Shin-Shan Eiko Yu Department of Physics

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Shin-Shan Eiko Yu Department of Physics

National Central University, Taiwan

15 December 2020

Colloquium, Department of Physics National Taiwan University

Search for Dark Matter in pp

Collisions with CMS

(2)

Shin-Shan Eiko Yu

• Dark matter searches at colliders

• ^Overview

• Introduction to LHC and CMS

• Experimental techniques

• Interpretation of results

• Conclusion and outlook

2

Outline

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Shin-Shan Eiko Yu 3

How Do You “See” an Object?

Reflection Thermal Radiation

Visible for T=3800~7600 K

(4)

4

In our galaxy, besides visible stars, is there

something else?

(5)

5

Cold Dark Matter:

(CDM) 25%

Dark Energy : ( ) 70%

Stars:

0.8%

H & He gas: 4%

Chemical Elements:

(other than H & He) 0.025%

Neutrinos:

0.17%

CDM CDM

Radiation:

0.005%

CDM CDM

inflationary perturbations baryo/lepto genesis

If I had been present at creation, I would have suggested a simpler scheme. - Alfonse the Wise

Rocky Kolb

(6)

What Is Dark Matter?

6

• “Dark Matter” is a temporary name

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Shin-Shan Eiko Yu 7

“Dark Matter” in Chemistry: Argon

Lo rd Ra yl ei gh Si r Wi lli am Ra ms ay Nitrogen extracted from air is heavier

than that extracted from the chemical reaction by 0.5%

☞ New Unknown Gas: Argon

Discovered in 1894

(8)

What Is Dark Matter?

• Influenced by gravitational interaction and no other standard model (SM) interactions

• Interact weakly with normal matter →may need a new type of interaction

8

• “Dark Matter” is a temporary name

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Shin-Shan Eiko Yu 9

Why Dark Matter?

M33 galaxy

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Shin-Shan Eiko Yu 10

Reminder of Gravitation Law (Outside the Earth)

r

F r ( ) > R ^∝ ^M _r ^total ² m v _particle ²

r ∝ M _total

r ²

⇒ v _particle ∝ M _total r

R

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Reminder of Gravitation Law: Inside the Earth

r

F r ( ) < R ^∝ ^{M r} ( )

r

²

=

ρ ⁴ π

3 r

³

⎛

⎝⎜

⎞

⎠⎟

r

²

= r m v

_particle²

r ∝r

⇒ v

_particle

∝r

R

(12)

Reminder of Gravitation Law: Inside the Earth

r

F r ( ) < R ^∝ ^{M r} ( )

r

²

=

ρ ⁴ π

3 r

³

⎛

⎝⎜

⎞

⎠⎟

r

²

= r m v

_particle²

r ∝r

⇒ v

_particle

∝r

R

(13)

Extended to the Stars in a Galaxy

r

v ∝ M r ( )

r

v r ( ) < R ^∝r

v r ( ) > R ^∝ ¹ _r

(14)

13

Rotational Curves

Vera Rubin 1928-2016 Measured

~200km/s

Expectation

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13

Rotational Curves

Vera Rubin

1928-2016

(16)

Extended to the Stars in a Galaxy

r

v

_particle

( ) r > R ^∝ ^M _r

^total

v

_particle

( ) r > R ^∝ ^{M r} ( )

r

⇒ M r ( ) ^∝r

(17)

Gravitation Lensing

15

Abell 2218 Cluster

The size of the Einstein ring is

related to the mass of the lensing

θ ∝ M

_lense

(18)

Gravitation Lensing

15

Abell 2218 Cluster

The size of the Einstein ring is

related to the mass of the lensing

θ ∝ M

_lense

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Gravitation Lensing

15

Abell 2218 Cluster

The size of the Einstein ring is

related to the mass of the lensing

θ ∝ M

_lense

(20)

Bullet Clusters

16

2006 observed

1E0657-558

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Bullet Clusters

16

Normal Matter

X-ray image Dark Matter

2006 observed

1E0657-558

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Bullet Clusters

17

(23)

Bullet Clusters

17

(24)

