118938933
Flavor dependence of annihilation parameters in QCD factorization
For $B_{d,s} \to \pi^\mp K^\pm$ and $K^{(\ast)} K^{(\ast)}$ decays, the flavor symmetry breaking effects may be particularly small since the final state interactions should be the same between the corresponding $B_d$ and $B_s$ decays due to the charge conjugation symmetry of the final states. This is consistent with the newly measured direct CP asymmetry of $B_s \to \pi^+ K^-$. These decays are thus supposed to be important in testing the Standard Model and in probing new physics effects. However, the observation of pure annihilation decay $B_s \to \pi^+ \pi^-$ appears to imply a large annihilation scenario with $\rho_A \sim 3$, in contrast to the case of $\rho_A \sim 1$ in $B_{u,d}$ decays in the framework of QCD factorization. This seems to indicate unexpectedly large flavor symmetry breaking effects between the annihilation amplitudes of $B_s$ and $B_{u,d}$ decays. This apparent contradiction could be resolved by noticing that there is a priori no reason to justify the common practice of assuming the universality of annihilation parameters for different Dirac structures of effective operators. We then argue that, for $B_{d,s} \to \pi^\mp K^\pm$ decays, the flavor symmetry breaking effects of annihilation amplitudes have all been included in the initial state decay constants and are thus small. But the flavor symmetry breaking effects in $B_{d,s} \to K^{(\ast)} K^{(\ast)}$ decays are likely to be much larger, as part of the annihilation topologies of $B_s \to K K$ decay could be related to $B_s \to \pi^+ \pi^-$ decay. Therefore when new physics effects are searched for in these decay channels, care must be taken to consider the potentially large flavor symmetry breaking effects in more details.
118676148
Can Up FCNC solve the $\Delta A_{CP}$ puzzle?
We investigate the attempt using flavor violation gauge interaction in the up sector to explain the LHCb recently observed large $\Delta A_{CP}$ ($A_{CP}(D^{0}\to K^{+}K^{-})-A_{CP}(D^{0}\to \pi^{+}\pi^{-})$). We study an Abelian model that only right-handed up quarks is charged under it and the 1-3 coupling is maximized. The simultaneous 1-3 2-3 mixing is realized by a quark mixing of 1-2 generation. Given the easy identification of top quark, the model can be directly tested by $\Delta F=1$ and $\Delta F=2$ processes at the hadron colliders as associated top production $g c \to t Z^{\prime}$ or same-sign top scattering $u u\to t t$. The direct search bounds are still consistent with the assumption that $ut$ and $ct$ couplings are equal but the same-sign top scattering bound is expected to be reached very soon. However, since there is no CKM-like suppression, the corresponding parameter space for generating $\Delta A_{CP}$ is completely excluded by the $D^{0}-\bar{D}^{0}$ mixing. We conclude that the up FCNC type models cannot explain the $\Delta A_{CP}$ while to be consistent with the $D^{0}-\bar{D}^{0}$ mixing constraint at the same time. On the other hand, a model as SM with fourth family extension has better chance to explain the large $\Delta A_{CP}$ consistently.
