Refine
Year of publication
- 2021 (175)
- 2022 (164)
- 2020 (154)
- 2019 (142)
- 2017 (140)
- 2018 (131)
- 2023 (111)
- 2015 (85)
- 2016 (69)
- 2014 (56)
- 2012 (46)
- 2004 (36)
- 2013 (30)
- 2024 (29)
- 2010 (25)
- 2003 (23)
- 2011 (21)
- 2002 (20)
- 2007 (20)
- 2005 (19)
- 2008 (17)
- 1986 (15)
- 1994 (15)
- 1992 (14)
- 1983 (13)
- 1999 (13)
- 2001 (13)
- 2006 (13)
- 1966 (12)
- 1993 (12)
- 1995 (12)
- 1972 (11)
- 1981 (11)
- 1984 (11)
- 1997 (11)
- 1980 (10)
- 1987 (10)
- 2009 (10)
- 1962 (9)
- 1976 (9)
- 1988 (9)
- 1954 (8)
- 1965 (8)
- 1974 (8)
- 1978 (8)
- 1982 (8)
- 1991 (8)
- 1971 (7)
- 1985 (7)
- 1990 (7)
- 1998 (7)
- 1967 (6)
- 1977 (6)
- 1989 (6)
- 1996 (6)
- 1957 (5)
- 1958 (5)
- 1959 (5)
- 1973 (5)
- 1979 (5)
- 2000 (5)
- 1953 (4)
- 1956 (4)
- 1960 (4)
- 1970 (4)
- 1975 (4)
- 1950 (3)
- 1952 (3)
- 1964 (3)
- 1969 (3)
- 1947 (2)
- 1961 (2)
- 1968 (2)
- 1949 (1)
- 1951 (1)
- 1955 (1)
- 1963 (1)
Document Type
- Article (1918) (remove)
Has Fulltext
- yes (1918) (remove)
Is part of the Bibliography
- no (1918) (remove)
Keywords
- Heavy Ion Experiments (20)
- heavy ion collisions (16)
- BESIII (15)
- LHC (15)
- Kollisionen schwerer Ionen (14)
- e +-e − Experiments (12)
- Hadron-Hadron Scattering (11)
- Hadron-Hadron scattering (experiments) (11)
- Relativistic heavy-ion collisions (10)
- Branching fraction (9)
Institute
- Physik (1918) (remove)
We fabricated memristive devices using focused electron beam-induced deposition (FEBID) as a direct-writing technique employing a Pt/TiO2/Pt sandwich layer device configuration. Pinching in the measured current-voltage characteristics (i-v), the characteristic fingerprint of memristive behavior was clearly observed. The temperature dependence was measured for both high and low resistive states in the range from 290 K down to about 2 K, showing a stretched exponential behavior characteristic of Mott-type variable-range hopping. From this observation, a valence change mechanism of the charge transport inside the TiO2 layer can be deduced.
The first evaluation of an ultra-high granularity digital electromagnetic calorimeter prototype using 1.0–5.8 GeV/c electrons is presented. The 25 × 106 pixel detector consists of 24 layers of ALPIDE CMOS MAPS sensors, with a pitch of around 30 μm, and has a depth of almost 20 radiation lengths of tungsten absorber. Ultra-thin cables allow for a very compact design. The properties that are critical for physics studies are measured: electromagnetic shower response, energy resolution and linearity. The stochastic energy resolution is comparable with the state-of-the art resolution for a Si-W calorimeter, with data described well by a simulation model using Geant4 and Allpix2. The performance achieved makes this technology a good candidate for use in the ALICE FoCal upgrade, and in general demonstrates the strong potential for future applications in high-energy physics.
Using (10087±44)×106 J/ψ events collected with the BESIII detector, numerous Ξ− and Λ decay asymmetry parameters are simultaneously determined from the process J/ψ→Ξ−Ξ¯+→Λ(pπ−)π−Λ¯(n¯π0)π+ and its charge-conjugate channel. The precisions of α0 for Λ→nπ0 and α¯0 for Λ¯→n¯π0 compared to world averages are improved by factors of 4 and 1.7, respectively. The ratio of decay asymmetry parameters of Λ→nπ0 to that of Λ→pπ−, ⟨α0⟩/⟨αΛ−⟩, is determined to be 0.873±0.012+0.011−0.010, where the first and the second uncertainties are statistical and systematic, respectively. The ratio is smaller than unity more than 5σ, which signifies the existence of the ΔI=3/2 transition in Λ for the first time. Beside, we test for CP violation in Ξ−→Λπ− and in Λ→nπ0 with the best precision to date.
