We search for invisible decays of the Upsilon(1S) meson using a sample of 91.4 x 10^{6} Upsilon(3S) mesons collected at the BaBar/PEP-II B-factory. We select events containing the decay Upsilon(3S) -> pi+ pi- Upsilon(1S) and search for evidence of an undetectable Upsilon(1S) decay recoiling against the dipion system. We set an upper limit on the branching fraction BR(Upsilon(1S) -> invisible) < 3.0 x 10^{-4} at the 90% confidence level.
We present a measurement of the branching fraction of invisible Upsilon(1S) decays, using 1.2 fb^{-1} of data collected at the Upsilon(2S) resonance with the CLEO III detector at CESR. After subtracting expected backgrounds from events that pass selection criteria for invisible Upsilon(1S) decay in Upsilon(2S) -> pi+ pi- Upsilon(1S), we deduce a 90% C.L. upper limit of B[Upsilon(1S) -> invisible] < 0.39%.
We search for single-photon decays of the Upsilon(1S) resonance, Upsilon->gamma+invisible, where the invisible state is either a particle of definite mass, such as a light Higgs boson A0, or a pair of dark matter particles, chi chi-bar. Both A0 and chi are assumed to have zero spin. We tag Upsilon(1S) decays with a dipion transition Upsilon(2S)->pi+pi-Upsilon(1S) and look for events with a single energetic photon and significant missing energy. We find no evidence for such processes in the mass range m_A0<=9.2 GeV and m_chi<=4.5 GeV in the sample of 98e6 Upsilon(2S) decays collected with the B…
We search for a light scalar particle produced in single-photon decays of the Upsilon(3S) resonance through the process Upsilon(3S) -> gamma A0, A0 -> invisible. Such an object appears in Next-to-Minimal Supersymmetric extensions of the Standard Model, where a light CP-odd Higgs boson naturally couples strongly to b-quarks. If, in addition, there exists a light, stable neutralino, decays of A0 could be preferentially to an invisible final state. We search for events with a single high-energy photon and a large missing mass, consistent with a 2-body decay of Upsilon(3S). We find no evidence for…
We report results of a search for the invisible decay of the Upsilon(1S) via the Upsilon(3S)->pi+pi-Upsilon(1S) transition using a data sample of 2.9 fb^{-1} at the Upsilon(3S) resonance. The data were collected with the Belle detector at the KEKB asymmetric-energy e+e- collider. No signal is found, and an upper limit for the branching fraction at the 90% confidence level is determined to be B(Upsilon(1S)->invisible) < 2.5x10^{-3}.
Invisible psi and Upsilon decays into light neutralinos, within the MSSM or N(n)MSSM, are smaller than for nu nubar production, even if light spin-0 particles are coupled to quarks and neutralinos. In a more general way, light dark matter particles are normally forbidden, unless they can annihilate sufficiently through a new interaction stronger than weak interactions (at lower energies), as induced by a light spin-1 U boson, or heavy-fermion exchanges in the case of scalar dark matter. We discuss the possible contributions of U-boson, heavy-fermion, or spin-0 exchanges to invisible psi and Up…
In this paper we present two searches for new physics in Upsilon(3S) decays collected by the BABAR detector. We search for charged lepton-flavour violating decays of the Upsilon(3S), which are unobservable in the Standard Model but are predicted to occur in several beyond-the-Standard Model scenarios. We also search for production of a light Higgs or Higgs-like state produced in radiative decays of the Upsilon(3S) and decaying to muon pairs.
We report the first observation of the transition Upsilon(2S) > eta Upsilon(1S), with branching fraction B=(2.1+0.7-0.6(stat.)+-0.3(syst.)) x 10^{-4} and statistical significance 5.3 sigma. Data were acquired with the CLEO detector at the CESR e+ e- symmetric collider. This is the first process observed involving a b-quark spin flip. Upper limits at 90% confidence level for related processes, in units of 10^{-4}, are B[Upsilon(2S) -> pi0 Upsilon(1S)] < 1.8, B[Upsilon(3S) -> eta Upsilon(1S)] < 1.8, B[Upsilon(3S) -> pi0 Upsilon(1S)] < 0.7, and B[Upsilon(3S) -> pi0 Upsilon(2S)] < 5.1.
