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.
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.
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.
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.
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.
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.
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
117044754
Natural Quark Mass Matrices
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.