Dark Matter Detection

DM

DM SM

Direct Detection

SM

Indirect Detection

DM

DM SM

SM

Production at Colliders

DM

DM SM

SM

(25)

Introduction to LHC and CMS

19

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High Energy Physics Dictionary

• LHC ( )

20

• CERN

– Conseil Européen pour la Recherche Nucléaire – European Council for Nuclear Research

– Location of LHC and the experiments

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CERN

•

23 member states

•

Yearly budget 10⁹ CHF (= 3.2 × 10¹⁰TWD)

‣

Germany UK France Italy

‣

LHC cost ~ 4.3 × 10⁹ CHF

21

•

Established by 12 European countries on 1954/09/29

•

Origin of WWW

‣

Tim Berners-Lee in 1989

•

^Director

‣

Fabiola Gianotti

(28)

Users Around the World

(29)

23

LHC Birdview

(30)

23

LHC Birdview

ATLAS

(31)

23

LHC Birdview

CMS

(32)

23

LHC Birdview

Our offices

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24

Text

Tunnel circumference 26.7 km, tunnel diameter 3.8 m Depth : ~ 70-140 m – tunnel is inclined by ~ 1.4% 50-175

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LHC Tunnel

1232 superconducting dipoles Operating temperature: 1.9 K Magnetic dipole field: 8.3 Tesla

Beam-pipe pressure: 10^-13 atm

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LHC Tunnel

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LHC Tunnel

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CMS Detector Sketch

(38)

27

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27

(40)

28

Muon Chamber

Superconducting Magnet

B=3.8 Tesla Hadron

Calorimeter

Silicon Tracker Electromagnetic

Calorimeter

CMS Detector

(41)

28

Muon Chamber

Superconducting Magnet

B=3.8 Tesla Hadron

Calorimeter

Silicon Tracker Electromagnetic

Calorimeter

CMS Detector

(42)

Path of Various Particles

29

(43)

Path of Various Particles

29

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Shin-Shan Eiko Yu

•

Neutral, weakly-interactive, massive, and stable on the distance- scales of tens of meters

•

Dark matter appears as missing transverse momentum in collider detectors

30

What Is Dark Matter at Colliders?

Missing

transverse momentum

7m0m3.5 m

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Shin-Shan Eiko Yu

µ

jet

Momentum imbalance ν ME

_T

μ

•

The negative of the total transverse momentum of all observed particles in the detector

31

Missing Transverse Momentum

neutrinos or

dark matter

(46)

•

Mediator has minimal decay width

•

Minimal set of parameters

•

coupling structure, MMED, mDM, gSM (gq), gDM

Simplified Models for Direct DM Production

q

!

Mediator gSM

(gq) gDM

MMED

mDM

(47)

•

• Simplified Models for Direct DM Production

Features of Mediators

Tae Min Hong, LHCP 2017

q

!

Mediator gSM

(gq) gDM

MMED

mDM

(48)

•

• Simplified Models for Direct DM Production

q

!

Mediator gSM

(gq) gDM

MMED

mDM

(49)

•

• Simplified Models for Direct DM Production

q

!

Mediator gSM

(gq) gDM

MMED

mDM

(50)

•

• Simplified Models for Direct DM Production

q

(51)

Amount of Data We Use

(52)

Amount of Data We Use

σ_tt ∼ 800 pb N_tt = Lσ_tt

∼ 3.2 ×10⁷

(53)

DM Searches with Missing Transverse Momentum Signatures

34

q

!

Mediator gSM

(gq) gDM

MMED

mDM

(54)

Mono-X Diagrams of Direct DM Production

Mono-jet Mono-Z(leptonic) Mono-W/Z(hadronic)

Mono-photon Mono-h (bb, "") Mono-tt/bb

Mono-top

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Shin-Shan Eiko Yu

•

Anomalous high MET can be due to:

•

Particles striking sensors in the ECAL photodetectors

•

^{Beam halo}

•

Dead cells in ECAL or HCAL

•

Noise in ECAL or HCAL

36

Challenges of Missing Transverse Momentum

[GeV]

miss

ET

500 1000 1500 2000 2500 3000

Events / 30 GeV

−1

10 1 10 102

103

104

105 ^{Top quark}

EWK

QCD

Data after cleaning

Data before cleaning

(13 TeV, 2016) 12.9 fb-1

CMS

Preliminary

Raman Khurana Ching-Wei Chen

CMS-PAS-JME-16-004

Events passing dijet selection

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Fake Missing Transverse Momentum: Noise

