Search results for "Antiparticle"
showing 10 items of 69 documents
Constraining Nonstandard Neutrino-Electron Interactions
2007
We present a detailed analysis on nonstandard neutrino interactions (NSI) with electrons including all muon and electron (anti)-neutrino data from existing accelerators and reactors, in conjunction with the ``neutrino counting'' data (e- e+ -> nu nu gamma) from the four LEP collaborations. First we perform a one-parameter-at-a-time analysis, showing how most constraints improve with respect to previous results reported in the literature. We also present more robust results where the NSI parameters are allowed to vary freely in the analysis. We show the importance of combining LEP data with the other experiments in removing degeneracies in the global analysis constraining flavor-conservin…
CPT violation in entangled B0–B¯0 states and the demise of flavour tagging
2005
Abstract We discuss the demise of flavour tagging due to the loss of the particle–antiparticle identity of neutral B -mesons in the Einstein–Podolsky–Rosen correlated states. Such a situation occurs in cases where the CPT operator is ill-defined, as happens, for example, in quantum gravity models with induced decoherence in the matter sector. The time evolution of the perturbed B 0 – B ¯ 0 initial state, as produced in B -factories, is sufficient to generate new two-body states. For flavour specific decays at equal times, we discuss two definite tests of the two body entanglement: (i) search for the would-be forbidden B 0 B 0 and B ¯ 0 B ¯ 0 states; (ii) deviations from the indistinguishabl…
CPT Violating Decoherence and LSND: a possible window to Planck scale Physics
2004
Decoherence has the potential to explain all existing neutrino data including LSND results, without enlarging the neutrino sector. This particular form of CPT violation can preserve the equality of masses and mixing angles between particle and antiparticle sectors, and still provide seizable differences in the oscillation patterns. A simplified minimal model of decoherence is sufficient to explain the existing neutrino data quite neatly, while making dramatic predictions for the upcoming experiments. Some comments on the order of the decoherence parameters in connection with theoretically expected values from some models of quantum-gravity are given. In particular, the quantum gravity decoh…
New measurement of the K±→π±μ+μ− decay
2011
Abstract A sample of 3120 K ± → π ± μ + μ − decay candidates with ( 3.3 ± 0.7 ) % background contamination has been collected by the NA48/2 experiment at the CERN SPS, allowing a detailed study of the decay properties. The branching ratio was measured to be BR = ( 9.62 ± 0.25 ) × 10 − 8 . The form factor W ( z ) , where z = ( M μ μ / M K ) 2 , was parameterized according to several models. In particular, the slope of the linear form factor W ( z ) = W 0 ( 1 + δ z ) was measured to be δ = 3.11 ± 0.57 . Upper limits of 2.9 × 10 − 2 and 2.3 × 10 − 2 on possible charge asymmetry and forward–backward asymmetry were established at 90% CL. An upper limit BR ( K ± → π ∓ μ ± μ ± ) 1.1 × 10 − 9 was e…
Search for a Low-Mass Higgs Boson inΥ(3S)→γA0,A0→τ+τ−atBABAR
2009
We search for a light Higgs boson, $A^0$, in the radiative decay $\Upsilon(3S)\to\gamma A^0$, $A^0\to\tau^+\tau^-$, $\tau^+\to e^+\nu_e \overline{\nu}_{\tau}$ or $\tau^+\to \mu^+ \nu_{\mu} \overline{\nu}_{\tau}$. The data sample contains 122 million $\Upsilon(3S)$ events recorded with the \babar detector. We find no evidence for a narrow structure in the studied $\tau^+\tau^-$ invariant mass region of $4.03(1.5-16)\times 10^{-5}$ across the $m_{\tau^+\tau^-}$ range. We also set a 90% C.L. upper limit on the $\tau^+\tau^-$-decay of the $\eta_b$ at ${\mathcal{B}}(\eta_b\to \tau^+\tau^-)<8%$.
A heavy-quark effective field Lagrangian keeping particle and antiparticle mixed sectors
1998
We derive a tree-level heavy quark effective Lagrangian keeping particle-antiparticle mixed sectors allowing for heavy quark-antiquark pair annihilation and creation. However, when removing the unwanted degrees of freedom from the effective Lagrangian one has to be careful in using the classical equations of motion obeyed by the effective fields in order to get a convergent expansion on the reciprocal of the heavy quark mass. Then the application of the effective theory to such hard processes should be sensible for special kinematic regimes as for example heavy quark pair production near threshold.
Barkas effect with use of antiprotons and protons.
1989
The difference in the range of protons and antiprotons in matter, an example of the Barkas effect, is observed in a simple time-of-flight apparatus. The ranges of 5.9-MeV antiprotons and protons differ by about 6% in a degrader made predominantly of aluminum.
Ds+ meson production at central rapidity in proton–proton collisions at s=7 TeV
2012
The pt-differential inclusive production cross section of the prompt charm-strange meson D_s in the rapidity range |y| phi pi, with phi -> KK, and its charge conjugate, about 480 D_s mesons were counted, after selection cuts, in the transverse momentum range 2
Identified charged particles in quark and gluon jets
2000
A sample of 2.2 million hadronic Z decays, selected from the data recorded by the Delphi detector at LEP during 1994-1995 was used for an improved measurement of inclusive distributions of pi+, K+ and p and their antiparticles in gluon and quark jets. The production spectra of the individual identified particles were found to be softer in gluon jets compared to quark jets, with a higher multiplicity in gluon jets as observed for inclusive charged particles. A significant proton enhancement in gluon jets is observed indicating that baryon production proceeds directly from colour objects. The maxima, xi^*, of the xi-distributions for kaons in gluon and quark jets are observed to be different.
Direct measurement of the mass difference between top and antitop quarks
2009
We present a direct measurement of the mass difference between top and antitop quarks (dm) in lepton+jets top-antitop final states using the "matrix element" method. The purity of the lepton+jets sample is enhanced for top-antitop events by identifying at least one of the jet as originating from a b quark. The analyzed data correspond to 3.6 fb-1 of proton-antiproton collisions at 1.96 TeV acquired by D0 in Run II of the Fermilab Tevatron Collider. The combination of the e+jets and mu+jets channels yields dm = 0.8 +/- 1.8 (stat) +/- 0.5 (syst) GeV, which is in agreement with the standard model expectation of no mass difference.