Thursday, 15 October 2015

CosPA 2015 Liveblog: Day Four Session Three

This afternoon looks to be about colliders (at least for me).
2:00 pm: Overview of Dark Matter searches and status in run 2 at the CMS experiment, DongHee Kim

A review of non-SUSY DM searches, focusing I think on Mono-X searches. Discussion of EFT limitations.  Cut-off must be greater than Λ/2π to be consistent.

Mono-jets from ISR.  Z/W plus jets main background, plus QCD misidentification.  Latter extracted from single top and multi-jet events.  Comparatively easy search.  As usual, wins at low mass (<10 GeV) and in spin-dependent scattering channels.

Mono-photons, pretty similar including similar (origin of) backgrounds.  630 events vs 614 ± 63 expected.  Weaker constraints (EM vs QCD) but still wins over DD as above.

Mono-W (mono-lepton).  Sensitive to isospin nature of couplings.  In particular, interference possible and can have strong effect.  Constraints not strongly sensitive to SD vs SI, dark matter mass; very sensitive to interference.  When constructive interference, actually stronger than mono-jet constraints.

Mono-top.  RPV SUSY or FC top couplings.  CMS (ATLAS) used hadronic (leptonic) tops.

ttbar plus MET.

Mono-Z (dilepton plus MET).  Newest results of this type; not published yet.  Order 100 events expected & seen.  Conservative limits removing events with high momentum flow (do not trust EFT).

Discussion of breakdown of EFT.  Run2 efforts for going beyond EFT to more reliable description: Simplified Models.  In simplest UV complete models run1 limits don't change much, especially at low mass; in some cases stronger!

2:35 pm: The ATLAS detector: status and performance in run 2, Steven Schramm

Review of improvements  in ATLAS detector, triggering and operation.  Replaced or upgraded a lot of electronics and improved hermeticity for muon trackers.  New IBL: trackers only 3.3cm from interaction point.

New triggering architecture; can actually record data at 1kHz (3GB/s).  Record all events with jet pT > 400 GeV.

Early data from this year used to update detector alignment & description/MC.

IBL gives factor of 2 improvement in tracking.

B-jet rejection of light flavour jets 4 times better.

New MET algorithm, less sensitive to pile up.

Already (85 ipb) statistical uncertainties on W/Z cross sections comparable to theory uncertainties.

2:50 pm: Overview of Dark Matter searches at the ATLAS experiment, Bernhard Meirose

Higgs invisible width.

Hadronic mono-W/Z.

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