Neutrino Deep Inelastic Scattering on nuclei is an essential process to constrain the strange quark parton distribution functions in the proton. The critical component on the way to using the neutrino DIS data in a proton PDF analysis is understanding the nuclear effects in parton distribution functions. We parametrize these effects by nuclear parton distribution functions. Here we compare results from two analysis of NPDF both done at next-to-leading order in QCD. The first uses neutral current charged-lepton lA Deeply Inelastic Scattering and Drell-Yan data for several nuclear targets and the second uses neutrino-nucleon DIS data. We compare the nuclear corrections factors F_2^Fe/F_2^D for the charged-lepton data with other results from the literature. In particular, we compare and contrast fits based upon the charged-lepton DIS data with those using neutrino-nucleon DIS data.
We perform a χ^2-analysis of Nuclear Parton Distribution Functions (NPDFs) using neutral current charged-lepton Deeply Inelastic Scattering (DIS) and Drell-Yan data for several nuclear targets. The nuclear A dependence of the NPDFs is extracted in a next-to-leading order fit. We compare the nuclear corrections factors F2(Fe)/F2(D) for this charged-lepton data with other results from the literature. In particular, we compare and contrast fits based upon the charged-lepton DIS data with those using neutrino-nucleon DIS data.
The precision measurement of the W boson mass allows to perform stringent consistency tests of the Standard Model by means of global electroweak fits. The accurate determination of the W boson mass is one of the legacy results of the Tevatron, where the experimental accuracy is such that $M_W$ is now limited by theoretical uncertainties related to the parton distributions of the proton. In this contribution, we show how to quantify the impact of PDF uncertainties in the measurement of $M_W$ at the Tevatron and the LHC by means of a template method, and study both the use of the W transverse ma…
In this paper we discuss the effect of the complete leading-order QED corrections to the DGLAP equations in the perturbative evolution of parton distribution functions (PDFs). This requires the extension of the purely QCD DGLAP evolution, including a PDF for the photons and, consistently, also for the charged leptons $e^{\pm}$, $μ^\pm$ and $τ^\pm$. We present the implementation of the QED-corrected DGLAP evolution in the presence of photon and lepton PDFs in the APFEL program and, by means of different assumptions for the initial scale PDFs, we produce for the first time PDF sets containing ch…
We examine the effect of including the `combined' HERA structure function data in the MSTW global fit for parton distribution functions (PDFs). The combined neutral-current HERA data have a significant, if not dramatic, effect, of up to 2--3% at NLO for Z boson and Higgs production at the Tevatron and LHC, and a generally slightly smaller effect, particularly on LHC processes, at NNLO. This is an amount comparable, or less than, the typical PDF uncertainties, and hence we do not intend to release an imminent update to the MSTW 2008 fit. We also investigate the consistency with the recent D0 da…
Precision determinations of Standard Model (SM) Electro-Weak (EW) parameters at the Large Hadron Collider (LHC) are dominated by uncertainties due to Parton Distribution Functions (PDFs). Reweighting and profiling techniques are routinely employed to treat this. We explore approaches based on combining measurements of charged current and neutral current Drell-Yan (DY) asymmetries to improve PDF uncertainties. We present the results of a numerical analysis performed with the open-source platform xFitter. PDF uncertainties are examined for lepton-charge and forward-backward asymmetries in region…
We address the impact of future measurements of charged and neutral current Drell-Yan (DY) asymmetries and their combination on Parton Distribution Functions (PDFs) uncertainties. We quantify the reduction of PDF uncertainties using the QCD tool xFitter. We examine the effects of such reduced PDF errors on both Standard Model (SM) and Beyond SM (BSM) observables.
Understanding nuclear effects in parton distribution functions (PDF) is an essential component needed to determine the strange and anti-strange quark contributions in the proton. In addition Nuclear Parton Distribution Functions (NPDF) are critically important for any collider experiment with nuclei (e.g. RHIC, ALICE). Here two next-to-leading order chi^2-analyses of NPDF are presented. The first uses neutral current charged-lepton Deeply Inelastic Scattering (DIS) and Drell-Yan data for several nuclear targets and the second uses neutrino-nucleon DIS data. We compare the nuclear corrections f…
The reweighting method presented in earlier publications is applied for incorporating the LHC W lepton asymmetry data published in 2010 into the NNPDF2.1 NNLO analysis. We confirm the result of the NLO analysis which indicated that these data reduce PDF uncertainties of light quarks in the medium and small-x region, providing the first solid constraints on PDFs from LHC data.
