Gamma Decay Modes Research Articles

Constraints on the spin-parity and anomalousHVVcouplings of the Higgs boson in proton collisions at 7 and 8 TeV

The study of the spin-parity and tensor structure of the interactions of the recently discovered Higgs boson is performed using the H to ZZ, Z gamma*, gamma* gamma* to 4 l, H to WW to l nu l nu, and H to gamma gamma decay modes. The full dataset recorded by the CMS experiment during the LHC Run 1 is used, corresponding to an integrated luminosity of up to 5.1 inverse femtobarns at a center-of-mass energy of 7 TeV and up to 19.7 inverse femtobarns at 8 TeV. A wide range of spin-two models is excluded at a 99% confidence level or higher, or at a 99.87% confidence level for the minimal gravity-like couplings, regardless of whether assumptions are made on the production mechanism. Any mixed-parity spin-one state is excluded in the ZZ and WW modes at a greater than 99.999% confidence level. Under the hypothesis that the resonance is a spin-zero boson, the tensor structure of the interactions of the Higgs boson with two vector bosons ZZ, Z gamma, gamma gamma, and WW is investigated and limits on eleven anomalous contributions are set. Tighter constraints on anomalous HVV interactions are obtained by combining the HZZ and HWW measurements. All observations are consistent with the expectations for the standard model Higgs boson with the quantum numbers J[PC]=0[++].

H→Zγin gauge-Higgs unification

In our previous paper, we have investigated effects of a simple gauge-Higgs unification model on the diphoton signal events from the Higgs boson production at the Large Hadron Collider. We have found that in this model the effective Higgs-to-diphoton coupling can be enhanced by 1-loop corrections with Kaluza-Klein (KK) modes of bulk fields. This result can be an explanation for the observed excess of the signal strength in the Higgs to diphoton decay channel. In this paper, we investigate KK-mode effects on another Higgs boson decay mode, H to Z gamma. One naturally expects that the KK modes also contribute to the effective H-Z-gamma coupling and can cause some deviation for the H to Z gamma decay mode from the Standard Model prediction. Revealing a correlation between the KK-mode effects on the Higgs-to-diphoton and H-Z-gamma couplings is an interesting topic in terms of a possibility to discriminate a variety of models for physics beyond the Standard Model. We show a very striking result for the gauge-Higgs unification model, namely, the absence of KK-mode contributions to the H-Z-gamma coupling at the 1-loop level. This is a very specific and general prediction of the gauge-Higgs unification scenario.

Observation of a NewχbState in Radiative Transitions toΥ(1S)andΥ(2S)at ATLAS

The chi_b(nP) quarkonium states are produced in proton-proton collisions at the Large Hadron Collider (LHC) at sqrt(s) = 7 TeV and recorded by the ATLAS detector. Using a data sample corresponding to an integrated luminosity of 4.4 fb^-1, these states are reconstructed through their radiative decays to Upsilon(1S,2S) with Upsilon->mu+mu-. In addition to the mass peaks corresponding to the decay modes chi_b(1P,2P)->Upsilon(1S)gamma, a new structure centered at a mass of 10.530+/-0.005 (stat.)+/-0.009 (syst.) GeV is also observed, in both the Upsilon(1S)gamma and Upsilon(2S)gamma decay modes. This is interpreted as the chi_b(3P) system.

K→πγdecays and space-time noncommutativity

We propose the K -> pi gamma decay mode as a signature of the violation of the Lorentz invariance and the appearance of new physics via space-time noncommutativity.

Single-proton-transfer studies of 153Eu levels

Levels in 153Eu have been studied with the (t, α) reaction at 15 MeV. Earlier ( 3He,d) and ( α,t) results have also been supplemented by new measurements with improved resolution at selected angles. Spectroscopic strengths were extracted, using distorted wave Born analysis methodology, and interpreted in terms of the Nilsson model with Coriolis mixing. Several new level and band assignments are proposed. For the 5/2 + levels at 694 and 706 keV an interpretation consistent with all experimental data requires admixtures of the 1/2 +[420] and 5/2 +[402] orbitals, as well as other types of components. Specifically, in addition to the 5/2 −[532]+ Q 30 components previously proposed to explain gamma-decay modes of these levels, (t,p) results indicate that complex configurations involving pairing excitations are important for the 706 keV and other 5/2 + levels. The 5/2 +[402] strength is fragmented over several levels. A successful description of these complex structures will require consideration of several effects, including quasiparticle–phonon interactions, Coriolis mixing, and a detailed treatment of pairing correlations.

