Searches for Higgs Invisible - Vukasin Milosevic (IHEP Beijing) on behalf of the CMS Collaboration - DESY Indico
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Searches for Higgs Invisible
Vukasin Milosevic (IHEP Beijing)
on behalf of the CMS Collaboration
EPS-HEP CONFERENCE 2021
26-30.7.2021.
Introduction
Motivation
Why are we interested in the
invisibly decaying Higgs?
What are the main topologies
of interest and strategies?
Introduction
H(invisible) status
What are the previous results?
Early Run 2 combination
What is new in terms of full
Run 2 measurements?
Introduction Future projections and summary
Motivation: Why the interest for the invisibly decaying Higgs?
The ”crown jewel” of the experimental particle physics:
Higgs boson was discovered by ATLAS and CMS experiments at CERN in 2012
All of the following measurements of its properties have been consistent with the
Standard Model (SM)
Large uncertainties of these measurements can allow for physics beyond the SM
Eur. Phys. J. C 79 (2019) 421
Why the interest in
the invisible final state?
According to the SM, the probability of Br(!H → 4ν) ~ 0.1 %
Can represent a good way of testing for BSM physics!
Higgs boson could be a mediator between SM and DM sector
Detection would require it to recoil against a visible system
Vukašin Milošević 1 EPS-HEP 2021
Motivation: Why the interest for the invisibly decaying Higgs?
Higgs boson can take a role of a mediator between SM and DM particles:
Detection requires for the Higgs to recoil against a visible system
Large missing transverse energy (MET)
qqH : Higgs boson is produced in a vector boson
fusion topology (VBF)
VH: Higgs boson production with a vector boson
ggH: Higgs boson produced via gluon fusion.
Vukašin Milošević 2 EPS-HEP 2021
Motivation: Why the interest for the invisibly decaying Higgs?
Higgs boson can take a role of a mediator between SM and DM particles:
Detection requires for the Higgs to recoil against a visible system
Large missing transverse energy (MET)
qqH : Higgs boson is produced in a vector boson
fusion topology (VBF)
VH: Higgs boson production with a vector boson
ggH: Higgs boson produced via gluon fusion.
Vukašin Milošević 2 EPS-HEP 2021Motivation: Why the interest for the invisibly decaying Higgs?
Higgs boson can take a role of a mediator between SM and DM particles:
Detection requires for the Higgs to recoil against a visible system
Large missing transverse energy (MET)
qqH : Higgs boson is produced in a vector boson
fusion topology (VBF)
VH: Higgs boson production with a vector boson
ggH: Higgs boson produced via gluon fusion.
Vukašin Milošević 2 EPS-HEP 2021Motivation: VBF production mode
VBF production mode of the Higgs boson has a characteristic signature:
Two jets with a large geometrical separation
High dijet invariant mass (a good way to control S/B)
Represents a channel with the largest sensitivity
Main backgrounds:
QCD and EWK produced V+jets (where V= W/Z)
Irreducible when Z->νν and W->lν
With the charged lepton being missed in the detection
Estimated through dedicated control regions in data (CR):
Z or W boson associated with the same dijet topology
Resulting in four CRs separated by lepton flavour (e/")
QCD multi jet processes - data driven estimation
Vukašin Milošević 3 EPS-HEP 2021Motivation: VH production mode
Mono V channel: Mono Jet channel:
Main characteristics: Main characteristics:
Energetic jets - due to V(qq) A jet originating from ISR
Imbalance in MET due to Interpreted as ggH production
undetected particles associated with one jet
Z(ll)H channel:
Main characteristics:
The production of a lepton
pair originating from Z(ll)
A large MET
Vukašin Milošević 4 EPS-HEP 2021Motivation: VH production mode
Mono V channel: Mono Jet channel:
Main characteristics: Main characteristics:
Energetic jets - due to V(qq) A jet originating from ISR
Imbalance in MET due to Interpreted as ggH production
undetected particles associated with one jet
Z(ll)H channel:
Main characteristics:
The production of a lepton
pair originating from Z(ll)
A large MET
Vukašin Milošević 4 EPS-HEP 2021Motivation: VH production mode
Mono V channel: Mono Jet channel:
Main characteristics: Main characteristics:
Energetic jets - due to V(qq) A jet originating from ISR
Imbalance in MET due to Interpreted as ggH production
undetected particles associated with one jet
Z(ll)H channel:
Main characteristics:
The production of a lepton
pair originating from Z(ll)
A large MET
Vukašin Milošević 4 EPS-HEP 2021Where are we now? Early Run 2 combination
The first combination measurement using Run 2 data was published using the 2016 dataset
No significant deviation from the SM was reported:
The result of the measurement is expressed as the 95% CL upper limit on the B(!H → inv.)
