Post on 08-Jul-2020
How Wide is the Higgs Boson:off-shell constraints from CMS
Andrei Gritsan
Johns Hopkins University
May 29, 2014
LBNL Research Progress Meeting
Overview
• Introduction
• The Higgs boson
• How we see it
• Off-shell production
• Data analysis
– H → Z∗Z∗ → 4ℓ
– H∗ → ZZ → 4ℓ
– H∗ → ZZ → 2ℓ2ν
• Theoretical considerations
• Summary and outlook
Andrei Gritsan, JHU II May 29, 2014
A FEW SLIDES OF HISTORY
July 2012: Observation of a New Boson
• Observation of a New Boson on CMS: 5σ excess
X → Z(∗)Z(∗) X → γγ
• Probability of background
∼ 0.2× 10−6
Higgs boson mass (GeV)116 118 120 122 124 126 128 130
Loca
l p-v
alue
-1210
-1110
-1010
-910
-810
-710
-610
-510
-410
-310
-210
-110
1σ1σ2
σ3
σ4
σ5
σ6
σ7
Combined obs.
Exp. for SM H
γγ →H
ZZ→H
WW→H
CMS Preliminaryγγ ZZ + WW + →H
-1 = 7 TeV, L = 5.1 fbs-1 = 8 TeV, L = 5.3 fbs
Andrei Gritsan, JHU IV May 29, 2014
July 2012: Observation of a New Boson
• Observation of a New Boson on ATLAS: 5σ excess
X → Z(∗)Z(∗) X → γγ
[GeV]4lm100 150 200 250
Even
ts/5
GeV
0
5
10
15
20
25
30
35
-1Ldt = 4.8 fb∫ = 7 TeV: s-1Ldt = 5.8 fb∫ = 8 TeV: s
4l→(*)ZZ→H
Data(*)Background ZZ
tBackground Z+jets, t=125 GeV)
HSignal (m
=150 GeV)H
Signal (m=190 GeV)
HSignal (mSyst.Unc.
Preliminary ATLAS
100 110 120 130 140 150 160
Eve
nts
/ GeV
0
200
400
600
800
1000
1200
1400
1600
1800
2000
2200
2400
Data 2011 and 2012 = 126.5 GeV)
HSig + Bkg inclusive fit (m
4th order polynomial
Selected diphoton sample
-1 Ldt = 4.8 fb∫ = 7 TeV, s
-1 Ldt = 5.9 fb∫ = 8 TeV, s
ATLAS Preliminary
[GeV]γγm
100 110 120 130 140 150 160
Dat
a - B
kg
-100
0
100
• Probability of background
∼ 0.2× 10−6
[GeV]Hm
110 115 120 125 130 135 140 145 150
0Lo
cal p
-710
-410
-110
210
510
810
Exp. Comb.
Obs. Comb.γγ →Exp. H
γγ →Obs. H
llll→ ZZ* →Exp. H
llll→ ZZ* →Obs. H
νlν l→ WW* →Exp. H
νlν l→ WW* →Obs. H
bb→Exp. H
bb→Obs. H
ττ →Exp. H
ττ →Obs. H
ATLAS Preliminary 2011 + 2012 Data = 7 TeVs, -1 L dt ~ 4.6-4.8 fb∫ = 8 TeVs, -1 L dt ~ 5.8-5.9 fb∫
σ0 σ1 σ2
σ3
σ4
σ5
Andrei Gritsan, JHU V May 29, 2014
The Higgs Boson Signal on CMS
• Excellent signal H → ZZ,WW, γγ, τ+τ−, bb̄
6.8, 4.3, 3.2, 3.2, 2.1σ
(6.7, 5.8, 3.9, 3.7, 2.1σ expected)
Andrei Gritsan, JHU VI May 29, 2014
Discovery of a Higgs Boson
• Discovery of a Higgs Boson
– absolutely new form of matter-energy
– consistent with fundamental JP = 0+
scalar excitation of a vacuum field
• It would be foolish to stop here
– mass (is Universe stable, are EW data consistent?..)
