Higgs Decay with Displaced Vertices Nathaniel Craig UC Santa Barbara Based on work in progress with S. Alipour-Fard International Workshop on CEPC, Beijing 207
Higgs Displaced Decays Much attention of the precision Higgs program currently focused on SM measurements, prompt exotic decays of the Higgs But displaced exotic Higgs decays an increasingly hot topic: 2
Model For example: Twin Higgs [Chacko, Goh, Harnik 05] Standard Model Z2 Standard Radiative corrections to the Higgs mass are SU(4) symmetric thanks to Z2: V (H) 9 64 2 g2 2 H A 2 + H B 2 Higgs is a PNGB of ~SU(4), but partner states neutral under SM. L y t H A Q A 3 ū A 3 y t H B Q B 3 ū B 3 h +... f h 2 2f +... 3
[NC, Katz, Strassler, Sundrum 5] Fraternal twins g g Q Q Z H H W Z W L L γ What really matters for naturalness: SU(3)xSU(2) & third generation Dark QCD 4
f@gevd Exotic Higgs Decays Twin sector must have twin QCD, confines around QCD scale Higgs boson couples to bound states of twin QCD Various possibilities. Glueballs most interesting; have same quantum # as Higgs 400 200 000 800 6 3 0 cth0 ++ L@log 0 HmLD -3 0 20 40 60 80 00 m 0 @GeVD -6 5 h L 0 3 6 v f h a f G0 µ G 0 µ a [NC, Katz, Strassler, Sundrum 5] 0 ++ 0 ++ h* h* SM SM Produce in rare Higgs decays (BR~0-3 -0-4 ) gg! h! 0 ++ +0 ++ +... Decay back to SM via Higgs 0 ++! h! f f Long-lived, decay length is macroscopic; length scale ~ collider detectors
Displaced Decays @ CEPC LHC advantage: 3x0 7 Higgses produced at ATLAS+CMS with 300/fb at 4 TeV LHC disadvantage: Triggering (e.g. no vertexbased displaced search sensitive to Higgs @ 8 TeV) CEPC in principle: x0 6 Higgses with 5/ab at 240 GeV Significantly reduced triggering & cleaner environment Maximal CEPC sensitivity: BR ~ 4x0-6 (4 evts, no bkg, perfect acceptance) Little/no study of BSM displaced physics objects so far (Exception: RHN, [Antusch, Cazzato, Fischer 6]) 6
Simulation Model: h XX, X qq (80% bb) loys a.8 meter radius TPC tracker, silicon vertex and detector, ultra high granularity calorimeter system, and a j j j X h e+ j X e- Z ℓ ℓ MadGraph: e+e- Zh located in the forward region providing a solid anmeter is located close to the beam pipe at the very 24 μm +XX ( s = 240 GeV).8m tor surrounded by a large TPC. The silicon tracking d on pixel technology), silicon inner tracker (SIT, p technologies), silicon external tracker (SET, strip technology). The VTX and SIT provide excellent ex reconstruction and jet flavor tagging. The SET patial resolution with the maximal possible track m resolution. The FTD significantly increases the TPC has a half-length of 2.35 meter and an outer Pythia: X qq, hadronization/showering Delphes: SiD card for generic object efficiencies 7
Analysis Reproduce Higgs selection w/ recoil mass in leptonic Zh: Z ee or μμ. Lepton pt: 0 pt(l) 90 GeV. Dilepton invt mass: 70<Mee<0 GeV, 8<Mμμ<0 GeV. Recoil mass requirement: 20<mrecoil<50 GeV. Plus selection for displaced Higgs decay: Require two jets (vetoing hadronic τs), R=0.5 Construct secondary vertex, require dmin < d <.8m Assume most backgrounds handled by Higgs selection Irreducible backgrounds: e + e - ZZ + - + bb /cc /τhτh 8
Secondary vertices Roughly emulating CMS secondary vertex-finding algorithm. Form clusters using a depth-first algorithm running over all possible jet pairs, clustering tracks w/ origins within mm of another track. 2 2 2.Take highest-multiplicity cluster containing at least one track from each of the two jets. 3. Average origins of tracks in this cluster to define displacement. 9
Acceptance x Efficiency ZZ bbll mx = 30 GeV, cτ = cm mx = 30 GeV, cτ = 0cm mx = 30 GeV, cτ = m mx = 30 GeV, cτ = 0m pt(l), Mll 0.95 0.96 0.96 0.96 0.96 mrecoil 0.0055 0.9 0.9 0.9 0.9 2j 0.0027 0.5 0.5 0.36 0.047 displaced dijet w/ dmin= cm 0.0005 0.8 0.42 - - displaced dijet w/ dmin = 0cm 0.0003 - - 0.25 0.06 0
Preliminary Results 0.00 0.00 m X =20 GeV 0.00 0.00 m X =30 GeV All cuts w/ backgrounds Br(h XX) 0.00 Br(h XX) 0.00 0-4 0-4 0-5 5 0 50 00 500000 cτ [cm] 0-5 5 0 50 00 500000 cτ [cm] All cuts w/o backgrounds 0.00 m X =40 GeV 0.00 m X =50 GeV 0.00 0.00 Br(h XX) 0.00 0-4 0-5 5 0 50 00 500000 cτ [cm] Br(h XX) 0.00 0-4 0-5 5 0 50 00 500000 cτ [cm] Ideal case (optimal geometric acceptance, Z ll BR)
[Curtin & Verhaaren 5] vs LHC No official projections of LHC4 sensitivity, just theory estimates [Curtin & Verhaaren 5, Csaki, Kuflik, Lombardo, Slone 5] 0.00 m X =30 GeV LHC projections account only for trigger efficiency & geometric acceptance; assume no background, no pileup, and neglect systematics Br(h XX) 0.00 0.00 0-4 0-5 5 0 50 00 500000 2 cτ [cm]
Conclusions Displaced decays of the Higgs provide a highly motivated target for a precision Higgs program. CEPC capable of improving the limits on displaced Higgs decays relative to LHC. Current results preliminary; significant refinement & expansion of the analysis forthcoming, w/ improved background discrimination. Improved sensitivity for lighter X possible with a dedicated boosted analysis. Hadronic Z decays also merit consideration Thank you!