Linear electron-electron colliders

In the framework of the discussion on what shape the future machine arsenal should take so as to maximize the chances of penetrating beyond the realm where the present astonishingly successful Standard Model of Particle Interactions holds undisputed sway, the present contribution is somewhat unusual: the author is not here to convince the community to build yet another machine. Instead, his task is to convince you that in the established choices that the accelerator community is headed towards, it is of great importance that the Electron Collider of the next generation, i.e., in the 0.5 to 1.5 TeV energy range, should be configured just such, as an Electron collider, NOT dedicated to just one incoming charge state (say, e{sup +}e{sup {minus}}). Now that the energy range that can be reached with circular/recirculating machines has been exceeded, designers are freed from the need to have oppositely charged electrons as projectiles and targets. The colliding linac configuration sets no preferential condition on the chosen net charge; in fact, this is the first time such a machine may well serve to collide a variety of initial states at full energy 2E{sub B} and luminosity (e{sup +}e{sup +}, e{sup +}e{sup {minus}}, e{sup {minus}}e{sup {minus}}), or at slightly reduced center-of-mass energy, but still full luminosity ({gamma}-e, {gamma}-{gamma})

The Noncommutative Standard Model and Forbidden Decays

In this contribution we discuss the Noncommutative Standard Model and the associated Standard Model-forbidden decays that can possibly serve as an experimental signature of space-time noncommutativity.Comment: 15 pages, 1 figure, Invited talk at 9th Adriatic Meeting and Central European Symposia on Particle Physics and The Universe, Dubrovnik, Croatia, 4-14 Sep 200

Effective Lagrangian Approach to the Theory of Eta Photoproduction in the N∗(1535)N^{*}(1535) Region

We investigate eta photoproduction in the $N^{*}(1535)$ resonance region within the effective Lagrangian approach (ELA), wherein leading contributions to the amplitude at the tree level are taken into account. These include the nucleon Born terms and the leading $t$-channel vector meson exchanges as the non-resonant pieces. In addition, we consider five resonance contributions in the $s$- and $u$- channel; besides the dominant $N^{*}(1535)$, these are: $N^{*}(1440),N^{*}(1520),N^{*}(1650)$ and $N^{*}(1710)$. The amplitudes for the $\pi^\circ$ and the $\eta$ photoproduction near threshold have significant differences, even as they share common contributions, such as those of the nucleon Born terms. Among these differences, the contribution to the $\eta$ photoproduction of the $s$-channel excitation of the $N^{*}(1535)$ is the most significant. We find the off-shell properties of the spin-3/2 resonances to be important in determining the background contributions. Fitting our effective amplitude to the available data base allows us to extract the quantity $\sqrt{\chi \Gamma_\eta} A_{1/2}/\Gamma_T$, characteristic of the photoexcitation of the $N^{*}(1535)$ resonance and its decay into the $\eta$-nucleon channel, of interest to precise tests of hadron models. At the photon point, we determine it to be $(2.2\pm 0.2)\times 10^{-1} GeV^{-1}$ from the old data base, and $(2.2\pm 0.1) \times 10^{-1} GeV^{-1}$ from a combination of old data base and new Bates data. We obtain the helicity amplitude for $N^{*}(1535)\rightarrow \gamma p$ to be $A_{1/2}=(97\pm 7)\times 10^{-3} GeV^{-1/2}$ from the old data base, and $A_{1/2}=(97\pm 6)\times 10^{-3} GeV^{-1/2}$ from the combination of the old data base and new Bates data, compared with the results of the analysis of pion photoproduction yielding $74\pm 11$, in the same units.Comment: 43 pages, RevTeX, 9 figures available upon request, to appear in Phys. Rev.

INVERSE NEUTRINOLESS DOUBLE-BETA DECAY IN GAUGE THEORIES WITH CP VIOLATION

We investigate the reactions $e^-e^- \rightarrow W_i^-W_j^-$ for various gauge bosons production processes in the frame of the standard model with additional right-handed neutrinos and the Left-Right symmetric model. The present bounds on the various model parameters are taken into account. The question of the cross section behaviour for large energy and the CP violation problems are discussed.Comment: 21 pages,latex, figures not included (hard copy available on request

Inverse Neutrinoless Double Beta Decay Revisited

We critically reexamine the prospects for the observation of the $\Delta L=2$ lepton-number-violating process \eeWW using the $e^-e^-$ option of a high-energy $e^+e^-$ collider (NLC). We find that, except in the most contrived scenarios, constraints from neutrinoless double beta decay render the process unobservable at an NLC of $\sqrt{s}<2$ TeV. Other $\Delta L=2$ processes such as \ggllww, \egnllw, \eennll ($\ell=\mu,\tau$), and \egeww, which use various options of the NLC, require a $\sqrt{s}$ of at least 4 TeV for observability.Comment: paper in LATEX, 24 pages, 10 figures in separate uuencoded psfile. Complete psfile available via anonymous ftp at ftp://lapphp0.in2p3.fr/pub/preprints-theorie/doublebeta.uu or via www at http://lapphp0.in2p3.fr/preplapp/psth/doublebeta.ps.g

