Searches for Higgs Boson at CDF

Higgs Boson

Indirect Search for SM Higgs Boson:

In the SM, all the particles acquire its masses from its interaction with the Higgs field through the exchange of the Higgs boson. The  Higgs boson has not been observed yet experimentally. However some of its properties can be inferred from Electroweak measurements. As the Higgs boson prefers to couple to heavy particles, this means that one can learn about the Higgs boson via the measurement of the masses of the Top quark and W boson. Figure below shows the one sigma contour of the Higgs mass obtained from the latest world average measurements of the Top quark mass and the W boson mass. It seems to indicate that a lighter Higgs is preferred.

The one sigma contour of the Higgs mass extracted from Electroweak fit, and using the latest world average measurements of the Top quark and W boson masses.

Direct Searches for the SM Higgs Boson At Tevatron

SM Higgs boson can be produced in several processes, and the channels that the Higgs boson decays depends very much on its mass.  At CDF many direct searches for the SM Higgs boson are being performed. Academia Sinica has performed searches for the Higgs boson in a few final state signatures :

Missing Transverse Energy + BJets

Academia Sinica collaborates with Purdue University and  the CIEMAT Institute in Madrid, to search for the Higgs boson in the missing energy and b-jets channel. This channel contains the contributions from ZH→ννbb and from WH→lνbb (charged lepton not identified). The missing energy comes from the neutrinos in the W/Z decays, and from the un-identified charged lepton in the W decay. This channel has good sensitivity due to its relativity large predicted production cross section, and the large decay branching fraction of Z→νν.  The analysis was performed on a data sample with integrated luminosity of 1 fb-1. We find 268 (16) single (double) b-tagged candidate events, where 248 +- 43 (14.4 +- 2.7) are expected from standard model background processes. We observe no significant excess over the expected background and thus set 95% confidence level upp limit on the Higgs boson production cross section for Higgs boson masses ranging from 110 to 140 GeV/c2. For a mass of 115 GeV/c2, the observed (expected) limit is 20.4 (14.2) times the standard model prediction. These results are now published in Physical Review Letters journal ( PRL 100, 211801 (2008) ).

This result is then combined with results from other CDF searchres. The results from individual channels, and combined results are shown in Figure below.

Feynman diagrams for Higgs boson production in association with a W or Z boson.

Reconstructed di-jet invariant mass (in GeV unit). (LEFT single b-tagged, (RIGHT) double b-tagged.

Event display of a p-pbar collision event with 2 b-tagged jets and large missing transverse energy.

Summer 2007 results on the search for SM Higgs from CDF.

All-Hadronic (Multi-jets)

In this analysis Academia Sinica searched for the Higgs boson that is produced in association with a W or Z boson (associated production), or produced through the vector boson fusion process. In the associated production process, we consider the channels where the W or Z boson decays hadronically.
For both associated production and vector boson fusion channels, we consider the Higgs boson decays into a pair of b-quarks. Thus the final state contains at least four jets, with at least two b-jets. The dominant background comes from QCD multi-jet production, with a small fraction of background from ttbar, single-top, W/Z+jets and diboson. The analysis is performed on 4 fb-1 of data sample.  An innovative technique is used to estimate the background and several methods are used to increase the Higgs search sensitivity :
The latest analysis is performed with the full CDF run II data sample with L~10 fb-1.  The observed (expected) upper limit at 95% C.L. on the Higgs production cross section times branching ratio varies between 7.0 (7.6) and 26.2 (25.8) times the SM prediction for Higgs boson masses between 110 and 140 GeV/c2.
The results are published in JHEP 02 (2013) 004 and is also shown in Fermilab Today: Result of the Week .

Feynman diagrams for production and decay channels considered in the all-hadronic channel search. (LEFT, MIDDLE) Associated production, (RIGHT) Vector Boson Fusion.

NN outputlimit jjbb 10fb
(LEFT) Neural Network output distribution for the SS channel , (RIGHT) Results of the observed and expected limit of the Higgs search in the all-hadronic channel using 10 fb-1 data sample.

result of week

Published Papers / Public Notes


Last modification : April 25th 2013, Song-Ming Wang