### Streamlining resummed QCD calculations using Monte Carlo integration

Some of the most arduous and error-prone aspects of precision resummed calculations are related to the partonic hard process, having nothing to do with the resummation. In particular, interfacing to parton-distribution functions, combining various channels, and performing the phase space integration can be limiting factors in completing calculations. Conveniently, however, most of these tasks are already automated in many Monte Carlo programs, such as MadGraph [1], Alpgen [2] or Sherpa [3]. In this paper, we show how such programs can be used to produce distributions of partonic kinematics with associated color structures representing the hard factor in a resummed distribution. These distributions can then be used to weight convolutions of jet, soft and beam functions producing a complete resummed calculation. In fact, only around 1000 unweighted events are necessary to produce precise distributions. A number of examples and checks are provided, including e

^{+}e^{–}two- and four-jet event shapes,*n*-jettiness and jet-mass related observables at hadron colliders at next-to-leading-log (NLL) matched to leading order (LO). Furthermore, the attached code can be used to modify MadGraph to export the relevant LO hard functions and color structures for arbitrary processes.- Publication Date:

- Grant/Contract Number:
- SC0013607

- Type:
- Accepted Manuscript

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

- Additional Journal Information:
- Journal Name: Journal of High Energy Physics (Online); Journal Volume: 2016; Journal Issue: 8; Journal ID: ISSN 1029-8479

- Publisher:
- Springer Berlin

- Research Org:
- Harvard Univ., Cambridge, MA (United States)

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

- Country of Publication:
- United States

- Language:
- English

- Subject:
- 97 MATHEMATICS AND COMPUTING; 72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS; jets; QCD phenomenology

- OSTI Identifier:
- 1363956

```
Farhi, David, Feige, Ilya, Freytsis, Marat, and Schwartz, Matthew D.
```*Streamlining resummed QCD calculations using Monte Carlo integration*. United States: N. p.,
Web. doi:10.1007/JHEP08(2016)112.

```
Farhi, David, Feige, Ilya, Freytsis, Marat, & Schwartz, Matthew D.
```*Streamlining resummed QCD calculations using Monte Carlo integration*. United States. doi:10.1007/JHEP08(2016)112.

```
Farhi, David, Feige, Ilya, Freytsis, Marat, and Schwartz, Matthew D. 2016.
"Streamlining resummed QCD calculations using Monte Carlo integration". United States.
doi:10.1007/JHEP08(2016)112. https://www.osti.gov/servlets/purl/1363956.
```

```
@article{osti_1363956,
```

title = {Streamlining resummed QCD calculations using Monte Carlo integration},

author = {Farhi, David and Feige, Ilya and Freytsis, Marat and Schwartz, Matthew D.},

abstractNote = {Some of the most arduous and error-prone aspects of precision resummed calculations are related to the partonic hard process, having nothing to do with the resummation. In particular, interfacing to parton-distribution functions, combining various channels, and performing the phase space integration can be limiting factors in completing calculations. Conveniently, however, most of these tasks are already automated in many Monte Carlo programs, such as MadGraph [1], Alpgen [2] or Sherpa [3]. In this paper, we show how such programs can be used to produce distributions of partonic kinematics with associated color structures representing the hard factor in a resummed distribution. These distributions can then be used to weight convolutions of jet, soft and beam functions producing a complete resummed calculation. In fact, only around 1000 unweighted events are necessary to produce precise distributions. A number of examples and checks are provided, including e+e– two- and four-jet event shapes, n-jettiness and jet-mass related observables at hadron colliders at next-to-leading-log (NLL) matched to leading order (LO). Furthermore, the attached code can be used to modify MadGraph to export the relevant LO hard functions and color structures for arbitrary processes.},

doi = {10.1007/JHEP08(2016)112},

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

number = 8,

volume = 2016,

place = {United States},

year = {2016},

month = {8}

}