Electromagnetic Strength Research Articles

Electromagnetic strength of neutron and proton single-particle halo nuclei

Electromagnetic strength functions of halo nuclei exhibit universal features that can be described in terms of characteristic scale parameters. For a nucleus with nucleon + core structure the reduced transition probability, as determined, e.g., by Coulomb dissociation experiments, shows a typical shape that depends on the nucleon separation energy and the orbital angular momenta in the initial and final states. The sensitivity to the final-state interaction (FSI) between the nucleon and the core can be studied systematically by varying the strength of the interaction in the continuum. In the case of neutron + core nuclei analytical results for the reduced transition probabilities are obtained by introducing the effective-range expansion. The scaling with the relevant parameters is found explicitly. General trends are observed by studying several examples of neutron + core and proton + core nuclei in a single-particle model assuming Woods–Saxon potentials. Many important features of the neutron halo case can be obtained from a square-well model. Rather simple analytical formulas are found. The nucleon–core interaction in the continuum affects the determination of astrophysical S factors at zero energy in the method of asymptotic normalisation coefficients (ANC). It is also relevant for the extrapolation of radiative capture cross sections to low energies.

Search for bosonic stop decays in R-parity violating supersymmetry in e+pe+p collisions at HERA

A search for scalar top quarks in R-parity violating supersymmetry is performed in e+p collisions at HERA using the H1 detector. The data, taken at s=319GeV and 301 GeV, correspond to an integrated luminosity of 106pb−1. The resonant production of scalar top quarks t˜ in positron quark fusion via an R-parity violating Yukawa coupling λ′ is considered with the subsequent bosonic stop decay t˜→b˜W. The R-parity violating decay of the sbottom quark b˜→dν¯e and leptonic and hadronic W decays are considered. No evidence for stop production is found in the search for bosonic stop decays nor in a search for the direct R-parity violating decay t˜→eq. Mass dependent limits on λ′ are obtained in the framework of the minimal supersymmetric Standard Model. Stop quarks with masses up to 275GeV can be excluded at the 95% confidence level for a Yukawa coupling of electromagnetic strength.

Effective-Range Approach and Scaling Laws for Electromagnetic Strength in Neutron-Halo Nuclei

We study low-lying multipole strength in neutron-halo nuclei. The strength depends only on a few low-energy constants: the neutron separation energy, the asymptotic normalization coefficient of the bound-state wave function, and the scattering length that contains the information on the interaction in the continuum. The shape of the transition probability shows a characteristic dependence on few scaling parameters and the angular momenta. The total E1 strength is related to the root-mean-square radius of the neutron wave function in the ground state and shows corresponding scaling properties. We apply our approach to the E1 strength distribution of 11Be.

Search for bosonic stop decays in R-parity violating supersymmetry in [formula omitted] collisions at HERA

A search for scalar top quarks in R-parity violating supersymmetry is performed in e+p collisions at HERA using the H1 detector. The data, taken at s=319GeV and 301 GeV, correspond to an integrated luminosity of 106pb−1. The resonant production of scalar top quarks t˜ in positron quark fusion via an R-parity violating Yukawa coupling λ′ is considered with the subsequent bosonic stop decay t˜→b˜W. The R-parity violating decay of the sbottom quark b˜→dν¯e and leptonic and hadronic W decays are considered. No evidence for stop production is found in the search for bosonic stop decays nor in a search for the direct R-parity violating decay t˜→eq. Mass dependent limits on λ′ are obtained in the framework of the minimal supersymmetric Standard Model. Stop quarks with masses up to 275GeV can be excluded at the 95% confidence level for a Yukawa coupling of electromagnetic strength.

Modification of the Physicomechanical Properties of Polycaproamide Fibres by Exposure to Ultrahigh-Frequency Electromagnetic Vibrations

Modification of the physicomechanical properties of textured PCA fibres with UHF electromagnetic vibrations was investigated. The dependence of the unit breaking force of PCA fibres on the duration of exposure to an UHF field in different orientation of the sample relative to the electromagnetic wave strength vector was established.

