Continuum Amplitudes Research Articles

Measurement of the branching fraction of ψ(2S)→γπ0

Based on (2712.4±14.1)×106 ψ(2S) events, 7.9 fb−1 ψ(3773) data, and 0.8 fb−1 off-resonance data samples collected with the BESIII detector, we measure the branching fraction of ψ(2S)→γπ0 and e+e−→γπ0 form factor at momentum transfers Q2∼13 GeV2. The e+e−→γπ0 cross section is fitted with considering the interference between the ψ(2S) and continuum amplitudes and two solutions are found, B=3.74×10−7 with ϕ=3.93 rad and B=7.87×10−7 with ϕ=2.08 rad. Here, B is the branching fraction of ψ(2S)→γπ0 and ϕ is the relative phase angle between the ψ(2S) and continuum amplitudes. Due to insufficient off-resonance data, the branching fraction B(ψ(2S)→γπ0) is determined to be in the range [2.7,9.7]×10−7 within 1 standard deviation of the contour region. Published by the American Physical Society 2024

Impact of the interference between the resonance and continuum amplitudes on vector quarkonia decay branching fraction measurements

The measurement of the branching fraction of a heavy quarkonium decaying into light hadronic final state at $e^+e^-$ colliders is revisited. In $e^+e^-$ annihilation experiments, background contributions from the continuum amplitude and its interference with the resonance amplitude are irreducible. These effects become more and more significant as the precision of experimental measurements improves. While the former can be easily subtracted with data taken off the resonance peak, the latter depends on the relative size and phase between the resonance and continuum amplitudes. Two ratios are defined to estimate the size of these effects, $r_{R}^{f}$ for the ratio of the contribution of the interference term to the resonance term and $r_{c}^{f}$ for that to the continuum term. We find that $r_{R}^{f}$ could be as large as a few percent for narrow resonances, and both $r_{R}^{f}$ and $r_{c}^{f}$ could be large for broad resonances. This indicates that the interference effect is crucial for the measurements of the branching fractions aiming at the percent level or better precision and needs to be measured or estimated properly.

Spectral Line Registration Backend Based on USRP X300 Software Defined Radio

This paper presents implementation of spectrometer based on off-the-shelf software defined radio (SDR) Ettus Research USRP X300 equipped with TwinRX daughterboard. Parallelized software, employing Fast Fourier Transform (FFT), is developed which allows two channel spectrum processing in real time with bandwidths up to 50[Formula: see text]MHz per channel, sample resolution of 14 bits and FFT lengths up to 32k points. Measured Allan stability time of the spectrometer is at least 750 sin laboratory environment. Software has network server-type interface that allows to conveniently integrate the spectrometer in radio telescope observation control and monitoring system with versatility of SDR allowing to implement various observation modes, for example, total power detection functionality with high frequency selectivity, which allows to carry continuum amplitude calibration in presence of near-by radio frequency interference. Presented spectrometer has been successfully integrated and used at RT-32 and RT-16 radio telescopes of Ventspils International Radio Astronomy Centre.

Measurement and temperature dependence of the water vapor self-continuum between 70 and 700 cm−1

We present new measurements and analysis of the water absorption spectra in the region of the rotational band, between 70 and 700 cm−1. The higher pressures of the recordings (up to 16 mbar) as compared to our previous measurements allowed us to extend the retrieval of the water vapor self-continuum absorption from 500 to 700 cm−1 and to test our earlier results up to 500 cm−1. As a result, the continuum amplitude at high wavenumbers, determined with smaller uncertainty, shows an improved agreement with literature experimental data. The measurements were performed at two temperatures (296 and 326 K) using two radiation sources of significantly different power ranges: SOLEIL synchrotron and globar. The quadratic pressure dependence of the self-continuum absorption was verified leading to consistent values of cross-sections derived at various experimental conditions. In addition, we obtained the first data concerning the water vapor self-continuum temperature dependence in the 84-365 cm−1 spectral range for which we present the preliminary analysis considering the available measurements and theoretical data.

Single-pole nature of the detectable Lambda(1405)

We have investigated the single-pole nature of the detectable $$\Lambda(1405)$$ in detail, by employing a chiral model having double poles of a $$\bar KN$$–$$\pi \Sigma$$ coupled-channel $$T$$-matrix. The effects of the first pole and the second pole on the observed $$\pi \Sigma$$ mass spectrum in the $$\Lambda(1405)$$ region have been analyzed almost separately. It is concluded that the first pole is responsible for both peak structures seen in the $$T_{\pi \Sigma \leftarrow \bar KN}$$($$T_{21}$$) and $$T_{\pi \Sigma \leftarrow \pi \Sigma}$$($$T_{22}$$) invariant-mass spectra, and, due to an energy-dependent chiral interaction, the second pole provides continuum amplitudes affecting the shape of the peak structures of the first pole in the experimentally observable spectrum of $$\Lambda(1405)$$.

