photons in ATLAS Yohei Yamaguchi Osaka University on behalf of the - - PowerPoint PPT Presentation

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photons in ATLAS Yohei Yamaguchi Osaka University on behalf of the - - PowerPoint PPT Presentation

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Latest results on Higgs final-states with photons in ATLAS Yohei Yamaguchi Osaka University on behalf of the ATLAS collaboration Photon 2015@Novosibirsk, Russia 15/6/2015 1 Outline Introduction Photon reconstruction with ATLAS

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SLIDE 1

Latest results on Higgs final-states with photons in ATLAS

Yohei Yamaguchi

Osaka University

  • n behalf of the ATLAS collaboration

Photon 2015@Novosibirsk, Russia 15/6/2015

1

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SLIDE 2

Outline

  • Introduction
  • Photon reconstruction with ATLAS detector
  • Higgs boson property measurements with 𝐼 β†’ 𝛿𝛿 channel

– mass: Phys. Rev. D. 90, 052004 (2014) arXiv:1503.07589 – coupling: Phys. Rev. D. 90, 112015 (2014) Physics Letters B 740 (2015) 222-242 – spin: ATLAS-CONF-2015-008 – total and differential cross section: arXiv:1504.05833

  • BSM search using 𝐼 β†’ 𝛿𝛿

– β„Žβ„Ž β†’ 𝛿𝛿𝑐 𝑐: Phys. Rev. Lett. 114, 081802 (2015) – 𝐼 β†’ 𝛿𝛿 + 𝐹T

miss: arXiv:1506.01081

– SUSY + β„Ž β†’ 𝛿𝛿: Eur. Phys. J. C (2015) 75:208 – FCNC: JHEP06(2014)008 – Higgs boson to SUSY: ATLAS-CONF-2015-001

2

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SLIDE 3

𝐼 β†’ 𝛿𝛿

3

W H g g W H

g g

H

g g

t, b

  • Sensitive to relative sign of top-Higgs Yukawa coupling with respect to HWW gauge

coupling because of interference between loop terms

  • 𝐼 β†’ 𝛿𝛿 + X: Direct search of Beyond the SM (BSM)
  • di-higgs
  • SUSY
  • dark matter
  • …
  • Significant contribution to discovery of the Standard Model (SM) like Higgs boson
  • has great advantages of Higgs boson property measurements
  • coupling, mass, spin, …
  • Higgs boson decays to di-photon through top/W loop

Interference

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SLIDE 4

𝐼 β†’ 𝛿𝛿 analysis

4

  • Challenge: small branching ratio BR(𝐼 β†’ 𝛿𝛿) = 2.28 x 10-3
  • 𝑛𝛿𝛿 distribution has peak at Higgs boson mass
  • Peak is narrow owing to excellent mass resolution
  • natural width: 4 MeV

Requirements

  • Good photon-jet separation
  • High photon reconstruction efficiency
  • Good photon energy resolution

𝑛𝛿𝛿 Process Ξ³Ξ³ Ξ³-jet jet-jet Relative cross section 1 104 107 Smoothly falling QCD background

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SLIDE 5

Photon energy calibration

5 energy resolution energy scale validation with π‘Ž β†’ ℓℓ𝛿 0.3 % energy scale uncertainty for photons from Higgs boson

  • Eur. Phys. J. C (2014) 74: 3071
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SLIDE 6

Photon-jet separation

6 EM calorimeter

TRT

  • Isolation
  • Signal photon is isolated
  • Ο€0 which fakes photon has

jet constituents around

1 : 0.18 : 0.01 ID + isolation

  • Phys. Rev. D. 90, 112015 (2014)
  • Ο€0 (β†’ Ξ³Ξ³) in jets: fake photon
  • Identification with EM shower shape

