A sizeable difference in the differential production cross section of top- compared to antitop-quark production, denoted charge asymmetry, has been observed at the Tevatron. The experimental results seem to exceed the theory predictions based on the Standard Model by a significant amount and have triggered a large number of suggestions for "new physics". In the present paper the Standard Model predictions for Tevatron and LHC experiments are revisited. This includes a reanalysis of electromagnetic as well as weak corrections, leading to a shift of the asymmetry by roughly a factor 1.1 when compared to the results of the first papers on this subject. The impact of cuts on the transverse momentum of the top-antitop system is studied. Restricting the ttbar system to a transverse momentum less than 20 GeV leads to an enhancement of the asymmetries by factors between 1.3 and 1.5, indicating the importance of an improved understanding of the $t\bar t$-momentum distribution. Predictions for similar measurements at the LHC are presented, demonstrating the sensitivity of the large rapidity region both to the Standard Model contribution and effects from "new physics".
We compute, for top quark pair production at the Tevatron and the Large Hadron Collider, the collider-independent forward-backward asymmetries defined in [1] in the standard model at next-to-leading order in QCD, including also electromagnetic and weak corrections.
We introduce the forward-backward asymmetries A_u, A_d corresponding to u ubar, d dbar -> t tbar production, respectively, at hadron colliders. These are collider- and center-of-mass-independent observables, directly related to the forward-backward and charge asymmetries measured at the Tevatron and the LHC, respectively. We discuss how to extract these asymmetries from data. Because these asymmetries are collider-independent, their measurement at these two colliders could elucidate the nature of the anomalous forward-backward asymmetry measured at the Tevatron. Our framework also shows in a m…
We review the asymmetries in top quark pair production at the Tevatron and the LHC. We summarize the experimental measurements and the interpretations of a possible excess in terms of new physics. We also review other top quark properties-emphasizing effects related to the $t \bar t$ asymmetries-as well as other collider signals.
We calculate the single transverse spin asymmetries(SSA) for forward inclusive particle production in pp and pA collisions using a hybrid approach. It is shown that the Sivers type contribution to the SSA drops out due to color entanglement effect, whereas the fragmentation contribution to the spin asymmetry is not affected by color entanglement effect. This finding offers a natural solution for the sign mismatch problem.
We revisit the effect of the (Dirac) CP-violating phase on neutrino lepton number asymmetries in both mass- and flavor-basis. We found that, even if there are sizable effects on muon- and tau-neutrino asymmetries, the effect on the asymmetry of electron-neutrinos is at most similar to the upper bound set by BBN for initial neutrino degeneracy parameters smaller than order unity. We also found that, for the asymmetries in mass-basis, the changes caused by CP-violation is of sub-\% level which is unlikely to be accesible neither in the current nor in the forthcoming experiments.
The capability of the NLC run in the $γe$ collision mode to probe the CP-conserving $γWW$ and $γZZ$ anomalous couplings through the use of the polarization asymmetry is reviewed. When combined with other measurements, very strong constraints on both varieties of anomalous couplings can be obtained. We show that these bounds are complementary to those that can be extracted from data taken at the LHC.
