We investigate identical pion HBT intensity interferometry in central Au+Au collisions at 1.23A GeV. High-statistics π−π− and π+π+ data are measured with HADES at SIS18/GSI. The radius parameters, ...derived from the correlation function depending on relative momenta in the longitudinally comoving system and parametrized as three-dimensional Gaussian distribution, are studied as function of transverse momentum. A substantial charge-sign difference of the source radii is found, particularly pronounced at low transverse momentum. The extracted source parameters agree well with a smooth extrapolation of the center-of-mass energy dependence established at higher energies, extending the corresponding excitation functions down towards a very low energy.
In this letter we report the first multi-differential measurement of correlated pion-proton pairs from 2 billion Au+Au collisions at sNN=2.42 GeV collected with HADES. In this energy regime the ...population of Δ(1232) resonances plays an important role in the way energy is distributed between intrinsic excitation energy and kinetic energy of the hadrons in the fireball. The triple differential d3N/dMπ±pdpTdy distributions of correlated π±p pairs have been determined by subtracting the πp combinatorial background using an iterative method. The invariant-mass distributions in the Δ(1232) mass region show strong deviations from a Breit-Wigner function with vacuum width and mass. The yield of correlated pion-proton pairs exhibits a complex isospin, rapidity and transverse-momentum dependence. In the invariant mass range 1.1<Minv(GeV/c2)<1.4, the yield is found to be similar for π+p and π−p pairs, and to follow a power law 〈Apart〉α, where 〈Apart〉 is the mean number of participating nucleons. The exponent α depends strongly on the pair transverse momentum (pT) while its pT-integrated and charge-averaged value is α=1.5±0.08st±0.2sy.
Abstract
Nucleon knockout experiments using beryllium or carbon targets reveal a strong dependence of the quenching factors, i.e., the ratio (
$$\hbox {R}_{\textrm{s}}$$
R
s
) of theoretical to the ...experimental spectroscopic factors (
$$\hbox {C}^2{\textrm{S}}$$
C
2
S
), on the proton-neutron asymmetry in the nucleus under study. However, this dependence is greatly reduced when a hydrogen target is used. To understand this phenomenon, exclusive
$$^{1}\text {H}(^{17}\text {Ne},$$
1
H
(
17
Ne
,
$$2\hbox {p}~^{16}\text {F})$$
2
p
16
F
)
and inclusive
$$^{12}\text {C}(^{17}\text {Ne},2\hbox {p}~^{16}\text {F})\hbox {X}$$
12
C
(
17
Ne
,
2
p
16
F
)
X
,
$$^{12}\text {C}(^{17}\text {Ne},$$
12
C
(
17
Ne
,
$$^{16}\text {F})\hbox {X}$$
16
F
)
X
as well as
$$^{1}\text {H}(^{17}\text {Ne},^{16}\text {F})\hbox {X}$$
1
H
(
17
Ne
,
16
F
)
X
(X-denotes undetected reaction products) reactions with
$$^{16}\text {F}$$
16
F
in the ground and excited states were analysed. The longitudinal momentum distribution of
$$^{16}{\textrm{F}}$$
16
F
and the correlations between the detached protons were studied. In the case of the carbon target, there is a significant deviation from the predictions of the eikonal model. The eikonal approximation was used to extract spectroscopic factor values
$$\hbox {C}^2{\textrm{S}}$$
C
2
S
. The experimental
$$\hbox {C}^2\hbox {S}$$
C
2
S
value obtained with C target is markedly lower than that for H target. This is interpreted as rescattering due to simultaneous nucleon knockout from both reaction partners,
$$^{17}\text {Ne}$$
17
Ne
and
$$^{12}\text {C}$$
12
C
.
.
The HADES data from p + Nb collisions at a center-of-mass energy of
GeV are analyzed employing a statistical hadronization model. The model can successfully describe the production yields of the ...identified hadrons
,
,
,
K
0
s
,
with parameters
MeV and
MeV, which fit well into the chemical freeze-out systematics found in heavy-ion collisions. In addition, we reanalyze our previous HADES data from Ar + KCl collisions at
GeV with an updated version of the model. We address equilibration in heavy-ion collisions by testing two aspects: the description of yields and the regularity of freeze-out parameters from a statistical model fit as a function of colliding energy and system size. Despite its success, the model fails to describe the observed
yields in both, p + Nb and Ar + KCl . Special emphasis is put on feed-down contributions from higher-lying resonance states as a possible explanation for the observed excess.