photon Ο€0

  • High efficiency (> 90 %) for photons

from Higgs boson

  • Good jet rejection
  • Ξ³-Ξ³ : Ξ³-jet : jet-jet = 1 : ~104 : ~107

inner tracker

SCT Pixel

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SLIDE 7

Higgs boson property measurements with 𝐼 β†’ 𝛿𝛿 channel

7

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SLIDE 8

Data sample / 𝐼 β†’ 𝛿𝛿 candidates

8

  • Data sample: 4.5 fb-1 at 𝑑 = 7 TeV, 20.3 fb-1 at 𝑑 = 8 TeV
  • Selection: isolated 2 photons pT/mΞ³Ξ³ > 0.35, 0.25
  • Total selected events in mΞ³Ξ³ [105 : 160] GeV: 1.1 x 105 evt
  • Total expected signal events: 468 evt for mH = 125.4 GeV
  • Vector Boson Fusion (VBF) 𝐼 β†’ 𝛿𝛿 candidate
  • di-photon + forwards 2 jets
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SLIDE 9

Mass measurement

9 𝐼 β†’ 𝛿𝛿 alone

  • Higgs boson mass: input parameter of SM
  • determined by experiments to complete SM
  • 𝐼 β†’ 𝛿𝛿: most precise measurement
  • mass resolution: 1.65 GeV
  • Dominant systematic uncertainty: energy scale uncertainty due to material

amount uncertainty in front of EM calorimeter

  • combining ATLAS and CMS:

combine with 𝐼 β†’ π‘Žπ‘Ž β†’ 4β„“ analysis

  • Phys. Rev. D. 90, 052004 (2014)

arXiv:1503.07589

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SLIDE 10

Coupling measurement

10

g g t, b H q q H q

π‘Ÿ

g g H t t W/Z W/Z W/Z H

gluon-gluon fusion (ggF) vector boson fusion (VBF) associated production (VH) associated production with t 𝑒 (ttH) tH production

  • To measure gauge coupling and Yukawa coupling individually, events are

categorized based on event signature of production process

Largest cross section (87 %

  • f Higgs boson production)

Leptons/jets/Missing ET from W/Z boson Forwards high pT 2 jets b-jets/W bosons from top- quarks b-jets/W bosons gauge coupling gHWW, gHZZ: VBF, VH top-Higgs Yukawa Ξ₯t: ggF, ttH, tH ttH, tH: direct Ξ₯t measurement

  • Phys. Rev. D. 90, 112015 (2014)

Physics Letters B 740 (2015) 222-242

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SLIDE 11

Coupling measurement

11 tH cross section is sensitive to relative sign between Ξ₯t and gHWW as well as BR(𝐼 β†’ 𝛿𝛿) because of interference Interference ΞΊt = Ξ₯t / Ξ₯t

SM

ΞΊt = 0 means

  • turn off ttH process
  • remove top quark contribution to tH and to

𝐼 β†’ 𝛿𝛿 ΞΊt < 0 enhances tH cross section and BR(𝐼 β†’ 𝛿𝛿) Dependence of ttH and tH cross sections and BR(𝐼 β†’ 𝛿𝛿) on ΞΊt

  • Phys. Rev. D. 90, 112015 (2014)

Physics Letters B 740 (2015) 222-242

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SLIDE 12

Coupling measurement

12 ΞΌ = Οƒ x BR(𝐼 β†’ 𝛿𝛿) ΟƒSM x BRSM(𝐼 β†’ 𝛿𝛿)

  • lower limit: -1.3
  • upper limit: 8.0
  • One of dominant systematic uncertainties

is photon energy resolution

ΞΌggF ΞΌVBF ΞΌWH ΞΌZH ΞΌttH 1.32 Β± 0.38 0.8 Β± 0.7 1.0 Β± 1.6 0.1+3.7

  • 0.1 1.6+2.7
  • 1.8

95 % CL on ΞΊt

  • Combined measurement of coupling

ATLAS-CONF-2015-007

  • ttH search in other channels

ATLAS-CONF-2015-006 arXiv:1503.05066

  • Phys. Rev. D. 90, 112015 (2014)