We study azimuthal asymmetries in heavy quark pair production in unpolarized electron-proton and proton-proton collisions, where the asymmetries originate from the linear polarization of gluons inside unpolarized hadrons. We provide cross section expressions and study the maximal asymmetries allowed by positivity, for both charm and bottom quark pair production. The upper bounds on the asymmetries are shown to be very large depending on the transverse momentum of the heavy quarks, which is promising especially for their measurements at a possible future Electron-Ion Collider or a Large Hadron …
We study the general Higgs-weak boson coupling with CP-violation via the process e+e- -> f \bar f h. We categorize the signal channels by sub-processes Zh production and ZZ fusion and construct four CP asymmetries by exploiting polarized e+e- beams. We find complementarity among the sub-processes and the asymmetries to probe the real and imaginary parts of the CP-violating form factor. Certain asymmetries with unpolarized beams can retain significant sensitivity to the coupling. We conclude that at a linear collider with high luminosity, the CP-odd ZZh coupling may be sensitively probed via me…
We discuss forward-backward charge asymmetries for lepton pair production in association with a large transverse momentum jet at hadron colliders. The measurement of the lepton charge asymmetry relative to the jet direction A_{FB}^j gives a new determination of the effective weak mixing angle sin^2{θ_{eff}^{lept}(M_Z^2)} with in principle a statistical precision after cuts of \sim 10^{-3} (8 x 10^{-3}) at LHC (Tevatron), due to the large cross section of the process with initial gluons. The identification of b jets also allows for the measurement of the bottom quark Z asymmetry A_{FB}^b at had…
Parity violating left-right scattering asymmetries at future high energy e+e- and e-e- colliders are examined. The utility of two polarized beams for precision measurements is pointed out. Sensitivity to ``new'' short-distance physics is briefly discussed. Electroweak radiative corrections due to the running of sin^2(theta_W)(q^2) are exhibited.
We study the production cross sections for squarks and gluinos in collision of longitudinally polarized hadrons. The corresponding polarized partonic cross sections are computed in leading order supersymmetric QCD. The resulting asymmetries are evaluated for the polarized proton collider RHIC, as well as for hypothetical polarized options of the Tevatron and the LHC. These asymmetries turn out to be sizable over a wide range of supersymmetric particle masses, thus potentially opening a window to detailed sparticle spectroscopy at future polarized hadron colliders.
In the Minimal Supersymmetric Standard Model, physical phases of complex parameters lead to CP violation. We show how triple products of particle momenta or spins can be used to construct asymmetries, that allow us to probe these CP phases. To give specific examples, we discuss the production of neutralinos at the International Linear Collider. For the Large Hadron Collider, we discuss CP asymmetries in squark decays, and in the tri-lepton signal. We find that the CP asymmetries can be as large as 60%.
We present a comprehensive analysis on the MSSM Higgs sector CP violation at photon colliders including the chargino contributions as well as the contributions of other charged particles. The chargino loop contributions can be important for the would-be CP odd Higgs production at photon colliders. Polarization asymmetries are indispensable in determining the CP properties of neutral Higgs bosons.
By considering left-right (L-R) asymmetries we study the capabilities of lepton colliders in searching for new exotic vector bosons. Specifically we study the effect of a doubly charged bilepton boson and an extra neutral vector boson appearing in a 3-3-1 model on the L-R asymmetries for the processes $e^-e^-\to e^-e^-$, $μ^-μ^-\toμ^-μ^-$ and $e^-μ^-\to e^-μ^-$ and show that these asymmetries are very sensitive to these new contributions and that they are in fact powerful tools for discovery this sort of vector bosons.