We quantify the impact of unpolarized lepton-proton and lepton-nucleus inclusive deep-inelastic scattering (DIS) cross section measurements from the future Electron-Ion Collider (EIC) on the proton and nuclear parton distribution functions (PDFs). To this purpose we include neutral- and charged-current DIS pseudodata in a self-consistent set of proton and nuclear global PDF determinations based on the NNPDF methodology. We demonstrate that the EIC measurements will reduce the uncertainty of the light quark PDFs of the proton at large values of the momentum fraction $x$, and, more significantly…
We demonstrate that theoretical predictions using current resummation techniques for the lepton pair production (LPP) rapidity and $x_F$ distributions can be inconsistent with data in high rapidity and $x_F$ kinematic regions by observing their effect in global fits of parton distribution functions (PDFs). We present an enhanced resummation technique for the LPP rapidity and $x_F$ distributions that agrees with LPP data. The enhanced resummation method is used in conjunction with threshold resummation in deep inelastic scattering (DIS) to perform two global fits of PDFs using the minimal and B…
We study nuclear effects in charged current deep inelastic neutrino-iron scattering in the frame-work of a chi^2 analysis of parton distribution functions. We extract a set of iron PDFs and show that under reasonable assumptions it is possible to constrain the valence, light sea and strange quark distributions. Our iron PDFs are used to compute x_{Bj}-dependent and Q^2-dependent nuclear correction factors for iron structure functions which are required in global analyses of free nucleon PDFs. We compare our results with nuclear correction factors from neutrino-nucleus scattering models and cor…
A final state consisting of one charged lepton, at least one jet, and little missing transverse energy can be a very promising signature of new physics at the LHC across a wide range of models. However, it has received only limited attention so far. In this work we discuss the potential sensitivity of this channel to various new physics scenarios. To demonstrate our point, we consider its application to lepton parton density functions (PDFs) at the LHC in the context of supersymmetry. These lepton PDFs can lead to resonant squark production (similar to leptoquarks) via lepton number violating …
We study the charged current Drell-Yan process and we evaluate the proton parton densities uncertainties on the lepton transverse momentum distribution and their impact on the determination of the W-boson mass. We consider the global PDF sets CT10, MSTW2008CPdeut, NNPDF2.3, NNPDF3.0, MMHT2014, and apply the PDF4LHC recipe to combine the individual results, obtaining an uncertainty on MW that ranges between +-18 and +-24 MeV, depending on the final state, collider energy and kind. We discuss the dependence of the uncertainty on the acceptance cuts and the role of the individual parton densities…
Measurements of the forward-backward asymmetry in neutral-current Drell-Yan di-lepton production have primarily been used for determinations of the weak mixing angle $θ_W$. We observe that, unlike the case of Run-I of the Large Hadron Collider (LHC Run-I), for the first time at the LHC Run-II the reconstructed forward-backward asymmetry has the capability of placing useful constraints on the determination of the parton distribution functions (PDFs). By examining the statistical and the PDF uncertainties on the reconstructed forward-backward asymmetry, we investigate its potential for disentang…
We discuss the effect of the Photon Initiated (PI) process on the dilepton channel at the LHC. Adopting various QED PDF sets, we evaluate the contribution produced by two resolved photons which is not included in the Equivalent Photon Approximation (EPA). We compare the PI central value as predicted by the CTEQ, MRST and NNPDF collaborations. With the NNPDF2.3QED set of replicas we also estimate the PDF uncertainties on the PI central value. We show the effect of the inclusion of the PI contribution and its PDF uncertainties on neutral heavy Z'-boson searches. We explore the two scenarios of n…
The observation of charged lepton flavor violation is a clear sign of physics beyond the Standard Model (SM). In this work, we investigate the sensitivity of future lepton colliders to charged lepton flavor violation via on-shell production of bileptons, and compare their sensitivity with current constraints and future sensitivities of low-energy experiments. Bileptons couple to two charged leptons with possibly different flavors and are obtained by expanding the general SM gauge invariant Lagrangians with or without lepton number conservation. We find that future lepton colliders will provide…
The neutrino deep inelastic scattering (DIS) data is very interesting for global analyses of proton and nuclear parton distribution functions (PDFs) since they provide crucial information on the strange quark distribution in the proton and allow for a better flavor decompositon of the PDFs. In order to use neutrino DIS data in a global analysis of proton PDFs nuclear effects need to be understood. We study these effects with the help of nuclear PDFs extracted from global analyses of charged-lepton DIS, Drell-Yan and neutrino DIS data at next-to-leading order in QCD.