– width / lifetime (are there missing final states?)
– quantum numbers (is there CP violation?..)
– coupling strength in production and decay (is it the right Higgs?..)
• It is also a triumph of predictive power of scientific knowledge
– we knew where to look
– but a discovery was not guaranteed, also true for the next steps
Andrei Gritsan, JHU VII May 29, 2014
The Higgs→ ZZ → 4ℓ Signal on CMS
Andrei Gritsan, JHU VIII May 29, 2014
The Higgs→ ZZ → 4ℓ Signal on CMS
Andrei Gritsan, JHU IX May 29, 2014
The Higgs→ ZZ → 4ℓ Signal on CMS
Andrei Gritsan, JHU X May 29, 2014
TOPIC FOR TODAY
References for Today Presentation
• ”Constraints on the Higgs boson width
from off-shell production and decay to Z-boson pairs”
CMS-HIG-14-002 (Moriond - 2014), arXiv:1405.3455 [hep-ex]
submitted to PLB on May 14, 2014
• ”Measurement of the properties of a Higgs boson
in the four-lepton final state” (CMS H → ZZ Run1 ”legacy”)
CMS-HIG-13-002 (Moriond - 2013), arXiv:1312.5353 [hep-ex]
published in PRD,89,092007 on May 14, 2014
• ”Higgs Working Group Report
of the Snowmass 2013 Community Planning Study”
arXiv:1310.8361 [hep-ex]
Andrei Gritsan, JHU XII May 29, 2014
The Large Hadron Collider
Andrei Gritsan, JHU XIII May 29, 2014
The CMS Detector
• Complex detector
to sort collision debris out
Andrei Gritsan, JHU XIV May 29, 2014
The CMS Detector
Total weight 12500 t
Diameter 15 m
Length 22 m
Magnetic field 4 T
Andrei Gritsan, JHU XV May 29, 2014
The Experiment
Andrei Gritsan, JHU XVI May 29, 2014
Detection of Major Objects
• Leptons: ℓ± in Si Tracker: e± (EM Calorimeter), µ± (Muon System)
• Photons: γ (EM Calorimeter)
• Quark q & gluon g jets → ”Particle Flow” thru Hadronic Calorimer
• Neutrinos ν ⇒ missing energy (”MET”)
ZZ → (µ+µ−)(νν̄)
Andrei Gritsan, JHU XVII May 29, 2014
Production and Decay of a Higgs Boson
• Excite vacuum: gg, VBF,.. → H → ZZ(∗), WW (∗), γγ, τ+τ−, bb̄,..
[GeV] HM80 100 200 300 400 1000
H+
X)
[pb
]
→(p
p
σ
-210
-110
1
10
210= 8 TeVs
LH
C H
IGG
S X
S W
G 2
01
2
H (NNLO+NNLL QCD + NLO EW)
→pp
qqH (NNLO QCD + NLO EW)
→pp
WH (NNLO QCD + NLO EW)
→pp
ZH (NNLO QCD +NLO EW)
→pp
ttH (NLO QCD)
→pp
[GeV]HM80 100 120 140 160 180 200
Hig
gs B
R +
Tot
al U
ncer
t
-410
-310
-210
-110
1
LH
C H
IGG
S X
S W
G 2
013
bb
ττ
µµ
cc
gg
γγ γZ
WW
ZZ
gg→Hqq→qqH
V→V H
Andrei Gritsan, JHU XVIII May 29, 2014
Signal and Background
• At LHC might have produced > 200000 Higgs bosons / experiment
