Search for resonances and quantum black holes using dijet mass spectra in proton-proton collisions ats=8  TeV

Abstract

A search for resonances and quantum black holes is performed using the dijet mass spectra measured in proton-proton collisions at ffiffi ffi s p ¼ 8 TeV with the CMS detector at the LHC. The data set corresponds to an integrated luminosity of 19.7 fb −1 . In a search for narrow resonances that couple to quark-quark, quarkgluon, or gluon-gluon pairs, model-independent upper limits, at 95% confidence level, are obtained on the production cross section of resonances, with masses above 1.2 TeV. When interpreted in the context of specific models the limits exclude string resonances with masses below 5.0 TeV; excited quarks below 3.5 TeV; scalar diquarks below 4.7 TeV; W 0 bosons below 1.9 TeV or between 2.0 and 2.2 TeV; Z 0 bosons below 1.7 TeV; and Randall-Sundrum gravitons below 1.6 TeV. A separate search is conducted for narrow resonances that decay to final states including b quarks. The first exclusion limit is set for excited b quarks, with a lower mass limit between 1.2 and 1.6 TeV depending on their decay properties. Searches are also carried out for wide resonances, assuming for the first time width-to-mass ratios up to 30%, and for quantum black holes with a range of model parameters. The wide resonance search excludes axigluons and colorons with mass below 3.6 TeV, and color-octet scalars with mass below 2.5 TeV. Lower bounds between 5.0 and 6.3 TeV are set on the masses of quantum black holes.

tt¯bb¯ as a probe of new physics at the LHC

“…On the other hand, diagram D4 is in general explored in extra scalar SUSY searches [13,14], however always an extra b is required and one finishes in diagrams D1 and D3. It is interesting to notice that a bb resonance search with no extra b -which would correspond to D2-is a difficult task due to large background for small M and to the difficulty in tagging b-jets for large M [10,11]. It is worth observing that a new resonance with M < 2m t and large couplings to tops would be detectable through processes as D1 and D2, in both cases with Y → bb.…”

“…In fact, since very hard b's have a small tagging efficiency [10,11], in this limit it is convenient to have the b quarks coming from the gluon-splitting in D1 and the new particle decaying to top quarks, Y → tt. Moreover, very hard tops are easy to tag using boosted top tagging techniques.…”

“…The study of pairs of third generation of quarks has given SM-expected results for tt at the LHC [7,8] and Tevatron [9], whereas bb is a difficult process to study in these hadronic machines because of the huge background and very few clean results are available at present time [10,11]. However, at LEP the final state bb left one of its larger deviations in what is known as the LEP b-anomaly [12].…”

A Heavy Scalar at the LHC from Vector-Boson Fusion

“…Current direct constraints include the 8 TeV LHC bounds such as GGF+VBF ( → ℎ 2 ) × Br(ℎ 2 → gg) ≤ 200 fb [32,33] and GGF+VBF ( → ℎ 2 ) × Br(ℎ 2 → ) ≤ 0.5 fb [34] in the mass region below 200 GeV, as well as VBF ( → ℎ 2 ) × Br(ℎ 2 → ZZ) [16] and VBF ( → ℎ 2 ) × Br(ℎ 2 → WW) [17] in the mass region above 200 GeV. For illustration, we have shown in Figure 2 direct constraint on mixing angle in low mass region.…”

Searches for resonant and non-resonant new phenomena in CMS

“…Searches for new physics at the LHC in the dijet mass spectra has been performed in CMS and published in a Run1 legacy paper in [2]. The particle flow candidates are clustered into jets using the anti-k t algorithm with ∆R = 0.5.…”