Double-charming Higgs boson identification using machine-learning assisted jet shapes

We study the possibility of identifying a boosted resonance that decays into a charm pair against different sources of background using QCD event shapes, which are promoted to jet shapes. Using a set of jet shapes as input to a boosted decision tree, we find that observables utilizing the simultaneous presence of two charm quarks can access complementary information compared to approaches relying on two independent charm tags. Focusing on Higgs associated production with subsequent $H\to c\overline{c}$ decay and on a $CP$-odd scalar $A$ with $m_A\le 10\mathrm{GeV}$ we obtain the limits $\mathcal{B}r(H\to c\overline{c})\le 6.48\%$ and $\mathcal{B}r(H\to A(\to c\overline{c})Z)\le 0.01\%$ at 95% C.L.

Figure 1

Correlation coefficients for the observables used in the analysis $pp\to H(\to c\overline{c})Z$ (signal) vs the combination $pp\to Z+\text{jets}$ and $pp\to H(\to b\overline{b})Z$ (background).

Figure 2

Histograms for the main discrimination event shapes when selecting $pp\to H(\to c\overline{c})Z$ against the combination $pp\to Z+\text{jets}$ and $pp\to H(\to b\overline{b})Z$.

Figure 3

Double $c$-jet selection efficiency (from $H\to c\overline{c}$) against the QCD-jet rejection achieved by the event-shapes tagger. The curves are obtained from independent optimizations considering different subsamples with zero (nonleptonic), one (single leptonic), and two (double leptonic) leptons inside the highest transverse momentum fat jet.

Figure 4

Double $c$-jets selection efficiency against the double light jets rejection achieved by the event-shapes tagger per leptonic study.

Figure 5

Double $c$-jets selection efficiency against the double light jets rejection achieved by the ATLAS JetFitterCharm tagger and the combined event-shapes tagger.

Figure 6

Correlation coefficients for the observables used in the analysis $pp\to H(\to c\overline{c})Z$ (signal) vs $pp\to Z+\text{light jets}$ (background).

Figure 7

Histograms for the main discrimination event shapes when selecting $pp\to H(\to c\overline{c})Z$ against $pp\to Z+\text{light}\text{jets}$.

Figure 8

Double $c$-jets selection efficiency (from $A\to c\overline{c}$) against the QCD-jets rejection achieved by the event-shapes tagger per leptonic study. Here we are considering $m_A=4\mathrm{GeV}$.

Figure 9

Double $c$-jets selection efficiency (from $A\to c\overline{c}$) against the QCD-jets rejection achieved by the event-shapes tagger per leptonic study. Here we are considering $m_A=10\mathrm{GeV}$.

Figure 10

Correlation coefficients for the observables used in the analysis of the $CP$-odd THDM scalar $A$, for $m_A=4\mathrm{GeV}$.

Figure 11

Correlation coefficients for the observables used in the analysis of the $CP$-odd THDM scalar $A$, for $m_A=10\mathrm{GeV}$.

Figure 12

Histograms for the main discrimination event shapes when selecting $pp\to H(\to A(\to c\overline{c})Z)+\text{jets}$ against $pp\to Z+\text{jets}$ for $m_A=4\mathrm{GeV}$.

Figure 13

Histograms for the main discrimination event shapes when selecting $pp\to H(\to A(\to c\overline{c})Z)+\text{jets}$ against $pp\to Z+\text{jets}$ for $m_A=10\mathrm{GeV}$.