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!
SM Higgs Production than can be absorbed in the time allotted for my talk.
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.
SM Higgs decay modes than can be absorbed in the time allotted for my talk.
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 Since superseded in some modes.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.
4 s02, s19-s54 (2003), also showing ATLAS TDR results. Since superseded in some modes. ttH re-examined by Cammin and Schumacher.l bonus: Higgs JCP. Generalization of an old idea...
...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
(Weak) Vector Boson Fusion (sim with ATLFAST) s02, s19-s54 (2003), also showing ATLAS TDR results. Since superseded in some modes. ttH re-examined by Cammin and Schumacher.
Asai, et al., Eur Phys J C 32, s02, s19-s54 (2003).
(Weak) Vector Boson Fusion, s02, s19-s54 (2003), also showing ATLAS TDR results. Since superseded in some modes. ttH re-examined by Cammin and Schumacher.ττ → lepton + tau jet ...
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
Includes parity-violating sign s02, s19-s54 (2003), also showing ATLAS TDR results. Since superseded in some modes. ttH re-examined by Cammin and Schumacher.
Karl Jakobs at SUSY07 s02, s19-s54 (2003), also showing ATLAS TDR results. Since superseded in some modes. ttH re-examined by Cammin and Schumacher.
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: