Di-photon at 750 GeV! (A first read)

Transcription

1 Di-photon at 750 GeV! (A first read) LianTao Wang ( )! U. Chicago Jan. 1, IAS HKUST

2 Excess around 750 GeV?! Events / 40 GeV ATLAS Preliminary Data Background-only fit -1 s = 13 TeV, 3. fb Events / ( 0 GeV ) 1-1 CMS Preliminary Data Fit model ± 1 σ ± σ -1.6 fb (13 TeV) EBEB category Data - fitted background BR [fb] 95% CL Upper Limit on σ fid , , 1. m γγ [GeV] 3 Observed ATLAS Preliminary 1-1 s = 13 TeV, 3. fb Expected ± 1 σ ± σ (data-fit)/σ stat m γ γ 3 (GeV) m X [GeV] 3.6 (local) (global).6 (local) 1. (global) Certainly too early to claim victory. But, tantalizing

3 Exactly 4 years ago, m!! 15 7 Events / 1 GeV Inclusive diphoton sample Data 011 Background model SM Higgs boson m = 10 GeV (MC) H -1 s = 7 TeV, Ldt = 4.9 fb ) Events / ( 1 GeV/c CMS preliminary -1 s = 7 TeV L = 4.76 fb All Categories Combined Data Bkg Model!1"! " 5xSM m H =10 GeV Data - Bkg model 0 ATLAS Preliminary m γ γ [GeV] m!! (GeV/c ) Observed CL s limit 0. Observed CLs Limit Figure 1: Background model fit to the m Figure 1: Invariant mass 7 distribution Expected for the inclusive CL limit gg distributioncms forpreliminary the combined data in all 4 event s data sample, H γ γ overlaid with the sum of the Median Expected CLs Limit background-only fits in different categories described in Sections 3 and 4 and the signal expectation classes, together with a simulated signal (m ± 1σ ATLAS Preliminary H =10 GeV/c s = 7 TeV L = 4.76 fb ± 1# Expected CLs ). The magnitude of the signal is what for a mass hypothesis of 6 10 GeV corresponding ± σ to the Data SM011, cross section. s = 7 The TeVfigure below displays wouldthe be expected if 0.18 ± # Expected CLs its cross section were 5 times the SM expectation. residual of the data with respect to the background-only fit sum Ldt = 4.9 fb 0.14 Given the narrowness0.1 of the Higgs mass peak which has a resolution approaching 1 GeV/c in 4 the classes with best resolution, 0.1 the search is carried out in steps of 0.5 GeV/c # Table 3 lists the sources of systematic uncertainty that have been taken into SM account in the 0.06 evaluation of the limits, together with the magnitude of the variation of the source that has 0.04 been applied # SM The limit set on the cross 0 section of a Higgs boson decaying to two photons using the frequentist CL S computation and an unbinned evaluation of the likelihood, is shown m H (GeV/c ) in Fig.. Figure 3 m H [GeV] shows the limit Figure relative : Exclusion to the limit SM on the expectation, cross section of where a SM Higgs the theoretical boson decaying uncertainties into two photons on the expected cross as sections a functionfrom of the the boson different mass. production mechanisms are individually included as Figure 8: The observed and expected 95% confidence level limits, normalised to the SM Higgs boson.8 (local) systematic uncertainties in the limit setting.31 procedure. (local) The fluctuations of the observed limit cross sections, as a function of the hypothesized Higgs boson mass. about the expected limit are consistent with statistical fluctuations to be expected in scanning the mass range. It has also been verified that the shape of the observed limit obtained is unchanged if the choice of background model 0.79 fitting(global) function is changed over a wide range of 1.5 (global) functional forms, although the expected limit improves by as much as % if functions with less free parameters than the 5 th Observed CLs Limit CMS preliminary order Median Expected polynomial CLs Limit -1 are used. 95% CL limit on σ/σ SM - 5 ± There is some hope this time too? ± 4 (pb) 95%CL # BR(H"!!)!) /#(H"! SM 400 # Expected CLs The results obtained from the binned evaluation of the likelihood are in excellent agreement with the results shown in Figs. and 3. 95%CL!) Figure 4 shows the local3 p-value calculated, using the asymptotic approximation, at 0.5 GeV/c "! 1# Expected CLs s = 7 TeV L = 4.76 fb

4 Back to 750! Events / 40 GeV ATLAS Preliminary Data Background-only fit -1 s = 13 TeV, 3. fb Events / ( 0 GeV ) 1-1 CMS Preliminary Data Fit model ± 1 σ ± σ -1.6 fb (13 TeV) EBEB category 1 Data - fitted background BR [fb] 95% CL Upper Limit on σ fid m γγ [GeV] 3 1 ATLAS Preliminary -1 s = 13 TeV, 3. fb Observed Expected ± 1 σ ± σ (data-fit)/σ stat m γ γ 3 (GeV) m X [GeV] signal rate : 4-5 fb? Large. Same order as the SM Higgs to diphoton rate.

