AtlasPublic Web 
Internal TWiki
|
Search for new phenomena using events with $b$-jets and a pair of same-charge leptons in 3.2 fb$^{-1}$ of $pp$ collisions at $\sqrt{s}=13$ TeV with the ATLAS detector ATLAS-CONF-2016-032 16 June 2016
|
||
| Content | Preview | |
|---|---|---|
| Main document (CDS record) - internal | pdf from CDS | |
| Figures Tables | - | |
| Abstract | ||
| An analysis is presented of events containing jets including at least one $b$-tagged jet, sizable missing transverse momentum, and at least two charged leptons including a pair of the same electric charge, with the scalar sum of the jet and lepton transverse momenta being large. Standard Model processes rarely produce these final states, but several models of physics beyond the Standard Model predict an enhanced production rate of such events. Specific models with this feature are considered here: vector-like $T$ ,$B$, and $T_{5/3}$ quark pair production, and four-top-quark production under three scenarios (Standard Model, contact interaction, and extra dimensions). A data sample of 3.2 fb$^{-1}$ of $pp$ collisions at a center-of-mass energy of $\sqrt{s}= 13$ TeV recorded by the ATLAS detector at the Large Hadron Collider is used in this analysis. Several signal regions are defined, in which the consistency between the data yield and the background-only hypothesis is checked, and 95\% confidence level limits are set on various signal models. | ||
| Figures | ||
|
Figure 01a: Leading-order diagrams for (a) vector-like top quark pair production, and (b) four-top production from the contact interaction model. png (25kB) pdf (8kB) |
 |
|
|
Figure 01b: Leading-order diagrams for (a) vector-like top quark pair production, and (b) four-top production from the contact interaction model. png (18kB) pdf (6kB) |
 |
|
|
Figure 02a: Distributions of (a) the scalar sum of the jet and lepton transverse momenta HT, (b) ETmiss, and (c) Nb for data and the expected background for events in the low-HT+1b validation region. The bottom panels display the ratios of data to the total background prediction (`Bkg'). png (57kB) pdf (19kB) |
 |
|
|
Figure 02b: Distributions of (a) the scalar sum of the jet and lepton transverse momenta HT, (b) ETmiss, and (c) Nb for data and the expected background for events in the low-HT+1b validation region. The bottom panels display the ratios of data to the total background prediction (`Bkg'). png (60kB) pdf (21kB) |
 |
|
|
Figure 02c: Distributions of (a) the scalar sum of the jet and lepton transverse momenta HT, (b) ETmiss, and (c) Nb for data and the expected background for events in the low-HT+1b validation region. The bottom panels display the ratios of data to the total background prediction (`Bkg'). png (47kB) pdf (16kB) |
 |
|
|
Figure 03a: Distributions of (a) scalar sum of jet and lepton transverse momenta HT, (b) ETmiss, (c) Nb and (d) the jet multiplicity for the expected background and for some of the signals considered in the analysis, after applying the preselection criteria. All of the signal cross sections are scaled so that the signals are normalized to the same number of events as the total background. png (73kB) pdf (15kB) |
 |
|
|
Figure 03b: Distributions of (a) scalar sum of jet and lepton transverse momenta HT, (b) ETmiss, (c) Nb and (d) the jet multiplicity for the expected background and for some of the signals considered in the analysis, after applying the preselection criteria. All of the signal cross sections are scaled so that the signals are normalized to the same number of events as the total background. png (76kB) pdf (15kB) |
 |
|
|
Figure 03c: Distributions of (a) scalar sum of jet and lepton transverse momenta HT, (b) ETmiss, (c) Nb and (d) the jet multiplicity for the expected background and for some of the signals considered in the analysis, after applying the preselection criteria. All of the signal cross sections are scaled so that the signals are normalized to the same number of events as the total background. png (42kB) pdf (15kB) |
 |
|
|
