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LHC Searches from a Heavy Light Higgs
Jessie SheltonYale University
arXiv:1112.4996 with Y. Bai, P. Draper work in progress with M. Graesser
U. Michigan Higgs Symposium, April 19, 2012
What we’ve learned after 5 fb-1
• (Hints of) a SM-like Higgs boson around 125 GeV...
• ...and not much else
What we’ve learned after 5 fb-1
Mass scale [TeV]-110 1 10 210
Oth
erEx
cit. f
erm
.Ne
w qu
arks
LQV'
CIEx
tra d
imen
sions
llqmVector-like quark : NC, q!lmVector-like quark : CC, jjmColor octet scalar : dijet resonance, µµ
m)=1) : SS dimuon, µµ"L±± (DY prod., BR(HL
±±H (LRSM, no mixing) : 2-lep + jetsRW
Major. neutr. (LRSM, no mixing) : 2-lep + jets,WZT
mlll), !Techni-hadrons : WZ resonance (µµee/mTechni-hadrons : dilepton, #µ
m resonance, #-µExcited muon : #em resonance, #Excited electron : e-jjmExcited quarks : dijet resonance,
jet#m-jet resonance, #Excited quarks : ,missTE : 1-lep + jets + 0A0 + At t" exo. 4th gen.TT
Zbm Zb+X, "'bNew quark b' : b'
WtWt"4d4
generation : dth4 WbWb"4u
4 generation : uth4
WqWq"4Q4
generation : Qth4jj!µjj, µµ=1) : kin. vars. in !Scalar LQ pairs (jj!=1) : kin. vars. in eejj, e!Scalar LQ pairs (µT,e/mSSM W' : µµee/mSSM Z' :
,missTEuutt CI : SS dilepton + jets + ll
m combined, µµqqll CI : ee, )
jjm($qqqq contact interaction :
)jjm($
Quantum black hole : dijet, F Tp%=3) : leptons + jets, DM /THMADD BH (
ch. part.N=3) : SS dimuon, DM /THMADD BH (jetsN,
Tp%=3) : multijet, DM /THMADD BH ( tt
m l+jets, " t=-0.20 : tsg/qqgKK
gRS with llll / lljjm = 0.1 : ZZ resonance, PlM/kRS with
llm = 0.1 : dilepton, PlM/kRS with ##m = 0.1 : diphoton, PlM/kRS with
,missTE + ##UED :
Large ED (ADD) : diphotonLarge ED (ADD) : monojet
)Q/m! = qQ&Q mass (coupling 760 GeV (2011) [1112.5755]-1=1.0 fbL
)Q/m! = qQ&Q mass (coupling 900 GeV (2011) [1112.5755]-1=1.0 fbL
Scalar resonance mass1.94 TeV (2011) [ATLAS-CONF-2012-038]-1=4.8 fbL
massL±±H355 GeV (2011) [1201.1091]-1=1.6 fbL
(N) < 1.4 GeV)m mass (RW2.4 TeV (2011) [Preliminary]-1=2.1 fbL
) = 2 TeV)R(WmN mass (1.5 TeV (2011) [Preliminary]-1=2.1 fbL
))T'(m) = 1.1 T(am, Wm) + T((m) =
T'(m mass (
T'483 GeV (2011) [Preliminary]-1=1.0 fbL
) = 100 GeV)T((m) - T)/T'(m mass (T)/T
'470 GeV (2011) [ATLAS-CONF-2011-125]-1=1.1-1.2 fbL
*))µ = m(** mass (µ1.9 TeV (2011) [ATLAS-CONF-2012-023]-1=4.8 fbL
= m(e*))*e* mass (2.0 TeV (2011) [ATLAS-CONF-2012-023]-1=4.9 fbL
q* mass3.35 TeV (2011) [ATLAS-CONF-2012-038]-1=4.8 fbL
q* mass2.46 TeV (2011) [1112.3580]-1=2.1 fbL
) < 140 GeV)0(AmT mass (420 GeV (2011) [1109.4725]-1=1.0 fbL
b' mass400 GeV (2011) [Preliminary]-1=2.0 fbL
mass4d480 GeV (2011) [Preliminary]-1=1.0 fbL
mass4u404 GeV (2011) [1202.3076]-1=1.0 fbL
mass4Q350 GeV (2011) [1202.3389]-1=1.0 fbL
gen. LQ massnd2685 GeV (2011) [Preliminary]-1=1.0 fbL
gen. LQ massst1660 GeV (2011) [1112.4828]-1=1.0 fbL
W' mass2.15 TeV (2011) [1108.1316]-1=1.0 fbL
Z' mass2.21 TeV (2011) [ATLAS-CONF-2012-007]-1=4.9-5.0 fbL
*1.7 TeV (2011) [1202.5520]-1=1.0 fbL
(constructive int.)*10.2 TeV (2011) [1112.4462]-1=1.1-1.2 fbL
*7.8 TeV (2011) [ATLAS-CONF-2012-038]-1=4.8 fbL
=6)+ (DM4.11 TeV (2011) [ATLAS-CONF-2012-038]-1=4.7 fbL
=6)+ (DM1.5 TeV (2011) [ATLAS-CONF-2011-147]-1=1.0 fbL
=6)+ (DM1.25 TeV (2011) [1111.0080]-1=1.3 fbL
=6)+ (DM1.37 TeV (2010) [ATLAS-CONF-2011-068]-1=35 pbL
KK gluon mass1.03 TeV (2011) [ATLAS-CONF-2012-029]-1=2.1 fbL
Graviton mass845 GeV (2011) [1203.0718]-1=1.0 fbL
Graviton mass2.16 TeV (2011) [ATLAS-CONF-2012-007]-1=4.9-5.0 fbL
Graviton mass1.85 TeV (2011) [1112.2194]-1=2.1 fbL
Compact. scale 1/R (SPS8)1.23 TeV (2011) [1111.4116]-1=1.1 fbL
(GRW cut-off)SM3.0 TeV (2011) [1112.2194]-1=2.1 fbL
