1. Higgs Searches at the Tevatron (Run I)
Lorenzo Moneta
University of Geneva
on behalf of
CDF and D collaboration
Introduction
SM Higgs
ZH & WH with H  bb (CDF & D)
MSSM Higgs
bbf with f=H0,h0,A0 (CDF)
H+ (CDF & D)
Fermiophobic Higgs
H  gg (CDF & D)
Conclusions
Lorenzo Moneta
Moriond QCD March 2001

2. Introduction
Electroweak Symmetry breaking in the SM predicts existence of an Higgs boson but with unspecified mass
Higgs mass constraints scale  where SM might break down
if  = MPlank then 130 < M(H) < 180
Current Status of Higgs searches
SM fit to Electroweak data indicates a light Higgs
M(H) < ~ % CL
Direct searches from LEP2
95 % CL limit is ~ 113 GeV
Indication of Higgs-like events
in the last year data:
excess ~ 3 at M(H) 115 GeV
Lorenzo Moneta
Moriond QCD March 2001

3. proton-antiproton collision @ s = 1.8 TeV
Tevatron (Run I)
Tevatron
proton-antiproton s = 1.8 TeV
CDF DØ
Silicon Vertex Detector
Run I (Oct. 92  Feb. 96)
total integrated luminosity
~ pb / detector
Expected ~ 2 fb-1 in Run IIa !
Lorenzo Moneta
Moriond QCD March 2001

4. SM H0 production @ Tevatron
Gluon Fusion
too difficult (QCD background)
Higgsstrahlung
SM cross section is very small
1/20 s(t-tbar)
1/500 s(Z/W +  2 jets)
possible with Run II luminosity !
larger s with new physics ??
LEP
s = 0.70 pb
for M(H) = 120 Gev/c2
with QCD NLO correction
WH: s = 0.16 pb
ZH: s = 0.10 pb
Vector Boson fusion
radiation off heavy quark
very small s in the SM
Lorenzo Moneta
Moriond QCD March 2001

5. SM Higgs decays M(H) < 130 GeV M(H) > 130 GeV dominant decay is
final states are for W/ZH
need lepton ID/MET + b-tags
M(H) > 130 GeV
final state with  2 leptons
but smaller cross-section
interesting at RunII !
LEP
For M(H) = 120 GeV/c2
Lorenzo Moneta
Moriond QCD March 2001

6. SM H signatures (W /Z + H)
Tevatron Run I channels : (W/Z + H with M(H) < 130 GeV)
BG: QCD multijets
BG:
BG: QCD,
( 50% of W/Z H )
( 9% )
( 5.4%)
( 1.8%)
Essential for these analyses:
b tagging
good di-jet mass resolution
Lorenzo Moneta
Moriond QCD March 2001

7. b tagging at the Tevatron
Techniques developed for top analyses. Two algorithms:
Soft Lepton Tagging (SLT) (CDF & DØ)
semileptonic b decays:
DØ: m ( pT > 4 GeV) CDF: m & e (pT > 2 GeV)
Secondary Vertex Tagging (SVX) (CDF)
reconstruct a displaced vertex in the jet
b lifetime ~ 1.5 ps  decay length ~ few mm
use capability of Silicon vertex detectors b
e,µ (in jets)
e(b-tag) ~ 7%/b-jet
e(mistag) ~ 0.5%/jet
s(decay-length) ~ 100 mm
b jet
e(b-tag) ~ 20%/b-jet
e(mistag) ~ 0.2%/jet
secondary vertex
primary vertex
Lorenzo Moneta
Moriond QCD March 2001

8. Search for mbb Final states are lepton (e/m) + MET + b’s
Event selection:
high pTlepton: pT(lep) > 20 GeV & h<1
MET>20
2 jets with ET(j)>15, h<2
b-tags (single OR double jet tag)
Backgrounds:
Results (CDF & D) 106 pb-1
CDF
1 b-tag
2 b-tags
mbb
~ 0.2 – 0.3 % 6
3  1
2 b-tags
CDF
~ % 27
25  3
1 b-tag D
~ 0.6 – 0.8 % 36
30  5
Br x accept.
(90<m(H)<130)
data
backg
channel
Exp.
from fit to di-jets mass:
95% CL Limit on sBR:
26-28 pb for 90<MH<130 (CDF)
40-19 pb for 90<MH<120 (D)
Lorenzo Moneta
Moriond QCD March 2001

9. Search for Final states is MET + b’s Event selection (CDF):
MET>40 (trigger >35) + lepton veto
2 or 3 jets with ET(j)>15,  <2
DF(MET,j) > 60° for all jets (ET>8)
DF(j1,j2) < 150°
b-tags (single OR double)
Backgrounds:
QCD and
Results (88 pb-1)
~ 0.4 – 0.5 % 4
4  1
2 b-tags
CDF
~ 0.5 – 0.8 % 40
39  4
1 b-tag
Br x accept.
(90<m(H)<130)
data
backg
channel
Exp.
95% CL Limit on sBR:
~ 8 pb for 90<MH<130
Lorenzo Moneta
Moriond QCD March 2001

10. Search for mbb Final states is di-leptons + b’s Event selection (CDF):
pT(lep)>20,10 GeV
76<M(l,l)<106 GeV
2 or 3 jets with ET(j)>15, h<2
MET < 50 GeV (against top di-lepton evts)
1 b-tag
Backgrounds:
Results (106 pb-1)
mbb
~ 0.2 % 5
3  1
1 b-tag
CDF
Br x accept.
(90<m(H)<130)
data
backg
channel
Exp.
95% CL Limit on sBR:
56-24 pb for 90<MH<130
Lorenzo Moneta
Moriond QCD March 2001