Physics Le*ers B 793 2019
0.33 (0.25)
0.26 (0.20)
Vukašin Milošević 5 EPS-HEP 2021Where are we now? Run 1 + early Run 2 combination
This publication also included a first combination of Run 1 and 2015+2016 data
Setting the B(#H → inv) limit to be at 0.19 (0.15) for the observed (expected) value
0.19 (0.15)
Physics Le*ers B 793 2019
90% CL upper limits on the spin-independent DM-nucleon scattering cross section in
Higgs portal models, assuming a scalar or fermion DM candidate.
Vukašin Milošević 6 EPS-HEP 2021Z(ll)H(invisible): Full Run 2 measurement
The Z(ll)H(invisible) measurement using full Run 2 data
Interpretation of a wider search for Dark Matter in association with a Z boson (EPJC 81 2021)
No significant deviation from the Standard Model was reported
The observed (expected) 95% CL upper limit computed using m
! H= 125 GeV:
B(H → inv) = 0.29 (0.25)
Vukašin Milošević 7 EPS-HEP 2021Mono jet/mono V: Full Run 2 measurement - Overview
The mono jet/mono V measurement using full Run 2 data
Interpretation of a wider search for new particles in association with jets and !ET,miss
Published in: CMS-PAS-EXO-20-004
Implementation of ML techniques in search for the V(qq) events (separating from QCD multijet events)
Neural network tagger - categories based on the DeepAK8 tagger score (JINST 15 P06005)
High purity VH (90% VH), Low purity VH (40% VH) and mono Jet (75% ggH, 20% VBF)
Performing a simultaneous fit in the Signal Region (SR) and
Control Regions (CRs):
In bins of the E
! T,miss
Connecting the CRs to the SR using the Transfer Factor approach
Z(νν) and W(lν) normalization estimated from a simultaneous
CR+SR fit
Dedicated CR region for QCD multijet estimation
Vukašin Milošević 8 EPS-HEP 2021Mono jet/mono V: Full Run 2 measurement - Results
41.5 fb-1 (13 TeV) 59.7 fb-1 (13 TeV)
The mono jet/mono V measurement using full Run 2 data
Events / GeV
Events / GeV
104 104
Data Z(ν ν )+jets Data Z(ν ν )+jets
CMS Preliminary CMS Preliminary
10 3 Mono-V (low-purity) W(lν )+jets WW/ZZ/WZ 3 Mono-V (low-purity) W(lν )+jets WW/ZZ/WZ
10
No significant deviation from the Standard Model was reported 102
2017
Top quark QCD
102
2018
Top quark QCD
The observed (expected) 95% CL upper limit computed using m
H(inv), BR = 25% H(inv), BR = 25%
! H= 125 GeV: 10
Axial, mmed = 2 TeV
mχ = 1 GeV 10
Axial, mmed = 2 TeV
mχ = 1 GeV
1
B(H → inv) = 0.28 (0.25)
1
10−1 10−1
10−2 10−2
(Data-Pred.) Data / Pred.
(Data-Pred.) Data / Pred.
