In search of Super Charm Search for Scalar Charm Quark Pair Production in pp Collisions at √s =8 TeV with the ATLAS Detector arxiv:1501.01325 [hep-ex], Phys. Rev. Lett. 114, 161801 W. Kalderon1,A.Barr1,A.Dafinca1,T.Golling2,D.Guest2,C.Gwenlan1,A.Henrichs2 [1] University of Oxford, [2] Yale University

Supersymmetryp Super Charmp c Supersymmetry is an extension to Here, we search for the partner • the standard model (SM) of par- • of the charm quark (c˜)knownas p c˜ 0 ticle physics, predicting that each ‘scalar charm’, ‘scharm’ or (infor- χ˜1 SM particle has a ‘superpartner’ mally) ‘super charm’ 0 This extension helps solve various c˜ χ˜1 • If they exist, scharms will be pro- p outstanding questions in particle • duced in pairs, and each quickly de- c physics, such as the nature of dark cay to a charm quark and a ‘neu- matter, the low value of the Higgs tralino’ - an invisible SUSY particle Signature: two high-momentum c- boson mass and the unification of 3 jets (from c-quarks), and large miss- that might explain dark matter miss of the 4 fundemental forces ing transverse momentum (ET )

Charm Tagging - JetFitterCharm Algorithm (ATL-PHYS-PUB-2015-001)p Tracking information input to neu- • ral network (algorithm trained to distinguish c from b and light) Primary VTX c-hadron s-hadron Gives probabilities Pc, Pb, Plight b-hadron 3rd VTX • Cuts in 2D plane: distinguish c jets 2ndary VTX • from both b and light (u,d,s, g)jets http://acfahep.kek.jp/acfareport/node35.html Plot description: each jet falls some- • where on (Pc/P ,Pc/P )plane. b-hadrons fly mm before decaying light b • ∼ At this point, pixel colour value Reconstructed tracks can reveal is incremented by (R,G,B) for jet • these secondary decay vertices flavour = (b, c,light) b-jets at bottom, light jets at top ‘Light’ jets (from u, d, s quarks and • • left, c-jets at top right, comination gluons) do not have these features in middle (white region) c-jets are an intermediate, since Patterns due to discrete inputs (e.g. • • c-hadrons fly a measurable but number of vertices with 2tracks) ≥ smaller distance than b-hadrons and Performance: εc 17%, εb 12%, Distribution of tagging algorithm outputs • ∼ ∼ b-hadrons decay via c-hadrons εlight 0.8% for c, b and light jets in tt¯ simulation ∼

Signal Candidate Event Displayp Selection and Resultsp Unfortunately, data matched the • background-only predictions no sign of c˜ → Set limits on c˜ masses that can exist • In combination with the ‘stop-to-charm’ • search1,limitsareasignificantlystronger then previous best (‘inclusive’2,ingrey)

To distinguish signal from large back- • grounds, require two c-tagged jets as well miss as high jet pT and high ET Use kinematic variables m (plotted) and • CT mcc to exploit topology of signal Measure backgrounds in dedicated regions, • extend to search regions with simulation

[1] Search for pair-produced third-generation squarks decaying via charm quarks or in compressed miss supersymmetric scenarios in pp collisions at √s =8TeV with the ATLAS detector,Phys.Rev.D90,052008(2014) Two high-p c-tagged jets and high E , mcc and m T T CT [2] Search for squarks and gluinos with the ATLAS detector in final states with jets and missing transverse momentum using Lower right panel shows a displaced vertex in a c-tagged jet √s =8TeV proton–proton collision data,JHEP09(2014)176 Inclusive JHEP JetFitterCharm Scharm paper PRL Stop-to-charm PRD Super Charm ATLAS Super Charm Oxford