BSM searches at ILC. Tohoku Forum for Creativity Tohoku Univ. Eriko Kato 1/29

Transcription

1 BSM searches at ILC Tohoku Forum for Creativity Tohoku Univ. Eriko Kato 1/29

2 New Physics at the TeV scale 2/24 Issues motivating physics study at TeV scale: Naturalness Radiative correction to Higgs mass term has quadratic divergence Require new physics / new particles in the TeV range to avoid excessive fine-tuning e.g. Supersymmetry (SUSY), Composite Higgs, Extra Dimensions Dark Matter (DM) WMAP relic density predicts O(100) GeV WIMP New physics models predict natural DM candidates So far LHC8 hasn t observed any New Physics. What can be happening?

3 Possible scenarios for New Physics 3/24 No NP Within LHC kinematic reach, but cannot observe. e.g. in many models q, g are heavy. small σ electroweak, large bkg e.g. small visible energy. Contracted mass spectrum e.g. purely hadronic decay No NP Out of kinematic reach of LHC NP Found SM deviation Where can ILC contribute?

4 ILC characteristics 4/24 Elementary process Well-understood at LEP Theoretical uncertainty <1% e Beam Tunable energy (250GeV~1TeV) Polarization P electron = ±80% P positron = ±30% γ/z/z Production New particles Dark Matter etc e + Detection Low background hermetic Highly granular sensors Trigger free operation

5 Possible scenarios for New Physics 5/24 No NP Within LHC kinematic reach, but cannot observe. e.g. in many models q, g are heavy. small σ electroweak, large bkg e.g. small visible energy. Compressed mass spectrum e.g. purely hadronic decay ILC strong point for discovery No NP Out of kinematic reach of LHC ILC will probe NP though loop effects(electroweak precision meas.) NP Found SM deviation ILC will disentangle complicated NP phenomenon's and conduct NP precision measurements.

6 Some examples. (MOSTLY SUSY)

7 Electroweakino Direct Production 7/24 (Electroweakinos: collective name for gauginos and Higgsinos) - q χ ± i q χ + i q χ 0 i q W χ 0 j q γ/z χ j q Z χ 0 j (a) (b) (c) For LHC: Decays: For ILC: Dominant production: Wino pair production: cha-cha, cha-neu Higgsino pair production: cha-cha, cha-neu, neu-neu

8 From LHC 8/24 3 leptons + MET 100% BR into W/Z assumed ATLAS-CONF

9 ILC 500 GeV Chargino / Neutralino can be discovered + studied with mass resolution O(1)% Gaugino pair production 9/24 ILC can search for SUSY particles with mass below s/2 Consider pair production of χ 1± / χ 10 whose masses are close e + e χ 1+ χ 1 χ 10 χ 10 W + W e + e χ 20 χ 2 0 χ 10 χ 10 Z 0 Z 0 If soft jets challenging signature Discovery + mass measurement via detection of kinematic edges: Suehara, List [arxiv: ]

10 4 jets 4 jets + missing 4-momentum 10/24 General strategy: Reconstruct the hadronic decay of the chargino: 4 jets + missing 4-momentum signature. Choose jet combination most consistent with the same dijet mass. Event selection based on: Number of particles Large missing energy Missing momentum not along the beam pipe Require minimum jet energy Jet finder transition values

11 able 7: Number of events passing off in the SM background near the final neutralino selection, following the preselection in Tab. 4, for an ntegrated luminosity of 500 fb s = 230 GeV is due to urpose so that a signal-free region is available to fix the function with two free parameters Higgsino 1 and P (e +,e )= (+ 30%, 80% ). f (x) = p 1 epair production p 2 x to tep, eu tralin a straight o m ass lineriseconstru added onction top of the background to mulated data in the endpoint region (red line). T he two ds to innaturalness thevalues chargino obtained case, argument the frommass the of SMthe calls -only χ 0 2 fi is for t in reconstructed the light wider Higgsinos from s determined e.g. using the case the ISRof photon. As re pposed stableto against the chargino reasonable case, variations the m asses of of the the fi t two ranges produced or neutralinos are not equal, but their difference s MSSM: hargino smallermass thanisthe fitted resolution to of±1.4 the GeV s method. in the dmt 1600 herefore we use the approximation of two equal mass e. articles being produced and calibrate the method in the end. Higgsinos small mass gaps 11/24 Events/10 GeV 1000 ~ + - c ~ c g 1 1 ~ 0 0 c ~ c g SM 600 simul. data fit M~± c 1 dm770 = ± 1.0 GeV Events ~ c ~ c ~ c ~ c SM g g simul. data fit M ~ 0 c 2 dm770 = ± 0.8 GeV s /GeV s /GeV sigure energy 9: ( Distribution s ) of the system of therecoiling reduced against center-of-mass the hard energy ISR ( Berggren, Bruemmer, List, Moortgat-Pick, Robens, Rolbiecki, Sert [arxiv: ] s ) of the system recoiling against the hard SR for an photon integrated for all luminosity events passing of 500 fb the 1 neutralino with P (e +,e selection )= for an integrated luminosity of 500 fb 1 with fi(e t + to,e the Even )= distribution for sub-gev (+ 30%, 80% near mass ). the M χ endpoint. differences, 0 Left: the dmcharginos/neutralinos 1600 can be discovered / 2 is determined from fitting the sum (red curve) of a straight line for the ignal and measured the background to O(1)% parametrisation in mass. (blue curve) to the distribution near the endpoint. Left: dm 1600