Observation of radiative B-->phi K gamma decays.

The radiative decay B-->phi K gamma is observed for the first time. The branching fraction for the charged B--->phi K- gamma decay mode is measured to be B(B--->phi K- gamma)=(3.4+/-0.9+/-0.4)x10(-6). The photon energy distribution for the B--->phi K- gamma decay is presented. The signal for the neutral B(0)-->phi K(0)gamma decay mode is not statistically significant and an upper limit, B(B(0)-->phi K(0)gamma)<8.3x10(-6) at 90% C.L., is set. The analysis is based on a data set of 90 fb(-1) collected by the Belle experiment at the e(+)e(-) asymmetric collider KEKB.

KL→π0γγand the bound on theCP-conservingKL→π0e+e−

It has been known for many years that there is a CP-conserving component for the decay mode K_L -> pi0 e+e- and that its magnitude can be obtained from a measurement of the amplitudes in the K_L -> pi0 gamma gamma decay mode. We point out that the usual description of the latter in terms of a single parameter, a_V, is not sufficient to extract the former in a model independent manner. We further show that there exist known physics contributions to K_L -> pi0 gamma gamma that cannot be described in terms of the single parameter a_V. We conclude that a model independent analysis requires the experimental extraction of three parameters.

The structure of28Si above 10 MeV excitation energy I: gamma-decay modes and radiative widths of levels

The systematics ofγ-decay modes and radiative widths of highly excited states in28Si has been extended by takingγ-ray spectra on 60 resonances of the27Al(p,γ) reaction in the range 1097 keV≤Ep≤ 4492 keV (12643 keV≤Ex≤ 15915 keV) and on the24Mg(α,γ) resonances atEα=3355, 3431, 4003 keV (Ex=12860, 12925, 13 415 keV). Theγ-decay modes of levels in the sub-resonance region (Ex=10−12.5 MeV) were studied with both the27A1(p, γ) reaction and the27A1(d, nγ) reaction at Ed=4,5,6 MeV. Information on radiative widths of levels was obtained by measuring the resonance strengthsSγ=(2I+1)ΓpΓγ/Γ for 52 resonances of the27Al(p, γ) reaction with an emphasis on prospective T=1 states.

The structure of25Mg

Gamma-decay modes and spin(-parity) assignments of levels in25Mg have been systematically investigated up to 10 MeV excitation energy by particle-γ-ray angularcorrelation measurements with the24Mg(d, pγ) reaction at 6.5 MeV bombarding energy and with the22Ne(α,nγ) reaction at 11.8, 12.5, 14.4 and 15.5 MeV bombarding energy. A level scheme has been established which is comprehensive up to 8.3 MeV excitation energy forI≦9/2 and up to 10 MeV for 9/2<I≦15/2. The excitation energies and electromagnetic properties of more than 70 states for which positive parity has been established or is most probable are compared with the results of shell-model calculations which use the complete configuration space of theO d5/2 — 1s1/2-O d3/2 shell and the unifieds-d shell Hamiltonian. The agreement is good to excellent. The first intruder states are located near 6.8 MeV excitation energy. The collective properties of25Mg beyond the well established rotational bands are investigated using both the new experimental information and theB(E2)'s obtained from the shell model. The spectrum of25Mg is completely rotational for the first five to six MeV above the yrast line. Shell modelB (M 1)'s reflect the Nilsson model structure of25Mg in great detail. The prospectiveIπ=9/2−, 13/2−, and 15/2− members of the established negative-parity,K=1/2 band are found in levels atEx=7801, 9410, and 8896 keV.

