共查询到20条相似文献,搜索用时 265 毫秒
1.
M. Anikina L. Chkhaidze T. Djobava V. Garsevanishvili L. Kharkhelauri 《The European Physical Journal A - Hadrons and Nuclei》2000,7(1):139-145
The light front analysis of π− mesons in He(Li,C), C-Ne, C-Cu and O-Pb collisions is carried out. The phase space of secondary pions is divided into two
parts in one of which the thermal equilibrium assumption seems to be in a good agreement with the data. Corresponding temperatures
T are extracted and their dependence on (A
P·A
T)1/2 is studied. The results are compared with the predictions of the Quark-Gluon String Model (QGSM). The QGSM satisfactorily
reproduces the experimental data for light and intermediate-mass nuclei.
Received: 29 September 1999 相似文献
2.
We study the π± spectra obtained in 2, 4, 6 and 8A GeV Au - Au collisions within the thermal model. We find that the main features of the data can be well described after we
include the pions from the decay of the Δ -resonance with medium mass modification. 相似文献
3.
The pseudo-rapidity distribution has been studied for 50 GeV/cπ
−-colliding with various groups of target nuclei in emulsion. These data are compared with the published data onp-A collisions. It is observed that leading component multiplicity inπ
−-Em collisions decreases withN
h
in highη-region. It is also observed that nearly 20% of the interactions proceed via single cluster formation at this projectile energy. 相似文献
4.
5.
J.G. Messchendorp A. Sibirtsev W. Cassing V. Metag S. Schadmand 《The European Physical Journal A - Hadrons and Nuclei》2001,11(1):95-103
Simulations based on a coupled-channel transport model have been performed to analyze the feasibility to study the in-medium
ω mass exploiting the process γ + A→π0γ + X for C, Ca and Nb nuclei. The distortions due to final-state interactions of the π0 and background contributions from the reaction γ + A→π0π0 + X are found to be small in the mass range of interest ( 0.6 < M
π0γ < 0.8 GeV). Furthermore, the effect of the detector resolution on the π0γ mass determination is discussed.
Received: 5 December 2000 / Accepted: 18 May 2001 相似文献
6.
H Machner M Betigeri J Bojowald A Budzanowski A Chatterjee J Ernst L Freindl D Frekers W Garske K Grewer A Hamacher J Ilieva L Jarczyk K Kilian S Kliczewski W Klimala D Kolev T Kutsarova J Lieb H Machner A Magiera H Nann L Pentchev HS Plendl D Protić B Razen P Von Rossen BJ Roy R Siudak J Smyrski RV Srikantiah A Strzałkowski R Tsenov K Zwoll 《Pramana》2001,57(2-3):399-416
Total and differential cross sections for the reactions p + d → 3He + m
0 with m=π, η and p + d → 3H+π+ were measured with the GEM detector at COSY for beam momenta between threshold and the maximum of the corresponding baryon
resonance. For both reactions a strong forward-backward asymmetry was found. The data were compared with model calculations.
The aspect of isospin symmetry breaking is studied.
Representing the GEM Collaboration 相似文献
7.
S. Abd El-Bary S. Abd El-Samad R. Bilger K. -Th. Brinkmann H. Clement M. Dietrich E. Doroshkevich S. Dshemuchadse K. Ehrhardt A. Erhardt W. Eyrich A. Filippi H. Freiesleben M. Fritsch R. Geyer A. Gillitzer C. Hanhart J. Hauffe K. Haug D. Hesselbarth R. Jaekel B. Jakob L. Karsch K. Kilian H. Koch J. Kress E. Kuhlmann S. Marcello S. Marwinski R. Meier K. Möller H. P. Morsch L. Naumann J. Ritman E. Roderburg P. Schönmeier M. Schulte-Wissermann W. Schroeder M. Steinke F. Stinzing G. Y. Sun J. Wächter G. J. Wagner M. Wagner U. Weidlich A. Wilms P. Wintz S. Wirth G. Zhang P. Zupranski 《The European Physical Journal A - Hadrons and Nuclei》2008,37(3):267-277
The two-pion production reaction pp → ppπ+π− was measured with a polarized proton beam at T
p
≈ 750 and 800MeV using the short version of the COSY-TOF spectrometer. The implementation of a delayed-pulse technique for
Quirl and central calorimeter provided positive π+ identification in addition to the standard particle identification, energy determination as well as time-of-flight and angle
measurements. Thus all four-momenta of the emerging particles could be determined with 1–4 overconstraints. Total and differential
cross-sections as well as angular distributions of the vector analyzing power have been obtained. They are compared to previous
data and theoretical calculations. In contrast to predictions we find significant analyzing-power values up to A
y
= 0.3. The data taken in the energy region of the excitation of the Roper resonance confirm that its dominant ππ decay channel
is N
* → Nσ. 相似文献
8.