We present the results of a PDF fit to differential top quark production within the MMHT framework. We in particular consider ATLAS data in the lepton + jet and dilepton channels and CMS data in the lepton + jet channel, at 8 TeV. While the fit quality to the ATLAS dilepton data is good, for the CMS case we see some issues in achieving a good fit quality for certain distributions. However, we focus on the ATLAS lepton + jet data, for which correlations of the statistical and systematic errors are provided across the four relevant distributions for PDF determination, namely $p_T^t$, $M_{tt}$, $…
We propose $S_4$ symmetric four-generation models for charged leptons. Although an $S_4$ symmetric four-generation model has been already proposed, there are some additional symmetries in the model. We construct four-generation models for charged leptons with only requirement of exact $S_4$ symmetry. It turned out that at least one of the models is consistent with observations of charged lepton masses and predicts the mass of the charged lepton of the fourth generation to be 556 GeV.
We study the production and decay of fourth generation leptons at the Large Hadron Collider (LHC).We find that for charged leptons with masses under a few hundred GeV, the dominant collider signal comes from the production through a W-boson of a charged and neutral fourth generation lepton. We present a sensitivity study for this process in events with two like-sign charged leptons and at least two associated jets. We show that with sqrts = 7 TeV and 1 inverse fb of data, the LHC can exclude fourth generation charged leptons with masses up to 250 GeV.
Many Standard Model extensions predict doubly-charged scalars; in particular, all models with resonances in charged lepton-pair channels with non-vanishing lepton number; if these are pair produced at the LHC, the observation of their decay into $l^\pm l^\pm W^\mp W^\mp$ will be necessary in order to establish their lepton-number violating character, which is generally not straightforward. Nonetheless, the analysis of events containing four charged leptons (including scalar decays into one or two taus as well as into W bosons) makes it possible to determine whether the doubly-charged excitatio…
The hyperon decays with 2 negative charged leptons in the final states can be of interest as possible tests for the Majorana netrinos. The study of these decays are complementary to the double beta decays of heavy nuclei.
We studied the signatures at the LHC of the electroweak SU(2) lepton doublet which embeds a doubly charged lepton. The doubly charged lepton pair and single production rates, which are different from the triplet case, are studied and all the detectable decay modes are considered. We also applied the same kinematic cuts as in triplet case to reduce the background at LHC and the needed integrated luminosities to find the doubly charged leptons with different masses are analyzed. We also suggested a method to distinguish the exotic lepton doublet and triplet.
We perform the next-to-next-leading-order (NNLO) QCD global fit of PDFs using inclusive charged-lepton and neutrino DIS data down to Q = 1 GeV. We also consider the data on neutrino-nucleon dimuon production, that allows us to disentangle the strange sea distribution. The fit results in χ^2/NDP = 5150/4338 = 1.2 that demonstrates a good consistency of the data sets used in analysis. The resulting value of α_s(M_Z) = 0.1136+- 0.0007(exp.) is in a good agreement with the previous version of the fit with a more stringent cut on Q. This analysis allows us to improve the accuracy of PDFs. The HT te…
We study the charged lepton electric dipole moment which is induced by the scalar unparticle mediation and we predict the appropriate range for the free parameters appearing in the effective lagrangian which drives the unparticle-standard model lepton interactions. We observe that the charged lepton electric dipole moment is strongly sensitive to the scaling dimension d_u of the unparticle and the new couplings in the effective interaction. Furthermore, we see that the current experimental limits of charged lepton electric dipole moments can ensure an appropriate range for these free parameter…
We study charm production in charged-current deep-inelastic scattering (DIS) using the xFitter framework. Recent results from the LHC have focused renewed attention on the determination of the strange-quark parton distribution function (PDF) and the DIS charm process provides important complementary constraints on this quantity. We examine the current PDF uncertainty, and use LHeC pseudodata to estimate the potential improvement from this proposed facility. As xFitter implements both fixed-flavor- and variable-flavor-number schemes, we can compare the impact of these different theoretical choi…
We studied the signatures of an electroweak SU(2) lepton triplet which contains a doubly charged heavy lepton. The most interesting and easily detected final states are originating from the doubly charged lepton pair and single production, that we analyzed at a center of mass energy of 14 TeV. We propose useful kinematic cuts to reduce the backgrounds and computed the integrated luminosity needed to discover or exclude the doubly charged leptons for various masses.
