People interested: Bryan Zaldivar, José Zurita, Jérémie Quevillon, Jose Miguel No, Nishita Desai, Julia Harz, Daniele Barducci, Dipan Sengupta (dipan@pa.msu.edu), Haiying Cai, Felix Bruemmer, Andreas Goudelis, Gabriel Facini, Sezen Sekmen

Understand the connection between freeze-in models and LLP signatures at the LHC. Is it a generic feature of freeze-in models? 

* TODO-list + description + volunteers: {{ :2017:groups:np:todo.pdf |}}


References: 
  - Original freeze-in paper: Hall, Jedamzik, John March-Russell, West [[https://arxiv.org/abs/0911.1120 | arXiv ]]
  - LLP signatures: Co, D'Eramo, Hall, Pappadopulo [[https://arxiv.org/abs/1506.07532 |arxiv]] 
  - A concrete realization of the FIMP with LLPs @ LHC, and yielding a standard cosmological history, which turns out to be complementary in DM mass range to the one we have been discussed so far: [[https://arxiv.org/abs/1405.1259 |arxiv]] [[https://arxiv.org/abs/1611.09540 |arxiv]] 
  - A second realization of non-thermal DM and LLPs (appearing today) [[https://arxiv.org/pdf/1706.06815.pdf]]
  - MATHUSLA original paper: Chou, Curtin, Lubatti  [[https://arxiv.org/abs/1606.06298 |arxiv]]
  - MATHUSLA measurements : Curtin, Peskin [[https://arxiv.org/abs/1705.06327 |arxiv]]
  - BBN constraints: Fradette, Pospelov [[https://arxiv.org/abs/1706.01920 | arxiv]]

Deliverables:

- A minimal UFO model implementing the idea (YMMV!) [[https://www.dropbox.com/s/088u4g1nj282ows/FIMP_LH.zip?dl=0|External Link]] -> cross section of 0.687 fb for the reference point shown in the FIMP note. For the specific final states: (+,0),(+,-),(-,0),(0,0) = 0.341,0.122,0.113,0.111.

- Mathematica Notebook (or similar) calculating input parameters (TBD).

- Note on "FIMP production via decay" by Bryan {{ :2017:groups:np:boltzmann_fimp.pdf |}}

- Note on the numerical solution and a comparison with the analytical formulae {{ :2017:groups:np:boltzmann_numerical.pdf  |}}

- Notes on the classification of signatures for freeze-in according to the quantum numbers of parent particle (and SM decay product) {{ :2017:groups:np:LLPs_classification.pdf |}}

Triggers (ATLAS):
There was some discussion as to what triggers are possible for displaced leptons. 
  - This talk from the LLP workshop has some hand drawn plots outlining the trigger possibilities in each region (pg 7-8) https://indico.cern.ch/event/607314/contributions/2542332/attachments/1449594/2234900/LLP_trigger_discussion_group_summary_26april2017.key.pdf It is a bit annoying to read but it is public :p. 
  - For muons you can go all the way out to the MS while prompt muon triggers pick decays out to 1 cm with pT~20 GeV (this is for your general consideration, don't quote that in a paper, please)
  - For electrons, there is no explicit d0 cut in the trigger, but I am trying to find out if there are hit level requirements such as requiring a hit on the first tracking layer which might limit the acceptance.