BSM search using Higgs to invisible decay at the ILC Yu Kato, Jacqueline Yan(KEK), Junping Tian, Satoru Yamashita The University of Tokyo Hello everyone, this is Yu Kato, from the University of tokyo, and I will be talking about BSM Search using Higgs to Invisible Decay at the ILC. The 50th general meeting @KEK Feb. 4, 2017

BSM search using Higgs to invisible decay Status Reproduced all root file without using kt algorithm, and reanalyzed Evaluated UL based on Yamashita san’s advice Made presentation in LCWS2016 Pause analysis for TPC experiment Plans Come back around June Improve sensitivity through further optimization of analysis methods and jet energy resolution Analysis at E cm = 350, 500 GeV, compare between different scenarios --> contribute to optimization of ILC run scenario 2017/2/7 50th g.m.@KEK BSM search using Higgs to invisible decay

Setting & Flow of Analysis Generator: WHIZARD 1.95 Samples: DBD sample + Dirac sample ( e + e − →qqH, H→ ZZ ∗ →4𝜈) Detector: ILD full simulation Ecm = 250 GeV, ∫𝐿𝑑𝑡 = 250 fb-1 , 𝑃 𝑒 − , 𝑃 𝑒 + = −0.8,+0.3 , (+0.8,−0.3) Flow of analysis Isolated lepton tagging → veto Jet clustering forced 2-jet reconstruction using LCFIPlus Event selection (next page) assume BR(H→invisible)=10% Fit & Toy Monte Carlo to set upper limit Next, I shall explain the setup and flow of analysis. First the set up for simulation. The samples are generated using WHIZARD1.95.  The study is based on full ILD detector simulation, conducted at center of mass energy 250 GeV, and assumes 250 fb-1 for each polarization. The beam parameters in the ILD is taken into account.  The flow of analysis is shown below. First, I conduct isolated lepton tagging in order to veto leptons from PFOs. At the stage of jet clustering, LCFIPlus is used for 2-jet clustering. After that, at the stage of event selection, I designed cuts assuming a BR(H→invisible) of 10%. Then finally I fit the spectrum of signal and bkg, and used Toy MC to set the UL of the BR. 2017/2/7 50th g.m.@KEK BSM search using Higgs to invisible decay

BSM search using Higgs to invisible decay Event Selection isolated lepton veto loose restriction of transverse di-jet momentum, di-jet invariant mass, and recoil mass from di-jet number of PFOs and charged tracks: Npfo, Ntrack di-jet (Z) pt: PtZ di-jet mass: MZ di-jet polar angle: θZ recoil mass: Mrecoil multi-variate analysis: Boosted Decision Tree(BDT) method Here are the details of the event selection. I will not go through everything, but in general, I apply cuts on the number of PFOs and charged tracks, also on the Pt, mass and angle of the di-jet system. Last of all, I apply a MVA analysis. 2017/2/7 50th g.m.@KEK BSM search using Higgs to invisible decay

Recoil Mass Plots [Ecm = 250 GeV, 250 fb-1,BR(H->inv.)=10%] Preliminary Recoil Mass Plots [Ecm = 250 GeV, 250 fb-1,BR(H->inv.)=10%] Left Right significance: 15.5 efficiency: 63.5% significance: 19.7 efficiency: 65.9% This is the recoil mass plot after the event selection. The left plot is the left polarization case, and the right plot is the right polarization case. The table on the bottom right is the cut table. As you can see, W bkg is much reduced for the right polarization, and the peak is obviously sharper. The significance is 15.5 for left, and 19.7 for right　and signal efficiency is … No. Cut 1 Isolated lepton veto 5 80 < Mz < 100 2 Loose Cut (Ptz,Mz,Mrecoil) 6 |cosθZ|<0.9 3 Npfo>15 & Ntrack>6 & Ntrackji>1 7 100 < Mrecoil < 160 4 20 < Ptz < 80 8 BDT cut MVA input variables mz cosj1 cosz cosj2 TMVA v-4.2.0 2017/2/7 50th g.m.@KEK BSM search using Higgs to invisible decay

Fit Signal & Background Preliminary Fit Signal & Background signal: GPET (Gaussian + Exponential) bkg : 5th order polynomial Left These are the results for the fitting of the signal and bkg on the previous page. I used GPET for the signal and 5th order polynomial for the bkg. Right 2017/2/7 50th g.m.@KEK BSM search using Higgs to invisible decay

Toy Monte Carlo to Set Upper Limit Preliminary Toy Monte Carlo to Set Upper Limit Left polarization Right polarization UL=1.03% (95%CL) UL=0.69% (95%CL) Then, I generated Toy Mc events using the fitted results on the previous page, and used that to determine the UL. I set the signal yield as 0, bkg shape fixed and the each yields floated, then generated 10000 pseudo experiments. The BR is derived from the number of signal of each pseudo experiment. Here, SM Higgs to invisible decay is not included in the # of signals. Assuming luminosity of 250 fb^-1 for each polarization, the result for the 95%CL is 1.03% for left and 0.69% for right. bkg : shape fixed, yields floated ∫𝐿𝑑𝑡 = 250 fb-1 bkg yields floated → 10000 times pseudo experiment not include SM Higgs to invisible decay 2017/2/7 50th g.m.@KEK BSM search using Higgs to invisible decay