The structure of27Al

Gamma decay modes and spin assignments of levels in27Al have been investigated by proton-γ-ray angular correlation measurements in the24Mg(α, pγ) reaction at 14.2, 15 and 15.6 MeV bombarding energy and byγ-ray angular distribution measurements on the Ep=1820, 2114, 2293 and 2574 keV resonances of the26Mg(p, γ) reaction. Unique spin assignments were obtained as follows: I=3/2 for the 5827 keV state, I=5/2 for the 6115, 6465, 6765, 7577, 7721, 8097, 8136, 8324 keV states, I=7/2 for the 5433, 6533, 7413, 8037, 8442, 8586 keV states, I=9/2 for the 5418, 6512, 6713, 7997 keV states, I=11/2 for the 5500, 6948, 7400, 8396 keV states. The level scheme and electromagnetic properties of levels are compared with the results of shell model calculations which use the complete configuration space of the 0d5/2-1s1/2-0d3/2 shell and the unifieds-d shell Hamiltonian. The agreement is good to excellent and extends into the region of high level density above 7 MeV excitation energy. The total B(M1↑) below 8.5 MeV excitation energy is evaluated, using published resonance fluorescence and (e, e′) data, and quenching relative to the free-nucleon predictions is reexamined. Evidence in favour of a prolate ground state deformation of27Al and implications of this work for the astrophysically interesting26Al(p, γ) reaction are discussed.

Muon-induced fission in 235U and 238U

Muon-induced prompt and delayed fission yields in 235U and 238U have been measured. A coincidence with the muonic uranium Kα X-rays was used to identify the muon stop in the target. The experimental absolute fission yields per muon stop were 0.142 ± 0.023 for 235U and 0.068 ± 0.013 for 238U. The disappearance rate of muons from the 1s state of muonic uranium has also been measured in the fission mode. Muon-induced fission lifetimes were 71.6 ± 0.6 ns for 235U and 77.2 ± 0.4 ns for 238U. No evidence for a short-lifetime fission – isomer component was found. Comparison of lifetime results with previously measured values in the electron, gamma, and neutron decay modes indicated that the systematic discrepancies could be explained by muon capture on fission fragments produced from prompt fission.

High spin states in91Tc

A shell model calculation for the states of91Tc has been carried out using the (1g9/2, 2p1/2) model space with residual interactions determined from previous studies and assuming thatZ=38N=50 is a closed shell. The results, both for the spectrum and the gamma decay modes, support the experimental angular momentum assignments made for the high spin states. The predicted binding energy of the 9/2+ ground state relative to88Sr is within 75 keV of the experimental value and the calculated excitation energy of the 1/2− state is 183 keV. There is only one instance where theory and experiment disagree: the highest energy excited state, the 41/2− at 7.715 MeV, is predicted to undergo quadrupole decay to the 37/2− and this decay mode is not seen.

On the Triaxial Deformation in Transitional Odd-A Nuclei

The essential difference as well as the apparent identity between the triaxial-rotor model and the gamma-vibrational model have been discussed. From the gamma decay mode, the [19/2 - ] 1 states of the j =11/2 - family in 187 Ir and 189 Ir have been identified as the K = j +4 states, the presence of which contradicts the particle plus triaxial-rotor model.

The electromagnetic decay of the T = 3/2 states in19F

The gamma-decay modes of the first two T = 3/2 levels in 19F at Ex = 7538 ± 2 and 7659 ± 2 keV have been studied at resonances in the 15N(α, γ)19F reaction at Eα = 4.465 and 4.618 MeV. Several weak decay branches have been seen: 7.54 → 5.11 MeV, 1.7 ± 0.4%; 7.54 → 1.35 MeV, 1.2 ± 0.4%; 7.66 → 4.55 MeV, 5.1 ± 0.3%; 7.66 → 5.11 MeV, 5.9 ± 0.5%. Comparison with (sd)3 shell model calculations indicate that the 4.55 and 5.11 MeV levels can be associated with the second and third calculated 5/2+ states. Using the DSAM, upper limits have been set on several lifetimes: 4377 ± 1 keV, &lt; 22 fs; 4548 ± 2 keV, &lt; 50 fs; 5105 ± 2 keV, &lt; 30 fs.

