Four-body Decay Research Articles

Triple-product asymmetries inK,D(s), andB(s)decays

One distinguishes between "true" CP violating triple product (TP) asymmetries which require no strong phases and "fake" asymmetries which are due to strong phases but require no CP violation. So far a single true TP asymmetry has been measured in $K_L\to \pi^+\pi^- e^+e^-$. A general discussion is presented for T-odd TP asymmetries in four-body decays. It is shown that TP asymmetries vanish for two identical and kinematically indistinguishable particles in the final state. Two examples are $D^0\to K^-\pi^+\pi^-\pi^+$ and $D^+\to K^-\pi^+\pi^+\pi^0$. A non-zero TP asymmetry can be expected when non-trivial kinematic correlations exist, as in the decay $K_L \to e^+ e^- e^+ e^-$. Triple product asymmetries measured in charmed particle decays indicate an interesting pattern of final-state interactions. We reiterate a discussion of TP asymmetries in $B$ meson decays to two vector mesons each decaying to a pseudoscalar pair, extending results to decays where one vector meson decays into a lepton pair. We derive expressions for time-dependent TP asymmetries for neutral B decays to flavorless states in terms of the neutral $B$ mass difference $\Delta m$ and the width-difference $\Delta\Gamma$. Time-integrated true CP violating asymmetries, measurable for untagged $B_s$ decays, are shown to be suppressed by neither $\Gamma_s/\Delta m_s$ nor $\Delta\Gamma_s/\Gamma_s$ if transversity amplitudes for CP-even and CP-odd states involve different weak phases. In contrast, fake asymmetries require flavor tagging and are suppressed by the former ratio when time-integrated. We apply our results to $B\to K^*\phi$ and $B_s\to\phi\phi$ data and suggest an application for $B_s\to J/\psi\phi$.

Lepton number violation in top quark and neutralBmeson decays

Lepton number violation (LNV) can be induced by Majorana neutrinos in four-body decays of the neutral B meson and the top quark. We study the effects of Majorana neutrinos in these |\Delta L|=2 decays in an scenario where a single heavy neutrino can enhance the amplitude via the resonant mechanism. Using current bounds on heavy neutrino mixings, the most optimistic branching ratios turn out to be at the level of 10^{-6} for \bar{B} -> D^+e^-e^-\pi^+ and t -> bl^+l^+W^- decays. Searches for these LNV decays at future facilities can provide complementary constraints on masses and mixings of Majorana neutrinos.

Investigations of three-, four-, and five-particle decay channels of levels in light nuclei created using aC9beam

The interactions of an $E/A=70$-MeV $^{9}\mathrm{C}$ beam with a Be target was used to populate levels in Be, B, and C isotopes, which undergo decay into many-particle exit channels. The decay products were detected in the HiRA array and the level energies were identified from their invariant mass. Correlations between the decay products were examined to deduce the nature of the decays, specifically to what extent all the fragments were created in one prompt step or whether the disintegration proceeded in a sequential fashion through long-lived intermediate states. In the latter case, information on the spin of the level was also obtained. Of particular interest is the five-body decay of the $^{8}\mathrm{C}$ ground state, which was found to disintegrate in two steps of two-proton decay passing through the $^{6}\mathrm{Be}$${}_{g.s.}$ intermediate state. The isobaric analog of $^{8}\mathrm{C}$${}_{g.s.}$ in $^{8}\mathrm{B}$ was also found to undergo two-proton decay to the isobaric analog of $^{6}\mathrm{Be}$${}_{g.s.}$ in $^{6}\mathrm{Li}$. A 9.69-MeV state in $^{10}\mathrm{C}$ was found to undergo prompt four-body decay to the 2$p$ $+$ 2$\ensuremath{\alpha}$ exit channel. The two protons were found to have a strong enhancement in the diproton region and the relative energies of all four $p$-$\ensuremath{\alpha}$ pairs were consistent with the $^{5}\mathrm{Li}$${}_{g.s.}$ resonance.

