Chung – Yao Fellowship Interview
Bibhuti Parida
Postdoctoral Researcher at SJTU, Shanghai
May, 8th 2016
Bibhuti Parida 2
Resume
Previous works and achievements
– Search for High mass Higgs in 8 TeV at CMS
– Pileup mitigation techniques for jets in 13 TeV
Future working plans
– Search for Dark matter with events having Large MET + Highly Boosted jet in ATLAS
– LHC related phenomenological work
Outline
Chung – Yao Fellowship
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Personal Date of Birth: 15th June, 1985 Nationality: Indian
Positions Feb., 2016 – Present : Postdoctoral Researcher, SJTU, Shanghai (ATLAS Experiment at CERN)
Aug., 2015 – Dec., 2015 : Visitor, IIT, Madras (CMS Experiment at CERN)
Jan., 2015 – July, 2015 : Visiting Scientist, LPC, Fermilab (CMS Experiment at CERN)
Oct., 2013 – April, 2014 : Graduate Research Intern under LPC Guest & Visitor Program, Fermilab
(Worked with Prof. Dan Green and Dr. Nhan Tran as mentors in the LPC, Fermilab)
Education Ph. D. in Experimental High Energy Physics (CMS Experiment) (2010-2015) – Thesis Title: Search for a SM-like Higgs boson decaying into W +W- →lνqq using pp collision data recorded by the -
CMS detector at LHC
– Institution: Tata Institute of Fundamental Research, Mumbai, India
– Thesis supervisor: Prof. Gagan Bihari Mohanty (Associate Professor at TIFR, India)
– Awarded by the LPC Visiting Fellowship at Fermilab, USA (6 – months in 2013-14)
– Awarded by the Junior Research Fellowship (JRF) at TIFR , Ph.D. Fellowship (5- Years, 2010-15)
– Grants from DAE, Govt. of India and TIFR to visit CERN (5 times, each for ~3 months)
M. Tech. in Computational Seismology (2008-2010)
– Thesis Title: Study of Receiver function techniques to determine earth’s internal structure
– Thesis Supervisor: Dr. D. Srinagesh, Chief Scientist, NGRI, Hyderabad, India
– University: Tezpur University, India
– Awarded by the Fellowship from DST, Govt. India to carry out M. Tech. (2- years)
M. Phil. in Physics ( 2007-2008)
– Institution: Sambalpur University, India
– Thesis Title: Phonon anomaly study of normal and superconducting properties of some heavy fermion systems
– Supervisor: Prof. Pratibindhya Nayak, Head, Physics Department, (now CSIR Emeritus Scientist), Sambalpur University
Resume
Chung – Yao Fellowship Bibhuti Parida
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Led the Analysis for the Search for Heavy Higgs in W+ W- → lvqq’ final state
• SM-like Higgs boson has been discovered at ~125 GeV by the ATLAS and CMS experiment in 2012
• We have searched for a SM-like Higgs boson decaying into WW → lvqq' in the high mass region (600- 1000 GeV)
• We search Higgs in the semi leptonic final state in both inclusive and exclusive jet bins
• Used the novel jet substructure techniques
This search is the benchmark for the analysis of WW scattering
and aTGC
Higgs Production mechanisms
• Gluon gluon fusion (ggH) & Vector boson fusion (VBF)
Editor of the Publications/Notes • JHEP 10(2015)144 • HIG-14-008 • HIG-13-008 • CMS-AN-13-414 • CMS-AN-12-381 • Corresponding Twikis
Chung – Yao Fellowship Bibhuti Parida
Previous Research Work (I)
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Analysis Feature
W→lν
High pT lepton + high MET
W→qq’
Because of High boost, jets merged together to form a Fat Jet
Signal:
ggH + qqH,
(mH= 600-1000 GeV)
Backgrounds:
W+ jets (dominant)
ttbar, single top ,
WW/WZ/ZZ
Data sample:
Full 2012, Ele + Muon,
𝒔 = 𝟖 TeV, 19.3 fb-1
Signature WW → {lepton + MET} + Merged Jet
Use Jet Substructure
techniques to identify single
jets containing decay products
of hadronic W
Kinematics: boosted leptonic W back-to-back to a merged jet
Discriminating observables: pruned jet mass(mJ) and three-body mass (mlνJ )
Unbinned shape limits using mlνJ distributions
Background estimation
Data-driven Background extraction using mJ sideband for W+ jets
and top enriched control regions
Chung – Yao Fellowship Bibhuti Parida
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W-Tagging using Jet-Substructure
Grooming techniques: remove soft radiation and pileup from the jet (e.g.: pruning) Pruned jet mass: [65-105] GeV → signal region [40,65] and [105,130] → side band
N Subjettiness (arXiv:1011.2268)
Cut on N-subjettiness ; τ2 /τ1 < 0.5
Chung – Yao Fellowship Bibhuti Parida
I have studied the other grooming techniques such as filtering and
trimming and optimized that the pruning is the most aggressive
among all in 8 TeV.
