# DPF2015

4-8 August 2015
America/Detroit timezone

## Flavor Tagging TeV Jets for BSM and QCD

5 Aug 2015, 15:00
20m
Room 4 (Michigan League)

QCD Theory

### Speaker

Keith Pedersen (Illinois Institute of Technology)

### Description

We present a new scheme for tagging *b*-jets with $p_{T}>500$ GeV, which we call $\mu_{x}$ tagging. At the LHC, the primary method to tag *b*-jets (jets which originate from bottom quarks) relies on tracking their charged constituents. However, when jets are highly boosted, their dense, collimated environment makes precise tracking difficult. Thus, as jet $p_{T}$ approaches 1 TeV, track-based *b*-tags lose efficiency, and the probability to mis-tag light jets rises dramatically. This is a problem, since many heavy BSM resonances ($W^{\prime}\rightarrow tb$, $Z^{\prime}/G^{*}\rightarrow t\bar{t}/b\bar{b}$, etc.) require tagging at least one energetic *b*-jet and rejecting the light-jet background. Using muons from semi-leptonic *b*-hadron decay, we define a variable $x$ which encodes angular correlations between the muon and the boosted subjet of the decay. Requiring $x\leq x_{max}$ allows us to tag *b*-jets and effectively discriminate the light-jets (including those which undergo gluon splitting). This is especially useful at ATLAS, which has excellent capabilities for standalone muons. We find an efficiency to tag *b*-jets, *c*-jets and light-jets of $\epsilon_{b}\approx14\%$, $\epsilon_{c}\approx6.5\%$ and $\epsilon_{light}\approx0.65\%$ respectively (where primary gluons splitting to heavy flavors are classified as light-jets). For heavy flavor jets (*b* / *c*), these efficiencies are essentially flat (over $-2.5\leq\eta\leq2.5$ and $0.5\,\mathrm{TeV}\leq p_{T}\leq2.1\,\mathrm{TeV}$). For light-jets, the rejection rate improves slightly with $p_{T}$. This scheme could be immediately useful in discovering a heavy, "leptophobic" $Z^{\prime}$ in the dijet channel. We simulate such a $Z^{\prime}$ at several TeV-scale masses and, using only the $\mu_{x}$ tag, predict a substantial increase in the sensitivity to discover heavy $Z^{\prime}$ at the LHC Run II. Additionally, since $\mu_{x}$ and track-based tagging are not mutually exclusive, using both should maximize the total *b*-tagging efficiency.
Oral or Poster Presentation Oral

### Primary author

Keith Pedersen (Illinois Institute of Technology)

### Co-author

Zack Sullivan (Illinois Institute of Technology)