2p Cross Sections Research Articles

Development of a Two-Photon-Responsive Chromophore, 2-(p-Aminophenyl)-5,6-dimethoxy-1-(hydroxyinden-3-yl)methyl Derivative, as a Photoremovable Protecting Group.

Photoremovable protecting groups (PPGs) are powerful tools that are widely used to investigate biological events in cells. An important requirement for PPGs is the efficient release of bioactive molecules by using visible to near-infrared light in the biological window (650-1350 nm). In this study, we report a new two-photon (2P)-responsive PPG, 2-(p-aminophenyl)-5,6-dimethoxy-1-(hydroxyinden-3-yl)methyl, with a donor-π-donor cyclic stilbene structure. The 2P cross section was approximately 40-50 GM at ∼700 nm. The quantum yield of the uncaging process of caged benzoate was greater than 0.7, demonstrating that the 2P uncaging efficiency was approximately 30 GM at around 700 nm. This newly developed 2P-responsive chromophore can be used in future biological experiments. The mechanism of the photo-uncaging reaction via the carbocation intermediate was elucidated using transient absorption spectroscopy and product analysis.

Measurement of e+e− → π+π−π0 at BABAR and calculation of (g−2)μ

We present a study of the process e+e−→π+π−π0 at BABAR using the initial-state radiation technique. The analysis is based on the full BABAR data set, 469fb−1, recorded at and near the ϒ(4S) resonance. From the fit to the measured three pion mass spectrum we determine the products Γ(V→e+e−)B (V→π+π−π0) for the ω and ϕ resonances, and the branching ratio B (ρ→π+π−π0). The latter isospin-breaking decay is observed with 6σ significance. The e+e−→π+π−π0 cross section is measured from 0.62 GeV to 3.5 GeV. The measured cross section is used to calculate the leading-order hadronic contribution to the muon anomalous magnetic moment from this exclusive final state with improved accuracy. A short status is given on the current discrepancy between the predicted value and the measured value of the muon anomalous magnetic moment.

A new empirical systematic for (n, 2p) reaction cross sections around 14 MeV

In the present work, we proposed a new empirical systematic with which we can predict the (n, 2p) cross sections as an extension of the empirical rule on the basis of the statistical theory of nuclear reactions. It is obtained by fitting the experimental cross sections as a function of mass number, reaction Q–value, threshold energy and projectile energy. A new analysis of experimental data is performed for (n, 2p) reactions around 14 MeV energy. Besides, the present formula was expressed by a simple systematic with two fitting parameters. The predictions of this formula were discussed and compared with cross section measurements and empirical formulas found in the literature. Results show that the new empirical formula gives a good fit to predict the (n, 2p) cross sections around 14 MeV. This study can provide a reference to the (n, 2p) reaction channel considering the lack of measured cross section values.

Measurement of e+e−→ K+K−π0 cross section and observation of a resonant structure

Based on e+e− collision data collected by the BESIII detector at the BEPCII collider at center-of-mass energies from 2.000 to 3.080 GeV, a partial-wave analysis is performed for the process e+e−→ K+K−π0. The Born cross section of the process e+e−→ K+K−π0 and its subprocesses e+e−→ ϕπ0, K*+(892)K− and {K}_2^{ast +} (1430)K− are measured. The results for e+e−→ K+K−π0 and ϕπ0 are consistent with the BaBar measurements and with improved precision. By analyzing the cross sections of the subprocesses e+e−→ K*+(892)K− and {K}_2^{ast +} (1430)K−, a structure with mass MR = (2190 ± 19 ± 37) MeV/c2 and width ΓR = (191 ± 28 ± 60) MeV is observed with a combined statistical significance of 7.1σ. The measured resonance parameters suggest it can be identified as the ϕ(2170), thus the results provide valuable input to understand the internal nature of this state.