In addition to N-subjettiness, I have studied energy flow variables,
Q-jet volatility, mass drop and optimized that N-subjettiness along
with pruning are the best for the final analysis.
mlvJ Distributions
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mlvJ distribution for 2- jet bin mlvJ distribution for 0-1 jet bin
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Statistical Interpretation
• No significant excess observed in the investigated mass region
• Improvement of the limit especially in the high mass, where VBF contribution is more important
• An expected sensitivity to exclude at 1.1 (3.3) times the SM cross section for a Higgs boson mass of 600
(1000) GeV
• Local excesses of 2.64σ and 2.56σ are observed in the mass range between 700 and 800 GeV
Chung – Yao Fellowship Bibhuti Parida
Presentations
Pre-approval talk of HIG-14-008
APS Conference, April, 2015 at Baltimore,
MD,USA
New Perspective Conference and Fermilab
User’s meeting, 2015
LPC Physics Forum, Fermilab, May, 2014
BELLE Analysis Workshop, January 23, 2013
XXth DAE-BRNS High Energy Physics
Symposium, Kolkata, January, 13 - 18, 2013.
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Performed the Jet substructure study for Run-II
Editor of the Publications • JME-14-001
• CMS-AN-14-175
• Twiki
• Pileup is one of the main challenges in jet reconstruction in the
LHC Run II.
• I have Investigated various pileup mitigation tools such as
– Charged Hadron Subtraction (CHS)
– Grooming techniques (trimming, pruning, soft drop) with
varying the parameters
– PUPPI
• Compare with PF and PF+CHS for large radius jets (R=0.8)
• Focus on the preparation for Run II of LHC
Chung – Yao Fellowship Bibhuti Parida
Previous Research Work (II)
Poster presented at New Perspectives Conference and Annual Fermilab User’s Meeting - 2015,
Fermilab
• Comparison of the trimmed average jet mass vs. PU for various
trimming parameters using PF or PF+CHS inputs
PF PF+ CHS
• Trimming is stable against pileup regardless of the input (PF or PF CHS)
Trimmed Mass Vs. Pile-up
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# More plots are in backup
Explored a new PU mitigation techniques : Pileup Per Particle Identification (PUPPI) (arXiv:1407.6013)
PUPPI attempts to use local shape, pileup event properties and tracking information to reduce the pileup
Evaluate the performance on simulation: CSA14(40 PU, 50 ns) @ 13 TeV
W mass resolution : RMS and (mreco - mW)
• Use anti-kT jets, R=0.8, 4-vector corrected
• Leading jet (pT > 300 GeV) in multijet and
RS Graviton → WW
• Using PF jets with and without CHS
• Look at jet mass and their stability Vs. PU
• PUPPI with and without 4-vector
safe subtraction are very similar
• PF + CHS+ Grooming improves
resolution over PF
• Trimming shows best resolution
• PUPPI : visible improvement for
grooming
4-vector safe subtracted
4-vector safe subtraction
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New PU Mitigation Technique: PUPPI
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Work plan (2016-18)
Chung – Yao Fellowship Bibhuti Parida
• The discovery of a Higgs boson, provides a new opportunity to search for Dark Matter production via the Higgs
+ MET signature
• After joining SJTU in February, 2016, I started working on the search for DM pair production in association with
a Higgs boson decaying to a pair of bottom quarks in pp collisions at 13 TeV by the ATLAS detector
Current Focus is the search of events having Large MET + Highly Boosted Jet with mass consistent with
Higgs/W/Z boson using Jet substructure Techniques
The decay of the Higgs boson is reconstructed as a high-momentum bb system with either a pair of small-radius
jets, or a single large-radius jet with substructure. I will perform the large radius jet and substructure based
analysis.
• Started working in b-tagging in high pileup environment
• Plan to carry out some LHC related phenomenological works.
Feynman Diagram for a Simplified
model where Z’ decays to pair of DM
candidates after emitting a Higgs boson
arXiv:1309.4017v2
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CMS Public Documents (PAS)
Publications as a Primary Author
Chung – Yao Fellowship Bibhuti Parida
1. JHEP 10 (2015) 144
2. JHEP 12 (2014) 017
1. CMS-PAS-JME-14-001
2. CMS-PAS-HIG-14-008
3. CMS-PAS-HIG-13-008
4. CMS-PAS-HIG-13-031
5. CMS-PAS-EXO-12-021
6. CMS-PAS-SMP-13-012
1. CMS-AN-2014-175
2. CMS-AN-2013-414
3. CMS-AN-2012-381
4. CMS-AN-2012-366
5. CMS-AN-2013-139
6. CMS-AN-2013-123.
1. Indian Jorn. Sc.Tech., Vol 6 (9) (2013).
2. Journal of Elec. and Comm. Eng. Vol.2, Issue 3 (2014)p:01-06,
ISSN:2321-5941
3. Indian J. Phys. 84 (10),1333-1339 (2010).
Outside of the CMS Collaboration
CMS Internal Notes (AN)
Journals
Besides these, I am a co-author of 403 publications of CMS papers since 2011.