Excited levels of85Sr (studied via85Y decay and85Rb(p,n))

The gamma ray spectra following the decay of 85Y isomers (2.68 h and 4.8 h) have been investigated. The previously proposed doublets at 614, 1400 and 2120 keV and several other unreported structures have been clearly resolved. Sixteen new gamma rays have been identified in the decay work and comparatively accurate values for the energies and the relative intensities of the observed transitions are presented. In addition, in-beam gamma ray measurements following the 85Rb(p,n gamma )85Sr reaction have been made at an incident proton energy of 3.8 MeV. 23 levels have been proposed through decay studies, of which 12 levels below 1.6 MeV excitation in 85Sr are evidenced by (p,n gamma ) measurements. New levels are proposed at energies of 785.4, 936.9, 1398.0, 1588.5, 1987.6, 2086.0, 2165.8 and 2748.4 keV. From the deduced log ft values and the observed gamma decay modes, probable Jpi assignments for the levels in 85Sr have been made. The level structure is compared with the existing theoretical calculations.

Nuclear data sheets for A = 84

Nuclear structure information from radioactive decay studies and nuclear reactions pertaining to mass 84 nuclei are compiled, and adopted level schemes are presented. It was found that there are relatively few data for several of these nuclei and, therefore, all data and adopted values for 84As, 84Se, 84Kr and 84Sr are presented in the Summary Sheets. There are no separate Data Sheets for these nuclei. Many levels have been populated in 84Sr and, to a lesser extent, in 84Kr from the decay of 84Y and 84Br, respectively. However, the properties of most of these levels, other than their energies and gamma-decay modes, are unknown. There also appears to be some uncertainty as to placement of the highest energy beta transition observed in the decay of 84Y. Only two excited states have been studied in each of the odd-odd nuclei, 86Br and 86Rb, one of them being a long-lived metastable state in each case. The decay of 86mRb is rather interesting since, if the presently adopted gammaray intensities and decay scheme are correct, a large E4/M3 or M4/E3 mixing ratio is indicated for one of the transitions. The adopted level properties are based on data received through July 1970. Data from a recent study of 84Rb have been added in proof.

Spin assignment for the 4.28 MeV level in48Ca by means of the48Ca (p, p′γ) reaction

The gamma decay mode and the possible spin values of the second excited state of48Ca (Ex=4.28 MeV) were investigated by studying the48Ca(p, p′γ) reaction at an incident proton energy of 10.30 MeV. No ground state gamma transition was observed. The analysis of thep2-γ angular correlation — using method II of Litherland and Ferguson — supports the spin assignmentI=0 for this level and excludes all spin values higher thanI=1.

Lifetime measurements in 16O

The lifetimes of three excited states in 16O have been measured by the Doppler shift attenuation method. The states studied were 8.87 MeV (2 −), 240 ± 40 fs, 10.95 MeV (0 −), 8 ± 5 fs, and 11.08 MeV (3 +), 57 ± 19 fs. The gamma decay modes of the latter two states were also studied and branching ratios were extracted.

Spin assignment for the 1.89 MeV level in42Sc

The gamma decay mode and the spin value of the 1.89 MeV state of42Sc were investigated by studying the40Ca(3He,p γ)42Sc reaction at 10.0 MeV energy of the incident3He beam. The analysis of thep-γ angular correlation of the 1.89 MeV ground state transition — using method II of Litherland and Ferguson — yields the spin assignmentJ=1 for this level.

Decay schemes of excited states in Mg 24 and Si 28 and the collective model

Gamma decay modes of the first six excited states of Mg 24 and the first four excited states of Si 28 have been determined with inelastic proton scattering. Mg 24 has been interpreted both on the axially symmetric rotational-vibrational, and the rotating triaxial ellipsoid colletive models. The decay modes require, on the former model, < 2% amplitude band mixing; they imply γ≈14° on the latter model, while the positions of the spin 2 levels suggest γ=22°. The higher Si 28 levels cannot be explained on either model. Thus Mg 24 is more susceptible to a deformed nucleus collective model interpretation than Si 28; this is correlated with the known greater nuclear deformation of Mg 24.