Using e+e− collision data, corresponding to an integrated luminosity of 892pb−1 collected at center-of-mass energies from 4.84 to 4.95\,GeV with the BESIII detector, we search for the process e+e−→K+K−ψ(3770) by reconstructing two charged kaons and one D meson from ψ(3770). No significant signal of e+e−→K+K−ψ(3770) is found and the upper limits of the Born cross sections are reported at 90\% confidence level.
The ALICE Collaboration measures the production of low-mass dielectrons in pp, p-Pb and Pb-Pb collisions at the LHC. The main detectors used in the analyses are the Inner Tracking System, Time Projection Chamber and Time-Of-Flight detector, all located around mid-rapidity. The production of virtual photons relative to the inclusive yield in pp collisions is determined by analyzing the dielectron excess with respect to the expected hadronic sources. The direct photon cross section is then calculated and found to be in agreement with NLO pQCD calculations. Results from the invariant mass analysis in p-Pb collisions show an overall agreement between data and hadronic cocktail. In Pb-Pb collisions, uncorrected background-subtracted yields have been extracted in two centrality classes. A feasibility study for LHC run 3 after the ALICE upgrade indicates the possibility for a future measurement of the early effective temperature.
We investigate the thermodynamic geometry of the quark-meson model at finite temperature, T, and quark number chemical potential, μ. We extend previous works by the inclusion of fluctuations exploiting the functional renormalization group approach. We use recent developments to recast the flow equation into the form of an advection-diffusion equation. We adopt the local potential approximation for the effective average action. We focus on the thermodynamic curvature, R, in the (μ,T) plane, in proximity of the chiral crossover, up to the critical point of the phase diagram. We find that the inclusion of fluctuations results in a smoother behavior of R near the chiral crossover. Moreover, for small μ, R remains negative, signaling the fact that bosonic fluctuations reduce the capability of the system to completely overcome the fermionic statistical repulsion of the quarks. We investigate in more detail the small μ region by analyzing a system in which we artificially lower the pion mass, thus approaching the chiral limit in which the crossover is actually a second order phase transition. On the other hand, as μ is increased and the critical point is approached, we find that R is enhanced and a sign change occurs, in agreement with mean field studies. Hence, we completely support the picture that R is sensitive to a crossover and a phase transition, and provides information about the effective behavior of the system at the phase transition.
The photoelectric effect describes the ejection of an electron upon absorption of one or several photons. The kinetic energy of this electron is determined by the photon energy reduced by the binding energy of the electron and, if strong laser fields are involved, by the ponderomotive potential in addition. It has therefore been widely taken for granted that for atoms and molecules, the photoelectron energy does not depend on the electron’s emission direction, but theoretical studies have questioned this since 1990. Here, we provide experimental evidence that the energies of photoelectrons emitted against the light propagation direction are shifted toward higher values, while those electrons that are emitted along the light propagation direction are shifted to lower values. We attribute the energy shift to a nondipole contribution to the ponderomotive potential that is due to the interaction of the moving electrons with the incident photons.
The ALICE experiment at the LHC investigates the properties of the hot and dense nuclear matter created in heavy-ion collisions. By comparing the particle production in pp and p-Pb collisions, possible nuclear initial state effects can be isolated. Measurements of the ω meson pT-spectra in pp and p-Pb collisions not only allow for a determination of the nuclear modification factor RpPb, but also provide insight into the fragmentation process and serve as vital input for decay background simulations for direct photons. In this contribution, measurements of the ω meson production in pp and p-Pb collisions at √sNN=5.02 TeV are presented. This includes the signal extraction and various corrections of the ω meson yields, leading to their production cross sections and the first measured nuclear modification factor RpPb of the ω meson at LHC energies.
Observation of χcJ → 3(K⁺K⁻)
(2024)
By analyzing (27.12±0.14)×108 𝜓(3686) events collected with the BESIII detector operating at the BEPCII collider, the decay processes 𝜒𝑐𝐽→3(𝐾+𝐾−) (𝐽=0, 1, 2) are observed for the first time with statistical significances of 8.2𝜎, 8.1𝜎, and 12.4𝜎, respectively. The product branching fractions of 𝜓(3686)→𝛾𝜒𝑐𝐽, 𝜒𝑐𝐽→3(𝐾+𝐾−) are presented and the branching fractions of 𝜒𝑐𝐽→3(𝐾+𝐾−) decays are determined to be ℬ𝜒𝑐0→3(𝐾+𝐾−)=(10.7±1.8±1.1)×10−6, ℬ𝜒𝑐1→3(𝐾+𝐾−)=(4.2±0.9±0.5)×10−6, and ℬ𝜒𝑐2→3(𝐾+𝐾−)=(7.2±1.1±0.8)×10−6, where the first uncertainties are statistical and the second are systematic.