CBM Collaboration

Using 2917pb−1 of data accumulated at 3.773GeV, 44.5pb−1 of data accumulated at 3.65GeV and data accumulated during a ψ(3770) line-shape scan with the BESIII detector, the reaction e+e−→pp¯ is studied considering a possible interference between resonant and continuum amplitudes. The cross section of e+e−→ψ(3770)→pp¯, σ(e+e−→ψ(3770)→pp¯), is found to have two solutions, determined to be (0.059−0.020+0.070±0.012)pb with the phase angle ϕ=(255.8−26.6+39.0±4.8)° (<0.166pb at the 90% confidence level), or σ(e+e−→ψ(3770)→pp¯)=(2.57−0.13+0.12±0.12)pb with ϕ=(266.9−6.3+6.1±0.9)° both of which agree with a destructive interference. Using the obtained cross section of ψ(3770)→pp¯, the cross section of pp¯→ψ(3770), which is useful information for the future PANDA experiment, is estimated to be either (9.8−3.9+11.8)nb (<27.5nb at 90% C.L.) or (425.6−43.7+42.9)nb.

Study of [formula omitted] in the vicinity of [formula omitted

Using 2917 pb−1 of data accumulated at 3.773 GeV, 44.5 pb−1 of data accumulated at 3.65 GeV and data accumulated during a ψ(3770) line-shape scan with the BESIII detector, the reaction e+e−→pp¯ is studied considering a possible interference between resonant and continuum amplitudes. The cross section of e+e−→ψ(3770)→pp¯, σ(e+e−→ψ(3770)→pp¯), is found to have two solutions, determined to be (0.059−0.020+0.070±0.012) pb with the phase angle ϕ=(255.8−26.6+39.0±4.8)° (<0.166 pb at the 90% confidence level), or σ(e+e−→ψ(3770)→pp¯)=(2.57−0.13+0.12±0.12) pb with ϕ=(266.9−6.3+6.1±0.9)° both of which agree with a destructive interference. Using the obtained cross section of ψ(3770)→pp¯, the cross section of pp¯→ψ(3770), which is useful information for the future PANDA experiment, is estimated to be either (9.8−3.9+11.8) nb (<27.5 nb at 90% C.L.) or (425.6−43.7+42.9) nb.

Strong and electromagneticJ/ψandψ(2S)decays into pion and kaon pairs

A combined analysis of the electromagnetic pion and kaon form factors in the neighborhood of J/{psi} and {psi}(2S) and of the strong decay amplitude of these resonances into kaons is presented. In the presence of a large relative phase between strong and electromagnetic resonance amplitudes the branching ratio, as measured in electron-positron annihilation, receives an additional contribution from the interference between resonance and continuum amplitude neglected in earlier papers. We note that the large relative phase between strong and electromagnetic amplitudes observed in earlier phenomenological analyses relies critically on the specific assumptions on SU(3) symmetry and breaking. Without these assumptions this phase remains effectively undetermined. Also, the modulus of their ratio depends critically on the details of the theory input.

MEASUREMENT OF THE EXCLUSIVE LIGHT HADRON DECAYS OF THE ψ″ IN e+e- EXPERIMENTS

The measurement of the exclusive light hadron decays of the ψ″ in e+e- experiments with significant interference between the ψ″ and continuum amplitudes is discussed. The radiative correction and the Monte Carlo simulation are studied. It is possible to verify the destructive interference for the detectors with energy–momentum resolution of (1~2)%.