The isoscalar-isovector (ρ-ω) interferences in the exclusive reactions π-
p↦ne
+
e
- and π+
n↦pe
+
e
- near the ω threshold leads to a distinct difference of the dielectron invariant-mass distributions depending on beam energy.
The strength of this effect is determined by the coupling of resonances to the nucleon vector-meson channels and other resonance
properties. Therefore, a combined analysis of these reactions can be used as a tool for determining the baryon resonance dynamics.
Received: 14 August 2001 / Accepted: 3 October 2001 相似文献
9.
F. Laue I. Böttcher M. Debowski A. Förster E. Grosse P. Koczoń B. Kohlmeyer M. Mang M. Menzel L. Naumann H. Oeschler F. Pühlhofer E. Schwab P. Senger Y. Shin J. Speer H. Ströbele C. Sturm G. Surówka F. Uhlig A. Wagner W. Waluś 《The European Physical Journal A - Hadrons and Nuclei》2000,9(3):397-410
Production cross-sections of charged pions, kaons and antikaons have been measured in C+C and C+Au collisions at beam energies
of 1.0 and 1.8 AGeV for different polar emission angles. The kaon and antikaon energy spectra can be described by Boltzmann
distributions whereas the pion spectra exhibit an additional enhancement at low energies. The pion multiplicity per participating
nucleon M(π+)/<A
part> is a factor of about 3 smaller in C+Au than in C+C collisions at 1.0 AGeV whereas it differs only little for the C and the
Au target at a beam energy of 1.8 AGeV. The K+ multiplicities per participating nucleon M(K+)/ <A
part> are independent of the target size at 1 AGeV and at 1.8 AGeV. The K- multiplicity per participating nucleon M(K-)/ <A
part> is reduced by a factor of about 2 in C+Au as compared to C+C collisions at 1.8 AGeV. This effect might be caused by the
absorption of antikaons in the heavy target nucleus. Transport model calculations underestimate the K-/K+ ratio for C+C collisions at 1.8 AGeV by a factor of about 4 if in-medium modifications of K-mesons are neglected.
Received: 10 December 1999 / Accepted: 14 November 2000 相似文献
10.
A. D'Angelo O. Bartalini V. Bellini J. P. Bocquet P. Calvat M. Capogni L. Casano M. Castoldi J. -P. Didelez R. Di Salvo A. Fantini D. Franco G. Gervino F. Ghio G. Giardina B. Girolami A. Giusa M. Guidal E. Hourani V. Kouznetsov R. Kunne A. Lapik P. Levi Sandri A. Lleres F. Mammoliti G. Mandaglio D. Moricciani A. N. Mushkarenkov V. Nedorezov L. Nicoletti C. Randieri D. Rebreyend F. Renard N. Rudnev T. Russew G. Russo C. Schaerf M. -L. Sperduto M. -C. Sutera A. Turinge V. Vegna 《The European Physical Journal A - Hadrons and Nuclei》2007,31(4):441-445
Meson photoproduction with polarized photons has proved to be a powerful tool to identify contributions of baryon resonances
that are not evident in the differential cross-sections. It provides information that are complementary to those extracted
using pion-nucleon scattering data. Extensive results have been produced in the past on beam asymmetries by the Graal collaboration
for η and π
0 on the proton. New results are now available for the same reactions on the quasi-free neutron and for the K+ photoproduction on the proton. Contributions from hitherto undetected baryon resonances may be important to understand the
results. 相似文献
11.