Figure 03d: Distributions of (a) scalar sum of jet and lepton transverse momenta HT, (b) ETmiss, (c) Nb and (d) the jet multiplicity for the expected background and for some of the signals considered in the analysis, after applying the preselection criteria. All of the signal cross sections are scaled so that the signals are normalized to the same number of events as the total background. png (41kB) pdf (15kB) |
 |
|
|
Figure 04: Expected background yields and observed data events in various signal regions. Uncertainties include both the statistical and systematic errors added in quadrature. The bottom panel displays the ratio of data to the total background prediction (`Bkg'). png (98kB) pdf (18kB) |
 |
|
|
Figure 05a: Distributions of (a) the scalar sum of the jet and lepton transverse momenta HT, (b) ETmiss, and (c) Nb for data and the expected background for events in the eight signal regions. The bottom panels display the ratios of data to the total background prediction (`Bkg'). png (111kB) pdf (18kB) |
 |
|
|
Figure 05b: Distributions of (a) the scalar sum of the jet and lepton transverse momenta HT, (b) ETmiss, and (c) Nb for data and the expected background for events in the eight signal regions. The bottom panels display the ratios of data to the total background prediction (`Bkg'). png (111kB) pdf (19kB) |
 |
|
|
Figure 05c: Distributions of (a) the scalar sum of the jet and lepton transverse momenta HT, (b) ETmiss, and (c) Nb for data and the expected background for events in the eight signal regions. The bottom panels display the ratios of data to the total background prediction (`Bkg'). png (52kB) pdf (17kB) |
 |
|
|
Figure 06a: Observed (solid line) and expected (dashed line) 95% CL upper limits on (a) the Banti-B cross section as a function of the B mass, and (b) the Tanti-T cross section as a function of the T mass. These limits assume branching ratios given by the model where the B and T quarks exist as weak isospin singlets [25]. The surrounding shaded bands correspond to ± 1 and ± 2 standard deviations around the expected limit. The blue line shows the theoretical prediction. png (78kB) pdf (16kB) |
 |
|
|
Figure 06b: Observed (solid line) and expected (dashed line) 95% CL upper limits on (a) the Banti-B cross section as a function of the B mass, and (b) the Tanti-T cross section as a function of the T mass. These limits assume branching ratios given by the model where the B and T quarks exist as weak isospin singlets [25]. The surrounding shaded bands correspond to ± 1 and ± 2 standard deviations around the expected limit. The blue line shows the theoretical prediction. png (75kB) pdf (16kB) |
 |
|
|
Figure 07a: (a) Expected and (b) observed 95% CL lower limit on the mass of the B quark in the plane of BR(B→ Hb) versus BR(B→ Wt). Contour lines of constant mass limit values are are provided to guide the eye. png (128kB) pdf (18kB) |
 |
|
|
Figure 07b: (a) Expected and (b) observed 95% CL lower limit on the mass of the B quark in the plane of BR(B→ Hb) versus BR(B→ Wt). Contour lines of constant mass limit values are are provided to guide the eye. png (139kB) pdf (19kB) |
 |
|
|
Figure 08a: (a) Expected and (b) observed 95% CL lower limit on the mass of the T quark in the plane of BR(T→ Ht) versus BR(T→ Wb). Contour lines of constant mass limit values are are provided to guide the eye. png (129kB) pdf (18kB) |
 |
|
|
Figure 08b: (a) Expected and (b) observed 95% CL lower limit on the mass of the T quark in the plane of BR(T→ Ht) versus BR(T→ Wb). Contour lines of constant mass limit values are are provided to guide the eye. png (139kB) pdf (19kB) |
 |
|
|
Figure 09: Observed (solid line) and expected (dashed line) 95% CL upper limits on the T5/3overlineT5/3 cross section as a function of the T5/3 mass. The surrounding shaded bands correspond to ± 1 and ± 2 standard deviations around the expected limit. The blue line shows the theoretical prediction.. png (75kB) pdf (16kB) |
 |
|
|
