Bottom-quark Fusion Processes at the LHC for Probing Z Models and B-meson Decay Anomalies

Transcription

1 Bottom-quark Fusion Processes at the LHC for Probing Z Models and B-meson Decay Anomalies My Daughter Teruki Kamon Mitchell Institute for Fundamental Physics and Astronomy Texas A&M University 26 th International Conference on Supersymmetry and Unification of Fundamental Interactions (SUSY2018) 23 rd 27 th July, Barcelona, Spain July 26, 2018 [Credits] Images of Baryon Acoustic Bscillations with Cosmic Microwave Background by E.M. Huff, the SDSS-III team, and the South Pole Telescope team. Graphic by Zosia Rostomian (Lawrence Berkeley National Laboratory) Image of Neutrino Astrophysics, taken from Image of the LHC by CERN Photo Image of Bullet Cluster by NASA/ Chandra X-ray Center B-Fusion Zprime 1

2 Prologue 4 sigma tension in flavor physics? SM BSM Nature of flavor physics? Phenomenology study: MADGRAPH5 v PYTHIA 8.2 DELPHES 3.4 R K ( ) R D ( Corpus Christi, Texas, USA arxiv: , Phys. Rev. D 97 (2018)

3 Puzzle with Anomalies in B Decays 1 Deviation at 2.4σ - 2.6σ from the SM Compatible with other anomalies observed in b sμμ transition ~4σ tension with SM New contribution? 3

4 ҧ ҧ ҧ Physics Model for B Anomalies New physics contribution can be expressed as: 2 The best fit values for C 9 is: Z in a minimal phenomenological setting is: L Z μ [g V μ μγ α μ + g V μ ν μ γ α P L ν μ + g b q= t,b Selective U(1) fermion charges to evade current LH and LEP constraints. Coupling to muons in leptonic sector and b-s in fermionic sector. Adding muon neutrino and top quark couplings to preserve SU(2). Considering tau decays തqγ α L P L q + (g b δ bs sγ α P L b + h. c. ) ] 3 4 4

5 ҧ ҧ ҧ Z Production via B-Fusion at LHC L Z μ [g V μ μγ α μ + g V μ ν μ γ α P L ν μ + g b q= t,b തqγ α L P L q + (g b δ bs sγ α P L b + h. c. ) ] 3 g b δ bs Bottom Fermion Fusion (BFF) sҧ Bottom-strange quark fusion 5

6 Production Cross Section at LHC g b δ bs sҧ Larger g b (bb fusion) 2b+2m+jets Smaller g b (bs fusion) 1b+2m+jets M Z = 350 GeV g μ = 0.13 σ Z to be consistent with anomalies in B meson decays depends on g b for larger g b or g b δ bs for smaller g b : g b δ bs gv μ 100 GeVΤM Z

7 Z μμ at ATLAS and CMS Physics Letters B 761 (2016) JHEP 06 (2018) 120 Fig. 3 Fig. 3b ~15 fb at 500 GeV R = at 500 GeV [Constraints from current inclusive di-muon resonance searches] The ATLAS limit for 500-GeV Z is ~15 fb from Fig. 3. The leptonic production for the SM Z is nb from the ATLAS paper (cf nb at DYNNLO). Thus the ATLAS limit on the cross section ratio R = 15 fb / 1.9 nb = 7.9x10^-6. The corresponding CMS limit on R is 1.4x10^-6 from Fig. 3b (CMS-EXO , CERN- EP ), which is stringent compared to the ATLAS result. SM background becomes dominant for M Z < 500 GeV. Di-jet, ttҧ resonance searches produce weaker limits. Below 500 GeV, di-muon resonance + 1 b tagged jet. 7

8 Final States at LHC Two main backgrounds: (i) SM DY γ /Z + jets, (ii) top quark production. Use ISR jets to reduce the SM background 8

9 Final States at LHC Two main backgrounds: (i) SM DY γ /Z + jets, (ii) top quark production. Use ISR jets to reduce the SM background 2 b-s fusion both b and s from gluon splitting 9

10 Final States at LHC Two main backgrounds: (i) SM DY γ /Z + jets, (ii) top quark production. Use ISR jets to reduce the SM background All jet multiplicities must be generated together to resolve ambiguities between sea bottom-quarks from the PDFs and bottomquark pairs from gluino splitting: pp > zp zp, zp > mu+ pp > zp j, zp > mu+ pp > zp j j, zp > mu+ with p = p b b~ and j = j b b~ 2 b-s fusion both b and s from gluon splitting MLM matching with xqcut = 30 and qcut = 60 for smooth DJR and being insensitive to physical observables (e.g., cross section, kinematical distributions) OS di-muon resonance + 1 b tagged jet (at least 2jets) 10