11. Search for mbb Multi-jet final state with b’s Event selection (CDF):
Multi-jets trigger
 4 jets with SET>125 GeV & ET>15
double b-tag
pT(bb)>50 GeV
Backgrounds:
mainly QCD (b’s + fakes)
also top and Z + jets
Results (91 pb-1)
mbb
~ 1.5 – 2.9 %
589
~ 600
2 b-tag
CDF
Br x accept.
(90<m(H)<130)
data
back.
channel
Exp.
95% CL Limit on sBR:
30-16 pb for 90<MH<130
 Need good Mbb resolution against background
Lorenzo Moneta
Moriond QCD March 2001

12. Combined limit for SM Higgs
CDF combination of
95 % CL limit on
slimit = pb
for mH = GeV/c2
x 30 SM cross-section (mH = 115)
Limit is dominated by nnbb
Expected best limits from:
nnbb and lnbb
poor lnbb limit due to a small excess in observed events
Need more luminosity
RUN II
LEP SM
115
Lorenzo Moneta
Moriond QCD March 2001

13. MSSM Higgs Search Two Higgs doublets in the MSSM 5 Higgs particles
two neutral CP-even: h0,H0
One neutral CP odd: A0
Two charged: H+,H-
two free parameters: tanb and mA
Mass relations at tree level:
m(h0) < m(Z0) < m(H0); m (A0) < m(H0); m(H+) < m(W)
but after radiative corrections m(h0) < 130 GeV
Couplings at large tanb:
enhanced to d-type quark and leptons
suppressed to u-type quark
Lorenzo Moneta
Moriond QCD March 2001

14. MSSM Higgs production s(pb) s(pb) Small tanb : Large tanb ¯ ¯ ¯ ¯ ¯
SM-like cross-sections
Large tanb
enhanced hbb coupling
hbb/Hbb/Abb can have large cross-sections ( tan2b)
In general dominant Higgs’s Branching Ratio are to bb (90%) and t+t- (10%)
Lorenzo Moneta
Moriond QCD March 2001

15. Search for
Exploit enhanced Yukawa couplings looking for bb production (j = h,HA)
large cross sections ( tanb2)
4-b’s jets final state
Event selection (CDF):
Multi-jets trigger
4 jets with S(ET)>125 GeV & ET>15
ET(j) cuts depending on m(j)
 3 b-tags
DF(bb) > 109° (against gbb)
Backgrounds:
QCD (bb/cc), Z/Wjj, top
CDF results (91 pb-1)
0.28 % 2
3.5  1.1
120
0.59 %
0.1  0.4
300
0.16 % 5
4.6  1.4 70
Br x accept.
data
backg
BR x acc.
M(j) (GeV)
Lorenzo Moneta
Moriond QCD March 2001

16. Limit for Limit (95%CL for Mj = 100 GeV):
convert sBR limit in tanb vs Higgs mass exclusion
No mixing & Maximal Mixing for the stop
sBR < 25.7 pb
tanb vs m(h)
tanb vs m(A)
Tevatron complements LEP !
Lorenzo Moneta
Moriond QCD March 2001

17. Charged Higgs Searches
Searches for t H+b when M(H+) < mt - mb
decay t H+b can compete with SM decay t W+b
BR(t H+b) depends on tanb
Direct Search (CDF):
look for H+  tn in t-tbar evts
BR(H+  tn) ~ 1 for large tanb
WHbb or HHbb channels in addition to WWbb
look for l + t + MET + jj events (l = e,m,t)
use t identifications via hadronic decays (tracking + calorimeter)
backgrounds:
Z  tt + jj, W+3 jets, WW/WZ
acceptances for single and double H production
Lorenzo Moneta
Moriond QCD March 2001

18. Charged Higgs Searches
Indirect Search (CDF + D)
look for lepton disappearance in t-tbar events
suppression of dileptons and lepton + jets events
rate of the two depends on BR(t  H+b)
t-tbar cross-section independent of m(H), tanb
given measured x-section (when BR(t  H+b) = 0)
exclusion regions in the
m(H+)-tanb plane D0
LEP2 (ADLO)
New Exclusion regions at low and high tanb
Lorenzo Moneta
Moriond QCD March 2001

19. Fermiophobic Higgs In some models Higgs couples only to vector bosons
BR(H  gg) dominant for light Higgs (m(H) < 100)
Searches for W/Z + H  ggjj
D search:
di-photons + jets
Backgrounds from QCD
fakes or real g in jets
CDF search
di-photons with e/m + MET or jj
Limit For SM cross-section:
M(H) > ~ 80 GeV (95% CL)
LEP limit is ~ 105 GeV D0
Lorenzo Moneta
Moriond QCD March 2001

20. Conclusions SM Higgs searches are luminosity limited in Run I
no sensitivity to SM cross sections
no excess seen and set limits at ~30 SM cross-section
provided experience for Run II
developed techniques for low mass Higgs searches
b tagging and di-jet mass resolution are crucial !
good expectations for Run II
see next talk on Run II prospects
Nice exclusion results for MSSM Higgs:
bbj search with sensitivity for high tanb region
charged Higgs from t  H+b
probed regions inaccessible to LEP
very interesting in Run II
report of the Tevatron Higgs Working Group (hep-ph/ )
Lorenzo Moneta
Moriond QCD March 2001