Search forψ(3770)→ρπat the BESII detector at the Beijing Electron-Positron Collider

Non-DD¯ decay ψ(3770)→ρπ is searched for using a data sample of (17.3±0.5) pb−1 taken at the center-of-mass energy of 3.773 GeV by the BESII detector at the BEPC. No ρπ signal is observed, and the upper limit of the cross section is measured to be σ(e+e−→ρπ)<6.0 pb at 90% C. L. Considering the interference between the continuum amplitude and the ψ(3770) resonance amplitude, the branching fraction of ψ(3770) decays to ρπ is determined to be B(ψ(3770)→ρπ)∈(6.0×10−6,2.4×10−3) at 90% C. L. This is in agreement with the prediction of the S- and D-wave mixing scheme of the charmonium states for solving the “ρπ puzzle” between J/ψ and ψ(2S) decays.Received 21 July 2005DOI:https://doi.org/10.1103/PhysRevD.72.072007©2005 American Physical Society

Systematic speedup of path integrals of a genericN-fold discretized theory

We present and discuss a detailed derivation of a new analytical method that systematically improves the convergence of path integrals of a generic $N$-fold discretized theory. We develop an explicit procedure for calculating a set of effective actions $S^{(p)}$, for $p=1,2,3,...$ which have the property that they lead to the same continuum amplitudes as the starting action, but that converge to that continuum limit ever faster. Discretized amplitudes calculated using the $p$ level effective action differ from the continuum limit by a term of order $1/N^p$. We obtain explicit expressions for the effective actions for levels $p\le 9$. We end by analyzing the speedup of Monte Carlo simulations of two different models: an anharmonic oscillator with quartic coupling and a particle in a modified P\"oschl-Teller potential.

Systematically Accelerated Convergence of Path Integrals

We present a new analytical method that systematically improves the convergence of path integrals of a generic N-fold discretized theory. Using it we calculate the effective actions S(p) for p< or =9, which lead to the same continuum amplitudes as the starting action, but that converge to that continuum limit as 1/N(p). We checked this derived speedup in convergence by performing Monte Carlo simulations on several different models.

The interference between virtual photon and 1−− charmonium in e+e− experiment

e+e− experiments producing charmonium are reviewed. It is found that the contribution of the continuum amplitude via virtual photon was neglected in almost all the experiments and the channels analyzed. It is shown that the contribution of the continuum part may affect the final results significantly in ψ(2S) and ψ(3770) decays, while the interference between continuum and resonance amplitudes may even affect the J/ψ decays as well as the ψ(2S) and ψ(3770). This should be considered in analyzing the “ρπ puzzle” between J/ψ and ψ(2S) decays, and the difference between inclusive hadron and DD̄ cross sections in ψ(3770) decays.

Measuring ψ″→ρπ in e+e− experiment

In S- and D-wave mixing scheme, the branching ratio of ψ″→ρπ is estimated. Together with the continuum cross section of ρπ estimated by form factor, the observed cross section of ρπ production at ψ″ in e+e− experiment is calculated taking into account the interference effect between the resonance and continuum amplitudes and the initial state radiative correction. The behavior of the cross section reveals that the disappearance of ρπ signal just indicates the existence of the corresponding branching ratio Bψ″→ρπ at the order of 10−4.

Spectral purity and sources of noise in femtosecond-demodulation terahertz sources driven by Ti:sapphire mode-locked lasers

Direct measurements of the spectral purity in terahertz femtosecond-demodulation sources are reported and compared to theory. Because these sources operate at very high harmonics (/spl sim/102-10/sup 4/) of the mode-lock frequency, a high spectral purity source is very dependent on a low-jitter femtosecond laser. Conversely, the spectral content of the terahertz sources provides detailed information about timing jitter and stringent tests of models used to describe the jitter. We find that both the behavior of the central core, and the noise skirts of the power spectrum of our sources, can be quantitatively related to measured ripple and continuum amplitude noise on the Ar/sup +/ pump laser by use of modulation theory.

Measuring the Higgs CP property through top quark pair production at photon linear colliders

We present a model-independent study of the effects of a neutral Higgs boson without definite $\mathrm{CP}$ parity in the process $\ensuremath{\gamma}\stackrel{\ensuremath{\rightarrow}}{\ensuremath{\gamma}}t\overline{t}$ around the mass pole of the Higgs boson. Near the resonance pole, the interference between the Higgs exchange and the continuum amplitudes can be sizable if the photon beams are polarized and helicities of the top quark and top antiquark are measured. The study of these interference effects enables one to determine the $\mathrm{CP}$ property of the Higgs boson completely. An example of the complete determination is demonstrated in the context of the minimal supersymmetric standard model.

