PhD Thesis at IFIC

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E. Torró 3 Nov 2020

EMMA TORRÓ PASTOR — GenT Researcher 1

•

Physics Bachelor at UV

•

PhD Thesis at IFIC:

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“Study of supersymmetric signals with R-parity violation in ATLAS at LHC”

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Postdoctoral Research Associate at University of Washington (Seattle)

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Searching for Long-lived particles in the ATLAS detector

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Working in the ATLAS Trigger and Data Acquisition system

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Joined the Mathusla collaboration — searching for Ultra-LLPs

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Postdoctoral Research Associate at University of Washington (Seattle)

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Joined the IRIS-HEP project — facing Run3/Run4 computing challenges

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CIDEGENT at IFIC

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Searching for Long-lived particles in the ATLAS detector

•

Working on the design of the Mathusla experiment

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Searching for New Physics. Where should we look? 2

ATLAS

MATHUSLA ATLAS

LHCb CMS

ALICE

ALICE CMS

LHCb

France Switzerland

• ATLAS, CMS, LHCb have a wide program to search for Long-lived Particles (LLPs)

•

need dedicated searches, as standard ones are not sensitive

•

~20 different searches in ATLAS dedicated to LLPs and unconventional signatures

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However these searches are limited by a number of factors:

• triggers

• backgrounds from collisions (including pileup)

• cosmics

• the size of the detector: LLPs could decay outside!

•

A detector on the surface would be sensitive to ultra-Long-lived particles!

• In this project we want to make the best use of the LHC data, both in ATLAS and in the Mathusla

detector

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Long-lived particles in ATLAS 3

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The signature of a LLP in the detector can be very different depending on:

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nature of the LLP (charged/neutral)

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decay mode (hadronic, leptonic, photons, invisible)

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where in the detector it decays

Displaced jets in the ID

Displaced Lepton-jets Late photons

Disappearing tracks

Displaced jets in the Calorimeter

Highly ionising particles

Displaced jets in the MS Displaced

vertices + MET Displaced leptonic vertices

(Meta-) Stable Charged LLPs Stopped LLPs

NOT IN FILLED BUNCH

CROSSING

neutral particle jet

charged particle

highly ionizing particle electron

muon photon

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Long-lived particles in ATLAS 4

Displaced jets in the ID

Displaced Lepton-jets Late photons

Disappearing tracks

Displaced jets in the Calorimeter

Highly ionising particles

Displaced jets in the MS Displaced

vertices + MET Displaced leptonic vertices

(Meta-) Stable Charged LLPs Stopped LLPs

NOT IN FILLED BUNCH

CROSSING

neutral particle jet

charged particle

highly ionizing particle electron

muon photon

•

Our project focuses on searches for neutral long-lived particles decaying

hadronically in the ATLAS calorimeters

•

also participating in LLP decays in the ID and the MS

•

The signature of a LLP in the detector can be very different depending on:

•

nature of the LLP (charged/neutral)

•

decay mode (hadronic, leptonic, photons, invisible)

•

where in the detector it decays

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Long-lived particles in ATLAS 5

s s p

p f

f¯

f¯ f

s proper decay length [m]

−1

10 1 10 10²

[pb] ss→ΦB×σ95% CL Upper Limit on ³⁻10

−2

10

−1

10 1 10 102

103

104

ATLAS s = 13 TeV = 150 GeV = 600 GeV, ms

mΦ

-1 ] CR limit [33.0 fb

-1 ] MS2 limit [36.1 fb CR+MS2 limit

Obs.

1σ Exp. ±

s proper decay length [m]

−1

10 1 10 10²

ss→ΦB95% CL Upper Limit on

−4

10

−3

10

−2

10

−1

10 1 10 102

103

104

105

ATLAS s = 13 TeV = 25 GeV = 125 GeV, ms

mΦ

-1 ] CR limit [10.8 fb

-1 ] MS1+MS2 limit [36.1 fb CR+(MS1+MS2) limit

Obs.