11 Search for BFF Z at LHC [Preselection] OS di-muon + 1 b tagged jet (at least 2jets) MADGRAPH5 v PYTHIA 8.2 DELPHES 3.4 (CMS card) M bμ or M μj > 170 GeV (top mass bound) H T L T < 0 (hadronic vs. leptonic activity) miss E T M μμ <

12 Unboosted m T2 - I am Number Four m T2 unboosted m T2 We didn t use the 4th requirement (unboosted m T2 ), which provides a good discrimination, but does not improve its sensitivity. 12

13 Limit Extraction g μ = 1 for calculating Z decay width The significance increases for smaller g μ. 13

14 Current & Future Constraints Allowed regions (yellow/green) in δ bs -g b M Z = 200 GeV M Z = 350 GeV M Z = 500 GeV δ bs Neutrino trident constraints g b CMS Inclusive search BFF Z search [Phys. Rev. D 97 (2018) ] 1 s.d. band for B anomalies 2 s.d. band for B anomalies 14

15 BFF Z Summary My Daughter Anomalies in B meson decays - one of hot topics Can be explained with models of Z coupling to b, s and muon. Prospects for a dedicated search for b-associated Z production by ATLAS and CMS [Phys. Rev. D 97 (2018) ]: 1) Z couples to third generation SM particles should be studied with di-muon + 1 b events via b-fusion processes and flavor violating b-s- Z process. The flavor violating b-s-z coupling introduces a minimum production cross-section. 2) The limits on σ B in the existing inclusive di-muon searches can be applied to these model parameter space. The reach can be improved by utilizing di-muon + 1 b for 350 GeV or lighter Z. 3) pp Z bb or bs and pp Z tt for further understanding of such models. 15

16 Backups 16

17 Operators and New Physics [Altmannshofer, DPF 17 talk] Dipole Operators do not break lepton universality. Scalar operators are strongly constrained by B s l + l [Alonso, Grinstein, Martin Camalich, 14] Semileptonic operators are needed. Right handed current produce anti-correlation between R k and R k* [Hiller, Schmaltz, 14] 17

18 ҧ ҧ ҧ ҧ ҧ Minimal Lagrangian: Simple Models L Z μ [g V μ μγ α μ + (g b δ bs sγ α P L b + h. c. ) ] e 2 V tb V ts 16π 2 C 9 = g b δ L bs gv μ L v2 2 2M Z Many models can generate this Lagrangian, e.g., using Vectorlike quarks (Q): e.g., Altmannshofer, Yavin, 2015, Many more references (see, arxiv: for a full list) L Z μ [g V μ μγ α μ + g V μ ν μ γ α P L ν μ + g b q=t,b തqγ α L P L q + (g b δ bs sγ α P L b + h. c. ) ] Avoid first generation coupling to Z : strong constraint O(few TeV) 18

19 Production Z is suppressed by a factor of 1/M(Z ) 2 in addition to the bottom PDF The radiative suppression is solved with g bb, but adding a gluon splitting fraction in addition to the bottom PDF Bottom quark fusion via gluon splitting to bb -- Z production associated with b jets 19

20 ҧ ҧ ҧ Z Decay Widths L Z μ [g V μ μγ α μ + g V μ ν μ γ α P L ν μ + g b q=t,b തqγ α L P L q + (g b δ bs sγ α P L b + h. c. ) ] 20

21 Some Constraints D BS =0.07 ± 0.09 Allanach, Queiroz, Strumia, Sun, 2016 Weak constraints from neutrino trident production and contributions to muon g-2 21

22 Q&A for BFF Z Models 1) We assume same couplings to bb and tt (g_b). In the simplified model, we assume the Z couples uniformly to top and bottom because of SU(2) invariance. The Lagrangian is written with (ν μ, μ) and (t, b), and δ bs, g μ and g b to explain B-meson decay anomalies, We can test via Z ( μμ) + bb and Z ( bb) + bb. Since we don t know a true nature of Z yet, using a simple framework is good enough. Once we see any excess, we can move to more detailed models. 2) We obtain a better result than current analysis (for low mass Z') by having dedicated search for Z'-->mumu + b s. The acceptance of requiring extra jets and at least one b-tag among them is of course worse than just requiring muons. But the losses in acceptance for the signal are outdone by the background suppression, most notably on the DY part (total acceptance for offshell DY events is ~10^-4 while it is ~10^-3 for ttҧ evets), when you look for smaller Z masses closer to the Z peak. Our dominant background becomes ttbar beyond around 150 GeV in our dimuon mass spectrum, as is most easily visible in Figure 3. So for higher masses, the inclusive analysis will always outdo the BFF analysis. For lower masses though, S/sqrt(S+B) looks better in this Delphes study. 22