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
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.
118409650
NLSP gluino search at the Tevatron and early LHC
We investigate the collider phenomenology of gluino-bino co-annihilation scenario both at the Tevatron and 7 TeV LHC. This scenario can be realized, for example, in a class of realistic supersymmetric models with non-universal gaugino masses and t − b−τ Yukawa unification. The NLSP gluino and LSP bino should be nearly degenerate in mass, so that the typical gluino search channels involving leptons or hard jets are not available. Consequently, the gluino can be lighter than various bounds on its mass from direct searches. We propose a new search for NLSP gluino involving multi-b final states, arising from the three-body decay $ \tilde{g} \to b\overline b \tilde{\chi }_1^0 $. We identify two realistic models with gluino mass of around 300 GeV for which the three-body decay is dominant, and show that a 4.5 σ observation sensitivity can be achieved at the Tevatron with an integrated luminosity of 10 fb−1. For the 7TeV LHC with 50 pb−1 of integrated luminosity, the number of signal events for the two models is $ \mathcal{O}\left( {10} \right) $, to be compared with negligible SM background events.
119113681
Color Sextet Scalars at the CERN Large Hadron Collider
Taking a phenomenological approach, we study a color sextet scalar at the LHC. We focus on the QCD production of a color sextet pair ${\ensuremath{\Phi}}_{6}{\overline{\ensuremath{\Phi}}}_{6}$ through $gg$ fusion and $q\overline{q}$ annihilation. Its unique coupling to ${\overline{\ensuremath{\psi}}}^{c}\ensuremath{\psi}$ allows the color sextet scalar to decay into same-sign diquark states, such as ${\ensuremath{\Phi}}_{6}\ensuremath{\rightarrow}tt/t{t}^{*}$. We propose a new reconstruction in the multijet plus same-sign dilepton with missing transverse energy samples ($bb+{\ensuremath{\ell}}^{\ifmmode\pm\else\textpm\fi{}}{\ensuremath{\ell}}^{\ifmmode\pm\else\textpm\fi{}}+{\mathrm{E\ensuremath{\llap{\not\;}}}}_{T}+Nj$, $N\ensuremath{\ge}6$) to search for on-shell $tt\overline{t}\overline{t}$ final states from sextet scalar pair production. Thanks to the large QCD production, the search covers the sextet mass range up to 1 TeV for $100\text{ }\text{ }{\mathrm{fb}}^{\ensuremath{-}1}$ integrated luminosity.
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.
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.
110466342
Performance and Aging Studies of BaBar Resistive Plate Chambers
The BaBar detector is currently operating nearly 200 Resistive Plate Chambers (RPCs), constructed as part of an upgrade of the forward endcap muon detector in 2002. Although the average RPC efficiency remains high, numerous changes in the RPC performance (increased currents and rates) have been observed. A few of the highest rate RPCs have suffered efficiency losses of more than 15%. Several types of efficiency loss have been observed. Tests with humidified gas have shown that some of the lost efficiency is recoverable. However, efficiency losses in the highest rate regions have not yet improved with humid gases.
9128580
BaBar forward endcap upgrade
The muon and neutral hadron detector (instrumented flux return or IFR) in the forward endcap of the BaBar detector at SLAC was upgraded by the installation of a new generation of resistive plate chambers (RPCs) and by increasing the absorber. The chamber replacement was made necessary by the rapid aging and efficiency loss of the original BaBar RPCs. Based on our experience with those original RPCs and 24 RPCs with thinner linseed oil treatments, improvements in the design, construction, and testing of the new generation RPCs were implemented and are described in detail.
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