Microstructural Effects of Electromagnetic Stirring Strength and Casting Speed in Continuous Casting of Al Alloy

Semi-solid forming usually requires feed stock material in form of cylindrical billets with a uniform, globular and fine grain microstructure. These billets are commonly being produced by continuous casting involving agitation of the solidifying melt. The paper will present the development of a horizontal continuous casting machine using circumferential electromagnetic stirring to generate melt flow and shear rate in the continuous casting mould. The machine has been used to study the influence of various process parameters such as electromagnetic stirring strength and casting speed in the production of Al billet with a diameter of 76mm. In order to establish the quantitative relationship between microstructure and the process parameters, the morphology and primary crystal size of billet were observed according to the casting speed and electromagnetic stirring strength. A depth and distance of surface defect on the billet was decreased with increasing a casting speed and a very good smooth surface without any surface defect appeared on the billet produced at a casting speed of 600mm/min. A thickness of the solidifying shell was decreased with increasing the casting speed and the maximum casting speed without a break-out was 600mm/min in horizontal continuous caster designed in this study. Both the size and the aspect ratio of primary crystal were decreased with increasing the casting speed and electromagnetic stirring strength in the range of this study.

Nonexotic neutral gauge bosons

We study theoretical and experimental constraints on electroweak theories including a new color-singlet and electrically-neutral gauge boson. We first note that the electric charges of the observed fermions imply that any such Z' boson may be described by a gauge theory in which the Abelian gauge groups are the usual hypercharge along with another U(1) component in a kinetic-diagonal basis. Assuming that the observed quarks and leptons have generation-independent U(1) charges, and that no new fermions couple to the standard model gauge bosons, we find that their U(1) charges form a two-parameter family consistent with anomaly cancellation and viable fermion masses, provided there are at least three right-handed neutrinos. We then derive bounds on the Z' mass and couplings imposed by direct production and Z-pole measurements. For generic charge assignments and a gauge coupling of electromagnetic strength, the strongest lower bound on the Z' mass comes from Z-pole measurements, and is of order 1 TeV. If the new U(1) charges are proportional to B-L, however, there is no tree-level mixing between the Z and Z', and the best bounds come from the absence of direct production at LEPII and the Tevatron. If the U(1) gauge coupling is one or two orders of magnitude below the electromagnetic one, these bounds are satisfied for most values of the Z' mass.

Wobbling phonon excitations in strongly deformed triaxial nuclei

The wobbling mode is uniquely related to triaxiality and introduces a series of bands with increasing wobbling phonon number, $n_{\rm w}$ . The pattern of $\gamma$ -transitions between the wobbling excitations will be influenced by the presence of an aligned particle. Evidence for the wobbling mode was obtained recently, and even a two-phonon wobbling excitation has now been identified in 163 Lu. The similarity of the data in 163 Lu to new strongly deformed triaxial bands and connecting transitions in the neighbouring nuclei, 165 Lu and 167 Lu, establishes wobbling as a more general phenomenon in this region. The higher phonon wobbling excitations show some anharmonicity, but the characteristic large $\Delta n_{\rm w} = 1$ E2 strength is observed. The wobbling interpretation is based on the comparison of electromagnetic decay strength between bands to particle-rotor calculations in which an i 13/2 proton is coupled to a triaxial core.

Low-energy electromagnetic excitation strengths in121Sband123Sb

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A search for leptoquark bosons in e−p collisions at HERA

A search for scalar and vector leptoquarks coupling to first generation fermions is performed in the H1 experiment at the ep collider HERA. The analysis uses e−p data collected in 1998 and 1999 at a centre-of-mass energy of 320 GeV, corresponding to an integrated luminosity of ∼15 pb−1. No evidence for the direct production of such particles is found in a data sample with a large transverse momentum final state electron or with large missing transverse momentum, and constraints on leptoquark models are established. For a Yukawa coupling of electromagnetic strength leptoquarks are excluded for masses up to ∼290 GeV. This analysis complements the leptoquark searches performed previously using data collected whilst HERA was operating with positrons instead of electrons.