Charged lepton-flavor violating processes are extremely rare in the Standard Model, but they may occur in several beyond-the-Standard Model theories, including Supersymmetry or models with leptoquarks or compositeness. We present a search for such processes in a sample of 117M Upsilon(3S) decays recorded with the BaBar detector. We place upper limits on the branching fractions BF(Upsilon(3S) -> e tau) < 5.0e-6 and BF(Upilon(3S) -> mu tau) < 4.1e-6 at 90% confidence level. These results are used to place lower limits on the mass scale of beyond-the-Standard Model physics contributing to lepton-…
We search for a low-mass scalar CP-odd Higgs boson, A0, produced in the radiative decay of the Upsilon resonance and decaying into a tau+tau- pair: Upsilon(1S)->gamma A0. The production of Upsilon(1S) mesons is tagged by Upsilon(2S)->pi+pi-Upsilon(1S) transitions, using a sample of (98.3+/-0.9) million Upsilon(2S) mesons collected by the BaBar detector. We find no evidence for a Higgs boson in the mass range 3.5 GeV<= m(A0)<=9.2 GeV, and combine these results with our previous search for the tau decays of the light Higgs in radiative Upsilon(3S) decays, setting limits on the coupling of A0 to …
We present the analysis technique and preliminary results of two ongoing analyses at CLEO which put lepton universality and lepton flavor conservation to the test in Upsilon decays.
We study inclusive di-pion decays using a sample of 108 x 10^6 Upsilon(3S) events recorded with the BABAR detector. We search for the decay mode Upsilon(3S) --> pi+ pi- h_b(1P) and find no evidence for the bottomonium spin-singlet state h_b(1P) in the invariant mass distribution recoiling against the pi+ pi- system. Assuming the h_b(1P) mass to be 9.900 GeV/c^2, we measure the upper limit on the branching fraction B[Upsilon(3S) --> pi+ pi- h_b(1P)] < 1.2 x 10^{-4}, at 90% confidence level. We also investigate the chi_{bJ}(2P) --> pi+ pi- chi_{bJ}(1P), Upsilon(3S) --> pi+ pi- Upsilon(2S), and U…
We search for evidence of a light scalar boson in the radiative decays of the Upsilon(2S) and Upsilon(3S) resonances: Upsilon(2S,3S)-> gamma A0, A0 -> mu^+ mu^-. Such a particle appears in extensions of the Standard Model, where a light CP-odd Higgs boson naturally couples strongly to b-quarks. We find no evidence for such processes in the mass range 0.212<= m(A0)<= 9.3 GeV in the samples of 99*10^6 Upsilon(2S) and 122*10^6 Upsilon(3S) decays collected by the BABAR detector at the PEP-II B-factory and set stringent upper limits on the effective coupling of the b quark to the A0. We also limit …
We have searched for the bottomonium eta_b(1S) via the hindered magnetic dipole (M1) photon transition Upsilon(3S) -> gamma eta_b(1S). No evidence for such a transition is found in the data sample of 4.7 x 10^6 Upsilon(3S)'s collected with the CLEO-III detector. We set upper limits on the branching ratio from 9.30 to 9.43 GeV/c^2 of eta_b(1S) masses. These upper limits rule out many previously published phenomenological estimates of the rate for this transition.