Toy Monte Carlo to Set Upper Limit Preliminary Toy Monte Carlo to Set Upper Limit Left polarization Right polarization 250 fb-1 250 fb-1 250 fb-1 UL=1.03% (95%CL) UL=0.69% (95%CL) H20 (800 fb-1 ) 800 fb-1 800 fb-1 Here are the results assuming the H20 scenario, where we have 800 fb^-1 for each pol., using the same methods. UL=0.58% (95%CL) UL=0.39% (95%CL) 2017/2/7 50th g.m.@KEK BSM search using Higgs to invisible decay

How to set UL [Statistical method] Template Assume BR(H→invisible)=[1,2,…,10]% -> Event selection Get # of events (NS+B) in window range (Mrecoil∈[120,140] GeV) Generate Poisson distribution of NS+B -> Get 95% CL limit (NUL) Repeat for each BR(H→invisible)=[1,2,…,10]% -> Get calibration line between NUL and UL Toy MC Fit template bkg -> Generate pseudo experiment by fluctuated bkg function Translate NS+B into UL of BR(H→invisible) using calibration line Repeat 10000 times -> Obtain UL distribution Up to here we have used the conventional method, but from now on we will reanalyze the UL statistical fluctuation by the following method. ad lib UL NS+B NS+B NUL 2017/2/7 50th g.m.@KEK BSM search using Higgs to invisible decay

Statistical fluctuation of Upper Limit Preliminary Statistical fluctuation of Upper Limit Left polarization Right polarization 250 fb-1 250 fb-1 250 fb-1 UL=0.95±0.45% UL=0.53±0.31% H20 (800 fb-1 ) Here are the results. ad lib 800 fb-1 800 fb-1 UL=0.55±0.25% UL=0.25±0.17% 2017/2/7 50th g.m.@KEK BSM search using Higgs to invisible decay

BSM search using Higgs to invisible decay Summary Use measurement of BR(H→𝑖𝑛𝑣.) as a means for indirect BSM search Motivation set upper limit (UL) on BR(H→𝑖𝑛𝑣.) develop analysis method to achieve high sensitivity compare between alternative polarization study is based on full ILD detector simulation, at E cm = 250 GeV, assuming 250 fb −1 Status optimized data selection methods set UL using toy MC for both left and right scenario Left polarization Right polarization significance [250 fb −1 ] 15.5 19.7 Here is the summary. We use measurement of BR(H→𝑖𝑛𝑣.) as a means for indirect BSM search. Regarding motivation, we want to set upper limit (UL) on BR(H→𝑖𝑛𝑣.). So as to set UL, we have to develop analysis method to achieve high sensitivity. And we also compare between alternative polarization, left and right mode. This study is based on full ILD detector simulation, at Ecm = 250 GeV, assuming 250 fb^−1. As for our status, we optimized data selection methods and significance is 15.5 for left pol. and 19.7 for rightl. After that, the UL we obtained ,assuming 250 fb^-1 for each pol. is 1.03% for left and 0.69% for right. And assuming H20 scenario, the UL is 0.58% for left and 0.39% for right. These results are consistent within 1σ. UL of BR [%] (95%CL) Left polarization Right polarization Statistical Left Right 250 fb −1 1.03 0.69 0.95±0.45 0.53±0.31 H20 scenario (800 fb −1 ) 0.58 0.39 0.55±0.25 0.25±0.17 Previous study(250 fb −1 ) 0.95 - 2017/2/7 50th g.m.@KEK BSM search using Higgs to invisible decay

BSM search using Higgs to invisible decay Back Up 2017/2/7 50th g.m.@KEK BSM search using Higgs to invisible decay

BSM search using Higgs to invisible decay Motivation In SM, Higgs decays invisibly through H→Z Z ∗ →4𝜈 (BR(H→𝑖𝑛𝑣.)~0.1%) If BR(H→𝑖𝑛𝑣.) exceeds SM prediction , It signifies new physics beyond SM (BSM) In this study, we estimate upper limit of BR(H→𝑖𝑛𝑣.) Compare between left & right polarization at the ILC q BSM X invisible Dark Matter… SUSY… visible 𝐵𝑅 H→XX ~???% q SM Z ν 𝐵𝑅 H→ ZZ ∗ →4𝜈 ~0.1% invisible visible First, I shall explain the motivation of this study.  In the SM, this is the only process in which the Higgs decays invisibly. The BR is about 0.1%. On the other hand, if the Higgs decay in non-SM process, because the invisible decay products cannot be seen in the detector, the BR of H to inv. would exceed the SM prediction. In other words, this is an indication of new physics beyond the standard model. I aim to establish the upper limit of the BR for invisible Higgs decay and to compare results between different polarizations. 𝑁 𝑆 ∝ 𝜎 ZH ・𝐵𝑅 H→𝑖𝑛𝑣𝑖𝑠𝑖𝑏𝑙𝑒 A. Ishikawa (Tohoku Univ.), ”Search for Invisible Higgs Decays at the ILC” LCWS2014@Belgrade M. A. Thomson (Univ. of Cambridge), arXiv: 1509.02853 (2015) 2017/2/7 50th g.m.@KEK BSM search using Higgs to invisible decay