Removal of the continuum of X-ray spectra using morphological operators

In energy dispersive X-ray fluorescence analysis, the estimation and removal of the continuum on which the X-ray spectrum is superimposed is a primary requirement. The algorithms commonly used are either complex, or in the case of, e.g., neural network algorithms, computation-intensive. They usually require strong constraints and/or hypotheses on the data or the shape of the continuum. Moreover, if the continuum amplitude is comparable to or bigger than the peak amplitudes, some of these algorithms can lose peaks. A new approach to continuum removal based on mathematical morphology is proposed here. The new algorithm permits fast continuum elimination without peak deterioration. Other than a rough estimate on the widths of the peaks, the new method does not require additional information about the spectrum. The method can also be applied without modification to background elimination from gamma ray spectra. This new method is described and results obtained from real and simulated spectra are discussed and evaluated.

A high-resolution study of the threshold photoelectron spectrum of helium

Measurements of the threshold photoelectron spectrum of helium have been made at the Gas Phase beamline at Elettra Synchrotron, Trieste. The energy region studied spans the thresholds of the satellite states, beginning with N = 2, up to the threshold. The energy resolution in the new spectrum is five times better than that of previous measurements and has enabled us to resolve satellite states with N = 13-19 for the first time. The part of the spectrum in the region of the double-ionization threshold exhibits a cusp-like feature in accordance with predictions of the Wannier model for threshold photo-double ionization. This region has been used to examine the role of doubly excited neutral states in single-ion formation and also to compare with previous experiments the ratio of the discrete and continuum amplitudes of the cusp. The use of the threshold photoelectron technique as an accurate and convenient method to calibrate the energy scales of optical monochromators for synchrotron radiation is noted.

A time-dependent theory of resonant multiphoton ionization of atoms by short pulses. I. Weak-field results for the two-photon ionization of caesium

We develop a time-dependent theory of resonant multiphoton ionization of an atom by a laser pulse, whose envelope is taken to be a hyperbolic secant in time. The choice of this shape enables us to solve the time-dependent Schrodinger equation analytically for an n-state system, of which up to (n-1) levels can be in resonance with the ground state for par of the time. Using the expressions deduced for excited-state amplitudes, a closed-form representation for continuum amplitudes is derived, from which the photoelectron energy spectrum is calculated. Stark shifts of the bound states explicitly retained in the eigenfunction expansion due to coupling to omitted levels are included perturbatively. The theory is applied in this paper to the two-photon ionization of caesium by weak fields. A new kind of structure is predicted. The results are compared to the spectrum generated by a weak rectangular pulse.

The discovery of a young radio galaxy at Z = 2.390 - Probing initial star formation at Z less than approximately 3.0

We present the discovery of a weak radio galaxy from the Leiden Berkeley Deep Survey at a redshift of 2.390, the faint optical and IR counterpart of the steep-spectrum, compact radio source 53W002. Its λ dependent optical continuum morphology is compact with linear size ~10-35 kpc (H_0_= 50, q_0_ = 0). In redshifted Lyα, the galaxy is somewhat more extended (&lt;~67 kpc x 40 kpc). Its radio source is 7 times smaller than, and confined by, the Lyα gas. It shows alignment with the Lyα gas and the best seeing optical continuum images. We present nine-band photometry (Lyα UBgriJHK) for the galaxy as well as surrounding objects. The source 53W002 is not variable on time scales of years, in either radio or optical. We compare its rest-frame UV continuum with IUE spectra of various nearby galaxies with relatively recent starbursts, and nearby active galactic nuclei (AGNs). The C IV/Lyα and N V/Lyα ratios suggest that 53W002 has a Seyfert 1-like AGN, and constrain the nonthermal component to be ~35% of the observed UV continuum. Several independent age estimates yield a consistent value of 0.25-0.32 Gyr: (1) its small 4000 A break or UV-visual continuum amplitude compared with nearby galaxies; (2) a best model fit to the downturn of its UV spectrum below ~2000 A; (3) limits from the lack of detected stellar absorption features; (4) its total stellar mass (from its V- and K-band luminosity) compared with its SFR [from W<SUB>lambda</SUB>(Lyα, z = 0)]. These parameters together suggest that at z = 2.390, 53W002 had processed only a few times 10^11^ M_sun_ into stars, significantly less than most powerful radio galaxies have converted into stars at z ~2-3.8. Hence, star formation in 53W002 has proceeded slower, and started at a later epoch, than in the most powerful high-redshift radio galaxies. The available data are consistent with 53W002 being a genuinely young (radio) galaxy seen at z = 2.390 during its first major starburst. It likely started forming most of its current stars at redshifts 2.5-3.0 (for H_sun_ = 50-100, q_0_ = 0.0-0.5). This suggests that (radio) galaxies do not form the bulk of their stars coevally, but start doing so over a wide range of cosmic time.