The results of a search for the bottomonium counterpart, denoted as Xb, of the exotic charmonium state X(3872) is presented. The analysis is based on a sample of pp collisions at sqrt(s) = 8 TeV collected by the CMS experiment at the LHC, corresponding to an integrated luminosity of 20.7 inverse femtobarns. The search looks for the exclusive decay channel Xb to Upsilon(1S) pi+ pi- followed by Upsilon(1S) to mu+ mu-. No evidence for an Xb signal is observed. Upper limits are set at the 95% confidence level on the ratio of the inclusive production cross sections times the branching fractions to …
In this Letter we describe a search for lepton flavor violation (LFV) in the bottomonium system. We search for leptonic decays of Upsilon(nS)(n=1,2, and 3) into muon and tau using the data collected with the CLEO III detector. We identify the tau lepton using its leptonic decay into electron and utilize multidimensional likelihood fitting with PDF shapes measured from independent data samples. We report our estimates of 95% CL upper limits on LFV branching fractions of Upsilon mesons. We interpret our results in terms of the exclusion plot for the energy scale of a hypothetical new interaction…
I present highlights of recent CLEO studies on the Upsilon(1S), Upsilon(2S), and Upsilon(3S). The preliminary results presented here include the first observation of a hadronic cascade in the Upsilon system not involving pions, Upsilon(3S) to gamma chi(b1,2)(2P) followed by chi(b1,2)(2P) to omega Upsilon(1S). I also present preliminary results on a search for inclusive psi production in Upsilon(1S) decays. I end with a search for nine different two body hadronic decays of the Upsilon(nS), n=1,2,3, resulting in the discovery of two such decays, and vastly improved upper limits on the branching …
Production of the Upsilon(1S) meson in association with a vector boson is a rare process in the standard model with a cross section predicted to be below the sensitivity of the Tevatron. Observation of this process could signify contributions not described by the standard model or reveal limitations with the current non-relativistic quantum-chromodynamic models used to calculate the cross section. We perform a search for this process using the full Run II data set collected by the CDF II detector corresponding to an integrated luminosity of 9.4/fb. The search considers the Upsilon(1S) to di-mu…
We search for a non-SM-like CP-odd Higgs boson (a0_1) with m(a0_1)< 2m(b) in radiative decays of the Upsilon(1S), using 21.5M Upsilon(1S) mesons directly produced in e+e- annihilation. We investigate a0_1 --> tau+tau- and a0_1 --> mu+mu- decay channels. No significant signal is found. We obtain upper limits on the product of B(Upsilon(1S)-->gamma a0_1) and B(a0_1-->tau+tau-) or B(a0_1-->mu+mu-). Our tau+tau- results are almost two orders of magnitude more stringent than previous upper limits. Our data provide no evidence for a Higgs state with a mass of 214 MeV decaying to mu+mu-. Existence of…
psi and Upsilon decays may be used to search for light neutral spin-1 or spin-0 bosons associated with a broken extra-U(1) symmetry, local or global, acting axially on quarks and leptons, as may be present in supersymmetric theories with a lambda H_1 H_2 S superpotential term. Recent data on Upsilon --> gamma + invisible neutral constrain an axial, pseudoscalar or scalar coupling to b to f_bA < 4 10^-7 m_U(MeV)/ sqrt B_inv, f_bP < 4 10^-3/ sqrt B_inv or f_bS < 6 10^-3/ sqrt B_inv, respectively. This also constrains, from universality properties, couplings to electrons to f_eA < 4 10^-7 m_U(MeV…
We report on a search for the radiative decay of Upsilon(1S) to the pseudoscalar mesons eta and etaprime in 21.2 +/- 0.2 times 10^6 Upsilon(1S) decays collected with the CLEO III detector at the Cornell Electron Storage Ring (CESR). The eta meson was reconstructed in the three modes eta to gamma-gamma, eta to pi+pi-pi0 and eta to 3pi0. The etaprime meson was reconstructed in the mode etaprime to pi+ pi- eta with eta decaying through any of the above three modes, and also etaprime to gamma rho, where rho decays to pi^+ pi^-. Five out of the seven sub-modes are found to be virtually background-f…
BaBar experiment scan around the Upsilon(4S) resonance and measure its mass and full width. They also measure Br(Upsilon(4S) -> B0 B0b) = 0.486 +/- 0.010 +/- 0.009 from 81.7 fb-1 Upsilon(4S) data. CLEO collaboration took about 0.42 fb-1 Upsilon(5S) data. They search for B_s in both inclusive and exclusive modes and find evidence for B_s production at the Υ(5S) and Br(Upsilon(5S) -> B_s^(*) B_s^(*)b) = (21 +/- 3 +/- 9)%.
