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Higgs Searches at the LHC: An Experimenter’s Perspective. Robert Cousins, UCLA 31 st Johns Hopkins Workshop on Current Problems in Particle Theory Heidelberg, 2 August 2007. Four Excellent Talks <2 Weeks Ago at EPS. ... And many more at SUSY07!.
Robert Cousins, UCLA
31st Johns Hopkins Workshop on Current Problems in Particle Theory
Heidelberg, 2 August 2007
... And many more at SUSY07!
BSM can change this in many ways, e.g. ,gg→Hbb.
Note: tot ~ 1011 pb, b ~ 109 pb, jet > 100 GeV ET > 106 pb
Need control regions in data to understand bkgnd.
BSM: γγ, , and bb changed in many ways, even within MSSM (M. Carena et al., hep-ph/0202167).
For effective Lagrangian approach to BSM ggHγγ, see Manohar and Wise, hep-ph/0601212: can be “dramatic”.
4T central B,
-2T in return yoke
Figure from VBF studies by Asai, et al., Eur Phys J C 32, s02, s19-s54 (2003), also showing ATLAS TDR results. Since superseded in some modes. ttH re-examined by Cammin and Schumacher.
For γγ, L. Carminati at PhysLHC-06 Cracow), NLO cuts analysis with K factors: S~6 from 120 to 140 GeV.
CMS Physics TDR (2006), and refs therein. Work continues; VBF -> WW re-examined; ttH pessimistic.The Approximate State of the Art in M.C. Studies
with K factors
LHC: ~1 fb-1 in 2008, increasing to 100 fb-1/year at design luminosity.
How safe is this? How to control? How to convince skeptics with more info than a mass peak?
CMS optimized: Artificial Neural Net with kinematics and g isolation as input, s/b per event
ATLAS likelihood: pT, angles
Significance for SM Higgs MH=130 GeV for 30 fb-1, NLO:
CMS Physics TDR: 6.0 cut-based, 8.2 optimized
ATLAS: 6.3 cut-based, 30-40% better with likelihood
tt and Zbb bkgnds reduced by isolation, impact parameter cuts: both to be understood from data.
...with much richer potential information.
... or with θ’s measured in Z frames
See Rainwater (2007) and refs therein, incl. VBF extension...
Not for the first year!
No color string to snap in central region
Asai, et al., Eur Phys J C 32, s02, s19-s54 (2003).
CMS Physics TDR, full sim and reconstruction
Asai, et al. (2003). ATLFAST.
... VBF needs further study in all modes.
Proving to be a very tough channel.
J.Cammin and M.Schumacher ATL-PHYS-2003-024:
S/sqrt(B) = 2.8, MH = 120 GeV, 30 fb-1 , being revisited.
CMS NOTE 2006/119
A. Djouadi, arXiv:hep-ph/0503173
Dominant production is at a tbH vertex. For heavy H:
For lighter H, on-shell tt production following by tHb.
Decays mostly to for mass < 180 GeV; tb mode opens above but seems hopeless, so remains the focus.
Tau polarization opposite to tau’s from W decay: useful handle!
Events are complex, with complex backgrounds (tt, tW, W+jets); b jets must be understood; some current search strategies are dominated by systematic errors.
Current effort is on how to reduce systematic errors with subsidiary measurements, ratios. (SM top, Z, etc.)
Refs: CMS Physics TDR; Mohn et al., ATL-PHYS-PUB-2007-006
Re-emphasizes importance of early SM studies of b quarks (in copious tt production) and tau’s (in Z), and modes such as Zbb.
Subsequent decay modes studied: μμ, ττ
Status in CMS Physics TDR:
ATLAS update for μμ: S. Gentile, et al., arXiv:0705.2801v1
Invisible Higgs decays ?
Possible searches: tt H ℓnb qqb + PTmiss
Z H ℓℓ + PTmiss
qq H qq + PTmiss
- J.F. Gunion, Phys. Rev. Lett. 72 (1994)
- D. Choudhury and D.P. Roy, Phys. Lett. B322 (1994)
- O. Eboli and D. Zeppenfeld, Phys. Lett. B495 (2000)
All three channels have been studied:
key signature: excess of events above SM backgrounds with large PTmiss ( > 100 GeV/c)
Experimental issues similar to the rest in this talk: resolution, tag jets, photon ID and isolation, b-tagging, background measurement.
NNLO calculation is not always needed for initial discovery of di-object resonance.
Nor do you initially need absolute rate to 5%.
How much does one want to rely on multi-variate techniques for early discovery physics at LHC?
How to do the controls?
CDF: “The question arises to which extent the results of the Matrix Element (ME), the Likelihood Function (LF), and the Neural Networks (NN) techniques are compatible... our compatibility measure ...is 0.65%.” [same data!]
D0: 3.4 “first evidence”
Note multi-b production.
More precise measurements and more precise theoretical calculations move into spotlight.
To many for discussions and references, including: