## Magnifying the ATLAS stealth stop splinter: impact of spin correlations and finite widths

## Abstract

In this paper, we recast a “stealth stop” search in the notoriously difficult region of the stop-neutralino Simplified Model parameter space for which m($$\tilde{t}$$ _{1})-m($$\tilde{X}$$~$$0\atop{1}$$)≃m _{t} . The properties of the final state are nearly identical for tops and stops, while the rate for stop pair production is O(10%) of that for $$t\overline{t}$$. Stop searches away from this stealth region have left behind a “splinter” of open parameter space when m($$\overline{t}$$ _{1})≃m _{t} . Removing this splinter requires surgical precision: the ATLAS constraint on stop pair production reinterpreted here treats the signal as a contaminant to the measurement of the top pair production cross section using data from s√=7 TeV and 8 TeV in a correlated way to control for some systematic errors. ATLAS fixed m($$\tilde{t}$$ _{1})≃mtandm($$\tilde{X}$$~$$0\atop{1}$$)=1 GeV, implying that a careful recasting of these results into the full m($$\tilde{t}$$ _{1})-m($$\tilde{X}$$~$$0\atop{1}$$) plane is warranted. We find that the parameter space with m($$\tilde{X}$$~$$0\atop{1}$$)≲55 GeV is excluded for m($$\tilde{t}$$ _{1})≃m _{t} — although this search does cover new parameter space, it is unable to fully pull the splinter. Along the way, we review a variety of interesting physical issues in detail: (i) when the two-body width is a good approximation; (ii) how assuming the narrow width approximation affects the total rate; (iii ) how the production rate is affected when the wrong widths are used; (iv ) what role propagating the spin correlations consistently through the multi-body decay chain plays in the limits. In addition, we provide a guide to using MadGraph for implementing the full production including finite width and spin correlation effects, and we survey a variety of pitfalls one might encounter.

- Authors:

- Univ. of Oregon, Eugene, OR (United States). Inst. of Theoretical Science and Center for High Energy Physics, Dept. of Physics

- Publication Date:

- Research Org.:
- Univ. of Oregon, Eugene (United States)

- Sponsoring Org.:
- USDOE Office of Science (SC)

- OSTI Identifier:
- 1499263

- Grant/Contract Number:
- SC0011640; SC0012008; SC0018191

- Resource Type:
- Accepted Manuscript

- Journal Name:
- Journal of High Energy Physics (Online)

- Additional Journal Information:
- Journal Name: Journal of High Energy Physics (Online); Journal Volume: 2018; Journal Issue: 7; Journal ID: ISSN 1029-8479

- Publisher:
- Springer Berlin

- Country of Publication:
- United States

- Language:
- English

- Subject:
- 72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS; supersymmetry phenomenology

### Citation Formats

```
Cohen, Timothy, Hopkins, Walter, Majewski, Stephanie, and Ostdiek, Bryan. Magnifying the ATLAS stealth stop splinter: impact of spin correlations and finite widths. United States: N. p., 2018.
Web. doi:10.1007/jhep07(2018)142.
```

```
Cohen, Timothy, Hopkins, Walter, Majewski, Stephanie, & Ostdiek, Bryan. Magnifying the ATLAS stealth stop splinter: impact of spin correlations and finite widths. United States. doi:10.1007/jhep07(2018)142.
```

```
Cohen, Timothy, Hopkins, Walter, Majewski, Stephanie, and Ostdiek, Bryan. Mon .
"Magnifying the ATLAS stealth stop splinter: impact of spin correlations and finite widths". United States. doi:10.1007/jhep07(2018)142. https://www.osti.gov/servlets/purl/1499263.
```

```
@article{osti_1499263,
```

title = {Magnifying the ATLAS stealth stop splinter: impact of spin correlations and finite widths},

author = {Cohen, Timothy and Hopkins, Walter and Majewski, Stephanie and Ostdiek, Bryan},

abstractNote = {In this paper, we recast a “stealth stop” search in the notoriously difficult region of the stop-neutralino Simplified Model parameter space for which m($\tilde{t}$1)-m($\tilde{X}$~$0\atop{1}$)≃mt . The properties of the final state are nearly identical for tops and stops, while the rate for stop pair production is O(10%) of that for $t\overline{t}$. Stop searches away from this stealth region have left behind a “splinter” of open parameter space when m($\overline{t}$1)≃mt . Removing this splinter requires surgical precision: the ATLAS constraint on stop pair production reinterpreted here treats the signal as a contaminant to the measurement of the top pair production cross section using data from s√=7 TeV and 8 TeV in a correlated way to control for some systematic errors. ATLAS fixed m($\tilde{t}$1)≃mtandm($\tilde{X}$~$0\atop{1}$)=1 GeV, implying that a careful recasting of these results into the full m($\tilde{t}$1)-m($\tilde{X}$~$0\atop{1}$) plane is warranted. We find that the parameter space with m($\tilde{X}$~$0\atop{1}$)≲55 GeV is excluded for m($\tilde{t}$1)≃mt — although this search does cover new parameter space, it is unable to fully pull the splinter. Along the way, we review a variety of interesting physical issues in detail: (i) when the two-body width is a good approximation; (ii) how assuming the narrow width approximation affects the total rate; (iii ) how the production rate is affected when the wrong widths are used; (iv ) what role propagating the spin correlations consistently through the multi-body decay chain plays in the limits. In addition, we provide a guide to using MadGraph for implementing the full production including finite width and spin correlation effects, and we survey a variety of pitfalls one might encounter.},

doi = {10.1007/jhep07(2018)142},

journal = {Journal of High Energy Physics (Online)},

number = 7,

volume = 2018,

place = {United States},

year = {2018},

month = {7}

}