Study of the process e+e−→π+π−π0 using initial state radiation with BABAR

The process e+e−→π+π−π0γ is studied at a center-of-mass energy near the ϒ(4S) resonance using a data sample of 469 fb−1 collected with the BABAR detector at the PEP-II collider. We have performed a precise measurement of the e+e−→π+π−π0 cross section in the center-of-mass energy range from 0.62 to 3.5 GeV. In the energy regions of the ω and ϕ resonances, the cross section is measured with a systematic uncertainty of 1.3%. The leading-order hadronic contribution to the muon magnetic anomaly calculated using the measured e+e−→π+π−π0 cross section from threshold to 2.0 GeV is (45.86±0.14±0.58)×10−10. From the fit to the measured 3π mass spectrum we have determined the resonance parameters Γ(ω→e+e−)B(ω→π+π−π0)=(0.5698±0.0031±0.0082) keV, Γ(ϕ→e+e−)B(ϕ→π+π−π0)=(0.1841±0.0021±0.0080) keV, and B(ρ→3π)=(0.88±0.23±0.30)×10−4. The significance of the ρ→3π signal is greater than 6σ. For the J/ψ resonance we have measured the product Γ(J/ψ→e+e−)B(J/ψ→3π)=(0.1248±0.0019±0.0026) keV.21 MoreReceived 4 October 2021Accepted 12 November 2021DOI:https://doi.org/10.1103/PhysRevD.104.112003Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI. Funded by SCOAP3.Published by the American Physical SocietyPhysics Subject Headings (PhySH)Research AreasParticle interactionsPhysical SystemsLight mesonsQuarkoniaTechniquesLepton collidersParticle productionParticles & Fields

Measurement of the e + e − → π+π−π0 cross section with the CMD-3 detector

The preliminary results of measurement of the e + e − → π+π−π0 cross section in the 1.05–2 GeV center-of-mass energy range with 30 pb–1 of experimental data collected using the CMD-3 detector are presented. The parameters of resonant states ω(1420) and ω(1650) are obtained.

Vectorization and Intracellular Distribution of a Two‐Photon‐Absorbing, Near‐Infrared‐Emitting π‐Extended Boranil Dye

AbstractA π‐extended boranil (PEB) dye has been synthesized and its photophysical properties have been recorded in a range of solvents. The dye exhibits an intense solvatochromic fluorescence emission covering the entire visible spectrum and the near infra‐red (NIR) region (from λ=534 to 764 nm) with quantum yields up to 69 %. Embedment of the PEB dye in the amphiphilic block copolymer Cremophor EL® leads to a strong emission (λem=617 nm, Φ=0.33) in PBS buffer. Moreover, two‐photon absorption (TPA) spectroscopy evidenced a large two‐photon (2P) cross section (420 GM), enabling the use of the PEB dye in 2P‐excitation fluorescence microscopy. The cellular uptake and distribution of PEB in HeLa cells was monitored using fluorescence lifetime imaging microscopy (FLIM) and real‐time widefield imaging. It was found that the emission of the dye is strongly influenced by the local environment and that the dye is preferentially internalized in acidic vesicles.

Hadronic light-by-light contribution to the muon g — 2

We have computed the hadronic light-by-light (LbL) contribution to the muon anomalous magnetic moment aμ in the frame of Chiral Perturbation Theory with the inclusion of the lightest resonance multiplets as dynamical fields (RχT). It is essential to give a more accurate prediction of this hadronic contribution due to the future projects of J-Parc and FNAL on reducing the uncertainty in this observable. We, therefore, computed the pseudoscalar transition form factor and proposed the measurement of the e+ e- →μ+ μ- π0 cross section and dimuon invariant mass spectrum to determine more accurately its parameters. Then, we evaluated the pion exchange contribution to αμ, obtaining (6.66 ± 0.21) • 10-10. By comparing the pion exchange contribution and the pion-pole approximation to the corresponding transition form factor (πTFF) we recalled that the latter underestimates the complete πTFF by (15-20)%. Then, we obtained the η(') TFF, obtaining a total contribution of the lightest pseudoscalar exchanges of (10.47 ± 0.54) • 10-10, in agreement with previous results and with smaller error.