The charged lepton mass relation $K \equiv (m_e +m_μ+m_τ)/(\sqrt{m_e} %+\sqrt{m_μ} +\sqrt{m_τ})^2= 2/3 $ is excellently satisfied by observed masses (pole masses). However, the formula $K=2/3$ should be never satisfied with the observed charged lepton masses. We will review a mechanism by proposed by Sumino and recent related topics.
I present a determination of the photon PDF from a fit to the recent ATLAS measurements of high-mass Drell-Yan lepton-pair production at $\sqrt{s} = 8$ TeV. This analysis is based on the {\tt xFitter} framework interfaced to the {\tt APFEL} program, that accounts for NLO QED effects, and to the {\tt aMCfast} code to account for the photon-initiated contributions within {\tt MadGraph5\_aMC@NLO}. The result is compared with other recent determinations of the photon PDF finding a general good agreement.
We derive the upper bounds on certain products of R-parity- and lepton-flavor-violating couplings from the decays of the neutral $B$ meson into two charged leptons. These modes of $B^0$ decays can constrain the product combinations of the couplings with one or more heavy generation indices. We find that most of these bounds are stronger than the previous ones.
We propose a dynamical mass-generation scenario which naturally realizes the mass hierarchy among the neutrinos, charged leptons and quarks, where the mass is dominated by the self-mass induced through the anomalous (i.e. non-minimal) gauge interactions.
We construct a class of renormalizable models for lepton mixing that generate predictions given in terms of the charged-lepton mass ratios. We show that one of those models leads, when one takes into account the known experimental values, to almost maximal CP-breaking phases and to almost maximal neutrinoless double-beta decay. We study in detail the scalar potential of the models, especially the bounds imposed by unitarity on the values of the quartic couplings.
If observed, charged lepton flavour violation is a clear sign of new physics - beyond the Standard Model minimally extended to accommodate neutrino oscillation data. We briefly review several extensions of the Standard Model which could potentially give rise to observable signals, also emphasising the rôle of charged lepton flavour violation in probing such new physics models.
The observation of lepton flavor violation indicates new physics beyond the Standard Model. Lepton colliders are ideal facilities to probe charged lepton flavor violation (CLFV) signals induced by new physics at high energy. In this work we perform a comprehensive study of the sensitivity of future lepton colliders to charged lepton flavor violation. We consider the most general renormalizable Lagrangian coupling two leptons to new bosonic particles, involving both $ΔL=0$ and $ΔL=2$ interactions. The CLFV processes are introduced by the exchange of off-shell new particles at tree-level. We fin…
We discuss charged lepton flavor violation in supersymmetric models with extended leptonic sectors at low energies. Contrary to the usual high-scale realizations of the seesaw mechanism, these non-minimal supersymmetric models have new superfields and/or interactions at the supersymmetric scale. As a consequence of this, the resulting lepton flavor violating phenomenology may be very different from that of minimal models.
The doubly-charged scalar boson H^{--} is involved in several new physics models for generating neutrino masses. Depending on new physics models, H^{--} has the Yukawa interaction with a pair of left-handed charged leptons or a pair of right-handed ones. In this talk, we see that these two Yukawa interactions can be distinguished by measuring energy distributions of charged pions produced by decays of tau leptons if pair-produced H^{++} H^{--} can decay sufficiently into four charged leptons which involve one or two tau leptons. The information on the Yukawa interaction of H^{--} will help to …
Description of Charged\text{-}Particle Multiplicity Distributions in High\text{-}Energy Proton\text{-}Proton Collisions Based on a Two-Component Model and Examination of Parton Distribution Functions
Possible single productions of the fourth standard model family charged leptons via anomalous interactions at the future ep colliders are studied. Signatures of such anomalous processes and backgrounds are discussed in detail.
