Search for Exotic and Rare Higgs Decays at CEPC Wei-Ming Yao(LBNL) For CEPC Physics and Simulation Group
Outline Introduction Motivation Higgs Exotic Decays H Invisible H bb χ0χ0 H bbbb H μτ, eτ Higgs Rare Decays: H Zγ H μμ H Vγ Conclusion 2
Introduction The discovery of Higgs boson at LHC completes the standard model. The data so far are consistent with the Higgs boson predicted by BroutEnglert-Higgs, a cornerstone of EWSB in the standard model (SM). However, current measurements of Higgs branching ratios at LHC still allow a significant fraction of invisible or exotic decays. 3
Constrains on Higgs Couplings at LHC Several BSM theories(such as SUSY, 2HDM...) Higgs Coupling: predict rare or non-sm Higgs decays. Current limit: Br(H BSM)<34% at 95%CL Exotic decays may provide hints of BSM... JHEP 1608(2016) 045 4
Circular e+e- Higgs Factory (CEPC) CEPC will produce 1M ZH events in 10 years at Ecm=240 GeV with lum=2*1034 cm-2s-1 and can also run at Z-pole to produce >10 B Z events. Provides great opportunities to search for the rare/exotic Higgs decays directly: 5
Introduction In extended run of LHC at 7 and 8 TeV, ATLAS and CMS made the anticipated discovery of Higgs boson, the culmination of a decades-long effort. 6
Precision Higgs Measurements High precision measurements of mass and width Model-independent measurement of Higgs coupling via HZ More than order of magnitude improvement over HL-LHC in Higgs coupling. 7
H Invisible In SM, the Higgs has B(H ZZ 4ν)=0.106%, decaying into invisible. A model-independent measurement of H invisible can be probed at CEPC: Tagging the products of Z ee, μμ, and qq against H invisible. Sensitive to the detector coverage due to a small L* (θ>10-20 degree). Channels Z μμ Z ee Z qq Combined Limits: 1.8% 0.125% 0.124% 1.2% 8
Impact of Detector Coverage on B(H Invisible) Full CEPC simulations(vv, sv, QQ, ZH) are used and the analysis is improved with additional cuts. Signal H ZZ 4ν consists of two jets from Z decay and recoiling against nothing else. Backgrounds dominated by ZZ qq νν. The sensitive is improved to 0.078% with the detector coverage of θ>10 deg and 23% worse if the coverage reduced to 20 degree. 9
Exotic H bb Χ Χ Decay 0 0 In SM, B(H ZZ bb νν)=0.157%, decaying into semi-invisible. A model-independent search of H bb Χ0Χ0 decay can be probed at CEPC: Tagging Z μμ, ee, qq against H recoiling. Sensitive to new theory models (SUSY,2HDM+S). Parameters for scan: Fix Mx01=0: Mh1=15,25,35,45,55,65; MΧ02=20,40,60,80,100,120 GeV Fix Mh1=30: Mx01=5,15,25,35,45,55; Mx20=20,40,60,80,100,120 GeV Upper limit on B(H bbx0x0)/b(h bb) at 95% CL, within range of (0.6 1.9)10-3. 10
Exotic H aa bbbb Decay B(H ZZ bbbb)=0.059%, decaying into 4 bjets. Probing model-independent of H aa 4b decay: Tagging Z μμ, ee, qq against H recoiling. Current limits at CMS at Run1: h aa μμττ,μμbb,μμμμ, ττττ. Pairing of two b's to minimize mass differences. Expected limits for B(H aa 4b): <10-2-10-3. Signal: ma=30gev Background: 11
H μτ, eτ Higgs LFV is translated to LFV interaction through effective theory(lagrangian) Constrains from τ μγ, eγ give an indirect limit B(H μτ,eτ)<10% at 95%CL. Current ATLAS limits: B(H eτ)<1.04% and B(H μτ)<1.43% at 95%CL Topology similar to H ττ, but leading lepton with harder Pt. Llimit at CEPC: B(H μτ,eτ)<10-4 @95%CL. JHEP 1511(2015)211 With 10B Z, the limit of B(Z μτ,eτ, eμ) is expected to be <10-8 @95%CL. 12
H Zγ B(H Zγ)=0.124% arises at the one-loop level in SM, is sensitive to BSM. Current ATLAS limit: <18.2xSM at 95% CL and measureable to 15% with 3ab-1. Signals consist of two jets from Z qq, one photon, recoiling missing Z νν. Initial study of ZH ZZγ qq νν γ is promising, close to 4 σ signal with 5ab-1. Including other Z decays are in progress! dmass=mzγ -MZ [GeV] 13
H μμ B(H μμ)=0.022% in SM is sensitive to Yukawa-coupling to 2nd generation. Signature: clean dimuon final state. Current ATLAS limit at 13TeV with 13.2 fb -1: <3.5xSM at 95%CL. Analysis strategy: Selecting 122<mμμ<127 GeV, recoiling against Z consisting of ZH events. Significance for cut based: Channels ZH(inclusive) Cut based 7.67(1.27) ZH(Z qq) 8.12(1.1) ZH( νν) 1.94(0.84) 14
H Vγ Decays Exclusive modes: BR(H Vγ)~10-6 (V = vector meson), allow extraction of Yukawa couplings to frst 2 quark generations. (Bodwin et al PRD 88(2013) 053003, Kagan et al PRL 114(2015) 101802) H J/Ψ γ (yc) H Φ γ (ys) H ρ γ (yu,d) Limits on H J/Ψ γ from LHC: Current @ LHC 8 TeV 20 fb-1 <1.5x10-3 LHC @14 TeV 300 fb-1 < 150 x10-6 HL-LHC @14 TeV 3 ab-1 <45x10-6 CEPC seems able to reach ~10-5, comparable to the HL-LHC. 15
Summary of Recent Progresses Most of analyses are updated based on full detector simulation. 16
Conclusion The Higgs boson discovery opens a new era of precision physics. The LHC is going strong: Current Higgs production and decay measurements are consistent with SM expectation Searches for exotic or rare Higgs decay become sensitive. CEPC provides an excellent opportunities for: Measuring the Higgs mass and width in a great precision. Measuring model-independent Higgs coupling via HZ at 1% level, more than one order of magnitude improvement than HL-LHC. Probing the exotic or rare Higgs decay in a clean environments and sensitive to the new physics at high energy scale beyond the LHC. 17