We study all the possible spin asymmetries that can arise in back-to-back electron-jet production, $ep\rightarrow e+\text{jet}+X$, as well as the associated jet fragmentation process, $ep\rightarrow e+ \text{jet} (h)+X$, in electron-proton collisions. We derive the factorization formalism for these spin asymmetries and perform the corresponding phenomenology for the kinematics relevant to the future electron ion collider. In the case of unpolarized electron-proton scattering, we also give predictions for azimuthal asymmetries for the HERA experiment. This demonstrates that electron-jet product…
We revisit the process of inverse neutrino-less double beta decay (e e -> W W) at future linear colliders. The cases of Majorana neutrino and Higgs triplet exchange are considered. We also discuss the processes e mu -> W W and mu mu -> W W, which are motivated by the possibility of muon colliders. For heavy neutrino exchange and center-of-mass energies larger than 1 TeV, we show that masses up to 10^6 (10^5) GeV could be probed for e-e and e-mu machines, respectively. The stringent limits for mixing of heavy neutrinos with muons render mu mu -> W W less promising, even though this process is n…
We investigate the forward-backward asymmetries in the pair production of fourth family fermions through the new Z' interactions in the e+e- collisions. The Z' boson having family universal couplings can contribute to the pair production of fourth family fermions via the s-channel exchange. The linear colliders will provide a clean environment for the physics of Z' boson to measure its couplings precisely. The effects of the Z' boson to the asymmetries are shown to be important in some parameter regions for different Z' models. Among these parameters, the invariant mass distribution m_FFbar wi…
The production of $W^{\pm}$ and $Z^0$ bosons in collisions of longitudinally polarized protons allows to access various combinations of the polarized quark distributions from the study of double and single spin asymmetries. We compute the ${\cal O}(α_s)$ corrections to these asymmetries as function of the vector boson rapidity $y$ in the hadron-hadron centre-of-mass frame. Detailed studies of the numerical impact of the next-to-leading order corrections are presented. The theoretical uncertainties of an extraction of polarized quark distributions from future vector boson production data are in…
Axigluons are colored heavy neutral gauge boson that couple to quarks through an axial vector current and the same strong coupling as gluons. The most important model-independent manifestation of axigluons is the generation of a forward--backward asymmetry in top-antitop quark production at $p\bar{p}$ collisions which originates from the charge asymmetry. We update our previous analysis for the inclusive QCD induced forward--backward asymmetry and define a new observable which is more sensitive to the effect than the forward--backward asymmetry. Furthermore, we find a lower limit of 1.2 TeV at…
We present predictions and projections for hadron-in-jet measurements and electron-jet azimuthal correlations at the future Electron-Ion Collider (EIC). These observables directly probe the three-dimensional (3D) structure of hadrons, in particular, the quark transversity and Sivers parton distributions and the Collins fragmentation functions. We explore the feasibility of these experimental measurements by detector simulations and discuss detector requirements. We conclude that jet observables have the potential to enhance the 3D imaging EIC program.
Several models predict the existence of heavy colored resonances decaying to top quarks in the TeV energy range that might be discovered at the LHC. In some of those models, moreover, a sizable charge asymmetry of top versus antitop quarks might be generated. The detection of these exotic resonances, however, requires selecting data samples where the top and the antitop quarks are highly boosted, which is experimentally very challenging. We asses that the measurement of the top quark charge asymmetry at the LHC is very sensitive to the existence of excited states of the gluon with axial-vector…
Recently it has been shown that measurement of charge asymmetry of top pair production at LHC excludes any flavor violating $Z'$ vector gauge boson that could explain Tevatron forward-backward asymmetry (FBA). We consider the general form of a $Z'$ gauge boson including left-handed, right-handed vector and tensor couplings to examine FBA and charge asymmetry. To evaluate top pair asymmetries at Tevatron and LHC, we consider $B^0_q$ mixing constraints on flavor changing $Z'$ couplings and show that this model still explain forward-backward asymmetry at Tevatron and charge asymmetry can not excl…
We study loop-induced parity violating asymmetries in the strong production of polarized top quark pairs at $pp$ and $p \bar p$ colliders. The electroweak ${\cal O}(α)$ corrections to the helicity amplitudes of $q \bar q \to t \bar t$ and $gg \to t \bar t$ are evaluated in a two Higgs doublet model (2HDM) and the minimal supersymmetric standard model (MSSM). While observables in top quark pair production receive little contribution from standard electroweak interactions, it is possible that they can be significantly enhanced in a 2HDM and the MSSM. We find that the one-loop MSSM electroweak co…
A successful interpretation of the cross sections for elastic and inelastic vector meson production can be made if one assumes the underlying dynamics to be governed by hard partonic subprocesses. Extending these partonic approaches to longitudinally polarized electron-proton collisions, we estimate the expected production asymmetries at the HERA collider. The anticipated statistical errors on these asymmetries mostly turn out to be larger than the asymmetries themselves, such that an experimental observation of these asymmetries at HERA looks not feasible.