Light stop decay in the MSSM with minimal flavour violation

In supersymmetric scenarios with a light stop particle $\tilde{t}_1$ and a small mass difference to the lightest supersymmetric particle (LSP) assumed to be the lightest neutralino, the flavour changing neutral current decay $\tilde{t}_1 \to c \tilde{\chi}_1^0$ can be the dominant decay channel and can exceed the four-body stop decay for certain parameter values. In the framework of Minimal Flavour Violation (MFV) this decay is CKM-suppressed, thus inducing long stop lifetimes. Stop decay length measurements at the LHC can then be exploited to test models with minimal flavour breaking through Standard Model Yukawa couplings. The decay width has been given some time ago by an approximate formula, which takes into account the leading logarithms of the MFV scale. In this paper we calculate the exact one-loop decay width in the framework of MFV. The comparison with the approximate result exhibits deviations of the order of 10% for large MFV scales due to the neglected non-logarithmic terms in the approximate decay formula. The difference in the branching ratios is negligible. The large logarithms have to be resummed. The resummation is performed by the solution of the renormalization group equations. The comparison of the exact one-loop result and the tree level flavour changing neutral current decay, which incorporates the resummed logarithms, demonstrates that the resummation effects are important and should be taken into account.

Hunting for CDF multi-muon “ghost” events at collider and fixed-target experiments

In 2008 the CDF collaboration discovered a large excess of events containing two or more muons, at least one of which seemed to have been produced outside the beam pipe. We investigate whether similar "ghost" events could (and should) have been seen in already completed experiments. The CDF di-muon data can be reproduced by a simple model where a relatively light X particle undergoes four-body decay. This model predicts a large number of ghost events in Fermilab fixed-target experiments E772, E789 and E866, applying the cuts optimized for analyses of Drell-Yan events. A correct description of events with more than two muons requires a more complicated model, where two X particles are produced from a very broad resonance Y. This model can be tested in fixed-target experiments only if the cut on the angles, or rapidities, of the muons can be relaxed. Either way, the UA1 experiment at the CERN ppbar collider should have observed O(100) ghost events.

Central exclusive quarkonium production with tagged forward protons at RHIC

We study the Central Exclusive Production (CEP) of χ cJ and η c mesons at RHIC in proton–proton collisions. We consider the χ cJ →J/ψ + γ decay channels and, recalling that the J z =0 suppression of the J=1,2 states can be compensated by their larger branchings to J/ψ + γ, present predictions of rates and distributions for χ c(0,1,2) production. Particular attention is paid to the impact of p ⊥ cuts applied to the outgoing protons, which can influence the relative rates significantly. The distribution in the azimuthal angle difference between the outgoing protons and the proton \(p_{\perp}^{2}\) is also studied, and shown to depend sensitively on the spin and parity of the centrally produced meson, as well as being affected by the soft-survival factors, S 2. Two- and four-body decays, which are particularly relevant for χ c0 production, are also considered. We show that in the two-body case, backgrounds from ‘direct’ QCD production based on both perturbative and non-perturbative models are expected to be under control.

Effect on Higgs boson decays from large light-heavy neutrino mixing in seesaw models

In seesaw models with more than one generation of light and heavy neutrinos, nu and N, respectively, it is possible to have sizable mixing between them for heavy-neutrino masses of order 100 GeV or less. We explore this possibility further, taking into account current experimental constraints, and study its effect on Higgs-boson decays in the contexts of seesaw models of types I and III. We find that in the type-I case the Higgs decay into a pair of light and heavy neutrinos, h -> nu N, could increase the total Higgs width in the standard model by up to almost 30% for a relatively light Higgs-boson, which would significantly affect Higgs searches at the LHC. The subsequent prompt decay of N into three light fermions makes this Higgs decay effectively a four-body decay. We further find that, in the presence of the large light-heavy mixing, these four-body Higgs decays can have rates a few times larger than their standard-model counterparts and therefore could provide a potentially important window to reveal the underlying seesaw mechanism.