Muon anomalous magnetic moment and leptoquark solutions

The recent measurement of the muon anomalous magnetic moment ${a}_{\ensuremath{\mu}}$ shows a $2.6\ensuremath{\sigma}$ deviation from the standard model value. We show that it puts an interesting bound on the mass of the second generation leptoquarks. To account for the data the leptoquark must have both left- and right-handed couplings to the muon. Assuming that the couplings have electromagnetic strength, the mass is restricted in the range 0.7 $\mathrm{TeV}l{M}_{\mathrm{LQ}}l2.2 \mathrm{TeV}\mathrm{}$ at 95% C.L. We also discuss constraints coming from other low energy and high energy experiments. If first-second-generation universality is assumed, constraints come from atomic-parity violation and charged-current universality. We show that the coexistence with other leptoquarks can satisfy these additional constraints and at the same time does not affect ${a}_{\ensuremath{\mu}}.$

Searches at HERA for squarks in R-parity violating supersymmetry

A search for squarks in R-parity violating supersymmetry is performed in e^+p collisions at HERA at a centre of mass energy of 300 GeV, using H1 data corresponding to an integrated luminosity of 37 pb^(-1). The direct production of single squarks of any generation in positron-quark fusion via a Yukawa coupling lambda' is considered, taking into account R-parity violating and conserving decays of the squarks. No significant deviation from the Standard Model expectation is found. The results are interpreted in terms of constraints within the Minimal Supersymmetric Standard Model (MSSM), the constrained MSSM and the minimal Supergravity model, and their sensitivity to the model parameters is studied in detail. For a Yukawa coupling of electromagnetic strength, squark masses below 260 GeV are excluded at 95% confidence level in a large part of the parameter space. For a 100 times smaller coupling strength masses up to 182 GeV are excluded.

Atomic parity violation, leptoquarks, and contact interactions

The recent measurement of atomic parity violation in cesium atoms shows a 2.3 σ deviation from the standard model prediction. We show that such an effect can be explained by four-fermion contact interactions with specific chiralities or by scalar leptoquarks which couple to the left-handed quarks. For a coupling of electromagnetic strength, the leptoquark mass is inferred to be 1.1 to 1.3 TeV. We also show that these solutions are consistent with all other low-energy and high-energy neutral-current data.

Single production of leptoquarks at the Fermilab Tevatron

We study the single production of first generation leptoquarks in association with a e+/- at the Fermilab Tevatron. We focus our attention on final states exhibiting a e+e- pair and jets, and perform a detailed analyses of signal and backgrounds. The single leptoquark production cross section depends on the leptoquark Yukawa coupling to lepton-quark pairs and we show that the study of this mode can extend considerably the leptoquark search for a large range of these couplings. In fact, for Yukawa couplings of the electromagnetic strength, the combined results of the Tevatron experiments can exclude the existence of leptoquarks with masses up to 260--285 (370--425) GeV at the RUN I (RUN II), depending on their type.

A search for leptoquark bosons and lepton flavor violation in $e^+ p$ collisions at HERA

A search for new bosons possessing couplings to lepton-quark pairs is performed in the H1 experiment at HERA using 1994 to 1997 data corresponding to an integrated luminosity of \(37\) pb\(^{-1}\). First generation leptoquarks (LQs) are searched in very high \(Q^2\) neutral (NC) and charged (CC) current data samples. The measurements are compared to Standard Model (SM) expectations from deep-inelastic scattering (DIS). A deviation in the \(Q^2\) spectrum previously observed in the 1994 to 1996 dataset at \(Q^2 \gtrsim 15000\) GeV\(^2\) remains, though with less significance. This deviation corresponded to a clustering in the invariant mass spectrum at \(M \simeq 200\) GeV which is not observed with the 1997 dataset alone. The NC DIS data is used to constrain the Yukawa couplings \(\lambda\) of first generation scalar and vector LQs in the Buchmuller–Ruckl–Wyler effective model. Scalar LQs are excluded for masses up to 275 GeV for a coupling of electromagnetic strength, \(\lambda = 0.3\). A sensitivity to coupling values \(\lesssim 1\) is established for masses up to 400 GeV for any LQ type. The NC and CC DIS data are combined to constrain \(\lambda\) for arbitrary branching ratios of the LQ into eq in a generic model. For a decay branching ratio into \(e^+ u\) pairs as small as 10%, LQ masses up to 260 GeV are ruled out for \(\lambda = 0.3\). LQs possessing couplings to mixed fermion generations, which could lead to signals of lepton flavor violation (LFV), are searched in events with a high transverse momentum \(\mu\) or \(\tau\). No \(\mu + X\) or \(\tau + X\) event candidate is found that is compatible with LQ kinematics. Constraints are set on the Yukawa coupling involving the \(\mu\) and \(\tau\) lepton in a yet unexplored mass range.