119611263
Pair production of doubly charged scalars: Neutrino mass constraints and signals at the CERN LHC
We study the pair production of doubly charged Higgs bosons at the CERN Large Hadron Collider (LHC), assuming the doubly charged Higgs to be part of an SU(2){sub L} triplet which generates Majorana masses for left-handed neutrinos. Such pair production has the advantage that it is not constrained by the triplet vacuum expectation value, which tends to make the single production rate rather small. We point out that, in addition to the Drell-Yan production mechanism, two-photon processes also contribute to H{sup ++}H{sup --} production at a level comparable to the QCD corrections to the Drell-Yan channel. Decays of the doubly charged Higgs into both the l{sup +}l{sup +} and W{sup +}W{sup +} modes are studied in detail to optimize the signal observation over the backgrounds. Doubly charged scalars should be observable at the LHC with 300 fb{sup -1} integrated luminosity in the l{sup {+-}}l{sup {+-}} channel up to the mass range of 1 TeV even with a branching fraction of about 60%, and in the W{sup {+-}}W{sup {+-}} channel up to a mass of 700 GeV. Such a doubly charged Higgs, if it is a member of a triplet that generates neutrino masses, cannot be long-lived on the scale ofmore » collider detectors although it might lead to a displaced secondary vertex during its decay if it is lighter than about 250 GeV.« less
30208210
Nearly degenerate gauginos and dark matter at the LHC
Motivated by dark-matter considerations in supersymmetric theories, we investigate in a fairly modelindependent way the detection at the LHC of nearly degenerate gauginos with mass differences between a few GeV and about 30 GeV. Due to the degeneracy of gaugino states, the conventional leptonic signals are likely lost. We first consider the leading signal from glu ino production and decay. We find that it is quite conceivable to reach a large statistical significance for the multi-jet plus missing energy signal with an integrated luminosity about 50 pb −1 (50 fb −1 ) for a gluino mass of 500 GeV (1 TeV). If gluinos are not too heavy, less than about 1.5 TeV, this channel can typically probe gaugino masses up to about 100 GeV below the gluino mass. We then study the Drell-Yan type of gaugino pair production in association with a hard QCD jet, for gaugino masses in the range of 100‐150 GeV. The signal observation may be statistically feasible with about 10 fb −1 , but systematically challenging due to the lack of distinct ive features for the signal distributions. By exploiting gaugino pair pr oduction through weak boson fusion, signals of large missing energy plus two forward-backward jets may be observable at a 4‐6σ level above the large SM backgrounds with an integrated luminosity of 100‐300 fb −1 . Finally, we point out that searching for additional isolated soft muons in the range pT ∼ 3‐10 GeV in the data samples discussed above may help to enrich the signal and to control the systematics. Signific ant efforts are made to explore the connection between the signal kinematics and the relevant masses for the gluino and gauginos, to probe the mass scales of the superpartners, in particular the LSP dark matter.
54180574
Inverse seesaw in supersymmetry
Abstract We study a mechanism where tiny neutrino masses arise only from radiative contribution in a supersymmetric model. Without tuning the Higgs vev or Yukawa coupling, the tree-level light neutrino mass is rotated away by introducing a new singlet neutrino s L that forms a Dirac mass term with the right-handed neutrino n R in each generation. Even with the U ( 1 ) Lep lepton number violation term as non-zero right-handed Majorana neutrino mass M R n R c ¯ n R , the lightest neutrino remains massless at tree level due to an approximate symmetry. Consequently, tiny neutrino masses then only arise from radiative contributions and the right-handed neutrino Majorana mass M R can be at O ( keV ) to give rise to the correct light neutrino mass at O ( eV ) . Supersymmetry ensures that the Majorana neutrino masses M R n R c ¯ n R and M R ⁎ s L c ¯ s L are not generated simultaneously.
119101850
Higgs precision measurements and flavor physics: a supersymmetric example
Rare decays in flavor physics often suffer from Helicity suppress and Loop suppress. Helicity flip is a direct consequence of chiral $$U(3)$$U(3) symmetry breaking and electroweak symmetry breaking. The identical feature is also shared by the mass generation of SM fermions. In this review, we use the Minimal Supersymmetric Standard Model (MSSM) as an example to illustrate an explicit connection between bottom Yukawa coupling and rare decay process of $$b\rightarrow s\gamma $$b→sγ. We take a symmetry approach to study the common symmetry breaking in supersymmetric correction to bottom quark mass generation and $$b\rightarrow s\gamma $$b→sγ. We show that Large Peccei-Quinn symmetry breaking effect and $$R$$R-symmetry breaking effect required by $$b\rightarrow s\gamma $$b→sγ inevitably lead to significant reduction of bottom Yukawa $${y}_{b}$$yb. To compromise the reduction in $$b\bar{b}$$bb¯, a new decay is also needed to keep the Higgs total width as the SM value.
117044754
Natural Quark Mass Matrices
122736097
A Study of Missing Transverse Energy in Minimum Bias Events with In-time Pile-up at The Large Hadron Collider using The ATLAS Detector and $\sqrt{s}$=7 TeV Proton-Proton Collision Data