Y(4143)is probably a molecular partner ofY(3930)

After discussing the various possible interpretations of the $Y(4143)$ signal observed by the CDF collaboration in the $J/\ensuremath{\psi}\ensuremath{\phi}$ mode, we tend to conclude that $Y(4143)$ is probably a ${D}_{s}^{*}{\overline{D}}_{s}^{*}$ molecular state with ${J}^{PC}={0}^{++}$ or ${2}^{++}$ while $Y(3930)$ is its ${D}^{*}{\overline{D}}^{*}$ molecular partner as predicted in our previous work [X. Liu, Z. G. Luo, Y. R. Liu, and Shi-Lin Zhu, Eur. Phys. J. C 61, 411 (2009)]. Both the hidden-charm and open-charm two-body decays occur through the rescattering of the vector components within the molecular states while the three- and four-body open-charm decay modes are forbidden kinematically. Hence, their widths are narrow naturally. CDF, BABAR and Belle collaborations may have discovered heavy molecular states already. We urge experimentalists to measure their quantum numbers and explore their radiative decay modes in the future.

Publisher’s Note:τ˜1lightest supersymmetric particle phenomenology: Two- versus four-body decay modes and resonant single slepton production at the LHC as an example [Phys. Rev. D79, 016002 (2009)

Publisher’s Note:<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:msub><mml:mover accent="true"><mml:mi>τ</mml:mi><mml:mo>˜</mml:mo></mml:mover><mml:mn>1</mml:mn></mml:msub></mml:math>lightest supersymmetric particle phenomenology: Two- versus four-body decay modes and resonant single slepton production at the LHC as an example [Phys. Rev. D<b>79</b>, 016002 (2009)

τ˜1lightest supersymmetric particle phenomenology: Two- versus four-body decay modes and resonant single slepton production at the LHC as an example

We investigate ${\mathrm{B}}_{3}$ minimal supergravity models, where the lightest stau ${\stackrel{\texttildelow{}}{\ensuremath{\tau}}}_{1}$ is the lightest supersymmetric particle. ${\mathrm{B}}_{3}$ models allow for lepton number and R-parity violation; the lightest supersymmetric particle can thus decay. We assume one nonzero ${\mathrm{B}}_{3}$ coupling ${\ensuremath{\lambda}}_{ijk}^{\ensuremath{'}}$ at ${M}_{\mathrm{GUT}}$, which generates further ${\mathrm{B}}_{3}$ couplings at ${M}_{Z}$. We study the renormalization group equations and give numerical examples. The new couplings lead to additional ${\stackrel{\texttildelow{}}{\ensuremath{\tau}}}_{1}$ decays, providing distinct collider signatures. We classify the ${\stackrel{\texttildelow{}}{\ensuremath{\tau}}}_{1}$ decays and describe their dependence on the minimal supergravity parameters. We exploit our results for single slepton production at the LHC. As an explicit numerical example, we investigate single-smuon production, focussing on like-sign dimuons in the final state. Also considered are final states with three or four muons.

Majorana neutrinos and lepton-number-violating signals in top-quark and W-boson rare decays

Abstract We discuss rare lepton-number-violating top-quark and W -boson four-body decays to final states containing a same-charge lepton pair, of the same or of different flavors: t → b W − l i + l j + and W + → J J ¯ ′ l i + l j + , where i ≠ j or i = j and J J ¯ ′ stands for two light jets originating from a u ¯ d or a c ¯ s pair. These Δ L = 2 decays are forbidden in the Standard Model and may be mediated by exchanges of Majorana neutrinos. We adopt a model independent approach for the Majorana neutrinos mixing pattern and calculate the branching ratios (BR) for these decays. We find, for example, that for O ( 1 ) mixings between heavy and light Majorana neutrinos (not likely but not ruled out) and if at least one of the heavy Majorana neutrinos has a mass of ≲ 100 GeV , then the BR's for these decays are: BR ( t → b l i + l j + W − ) ∼ 10 −4 and BR ( W + → l i + l j + J J ¯ ′ ) ∼ 10 −7 if m N ∼ 100 GeV and BR ( t → b l i + l j + J J ¯ ′ ) ∼ BR ( W + → l i + l j + J J ¯ ′ ) ∼ 0.01 if m N ≲ 50 GeV . Taking into account the present limits on the neutrino mixing parameters, we obtain more realistic values for these BR's: BR ( t → b l i + l j + W − ) ∼ 10 −6 and BR ( W + → l i + l j + J J ¯ ′ ) ∼ 10 −10 for m N ∼ 100 GeV and BR ( t → b l i + l j + J J ¯ ′ ) ∼ BR ( W + → l i + l j + J J ¯ ′ ) ∼ 10 −6 for m N ≲ 50 GeV .

