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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


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


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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


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

7 Chung – Yao Fellowship Bibhuti Parida

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


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


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


# 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)


• 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


1. JHEP 10 (2015) 144

2. JHEP 12 (2014) 017

1. CMS-PAS-JME-14-001

2. CMS-PAS-HIG-14-008



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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Thanks

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Backup


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In Journals

In CMS Public Documents (PAS)



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



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


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

19 Bibhuti Parida Chung – Yao Fellowship

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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


mJ fit distribution

W-Jet: Normalization Procedure(mJ fit)


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


muon channel

electron channel

Extrapolation function αMC (m lvJ)


Limit in Different categories

0+1, 2-jet bins and combination

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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)


• 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)


• 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


• 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


• 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

Bibhuti Parida Chung – Yao Fellowship 30

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