gluon fusion weak boson fusion associated production
• The challenge is to distinguish signal from backgrounds, examples:
qq̄ → ZZ(∗)(γ(∗)) qq̄ → Z(γ)+jets gg→ tt̄
Andrei Gritsan, JHU XIX May 29, 2014
Track / Mass Resolution
• H → ZZ → (ℓ+ℓ−)(ℓ+ℓ−)
– excellent mass resolution ∼ 1%
– good control with Z, J/ψ → ℓ+ℓ−
– measure mass mH and width ΓH
Andrei Gritsan, JHU XX May 29, 2014
Fit mass and width of Higgs→ ZZ → 4ℓ
• Employ a 3D fit
m4ℓ – invariant mass
Dkinbkg – MELA (matrix element likelihood) to suppress background
δm4ℓ – per-event error estimate on invariant mass
(GeV)l4m
120 130 140 150 160 170 180
bkg
kin
D
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
0.05
0.1
0.15
0.2
0.254e
µ4
µ2e2
CMS-1
= 8 TeV, L = 19.7 fbs ; -1
= 7 TeV, L = 5.1 fbs
Andrei Gritsan, JHU XXI May 29, 2014
Test with Z → 4ℓ
• Excellent candle Z → ℓ+ℓ−γ∗ → ℓ+ℓ−ℓ+ℓ−
mZ = 91.12± 0.37 GeV (compare PDG 91.19 GeV)
ΓZ = 3.6+1.0−0.8 GeV (compare PDG 2.50 GeV)
Andrei Gritsan, JHU XXII May 29, 2014
Mass H(126)
• Employ a 3D fit
mH = 125.6± 0.4 (stat.)± 0.2 (syst.) GeV
Andrei Gritsan, JHU XXIII May 29, 2014
Width H(126)
• Employ a 3D fit
ΓH = 0.0+1.3−0.0 GeV < 3.4 GeV at 95% CL
expect ΓSMH = 0.00415 GeV at mH = 125.6 GeV
Andrei Gritsan, JHU XXIV May 29, 2014
CAN WE DO BETTER?
Off-shell effects
• mH = 125.6 GeV < 2mZ = 182.4 GeV
⇒ H → Z(∗)Z∗ with off-shell Z∗ ⇒ suppression
• Higgs boson remains on shell dσgg→H→ZZ
dm2ZZ
∼g2ggHg
2HZZ
(m2ZZ −m2
H)2 +m2
HΓ2H
Andrei Gritsan, JHU XXVI May 29, 2014
Higgs off-shell effects
100
2 MW
2 MZ 2 Mt 1000
10−6
10−5
10−4
10−3
10−2
10−1
WW
ZZ
HTO powered by complex - pole - scheme
8 TeV
MV V [ GeV]
M2 VV
dσ
dM
2 VV
[pb]
• Sizeable off shell H
gg → H → Z(∗)Z∗
on shell H, suppressed Z∗
gg → H∗ → ZZ
suppressed H∗, on shell Z
N. Kauer, G. Passarino
arXiv:1206.4803 [hep-ph]
MC: gg2VV, LO in QCD
Tot [pb] mZZ > 2mZ [pb] R[%]
gg → H → all 19.146 0.1525 0.8
gg → H → ZZ 0.5462 0.0416 7.6
Andrei Gritsan, JHU XXVII May 29, 2014
Higgs boson width from off-shell production
dσgg→H→ZZ
dm2ZZ
∼g2ggHg
2HZZ
(m2ZZ −m2
H)2 +m2
HΓH2
• On peak (mZZ ∼ mH) and off peak (mZZ −mH ≫ ΓH)
F. Caola, K. Melnikov: arXiv:1307.4935 [hep-ph]
σonpeakgg→H→ZZ = constg2ggHg
2HZZ
ΓH
σoffpeakgg→H→ZZ = const′ g2ggHg2HZZ
⇒ measurement of ΓH
• Complication: signal - background destructive interference
Andrei Gritsan, JHU XXVIII May 29, 2014
Higgs boson width from off-shell production
σonpeakgg→H→ZZ = constg2ggHg
2HZZ