In an effective operator approach, the full set of leading contributions to anomalous top couplings comprises various new trilinear as well as higher interaction vertices, some of which are related to one another by gauge symmetry or equations of motion. In order to study trilinear top couplings to SM gauge bosons such as ttA, ttZ, tbW and ttg, the operator set can be restricted accordingly. However, the complete basis cannot be mapped onto an on-shell parametrisation of the trilinear vertices alone. Four-fermion contact terms qqtt and udtb must be included if the relation to the operator basi…
We discuss the possibilities of testing of perturbative quantum chromodynamics through azimuthal asymmetries in polarized ep in the context of future collider and fixed target facilities, such as Electron Ion Collider and TESLA-N.
I present new results for the Standard-Model predictions of the differential decay rates for $H\to \ell^{+} \ell^{-} γ$, where $\ell=e, μ$, and the forward-backward asymmetries defined in terms of the flight direction of the photon corresponding to the lepton momenta. The results dependend on the cuts on energies and invariant masses of the final state particles. For standard choices of these cuts the branching ratios $B(H\to e \bar e γ)=5.8\cdot 10^{-5}$ and $B(H\to μ\bar μγ)=6.4\cdot 10^{-5}$ as well as the forward-backward asymmetries $\mathcal{A}^{(e)}_{\text{FB}}=0.343$ and $\mathcal{A}^{…
We consider the next-to-leading order corrections, O(alpha_s), to forward-backward charge asymmetries for lepton-pair production in association with a large transverse momentum jet at large hadron colliders. We find that the leading order results are essentially confirmed. Although experimentally challenging and in practice with large backgrounds, these observables could provide a new determination of the weak mixing angle sin2 theta^lept_eff (M_Z^2) with a statistical precision for each lepton flavour of ~10^(-3) (7 x 10^{-3}) at LHC (Tevatron), and if b jets are identified, of the b quark Z …
In this talk we review the electroweak contribution to top quark pair production at hadron colliders. We discuss the phenomenological impact of these corrections on the cross sections and on the charge asymmetries at the Tevatron and the LHC.
The Weizsaecker-Williams transverse momentum dependent (TMD) gluon distributions can be probed in the production of a hard dijet in semi-inclusive DIS. This process is sensitive not only to the conventional but also to the linearly polarized gluon distribution. The latter gives rise to an azimuthal dependence of the dijet cross section and therefore can be distinguished from the former. Feasibility study of a measurement of these TMDs through dijet production at a future electron-ion collider shows that the extraction of the distribution of linearly polarized gluons with a statistical accuracy…
Analytic expressions for the angular distributions of the $b$-quarks associated with single $t$-quark production in $p \bar p \to W^* \to t \bar b \to b \bar b W$ and of the leptons from the subsequent decay $W \to lν$ are obtained in the laboratory system. CP violation in the $t$-production vertex is assumed. Different angular and total cross section CP violating asymmetries are considered. Relations testing CP violation solely in the $t$-decay vertex are also obtained. A numerical analysis is performed in the MSSM with a CP violating phase of the trilinear coupling $A_{\tilde t}$. The asymme…
We investigate the potentialities offered by the study of J/psi exclusive photo-production in ultra-peripheral collisions at a fixed-target experiment using the proton and lead LHC beams (generically denoted as AFTER@LHC) on hydrogen targets and at RHIC in the collider mode. We compare the expected counting rates in both set-ups. Studying Single-Transverse-Spin Asymmetries (A_N) in such a process provides a direct path to the proton Generalised Parton Distribution (GPD) E_g(x,xi,t). We evaluate the expected precision on A_N for realistic conditions with the LHCb detector in pH(pol) and PbH(pol…
In this review, we discuss recent developments in both the theory and the experimental searches of magnetic monopoles in past, current and future colliders and in the Cosmos. The theoretical models include, apart from the standard Grand Unified Theories, extensions of the Standard Model that admit magnetic monopole solutions with finite energy and masses that can be as light as a few TeV. Specifically, we discuss, among other scenarios, modified Cho-Maison monopoles and magnetic monopoles in (string-inspired, higher derivative) Born-Infeld extensions of the hypercharge sector of the Standard M…
We examine the effects of the R parity odd renormalizable interactions on flavor changing rates and CP violation asymmetries in the production of fermion-antifermion pairs at $e^-- e^+$ leptonic colliders. The produced fermions may be leptons, down-quarks or up-quarks, and the center of mass energies may range from the Z-boson pole up to $ 1000$ GeV. Off the Z-boson pole, the flavor changing rates are controlled by tree level amplitudes and the CP asymmetries by interference terms between tree and loop level amplitudes. At the Z-boson pole, both observables involve loop amplitudes. The lepton …
CP-violating asymmetries in the processes e+e- -> t tbar and gamma gamma -> ttbar can provide information about CP-violating couplings of the top quark, whose presence would signal physics beyond the standard model. Work on studies of different asymmetries has been described. Special emphasis has been laid on asymmetries in charged lepton distributions arising from top decay. The effect of longitudinal beam polarization has been discussed. Limits possible on the electric dipole moment of the top quark from different angular asymmetries have been obtained.