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Fake Missing Transverse Momentum: Noise

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Fake Missing Transverse Momentum: Noise

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Fake Missing Transverse Momentum: Noise

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Shin-Shan Eiko Yu

Events / GeV

−2

10

−1

10 1 10 102

103

104

105

106

(13 TeV) 35.9 fb-1

CMS monojet

Data

inv.

→ H(125)

= 2.0 TeV Axial-vector, mmed

)+jets ν ν Z(

)+jets ν W(l

WW/WZ/ZZ Top quark

+jets γ (ll), γ Z/

QCD

Data / Pred. 0.8 0.9 1 1.1 1.2

[GeV]

miss

pT

400 600 800 1000 1200 1400

Unc.(Data-Pred.) 2−

0 2

killed by MET &

veto of extra objects

PRD 97, 092005 (2018)

•

Rely on MET triggers (offline MET cut ≳200 GeV)

•

Major background from Z(→##)+jets, W(→l#)+jets

38

Mono-X Searches in Hadronic Final State

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Estimation of Z+Jets Background

(62)

Searches for Visible Mediator Decays

40

q

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Shin-Shan Eiko Yu

•

^high-p^T^/H^T trigger for large-Mjj, ISR "/jet tag or data with only trigger-level objects (data scouting) for small-Mjj

41

Visible Mediator Searches

q

Mediator with ISR

q

Mediator

600 800 1000 1200 1400 1600 1800 2000

[pb/TeV] jj/dmσd

(13 TeV) 27 fb-1

CMS _Data

Fit

gg (0.75 TeV) qg (1.20 TeV) qq (1.60 TeV)

/ NDF = 20.3 / 21 = 1.0 χ2

Wide Calo-jets < 2.04 TeV 0.49 < mjj

| < 1.3 η Δ

| < 2.5, | η

| 106

105

104

103

102

10 1

−1

10

Dijet mass [TeV]

Uncertainty(Data-Fit)

−32

−−011 2 3

0.6 0.8 1 1.2 1.4 1.6 1.8 2

[pb/TeV] jj/dmσd

(13 TeV) 36 fb-1

CMS _Data

Fit

gg (2.0 TeV) qg (4.0 TeV) qq (6.0 TeV)

/ NDF = 38.9 / 39 = 1.0 χ2

Wide PF-jets > 1.25 TeV mjj

| < 1.3 η Δ

| < 2.5, | η

| 104

103

102

10 1

−1

10

−2

10

−3

10

−4

10

Dijet mass [TeV]

Uncertainty(Data-Fit)

−32

−−011 2 3

2 3 4 5 6 7 8

JHEP 08 (2018) 130

(GeV) mSD

40 60 80 100 120 140 160 180

Events / 5 GeV

0 5000 10000 15000 20000

25000 ^Data W(qq)+jets (^×³⁾

Total SM pred. Z(qq)+jets (×3) Multijet pred. t/tt(qq)+jets (×3)

=135 GeV

=0.17, mZ'

Z'(qq), gq'

(13 TeV) 35.9 fb-1

CMS

: 500-600 GeV pT

(GeV) mSD

50 100 150

Data/Prediction

0.9 1 1.1

JHEP 01 (2018) 097

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Result Interpretation

42

(65)

Mono-X With Vector/Axial Mediators

Mono-jet

Mono-W/Z(hadronic) Mono-Z(leptonic)

Mono-photon

(66)

Collider Results Only (Vector Mediator)-Mono-X

(67)

Collider Results Only (Vector Mediator)

(68)

If We Use Different Parameter Values

(69)

Collider v.s. Non-Collider Experiments (SI)

gq=0.25, gDM=1

σ_SI^vector ! 6.9 × 10⁻⁴¹cm² g_qg_DM 0.25

⎛

⎝⎜

⎞

⎠⎟

2 1 TeV M_med

⎛

⎝⎜

⎞

⎠⎟

4 µ_n_χ 1 GeV

⎛

⎝⎜

⎞

⎠⎟

2

MMed

mDM

$

(70)