Charged lepton flavor violating processes are unobservable in the standard model, but they are predicted to be enhanced in several extensions to the standard model, including supersymmetry and models with leptoquarks or compositeness. We present a search for such processes in a sample of 99M Y(2S) decays and 117M Y(3S) decays collected with the BABAR detector. We place upper limits on the branching fractions BF(Y(nS) -> e tau) and BF(Y(nS) -> mu tau) (n = 2, 3) at the 10^(-6) level and use these results to place lower limits of order 1 TeV on the mass scale of charged lepton flavor violating e…
We search for evidence of a light Higgs boson (A0) in the radiative decays of the narrow Upsilon(3S) resonance: Upsilon(3S) -> gamma A0, where A0 -> invisible or A0 -> mu+mu-. Such an object appears in extensions of the Standard Model, where a light CP-odd Higgs boson naturally couples strongly to b-quarks. We find no evidence for such processes in a sample of 122 million Upsilon(3S) decays collected by the BaBar collaboration at the PEP II B-factory, and set 90% C.L. upper limits on the product of the corresponding branching fractions. We also set a limit on the di-muon branching fraction of …
Recent investigations have suggested that the six-quark combination uuddss could be a deeply bound state (S) that has eluded detection so far, and a potential dark matter candidate. We report the first search for a stable, doubly strange six-quark state in Upsilon -> S anti-Lambda anti-Lambda decays based on a sample of 90 million Upsilon(2S) and 110 million Upsilon(3S) decays collected by the BABAR experiment. No signal is observed, and 90% confidence level limits on the combined Upsilon(2S,3S) -> S anti-Lambda anti-Lambda branching fraction in the range (1.2-1.4)x10^-7 are derived for m_S < …
Recent CLEO results on the observation of the $Υ(1D)$ state and a search for the $η_b(1S)$ state from a data sample of $4.7 \times 10^6\,Υ(3S)$ decays collected with the CLEO-III detector, and a measurement of the $η^{\prime}$ production spectrum using $1.9 \times 10^6\,Υ(1S)$ decays collected with the CLEO-II detector are described.
We summarize recent results on B+ -> tau+ nu setting constraints on the charged Higgs mass, discuss the CP puzzle in B -> K pi decays and present searches for a light neutral Higgs in radiative Upsilon(2S) and Upsilon(3S)decays.
Searches for lepton-flavor-violating decay of a tau lepton to a lighter mass lepton and a photon have been performed with the entire dataset of (963 +- 7) x 10^6 tau decays collected by the BaBar detector near the Upsilon(4S), Upsilon(3S) and Upsilon(2S) resonances. The searches yield no evidence of signals and we set upper limits on the branching fractions of BR(tau -> e gamma) < 3.3 x 10^-8 and BR(tau -> mu gamma) < 4.4 x 10^-8 at 90% confidence level.
We present an inclusive search for strange pentaquark production in e+e- interactions at a center-of-mass energy of 10.58 GeV using 123 fb-1 of data collected with the BaBar detector. We look for the states that have been reported previously: the Theta+(1540), interpreted as a ududsbar state; and the Xi--(1860) and Xi0(1860), candidate dsdsubar and uss(uubar+ddbar) states, respectively. In addition we search for other members of the antidecuplet and corresponding octet to which these states are thought to belong. We find no evidence for the production of such states and set preliminary limits …
I present two analyses done with the CLEOIII detector at CESR. The first is a search for the Lepton Flavor Violating decay Upsilon to mu tau, with preliminary results, and the second constrains Lepton Universality in Upsilon to tau tau relative to Upsilon to mu mu. This second analysis, whose results are final, has dramatically improved uncertainties relative to other such measurements, and is also the first observation of the decay Upsilon(3S) to tau tau. A limit is also set on the involvement of a CP odd Higgs in the decay of the Upsilon(1S) to tau pairs.