Large enhancement of deuteron polarization with frequency modulated microwaves

We report a large enhancement of 1.7 in deuteron polarization up to values of 0.6 due to frequency modulation of the polarizing microwaves in a two liters polarized target using the method of dynamic nuclear polarization. This target was used during a deep inelastic polarized muon-deuteron scattering experiment at CERN. Measurements of the electron paramagnetic resonance absorption spectra show that frequency modulation gives rise to additional microwave absorption in the spectral wings. Although these results are not understood theoretically, they may provide a useful testing ground for the deeper understanding of dynamic nuclear polarization.Comment: 10 pages, including the figures coming in uuencoded compressed tar files in poltar.uu, which also brings cernart.sty and crna12.sty files neede

Production of Weak Bosons and Higgs Bosons at e-e- Colliders

We present calculations of cross sections for single $W^-$ and $Z$ production and $W^-W^-, W^-Z, W^-\gamma, ZZ$, and $W^+W^-$ pair production within the Standard Model at $e^-e^-$ linear colliders. We evaluate Standard-Model Higgs boson production in the channels $e^-e^- \to e^-e^- H$, $e^-\nu W^- H$, and $e^-e^- ZH$. We also illustrate the enhancements in the $W^-W^-$ cross section that would result from a strongly-interacting Higgs sector or from a $H^{--}$ resonance in a Higgs doublet + triplet model.Comment: Standard Latex, 19 pages of text. 11 postscript figures included; hardcopies by fax or mail available upon request. MAD/PH/77

Lepton flavour violation in e^{\pm}e^{-}\to \ell^{\pm}e^{-} (\ell = \mu,\tau) induced by R-conserving supersymmetry

The lepton flavour violating signals $e^{+}e^{-}\to \ell^{+}e^{-}$ and $e^{-}e^{-}\to \ell^{-}e^- (\ell=\mu,\tau)$ are studied in the context of low energy R-parity conserving supersymmetry at center of mass energies of interest for the next generation of linear colliders. Loop level amplitudes receive contributions from electroweak penguin and box diagrams involving sleptons and gauginos. Lepton flavour violation is due to off diagonal elements in $SU(2)_L$ doublet slepton mass matrix. These masses are treated as model independent free phenomenological parameters in order to discover regions in parameter space where the signal cross section may be observable. The results are compared with (a) the experimental bounds from the non-observation of rare radiative lepton decays $\mu, \tau \to e\gamma$ and (b) the general mSUGRA theoretical scenario with seesaw mechanism where off diagonal slepton matrix entries are generated by renormalization group evolution of neutrino Yukawa couplings induced by the presence of new energy scales set by the heavy $SU(2)_L$ singlet neutrino masses. It is found that in $e^- e^-$ collisions the ($e\tau$) signal can be observable with a total integrated luminosity of 100 fb$^{-1}$ and the that the background can be easily suppressed. In $e^+ e^-$ collisions the cross section is smaller and higher luminosities are needed. The experimental bound on the decay $\mu \to e \gamma$ prevents the ($e\mu$) signal from being observable.Comment: 14 pages, 12 figures, Revtex

Searching for doubly charged Higgs bosons in M\"{o}ller scattering by resonance effects at linear e−e−e^-e^- collider

We discuss the parity-violating left-right asymmetries (LRAs) in M\"{o}ller scattering at the International Linear Collider (ILC) induced by doubly charged Higgs bosons in models with $SU(2)_L$ triplet and singlet scalar bosons, which couple to the left- and right-handed charged leptons, respectively. These bosons are important in the scenarios for the generation of the neutrino mass. We demonstrate that the contributions to the LRAs from the triplet and singlet bosons are opposite to each other. In particular, we show that the doubly charged Higgs boson from the singlet scalar can be tested at the ILC by using the resonance effect.Comment: 12 pages, 5 figures; version published in Eur.Phys.J.C60:119-124,200

Measurement of the B0-anti-B0-Oscillation Frequency with Inclusive Dilepton Events

The $B^0$-$\bar B^0$ oscillation frequency has been measured with a sample of 23 million \B\bar B pairs collected with the BABAR detector at the PEP-II asymmetric B Factory at SLAC. In this sample, we select events in which both B mesons decay semileptonically and use the charge of the leptons to identify the flavor of each B meson. A simultaneous fit to the decay time difference distributions for opposite- and same-sign dilepton events gives $\Delta m_d = 0.493 \pm 0.012{(stat)}\pm 0.009{(syst)}$ ps$^{-1}$.Comment: 7 pages, 1 figure, submitted to Physical Review Letter