On the extraction of cross sections for π0 and η photoproduction off neutrons from deuteron data

We discuss the procedure of extracting the photoproduction cross section for neutral pseudoscalar mesons off neutrons from deuteron data. The main statement is that the final-state interaction (FSI) corrections for the proton and neutron target are in general not equal, but for pi0 production there are special cases were they have to be identical and there are large regions in the parameter space of incident photon energy and pion polar angle, \theta^*, where they happen to be quite similar. The corrections for both target nucleons are practically identical for $\pi_0$ production in the energy range of the Delta(1232)3/2+ resonance due to the specific isospin structure of this excitation. Also above the $\Delta$-isobar range large differences between proton and neutron correction factors are only predicted for extreme forward angles ($\theta^*$ < 20 deg), but the results are similar for larger angles. Numerical results for the gp-->pi0p and gn-->pi0n correction factors are discussed. Also the model description for the available data on the differential gd-->pi0pn cross sections are given.

Two‐Photon‐Induced Fluorescence of Isomorphic Nucleobase Analogs

Five isomorphic fluorescent uridine mimics have been subjected to two-photon (2P) excitation analysis to investigate their potential applicability as non-perturbing probes for the single-molecule detection of nucleic acids. We find that small structural differences can cause major changes in the 2P excitation probability, with the 2P cross sections varying by over one order of magnitude. Two of the probes, both thiophene-modified uridine analogs, have the highest 2P cross sections (3.8 GM and 7.6 GM) reported for nucleobase analogs, using a conventional Ti:sapphire laser for excitation at 690 nm; they also have the lowest emission quantum yields. In contrast, the analogs with the highest reported quantum yields have the lowest 2P cross sections. The structure-photophysical property relationship presented here is a first step towards the rational design of emissive nucleobase analogs with controlled 2P characteristics. The results demonstrate the potential for major improvements through judicious structural modifications.

Neutron Interactions with 3He Revisited–II: Nonelastic Cross Sections in the Mega-Electron-Volt Range

Reliable nonelastic cross-section measurements of fast neutrons with 3He are sparse. In the energy range up to 40 MeV, the data are dominated by unpublished nonelastic n-3He values derived from measurements made in 1982. As mentioned elsewhere, n-3He elastic cross-section data reported in the same report had not been corrected for the outgoing neutron attenuation even though the sample size was >7 mol. To check the database of existing nonelastic n-3He cross-section data, and in particular those from 1982, a detailed balance calculation of time-reversed charged-particle data was performed. Because there are few existing independent data, we provide an updated detailed balance analysis in the energy range up to 31 MeV for both 3He(n,p)3H and 3He(n,d)2H, supplying accurate absolute-angle-dependent differential cross sections. Subtracting the integrals of these and the elastic cross sections from the total provides a prediction for the sum of the 3He(n,2n)2p and 3He(n,n + p)2H cross sections. The relevant experimental data are compared with their time-reversed counterparts.

Relaxation effects in 2p photoionization of Ar isonuclear sequence

The 2p photoionization cross sections of Ar, Ar6+ and Ar8+ have been investigated by the multiconfiguration Dirac-Fock method. Our results show excellent agreement with the previous measurements and calculations, the relaxation is not so important for inner subshells of neutral Ar and all subshells of Ar6+ and Ar8+ as generally accepted. In unrelaxed calculation, it is known that the inner-shell cross sections are essentially unchanged upon the presence or absence of outer electrons except for a shift in the corresponding thresholds. Specifically, the present results show that this is not entirely true, i.e., non-neglectable influence of the removal of outer electrons on the 2p cross sections is observed even when the relaxation effects are not considered, especially in energy region near the thresholds.

