Transcript Slide 1

Searches for Non-SM Higgs at the Tevatron
Thomas Wright
University of Michigan
on behalf of the CDF and DØ Collaborations
• This talk: neutral MSSM Higgs searches
• More exotic Higgs to follow (M. Mulhearn)
XLIIIth Rencontres de Moriond
QCD and High Energy Interactions
March 8-15, 2008
Higgs in the MSSM
• In the standard model, one complex doublet = four scalar fields
– Three turn into W/Z mass  one physical scalar
• Minimal Supersymmetric Standard Model (MSSM) requires two doublets
– One couples only to up-type fermions, the other only to down-type
– Ratio of VEV’s - “tanb”
– Eight scalar fields – three for W/Z mass = five physical scalars
– Three neutral (h, H, A), two charged (H±)
• Properties of the Higgs sector largely determined by two parameters:
– mA : mass of pseudoscalar
– tanb : ratio of VEV’s
– Higher-order effects introduce other SUSY parameters
(benchmark scenarios, see Carena et al., hep-ph/0511023)
• Typically, mh < mA < mH , and mH± ~ mA
• For tanb near 1, h is SM-like and light – SM Higgs limits apply
• Larger tanb and light mA shows more interesting behavior
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Higgs at High tanb
3
b
Processes involving bottom quarks
(down-type) can be enhanced
(goes like tan2b)
0
0
Boost from femtobarns to picobarns
b
Could be observable at Tevatron!
0 = h/H/A
b
via top loop
H = SM Higgs
here, H = A or h/H
Higgs at High tanb
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• Neutral sector
simplifies at high tanb
• A and h/H become
degenerate
• Other scalar SM-like,
low cross section
• Only need to search for
a single mass peak ()
• For the A and its twin h/H, at high tanb decays into bb (90%)
and tt (10%) dominate
• So, for example, won’t see enhancement in HWW* channel
• CDF and DØ are searching in both of these decay modes
The   tt Channel
• Unique final state – can look for inclusive  production
• Main backgrounds: Z  tt, W+jets, dibosons
• One tau decays leptonically: e/m (CDF) or m (DØ) (plus n’s)
– pT > 10 GeV/c (CDF), 15 GeV/c (DØ)
• Other tau hadronic (both) (and nt)
– One or three tracks (Sqtrk = ±1), opposite to lepton
– CDF : isolation 30°, shrinking t cone (10°  3°)
– DØ : three types (p±, p±p0, 3-prong), NN score
• No electron veto (allows em)
– pT > 15 GeV/c (1-prong), 20 GeV/c (3-prong)
• Also tt  em (CDF), pT > 10, 6 GeV/c
• Reject non-tt background
– Lepton and missing energy
inconsistent with W
– HT cut (CDF) or kinematic NN (DØ)
Multiple neutrinos  can’t
reconstruct tt mass very well
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th ID
t cone
isolation
CDF tt Results
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Moriond 2007, CDF 1 fb-1
mvis (GeV/c2)
Last year at this time, CDF
had a >2s excess around
160 GeV/c2 (<2s over all m)
• Updated Fall 2007 with an
additional 0.8 fb-1 of data
• No excess in e/m + thad
channel after update
mvis (GeV/c2)
CDF tt Results
No apparent excess in em
channel either
Set s x BR limits
mvis (GeV/c2)
mvis (GeV/c2)
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DØ tt Results
• Visible mass (like CDF)
• Just one input to search NN, along
with lepton, tau kinematics
• Do not see any excess
(as was the case last winter)
• Set s x BR limits
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MSSM Interpretation
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DØ btt 340 pb-1
Interpret s x BR limits as limits on tanb
vs mA in MSSM benchmark scenarios
• More data and analysis improvements on the way
• Project missing momentum onto t axes for boosted Higgs (improve mtt)
• Split into b-tagged and untagged samples (already demonstrated by
DØ)
• Updated results from DØ in tt and btt channels coming soon!
The bb Channel
b quark pT >20 GeV/c, |h|<2
with bb, 3b total
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too much
0
background
b
b
0
Dawson, Jackson, Reina, Wackeroth
hep-ph/0603112
b
• Inclusive H  bb is too hard due to QCD background
• Require one additional bottom quark jet besides the two from Higgs decay
– “3b” channel best compromise between signal and background rates
B-Jet Identification
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CDF
• CDF : displaced vertices
with Lxy/s cut
• Vertex mass separation
• DØ : combine vertex
properties and displaced
track info with NN
• Tag to h beyond 2
DØ
DØ 3b Channel
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• Result with 0.9 fb-1 (2006),
update coming soon!
• Search uses invariant mass of
the two leading jets m01 in
triple-tagged events
• Derive background shape from
double-tagged sample
• Correct for kinematic bias of
third jet tag
• Normalize background to data
in sideband region, look inside
the signal window
• No excess observed, set limits
on s x BR
mH = 120
CDF 3b Channel
• New result for Moriond QCD 2008,
using 1.9 fb-1
• Search in mass of two lead jets m12
• Backgrounds are events with two
true b-tags, and a b/c/fake tag
• Characteristic m12 spectra for each
• Start from bb+jet sample
(corrected double-tags), weight
events by flavor hypothesis
• Correct bbb and bcb shapes for
double/triple-tag selection bias
– Largest systematic error
• Fit the observed m12 spectrum with
the backgrounds and a Higgs shape
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CDF 3b Channel
• Improve prediction of total
background m12 using tag
properties
• Invariant mass of tracks in
each vertex mj
• m1+m2 : bbb+bbx / bcb+bqb
• m3 : bbx / bbb+bcb+bqb
• Unstack into 1D variable “xtags”
for plotting/fitting
• Fits are 2D – m12 vs xtags
• Four backgrounds
• Higgs signal template
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CDF 3b Results
• No significant excess observed
• Set limits on s x BR
• Background systematics limiting
improvement at low mH
• Focus of the next round
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MSSM Interpretation
• Interpret in MSSM scenarios
• Include effect of Higgs width
(~20% for tanb = 100)
• Lose sensitivity (lower S/B)
• Lowers event yield
• Best limits obtained in scenarios
with m < 0 (loop enhancements)
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Summary
• CDF and DØ are looking hard for neutral MSSM Higgs bosons
– Lots of progress but no discovery as of yet
• Techniques are well-advanced but still room for improvement
– Taus: split samples to improve mtt and S/B with b-tagging
– 3b: background shape systematics (CDF)
• DØ updates on all three channels (tt, btt, 3b) coming soon
• Combination of experiments/channels is planned
• Results today use 1-2 fb-1,
expect 5-6 by 2009 (7 by 2010?)
• Could probe down to tanb in
the 20’s with full Run II samples
• Or, with the right mA and tanb,
make a discovery!
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Backup Material
Charged Higgs
• CDF : use dilepton, l+jets (single and
double-tagged), and lepton+tau s’s
• Consider H+  tn, cs, t*b, W+bb
• Map out allowed and excluded regions
in mH+ vs tanb using CPsuperH and CDF
simulation to predict effects on top s’s
• Search in top decays
• t  H+b
• DØ : ration of cross
sections l+jets/dilepton
• BR(t  H+b) < 0.35 @
95% CL (for H+  cs)
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CDF tt Projections
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