ΓH
σoffpeakgg→H→ZZ = const′ g2ggHg2HZZ
• Given the signal strength at the peak µ = σ/σSM
⇒ off-shell signal ∝ ΓH , interference ∝√ΓH
Andrei Gritsan, JHU XXIX May 29, 2014
Monte Carlo Simulation (off shell)
100100100 200200200 300300300 400400400 500500500 600600600 700700700 800800800 900900900 100010001000
000
0.20.20.2
0.40.40.4
0.60.60.6
0.80.80.8
1.01.01.0
1.21.21.2
NNLO
LO
HHH virtuality [ GeV]
Lin
eshape
by Giampiero
arXiv:1312.2397
• gg → ZZ(∗)/Zγ∗ gg2VV and
MCFM: J. Campbell, K. Ellis, C. Williams
arXiv:1311.3589 [hep-ph]
– LO in QCD, Pythia shower
– running QCD scale µR,F = mZZ/2
– uncertainties µR,F ∈ [mZZ ,mZZ/4]
– signal K-factor ∼ 2
– bkg K-factor = signal K ±10%
(soft-collinear approximation arXiv:1304.3053 for gg → WW )
• No references for width studies in VBF: V ∗V ∗ → ZZ(∗)
use Phantom: A. Ballestrero et al., arXiv:0801.3359 [hep-ph]
• Generate sig, bkg, sig+bkg+interference ⇒ extract interference
match signal on-peak cross-section to best knownAndrei Gritsan, JHU XXX May 29, 2014
Monte Carlo Simulation
[GeV]T
p0 50 100 150 200 250
0
0.05
0.1
• On-shell signal MC arXiv:1309.4819
– NLO QCD production POWHEG
– H → V V → 4f decay JHUGen
– anomalous couplings with JHUGen
spin-0, 1, 2, qq̄, gg, VBF, V H, H2j
• Dominant qq̄ → ZZ background
– NLO QCD POWHEG
NLO EW re-weighting
follow arXiv:1307.4331, arXiv:1305.5402
−(5− 10)% in 220− 500 GeV range
∼ 40% uncertainty on the correction
Andrei Gritsan, JHU XXXI May 29, 2014
Use Kinematics to Suppress Background
• One challenge is the dominant qq̄ → ZZ background
• Follow the same approach as at the Higgs discovery
MELA technique
(Matrix Element Likelihood Approach)
to suppress qq̄ → ZZ
vs gg → ...→ ZZ
MELA > 0.5
Andrei Gritsan, JHU XXXII May 29, 2014
Matrix Element Likelihood Approach
Andrei Gritsan, JHU XXXIII May 29, 2014
Matrix Element Likelihood Approach
Andrei Gritsan, JHU XXXIV May 29, 2014
Matrix Element Likelihood Approach
vs.
• Optimal discriminant to separate gg → ZZ vs qq̄ → ZZ
Dgg =Pgg
tot
Pggtot + Pqq̄
bkg
=
1 +Pqq̄
bkg
10×Pggsig +
√10× Pgg
int + Pggbkg
−1
MCFM - continuum, JHUGen - onpeak signal, analytical
• Higgs discovery:
Dkinbkg =
P0+
P0+ + Pqq̄bkg
• Higgs spin-parity:
DJP =P0+
P0+ + PJP
Andrei Gritsan, JHU XXXV May 29, 2014
Kinematics
• MELA Dgg(mZZ ,mZ1,mZ2, cos θ1, cos θ2, cos θ∗,Φ,Φ1)
Andrei Gritsan, JHU XXXVI May 29, 2014
H∗ → ZZ → 4ℓ Mass after Kinematic Selection
• Optimal use of kinematic information