12 soft ISR photon + soft particles 12/24 Higgsino BR The ISR tag is critical in reducing γ γ backgrounds by kicking the hard forward electrons into detector acceptance. For the soft particles: Choose characteristic signature, e.g. lepton on one side + pions on the other side. Chen, Drees, Gunion [arxiv:hep-ph/ ]

13 Electroweakino parameter scan 13/24 Scan over M 1, M 2, μ (fix 1 as LSP, scan over the two parameters) The squark/slepton sectors are decoupled. Bino LSP χ ± χ 0 + W Higgsino LSP w/ ISR tag Berggren, Han, List, Padhi, Su, Tanabe Benchmark: even able to measure sub-gev mass difference

14 LHC/ILC Complementarity 14/24 SUSY electroweak naturalness prefers light Higgsinos Compressed mass spectrum μ~ gev LHC/I LC complementarity ILC higgsino factory! Green region: thermal higgsino relic abundance Ω h h 2 < 0.12 Baer, Barger [arxiv: ] Δ(M χ ± M χ 0 ) as small as 770 MeV can be measured Either discover Higgsinos or rule out SUSY electroweak naturalness

15 NLSP pair production 15/24 τ τ τ τ NLSP LSP + X. no long decay chains. Simple. If assume SUSY, σ is determined only by s & mass Systematically search for signals for all possible NLSP s, the entire space of models that are within the kinematic reach of the ILC can be covered.

16 NLSP pair production 16/24 No loopholes ILC is especially sensitive to regions of small Mass difference Difficult to LHC μ pair production τ pair production μ plot enlarged τ plot enlarged

17 DM with Single Photons 17/24 Consider the case where only DM is accessible at ILC Can still discover it with single photons m χ = 98 GeV Bartels, List [arxiv: ] Discovery of DM w/ mass precision Dm(c 0 1)/c 0 1 ~ 3% or better

18 600 GeV or above. And, indeed, there is still much room for the t 1 to be found at the LHC at a mass below 250 GeV. SUSY / DM Connection The polarized cross sections σ(e e! t t ) and σ(e e! t t ) allows a direct + L R + R L determination of the ( t L, t R ) mixing angle with an accuracy of a few degrees. This Neutralino LSP with scalar top with small mass difference is crucial information for light the theory of electroweak symmetry breaking in SUSYcan andprovide cross for the sections explanationconsistent for the Higgswith bosonwmap mass atdata 125 GeV. Decay modes: Freitas, Milstene, Schmitt, Sopczak C D M h WMAP 1σ 0.1 2σ ILC 1σ mt Scalar top discovery + Precision mass measurements Figure 62: Predicted dark matter density D M vs m t 1 in a stop coannihilation model. T he Can establish neutralino as WIMP dark matter scatter plot shows points allowed within 1σ experimental precision assuming δt 1 = 1.2 GeV 18/24

19 Neutrino ILC 19/24 What is the origin of neutrino mass? e.g. Seesaw induces flavor violating decay of sleptons e.g. Bilinear R-parity violation(rpv) LSP Br( χ 1 0 Wμ) Br( χ 1 0 Wτ) tan 2 θ atm By comparing with neutrino experiment results, ILC can test if neutrino mixing and mass generation is introduced by RPV

20 Alternative BSM theories 20/24 Little Higgs models Explains naturalness problem, dark matter e.g. Littlest Higgs model with T-Parity Global Symmetry : SU(5) f ~ 1 TeV SO(5) v ~ <h> subgroup : [ SU(2) L U(1) Y ] 2 SU(2) L U(1) Y U(1) Y T-parity H H H H H H AH H DM candidate - μh - - eh τh H T H H Triplet H T ILC high sensitivity Quadratic divergent terms in Higgs mass cancel at 1-loop order

21 Powerful ILC tools e.g. Little higgs models 21/24 Model independent mass measurements e.g. e + e Z H Z H A H A H HH Model parameter extraction (vev f, Yukawa coupling κ) Energy distribution others LH SG BG Many observables Cross section Angular distribution Polarization etc. Example of a decay process e - e + Z H A H Decay branch e H e - e H e + γ, Z e H e H GeV WH Able to disentangle and measure almost all introduced couplings

22 What we can test e.g. Little higgs models 22/24 Mass hierarchy Evidence of little higgs mass generation mechanism Dark matter relic density Lightest T-parity odd particle is a dark matter candidate Global symmetry vev(f) determines Ωh 2 Is LTP indeed the DM filled in the universe? Test various coupling relationships Global symmetry should include gauged subsets. Measure the structure of the Little Higgs Dark matter relic density Ωh

23 Model Discrimination 23/24 Phenomenology: X + + X W + + DM + W + DM How to discriminate different physics models? Spin of X: e.g. Inert Higgs (0), SUSY (1/2), Little Higgs (1) Angular analysis of X production + Threshold Scan Angular Analysis Threshold Scan Scalar Fermion Vector Scalar Fermion Vector Asano, Saito, Suehara et al. Model Discrimination with spin information

24 Summary 24/24 There are strong physics cases where the LHC might not be sensitive to NP but the ILC is. If LHC14 where to find some NP.. ILC s mission will to disentangle NP and do precision measurements to make predictions for higher energy. We gave examples.. light higgsinos Comprehensive bottom up coverage of NLSP-LSP combinations for slepton, squark, chargino and neutralino Bilinear R-parity violation for neutrino physics Generic WIMP searches Non SUSY models. e.g. Little Higgs models

25 BACKUP

26 26 On Naturalness M. Peskin, CSS2013 If this is the case, ILC will be a Higgsino factory!