Gravitino dark matter and cosmological constraints

The gravitino is a promising cold dark matter candidate. We study cosmological constraintson scenarios in which the gravitino is the lightest supersymmetric particle and a chargedslepton the next-to-lightest supersymmetric particle (NLSP). We obtain new results for thehadronic nucleosynthesis bounds by computing the four-body decay of the NLSP sleptoninto the gravitino, the associated lepton, and a quark–antiquark pair. The bounds fromthe observed dark matter density are refined by taking into account gravitinosfrom both late NLSP decays and thermal scattering in the early Universe. Weexamine the present free-streaming velocity of gravitino dark matter and the limitsfrom observations and simulations of cosmic structures. Assuming that the NLSPsleptons freeze out with a thermal abundance before their decay, we derive newbounds on the slepton and gravitino masses. The implications of the constraints forcosmology and collider phenomenology are discussed and the potential insightsfrom future experiments are outlined. We propose a set of benchmark scenarioswith gravitino dark matter and long-lived charged NLSP sleptons and describeprospects for the Large Hadron Collider and the International Linear Collider.

Four-body decay of the lighter top squark constrained by the lighterCP-even Higgs boson mass bound

We reinvestigated the parameter space allowing a large branching ratio (BR) of the 4-body decay of the lighter top squark (${\stackrel{\texttildelow{}}{t}}_{1}$) accessible at Tevatron Run-II by imposing the lighter $CP$-even Higgs boson mass (${m}_{{h}^{0}}$) bound from LEP. Important constraints were obtained in mSUGRA as well as in the unconstrained supersymmetric models. Our results show that the prospect of searching the lighter top squark via the 4-body decay mode, in particular, the $\ensuremath{\ell}+n\ensuremath{-}\mathrm{\text{jets}}+{\mathrm{E\ensuremath{\llap{\not\;}}}}_{T}$ signal, is not promising in mSUGRA due to the above bound on ${m}_{{h}^{0}}$. The existing bounds on ${m}_{{\stackrel{\texttildelow{}}{t}}_{1}}$ from Tevatron Run-I and LEP assuming 100% BR of the loop decay of ${\stackrel{\texttildelow{}}{t}}_{1}$ are, therefore, valid to a good approximation. We also find that large BRs of the above 4-body decay are allowed in the unconstrained model over significant regions of parameter spaces and the possibility that this decay mode is the main discovery channel at Tevatron Run-II is open. We have briefly reviewed the theoretical uncertainties in the calculation of ${m}_{{h}^{0}}$ and their consequences for the constraints obtained by us. We have commented upon, with illustrative examples, how the above parameter space is affected if future experiments push the Higgs boson mass bound upward.

Search for T violation in charm meson decays

Using data from the FOCUS (E831) experiment, we have searched for T violation in charm meson decays using the four-body decay channels D0→K−K+π−π+, D+→KS0K+π−π+, and Ds+→KS0K+π−π+. The T violation asymmetry is obtained using triple-product correlations and assuming the validity of the CPT theorem. We find the asymmetry values to be ATviol(D0)=0.010±0.057(stat.)±0.037(syst.), ATviol(D+)=0.023±0.062(stat.)±0.022(syst.), and ATviol(Ds+)=−0.036±0.067(stat.)±0.023(syst.). Each measurement is consistent with no T violation. New measurements of the CP asymmetries for some of these decay modes are also presented.

