Search for TeV Strings and New Phenomena in Bhabha Scattering at LEP2

A combined analysis of the data on Bhabha scattering at centre-of-mass energies 183 and 189 GeV from the LEP experiments ALEPH, L3 and OPAL is performed to search for effects of TeV strings in quantum gravity models with large extra dimensions. No statistically significant deviations from the Standard Model expectations are observed and lower limit on the string scale M_S = 0.631 TeV at 95 % confidence level is derived. The data are used to set lower limits on the scale of contact interactions ranging from 4.2 to 16.2 TeV depending on the model. In a complementary analysis we derive an upper limit on the electron size of 2.8 x 10^{-19} m at 95 % confidence level.Comment: 10 pages, 1 table, 3 figure

Are the reactions γγ→VV′\gamma\gamma\to VV' a challenge for the factorized Pomeron at high energies?

We would like to point to the strong violation of the putative factorized Pomeron exchange model in the reactions $\gamma\gamma\to VV'$ in the high-energy region where this model works fairly well in all other cases.Comment: 4 pages, LaTex, 1 fig. in postscript, minor typos corrected, to be published in Phys. Rev. D 60, 117503 (1999

A Non-supersymmetric Interpretation of the CDF e+e-\gamma\gamma + missing E_T Event

The \eegg event reported recently by the CDF Collaboration has been interpreted as a signal of supersymmetry in several recent papers. In this article, we report on an alternative non-supersymmetric interpretation of the event using an extension of the standard model which contains new physics at the electroweak scale that does not effect the existing precision electroweak data. We extend the standard model by including an extra sequential generation of fermions, heavy right-handed neutrinos for all generations and an extra singly charged SU(2)-singlet Higgs boson. We discuss possible ways to discriminate this from the standard supersymemtric interpretations.Comment: 7 pages, Latex, no figure

First Tests of a New Fast Waveform Digitizer for PMT Signal Read-out from Liquid Argon Dark Matter Detectors

Abstract A new generation Waveform Digitizer board as been recently made available on the market by CAEN. The new board CAEN V1751 with 8 Channels per board, 10 bit, 1 GS/s Flash ADC Waveform Digitizer (or 4 channel, 10 bit, 2 GS/s Flash ADC Waveform Digitizer -Dual Edge Sampling mode) with threshold and Auto-Trigger capabilities provides an ideal (relatively low-cost) solution for reading signals from liquid Argon detectors for Dark Matter search equipped with an array of PMTs for the detection of scintillation light. The board was extensively used in real experimental conditions to test its usefulness for possible future uses and to compare it with a state of the art digital oscilloscope. As results, PMT Signal sampling at 1 or 2 GS/s is appropriate for the reconstruction of the fast component of the signal scintillation in Argon (characteristic time of about 4 ns) and the extended dynamic range, after a small customization, allows for the detection of signals in the range of energy needed. The bandwidth is found to be adequate and the intrinsic noise is very low

Analytic Perturbation Theory: A New Approach to the Analytic Continuation of the Strong Coupling Constant αS\alpha_S into the Timelike Region

The renormalization group applied to perturbation theory is ordinarily used to define the running coupling constant in the spacelike region. However, to describe processes with timelike momenta transfers, it is important to have a self-consistent determination of the running coupling constant in the timelike region. The technique called analytic perturbation theory (APT) allows a consistent determination of this running coupling constant. The results are found to disagree significantly with those obtained in the standard perturbative approach. Comparison between the standard approach and APT is carried out to two loops, and threshold matching in APT is applied in the timelike region.Comment: 16 pages, REVTeX, 7 postscript figure

Implications of a possible 115 GeV supersymmetric Higgs boson on detection and cosmological abundance of relic neutralinos