Physics Letters B 740 (2015) 222-242

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SLIDE 13

Other property measurements

13

  • Spin measurement
  • spin 0 and 2 can be distinguished by

angular distribution of 2 photons

  • Total and differential cross section measurement
  • πœπ‘žπ‘žβ†’πΌ = 33.0 Β± 5.3 (stat) Β± 1.6 (sys) pb

spin 2 model with Universal couplings

ATLAS-CONF-2015-008 arXiv:1504.05833

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SLIDE 14

BSM search using 𝐼 β†’ 𝛿𝛿

14

  • In search of BSM with Higgs boson, Higgs can be tagged with some

final states (Ξ³Ξ³, WW, ZZ, bb, ττ, …)

  • 𝐼 β†’ 𝛿𝛿 is excellent final state because of good diphoton mass

resolution, and low backgrounds

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SLIDE 15

β„Žβ„Ž β†’ 𝛿𝛿𝑐 𝑐

15

  • Predicted cross section for di-higgs production in SM
  • ~ 10 fb at 𝑑 = 8 TeV (NNLO)
  • various BSM models (i.e. 2HDM) predict large di-higgs production
  • Selection:
  • 2 photons + 2 b-jets
  • 95 < mbb < 135 GeV
  • Dominant BG: QCD Ξ³Ξ³bb, ttH and (Zβ†’bb)H in SM

non-resonant search resonant search (X β†’ hh)

  • Signal is extracted from fit in mΞ³Ξ³
  • Counting on mΞ³Ξ³ and mΞ³Ξ³bb plane
  • Phys. Rev. Lett. 114, 081802 (2015)
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SLIDE 16

β„Žβ„Ž β†’ 𝛿𝛿𝑐 𝑐

16

  • Non-resonant di-higgs production
  • Upper limit on anomalous non-resonant di-higgs production

2.2 pb (observed) 1.0 pb (expected)

  • 2.4 Οƒ deviations from BG only hypothesis
  • Resonant search

cross section x BR of narrow resonance decaying to di-higgs

2.1 Οƒ deviation at mX = 300 GeV with considering look-elsewhere effect

di-higgs search for hh β†’ bbbb: arXiv:1506.00285

  • Phys. Rev. Lett. 114, 081802 (2015)
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SLIDE 17

𝐼 β†’ 𝛿𝛿 + 𝐹T

miss

17

  • Motivated by dark matter (DM)
  • Higgs boson is unlikely to be radiated with initial

state radiation

  • sensitive to structure of effective DM-SM

coupling

  • Selection:
  • 2 photons + π‘žT

𝛿𝛿 > 90 GeV + 𝐹T miss > 90 GeV

  • SM Higgs boson BG
  • (Z β†’ Ξ½Ξ½)H
  • (W β†’ β„“Ξ½)H
  • non-resonant BG
  • QCD
  • WΞ³Ξ³, Ξ³ + jet
  • ZΞ³Ξ³, Ξ³ + jet

arXiv:1506.01081

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SLIDE 18

𝐼 β†’ 𝛿𝛿 + 𝐹T

miss

18

  • Interpretation to limits on DM production in Effective Field Theory (EFT)
  • Likelihood ratio as a function of fiducial cross

section of BSM Higgs boson + DM production

  • Highly model independent
  • Small deviations from BG only hypothesis
  • Observed upper limit: 0.70 fb
  • Expected upper limit: 0.43 fb
  • mΟ‡: DM mass

arXiv:1506.01081

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SLIDE 19

SUSY + β„Ž β†’ 𝛿𝛿

19

  • Direct pair production of chargino

πœ“1

Β± and neutralino

πœ“2

  • Scenario:
  • masses of pseudo-scalar Higgs boson and sleptons >

𝑛

πœ“1

Β± and 𝑛

πœ“2

  • 𝑛

πœ“2

0 βˆ’ 𝑛

πœ“1

0 > mH

  • πœ“1

Β± and

πœ“2

0 wino-like and degenerate

  • πœ“1

Β± β†’ 𝑋 β†’ β„“πœ‰

πœ“1

0,

πœ“2

0 β†’ β„Ž

πœ“1

  • SM Higgs boson BG: WH, ZH, ttH
  • Continuous BG: WΞ³, ZΞ³

BG only fit to mΞ³Ξ³

  • No excess found

Limits on exclusion regions in 𝑛

πœ“1

Β±,

πœ“2

0 and 𝑛

πœ“1

0 mass plane

  • Eur. Phys. J. C (2015) 75:208
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SLIDE 20