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Chung – Yao Fellowship Bibhuti Parida
Thanks
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Backup
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In Journals
In CMS Public Documents (PAS)
Publications as a Primary Author
Chung – Yao Fellowship Bibhuti Parida
1. CMS Collaboration, “Search for a Higgs boson in the mass range from 145 to 1000 GeV decaying to a pair of W
or Z bosons”, arXiv:1504.00936v1 [hep-ex]; doi:10.1007/JHEP10(2015)144 ; JHEP 10 (2015) 144.
2. CMS Collaboration, “Identification techniques for highly boosted W bosons that decay into hadrons”,
arXiv:1410.4227 [hep-ex]; 10.1007/JHEP12(2014)017.
1. Study of Pileup Removal Algorithms for Jets, CMS-PAS-JME-14-001.
2. Search for a Standard Model Higgs-like boson decaying into WW→lvq(qbar) in exclusive jet bins in pp collisions
at sqrt{s}= 8 TeV", CMS-PAS-HIG-14-008.
3. Search for a Standard Model-like Higgs boson decaying into WW→lvq(qbar) pp collisions at sqrt{s}= 8 TeV",
CMS-PAS-HIG-13-008.
4. Search for a Higgs boson in the mass range from 145 to 1000 GeV decaying to a pair of W or Z bosons", CMS-
PAS-HIG-13-031 and CERN-PH-EP/2015-074.
5. Search for new resonances decaying to WW→lvq(qbar) in the final state with a lepton, missing transverse
energy and single reconstructed jet", CMS-PAS-EXO-12-021.
6. Measurement of the cross section of the electroweak production of a W boson with two jets in pp collisions at
sqrt{s}= 8TeV", CMS-PAS-SMP-13-012.
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CMS Internal Notes
Outside of the CMS Collaboration
Publications as a Primary Author
Chung – Yao Fellowship Bibhuti Parida
1. B. Parida et al. Study of Pileup Removal Algorithms for Jets", CMS-AN-2014-175.
2. B. Parida et al. Semi-leptonic decay of HWW at high mass in exclusive jet bins", CMS-AN-2013-414.
3. B. Parida et al. Searches for new physics in the WW→lvq(qbar) final state with hadronic W bosons merged into a
single jet", CMS-AN-2012-381.
4. B. Parida et al, Jet energy resolution with Z(µ + µ -) + jet events at at sqrt{s}= 7 TeV, CMS-AN-2012-366.
5. B. Parida et al. Search for high mass exotic resonances decaying to WW in the semi-leptonic channel", CMS-AN-
2013-139.
6. B. Parida et al, Measurement of the electroweak production cross section of a W boson with two jets in pp collisions
at sqrt{s}= 8 TeV", CMS-AN-2013-123.
1. B. Parida et al. Meson Spectra in p+p Collisions at LHC, Indian Jorn. Sc.Tech., Vol 6 (9) (2013).
2. B. Parida et al. Reduction of peak to average power ratio (PAPR) in orthogonal frequency division multiplexing
(OFDM) system, Journal of Elec. and Comm. Eng. Vol.2, Issue 3 (2014)p:01-06, ISSN:2321-5941. (Publication on
Electronics work with collaboration with a Master degree project student).
3. B. Parida et al. Effect of electron-phonon interaction and temperature dependence of resistivity in some heavy
fermion systems. Indian J. Phys. 84 (10),1333-1339 (2010). (M.Phil thesis work).
Besides these, I am a co-author of 403 publications of CMS papers since 2011.
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Selected Presentations in Conferences/Meetings/Workshops
Chung – Yao Fellowship Bibhuti Parida
1. Study of the Z boson production in association with jets with the CMS detector at LHC, VIII SERC School on
Experimental High Energy Physics, VECC, Kolkata, June 20 - July 10, 2011.
2. Study of jet substructure observables in the WW→ lvJ final state, 2nd Belle Analysis Workshop, TIFR, Mumbai,
January 21, 2013.
3. Study of jet substructure observables of merged W bosons in the WW→lvJ final state at XXth DAE-BRNS High
Energy Physics Symposium, Visva - Bharati, Santiniketan, January 13 - 18, 2013.
4. Search for H→ WW→lvJ at high mass in exclusive jet bins, LPC Physics Forum, Fermilab, May 15, 2014.
5. Several talks at the CMS physics group meetings including the pre-approval for HIG-14-008, CERN, April 24,
2014.