Using a sample of 122 million Upsilon(3S) decays collected with the BaBar detector at the PEP-II asymmetric energy collider at the SLAC National Accelerator Laboratory, we measure the ratio R_taumu=BR(Upsilon(1S)->tau^+tau^-)/BR(Upsilon(1S)->mu^+mu^-); the measurement is intended as a test of lepton universality and as a possible search for a light pseudoscalar Higgs boson in Next to Minimal Supersymmetric Standard Model (NMSSM) scenarios. Such a boson could appear in a deviation of the ratio R_taumu from the Standard Model expectation, that is 1, except for small lepton mass corrections. The …
Using 14.0 million $ψ(2S) events collected with the BES-II detector, a search for the decay of the $\jpsi$ to an invisible final state in $\psipto$ is performed. The $\jpsi$ peak in the distribution of mass recoiling against the $π^+π^-$ is used to tag $ψ$ invisible decay. No signal is found, and an upper limit at the 90% confidence level is determined to be $1.2\times 10^{-2}$ for the ratio $\frac{{\cal B}(\jpsi\ar {invisible})}{{\cal B}(\jpsi\arμ^+μ^-)}$. This is the first search for $J/ψ$ decay to an invisible final state.
Results are presented for the search for invisible Higgs boson production using the full LHC dataset corresponding to integrated luminosity of 5.1 fb^-1 and 19.6 fb^-1 of proton-proton collision data at sqrt(s)= 7 TeV and 8 TeV (respectively) collected by the CMS detector. The invisible Higgs is searched for in final states of missing transverse energy, with two leptons from a recoiling Z boson. No significant excess is found beyond standard model predictions, and limits are obtained on the branching fraction of the Higgs boson to invisible particles.
We have performed a search for the eta_b(1S) meson in the radiative decay of the Upsilon(2S) resonance using a sample of 91.6 million Upsilon(2S) events recorded with the BABAR detector at the PEP-II B factory at the SLAC National Accelerator Laboratory. We observe a peak in the photon energy spectrum at E_gamma = 609.3 {+4.6} {-4.5} (stat) +/- 1.9 (syst) MeV, corresponding to an eta_b(1S) mass of 9394.2 {+4.8} {-4.9} (stat) +/- 2.0 (syst) MeV/c^2. The branching fraction for the decay Upsilon(2S) --> gamma eta_b(1S) is determined to be [3.9 +/-1.1 (stat) {+1.1} {-0.9} (syst)] x 10^(-4). We fin…
We propose an experiment to search for invisible decays of orthopositronium (o-Ps) with a 90% confidence sensitivity in the branching ratio as low as $10^{-8}$. Evidence for this decay mode would unambigously signal new physics: either the existence of extra--dimensions or fractionally charged particles or new light gauge bosons. The experimental approach and the detector components of the proposed experiment are described.
We search for the flavor-changing neutral-current decays B->K(*)nu nubar, and the invisible decays J/psi->nu nubar and psi(2S)->nu nubar via B->K(*)J/psi and B->K(*)psi(2S) respectively, using a data sample of 471 x10^6 BB pairs collected by the BaBar experiment. We fully reconstruct the hadronic decay of one of the B mesons in the Upsilon(4S)->BB decay, and search for the B->K(*)nu nubar decay in the rest of the event. We observe no significant excess of signal decays over background and report branching fraction upper limits of BR(B+->K+nu nubar)<3.7 x10^-5, BR(B0->K0nu nubar)< 8.1 x10^-5, B…
We have investigated the invariant mass spectrum of dimuons collected by the CDF experiment during the 1992-1995 run of the Fermilab Tevatron collider to improve the limit on the existence of narrow resonances set by the experiments at the SPEAR e+e- collider. In the mass range 6.3-9.0 GeV/c^2, we derive 90% upper credible limits to the ratio of the production cross section times muonic branching fraction of possible narrow resonances to that of the Y(1S) meson. In this mass range, the average limit varies from 1.7 to 0.5%. This limit is much worse at the mass of 7.2 GeV/c^2 due to an excess o…
We present the first results of a search for invisible axion dark matter using a multiple-cell cavity haloscope. This cavity concept was proposed to provide a highly efficient approach to high mass regions compared to the conventional multiple-cavity design, with larger detection volume, simpler detector setup, and unique phase-matching mechanism. Searches with a double-cell cavity superseded previous reports for the axion-photon coupling over the mass range between 13.0 and 13.9$\,μ$eV. This result not only demonstrates the novelty of the cavity concept for high-mass axion searches, but also …