Other BSM searches

20

  • Flavor-changing neutral current
  • top quark decays to up-type (c, u) quark and Higgs boson
  • much suppressed in SM
  • BR(𝑒 β†’ 𝑑𝐼) ~ 3 x 10-15
  • π‘žπ‘ž β†’ 𝑒

𝑒 β†’ 𝑐𝑋 + π‘ŸπΌ β†’ 𝛿𝛿

JHEP06(2014)008

upper limit on 𝑒 β†’ π‘ŸπΌ branching ratio: 0.79 % no significant signal is observed

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SLIDE 21

Other BSM searches

21

  • Higgs boson to BSM
  • Higgs boson decays to neutralinos and/or gravitinos
  • β„Ž β†’ 𝛿 or 2𝛿 + 𝐹T

miss + 2 forward jets

  • predicted GMSB and NMSSM models in SUSY
  • GMSB: β„Ž β†’

𝐻 πœ“0 β†’ 𝐻 𝐻𝛿 or β„Ž β†’ πœ“0 πœ“0 β†’ 𝐻𝛿 𝐻𝛿

  • NMSSM: β„Ž β†’

πœ“2 πœ“1

0 β†’

πœ“1 πœ“1

0𝛿 or β„Ž β†’

πœ“2 πœ“2

0 β†’

πœ“1

0𝛿

πœ“1

0𝛿

  • not using β„Ž β†’ 𝛿𝛿 but using Higgs boson final-states with photons

ATLAS-CONF-2015-001

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SLIDE 22

Conclusions

  • 𝐼 β†’ 𝛿𝛿 analysis has great advantages of Higgs boson

property measurements

– one of the most accurate Higgs boson mass measurement – sensitive to Ξ₯t and gHWW as well as their relative sign

  • 𝐼 β†’ 𝛿𝛿 + X is a tool for BSM discovery

– di-higgs – SUSY – dark matter

  • LHC started physics at 13 TeV in 3rd June

– The discovery of Higgs boson was a great achievement in 7 TeV and 8 TeV run – We are excited for 13 TeV Higgs boson analysis

22

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SLIDE 23

23

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SLIDE 24

𝐼 β†’ π‘Žπ›Ώ

24

  • 𝐼 β†’ π‘Žπ›Ώ
  • rare process in SM
  • corss section (π‘žπ‘ž β†’ 𝐼 β†’ π‘Žπ›Ώ β†’ ℓℓ𝛿) = 2.3 fb at 8 TeV
  • sensitive to new heavy particles in loops
  • Ratio BF(𝐼 β†’ π‘Žπ›Ώ)/BF(𝐼 β†’ 𝛿𝛿) permits assessment
  • Phys. Lett. B 732C (2014), pp. 8-27

Number of signal expected = 9.0

  • bserved = 11.3
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SLIDE 25

ATLAS detector

25 Muon spectrometer photon muon electron π± Hadron calorimeter EM calorimeter Inner detector

  • Solenoid magnet

– supply 2T magnetic field to inner detector – very thin (0.66 X0)

  • Toroid magnet

– bend charged particle for Ξ·

  • Inner tracker
  • Calorimeter

– EM calorimeter – Hadron calorimeter

  • Muon spectrometer
  • Luminosity detector

Solenoid

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SLIDE 26

ATLAS EM calorimeter

26

  • Accordion structure Pb absorber
  • develop EM shower
  • cover full Ο† region + great Ο† uniformity
  • Ionization in Liquid Ar
  • 4 layers β†’ 3D shower reconstruction
  • photon direction reconstruction
  • energy calibration with shower shape

photon

pre-sampler: 1st layer: 2nd layer: 3rd layer: no absorber, correction for energy loss in inner detector high granularity along Ξ· β†’ separation of incoming particles deposit most of energy correction for high energy