1.4 1.4
1.2 1.2
1 59.7 fb-1 (13 TeV) 1
0.8 Post-fit Pre-fit 0.8 Post-fit Pre-fit
Events / GeV
0.6 Z(ν ν )+jets 0.6
105 CMS Preliminary Data
2 2
Monojet W(lν )+jets WW/ZZ/WZ
104 0 0
σ
σ
2018
−2 −2
Top quark QCD
103 300 400 500 600 700 800 900 1000 300 400 500 600 700 800 900 1000
H(inv), BR = 25%
102
pmiss
Axial, mmed = 2 TeV [GeV] pmiss [GeV]
T T
mχ = 1 GeV
10
0.60 (0.36) 59.7 fb-1 (13 TeV)
1
Events / GeV
103 CMS Preliminary Data Z(ν ν )+jets
−1
10
0.37 (0.31)
Mono-V (high-purity) W(lν )+jets WW/ZZ/WZ
2018 59.7 fb-1 (13 TeV)
10−2 102
Events / GeV
Top quark QCD
103 CMS Preliminary Data Z(ν ν )+jets
(Data-Pred.) Data / Pred.
1.4 H(inv), BR = 25%
10
0.28 (0.25) 1.2
1
0.8 102
Mono-V (high-purity)
2018
Axial, mmed =WW/ZZ/WZ
W(lν )+jets
mχ = 1 GeV
2 TeV
Post-fit Pre-fit Top quark
0.6 QCD
1
2 H(inv), BR = 25%
0 10
σ Axial, mmed = 2 TeV
−2 10−1
mχ = 1 GeV
400 600 800 1000 1200 1400 1
pmiss [GeV] 10−2
T
10−1
Data / Pred.
1.4
1.2
1
−2
100.8 Post-fit Pre-fit
0.6
(Data-Pred.)
2
/ Pred.
1.4
0
σ
1.2
−21
(Data-Pred.) Data
0.8 Post-fit Pre-fit
0.6 300 400 500 600 700 800 900 1000
2 pmiss [GeV]
T
0
σ
−2
300 400 500 600 700 800 900 1000
pmiss [GeV]
T
Vukašin Milošević 9 EPS-HEP 2021Future prospects
VBF H(invisible) was chosen for the HL-LHC study (CYRM-2019-007.221)
The most sensitive channel
Three different simulated scenarios for #ℒtotal = 300, 1000, 3000 fb #−1
Performing a set of fits in dijet mass for different versions of !ET,miss selection
For the best case scenario: B(!H → invisible) = 3.8%
But, this requires production mode targeting triggers
Need for a much lower E# T,miss selection than previously used
A similar study performed by the ATLAS Collaboration
Targeting the the second most sensitive channel - the VH production mode
Projects a limit of B(#H → invisible) = 8%
Under the assumption that both experiments perform similarly in all channels
Combination yields a projected limit of 2.5% for the HL-LHC phase
Vukašin Milošević 10 EPS-HEP 2021Summary
These slides have summarised the recent H(invisible) studies from the CMS Collaboration:
The latest combination focused on the Run 1 + early Run 2 measurements
Sets a limit on B(H → inv) at 0.19 (0.15) for the observed (expected) value
Measurements using the full Run 2 dataset:
Z(ll)H(invisible): B(H → inv) = 0.29 (0.25)
Mono V/mono Jet: B(H → inv) = 0.28 (0.25)
Results from the measurement of the VBF channel using full Run 2 dataset are being prepared
Stay tuned!
Studies of future prospects are indicating the need for better triggering approach:
Interesting time for these analyses: CMS future projections at B(#VBF H → invisible) = 3.8%
But this requires a new trigger strategy to lower the high #ET,miss thresholds
Possibilities for new approaches (ML vs cut based at the first triggering level)
Vukašin Milošević 11 EPS-HEP 2021Thank you for your time! Vukašin Milošević EPS-HEP 2021
BACKUP Vukašin Milošević EPS-HEP 2021
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