Using data samples with an integrated luminosity of 6.4~fb−1 collected by the BESIII detector operating at the BEPCII storage ring, the process of e+e−→γϕJ/ψ is studied. The processes of e+e−→ϕχc1,c2, χc1,c2→γJ/ψ are observed with a significance of more than 10σ. The s√-dependent cross section of e+e−→ϕχc1,c2 is measured between 4.600 and 4.951~GeV, and evidence of a resonance structure is found for the first time in the ϕχc2 process. We also search for the processes of e+e−→γX(4140), γX(4274) and γX(4500) via the γϕJ/ψ final state, but no obvious structures are found. The upper limits on the production cross section times the branching fraction for these processes at the 90% confidence level are reported.
The cross section of the process e+e−→K+K− is measured at a number of center-of-mass energies s√ from 2.00 to 3.08 GeV with the BESIII detector at the Beijing Electron Positron Collider (BEPCII). The results provide the best precision achieved so far. A resonant structure around 2.2 GeV is observed in the cross section line shape. A Breit-Wigner fit yields a mass of M=2239.2±7.1±11.3~and a width of Γ=139.8±12.3±20.6 MeV, where the first uncertainties are statistical and the second ones are systematic. In addition, the time-like electromagnetic form factor of the kaon is determined at the individual center-of-mass energy points.
Using a 3.19 fb−1 data sample collected at an 𝑒+𝑒− center-of-mass energy of 𝐸cm=4.178 GeV with the BESIII detector, we measure the branching fraction of the leptonic decay 𝐷+𝑠→𝜇+𝜈𝜇 to be ℬ𝐷+𝑠→𝜇+𝜈𝜇=(5.49±0.16stat±0.15syst)×10−3. Combining our branching fraction with the masses of the 𝐷+𝑠 and 𝜇+ and the lifetime of the 𝐷+𝑠, we determine 𝑓𝐷+𝑠|𝑉𝑐𝑠|=246.2±3.6stat±3.5syst MeV. Using the 𝑐→𝑠 quark mixing matrix element |𝑉𝑐𝑠| determined from a global standard model fit, we evaluate the 𝐷+𝑠 decay constant 𝑓𝐷+𝑠=252.9±3.7stat±3.6syst MeV. Alternatively, using the value of 𝑓𝐷+𝑠 calculated by lattice quantum chromodynamics, we find |𝑉𝑐𝑠|=0.985±0.014stat±0.014syst. These values of ℬ𝐷+𝑠→𝜇+𝜈𝜇, 𝑓𝐷+𝑠|𝑉𝑐𝑠|, 𝑓𝐷+𝑠 and |𝑉𝑐𝑠| are each the most precise results to date.
Using a data sample of 448.1×106 𝜓(3686) events collected at √𝑠=3.686 GeV with the BESIII detector at the Beijing Electron-Positron Collider II, we search for the rare decay 𝐽/𝜓→𝜙𝑒+𝑒− via 𝜓(3686)→𝜋+𝜋−𝐽/𝜓. No signal events are observed and the upper limit on the branching fraction is set to be ℬ(𝐽/𝜓→𝜙𝑒+𝑒−)<1.2×10−7 at the 90% confidence level, which is still about one order of magnitude higher than the Standard Model prediction.
We investigate the early time dynamics of heavy ion collisions studying the time evolution of the energy-momentum tensor as well as energy-momentum correlations within a uniformly thermalizing holographic QGP. From these quantities, we suggest a far-from equilibrium definition of shear viscosity, which is a crucial property of QCD matter as it significantly determines the generation of elliptic flow already at early times. During an exemplary initial heating phase of the holographic QGP the shear viscosity of entropy density ratio decreases down to 60%, followed by an overshoot to 110% of the near-equilibrium value, η/s=1/(4π). Implications for the QCD QGP are discussed. Subsequently, we consider a holographic QGP which is Bjorken-expanding. Its energy-momentum tensor components have a known hydrodynamic attractor to which all time evolutions collapse independent of the initial conditions. Based on this, we propose a definition for a far from equilibrium speed of sound, and analytically compute its hydrodynamic attractor. Subjecting this Bjorken-expanding plasma to an external magnetic field and an axial chemical potential, we study the chiral magnetic effect far from equilibrium.