Nagatomo T. Matsuta K. Hashimoto K. Ota M. Arimura K. Minamisono K. Sumikama T. Ogura M. Iwakoshi T. Miyake T. Kudo S. Akutsu K. Minamisono T. Fukuda M. Mihara M. Momota S. Nojiri Y. Kitagawa A. Torikoshi M. Kanazawa M. Suda M. Hirai M. Symons T. J. M. Krebs G. F. Alonso J. R. Zhu S. Y. Zhu J. Z. Xu Y. J. 《Hyperfine Interactions》2001,136(3-8):233-237
The nuclear spin alignments of the β-emitting fragments 12B(I
π=1+, T
1/2=20.2 ms) and 13B(I
π=3/2−, T
1/2=17.4 ms) produced in the 100A-MeV 13C, 15N + 9Be collisions respectively have been observed for the first time detecting asymmetric β-ray emission from these nuclei. By
means of the spin manipulation technique based on the hyperfine interaction of B isotopes in TiO2, both the polarization P and the alignment A were determined reliably. The obtained P and A were significantly smaller than the expectation from the kinematical model. From the fact that the quenching factors for
P and A are almost the same, there may be some depolarization mechanism in the collision process itself.
This revised version was published online in September 2006 with corrections to the Cover Date. 相似文献
12.
The Fredholm representation theory is well adapted to the construction of homotopy invariants of non-simply-connected manifolds
by means of the generalized Hirzebruch formula [σ(M)] = 〈L(M)ch
A
f*ξ, [M]〉 ∈ K
A
0(pt) ⊗ Q, where A = C*[π] is the C*-algebra of the group π, π = π
1(M). The bundle ξ ∈ K
A
0(Bπ) is the canonical A-bundle generated by the natural representation π → A.
Recently, the first author constructed a natural family of Fredholm representations that lead to a symmetric vector bundle
on the completion of the fundamental group with a modification of the Higson-Roe corona, provided that the completion is a
closed manifold. 相似文献
13.
Lamia Benhabib 《The European Physical Journal C - Particles and Fields》2009,62(1):197-201
In ultra-relativistic Heavy-Ion Collisions (HIC), the properties of the quark gluon plasma (QGP) can be explored, in particular,
via measurements of neutral pions. The π
0 is an important probe for both proton and heavy ion physics. In the former case, π
0 production provides an important mean of testing pQCD as well as useful data to constrain current and future theoretical
models. In the latter case, π
0 measurements will serve as a baseline for exploring the nature of the HIC hard scattering. In the ALICE experiment, π
0 mesons are identified as they decay into two photons (π
0→γ
γ) using the high-resolution photon spectrometer (PHOS). PHOS will measure π
0 transverse momentum over a wide range, from hundreds of MeV/c to several tens of GeV/c. An estimation of π
0 production cross-section in proton–proton collisions is calculated in a next-to-leading order (NLO) approximation and first
presented. The π
0 geometrical acceptance and the identification efficiency along with the analysis on the invariant mass are the two important
correction factors for obtaining a realistic π
0 spectrum discussed in this paper. 相似文献
14.
Antonio O. Bouzas 《The European Physical Journal A - Hadrons and Nuclei》2008,37(2):201-216
We compute the polarization of the final-state baryon, in its rest frame, in low-energy mesonbaryon scattering with unpolarized
initial state, in unitarized BChPT. Free parameters are determined by fitting total and differential cross-section data (and
spin-asymmetry or polarization data if available) for pK
−, pK
+ and pπ+ scattering. We also compare our results with those of leading-order BChPT. 相似文献
15.
A combined analysis of photoproduction data on γp↦ πN, ηN was performed including the data on KΛ and KΣ. The data are interpreted in an isobar model with s-channel baryon resonances and π, ρ (ω), K, and K
* exchange in the t-channel. Three baryon resonances have a substantial coupling to ηN, the well-known N(1535)S
11, N(1720)P
13, and N(2070)D
15. The inclusion of data with open strangeness reveals evidence for further new resonances, N(1840)P
11, N(1875)D
13 and, with weaker evidence, for N(2170)D
13. 相似文献
16.
S. M. Kiselev 《Physics of Atomic Nuclei》2009,72(3):517-521
Using the extrapolation of existing data, estimations of prompt-photon production at FAIR energies have been made. At y = y
c.m. the rapidity density of prompt photons with p
t
> 1.5 GeV/c per central Au + Au event at 25 A GeV is estimated as ∼10−4. With the planned beam intensity 109 per second and 1% interaction probability, for 10% of most central events one can expect the prompt-photon rate ∼102 photons per second. Direct photons from the hadron scenario of ion collisions generated by the Hadron-String-Dynamics (HSD)
transport approach with implemented meson scatterings πρ → πγ, ππ → ργ have been analyzed. Photons from short-living resonances (e.g., ω → π
0
γ) decaying during the dense phase of the collision should be considered as direct photons. They contribute significantly in
the directphoton spectrum at p
t
= 0.5–1 GeV/c. At the FAIR energy 25 A GeV in Au + Au central collisions the HSD generator predicts, as a lower estimate, γ
direct/ ≃ 0.5% in the region p
t
= 0.5–1 GeV/c. At p
t
= 1.5–2 GeV/c γ
prompt/ ≃ 2%. Thermal direct photons have been evaluated with the Bjorken Hydro-Dynamics (BHD) model. The BHD spectra differ strongly
from the HSD predictions. The direct-photon spectrumis very sensitive to the initial temperature parameter T
0 of the model. The 10-MeV increase in the T
0 value leads to ∼2 times higher photon yield.
