Alexei Safonov (Texas A&M University)For the CDF Collaboration

*Higgs Searches at CDF

“Higgs Searches at CDF”, A. Safonov, Aspen, CO, February 14, 2012 2

*Outline*Brief introduction to Higgs search strategies at the Tevatron*Summer 2011 combination and ingredients*New CDF analyses since Summer 2011*Ongoing work and plans*Summary

“Higgs Searches at CDF”, A. Safonov, Aspen, CO, February 14, 2012 3

*Higgs Production at Tevatron*Dominated by gluon fusion

*But large decay modes often come with large backgrounds

*Associated Production*While smaller cross section, offers cleaner final states

*Vector Boson Fusion (VBF) *Even smaller cross-section, but can help increase the overall sensitivity

*Have to use all accessible modes and many decay channels*Improving analysis techniques

“Higgs Searches at CDF”, A. Safonov, Aspen, CO, February 14, 2012 4

*Higgs Search Strategies*Sensitivity strongly depends on

backgrounds for a specific channel:*“High mass” m >~135 GeV:*WW (and ZZ) decay modes *Clean final states with leptons, any

production mode will do*“Low mass” m < ~135 GeV:*Associated production WH/ZH: *Rely on leptons/neutrinos to reduce

background, go after all decay modes (but bb dominates)

*Gluon fusion: *H→bb overwhelmed by backgrounds*H→tt:ok, but small BR

“Higgs Searches at CDF”, A. Safonov, Aspen, CO, February 14, 2012 5

*Summer 2011 Combination

*Of course LHC results since then excluded masses above ~135 GeV

“Higgs Searches at CDF”, A. Safonov, Aspen, CO, February 14, 2012

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*Ingredients of the Combination*High mass region

dominated by H→WW*Low mass region:*WH+ZH→MET+b

b*WH→lnbb*ZH→llbb*H→WW makes

key impact above 120 GeV

H→WW

ZH→llbb

VH→MET+bb

WH→lnbb

“Higgs Searches at CDF”, A. Safonov, Aspen, CO, February 14, 2012 7

*Selected Recent Analyses

“Higgs Searches at CDF”, A. Safonov, Aspen, CO, February 14, 2012 8

*Search for H→ with 10 fb-1*One of very recently updated results

*Follows the same technique as the 7 fb-1 analysis*At least one central photon ET>25

GeV*Many improvements including NN ID

for central photons, converted photon recovery in central region

*Fit for a bump plus a smooth curve (from the rest of the distribution after excluding 12 GeV window around searched Higgs mass)*Each of 4 categories separately

“Higgs Searches at CDF”, A. Safonov, Aspen, CO, February 14, 2012 9

*Search for H→ with 10 fb-1*Combine four channels at the

level of likelihoods*Bayesian limits for mH)<130

GeV at ~12xs(SM) except m~120 GeV*Previous limit used in the

combination was ~14-19xs(SM)

“Higgs Searches at CDF”, A. Safonov, Aspen, CO, February 14, 2012 10

*Search for H→tt w/ 1+ Jets*Result from Fall’11, L=8.3 fb-1

*Allow multiple production modes *Sensitivity dominated by VH (H→tt,

V→jets)*Channels: e/m+t+1jet, e/m+t+≥2jets, e+m+1jet,

e+m+≥2jets,

*Deploy Support Vector Machine (SVM) to discriminate against main backgrounds using event kinematics properties:*Z→tt+jets

*tt-bar (only for em+jets channel)

*QCD muti-jets

*Fit the distribution for the SVM outcome to extract limits (or claim discovery if there is significant excess)

“Higgs Searches at CDF”, A. Safonov, Aspen, CO, February 14, 2012 11

*SVM-Based H→tt Search Limits*Final exclusion limit is obtained by combining the four

channels at the level of likelihoods *Observed limit about 12xs(SM)*Combined limit is dominated by e/m+t+≥2jets channel