Hadronic mass spectrum analysis of [formula omitted] decay and measurement of the [formula omitted] mass and width

We present a Kπ mass spectrum analysis of the four-body semileptonic charm decay D+→K−π+μ+ν in the range of 0.65 GeV/c2<mKπ<1.5 GeV/c2. We observe a non-resonant contribution of 5.30±0.74−0.96+0.99% with respect to the total D+→K−π+μ+ν decay. For the K∗(892)0 resonance, we obtain a mass of 895.41±0.32−0.43+0.35 MeV/c2, a width of 47.79±0.86−1.06+1.32 MeV/c2, and a Blatt–Weisskopf damping factor parameter of 3.96±0.54−0.90+1.31 GeV−1. We also report 90% CL upper limits of 4% and 0.64% for the branching ratios Γ(D+→K¯∗(1680)0μ+ν)Γ(D+→K−π+μ+ν) and Γ(D+→K¯0∗(1430)0μ+ν)Γ(D+→K−π+μ+ν), respectively.

SDECAY: a Fortran code for the decays of the supersymmetric particles in the MSSM

We present the Fortran code SDECAY, which calculates the decay widths and branching ratios of all the supersymmetric particles in the Minimal Supersymmetric Standard Model, including higher order effects. Besides the usual two-body decays of sfermions and gauginos and the three-body decays of charginos, neutralinos and gluinos, we have also implemented the three-body decays of stops and sbottoms, and even the four-body decays of the stop; the important loop-induced decay modes are also included. The QCD corrections to the two-body decays involving strongly interacting particles and the dominant components of the electroweak corrections to all decay modes are implemented. Program summary Title of program: SDECAY Version 1.1a (March 2005) Catalogue identifier: ADVJ Program summary URL: http://cpc.cs.qub.ac.uk/summaries/ADVJ Program obtainable: CPC Program Library, Queen's University of Belfast, N. Ireland Licensing provisions: none Computer for which the program is designed: Any with a Fortran77 system Operating systems under which the program has been tested: Linux, Unix Typical running time: A few seconds on modern personal computers and workstations Programming language used: Fortran77 No. of lines in distributed program, including test data, etc.: 59 621 No. of bytes in distributed program, including test data, etc.: 338 478 Distribution format: tar.gz Memory required to execute (with test data): 7.3 MB Distribution format: ASCII Nature of physical problem: Numerical calculation of the decay widths and branching ratios of supersymmetric particles in the Minimal Supersymmetric Standard Model (MSSM). The program calculates two-, three- and four-body decays and loop decays. It includes the SUSY-QCD corrections to two-body decays involving strongly interacting particles. The top-quark decays within the MSSM are evaluated as well. Method of solution: Two-dimensional numerical integration of the analytic formulae for the double differential decay widths of the three-body decays. The other decay widths are calculated analytically. Restrictions on the complexity of the problem: In the higher order decay modes the total decay widths of the virtually exchanged (s)particles are not included in their respective propagators. The higher order decays are calculated when the two-body decays are kinematically closed.