Two-photon excitation of the fluorescent nucleobase analogues 2-AP and tC

We present two-photon (2P) excitation measurements of two commonly-used and commercially available fluorescent nucleobase analogues in aqueous solution: the environment-sensitive adenine analogue 2-aminopurine (2-AP), which emits in the UV region, and the environment-insensitive cytosine analogue 1,3-diaza-2-oxophenothiazine (tC), which emits in the green region. We studied the 2P excitation of free 2-AP and found that the same emissive states are accessed as via one-photon (1P) and three-photon (3P) excitation. The 2P cross section of 2-AP was 0.2 GM, which is similar to that of related molecules such as NADH. We studied tC incorporated in three single-stranded DNA oligonucleotides by 1P and 2P spectroscopy and microscopy. We found that the same emissive states were populated via either the resonant or non-resonant pathway with a 2P cross section of 1.5 GM. Time-resolved fluorescence studies suggested that tC exists in solution as two species, which we assigned as the amino and imino tautomers. Using confocal microscopy, we found that similar emission rates could be achieved for 2P excitation, as compared with 1P excitation, but without the strong photobleaching observed in the latter case. Although we were unable to detect tC fluorescence at the single-molecule level, these results indicate that multiphoton excitation of nucleobase analogues is a promising approach for imaging applications.

Cross section and double helicity asymmetry for η mesons and their comparison to π0 production at PHENIX

The η cross section and double helicity asymmetry as a function of transverse momentum have been measured at √s = 200 GeV at the PHENIX experiment at RHIC. The cross section data serve as important input to the extraction of η fragmentation functions, which were essentially unknown before. With the availability of fragmentation functions the asymmetry data can be included in future pQCD fits in order to further constrain the polarized parton distribution functions, in particular the helicity-dependent gluon distribution function. In addition, the η to π0 cross section ratio as a function of transverse momentum has been extracted in a single pass over the same data set, thus minimizing systematic uncertainties. The inclusion of these data in future fragmentation function extractions should allow for more precise results for both particle species.

π0 Double Longitudinal Helicity Asymmetry Measurements at PHENIX

Measurement of the gluon's contribution to the proton spin, ΔG, is an important component of the RHIC spin program. One particular avenue for constraining ΔG is through the π0 double longitudinal helicity asymmetry, ALL. The large p + p → π0 cross section coupled with the high resolution of the PHENIX EM-Calorimeter make this an attractive measurement. After some discussion of the measurement, existing PHENIX π0 ALL results at center of mass energies √s = 62.4 and 200 GeV are presented, including new 200 GeV results from the RHIC run ending in 2009. Projections for future 500 GeV results are also shown.

Emission of Neutral Pions with High Transverse Momenta in A-A and p-p Collisions at Energies Available at the BNL Relativistic Heavy Ion Collider

Invariant neutral pion (π0) yields in Au-Au and Cu-Cu collisions and invariant π0 cross sections in p-p collisions are studied in the framework of a two-cylinder model. The considered distributions of neutral pions at the maximum energy of the relativistic heavy ion collider (RHIC) have a tail part in the region of high transverse momentum. A two-component distribution based upon the two-cylinder model is used to describe the experimental data of the PHENIX collaboration.

Electronic structure of the band-filling-controlledCaVO3 andLaVO3 compounds

We studied the electronic structure of the band-fillingCaVO3 andLaVO3 compounds. The experimental techniques were photoemission (PES)and x-ray absorption (XAS) spectroscopy. The experimental resultswere analyzed using an extended cluster model. The ground states ofCaVO3 andLaVO3 are highly covalent and contain a considerable3dn + 1L contribution.The CaVO3 compound is in the charge transfer regime (Δ < U), whereas theLaVO3 material is in theintermediate regime (Δ ∼ U). The spectral weight distributions reveal thatCaVO3 is a coherentmetal and that LaVO3 is a p–d insulator. The photoemission ofCaVO3 shows the coherent peak (3d1C) and the incoherent feature(3d1L). The spectrum ofinsulating LaVO3 presents onlythe incoherent structure (3d2L), whereas the coherent peak is replaced by the Mott–Hubbard screening (3d2D). This transfer of spectral weight is responsible for the opening of the experimentalbandgap. The incoherent feature contains a considerable O 2p character and cannot beattributed to the lower Hubbard band. Further, the relative V 3d–O 2p cross section helps toexplain the photon energy dependence of the PES spectra. The addition spectra of bothCaVO3 andLaVO3 are dominatedby the 3dn + 1 final state configuration. The distribution of spectral weight is mainly dictated byintra-atomic exchange and crystal field splittings. The coherent contribution is lessimportant than in photoemission, and is greatly diminished in the O 1s x-ray absorptionspectra.