We consider the sneutrino resonance reaction l^+ l^- -> sneutrino -> tau^+ tau^- in the MSSM without R-parity. We introduce new CP-violating and CP-conserving tau-spin asymmetries which are generated already at the tree-level if there is sneutrino - sneutrino-bar mixing and that are forbidden in the SM. It is remarkable that these spin asymmetries can reach ~75% around resonance for a sneutrino mass splitting of Δm ~ Γand ~10% for a splitting as low as Δm ~ 0.1Γ, where Γis the sneutrino width. We show that they are easily detectable already at LEP2 so long as the beam energy is within ~10 GeV …
Branching fractions and CP-violating asymmetries of charmless $\bar B_s\to PP, VP, VV$ decays (P and V denoting pseudoscalar and vector mesons, respectively) are re-examined in the framework of QCD factorization (QCDF). We take into account subleading power corrections to the penguin annihilation topology and to color-suppressed tree amplitudes that are crucial for resolving the CP puzzles and rate deficit problems with penguin-dominated two-body decays and color-suppressed tree-dominated $π^0π^0$ and $ρ^0π^0$ modes in the $B_{u,d}$ sector. Many of the $B_s\to h_1h_2$ decays can be related to …
Forward-backward asymmetries $A_{FB}^t$ and $A_{FB}^\ell$ are observed in the top quark $t$ rapidity distribution and in the rapidity distribution of charged leptons $\ell$ from top quark decay at the Tevatron proton-antiproton collider, and a charge asymmetry $A_C$ is seen in proton-proton collisions at the Large Hadron Collider (LHC). In this paper, we update our previous studies of the Tevatron asymmetries using the most recent data. We provide expectations for $A_C$ at the LHC based first on model independent extrapolations from the Tevatron, and second based on new physics models that can…
Several parity violating left-right asymmetries in Møller electron-electron and muon-muon scattering are considered in the context of the electroweak standard model at tree level in fixed target and collider experiences. We show that in colliders the asymmetry with only one of the beam polarized is large enough to compensate the smaller cross section at high energies. We also show that these asymmetries are very sensitive to a doubly charged vector bilepton resonance but they are insensitive to scalar ones.