The permutation symmetry $S_3$ is appplied to obtain two equal Majorana neutrino masses, while maintaining three different charged-lepton masses and suppressing neutrinoless double beta decay. The resulting radiative splitting of the two neutrinos is shown to be suitable for solar neutrino vacuum oscillations.
We study the production of doubly charged excited leptons at the LHC. These exotic states are predicted in extended weak isospin composite models. A recent analysis of such exotic states was based on a pure gauge model with magnetic type interactions. We include here the mechanism of contact interactions and show that this turns out to dominate the production of the doubly charged leptons. We perform a feasibility analysis of the observation of the tri-lepton signature associated with the production of the exotic doubly charged lepton simulating the response of a generic detector. We give excl…
In this paper, we consider a pair of entangled charged lepton-neutrino embedded in a constant magnetic field, which can be produced in the purely leptonic decay of charged pseudoscalar mesons. Particles with nonzero magnetic dipole moment will precess in the present of external magnetic field and induce a nontrivial noncyclic geometric phase. The dependence of this geometric phase on neutrino mass can be used to determine the Dirac/Majorana nature of massive neutrinos.
In this work pair productions of charged and doubly charged scalars in the framework of littlest Higgs model at $e^+e^-$ colliders are studied. In the allowed parameter space of the littlest Higgs model, the production rates of the scalar pairs are calculated. It is obtained that pair productions of charged and doubly charged scalars are reachable at $e^+ e^-$ colliders with energy $\sqrt{S}\geq 1.7TeV$. Using the lepton flavor violating decays of charged scalars calculated in literature, final state analysis is done for pair production processes. This analysis show that depending on the model…
We consider an $SU(3)_L\otimes U(1)_N$ model for the electroweak interactions which includes extra charged leptons which do not mix with the known leptons. These new leptons couple to $Z^0$ only through vector currents. We consider constraints on the mass of one of these leptons coming from the $Z^0$-width and from the muon $(g-2)$ factor. The last one is less restrictive than the former.
We develop in more detail our reweighting method for incorporating new datasets in parton fits based on a Monte Carlo representation of PDFs. After revisiting the derivation of the reweighting formula, we show how to construct an unweighted PDF replica set which is statistically equivalent to a given reweighted set. We then use reweighting followed by unweighting to test the consistency of the method, specifically by verifying that results do not depend on the order in which new data are included in the fit via reweighting. We apply the reweighting method to study the impact of LHC W lepton as…
We study the contribution of antisymmetric tensor unparticle mediation to the charged lepton electric dipole moments and restrict the free parameters of the model by using the experimental upper bounds. We observe that the charged lepton electric dipole moments are strongly sensitive to the the scaling dimension d_U and the fundamental scales M_U and Λ_U. The experimental current limits of electric dipole moments are reached for the small values of the scaling dimension d_U.
New heavy charged lepton production and decay signatures at future electron-positron colliders are investigated at $\sqrt {s}=500$ GeV. The consequences of model dependence for vector singlets and vector doublets are studied. Distributions are calculated including hadronization effects and experimental cuts that suppress the standard model background. The final state leptonic energy distributions are shown to give a very clear signature for heavy charged leptons.
In the framework of the Standard Model we present predictions for partial widths, double and single differential distributions, and forward--backward lepton asymmetries for four-leptonic decays $B^- \to μ^+μ^- {\bar ν}_e\, e^-$, $B^- \to e^+ e^- {\bar ν}_μ\,μ^-$, $B^- \to μ^+ μ^-{\bar ν}_μ\,μ^-$, and $B^- \to e^+ e^- {\bar ν}_e\, e^-$. We consider the contributions of virtual photon emission from the light and heavy quarks of the $B^-$--meson, and we include bremsstrahlung of a virtual photon from the charged lepton in the final state. We use the model of vector meson dominance for calculation…
Generally the diagonalization of the mass matrix of the charged leptons is a part of the neutrino UPMNS matrix. However, usually this contribution is ignored by assuming a diagonal mass matrix for charged leptons. In this letter we test this common assumption in the context of neutrino physics. Our analytical and numerical results for two supersymmetric models reveal that such a simplification is not justified. Especially for the solar and reactor mixing angles important modifications are found.