6. Discovery of a new boson with a mass 126 GeV and measurement of its spin and parity, CMS Data Analysis
School, Fermilab, 2014.
7. Search for a Standard Model-like Higgs boson decaying into WW→lvq(qbar) in pp collisions at sqrt{s} = 8 TeV, APS
April meeting, 2015, Baltimore, MD, USA.
8. Search for a SM-like Higgs boson decaying into WW→lvq(qbar) final state in high mass, NP 2015: New
Perspectives 2015, 8-9 Jun 2015, Fermilab, Batavia, IL, USA.
9. Pileup Removal Algorithm for Jets for Run II, poster NP 2015: New Perspectives 2015, 8-9 Jun 2015, Fermilab,
Batavia, IL, USA.
Leptonic pT(W)
ΔȠjj
Hadronic pT(W)
Mjj
0-1 jet bin 0-1 jet bin
2- jet bin 2-jet bin
Data-MC Comparison
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Background Extraction
The final discriminating variable in this analysis is the shape of the three-body mlvJ distribution.
The limit is calculated from the unbinned shapes in mlvJ
Signal Shapes:
Fits from MC, reweighted line shape
Background Shapes
ttbar, single top, WW/WZ (non dominant)
- Fits from MC, normalization corrected by data-to-MC scale factors
- ttbar normalization taken from top-enriched control region
W+ jets (dominant) Data driven technique:
• Estimate W + jets background contribution from data via a sideband method, in order to extract both its shape and normalization
• W + jets shape in mlvJ is taken from the mJ sideband, later extrapolated into the signal region
• Extrapolation function (mlvJ – dependent ) is taken from MC
Where-
and SR= Signal region mJ = [65-105] GeV
LSB= Low sideband region, mJ = [40-65] GeV & mJ =[105-130] GeV
Extrapolation function
Chung – Yao Fellowship Bibhuti Parida
mJ fit distribution
W-Jet: Normalization Procedure(mJ fit)
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X =
Uncertainties on W+ jets shape/normalization from: W + jet sideband fit α function fit shape uncertainty Shape uncertainty from alternate parton shower and alternate fitting function
Final mlvj distribution
in signal region 2- jet bin
Background Estimation
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muon channel
electron channel
Extrapolation function αMC (m lvJ)
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Limit in Different categories
0+1, 2-jet bins and combination
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Chung – Yao Fellowship Bibhuti Parida
BSM Interpretation
• Search for an electroweak singlet scalar
mixed with the 125 GeV Higgs boson
• Unitarization: c² + c'² = 1
where c (c') is the coupling of the low (high) mass state
( BRnew = BR of the high-mass resonance to non-SM like decay modes )
• Jet grooming algorithms are basically used to clean up effects from PU/UE and soft QCD contribution to the jet
• The proposed algorithms are Filtering, Trimming, Pruning and Softdrop . These are meant to clean up jet but do so in different ways
Grooming Algorithm (Filtering, Trimming and Pruning)
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• Soft drop: decluster the jet recursively removing soft and wide angle radiation from the jet
- Decluster with Cambrige- Aechen (CA) Algorithm - At each step, for subjet j1 and j2, check the condition - If it is met, keep the jet otherwise drop the softer constituent and reiterate de-
clustering • Parameters of the algorithm: Soft threshold, zcut and Angular exponent beta (ß)
If Soft drop is called as Modified Mass Drop Tagger (MMDT)
Grooming Algorithm (Soft drop arXiv:1402.2657)
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• Comparison of the pruned average jet mass vs. PU for various
pruning parameters using PF or PF+CHS inputs
PF PF+ CHS
• Mass increases linearly with pile-up
• PF+CHS improves the pileup dependence wrt. to simple PF
Groomed Mass Vs. PU - Pruning
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• Comparison of the soft drop average jet mass vs. PU for various soft drop parameters using PF or PF+CHS inputs
• Average mass is quite stable wrt. PU • PF+CHS improves the pileup dependence wrt. to simple PF
PF PF+ CHS
Groomed Mass Vs. PU – Soft Drop
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• Jet mass response defined as (mreco- mgen) • Jet mass resolution is estimated from the
spread of (mreco- mgen)
- Trimming : RMS ~ 10 GeV - Pruning: RMS ~ 12-15 GeV - Soft Drop : RMS ~12-15 GeV
Trimming has the best mass resolution
Trimming
Pruning Soft Drop
Jet Mass Response
Bibhuti Parida Chung – Yao Fellowship 29
• Trimming has better response resolution wrt. to pruning and soft drop • Trimming shows also smaller tails (RMS vs. sigma) • Also more stable vs. PU
QCD jets W jets
Jet Mass Resolution- Trimming
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