BSM search using Higgs to invisible decay Recoil Mass Method We can measure Higgs without directly looking at it → model independent 𝑀 𝑟𝑒𝑐 2 = 𝑠 − 𝐸 𝑍 2 − 𝑝 𝑍 2 Higgs-strahlung cross section can be obtained using leptonic decay of Z 𝜎 ZH = 𝑁 𝑆 𝐵𝑅 Z→ 𝑙 + 𝑙 − ε 𝑆 𝐿 ε 𝑆 : signal efficiency, N S : # of signal, 𝐿 : integrated luminosity J.Yan(KEK) et al. Phys. Rev. D94 113002(arXiv:1601.07524 ) (2016) For BSM search, this study uses hadronic channel 𝑍→𝑞𝑞 and 𝐸 𝑐𝑚 =250 GeV This study uses the  Higgsstrahlung process. This method allows us to measure the Higgs without directly looking at the Higgs. This model independent measurement can only be realized at the ILC. The total ZH cross section, which is crucial for the BR measurement,  is given in this paper by Jacqueline.Yan et al, using the leptonic decay of the Z. On the other hand, this study will be conducted at center of mass energy 250 GeV, using the hadronic decay of the Z 2017/2/7 50th g.m.@KEK BSM search using Higgs to invisible decay

Cut table [Ecm=250GeV,250fb-1,Left] Hadronic Channel Analysis Cut table [Ecm=250GeV,250fb-1,Left] 2017/2/7 50th g.m.@KEK BSM search using Higgs to invisible decay

Cut table [Ecm=250GeV,250fb-1,Right] Hadronic Channel Analysis Cut table [Ecm=250GeV,250fb-1,Right] 2017/2/7 50th g.m.@KEK BSM search using Higgs to invisible decay

Toy Monte Carlo to set upper limit Preliminary Toy Monte Carlo to set upper limit Left Right UL=0.78% (95%CL) UL=0.52% (95%CL) bkg : shape & yields fixed ∫𝐿𝑑𝑡 = 250 fb-1 bkg fixed → 10000 times pseudo experiment not include SM Higgs to invisible decay 2017/2/7 50th g.m.@KEK BSM search using Higgs to invisible decay

BSM search using Higgs to invisible decay Previous Study A. Ishikawa (Tohoku Unv.), ”Search for Invisible Higgs Decays at the ILC” LCWS2014@Belgrade Smaller upper limit of BR(H→𝑖𝑛𝑣.) →　higher sensitivity to BSM We aim to improve this result ∫𝐿𝑑𝑡=250,350,500 fb-1 for E cm =250,350,500 GeV こちらは東北大学の石川さんによる、先行研究のデータです。 ULはご覧のような結果が得られています。 我々はこの結果を向上することを目標にします。 2017/2/7 50th g.m.@KEK BSM search using Higgs to invisible decay

Signal feature [hadronic channel] q X invisible 𝐵𝑅 H→XX ~???% Two-Jet Invisible particle exist 𝑀 𝑞𝑞 ≈ 𝑀 𝑍 (𝐵𝑅 Z→𝑞𝑞 ~70%) 𝑀 𝑟𝑒𝑐𝑜𝑖𝑙 ≈ 𝑀 𝐻𝑖𝑔𝑔𝑠 Major Backgrounds [hadronic channel] The major backgrounds have the final states qqll,qqlν,qqνν. ZZ semileptonic WW semileptonic Z 𝜈 𝑒 𝜈 𝑒 , Z→qq W 𝜈 𝑒 𝜈 𝑒 , W→qq ννH,H→ZZ,Z→𝑞𝑞 qqH,H→SM decay 2017/2/7 50th g.m.@KEK BSM search using Higgs to invisible decay

Signal feature [leptonic channel] 𝑙 + X invisible 𝐵𝑅 H→XX ~???% Two-leptons Invisible particles without neutrino 𝑀 𝑙𝑙 ≈ 𝑀 𝑍 (𝐵𝑅 Z→𝑙𝑙 ~3.4%) 𝑀 𝑟𝑒𝑐𝑜𝑖𝑙 ≈ 𝑀 𝐻𝑖𝑔𝑔𝑠 𝑙 − Major Backgrounds [leptonic channel] The major backgrounds have the final states with di-lepton & missing energy . ZZ leptonic WW leptonic single Z & 𝜈 𝑒 𝜈 𝑒 , Z→𝑙𝑙 single W & e 𝜈 𝑒 , W→e ν e ννH,H→ZZ,Z→𝑙𝑙 𝑙𝑙H,H→SM decay 2017/2/7 50th g.m.@KEK BSM search using Higgs to invisible decay