Many GUT models conserve the difference between the baryon and lepton number, $B-L$. These models can create baryon and lepton asymmetries from heavy Higgs or gauge boson decays with $B+L \neq 0$ but with $B-L=0$. Since the sphaleron processes violate $B+L$, such GUT-generated asymmetries will finally be washed out completely, making GUT baryogenesis scenarios incapable of reproducing the observed baryon asymmetry of the Universe. In this work, we revisit the idea to revive GUT baryogenesis, proposed by Fukugita and Yanagida, where right-handed neutrinos erase the lepton asymmetry before the s…
We examine the effect of the R parity odd renormalizable interactions on flavor non-diagonal rates and CP violation asymmetries in the production of slepton pairs at $e^- - e^+$ leptonic colliders, for center of mass energies spanning the interval from the Z-boson pole up to 1000 GeV. The lepton number violating interactions, associated with the lepton number violating coupling constants, are assumed to incorporate CP odd complex phases. The flavor changing rates are controlled by tree level amplitudes and quadratic products of different R parity violating coupling constants and the CP asymmet…
A new handed interaction between quarks could be at the origin of some small parity violating effects in the inclusive production of one-jet in polarized $pp$ collisions. This interaction could originate from compositeness or from the presence of a new massive vector boson. The measurement of such asymmetries could be performed within a few years by using the RHIC collider as a polarized proton-proton collider.
We investigate the TeV-scale stringy signals of the four-fermion scattering at the electron-positron collider with the center of mass energy 500-1000 GeV. The nature of the stringy couplings leads to distinguishable asymmetries comparing to the other new physics models. Specifically, the stringy states in the four-fermion scattering at the leading-order corrections are of spin-1 and 2 with the chiral couplings inherited from the gauge bosons identified as the zeroth-mode string states. The angular left-right, forward-backward, center-edge asymmetries and the corresponding polarized-beam asymme…
Predictions are made for the forward-backward and charge asymmetries in bottom-quark pair production at hadron colliders. Tree-level exchanges of electroweak (EW) gauge bosons dominate the Standard Model (SM) contribution to the asymmetry near the $Z$-pole. The mixed EW-QCD corrections are computed in an approximate way, and are found to be small in magnitude. These SM predictions are consistent with experimental results from CDF, D0, and LHCb. In particular, CDF and LHCb find that the asymmetry in the invariant mass bin containing the $Z$-pole is larger than in the adjacent bins, as predicted…
We study CP violation in chargino production and decay in the Minimal Supersymmetric Standard Model (MSSM) with complex parameters at an e^+ e^- linear collider with longitudinally polarized beams. We investigate CP-sensitive asymmetries by means of triple product correlations and study their dependence on the complex parameters M_1 and mu. We give numerical predictions for the asymmetries and their measurability at the future International Linear Collider. Our results show that the CP asymmetries can be measured in a large region of the MSSM parameter space.
Fermion pair production at $e^-e^+$ linear collider experiments with polarized $e^-$ and $e^+$ beams is examined in the GUT inspired $SO(5)\times U(1)\times SU(3)$ gauge-Higgs unification. There arises large parity violation in the couplings of leptons and quarks to Kaluza-Klein (KK) excited neutral vector bosons $Z'$s, which leads to distinctive polarization dependence in cross sections, forward-backward asymmetries, left-right asymmetries, and left-right forward-backward asymmetries in various processes. Those effects are detectable even for the KK mass scale up to about 15 TeV at future $e^…
We present new calculations of the differential decay rates for $H\to \ell^+\ell^- γ$ with $\ell=e$ or $μ$ in the Standard Model. The branching fractions and forward-backward asymmetries, defined in terms of the flight direction of the photon relative to the lepton momenta, depend on the cuts on energies and invariant masses of the final state particles. For typical choices of these cuts we find the branching ratios $B(H\to e \bar e γ)=5.8\cdot 10^{-5}$ and $B(H\to μ\bar μγ)=6.4\cdot 10^{-5}$ and the forward-backward asymmetries $\mathcal{A}^{(e)}_{\text{FB}}=0.343$ and $\mathcal{A}^{(μ)}_{\te…
