shamberger Esmeralda N. Yitamben Kenneth M. Beck Alan G. Joly Marjorie A. Olmstead Fumio S. Ohuchi 《Applied Physics A: Materials Science & Processing》2008,93(1):93-98
Phase transformation of thin film (∼30 nm)In2Se3/Si(111) (amorphous→crystalline) was performed by resistive annealing and the reverse transformation (crystalline→amorphous)
was performed by nanosecond laser annealing. As an intrinsic-vacancy, binary chalcogenide semiconductor, In2Se3 is of interest for non-volatile phase-change memory. Amorphous In
x
Se
y
was deposited at room temperature on Si(111) after pre-deposition of a crystalline In2Se3 buffer layer (0.64 nm). Upon resistive annealing to 380°C, the film was transformed into a γ-In2Se3 single crystal with its {0001} planes parallel to the Si(111) substrate and
parallel to Si
, as evidenced by scanning tunneling microscopy, low energy electron diffraction, and X-ray diffraction. Laser annealing with
20-ns pulses (0.1 millijoules/pulse, fluence≤50 mJ/cm2) re-amorphized the region exposed to the laser beam, as observed with photoemission electron microscopy (PEEM). The amorphous
phase in PEEM appears dark, likely due to abundant defect levels inhibiting electron emission from the amorphous In
x
Se
y
film. 相似文献