Limits on a light leptophobic gauge boson

We consider the phenomenology of a naturally leptophobic Z-prime boson in the 1 to 10 GeV mass range. The Z-prime's couplings to leptons arise only via a radiatively-generated kinetic mixing with the Z and photon, and hence are suppressed. We map out the allowed regions of the mass-coupling plane and show that such a Z-prime that couples to quarks with electromagnetic strength is not excluded by the current data. We then discuss possible signatures at bottom and charm factories.

Total interaction and proton-removal cross-section measurements for the proton-rich isotopes 7Be, 8B, and 9C

In an experiment performed at the FRS of GSI, we measured total interaction cross sections for 7Be, 8B, and 9C, one-proton-removal cross sections for 8B and 9C as well as two-proton-removal cross sections for 9C on targets ranging from carbon to lead at an energy of 285 MeV/nucleon. In addition, we performed measurements at 142 MeV/nucleon for 8B. The experimental results are compared to different calculations. Glauber-type calculations with different model·density distributions show that, down to incident energies of about 50 MeV/nucleon, total interaction cross-section measurements with light targets are not sensitive to an extended proton distribution in 8B. However, at lower incident energies, a tail in the proton density distribution is needed to explain the total interaction cross sections. Total interaction cross-section measurements with high-Z targets in the present experiment show a significant increase of the cross sections due to low-lying electromagnetic strength.

Search for lepton flavor violation in $ep$ collisions at 300 GeV center of mass energy

Using the ZEUS detector at the HERA electron-proton collider, we have searched for lepton flavor violation in ep collisions at a center-of-mass energy (root s) of 300 GeV. Events of the type e + p --> l + X with a final-state lepton of high transverse momentum, l = mu or tau, were sought. No evidence was found for lepton flavor violation in the combined 1993 and 1994 data samples, for which the integrated luminosities were 0.84 pb(-1) for e(-)p collisions and 2.94 pb(-1) for e(+)p collisions. Limits on coupling vs. mass are provided for leptoquarks and R-parity violating squarks, For flavor violating couplings of electromagnetic strength, we set 95% confidence level lower limits on leptoquark masses between 207 GeV and 272 GeV, depending on the leptoquark species and final-state lepton. For leptoquark,masses larger than 300 GeV, limits on flavor-changing couplings are determined, many of which supersede prior limits from rare decay processes.

Leptoquark mass limits from single leptoquark production at LEP and LEP200

We investigate the discovery potential for first generation leptoquarks at the LEP and LEP200 e + e − colliders. We consider single leptoquark production via resolved photon contributions which offers a much higher kinematic limit than the more commonly considered leptoquark pair production process. This process also has the advantage that it is independent of the leptoquark chirality, is almost insensitive to whether the leptoquark is scalar or vector, and only depends on the leptoquark charge. We estimate that from the nonobservation of energetic e - jet events that cannot be explained as backgrounds, the limits at LEP for all types of leptoquarks are M L Q > 90 GeV. For the just completed s = 161 GeV run at LEP200 we estimate potential scalar leptoquark mass limits of M L Q > 130 GeV for Q LQ = −2 3 , −4 3 and M L Q > 148 GeV for Q LQ = −1 3 , −5 3 and for vector LQ's the limits are ∼ 140 and ∼ 154 GeV respectively. Ultimately, LEP200 should be able to achieve discovery limits for leptoquarks of ∼ 188 GeV for the s = 190 GeV runs. In all cases we assume electromagnetic strength coupling.

Reconstructing space-time from world-lines of charged particles

It is possible to reconstruct a given space-time ( M, g) furnished with a 2-form Ω (the electromagnetic strength) from the 6-dimensional manifold parametrizing the world-lines in M of the particles with rest-mass m 0 (or 0) and charge ± e 0 (or 0).