before after Dgg > 0.65
Andrei Gritsan, JHU XXXVII May 29, 2014
Semileptonic Channel H → ZZ → 2ℓ2ν
• Partial reco, but ×5.5 higher branching
⇒ comparable to 4ℓ sensitivity at high mass
but no hope at low mass (overwhelmed with Z+jets background)
m2T =
[
√
pT,2ℓ2 +m2ℓ2 +
√
EmissT
2+m2ℓ
2
]2
−[
~pT,2ℓ + ~EmissT
]2
Andrei Gritsan, JHU XXXVIII May 29, 2014
Semileptonic Channel H → ZZ → 2ℓ2ν
• Partial reco, but ×5.5 higher branching
⇒ comparable to 4ℓ sensitivity at high mass
but no hope at low mass (overwhelmed with Z+jets background)
m2T =
[
√
pT,2ℓ2 +m2ℓ2 +
√
EmissT
2+m2ℓ
2
]2
−[
~pT,2ℓ + ~EmissT
]2
Andrei Gritsan, JHU XXXIX May 29, 2014
Look at enhanced signal region
• For illustration purpose define the enhanced signal regions
H → ZZ → 4ℓ H → ZZ → 2ℓ2ν
m4ℓ > 330 GeV, Dgg > 0.65 mT > 350 GeV, EmissT > 100 GeV
Andrei Gritsan, JHU XL May 29, 2014
Enhanced signal H → ZZ → 4ℓ and 2ℓ2ν
4ℓ 2ℓ2ν
(a) total gg (ΓH = ΓSM
H) 1.8±0.3 9.6±1.5
gg signal component (ΓH = ΓSM
H) 1.3±0.2 4.7±0.6
gg background component 2.3±0.4 10.8±1.7
(b) total gg (ΓH = 10× ΓSM
H) 9.9±1.2 39.8±5.2
(c) total VBF (ΓH = ΓSM
H) 0.23±0.01 0.90±0.05
VBF signal component (ΓH = ΓSM
H) 0.11±0.01 0.32±0.02
VBF background component 0.35±0.02 1.22±0.07
(d) total VBF (ΓH = 10× ΓSM
H) 0.77±0.04 2.40±0.14
(e) qq̄ background 9.3±0.7 47.6±4.0
(f) other backgrounds 0.05±0.02 35.1±4.2
(a+c+e+f) total expected (ΓH = ΓSM
H) 11.4±0.8 93.2±6.0
(b+d+e+f) total expected (ΓH = 10× ΓSM
H) 20.1±1.4 124.9±7.8
observed 11 91
Andrei Gritsan, JHU XLI May 29, 2014
How to Extract the Width• Relative size of low and high mass Higgs signal
– analysis at high mass ⇒ gggH gHZZ (gg→ H) or gHVV gHZZ (VBF)
– must relate to on-peak to measure Γ
• Composition of production: gg→ H vs VBF
– need to know to describe the shape
• Is the coupling gHVV(mZZ) running (anomalous)?
Andrei Gritsan, JHU XLII May 29, 2014
Extracting the Width
• Determine strength and production composition from the peak
– µggH and µVBF provide both (ratio to SM µ = σ/σSM)
Ponshelltot (~x) = µggH × [Pgg
sig(~x) + P tt̄Hsig (~x)] + µVBF × [PVBF
sig (~x) + PVHsig (~x)]
+ Pqq̄bkg(~x) + Pgg
bkg(~x) + . . .
• Relate to high mass
– ΓH is the only free parameter remaining
Poffshelltot (~x) =
µggH × ΓH
Γ0× Pgg
sig(~x) +
√
√
√
√µggH × ΓH
Γ0×Pgg
int(~x) + Pggbkg(~x)
+
µVBF ×ΓH
Γ0× PVBF
sig (~x) +
√
√
√
√µVBF ×ΓH
Γ0×PVBF
int (~x) + PVBFbkg (~x)
+ Pqq̄bkg(~x) + . . .