5 Di-photon resonance X 0

6 Di-photon resonance X 0 - Can be spin 0 or.! Not spin-1. Landau-Yang theorem.! Completely identical to the argument of the 15 GeV di-photon resonance.! - Spin 0 is much more compelling than spin-.! Very difficult to write down a complete model of spin-.

7 How can neutral particle goes to photon, which only couples to charged particles X 0 Must be charged particles here. For the SM higgs, they are top quark and W boson Can top and/or W do it for the X(750)?

8 No. Can not (just) be top or W. 750 GeV res. can not be alone.! Must have more new physics!!

9 t, W t, W - Say X couples to top and or W, with arbitrary coupling.! BR(di-photon) is less than -4.! 4 fb to di-photon means s -0 pb to ttbar and or WW.! A factor of 4 or 5 in the production rates between 8 and 13 TeV.! ttbar and/or WW signal of at least pb at 8 TeV.

10 Possible to have pb(s) level tt or WW resonance at Run 1? - No.! final state 700 GeV 750 GeV t t (narrow) 540 fb 450 fb CMS [6] t t (wide) 60 fb 50 fb CMS [6] WW (` jj) 60 fb 70 fb ATLAS [] -Must be more new physics in addition to the 750 GeV resonances!!

11 Production - Unlikely from qqbar.! Suppressed by small quark masses, otherwise suffer from sever flavor constraints.! - Possibly (like the Higgs) X Need more new physics here as well, colored!

12 What kind of scalar? - CP even, real scalar.! Typically will mix with the Higgs.! More constraining! Decays like Higgs with tiny BR to di-photon.! Difficult to work.! - CP odd, pseudo-scalar.! Much better candidate.

13 Pseudo-scalar (η) interaction L int = y f f (if L Hf R +h.c.)+ c B g g 0 16 B µ B µ + c W g g 16 W a µ W aµ + c g g s 4 Ga µ G aµ

14 Pseudo-scalar (η) interaction with SM top L int = y f f (if L Hf R +h.c.)+ c B g g 0 16 B µ B µ + c W g g 16 W a µ W aµ + c g g s 4 Ga µ G aµ

15 Pseudo-scalar (η) interaction with SM top anomaly-like L int = y f f (if L Hf R +h.c.)+ c B g g 0 16 B µ B µ + c W g g 16 W a µ W aµ + c g g s 4 Ga µ G aµ

16 Pseudo-scalar (η) interaction with SM top anomaly-like L int = y f f (if L Hf R +h.c.)+ c B g g 0 16 B µ B µ + c W g g 16 W a µ W aµ + c g g s 4 Ga µ G aµ cg fb 5 fb fb BRHh Æ ggl shgg Æ hl 0 fb 40 fb s = 13 TeV L f = 500 GeV L g = 500 GeV L f HGeVL fb 0.5 fb 5 fb fb BRHh Æ ggl shgg Æ hl fb 0 fb s = 13 TeV L g = 700 GeV c g = fb tt 0.5 fb 1 fb c g tt c g - Need anomaly contribution for large di-photon BR.! - Will have Z! and ZZ. M. Low, A. Tesi, LTW Figure 4. The diphoton rate at 13 TeV using g = 600 GeV and c g =. The blue region is excluded by t t searches. 4 The mass scale of a pseudoscalar In this section we describe a model in which one can naturally find a pseudoscalar of mass 750 GeV. In this model, both the Higgs and the are pngbs of a global symmetry. The argument is based on the composite Higgs scenario (for a nice review, see [18]) where the lightest particles of the composite sector are pngbs. The minimal case exacts identifies the pngb multiplet with

17 Z!, ZZ the next things to look for 8 jj BRHh Æ ZgL ê BRHh Æ ggl BRHh Æ ggl shgg Æ hl = 5 fb 1 8 jj BRHh Æ ZZL ê BRHh Æ ggl BRHh Æ ggl shgg Æ hl = 5 fb 5 6 ZZ ZZ 3 cw 4 WW 0.1 cw 4 WW Zg c B Zg c B - Also WW, ttbar, hh.! - And everything under 750

18 NP models

19 Simplified models X

20 Simplified models Start with scalar X

21 Simplified models Start with scalar X Add colored NP

22 Simplified models Start with scalar X Add colored NP Add charged NP

23 Simplified models Start with scalar X Add colored NP Add charged NP MNP > 0.5 MX. Vector like fermions.

24 Mass, why 750 GeV scalar?

25 Mass, why 750 GeV scalar? - We are already puzzled by m h (15), naturalness problem.

26 Mass, why 750 GeV scalar? - We are already puzzled by m h (15), naturalness problem. - Now another (pseudo)scalar?! Can make things much worse.! Not controlling weak scale masses in an obvious way. Even landscape may not help.