Collider v.s. Non-Collider Experiments (SI)

No upper bound Experimental limit

gq=0.25, gDM=1

⎛

⎝⎜

⎞

⎠⎟

2 1 TeV M_med

⎛

⎝⎜

⎞

⎠⎟

4 µ_n_χ 1 GeV

⎛

⎝⎜

⎞

⎠⎟

2

(71)

Collider v.s. Non-Collider Experiments (SI)

No upper bound Experimental limit Upper bound limited

by mediator mass (collider energy)

gq=0.25, gDM=1

⎛

⎝⎜

⎞

⎠⎟

2 1 TeV M_med

⎛

⎝⎜

⎞

⎠⎟

4 µ_n_χ 1 GeV

⎛

⎝⎜

⎞

⎠⎟

2

(72)

Collider v.s. Non-Collider Experiments (SD)

For the model parameters considered here, collider experiments can probe SD cross sections 2-3 orders of magnitude smaller than the non-collider experiments.

gq=0.25, gDM=1

σ_SD^axial ! 2.4 × 10⁻⁴²cm² g_qg_DM 0.25

⎛

⎝⎜

⎞

⎠⎟

2 1 TeV M_med

⎛

⎝⎜

⎞

⎠⎟

4 µ_nχ 1 GeV

⎛

⎝⎜

⎞

⎠⎟

2

(73)

CMS Phase-2 Upgrade

(74)

CMS Phase-2 Upgrade

(75)

The Detector Lab @ NCU

Grid computing room for AMS, CMS, KAGRA

Space for Scintillator+SiPM detector for muography Cleanroom for Silicon

detector for CMS/sPHENIX

~2000 cores

~500 TB

Space for testing, inspection,

repair and students

~45m²

Cleanroom

~26m²

Service room

~7m²

Buﬀer room

~10m²

~11m²

~41m²

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Shin-Shan Eiko Yu

•

cleanroom ~26m²

•

service + buffer room ~17m²

•

class 1000 with temperature and humidity controlled at 22℃

and relative humidity (RH) 55%

all year round

•

fully operation with pressured dry-air service

51

Cleanroom

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Shin-Shan Eiko Yu

•

left self-designed 8-inch probe station used for the large pad silicon sensors

•

right 4-inch probe station used for PHOBOS and CMS Preshower (being upgraded for sPHENIX)

•

A new 8-inch MPI probe station was installed in mid-November for CMS HGCal and sPHENIX

52

Probe Stations

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Shin-Shan Eiko Yu

•

Aerotech 1.25x1.25 m² robotic gantry with Labview control.

•

OGP optical 3d measurement

•

Hesse BJ820 automatic Bondjet and DAGE 4000 Bondtester(puller)

•

Manual probe station and picoprobes (not visible in this pic)

•

glue dispensers, mini-gantry, microscope, degassing chamber, Keithley 2410 and tools …

53

Cleanroom Equipments at NTU

Gantry

OGP Bondjet

Puller

mini-gantry Gantry

control

(79)

A set of jigs and tooling for 6-inch HGCal module assembly

54

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1. Deposit epoxy on Cu baseplate

2. Place gold-plated

Kapton film 3. Deposit epoxy and silver epoxy on Kapton

4.Place sensor on top of Kapton

5. Deposit epoxy on sensor, avoiding opening bond pads

6.Place PCB on top of sensor

(81)

Shin-Shan Eiko Yu

•

CMS has an extensive dark

matter program, including both searches for mediators and

searches in mono-X channels

•

^{137 fb}^-1 of full Run II data are yet to be analyzed

56

Conclusion and Outlook

•

Moving towards more advanced/sophisticated models

•

t-channel production

•

spin-2 mediators, long-lived mediators or intermediate

“dark” particles

•

Detector upgrade going on and Taiwan (NCU/NTU) is playing a major role in the endcap calorimeter

Shin-Shan Eiko Yu Department of Physics