We report the results of a search for the bottomonium ground state eta_b(1S) in the photon energy spectrum with a sample of (109 +/- 1) million of Upsilon(3S) recorded at the Upsilon(3S) energy with the BABAR detector at the PEP-II B factory at SLAC. We observe a peak in the photon energy spectrum at E_gamma = 921.2 {+2.1} {-2.8} (stat) +/- 2.4(syst) MeV with a significance of 10 standard deviations. We interpret the observed peak as being due to monochromatic photons from the radiative transition Upsilon(3S) -> gamma eta_b(1S). This photon energy corresponds to an eta_b(1S) mass of $9388.9 {+…
A search for invisible decays of Higgs bosons is performed using the vector boson fusion and associated ZH production modes. In the ZH mode, the Z boson is required to decay to a pair of charged leptons or a b b-bar quark pair. The searches use the 8 TeV pp collision dataset collected by the CMS detector at the LHC, corresponding to an integrated luminosity of up to 19.7 inverse femtobarns. Certain channels include data from 7 TeV collisions corresponding to an integrated luminosity of 4.9 inverse femtobarns. The searches are sensitive to non-standard-model invisible decays of the recently obs…
Searches for invisible decays of the Higgs boson are presented. The data collected with the CMS detector at the LHC correspond to integrated luminosities of 5.1, 19.7, and 2.3 inverse femtobarns at centre-of-mass energies of 7, 8, and 13 TeV, respectively. The search channels target Higgs boson production via gluon fusion, vector boson fusion, and in association with a vector boson. Upper limits are placed on the branching fraction of the Higgs boson decay to invisible particles, as a function of the assumed production cross sections. The combination of all channels, assuming standard model pr…
Despite dark matter abundance, its nature remains elusive. Many searches of dark matter particles are carried out using different technologies either via direct detection, indirect detection, or collider searches. In this work, the invisible Higgs sector was investigated, where Higgs bosons are produced via the vector boson fusion (VBF) process and subsequently decay into invisible particles. The hypothesis under consideration is that the Higgs boson might decay into a pair of weakly interacting massive particles (WIMPs), which are candidates for dark matter. The observed number of events are …
A search for J/psi radiative decay to weakly interacting neutral final states was performed using the CLEO-c detector at CESR. A total of 3.7 x 10^{6} tagged J/psi events was collected at the psi(2S) resonance and used to study the decay J/psi -> gamma+X, where X is a narrow state that is invisible to the detector. No significant signal was observed and upper limits on the branching fraction were set for masses m_X up to 960 MeV/c^2. The upper limit corresponding to m_X=0 is 4.3x 10^{-6} at the 90% confidence level.
The results of a search for $π^0$ decays to a photon and an invisible massive dark photon at the NA62 experiment at the CERN SPS are reported. From a total of $4.12\times10^8$ tagged $π^0$ mesons, no signal is observed. Assuming a kinetic-mixing interaction, limits are set on the dark photon coupling to the ordinary photon as a function of the dark photon mass, improving on previous searches in the mass range 60--110 MeV/$c^2$. The present results are interpreted in terms of an upper limit of the branching ratio of the electro-weak decay $π^0 \to γν\overlineν$, improving the current limit by m…
Recent investigations have suggested that the singlet six-quark combination $uuddss$ may be a deeply bound state $S$, called Sexaquark. An essentially stable state $S$ is a potentially excellent Dark Matter candidate. We present the first search for a stable, doubly strange six-quark state in the decays of $Υ(4S) \to Λ\barΛ$. Based on a data sample of $Υ(2S)$ and $Υ(3S)$ decays collected by the BABAR Experiment we report the most recent results and set stringent limits on the existence of such exotic particle.