Heavy quarks are useful probes to investigate the properties of the Quark-Gluon Plasma (QGP) produced in heavy-ion collisions at the LHC, since they are produced in initial hard scattering processes. To single out the signals that are characteristic of the QGP, it is nevertheless crucial to understand the primordial heavy-quark production in vacuum, and to disentangle hot from cold nuclear matter effects. Moreover, observations of collective effects in high-multiplicity pp and p-Pb collisions show surprising similarities with those in heavy-ion collisions. Heavy-flavour production in such collisions could give further insight into the underlying processes. The heavy-flavour production can be studied with e+e− pairs from correlated semileptonic decays of heavy-flavour hadrons. Compared to single heavy-flavour measurements, the dielectron yield contains information about the initial kinematical correlations between the charm and anti-charm quarks, which is otherwise not accessible, and is sensitive to soft heavy-flavour production. We report results on correlated e+e− pairs in pp collisions recorded by the ALICE detector at different collision energies. The production of heavy quarks is discussed by comparing the yield of dielectrons from heavy-flavour hadron decays as a function of invariant mass, pair transverse momentum and distance of closest approach to the primary vertex with different Monte Carlo event generators. The heavy-flavour production cross sections are also presented. Results from high-multiplicity pp collisions at √s=13 TeV and the status of the p-Pb analysis at √sNN=5.02 TeV are reported as well.
Electromagnetic probes such as photons and dielectrons (e+e− pairs) are a unique tool to study the space-time evolution of the hot and dense matter created in ultrarelativistic heavy-ion collisions. At low dielectron invariant mass (mee), thermal radiation from the hot hadronic phase contributes to the dielectron spectrum via decays of ρ mesons, whose spectral function is sensitive to chiral-symmetry restoration. At larger mee, thermal radiation from the quark–gluon plasma carries information about the early temperature of the medium. At LHC energies, it is nevertheless dominated by a large background from correlated heavy-flavor hadron decays affected by energy loss and flow in the medium. Complementary to the real photon measurements, dielectron data also allow the extraction of the real direct photon fraction, including thermal photons at low pair transverse momentum pT,ee. The latest ALICE results on dielectron studies in Pb-Pb, and in inelastic and high-multiplicity pp collisions, at √sNN = 5.02 TeV and at √s = 13 TeV, respectively, are presented and compared to simulations and expectations from theory. The status of the Run 3 analysis is also reported.
We reanalyze some critical exponents of the 𝑂(𝑁) model within the functional renormalization group (FRG) approach in the local potential approximation (LPA). We use recent advances which are based on the observation that the FRG flow equation in LPA can be put into the form of an advection-diffusion equation. This allows to employ well-tested hydrodynamical algorithms for its solution to better estimate various sources of errors. Our results complement previous results for the critical exponents obtained within the FRG approach in LPA and compare favorably with those obtained via other methods.
A search for a massless dark photon 𝛾′ is conducted using 4.5 fb−1 of 𝑒+𝑒− collision data collected at center-of-mass energies between 4.600 and 4.699 GeV with the BESIII detector at BEPCII. No significant signal is observed, and the upper limit on the branching fraction ℬ(Λ+𝑐→𝑝𝛾′) is determined to be 8.0×10−5 at 90% confidence level.
We report the first observation of the decay Λ+c→Σ−π+π+π0, based on data obtained in e+e− annihilations with an integrated luminosity of 567~pb−1 at s√=4.6~GeV. The data were collected with the BESIII detector at the BEPCII storage rings. The absolute branching fraction B(Λ+c→Σ−π+π+π0) is determined to be (2.11±0.33(stat.)±0.14(syst.))%. In addition, an improved measurement of B(Λ+c→Σ−π+π+) is determined as (1.81±0.17(stat.)±0.09(syst.))%.
Measurement of the absolute branching fraction of the singly Cabibbo suppressed decay Λc⁺ → pη′
(2022)
The singly Cabibbo suppressed decay Λ+𝑐→𝑝𝜂′ is measured using 4.5 fb−1 of 𝑒+𝑒− collision data collected at center-of-mass energies between 4.600 and 4.699 GeV with the BESIII detector at BEPCII. Evidence for Λ+𝑐→𝑝𝜂′ with a statistical significance of 3.6𝜎 is reported with a double-tag approach. The Λ+𝑐→𝑝𝜂′ absolute branching fraction is determined to be (5.62+2.46−2.04±0.26)×10−4, where the first and second uncertainties are statistical and systematic, respectively. Our result is consistent with the branching fraction obtained by the Belle collaboration within the uncertainty of 1𝜎.