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Bounding the Higgs Width using Interferometry

Bounding the Higgs Width using Interferometry. Lance Dixon (SLAC) with Ye Li [1305.3854] and Stefan Höche RADCOR2013, Lumley Castle, England Sept. 25, 2013. Introduction. O ften said that LHC cannot measure the width of the Higgs boson.

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Bounding the Higgs Width using Interferometry

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  1. Bounding the Higgs Width using Interferometry Lance Dixon (SLAC) with Ye Li [1305.3854] and Stefan Höche RADCOR2013, Lumley Castle, England Sept. 25, 2013 RADCOR2013

  2. Introduction • Often said that LHC cannot measure the width of the Higgs boson. • However, using interference with the continuum background for gggg, it will be possible to put an upper limit on the Higgs width that is much better than ~ 1-5 GeV possible directly. • It may eventually be possible to get close to the Standard Model width of 4 MeV. • Similar idea can work for ggZZ, far from Higgs resonance Kauer; Caola, Melnikov, 1307.4935 RADCOR2013

  3. Schrödinger’s Higgs How to use quantum superposition to learn something new about the Higgs (its lifetime) RADCOR2013

  4. Narrow resonance interference shifts peak position (apparent mass) shifts peak height (event yield)  or spin 2 “G” (assume) dominantly real RADCOR2013

  5. Interference effects and G LD, Y. Li 1305.3854 • All non-interference measurements at LHC give signal proportional to ci2 . cf2/ G • Invariant under scaling all ci,funiformly, ci,fxci,f G  x4G • Interference effects go like ci . cf, break this degeneracy • Allow one to measure or bound Higgs width RADCOR2013

  6. Mass shift from real part S. Martin, 1208.1533, 1303.3342; D. de Florian et al, 1303.1397 Smear lineshape with Gaussian with width s = 1.7 GeV  Perform least squares fit to Gaussian at mass M + dM dM~ 100 MeV in SM at LO RADCOR2013

  7. Diagrams for NLO mass shift LD, Y. Li, 1305.3854 Bern, de Freitas, LD, hep-ph/0109078 RADCOR2013

  8. Mass shift at NLO • Reduced by 40% from LO LD, Y. Li, 1305.3854 • Interference increases, but signal increases more RADCOR2013

  9. NLO mass shift vs. jet veto pT RADCOR2013

  10. NLO mass shift vs. lower cut on Higgs pT Also S. Martin 1303.3342 • Big cancellation between gg and qg channel at large pT • Allows use of pT> 30 or 40 GeV sample as “control” mass RADCOR2013

  11. Two other possible control masses • ZZ*  4 leptons • Mass in ggin VBF enhanced sample LD, S. Hoeche, Y. Li, in progress • In general, comparing two ggmasses could reduce systematics associated with e genergy calibration. Kauer, Passarino, 1206.4803 RADCOR2013

  12. Mass shift increases with G • Allows one to measure or bound Higgs width • All non-interference measurements at LHC give signal proportional to ci2 . cf2/ G • Interference effects go like ci . cf, break degeneracy of scaling all ci,funiformly, ci,fxci,f G  x4G RADCOR2013

  13. Coupling vs. width • Coupling product cg . cg= cgg determined by requiring that event yield is unaffected: • Ignoring I, RADCOR2013

  14. Mass shift vs. width • Measurement statistically limited now, ~ 800 MeV • Systematically limited in HL-LHC era, ~ 100-200 MeV RADCOR2013

  15. What about spin 2? LD, Höche, Li, to appear • Rejection of spin 2 vs. spin 0 relies on distribution in cosq* for gggg. • Without interference, this is ~ 1 spin 0 ~ 1 + 6 cos2q* + cos4q* 2m+ • How much distortion from interference effects? • SM Higgs: < few % LD, Siu, hep-ph/0302233 ATLAS, 1307.1432 RADCOR2013

  16. Strong helicity dependence of Im part of background 1-loop amplitude + Spin 0 - - - + + + Im = O(mq2/mH2) ~ 0 + Dicus, Willenbrock (1988) Non-minimal spin 2 can interfere with other helicity amplitudes, but only this helicityconfig. has Im part - Spin 2m+ + + Im = O(1) - RADCOR2013

  17. (spin 2) - 1-loop interferencesimple G RADCOR2013

  18. Im part remarkably flat in cosq LO pT cut RADCOR2013

  19. Size of interference as function of width G • Event yield ~ • Normalize to SM Higgs • at photon pTcut = 40 GeV. • Quadratic equation for • Constructive, • destructive solutions • Completelymodel • independent with respect • to coupling strengths, • other channels. RADCOR2013

  20. Spin 2 yield might be strongly affected– even if cosq* distribution is not RADCOR2013

  21. Conclusions • Interference effects, in particular the mass shift in gg, allow the possibility of bounding the Higgs width to well under the direct experimental resolution, maybe eventually approaching the SM width. Now under study experimentally. • A few possible control masses. • In principle, interference effects also important for testing non-SM hypotheses – e.g. spin 2 in gg. In practice, distortion of the cosq* distribution is very small where it is measurable. RADCOR2013

  22. Spin-2 mass shift from real part Smear lineshape with Gaussian with width s = 1.7 GeV. Do least squares fit to Gaussian at mass M + dM. RADCOR2013

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