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Analysis of events with $b$-jets and a pair of leptons of the same charge in $pp$ collisions at $\sqrt{s}=8$ TeV with the ATLAS detector

The collaboration
JHEP 1510 (2015) 150, 2015

Abstract (data abstract)
. An analysis is presented of events containing jets including at least one $b$-tagged jet, sizeable missing transverse momentum, and at least two leptons including a pair of the same electric charge, with the scalar sum of the jet and lepton transverse momenta being large. A data sample with an integrated luminosity of 20.3 fb$^{-1}$ of $pp$ collisions at $\sqrt{s} = 8$ TeV recorded by the ATLAS detector at the Large Hadron Collider is used. Standard Model processes rarely produce these final states, but there are several models of physics beyond the Standard Model that predict an enhanced rate of production of such events; the ones considered here are production of vector-like quarks, enhanced four-top-quark production, pair production of chiral $b^\prime$-quarks, and production of two positively charged top quarks. Eleven signal regions are defined; subsets of these regions are combined when searching for each class of models. In the three signal regions primarily sensitive to positively charged top quark pair production, the data yield is consistent with the background expectation. There are more data events than expected from background in the set of eight signal regions defined for searching for vector-like quarks and chiral $b^\prime$-quarks, but the significance of the discrepancy is less than two standard deviations. The discrepancy reaches 2.5 standard deviations in the set of five signal regions defined for searching for four-top-quark production. The results are used to set 95% CL limits on various models The selection for all signals requires: - two leptons (electron or muons) of the same charge (events with three or more leptons are also accepted) - electrons are required to have Et > 25 GeV and |neta| < 2.47, with the interval 1.37 < |eta| < 1.52 excluded - muons are required to have pt > 25 GeV and |eta| < 2.5 - at least two jets with pt > 25 GeV and |eta| < 2.5 - at least one b-tagged jet - Etmiss > 40 GeV - same-charge electron pairs are required have invariant mass > 15 GeV, and to not have invariant mass in the interval 81-101 GeV - Ht, defined as the scalar sum of all jet and lepton transverse momenta, must be > 400 GeV In addition to the above, there are signal-specific selection criteria: For positively-charged top quark pairs, events are required to have: - Ht > 450 GeV - < 5 jets - exactly two positively-charged leptons - deltaPhi between the leptons > 2.5 - the sample was split according to lepton flavor, resulting in three signal regions: SRttee, SRttemu, and SRttmumu For the vector-like quark, T5/3, and b' signatures, events were required to be in one of the following 8 signal regions: - SRVLQ0: exactly 1 b-tagged jet, 400 GeV < Ht < 700 GeV - SRVLQ1: exactly 2 b-tagged jets, 400 GeV < Ht < 700 GeV - SRVLQ2: > 2 b-tagged jets, 400 GeV < Ht < 700 GeV - SRVLQ3: exactly 1 b-tagged jet, Ht > 700 GeV, 40 GeV < Etmiss < 100 GeV - SRVLQ4: exactly 1 b-tagged jet, Ht > 700 GeV, Etmiss > 100 GeV - SRVLQ5: exactly 2 b-tagged jets, Ht > 700 GeV, 40 GeV < Etmiss < 100 GeV - SRVLQ6: exactly 2 b-tagged jets, Ht > 700 GeV, Etmiss > 100 GeV - SRVLQ7: > 3 b-tagged jets, Ht > 700 GeV For the four top quark signature, the subset of the above signal regions that require at least 2 b-tagged jets was used: SRVLQ1, SRVLQ2, SRVLQ5, SRVLQ6, and SRVLQ7. These regions are also known as SR4t0, SR4t1, SR4t2, SR4t3, and SR4t4, respectively.

• #### Table 1

Data from Table 7

10.17182/hepdata.67661.v1/t1

Observed and expected number of events with statistical (first) and systematic (second) uncertainties for the positively charged top pair signal...

• #### Table 2

Data from Table 8

10.17182/hepdata.67661.v1/t2

Observed and expected number of events with statistical (first) and systematic (second) uncertainties for five of the signal regions defined...

• #### Table 3

Data from Table 9

10.17182/hepdata.67661.v1/t3

Observed and expected number of events with statistical (first) and systematic (second) uncertainties for three of the signal regions defined...

• #### Table 4

Data from Figure 7a

10.17182/hepdata.67661.v1/t4

Observed limits on the pair production cross section as a function of mass for vector-like B quarks. These limits assume...

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Data from Figure 7b

10.17182/hepdata.67661.v1/t5

Observed limits on the pair production cross section as a function of mass for vector-like T quarks. These limits assume...

• #### Table 6

Data from Figure 10a

10.17182/hepdata.67661.v1/t6

Expected and observed cross section limits as a function of mass on T_5/3 pair production.

• #### Table 7

Data from Figure 10b

10.17182/hepdata.67661.v1/t7

• #### Table 9

Data from Figure 11b

10.17182/hepdata.67661.v1/t9

Expected and observed limits for the sgluon pair-production cross section times branching ratio to four top quarks as a function...

• #### Table 10

Data from Figure 11c

10.17182/hepdata.67661.v1/t10

Expected and observed limits on the four- top-quark production rate for the 2UED/RPP model in the symmetric case. The theory...