=2)+ (DM3.2 TeV (2011) [ATLAS-CONF-2011-096]-1=1.0 fbL
Only a selection of the available mass limits on new states or phenomena shown*
-1 = (0.04 - 5.0) fbLdt, = 7 TeVs
ATLASPreliminary
ATLAS Exotics Searches* - 95% CL Lower Limits (Status: March 2012)
A heavy light Higgs and physics beyond the Standard Model
• Physics beyond the SM so far is not showing up in easy and/or standard channels.
• Higgs: most sensitive piece of SM to new physics
• If we believe 125 GeV excesses are a SM-like Higgs, what channels does this suggest for new physics in 2012?
(Everyone in this room has their own answers!)
H
125 GeV + nothing else (yet)
• Heavy: no LEP constraints; (almost) anything goes!
Picture I:
New physics is SM-singlet, communicates only through Higgs portal
• Light Higgs: chance to observe light hidden degrees of freedom directly
H
125 GeV + nothing else (yet)
Picture II:
Weakly coupled EWSB, but SUSY EW scale stabilization mechanism is either tuned or non-standard
• Light Higgs: SUSY models are still sensible
• Heavy: ...but many minimal models look strained
I. Rare decays of a light Higgs
A light Higgs is narrow
• For , total width of SM Higgs is tiny:
[GeV]HM100 120 140 160 180 200
Bran
chin
g ra
tios
-310
-210
-110
1bb
cc
gg
Z
WW
ZZ
LHC
HIG
GS
XS W
G 2
010
[GeV]HM100 200 300 1000
[GeV
]H
-210
-110
1
10
210
310
LHC
HIG
GS
XS W
G 2
010
500
• light SM-like Higgs very sensitive to existence of new light degrees of freedom
mH<∼ 2mW
⇒
Rare decays of a light Higgs
Λ � m2 � v2
Λ = 0.05Λ = 0.1
0 20 40 60 800.0
0.2
0.4
0.6
0.8
1.0
ma
BR�SM�
• Even relatively small couplings to new sectors can disrupt Higgs branching fractions by
• New physics may well show up at the LHC first in rare decays of the Higgs
• Not necessarily hopeless! SM sensitivity is driven by rare modes
O(1)
Lint = λa2|H|2
Higgs to invisibles
• Will study invisibles: comprehensive update
• aim: estimate LHC sensitivity in low (i.e: not 14 TeV) run
• Example of many issues generic to study of rare decays:
• trigger considerations
• systematic uncertainties
H →
Spotting an invisible Higgs
• Weak boson fusion offers best signal to background (Eboli, Zeppenfeld ’00)
• Final state :
• Large GeV triggerable
• jet kinematics are set by EW process and distinctive
• WBF reference cuts:
• jets are energetic, GeV, TeV
• jets are widely separated,
• dominant scattering process does not involve QCD relatively little other jet activity
2j + E/T
E/T >∼ 100
pT >∼ 30 Mjj>∼ 1
∆ηjj > 4
⇒
Signal and backgrounds
• Dominant physics background: jets,
• both Drell-Yan and WBF processes are important
• jets where the lepton is lost is numerically as important
• Mismeasured QCD background is challenging to estimate
• suppress by MET quantity ( 100 GeV) and quality (Min 0.5) cuts
• finally, rate is so large that it contributes to reach despite small acceptance
Z+ Z → νν̄
W+
gg → H
E/T >∼∆φ(ji, �p/T ) >
Setting Limits
• Purely a counting experiment: systematic uncertainties critical for setting limits
• Theoretical predictions for WBF processes under excellent control
• Theoretical uncertainties on Z + jets still uncomfortably large: model from data
• But: natural control sample Z + jets, Z statistics limited
• New idea pioneered by jets + MET SUSY searches at CMS: use reweighted photon + jets
→ �+�−
Reweighting photons for Z+jets
from Bern et al. ’11
RatioZ + 2j +X
γ + 2j +Xis stable (Bern et al, ’11)
Expect we are in the region where this works:
• MET requirement similar to existing studies
• MET quality cut removes collinear region
Allows 10% precision on V+jets backgrounds
∆φ
Sensitivity to invisible Higgs
120 130 140 150 160 170
1.00
0.50
0.20
0.30
0.70
mH
!"