Dark matter particles, if sufficiently light, may be produced in decays of the Higgs boson. This Letter presents a statistical combination of searches for $H\to\textrm{invisible}$ decays where $H$ is produced according to the Standard Model via vector boson fusion, $Z(\ell\ell)H$, and $W\!/\!Z(\textrm{had})H$, all performed with the ATLAS detector using 36.1 fb$^{-1}$ of $pp$ collisions at a center-of-mass energy of $\sqrt s = 13$ TeV at the LHC. In combination with the results at $\sqrt s = 7$ and 8 TeV, an exclusion limit on the $H\to\textrm{invisible}$ branching ratio of $0.26 (0.17^{+0.07}…
A search for invisible decays of a Higgs boson is performed using proton-proton collision data collected with the CMS detector at the LHC in 2016 at a center-of-mass energy $\sqrt{s} =$ 13 TeV, corresponding to an integrated luminosity of 35.9 fb$^{-1}$. The search targets the production of a Higgs boson via vector boson fusion. The data are found to be in agreement with the background contributions from standard model processes. An observed (expected) upper limit of 0.33 (0.25), at 95% confidence level, is placed on the branching fraction of the Higgs boson decay to invisible particles, assum…
The NA62 experiment at CERN reports searches for $K^+\toμ^+N$ and $K^+\toμ^+νX$ decays, where $N$ and $X$ are massive invisible particles, using the 2016-2018 data set. The $N$ particle is assumed to be a heavy neutral lepton, and the results are expressed as upper limits of ${\cal O}(10^{-8})$ of the neutrino mixing parameter $|U_{\mu4}|^2$ for $N$ masses in the range 200-384 MeV/$c^2$ and lifetime exceeding 50 ns. The $X$ particle is considered a scalar or vector hidden sector mediator decaying to an invisible final state, and upper limits of the decay branching fraction for $X$ masses in th…
We establish upper limits on branching fractions for B0 decays to final states where the decay products are purely invisible (i.e., no observable final state particles) and for B0 decays to nu nubar gamma. Within the Standard Model, these decays have branching fractions that are below current experimental sensitivity, but various models of physics beyond the Standard Model predict significant contributions from these channels. Using 88.5 million B Bbar pairs collected at the Y(4S) resonance by the BaBar experiment at the PEP-II e+e- storage ring at the Stanford Linear Accelerator Center, we es…
In the year 2000 the four LEP experiments have collected data at energies between 200 and 209 GeV, for approximately 868 pb-1 integrated luminosity. The LEP working group for Higgs boson searches has combined these data with earlier data sets collected at lower centre-of-mass energies to search for a neutral CP-even Higgs boson, produced at the Standard Model rate, decaying into "invisible" particles. No statistically significant excess has been observed when compared to the Standard Model background prediction, and assuming that the Higgs boson decays only into such states a lower bound has b…
The Kamioka Liquid scintillator Anti-Neutrino Detector (KamLAND) is used in a search for single neutron or two neutron intra-nuclear disappearance that would produce holes in the $\it{s}$-shell energy level of $^{12}$C nuclei. Such holes could be created as a result of nucleon decay into invisible modes ($inv$), e.g. $n \to 3ν$ or $nn \to 2ν$. The de-excitation of the corresponding daughter nucleus results in a sequence of space and time correlated events observable in the liquid scintillator detector. We report on new limits for one- and two-neutron disappearance: $τ(n\to inv)> 5.8\times 10^{…
A search for evidence of invisible-particle decay modes of a Higgs boson produced in association with a Z boson at the Large Hadron Collider is presented. No deviation from the Standard Model expectation is observed in 4.5 fb$^{-1}$ (20.3 fb$^{-1}$) of 7 (8) TeV pp collision data collected by the ATLAS experiment. Assuming the Standard Model rate for ZH production, an upper limit of 75%, at the 95% confidence level is set on the branching ratio to invisible-particle decay modes of the Higgs boson at a mass of 125.5 GeV. The limit on the branching ratio is also interpreted in terms of an upper …