The production of
Σ
0
hyperons in proton proton collisions at a beam kinetic energy of 3.5 GeV impinging on a liquid hydrogen target was investigated using data collected with the HADES setup. The ...total production cross section is found to be
σ
(
p
K
+
Σ
0
)
=
17.7
±
1.7
(
s
t
a
t
)
±
1.6
(
s
y
s
t
)
µb. Differential cross section distributions of the exclusive channel
p
p
→
p
K
+
Σ
0
were analyzed in the center-of-mass, Gottfried–Jackson and helicity reference frames for the first time at the excess energy of 556 MeV. The data support the interplay between pion and kaon exchange mechanisms and clearly demonstrate the contribution of interfering nucleon resonances decaying to
K
+
Σ
0
. The Bonn–Gatchina partial wave analysis was employed to analyse the data. Due to the limited statistics, it was not possible to obtain an unambiguous determination of the relative contribution of intermediate nucleon resonances to the final state. However nucleon resonances with masses around 1.710
GeV
/
c
2
(
N
∗
(
1710
)
) and 1.900
GeV
/
c
2
(
N
∗
(
1900
)
or
Δ
∗
(
1900
)
) are preferred by the fit.
The tagged quasi-free np→npπ+π− reaction has been studied experimentally with the High Acceptance Di-Electron Spectrometer (HADES) at GSI at a deuteron incident beam energy of 1.25 GeV/nucleon ...(s∼2.42 GeV/c for the quasi-free collision). For the first time, differential distributions of solid statistics for π+π− production in np collisions have been collected in the region corresponding to the large transverse momenta of the secondary particles. The invariant mass and angular distributions for the np→npπ+π− reaction are compared with different models. This comparison confirms the dominance of the t-channel with ΔΔ contribution. It also validates the changes previously introduced in the Valencia model to describe two-pion production data in other isospin channels, although some deviations are observed, especially for the π+π− invariant mass spectrum. The extracted total cross section is also in much better agreement with this model. Our new measurement puts useful constraints for the existence of the conjectured dibaryon resonance at mass M∼2.38 GeV and with width Γ∼70 MeV.
We present data on dielectron emission in proton induced reactions on a Nb target at 3.5 GeV kinetic beam energy measured with HADES installed at GSI. The data represent the first high statistics ...measurement of proton-induced dielectron radiation from cold nuclear matter in a kinematic regime, where strong medium effects are expected. Combined with the good mass resolution of 2%, it is the first measurement sensitive to changes of the spectral functions of vector mesons, as predicted by models for hadrons at rest or small relative momenta. Comparing the e+e− invariant mass spectra to elementary p+p data, we observe for e+e− momenta Pee<0.8 GeV/c a strong modification of the shape of the spectrum, which we attribute to an additional ρ-like contribution and a decrease of ω yield. These opposite trends are tentatively interpreted as a strong coupling of the ρ meson to baryonic resonances and an absorption of the ω meson, which are two aspects of in-medium modification of vector mesons.
Due to their low noise, CMOS Monolithic Active Pixel Sensors are suited to sense X-rays with a few keV quantum energy, which is of interest for high resolution X-ray imaging. Moreover, the good ...energy resolution of the silicon sensors might be used to measure this quantum energy. Combining both features with the good spatial resolution of CMOS sensors opens the potential to build "color sensitive" X-ray cameras. Taking such colored images is hampered by the need to operate the CMOS sensors in a single photon counting mode, which restricts the photon flux capability of the sensors. More importantly, the charge sharing between the pixels smears the potentially good energy resolution of the sensors. Based on our experience with CMOS sensors for charged particle tracking, we studied techniques to overcome the latter by means of an offline processing of the data obtained from a CMOS sensor prototype. We found that the energy resolution of the pixels can be recovered at the expense of reduced quantum efficiency. We will introduce the results of our study and discuss the feasibility of taking colored X-ray pictures with CMOS sensors.
The alignment strategy of HADES Pechenova, O.; Pechenov, V.; Galatyuk, T. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
06/2015, Letnik:
785
Journal Article
Recenzirano
The global as well as intrinsic alignment of any spectrometer impacts directly on its performance and the quality of the achievable physics results. An overview of the current alignment procedure of ...the DiElectron Spectrometer HADES is presented with an emphasis on its main features and its accuracy. The sequence of all steps and procedures is given, including details on photogrammetric and track-based alignment.
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