Andrei Gritsan, JHU XLIII May 29, 2014
CONSTRAINTS FROM THE LOW MASS
Constraints from the low mass
• Employ a 3D fit and 2 jet tagging catetories
m4ℓ – invariant mass
Dkinbkg – MELA (matrix element likelihood) to suppress background
if at least 2 jets: Djet – to identify VBF or VH (mjj, ηjj)
if <2 jets: pT (4ℓ) – to identify VBF or VH
Andrei Gritsan, JHU XLV May 29, 2014
Constraints from the low mass
• Employ a 3D fit and 2 jet tagging catetories
m4ℓ – invariant mass
Dkinbkg – MELA (matrix element likelihood) to suppress background
if at least 2 jets: Djet – to identify VBF or VH (mjj, ηjj)
if <2 jets: pT (4ℓ) – to identify VBF or VH
(GeV)l4m
120 130 140 150 160 170 180
bkg
kin
D
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
0.05
0.1
0.15
0.2
0.254e
µ4
µ2e2
CMS-1
= 8 TeV, L = 19.7 fbs ; -1
= 7 TeV, L = 5.1 fbs
Andrei Gritsan, JHU XLVI May 29, 2014
Production Mechanism Results
Ponshelltot (~x) = µggH × [Pgg
sig(~x) + P tt̄Hsig (~x)] + µVBF × [PVBF
sig (~x) + PVHsig (~x)]
+ Pqq̄bkg(~x) + Pgg
bkg(~x) + . . .
µggH = 0.80+0.46−0.36 σSM(ggH + tt̄H) = 14.99 pb + 0.085 pb
µVBF = 1.7+2.2−2.1 σSM(VBF+ V H) = 1.214 pb + 0.896 pb
µ = σ/σSM = 0.93+0.26+0.13−0.23−0.09
Andrei Gritsan, JHU XLVII May 29, 2014
CONSTRAINTS FROM THE HIGH MASS
High Mass: H → ZZ → 4ℓ
Poffshelltot (~x) =
µggH × ΓH
Γ0× Pgg
sig(~x) +
√
√
√
√µggH × ΓH
Γ0×Pgg
int(~x) + Pggbkg(~x)
+
µVBF ×ΓH
Γ0×PVBF
sig (~x) +
√
√
√
√µVBF ×ΓH
Γ0× PVBF
int (~x) + PVBFbkg (~x)
ΓH = 1.9+11.7−1.9 MeV < 33 MeV at 95% CL
expected: 4.2+17.3−4.2 MeV < 42 MeV at 95% CL
Andrei Gritsan, JHU XLIX May 29, 2014
1D Fit in H → ZZ → 4ℓ
Andrei Gritsan, JHU L May 29, 2014
High Mass: H → ZZ → 2ℓ2ν
• Combine H → ZZ → 2ℓ2ν at high mass and 4ℓ at low mass
ΓH = 1.8+12.4−1.8 MeV < 33 MeV at 95% CL
expected: 4.2+19.3−4.2 MeV < 44 MeV at 95% CL
Andrei Gritsan, JHU LI May 29, 2014
Combined Result
ΓH = 1.8+7.7−1.8 MeV < 22 MeV = 5.4× ΓSM
H at 95% CL
expected: 4.2+13.5−4.2 MeV < 33 MeV = 8× ΓSM
H at 95% CL
Andrei Gritsan, JHU LII May 29, 2014
Model (in)dependence
σonpeakgg→H→ZZ = constg2ggHg
2HZZ
Γσoffpeakgg→H→ZZ = const′ g2ggHg
2HZZ
• Higgs boson coupling HV V (gHV V )
– experimental limits prefer tree-level SM HV V coupling
– anomalous HV V couplings enhance off-shell production
⇒ conservative limit
• Higgs boson production in gluon fusion (gggH)
– top quark dominance, no new particles in the loop
• Higgs boson production mechanism
– very mild dependence (e.g. VH vs VBF), fit directly in the data
• Background model
– no BSM in background; benefit from improved SM calculations
Andrei Gritsan, JHU LIII May 29, 2014
CP Results in H → ZZ → 4ℓ
• Assumed tree-level HV V coupling either in decay or VBF production