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SLIDE 27

Photon reconstruction

27

  • Energy clustering in EM calorimeter with fixed size window
  • Photon-electron separation with track matching
  • Conversion vertex reconstruction
  • Unconverted photon / Converted photon / Electron separation

energy deposit EM calorimeter Hadron calorimeter Solenoid magnet conversion vertex Beam Unconverted photon Converted photon Electron inner detector (Pixel, SCT, TRT)

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SLIDE 28

SM Higgs production

28 125 tH:

  • tHqb: 0.0172 pb
  • WtH: 0.0047 pb
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SLIDE 29

Vertex of photon pairs

29 H β†’ Ξ³Ξ³ candidate event 24 primary vertices

  • A. calo-pointing

extrapolate from barycenters of energy deposits in EM calorimeter layers

  • B. Ξ£p2

T

Primary vertex tends to have high pT tracks from underlying events β†’ primary vertex has higher Ξ£p2

T of tracks

  • C. conversion vertex

Converted photons have e+e- tracks β†’ extrapolate tracks to beam line

  • High peak luminosity of LHC β†’ many inelastic proton-proton interactions
  • Many pileup vertices in addition to primary vertex where Higgs is produced
  • Photons don’t have tracks β†’ a bit difficult to select primary vertex in H β†’ Ξ³Ξ³ analysis

Vertex selection efficiency is 85 % with combining A, B and C,

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SLIDE 30

primary vertex selection efficiency

30

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SLIDE 31

Photon energy scale uncertainty

31

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SLIDE 32

Compatibility of mass measurements

32 compatibility of mass measurements from H→γγ and H→ZZ ΔmH = 1.47 ± 0.72 GeV compatibility of 11 % (1.6 σ)

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SLIDE 33

Signal strength vs Higgs mass

33

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SLIDE 34

Differential cross section

34

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SLIDE 35

Spin

35 pT

Ξ³Ξ³ < 300 GeV

pT

Ξ³Ξ³ < 125 GeV

Spin 2 model with low gluon fraction and pT cut-off at 125 GeV

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SLIDE 36

SUSY + β„Ž β†’ 𝛿𝛿

36

  • Direct pair production of chargino

πœ“1

Β± and neutralino

πœ“2

  • Scenario:
  • masses of pseudo-scalar Higgs and sleptons > 𝑛

πœ“1

Β± and 𝑛

πœ“2

  • 𝑛

πœ“2

0 βˆ’ 𝑛

πœ“1

0 > mH

  • πœ“1

Β± and

πœ“2

0 degenerate

  • πœ“1

Β± β†’ 𝑋 β†’ β„“πœ‰

πœ“1

0,

πœ“2

0 β†’ β„Ž

πœ“1

  • Selection
  • 2 photons + 1 electron/muon + 𝐹T

miss > 40 GeV

  • W and Higgs are back-to-back on transverse plane
  • high 𝑛T

𝑋𝛿

  • 𝑛T

𝑋𝛿 =

𝑛T

𝑋 2 + 2𝐹T 𝑋𝐹T 𝛿 βˆ’ 2𝒒T 𝑋 βˆ™ 𝒒T 𝛿

  • BG
  • SM β„Ž β†’ 𝛿𝛿 (WH, ZH, ttH)
  • WΞ³
  • ZΞ³

BG only fit to mΞ³Ξ³

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SLIDE 37

SUSY + β„Ž β†’ 𝛿𝛿

37

  • Combined with β„Ž β†’ 𝑐

𝑐 and β„Ž β†’ 𝑋𝑋

  • No excess found
  • Limits on exclusion regions in 𝑛

πœ“1

Β± and

𝑛

πœ“2

0 mass plane

  • limits on signal cross section normalized

by the simplified-model prediction as a function of 𝑛

πœ“1

Β±,

πœ“2

0 for 𝑛

πœ“1

0 = 0