“Higgs Searches at CDF”, A. Safonov, Aspen, CO, February 14, 2012 12

*Search for H→tt Using MMC *Also a recent analysis using L=7.8

fb-1

*Traditional cut-based search, but attempts to improve di-tau mass reconstruction using MMC technique* Elagin, Murat, Pranko, and A.S., NIM A654, 481

(2011)

*MMC uses likelihood to solve an under-constrained system of equations*Uses Bayesian-like priors to pick

solutions consistent with tau decay kinematics and experimental uncertainties in measuring MET*A large improvement over collinear

approximation as MMC can handle back-to-back events (and no tail)

“Higgs Searches at CDF”, A. Safonov, Aspen, CO, February 14, 2012 13

*Search for H→tt Using MMC *Attempt to minimize systematic

uncertainties due to backgrounds by measuring normalizations from data*Require one of two taus to decay leptonically, another hadronically *No e+m events in this search

*Define 8 channels: *(1 or 3 prong) x (e/m) x (0/1+jets)*Count jets with ET>30 GeV

*Fit ditau mass reconstructed with MMC for signal + background

e+th channelNpr(t)=1

e+th channelNpr(t)=3

Njet=0

Njet=0

“Higgs Searches at CDF”, A. Safonov, Aspen, CO, February 14, 2012 14

*Search for H→tt Using MMC

e+th channelNpr(t)=1

m+th channelNpr(t)=3

m+th channelNpr(t)=1

e+th channelNpr(t)=3

Njet>0

*Use of MMC equivalent to ~x1.6 more data vs transverse mass*Sub-channel with Njet>0 is sensitive to VH production, reach can

be further improved by utilizing kinematics selections (will be in 10 fb-1 analysis)

“Higgs Searches at CDF”, A. Safonov, Aspen, CO, February 14, 2012 15

*Search for H→tt Using MMC *Combined limit of 8 channels:

~14xs(SM)@m=115 GeV/c2

*0-jet and “1+”-jet channels complementary*Updated analysis will use improved event

kinematics discrimination

“Higgs Searches at CDF”, A. Safonov, Aspen, CO, February 14, 2012 16

*Near Future Plans

“Higgs Searches at CDF”, A. Safonov, Aspen, CO, February 14, 2012 17

*Are We Done Yet?*Luminosity used in key

channels:*H→WW: 8.2 fb-1

*WH+ZH→MET+bb: 7.8 fb-1

*WH→lnbb: 7.5 fb-1

*ZH→llbb: 7.5-7.9 fb-1

*Less in secondary channels: weighted luminosity for low mass searches is ~7.5 fb-1

*CDF full certified dataset is now 10 fb-1

*Expect updated analyses showing up at La Thuile, Tevatron combination is more likely to be shown at Moriond

*Expect sensitivity scaling better than 1/sqrt(L) due to ongoing improvements to analyses

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*Tevatron and LHC Expectations *Why bother if the LHC

expects to settle the question by the end of 2012?*Will we know if what we

found is indeed the SM Higgs?*E.g. branching for H→bb:* Current CMS expected limit is

3-4xs(SM) for the bb channel*Complementary sensitivity in

the very low mass range*E.g. plot on the right: region

below 120 seems already excluded by CMS+Tevatron*Tevatron data will allow important cross-checks and help

answer questions that may not be answered by the LHC alone until after the long shutdown in 2012

“Higgs Searches at CDF”, A. Safonov, Aspen, CO, February 14, 2012 19

*Summary*CDF is busy updating its results to include the full 10 fb-1 dataset*Numerous improvements to analysis techniques are expected to improve sensitivity beyond just √L*Expect to see individual analyses at La Thuile, combination is

more likely to be first presented at Moriond*Apart from complementarity to global LHC+Tevatron sensitivity, Tevatron results will have an impact on our understanding the nature of Higgs should it be discovered at the LHC in 2012*One example is sensitivity to the H→bb mode, which is an important check-mark in distinguishing between SM non-SM Higgs cases