We consider the effects of adding a fourth generation to a model with two compactified extra dimensions -- one warped and the other flat. The extra dimensions lead to towers of Kaluza-Klein (KK) Z bosons. Interestingly, the higher KK-Z modes depending on the flat dimension contribute more than the warped dimension. These KK-Z modes enhance the cross-section of fourth generation charged leptons . The most promising signature is the heavy charged lepton decaying to a heavy neutrino and W boson.
New ZEUS data are added into the NLO QCD analysis of the ZEUS-JETS PDF fit. The addition of high-$Q^2$ NC and CC $e^-p$ inclusive cross-section data improves the determination of the $u$-valence quark at high $x$. The addition of high-$Q^2$ CC $e^+p$ inclusive cross-section data improves the determination of the $d$-valence quark at high $x$. The addition of lower-$Q^2$ NC $e^+p$ inclusive cross-section data, run at three different proton beam energies, improves the determination of the sea and gluon PDFs at small $x$. The new PDF fit is called the ZEUS09 PDF fit.
We re-analyze charged lepton corrections to neutrino mixing angles and CP phases, carefully including CP phases from the charged lepton sector. We present simple analytical formulae for including the charged lepton corrections and derive compact new results for small neutrino and charged lepton mixings $θ^ν_{13}$ and $θ^{e}_{13}$. We find a generic relation $θ_{12} + \frac{1}{\sqrt{2}} θ^{e}_{12} \cos(δ- π) \approx θ^ν_{12}$, which relates the prediction from the neutrino sector $θ^ν_{12}$ to the charged lepton mixing $θ^{e}_{12}$ and to the MNS neutrino oscillation phase $δ$. We apply our for…
A charged lepton mass formula $(m_e +m_μ+ m_τ)/(\sqrt{m_e}+\sqrt{m_μ} + \sqrt{m_τ})^2 =2/3$ is well-known. Since we can, in general, have two relations for three quantities, we may also expect another relation for the charged lepton masses. Then, the relation will be expressed by a form of $\sqrt{m_e m_μm_τ}/(\sqrt{m_e}+\sqrt{m_μ} + \sqrt{m_τ})^3$. According to this conjecture, a scalar potential model is speculated.
A model independent analysis of the leptonic Dirac CP-violating phase (δ) is presented. The analysis uses the experimentally determined values of the mixing angles in the lepton mixing matrix in order to explore the allowed values for δ and possible general forms for the charged lepton mixing matrix. This is done under two general assumptions: 1) that the mixing matrix in the neutrino sector is the so-called tribimaximal matrix and hence the non zero value for θ13 arises due to the mixing matrix in the charged lepton sector and 2) the charged lepton mixing matrix is parametrized in terms of th…
According to an idea that effective Yukawa coupling constants Y_f^{eff} are given vacuum expectation values < Y_f> of fields ("Yukawaons") Y_f as Y_f^{eff}=y_f < Y_f>/Λ, a possible superpotential form in the charged lepton sector under a U(3) [or O(3)] flavor symmetry is investigated. It is found that a specific form of the superpotential can lead to an empirical charged lepton mass relation without any adjustable parameters.
We study the effect on the parton distribution functions (PDFs) from the inclusion of projected measurements in the Drell-Yan (DY) di-lepton production neutral channel of the angular coefficient associated to the $Z$-boson longitudinal polarisation. The pseudodata, generated assuming two luminosity scenarios, is employed for the profiling of existing PDF sets using the open-source platform xFitter. We find the observable particularly relevant in constraining the gluon PDF, which in turn translates into a reduction of the systematic uncertainties of the Standard Model (SM) Higgs boson productio…
We consider the possible discovery potential for single production of charged heavy leptons via anomalous interactions at the envisaged Compact Linear Collider (CLIC) by taking into account initial state radiation (ISR) and beamstrahlung effects. We calculate the production cross sections and decay widths of charged heavy leptons in the context of anomalous interactions at center of mass energies $\sqrt{s}=1$ and 3 TeV. The signal and corresponding backgrounds are studied in detail for the mass range 300-1900 GeV.