A(HV V ) =1
v
(
a1m2V ǫ
∗1ǫ
∗2 + a2f
∗(1)µν f ∗(2),µν + a3f
∗(1)µν f̃ ∗(2),µν
)
SM Higgs 0+: (a1) CP ∼few% (a2) CP ∼10−10 ? (a3) CP6
(or beyond SM) (or beyond SM)
• Test with optimal MELA observables for many JP models, e.g. 0−
Andrei Gritsan, JHU LIV May 29, 2014
CP Results in H → ZZ → 4ℓ
• Exclude pure pseudo-scalar 0− at 99.95% CL
fa3 =σ(a3)
σ(a1) + σ(a3)= 0.00+0.17
−0.00 < 0.51 at 95%CL
• and many other models:
spin-0, 1, 2
consistent with JP = 0+
Andrei Gritsan, JHU LV May 29, 2014
Anomalous HV V Couplings and Off-shell Effects
A(HV V ) =1
v
(
g1m2V ǫ
∗1ǫ
∗2 + g2f
∗(1)µν f ∗(2),µν + g4f
∗(1)µν f̃ ∗(2),µν
)
• Higher-dimensional non-renormalizable operators lead to
σ4/σ1 blowing up at higher q2 (for pseudoscalar 0−)
same effect for 0+h , spin-2, spin-1; example of f f̄ → V ∗(q2) → V H
[GeV] s200 300 400 500 600 700 800 900 1000
[fb]
σ
1
10
210
310
410
[GeV] s200 300 400 500 600 700 800 900 1000
[fb]
σ
1
10
210
310
410
0−
0+h
0+m (SM) 0+m (SM)
arXiv:1309.4819 Analytic MELA calc.
Andrei Gritsan, JHU LVI May 29, 2014
Anomalous HV V Couplings and Off-shell Effects
• Same enhancement σi/σ1 with higher-dim. operators H∗(q2 = m2ZZ)
[GeV] ZZm200 400 600 800 1000 1200
1σ/ 4σ
0
10
20
30
40
50
60
[GeV] ZZm200 400 600 800 1000 1200
1σ/ 2σ
0
5
10
15
20
25
30
JHUGenMELA calc.
AnalyticMELA calc.
similar study also in arXiv:1403.4951 [hep-ph]
• Conclusion on anomalous HV V couplings:
– experimental data consistent with SM coupling a1
– there is still room for small anomalous contributions
– width constraint would be only tighter if those are present
Andrei Gritsan, JHU LVII May 29, 2014
Anomalous ggH Couplings
• In gg → H rely on the dominance of t-quark in the loop
– assume no new particles in the loop
– otherwise some modification to offshell / onshell ratio
Andrei Gritsan, JHU LVIII May 29, 2014
WHAT IS THE HIGGS BOSON LIFETIME
Higgs Boson Lifetime
• How long does the Higgs boson live?
τH =h̄
ΓH, expect 1.6× 10−22 s
we know it is not stable (H → ZZ, ...)
observe 0.3× 10−22 s < τH <∞
• Can we set a better upper bound?
– expect σv ∼ 50µm vertex resolution, p ∼ 50 GeV
– flight distance ∼ pmccτH ∼ 2 · 10−14 m = 20 fm ∼ 4× 10−10 × σv
could reach 0.3× 10−22 s < τH < (?) 0.4× 10−12 s <∞
Andrei Gritsan, JHU LX May 29, 2014
Summary: How Wide is the Higgs Boson?
0 < ΓH < 22 MeV = 5.4× ΓSMH at 95% CL
(0.3× 10−22 s < τH <∞)
mild assumptions (no new particles in ggH loop)
• Rich physics with the Higgs boson
– mass
– width and lifetime
– quantum numbers / CP
– production and decay couplings
• So far consistent picture
reduced room to decay to new states...
Andrei Gritsan, JHU LXI May 29, 2014