We show that a supersymmetric neutral Higgs boson with a mass of about 115 GeV and with the other prerequisites required by the LEP Higgs events would be compatible with the detection of relic neutralinos in current set-ups for WIMP direct search. Thus this putative Higgs would fit remarkably well in an interpretation in terms of relic neutralinos of the annual-modulation effect recently measured in a WIMP direct experiment. We also show that the cosmological abundance of the relevant neutralinos reaches values of cosmological interest.Comment: 15 pages, 6 figures, typeset with ReVTeX. The new version containes extended analysis. In order to reduce size, the version on the archive has low-resolution figures. The paper with high-resolution figures can be found at http://www.to.infn.it/~fornengo/papers

Neutron to Gamma Pulse Shape Discrimination in Liquid Argon Detectors with High Quantum Effciency Photomultiplier Tubes

Abstract A high Light Yield Liquid Argon chamber has been radiated with an Am/Be source for signal-to-background separation level characterization in a Dark Matter Liquid Argon based detector. Apart from the standard nuclear recoil and electron events, from neutron elastic interactions and gamma conversions respectively, an intermediate population has been observed which is attributed to inelastic neutron scatters on Argon nuclei producing Argon recoil and simultaneous gammas from nuclear de-excitation. Taking account of these events results in a better determination of the recoil-like to electron-like separation based on the shape of the scintillation pulse. The results of this recent study as well as from a previous study with a chamber with a lower Light Yield are presented

Bounds on the tau and muon neutrino vector and axial vector charge radius

A Majorana neutrino is characterized by just one flavor diagonal electromagnetic form factor: the anapole moment, that in the static limit corresponds to the axial vector charge radius . Experimental information on this quantity is scarce, especially in the case of the tau neutrino. We present a comprehensive analysis of the available data on the single photon production process $e^+ e^- -> \nu \bar\nu \gamma$ off Z-resonance, and we discuss the constraints that these measurements can set on for the tau neutrino. We also derive limits for the Dirac case, when the presence of a vector charge radius is allowed. Finally, we comment on additional experimental data on $\nu_\mu$ scattering from the NuTeV, E734, CCFR and CHARM-II collaborations, and estimate the limits implied for and for the muon neutrino.Comment: 20 pages, 2 eps figures. CCFR data included in the analysis. Conclusion unchange

Invisible Z-Boson Decays at e+e- Colliders

The measurement of the invisible Z-boson decay width at e+e- colliders can be done "indirectly", by subtracting the Z-boson visible partial widths from the Z-boson total width, or "directly", from the process e+e- -> \gamma \nu \bar{\nu}. Both procedures are sensitive to different types of new physics and provide information about the couplings of the neutrinos to the Z-boson. At present, measurements at LEP and CHARM II are capable of constraining the left-handed Z\nu\nu-coupling, 0.45 <~ g_L <~ 0.5, while the right-handed one is only mildly bounded, |g_R| <= 0.2. We show that measurements at a future e+e- linear collider at different center-of-mass energies, \sqrt{s} = MZ and \sqrt{s}s ~ 170 GeV, would translate into a markedly more precise measurement of the Z\nu\nu-couplings. A statistically significant deviation from Standard Model predictions will point toward different new physics mechanisms, depending on whether the discrepancy appears in the direct or the indirect measurement of the invisible Z-width. We discuss some scenarios which illustrate the ability of different invisible Z-boson decay measurements to constrain new physics beyond the Standard Model

H-->WW as the discovery mode for a light Higgs boson

The production cross section for a m_H=115 GeV, SM Higgs boson in weak boson fusion at the LHC is sizable. However, the branching fraction for H-->WW is expected to be relatively small. The signal, with its two forward jets, is sufficiently different from the main backgrounds that a signal to background ratio of better than 1:1 can nevertheless be obtained, with large enough rate to allow for a 5 sigma signal with 35 fb^{-1} of data. The H-->WW signal in weak boson fusion may thus prove to be the discovery mode for the Higgs boson at the LHC.Comment: 10 pages, 4 figures, uses revte