Two-body Final States Research Articles

New dark matter analysis of milky way dwarf satellite galaxies with madhatv2

We obtain bounds on dark matter annihilation using 14 years of publicly available Fermi-LAT data from a set of 54 dwarf spheroidal galaxies, using spectral information from 16 energy bins. We perform this analysis using our updated and publicly available code , which can be used to test a variety of models for dark matter particle physics and astrophysics in an accessible manner. In particular, we note that including Carina III in the analysis strengthens constraints on s-wave annihilation into two-body Standard Model final states by a factor of ∼3 but broadens the error on the constraint due to the large uncertainty of its J-factor. Our findings illustrate the importance of verifying if Carina III is in fact a dwarf spheroidal galaxy and measuring more precisely its J-factor. More generally, they highlight the significance of forthcoming discoveries of nearby ultrafaint dwarfs for dark matter indirect detection. Published by the American Physical Society 2024

Progress in the Partial-Wave Analysis Methods at COMPASS

Abstract. We study the excitation spectrum of light and strange mesons in diffractive scattering. We identify different hadron resonances through partial wave analysis, which inherently relies on analysis models. Besides statistical uncertainties, the model dependence of the analysis introduces dominant sys tematic uncertainties. We discuss several of their sources for the π−π−π+ and K0S K¯ final states and present methods to reduce them. We have developed a new approach exploiting a-priori knowledge of signal continuity over adjacent final-state-mass bins to stably fit a large pool of partial-waves to our data, al lowing a clean identification of very small signals in our large data sets. For two-body final states of scalar particles, such as K0S K¯, mathematical ambigui ties in the partial-wave decomposition lead to the same intensity distribution for different combinations of amplitude values. We will discuss these ambiguities and present solutions to resolve or at least reduce the number of possible so lutions. Resolving these issues will allow for a complementary analysis of the aJ-like resonance sector in these two final states.

Toward the ultimate reach of current imaging atmospheric Cherenkov telescopes and their sensitivity to TeV dark matter

Indirect detection opens a unique window for probing thermal dark matter (DM): the same annihilation process that determined the relic abundance in the early Universe drives the present day astrophysical signal. While TeV-scale particles weakly coupled to the Standard Model face undoubted challenges from decades of null searches, the scenario remains compelling, and simple realizations such as Higgsino DM remain largely unexplored. The fate of such scenarios could be determined by gamma-ray observations of the centre of the Milky Way with Imaging Atmospheric Cherenkov Telescopes (IACTs). We consider the ultimate sensitivity of current IACTs to a broad range of TeV-scale DM candidates - including specific ones such as the Wino, Higgsino, and Quintuplet. To do so, we use realistic mock H.E.S.S.-like observations of the inner Milky Way halo, and provide a careful assessment of the impact of recent Milky Way mass modeling, instrumental and astrophysical background uncertainties in the Galactic Center region, and the theoretical uncertainty on the predicted signal. We find that the dominant systematic for IACT searches in the inner Galaxy is the unknown distribution of DM in that region, however, beyond this the searches are currently statistically dominated indicating a continued benefit from more observations. For two-body final states at $1~{\rm TeV}$, we find a H.E.S.S.-like observatory is sensitive to $\langle \sigma v \rangle \sim 3 \times 10^{-26}-4 \times 10^{-25}~{\rm cm}^3{\rm s}^{-1}$, except for neutrino final states, although we find results competitive with ANTARES. In addition, the thermal masses for the Wino and Quintuplet can be probed; the Higgsino continues to be out of reach by at least a factor of a few. Our conclusions are also directly relevant to the next generation Cherenkov Telescope Array, which remains well positioned to be the discovery instrument for thermal DM.