With the next start of LHC, a huge production of top quarks is expected. There are several models that predict the existence of heavy colored resonances decaying to top quarks in the TeV energy range. A peak in the differential cross section could reveal the existence of such a resonance, but this is experimentally challenging, because it requires selecting data samples where top and antitop quarks are highly boosted. Nonetheless, the production of such resonances might generate a sizable charge asymmetry of top versus antitop quarks. We consider a toy model with general flavour independent co…
We calculate the neutral current jet production semi-inclusive deeply inelastic scattering process in this paper. Neutral current implies that interactions can be mediated by the photon, $Z^0$-boson and their interference. The initial electron is assumed to be polarized and then scattered off by a target particle with spin-1/2. Calculations are carried out up to twist-3 level in the quantum chromodynamics parton model by applying the collinear expansion formalism where multiple gluon scattering is taken into account and gauge links are obtained automatically. After obtaining the differential c…
We study neutralino production at the linear collider with the subsequent two-body decays ~chi^0_i -> ~chi^0_n Z^0 and Z^0 -> l^+ l^-, with l=e, mu, tau, or Z^0 -> q q- with q=c,b. We show that transverse electron and positron beam polarizations allow the definition of unique CP observables. These are azimuthal asymmetries in the distributions of the final leptons or quarks. We calculate these CP asymmetries and the cross sections in the Minimal Supersymmetric Standard Model with complex higgsino and gaugino parameters mu and M_1. For final quark pairs, we find CP asymmetries as large as 30%. …
We study angular observables in the $e^+e^-\to Z H\to \ell^+ \ell^-\,b\bar{b}$ channel at future circular $e^+ e^-$ colliders such as CEPC and FCC-ee. Taking into account the impact of realistic cut acceptance and detector effects, we forecast the precision of six angular asymmetries at CEPC (FCC-ee) with center-of-mass energy $\sqrt{s} =$ 240 GeV and 5 (30) ${\rm ab}^{-1}$ integrated luminosity. We then determine the projected sensitivity to a range of operators relevant for the Higgs-strahlung process in the dimension-6 Higgs EFT. Our results show that angular observables provide complementa…
We propose two new observables to measure the charge asymmetry in hadronic top-quark pair production in association with a hard jet. The incline asymmetry, based on the inclination between the planes of initial- and final-state momenta, probes the charge asymmetry in the quark-antiquark channel. Compared to the hitherto investigated rapidity asymmetries, the incline asymmetry provides improved access to the partonic charge asymmetry at both the Tevatron and the LHC. The energy asymmetry, based on the energy difference between top and antitop quarks, for the first time allows us to probe the ch…
We discuss the observability of CP-violating asymmetries in the process e+ e- -> X_1^0 X_2^0 -> X_1^0 X_1^0 l+ l-, with l = e,mu. We consider two examples of supersymmetric scenarios: (i) with decays X_2^0 -> l_R l -> X_1^0 l+ l-; (ii) with X_2^0 three-body decays. The asymmetries can be of order 0.1 but they are partially washed out by the large backgrounds from W+ W- and slepton pair production, being the observed asymmetries one order of magnitude smaller. However, with appropriate kinematical cuts they can be observed at an e+ e- collider with a centre of mass energy of 500 GeV and high lu…
Polarization of both electron and positron beams at a future linear collider (LC) allows for the measurement of transverse polarization asymmetries. These asymmetries have been shown to be particularly sensitive to graviton or other spin-2, $s-$channel exchanges in the process $e^+e^- \to f\bar f (f\neq e)$ which allows for a doubling of the usual search reach. A question then arises as to whether other $e^+e^-$ processes also show comparable sensitivity. Here we extend our previous analysis to the set of final states $e^+e^-, W^+W^-,~2γ$ and $~2Z$ as well as to the Møller scattering process $…
The large cross sections for gauge boson production at the Fermilab Tevatron and the CERN Large Hadron Collider (LHC) might give a chance to determine the electroweak parameters with high precision. We calculated two different forward-backward charge asymmetries (A^CS_FB and A^j_FB) of lepton pairs in events with a large transverse momentum jet p p (pbar) -> Z, gamma* + j -> e- e+ j at next-to-leading order (NLO), O(alpha_s) corrections, making use of the Monte Carlo programs MCFM and ALPGEN. These observables could provide a new determination of the weak mixing angle sin^2 theta^lept_eff (M_Z…