1σ Exp. ±

→ ss

BH

100%

→ ss

BH

10%

→ ss

BH

1%

• MS search more sensitive for low masses (soft pT)

• Some complementarity at short lifetimes

• CR search more sensitive for high masses (high pT)

• Some complementarity at large lifetimes

m^𝛟 = 125 GeV m𝛟 = 600 GeV

HCal DJ

MS DJ

combination

• Complementary results!

‣

common target model: Hidden sector with a heavy neutral

boson, 𝜙, decaying to two long- lived neutral scalars, s, that

decay to pairs of SM fermions.

‣

Plan to keep working on searches for displaced jets, extending to other final states including dark photons

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MATHUSLA: MAsive Timing Hodoscope for Ultra Stable neutraL pArticles 6

LLP Leptonic decay LLP Hadronic decay

100 m

• Aiming to reach to Big Bang Nucleosynthesis (BBN) limit (c𝛕 ~ 10⁷ - 10⁸ m) lifetime: need to suppress LHC backgrounds

• Dedicated detector placed on the surface above CMS during HL-LHC:

• O(60) meters of rock suppress most backgrounds

• Large volume filled with air as decay volume with several detector layers for tracking

70 m 60 m

20 m 5 m4 m

ground level

Point 5 (CMS)

IP

0.001 0.100 10 1000 10⁵ 10⁷

10^-6 10^-5 10^-4 0.001 0.010 0.100 1

10^-1 1 10 10² 10³ 10⁴

cτ_X (m)

Br(h->XX) σpp→h→XX(fb)

s = 14 TeV, 3ab^-1 h→XX, X→jj

m_X = 20 GeV BBNLimit HL-LHC h→invisible

sensitivity

ATLAS MS

1DV

MAT HUS

LA

atCMS

DecaysdominantlyinMainDetector

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The MATHUSLA Test Stand 7

• The MATHUSLA Test Stand is a small-scale experiment, built on the surface above the ATLAS detector

• Aiming at confirming the expected background for the Mathusla detector

• It collected data during 2018, both with LHC pp collisions and when the LHC was not colliding protons.

6.5 m

2.5 m

✩

Test stand

10 m

Rock

Access shaft

Cavern

Beamline

IP ATLAS

x

z

https://arxiv.org/abs/2005.02018

scin6llators RPCs

RPCs RPCs

scin6llators

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The MATHUSLA Test Stand 8

• The MATHUSLA Test Stand is a small-scale experiment, built on the surface above the ATLAS detector

• Aiming at confirming the expected background for the Mathusla detector

• It collected data during 2018, both with LHC pp collisions and when the LHC was not colliding protons.

6.5 m

2.5 m

✩

Test stand

10 m

Rock

Access shaft

Cavern

Beamline

IP ATLAS

x

z

https://arxiv.org/abs/2005.02018

scin6llators RPCs

RPCs RPCs

scin6llators

0 5 10 15 20 25 30

°] Zenith angle [ 0

50 100 150 200 250 Tracks / 0.5° 300

Upward data (with beam)

Cosmic ray inelastic backscattering IP muon simulation

Prediction uncertainty Upward data (with beam)

Cosmic ray inelastic backscattering IP muon simulation

Prediction uncertainty

muons from the

LHC collisions backscattered cosmic muons

• For the first time in the LHC we’ve measured the rate of muons from collisions reaching the surface

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MATHUSLA Documentation 9

• Original idea: J-P Chou, D. Curtin, H. Lubatti arXiv 1606.06298

• Mathusla Physics case - theory white paper to be published in Physics Reports: arxiv: 1806.07396

• Letter of Intent submitted to LHCC in November 2018: MATHUSLA LoI: arXiv 1811.00927

• Input to European Strategy for Particle Physics: arxiv 1901.04040

• Test stand paper: https://arxiv.org/abs/2005.02018

• Mathusla webpage: https://mathusla-experiment.web.cern.ch/

• Currently working on the Technical Design Report