Electron Impact Emission of N2 2P(v',v'') Bands Studied under Single-Collision Condition

As a confirmative study on electron impact emission of the second positive band group (2PG) of N 2 molecules, absolute emission cross section for the 2P(0,0) band and intensity ratios 2P(v',v”)/2P(0,0) have been measured. The absolute measurement has been made directly using a standard light source. From these results, the cross sections for excitation of C 3 Π u (v'=0, 1) vibrational states have been determined. Emphasis was placed on measurements under single-collision condition. Experimental errors have been assessed in some detail. The absolute 2P(0,0) cross section measured has the peak value of (11.1±1.1)×10 -18 cm 2 . This value is in good agreement with measurements reported recently by other two research groups. From the present and the two recent results, which were measured at low N 2 pressure and for which estimated errors are given, a weighted averaging value is calculated to be (11.0±0.7)×10 -18 cm 2 as a recommended emission cross section for 2P(0,0) band.

Study of thee+e−→π+π−π0process using initial state radiation withBABAR

The process e+e−→π+π−π0γ has been studied at a center-of-mass energy near the Υ(4S) resonance using a 89.3 fb−1 data sample collected with the BABAR detector at the PEP-II collider. From the measured 3π mass spectrum we have obtained the products of branching fractions for the ω and ϕ mesons, B(ω→e+e−)B(ω→3π)=(6.70±0.06±0.27)×10−5 and B(ϕ→e+e−)B(ϕ→3π)=(4.30±0.08±0.21)×10−5 and evaluated the e+e−→π+π−π0 cross section for the e+e− center-of-mass energy range 1.05 to 3.00 GeV. About 900 e+e−→J/ψγ→π+π−π0γ events have been selected and the branching fraction B(J/ψ→π+π−π0)=(2.18±0.19)% has been measured.13 MoreReceived 16 August 2004DOI:https://doi.org/10.1103/PhysRevD.70.072004©2004 American Physical Society

Atomic oxygen 3P → 3S0 (λ1304Å) transition revisited: Cross section near threshold

The direct excitation cross section for the atomic oxygen 3P → 3S0 transition (λ1304Å) has been measured at four incident energies between 13.4 and 40 eV. These measurements were made to add sufficient detail to previous direct excitation measurements to allow the near‐threshold cross section to be determined. Previous optical measurements of the 1304Å emission cross section disagree by up to a factor of 2 in this important energy region. We have also compared the atomic hydrogen e + H(1s) → H(2s + 2p) cross section, used previously as a secondary standard for our direct excitation measurements of atomic oxygen cross sections, to recent measurements of the total e + H → Lyman alpha cross section and have found agreement at the ±15% level, making a revision of our previously reported atomic oxygen cross sections unnecessary. The new direct excitation atomic oxygen cross section results, combined with previous measurements, support the emission cross section measured by Stone and Zipf [1974] and revised by Zipf and Erdman [1985] over the measurement of Wang and McConkey [1992]. Except for the region just above threshold at 10–25 eV incident energy, all the cross section measurements now agree to within ±20%. The 100 eV value of the atomic oxygen 3P → 3S0 emission cross section from a combination of the emission and direct excitation cross section experiments is 8.6 ± 11% × 10−18 cm2.