Continuing our studies of radiative Upsilon(1S) decays, we report on a search for Upsilon to gamma eta and Upsilon to gamma f_{J}(2220) in 61.3 pb^{-1} of e^{+}e^{-} data taken with the CLEO II detector at the Cornell Electron Storage Ring. For the gamma eta search the three decays of the eta meson to pi^{+}pi^{-}pi^{0}, pi^{0}pi^{0}pi^{0}, and gamma gamma were investigated. We found no candidate events in the two (3π)^{0} modes and no significant excess over expected backgrounds in the gamma gamma mode to set a limit on the branching fraction of B(Upsilon to gamma eta) < 2.1 x 10^{-5} at 90% …
A search for a Higgs boson produced via vector-boson fusion and decaying into invisible particles is presented, using 20.3 fb$^{-1}$ of proton--proton collision data at a centre-of-mass energy of 8 TeV recorded by the ATLAS detector at the LHC. For a Higgs boson with a mass of 125 GeV, assuming the Standard Model production cross section, an upper bound of 0.28 is set on the branching fraction of $H\to$ invisible at 95% confidence level, where the expected upper limit is 0.31. The results are interpreted in models of Higgs-portal dark matter where the branching fraction limit is converted into…
The NA62 experiment at the CERN SPS reports a study of a sample of $4 \times10^{9}$ tagged $π^0$ mesons from $K^+ \to π^+ π^0 (γ)$, searching for the decay of the $π^0$ to invisible particles. No signal is observed in excess of the expected background fluctuations. An upper limit of $4.4 \times10^{-9}$ is set on the branching ratio at 90% confidence level, improving on previous results by a factor of 60. This result can also be interpreted as a model-independent upper limit on the branching ratio for the decay $K^+ \to π^+ X$, where $X$ is a particle escaping detection with mass in the range 0…
We search for bottomonium states in Upsilon(2S)-> (bb-bar) gamma decays with an integrated luminosity of 24.7fb^-1 recorded at the Upsilon(2S) resonance with the Belle detector at KEK, containing (157.8+-3.6) X 10^6 Upsilon(2S) events. The (bb-bar) system is reconstructed in 26 exclusive hadronic final states composed of charged pions, kaons, protons, and K^0_S mesons. We find no evidence for the state recently observed around 9975 MeV (X_(bb-bar)) in an analysis based on a data sample of 9.3 X 10^6 Upsilon(2S) events collected with the CLEO III detector. We set a 90 % confidence-level upper l…
I present three recent results from searches for exotic physics at the BaBar/PEP-II B-factory. These results span many of the samples produced at the B-factory, including B mesons, tau leptons, and Upsilon(3S) mesons. We have searched for CPT-violation in B mixing and find no significant deviation from the no-violation hypothesis. We have also searched for lepton-flavor-violating decays of the tau using tau- -> omega l- and tau- -> l+ l- l+ and their charge conjugates. We find no evidence for these processes and set upper limits on their branching fractions. Finally, we have searched for a low…
We report a search for Higgs bosons that are produced via vector boson fusion and subsequently decay into invisible particles. The experimental signature is an energetic jet pair with invariant mass of $\mathcal{O}(1) $ TeV and $\mathcal{O}(100) $ GeV missing transverse momentum. The analysis uses 36.1 fb$^{-1}$ of $pp$ collision data at $\sqrt{s}=13$ TeV recorded by the ATLAS detector at the LHC. In the signal region the 2252 observed events are consistent with the background estimation. Assuming a 125 GeV particle with Standard Model cross sections, the upper limit on the branching fraction …
We search for single-photon events in 53 fb^-1 of e+e- collision data collected with the BaBar detector at the PEP-II B-factory. We look for events with a single high-energy photon and a large missing momentum and energy, consistent with production of a spin-1 particle A' through the process e+e->gamma A', A'->invisible. Such particles, referred to as "dark photons", are motivated by theories applying a U(1) gauge symmetry to dark matter. We find no evidence for such processes and set 90% confidence level upper limits on the coupling strength of A' to e+e- in the mass range m_A'<=8 GeV. In par…
Using a data sample of $Υ(2S)$ events collected with the CLEO II detector at the Cornell Electron Storage Ring, we have investigated the hadronic transitions between the $Υ(2S)$ and the $Υ(1S)$. The charged dipion transition $Υ(2S)\to Υ(1S)π^+π^-$ was studied using two different analysis techniques. Selecting events in which $Υ(1S)$ decays into a $μμ$ or $ee$ lepton pair(``exclusive'' analysis), we measured the branching fraction of B=0.189+-0.004+-0.009, while using a method allowing $Υ(1S)$ to decay into anything (``inclusive'' analysis) we found B=0.0196+-0.002+-0.010. The appropriate avera…