27 Mass, why 750 GeV scalar? - We are already puzzled by m h (15), naturalness problem. - Now another (pseudo)scalar?! Can make things much worse.! Not controlling weak scale masses in an obvious way. Even landscape may not help. - However, the 750 GeV pseudo-scalar may be the first hint of a natural theory.

28 Take a page from SM Scale factor/ p π 0 DECAY MODES Fraction (Γ i /Γ) Confidence level (MeV/c) γ (98.83±0.034) % S= ±

29 Take a page from SM Scale factor/ p π 0 DECAY MODES Fraction (Γ i /Γ) Confidence level (MeV/c) γ (98.83±0.034) % S= ± - π 0 of a new QCD?! - Will have many other mesons (typically s), will carry SM quantum numbers (colored, etc).

30 Take a page from SM Scale factor/ p π 0 DECAY MODES Fraction (Γ i /Γ) Confidence level (MeV/c) γ (98.83±0.034) % S= ± - π 0 of a new QCD?! - Will have many other mesons (typically s), will carry SM quantum numbers (colored, etc). Λ= TeV : new gluon and quarks TeV(s), resonances η: 750 GeV

31 Take a page from SM Scale factor/ p π 0 DECAY MODES Fraction (Γ i /Γ) Confidence level (MeV/c) γ (98.83±0.034) % S= ± - π 0 of a new QCD?! - Will have many other mesons (typically s), will carry SM quantum numbers (colored, etc). Λ= TeV : new gluon and quarks TeV(s), resonances η: 750 GeV Natural. But mass no relation with weak scale.

32 Composite Higgs Λ= TeV : new gluon and quarks m* TeV(s), resonances η: 750 GeV Higgs. m ' N cy t m 3 f. m ' 700 GeV m 3/ 600 GeV 1/. 1.3 TeV f Natural to have 750 with reasonable parameters

33 Di-photon rate in composite Higgs tt BRHh Æ ggl shgg Æ hl kh fb fb 4 fb 3 fb 7 fb 9 fb 5 fb f HGeVL

34 Di-photon rate in composite Higgs tt BRHh Æ ggl shgg Æ hl Can explain the excess kh fb fb 4 fb 3 fb 7 fb 9 fb 5 fb f HGeVL

35 New QCD vs composite Higgs branching ratio tt gg bb gg c g c g = 1, c w = 0 Zg ZZ branching ratio tt gg bb c g c g = 1, c w = 0 gg Zg ZZ - The presence of ttbar.! - Presence of top-partner.

36 Alternative: -step decay! If m a << MX 750 GeV, LHC may not be able to resolve the two photons. So it could be a di-photon resonance. X X May need m a < GeV. No compelling reason.! Life time of a challenging a a!!! Knapen et al Strassler et al

37 Alternative: -step decay! If m a << MX 750 GeV, LHC may not be able to resolve the two photons. So it could be a di-photon resonance. X X May need m a < GeV. No compelling reason.! Life time of a challenging a a!!! - Good straw man to test experimentally.! Knapen et al Strassler et al - Need a lot more new physics to complete the story.

38 Big picture - Likely to be a (pseudo)scalar at 750 GeV.! - Large rate to di-photon. Need additional new physics!! Both charged and colored.! Perhaps around 500 GeV to TeV-ish, exact range model dependent.! - Looking good for being part of a natural theory.! New physics span over a decade of energy beyond TeV.

39 Beyond the LHC, future facilities ILC in Japan CLIC Circular. Scale up LEP+LHC ~0 TeV pp collider FCC-hh (CERN), SppC(China) 50 GeV e e + Higgs Factory FCC-ee (CERN), CEPC(China)

40 Big ring ++ - The motivation for having a very large ring, with the goal of a super proton collider with higher energy (s to 0 TeV), would be super strong.! Completely unravel a new layer of new physics.! Another 50+ years exciting discoveries.! - Lepton colliders, such as CLIC(to lesser extent the ILC), can cover some ground, especially the new charge particles. But unlikely the full story.

41 For example: composite Higgs 1 ξ=1 LHC HL-LHC ILC TLEP / CLIC 8 FCC-ab -1 g ρ 6 FCC-1ab -1 4 HL-LHC m ρ [TeV]

42 For example: composite Higgs preferred 1 ξ=1 LHC HL-LHC ILC TLEP / CLIC 8 FCC-ab -1 g ρ 6 FCC-1ab -1 4 HL-LHC m ρ [TeV]

43 For example: composite Higgs preferred 1 ξ=1 LHC HL-LHC ILC TLEP / CLIC 8 FCC-ab -1 g ρ 6 FCC-1ab -1 4 HL-LHC new resonances m ρ [TeV]

44 For example: composite Higgs preferred 1 ξ=1 LHC HL-LHC ILC TLEP / CLIC 8 FCC-ab -1 g ρ 6 FCC-1ab -1 4 HL-LHC new resonances m ρ [TeV] new strong integration new gluon and quarks