A general study of decaying scalar dark matter: existing limits and projected radio signals at the SKA

We consider a decaying scalar dark matter (DM) with mass m χ in the range 10 GeV – 10 TeV and vary the branching ratios of allpossible two-body SM final states (excluding and including νν̅) in the range 0%-100% to derive constraints on the totaldecay width Γ using the data collected by severalastrophysical and cosmological observations. We find that,Γ ≲ 10-26 - 10-27 s-1 (excluding νν̅) and Γ ≲ 10-24 - 10-26 s-1 (including νν̅) are allowed, depending on the values of m χ, which are mostrobust upper limits on Γ for a generic decaying scalar DM.We then investigate the prospect of the upcoming Square KilometreArray (SKA) radio telescope in detecting the DM decay induced radiosignals originating inside the dwarf spheroidal (dSph) galaxies.We have classified the DM parameter space, allowed by the existingobservations, independently of the branching ratio of each individualtwo-body SM final state, based on the detectability at the SKA.Excluding the νν̅ decay mode, we find that, throughoutthe DM mass range considered,Γ ≳ 10-30 s-1 - 10-29 s-1 is detectable for all possible branching ratio combinationsat the SKA (assuming 100 hours of observation time), with conservativechoices for the relevant astrophysical parameters.On the other hand, when arbitrary branching ratios are allowedalso for the νν̅ decay mode, DM decays can be probedindependently of the branching ratio of each SM final statefor Γ ≳ 2 × 10-29 s-1,provided DM masses are greater than a few hundreds of GeV.

Two-current transition amplitudes with two-body final states

We derive the on-shell form of amplitudes containing two external currents with a single hadron in the initial state and two hadrons in the final state, denoted as $1+\mathcal{J}\to 2+\mathcal{J}$. This class of amplitude is relevant in precision tests of the Standard Model as well as for exploring the structure of excited states in the QCD spectrum. We present a model-independent description of the amplitudes where we sum to all orders in the strong interaction. From this analytic form we are able to extract transition and elastic resonance form factors consistent with previous work as well as a novel Compton-like amplitude coupling a single particle state to a resonance. The results also hold for reactions where the one-particle state is replaced with the vacuum, namely $\mathcal{J}\to 2+\mathcal{J}$ amplitudes. We also investigate constraints placed upon the formalism for the case of a conserved vector current in the form of the Ward-Takahashi identity. The formalism presented here is valid for currents of arbitrary Lorentz structure and quantum numbers with spinless hadrons where any number of two-particle intermediate channels may be open. When combined with the appropriate finite-volume framework, this work facilitates the extraction of physical observables from this class of amplitudes via lattice QCD calculations.

Linear power corrections for two-body kinematics in the qT subtraction formalism

Transverse-momentum cuts on undistinguished particles in two-body final states induce an enhanced sensitivity to low momentum scales. This undesirable feature, which ultimately leads to an instability of the fixed-order series, poses additional challenges to non-local subtraction schemes. In this letter, we address this issue for general colour-singlet processes within the qT-subtraction formalism, focusing on neutral-current Drell–Yan production. We present a simple procedure to reduce the dependence on the slicing parameter from linear to quadratic, by accounting for the linear power corrections through an appropriate recoil prescription. We observe a dramatical improvement of the numerical convergence and a reduction of the systematic uncertainties. We also discuss how a linear dependence in qT can be avoided for Drell–Yan production by using staggered cuts, which, to the best of our understanding, could be used in experimental analyses. We show that our approach can be successfully applied also to on-shell ZZ production. We finally study diphoton production and verify that our approach is insufficient to capture the linear power corrections introduced by the isolation procedure. The recoil prescription is available in version 2.1 of Matrix.

Learning new physics from an imperfect machine

We show how to deal with uncertainties on the Standard Model predictions in an agnostic new physics search strategy that exploits artificial neural networks. Our approach builds directly on the specific Maximum Likelihood ratio treatment of uncertainties as nuisance parameters for hypothesis testing that is routinely employed in high-energy physics. After presenting the conceptual foundations of our method, we first illustrate all aspects of its implementation and extensively study its performances on a toy one-dimensional problem. We then show how to implement it in a multivariate setup by studying the impact of two typical sources of experimental uncertainties in two-body final states at the LHC.