Λ(1405)andΛ¯(1405)inJ∕ψfour-body decays

We study the structure of the baryon resonances $\ensuremath{\Lambda}(1405)$ and $\overline{\ensuremath{\Lambda}}(1405)$ in $J∕\ensuremath{\psi}$ four-body decays $J∕\ensuremath{\psi}\ensuremath{\rightarrow}\ensuremath{\Sigma}\overline{\ensuremath{\Sigma}}\ensuremath{\pi}\ensuremath{\pi}$ in the framework of a coupled channel chiral unitary approach. With still sufficient freedom for model parameters, the $\ensuremath{\Lambda}(1405)$ and $\overline{\ensuremath{\Lambda}}(1405)$ resonances are generated by simultaneously taking the meson baryon and meson antibaryon final state interactions into account. The $\ensuremath{\pi}\ensuremath{\Sigma}\phantom{\rule{0.3em}{0ex}}(\ensuremath{\pi}\overline{\ensuremath{\Sigma}})$ invariant mass distributions peak around 1410 MeV, which favors the assertion that the $\ensuremath{\Lambda}(1405)\phantom{\rule{0.3em}{0ex}}[\overline{\ensuremath{\Lambda}}(1405)]$ is a superposition of the two $\ensuremath{\Lambda}(1405)\phantom{\rule{0.3em}{0ex}}[\overline{\ensuremath{\Lambda}}(1405)]$ states which dominantly couple to $\overline{K}N\phantom{\rule{0.3em}{0ex}}(K\overline{N})$ and $\ensuremath{\pi}\ensuremath{\Sigma}\phantom{\rule{0.3em}{0ex}}(\ensuremath{\pi}\overline{\ensuremath{\Sigma}})$, respectively. We also calculate the amplitude for isospin $I=1$ which gives hints of a possible $I=1$ baryon resonance in the energy region of the $\ensuremath{\Lambda}(1405)$, which up to now has not been observed.

Light scalar mesons inJ∕ψ→NN¯mesonmesondecays in a chiral unitary approach

We study the four-body decays $J/\psi\to N {\bar N}$ {\it meson meson} using a chiral unitary approach to account for the meson meson final state interaction (FSI). The calculation of the $J/\psi\to N \bar N \pi^+ \pi^-$ process properly reproduces the experimental data after taking the FSI of mesons and the contribution of intermediate $\rho$ meson into account. The isoscalar resonances $\sigma$, $f_0(980)$ and the isovector resonance $a_0(980)$ are generated through the FSI of the mesons in the channels $J/\psi\to N \bar N \pi^0 \pi^0$ and $J/\psi\to N \bar N \pi^0 \eta$, respectively. We also calculate the two mesons invariant mass distribution and the partial decay width of $J/\psi\to N \bar N K^+ K^-$ and $J/\psi\to N \bar N K^0 {\bar K}^0$, on which there is still no experimental data available.

Search for scalar quarks in e +e − collisions at [formula omitted] up to 209 GeV

Searches for scalar top, scalar bottom and mass-degenerate scalar quarks are performed in the data collected by the ALEPH detector at LEP, at centre-of-mass energies up to 209 GeV, corresponding to an integrated luminosity of 675 pb −1. No evidence for the production of such particles is found in the decay channels t ̃ → c/ uχ , t ̃ → bℓ ν ̃ , b ̃ → bχ , q ̃ → qχ or in the stop four-body decay channel t ̃ → bχ f f ̄ ′ studied for the first time at LEP. The results of these searches yield improved mass lower limits. In particular, an absolute lower limit of 63 GeV/ c 2 is obtained for the stop mass, at 95% confidence level, irrespective of the stop lifetime and decay branching ratios.

Measurement of the branching ratios of D(+) and D(+)(s) hadronic decays to four-body final states containing a K(S).

We have studied hadronic four-body decays of D(+) and D(+)(s) mesons with a K(S) in the final state using data recorded during the 1996-1997 fixed-target run of the Fermilab high energy photoproduction experiment FOCUS. We report a new branching ratio measurement of gamma(D(+)-->K(S)K-pi(+)pi(+))/gamma(D(+)-->K(S)pi(+)pi(+)pi(-)) = 0.0768+/-0.0041+/-0.0032. We make the first observation of three new decay modes with branching ratios gamma(D(+)-->K(S)K+pi(+)pi(-))/gamma(D(+)-->K(S)pi(+)pi(+)pi(-)) = 0.0562+/-0.0039+/-0.0040, gamma(D(+)-->K(S)K+K-pi(+))/gamma(D(+)-->K(S)pi(+)pi(+)pi(-)) = 0.0077+/-0.0015+/-0.0009, and gamma(D(+)(s)-->K(S)K+pi(+)pi(-))/gamma(D(+)(s)-->K(S)K-pi(+)pi(+)) = 0.586+/-0.052+/-0.043, where in each case the first error is statistical and the second error is systematic.