The text was submitted by the authors in English. 相似文献
17.
Results from RHIC have shown that there is an enhanced baryon/meson ratio in the intermediate transverse momentum range (2<pT<6 GeV/c) in Au+Au collisions at both =130 and 200 GeV. This was initially demonstrated by measurements of the p̄/π- ratio which was then extended in pT by the Λ/K0
S ratio. The data were successfully described by models utilising different hadronization mechanisms: those having recombination
of quarks and others having an interplay between flow, jet quenching and incorporating baryon junction loops. The strange
particle data from the first Au+Au run at =200 GeV gave tantalising hints that the observed enhancement of baryons compared to mesons was diminished by a pT of 6 GeV/c, but a lack of statistics in this range made a definitive statement impossible. Here we present an extended analysis
of identified strange baryons and mesons in Au+Au collisions at =200 GeV using data obtained by the STAR experiment from the 2004 running period. The increase in statistics extends the
measurement of Λ hyperons out to at least 7 GeV/c and K0
S mesons out to 9 GeV/c. This data allows us to place limits on the range where in-vacuum fragmentation functions are applicable
and the effect of baryon dominance is reduced. We also discuss the prospects for making these measurements using multiply-strange
baryons and mesons (Ω and ϕ). 相似文献
18.
Identification of baryon resonances in central heavy-ion collisions at energies between 1 and 2 AGeV
《The European Physical Journal A - Hadrons and Nuclei》1998,3(4):335-349
The mass distributions of baryon resonances populated in near-central collisions of Au on Au and Ni on Ni are deduced by
defolding the pt spectra of charged pions by a method which does not depend on a specific resonance shape. In addition the mass distributions
of resonances are obtained from the invariant masses of (p, π±) pairs. With both methods the deduced mass distributions are shifted by an average value of −60 MeV/c2 relative to the mass distribution of the free Δ(1232) resonance, the distributions descent almost exponentially towards mass
values of 2000 MeV/c2. The observed differences between (p, π−) and (p, π+) pairs indicate a contribution of isospin I = 1/2 resonances. The attempt to consistently describe the deduced mass distributions
and the reconstructed kinetic energy spectra of the resonances leads to new insights about the freeze out conditions, i.e.
to rather low temperatures and large expansion velocities.
Received: 26 June 1998 / Revised version: 2 September 1998 相似文献
19.
M. Ouchida 《Indian Journal of Physics》2011,85(6):977-980
We report on ω mesons’ production via radiative decay mode (ω → π
0
γ, π
0 → 2γ) in ?s\sqrt s = 200 GeV Au+Au collisions at RHIC-PHENIX. The main difficulty of this analysis is the huge combinatorial background inevitable
for reconstructing particles from the three- body decay mode. The emphasis is on the feasibility study using both simulation
and real data to search the best parameters that improve S/?BS/\sqrt B . For this purpose, we examine several sets of energy and momentum cuts for selecting π
0 and γ. To evaluate the remaining background, we consider three background sources; correlated/uncorrelated background and K
s
0 contribution, then we subtract them. The amount of these contributions is determined by a fit on a mass spectrum. The result
suggests that ω meson production is suppressed in central Au+Au collisions at high pT region. 相似文献
20.
M. I. Nagy 《Physics of Particles and Nuclei Letters》2011,8(9):1033-1036
A novel type of quantum mechanical correlations, hypothesized in the 1990’s, the (squeezed) back-to-back correlations, was
predicted to appear in heavy ion collisions among particle-antiparticle (eg. π+π−, K
+
K
−, p[`(p)]p\bar p) pairs, if their in-medium masses are different from the vacuum values. Observation of this correlation would provide new
insight in the freeze-out dynamics of the created matter. The latest status of the PHENIX measurement, comprising the first
measurement of this new effect, is presented. 相似文献