Rare decays of the positronium ion and molecule, Ps− → e−γ and Ps2 → e+e−γ , γγ , e+e−

Decay rates of the positronium molecule ${\text{Ps}}_{2}$ into two photons and into an electron-positron pair are determined. Previous studies find that these rates are very different, $\mathrm{\ensuremath{\Gamma}}({\text{Ps}}_{2}\ensuremath{\rightarrow}{e}^{+}{e}^{\ensuremath{-}})/\mathrm{\ensuremath{\Gamma}}({\text{Ps}}_{2}\ensuremath{\rightarrow}\ensuremath{\gamma}\ensuremath{\gamma})\ensuremath{\simeq}250$. This is puzzling since both processes have two-body final states and are of the same order in the fine-structure constant. We propose a simple calculational method and test it with the well-established decay of the positronium ion into an electron and a photon. We then employ it to correct predictions for both these ${\text{Ps}}_{2}$ decays. We find that previous studies overestimated the ${e}^{+}{e}^{\ensuremath{-}}$ channel and underestimated the $\ensuremath{\gamma}\ensuremath{\gamma}$ channel by factors of about 5.44 and 3.93, respectively. Our results give $\mathrm{\ensuremath{\Gamma}}({\text{Ps}}_{2}\ensuremath{\rightarrow}{e}^{+}{e}^{\ensuremath{-}})/\mathrm{\ensuremath{\Gamma}}({\text{Ps}}_{2}\ensuremath{\rightarrow}\ensuremath{\gamma}\ensuremath{\gamma})\ensuremath{\simeq}11.7$.

QED factorization of non-leptonic B decays

We show that the QCD factorization approach for B-meson decays to charmless hadronic two-body final states can be extended to include electromagnetic corrections. The presence of electrically charged final-state particles complicates the framework. Nevertheless, the factorization formula takes the same form as in QCD alone, with appropriate generalizations of the definitions of light-cone distribution amplitudes and form factors to include QED effects. More precisely, we factorize QED effects above the strong interaction scale ΛQCD for the non-radiative matrix elements leftlangle {M}_1{M}_2left|{Q}_iright|overline{B}rightrangle of the current-current operators from the effective weak interactions. The rates of the branching fractions for the infrared-finite observables overline{B}to {M}_1{M}_2left(gamma right) with photons of maximal energy ∆E ≪ ΛQCD is then obtained by multiplying with the soft-photon exponentiation factors. We provide first estimates for the various electromagnetic corrections, and in particular quantify their impact on the πK ratios and sum rules that are often used as diagnostics of New Physics.

Strong decays of the higher excited ΛQ and ΣQ baryons

In this work, we preform a systematic study of the strong decays for the higher singly heavy baryon resonances $\Lambda_Q(3S)$, $\Lambda_Q(2P)$, $\Lambda_Q(2D)$, $\Lambda_Q(1F)$, $\Sigma_Q(3S)$, $\Sigma_Q(2P)$, $\Sigma_Q(2D)$, and $\Sigma_Q(1F)$ within the $^3P_0$ model. Our results show that most of the $\lambda-$mode higher excited $\Lambda_Q$ and $\Sigma_Q$ states have a relatively narrow width, and mainly decay into two-body final states with one heavy meson plus one light baryon. Our calculations provide abundant theoretical information and demonstrate the general feature for these higher states, which may be valuable for future experimental searches and establishing the singly heavy baryon spectrum.

Prospects for CP and P violation in Λc+ decays at Super Tau Charm Facility

CP violation is an excellent tool for probing flavor dynamics as we learnt first with $K_L \to 2 \pi$ and later also with the weak decays of beauty mesons. LHCb 2019 data have shown CP violation for the first time in $D^0\to K^-K^+$ vs. $D^0\to\pi^-\pi^+$. Searching for CP asymmetries is of great interest in charm quark sector in the Standard Model (SM) or even more beyond it. In charm hadron decays, lots of work had focused on two-body final states, and the measurements of CP asymmetries in three- or four-body final states are rare. Dalitz plots have shown an excellent record for three-body final states, and more results are desired for four-body ones. In this work we study CP asymmetries in the decays $\Lambda^+_c \to p K^-\pi^+\pi^0$/$\Lambda \pi^+\pi^+\pi^-$/$pK_S\pi^+\pi^-$, where the SM gives zero values for the first two channels, while $3.3 \times 10^{-3}$ for the last one due to $K^0 - \bar K^0$ oscillation. We performed a fast Monte Carlo simulation study by using electron-positron annihilation data of 1~$\textrm{ab}^{-1}$ at center-of-mass energy $\sqrt{s}\, =\, 4.64$ GeV. The data is expected to be available by the next generation Super Tau Charm Facility proposed by China and Russia with one year (or even less) data taking operation. The results indicate that a sensitivity at the level of 0.2$\sim$0.5% is accessible for these processes, which would be enough to measure nonzero CP-violating asymmetries as large as 1%.