Figure 10a: Limits obtained from the search for four-top-quark production. (a) Expected and observed limits on the coupling constant |C4t| in the contact interaction model for four-top production as a function of the BSM physics energy scale Λ. The region in the upper left, corresponding to |C4t|/Λ2>3.5 TeV-2, is excluded at 95% CL. The lower bound on Λ is chosen so that the fraction of signal events with a partonic four-top-quark invariant mass above that value of Λ is below 30%, in order to to stay within the range of validity of the EFT approach. (b) Expected and observed limits on the four-top-quark production rate for the 2UED/RPP model in the symmetric case. The theory line corresponds to the production of four-top-quark events by tier (1,1) with a branching ratio of A(1,1) to tanti-t of 100%. The surrounding shaded bands correspond to ± 1 and ± 2 standard deviations around the expected limit. png (139kB) pdf (19kB) |
 |
|
|
Figure 10b: Limits obtained from the search for four-top-quark production. (a) Expected and observed limits on the coupling constant |C4t| in the contact interaction model for four-top production as a function of the BSM physics energy scale Λ. The region in the upper left, corresponding to |C4t|/Λ2>3.5 TeV-2, is excluded at 95% CL. The lower bound on Λ is chosen so that the fraction of signal events with a partonic four-top-quark invariant mass above that value of Λ is below 30%, in order to to stay within the range of validity of the EFT approach. (b) Expected and observed limits on the four-top-quark production rate for the 2UED/RPP model in the symmetric case. The theory line corresponds to the production of four-top-quark events by tier (1,1) with a branching ratio of A(1,1) to tanti-t of 100%. The surrounding shaded bands correspond to ± 1 and ± 2 standard deviations around the expected limit. png (41kB) pdf (16kB) |
 |
|
|
Figure 11: Expected and observed limit in the (mKK = 1/R4, ξ = R4/R5) plane for the 2UED/RPP model. The surrounding shaded bands correspond to ± 1 and ± 2 standard deviations around the expected limit. png (121kB) pdf (29kB) |
 |
|
|
Figure 12: e+e-μ+ event display passing the SR7 selection (HT = 0.9 TeV). Electron tracks are in blue and the muon track is in red. Blue cones represent b-tagged jets. png (1MB) |
 |
|
|
Figure 13: e-μ- event display passing the SR7 selection (HT = 1.1 TeV). The electron track is in blue and the muon track is in red. Blue cones represent b-tagged jets. png (2MB) |
 |
|
| Tables | ||
|
Table 01: Summary of the `preselection' criteria. png (24kB) pdf (43kB) |
 |
|
|
Table 02: Observed and expected numbers of events in the low-HT+1b validation region for the same-sign dilepton channels. The first uncertainty is statistical and the second is systematic. Systematic uncertainties are described in section refsec:syst. png (18kB) pdf (47kB) |
 |
|
|
Table 03: Observed and expected numbers of events in the low-HT+1b validation region for the trilepton channels. The first uncertainty is statistical and the second is systematic. Systematic uncertainties are described in section refsec:syst. png (27kB) pdf (47kB) |
 |
|
|
Table 04: Definitions of the different signal regions. The jet and b-jet multiplicities are denoted by N jets and Nb respectively. png (23kB) pdf (55kB) |
 |
|
|
Table 05: Uncertainty (in %) on the total background yield due to the leading sources of systematic uncertainty. png (21kB) pdf (26kB) |
 |
|
|
Table 06: Uncertainty (in %) on the yield of a representative signal (four top quark production with SM kinematics) due to the leading sources of experimental systematic uncertainty.Uncertainty (in %) on the yield of a representative signal (four top quark production with SM kinematics) due to the leading sources of experimental systematic uncertainty. png (38kB) pdf (24kB) |
 |
|
|
Table 07: Observed and expected number of events with the total uncertainties for the signal regions. The expected UED and Tanti-T yields are normalized to their theoretical cross sections of 75 fb and 295 fb, respectively, while the expected tanti-ttanti-t (SM) and tanti-ttanti-t (CI) are both normalized to a cross section of 100 fb. png (52kB) pdf (49kB) |
 |
|