BR
inv!!
SM
95# CL limits with 20 fb$1
at 7 TeV
Projected 95% CL limits on for 20 fb-1 at 7 TeVassuming 10% uncertainty on V+jets and 5% uncertainty on WBF processes
σ ×BR(h → inv)
stat only
theory syst.
20% syst
30% syst
120 130 140 150 160 170
1.00
0.50
0.20
0.30
0.70
mH
!"
BR
inv!!
SM
Sensitivity to invisible Higgs
Projected 95% CL limits on for 20 fb-1 at 7 TeVas a function of systematic error
σ ×BR(h → inv)
Update to 8 TeV coming...
Final comments about an invisible Higgs
• LHC experiments will be able to probe significantly below 1 in 2012
• ZH associated production can help extend reach
• enough to be interesting? Getting started...
• Invisible decay mode has two challenges: large EW background and lack of a mass feature
• Other rare decay modes may be more striking: 10% branching fractions not necessarily out of reach
• Triggers are not automatic (Strassler)
BR(H → inv)
II. Natural SUSY Spectra and Direct Stop Pair Production
A light Higgs and no SUSY signals
• Evidence for SM-like elementary Higgs, but gluinos and (degenerate) light squarks constrained to be TeV
• Main motivation for weak scale supersymmetry is electroweak hierarchy. Little hierarchy?
• Natural SUSY: particles tied directly to the weak scale
>∼
__________________
__________________
______
200
500
1200
200
500
1200
m�GeV
�
H̃
t̃1, t̃2b̃1
g̃
Searches in a natural SUSY spectrum
• If gluino is out of reach: direct stop pair production, more challenging (rate!)
• Near-degenerate Higgsinos all appear as (mostly) MET
• Charged and neutral branching fractions of squarks are similar:
�1.0 �0.5 0.0 0.5 1.0
0.2
0.4
0.6
0.8
cos Θt
BR�t 1�
b
t
left rightright
µ = 200tanβ = 20
�1.0 �0.5 0.0 0.5 1.0
0.2
0.4
0.6
0.8
cos Θt
BR�t 2�
right leftleft
b
t
µ = 200tanβ = 20
• If gluino is out of reach: direct stop pair production, more challenging (rate!)
• Near-degenerate Higgsinos all appear as (mostly) MET
• Charged and neutral branching fractions of squarks are similar:
Searches in a natural SUSY spectrum
�1.0 �0.5 0.0 0.5 1.0
0.2
0.4
0.6
0.8
cos Θb
BR�b 1�
left rightright
⇒ t b+ E/T
b
t
µ = 200tanβ = 20
• If gluino is out of reach: direct stop pair production, more challenging (rate!)
• Near-degenerate Higgsinos all appear as (mostly) MET
• Charged and neutral branching fractions of squarks are similar:
Searches in a natural SUSY spectrum
Direct stop pair production
t̃1
χ0 χ0
t̃∗1t̄
b̄
�+
ν
b
χ−Final state: b b �+ E/T
Unlike SM backgrounds (and unlike searches) the signal has asymmetric kinematics
t t̄+ E/T
0.0 0.2 0.4 0.6 0.8 1.0r�pT�
stops
top
r(pT ) =pT1 − pT2
pT1 + pT2
Top background
0 100 200 300 400mT�l,MET�
stops
dileptonic tops
semileptonic tops Main background: dileptonic tops with a missed lepton
• semileptonic tops, as well as Wbb, eliminated after cutting on mT
Unit-normalized transverse mass distributions
Strategies to suppress dileptonic top? (Kats, Meade, Reece, Shih ’11; Bai, Cheng, Gallicchio, Gu ’12)
Reducing dileptonic top background
Dileptonic top: have enough mass shell constraints to completely reconstruct the event
Reducing dileptonic top background
Dileptonic top: have enough mass shell constraints to completely reconstruct the event
After losing a lepton, no longer true.
Can instead choose solutions that minimize:• •
√s
Meff
• Discriminant based on goodness of reconstruction efficiently separates signal and background
Reducing dileptonic top backgrounds
-based discriminant evaluated on showered events takes b-tagged jet and leading non-tagged jet as input; keeps best assignment
�10 �5 0 5 10 15Log S
t b+ E/T
t t̄+ E/T
t t̄
√s
Concluding comments about light stops
• Direct stop pair production is challenging, but one of the most motivated targets
• Minimal natural SUSY spectrum has unique collider phenomenology which can be exploited
• Ideas for controlling large dileptonic top backgrounds can help in many similar searches
• Stay tuned for more results!
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