Measurement of CP observables in the process B0 \u2192 DK*0 with two- and four-body D decays

Measurements of CP observables in B0 → DK∗0 decays are presented, where D represents a superposition of D0 and {overline{D}}^0 states. The D meson is reconstructed in the two-body final states K+π−, π+K−, K+K− and π+π−, and, for the first time, in the fourbody final states K+π−π+π−, π+K−π+π− and π+π−π+π−. The analysis uses a sample of neutral B mesons produced in proton-proton collisions, corresponding to an integrated luminosity of 1.0, 2.0 and 1.8 fb−1 collected with the LHCb detector at centre-of-mass energies of sqrt{s}=7,8 and 13 TeV, respectively. First observations of the decays B0 → D(π+K−)K∗0 and B0 → D(π+π−π+π−)K∗0 are obtained. The measured observables are interpreted in terms of the CP -violating weak phase γ.

Indirect detection of the partial p wave via the s wave in the annihilation cross section of dark matter

For many dark matter models, the annihilation cross section to two-body final states is difficult to probe with current experiments because the dominant annihilation channel is velocity or helicity suppressed. The inclusion of gauge boson radiation for three-body final states can lift the helicity suppression, allowing a velocity-independent cross section to dominate the annihilation process, and providing an avenue to constrain these models. Here we examine experimental constraints on dark matter that annihilates to two leptons plus a bremsstrahlung boson, $\bar{\ell}+\ell+\gamma/W/Z$. We consider experimental constraints on photon final states from Fermi-LAT using both diffuse photon data and data from dwarf spheroidal galaxies, and compare to the implied constraints from 21 cm measurements. Diffuse photon line searches are generally the strongest over the entire mass regime. We in particular highlight the model in which dark matter annihilates to two neutrinos and a photon, and show that these models are more strongly constrained through photon measurements than through existing neutrino bounds.

D0-D̄0 mixing parameter y in the factorization-assisted topological-amplitude approach**Supported by National Natural Science Foundation of China (11347027, 11505083, 11375208, 11521505, 1162113100, 11235005, U1732101), Ministry of Science and Technology of R.O.C. (MOST-104-2112-M-001-037-MY3) and DFG Forschergruppe FOR 1873 “Quark Flavour Physics and Effective Field Theories”

We calculate the mixing parameter y in the factorization-assisted topological-amplitude (FAT) approach, considering contributions from , PV, and VV modes, where P (V) stands for a pseudoscalar (vector) meson. The and PV decay amplitudes are extracted in the FAT approach, and the decay amplitudes with final states in the longitudinal polarization are estimated via the parameter set for . It is found that the VV contribution to y, being of order of 10−4, is negligible, and that the PP and PV contributions amount only up to , a prediction more precise than those previously obtained in the literature, and much lower than the experimental data . We conclude that D0 meson decays into other two-body and multi-particle final states are relevant to the evaluation of y, so it is difficult to understand it fully in an exclusive approach.

Dark matter annihilation into four-body final states and implications for the AMS antiproton excess

We consider dark matter annihilation into a general set of final states of Standard Model particles, including two-body and four-body final states that result from the decay of intermediate states. For dark matter masses ~10-10^5 GeV, we use updated data from Planck and from high gamma-ray experiments such as Fermi-LAT, MAGIC, and VERITAS to constrain the annihilation cross section for each final state. The Planck constraints are the most stringent over the entire mass range for annihilation into light leptons, and the Fermi-LAT constraints are the most stringent for four-body final states up to masses ~10^4 GeV. We consider these constraints in light of the recent AMS antiproton results, and show that for light mediators it is possible to explain the AMS data with dark matter, and remain consistent with Fermi-LAT Inner Galaxy measurements, for m_\chi ~ 60-100 GeV mass dark matter and mediator masses m_\phi / m_\chi ~< 1.

Electroweak and Higgs boson internal bremsstrahlung. General considerations for Majorana dark matter annihilation and application to MSSM neutralinos

It is well known that the annihilation of Majorana dark matter into fermions is helicity suppressed. Here, we point out that the underlying mechanism is a subtle combination of two distinct effects, and we present a comprehensive analysis of how the suppression can be partially or fully lifted by the internal bremsstrahlung of an additional boson in the final state. As a concrete illustration, we compute analytically the full amplitudes and annihilation rates of supersymmetric neutralinos to final states that contain any combination of two standard model fermions, plus one electroweak gauge boson or one of the five physical Higgs bosons that appear in the minimal supersymmetric standard model. We classify the various ways in which these three-body rates can be large compared to the two-body rates, identifying cases that have not been pointed out before. In our analysis, we put special emphasis on how to avoid the double counting of identical kinematic situations that appear for two-body and three-body final states, in particular on how to correctly treat differential rates and the spectrum of the resulting stable particles that is relevant for indirect dark matter searches. We find that both the total annihilation rates and the yields can be significantly enhanced when taking into account the corrections computed here, in particular for models with somewhat small annihilation rates at tree-level which otherwise would not be testable with indirect dark matter searches. Even more importantly, however, we find that the resulting annihilation spectra of positrons, neutrinos, gamma-rays and antiprotons differ in general substantially from the model-independent spectra that are commonly adopted, for these final states, when constraining particle dark matter with indirect detection experiments.

Testing the parton evolution with the use of two-body final states

We consider the production of b{bar{b}} quarks and Drell–Yan lepton pairs under LHC conditions focusing attention on the total transverse momentum of the produced pair and on the azimuthal angle between the momenta of the outgoing particles. Plotting the corresponding distributions in bins of the final-state invariant mass, one can reconstruct the full map of the transverse momentum dependent parton densities in a proton. We give examples of how these distributions can look like at the LHC energies.

Dark matter decay to a photon and a neutrino: The double monochromatic smoking gun scenario

In the energy range from few TeV to 25 TeV, upper bounds on the dark matter decay rate into high energy monochromatic neutrinos have recently become comparable to those on monochromatic gamma-ray lines. This implies clear possibilities of a future double "smoking-gun" evidence for the dark matter particle, from the observation of both a gamma and a neutrino line at the same energy. In particular, we show that a scenario where both lines are induced from the same dark matter particle decay leads to correlations that can already be tested. We study this "double monochromatic" scenario by considering the complete list of lowest dimensional effective operators that could induce such a decay. Furthermore, we argue that, on top of lines from decays into two-body final states, three-body final states can also be highly relevant. In addition to producing a distinct hard photon spectrum, three-body final states also produce a line-like feature in the neutrino spectrum that can be searched for by neutrino telescopes.

Effective field theory approach to top-quark decay at next-to-leading order in QCD

We present analytical results for top-quark decay processes, in an effective field theory beyond the Standard Model, at next-to-leading order in QCD. We parametrize new physics effects using dimension-six operators, and consider all operators that give rise to non-standard interactions of the top quark. We investigate both the flavor-conserving and flavor-changing decay modes, including their two-body and three-body semi-leptonic final states. The QCD mixing among relevant operators are also taken into account. These results provide all information needed for a complete model-independent study of top-quark decay at next-to-leading order accuracy, paving the way to global analyses for new physics effects in an effective field theory approach.

Electroweak bremsstrahlung in binolike dark matter annihilations

We investigate the effects of electroweak bremsstrahlung on bino-like neutralino dark matter pair annihilations in the minimal supersymmetric standard model (MSSM). We calculate the nonrelativistic pair annihilation cross sections via $W$-strahlung from leptonic final states, $\chi\chi$ $\to$ $W\ell\bar{\nu}$, and compare them with the contributions of the relevant two-body final states. We explore the case that sleptons lie below the TeV scale, while squarks are extremely heavy. It is found that the electroweak bremsstrahlung can give a dominant contribution to the cross section for some parameter regions which include slepton coannihilation regions with the observed relic abundance. We also evaluate the neutrino spectra at injection in the Sun. It is shown that energetic neutrinos via weak bremsstrahlung processes can be dominant over contributions of the two-body final states.