A Higgs-bozon keresése: a kizárás és felfedezés statisztikus...

A Higgs-bozon keresése: a kizárás ésfelfedezés statisztikus kalandja

Search for the Higgs Boson: A Statistical Adventure of Exclusion

and Discovery

CCP-2013, XXV IUPAP Conference on Computational Physics,

Moscow, 21-24 August 2013

Dezso Horváthon behalf of the CMS Collaboration

[email protected]

Wigner Research Centre for Physics,

Institute for Particle and Nuclear Physics, Budapest, Hungary

& ATOMKI, Debrecen, Hungary

Horváth Dezso: Higgs-keresés StatFiz Szem., ELTE, 2014.11.19. – p. 1

Outline

The Higgs boson of the Standard Model

Statistical Methods of the Search

Exclusion at LEP

Observation at LHC

Is it the SM Higgs?

What next?

With the support of the Hungarian OTKA Grants K103917, K109703Horváth Dezso: Higgs-keresés StatFiz Szem., ELTE, 2014.11.19. – p. 2

References

The CMS Collaboration: Observation of a new boson at a mass of125 GeV with the CMS experiment at the LHC,Phys. Lett. B 716 (2012) 30-61.Long version: arXiv:1303.4571 submitted to JHEP

The CMS Collaboration: Measurements of the properties of thenew boson with a mass near 125 GeVCMS Physics Analysis Summary HIG-13-005, 14 March 2013

The ATLAS Collaboration: Observation of a new particle in thesearch for the Standard Model Higgs boson with the ATLAS detectorat the LHC, Phys. Lett. B 716 (2012) 1–29

The ATLAS Collaboration: Combined coupling measurements ofthe Higgs-like boson with the ATLAS detector using up to 25 fb−1 ofproton-proton collision dataATLAS NOTE, ATLAS-CONF-2013-034


The Zoo of the Standard Model

The elementary particles

3 fermion families:1 pair of quarks and1 pair of leptons in each

3 kinds of gauge bosons:the force carriers

All identified and studied!

+ the Higgs boson (?)

Color: the charge of the strong interactioncolored quarks ⇒ colorless composite hadrons of 2 kinds

hadrons = mesons (qq) + baryons (qqq)


The Standard Model

Derive 3 interactions of local U(1), SU(2) and SU(3)symmetries

Unify and separate e-m U(1) and weak SU(2) interactionsusing spontaneous symmetry breaking:

Anderson-Englert-Brout-Higgs-Guralnik-Hagen-Kibble (BEH) mechanism, 1963-64

Add a 4-component, symmetry breaking field to vacuum.Separate a good U(1) local symmetry from the ruined

U(1) ⊗ SU(2)

⇓electromagnetism + zero-mass photon, OK!

Turn 3 d.f. of Higgs-field to create masses for Z, W+, W−,get a correct weak interaction with 3 heavy gauge bosons.

4th degree of freedom: heavy scalar boson.Horváth Dezso: Higgs-keresés StatFiz Szem., ELTE, 2014.11.19. – p. 5

Glory Road of the Standard Model

Status in 2013

Includes hundreds ofmeasurements of all experiments

|Expt – theory|expt. uncertainty

Slightly deviating quantity usedto change

Now it is forward-backwardasymmetry of

e+e− → Z → bb

LEP Electroweak Working Group:

http://lepewwg.web.cern.ch/

Measurement Fit |Omeas−Ofit|/σmeas

0 1 2 3

0 1 2 3

∆αhad(mZ)∆α(5) 0.02750 ± 0.00033 0.02759

mZ [GeV]mZ [GeV] 91.1875 ± 0.0021 91.1874

ΓZ [GeV]ΓZ [GeV] 2.4952 ± 0.0023 2.4959

σhad [nb]σ0 41.540 ± 0.037 41.478

RlRl 20.767 ± 0.025 20.742

AfbA0,l 0.01714 ± 0.00095 0.01645

Al(Pτ)Al(Pτ) 0.1465 ± 0.0032 0.1481

RbRb 0.21629 ± 0.00066 0.21579

RcRc 0.1721 ± 0.0030 0.1723

AfbA0,b 0.0992 ± 0.0016 0.1038

AfbA0,c 0.0707 ± 0.0035 0.0742

AbAb 0.923 ± 0.020 0.935

AcAc 0.670 ± 0.027 0.668

Al(SLD)Al(SLD) 0.1513 ± 0.0021 0.1481

sin2θeffsin2θlept(Qfb) 0.2324 ± 0.0012 0.2314

mW [GeV]mW [GeV] 80.385 ± 0.015 80.377

ΓW [GeV]ΓW [GeV] 2.085 ± 0.042 2.092

mt [GeV]mt [GeV] 173.20 ± 0.90 173.26

March 2012


The Higgs boson of the Standard Model

Spinless, neutral, heavy particle

The scalar particle needed for renormalisation

Does it really exist? SM: it must!

Many jokes of the Higgs boson on internet...The Higgs boson walks into a bar. The bartender says"Watch out, there were some guys looking for you."

The Higgs boson walks into a church. The priest says „Yourkind is not welcome here”. The boson replies: „But withoutme how can you have mass?”


Viccek a Higgs-bozonról, elotte

A bárba besétál egy Higgs-bozon. A csapos nem érti...

Szeretnék végre látni egy jó Higgs-bozonos viccet.Biztosan létezik, de évekbe telhet, amíg rátalálunk.


Viccek a Higgs-bozonról, utána

A bárba besétál egy Higgs-bozon.A csapos megkérdezi: Mi van? mire o: Én!!

A Higgs-bozon felfedezése után a fizikusok tömegesenünnepeltek.

Nem tudom, mi a csuda az, de klassz, hogy felfedezték!

Ellenorizni kell. A múltkor is azt hittem, Higgs-bozonttaláltam az ágyam alatt, de csak egy üveggolyó volt.

Jó, hogy megvagy, Isten-részecske. Én csak egyátlagember vagyok, aki nem ért téged.


Spontán szimmetriasértésA történet:

Mechanizmus: Anderson javasolja 1963-ban

Kidolgozzák:F. Englert és R. Brout, 1964P. Higgs, 1964G.S. Guralnik, C.R. Hagen és T.W.B. Kibble , 1964

Skalár bozon: Peter Higgs, 1964-65

Bozon megfigyelve: ATLAS és CMS, 2012

Nobel-díj: F. Englert és P. Higgs, 2013

Az elnevezés (vitatéma)

Igazságos: Higgs-bozon, BEH-mechanizmus

Igazságtalan: Higgs-mechanizmus, -potenciál, -térHorváth Dezso: Higgs-keresés StatFiz Szem., ELTE, 2014.11.19. – p. 10

Statistical Concepts of Particle Physicists

are far from those of official math statistics!

LHC Statistics for Pedestrians by Eilam Grossin PHYSTAT-LHC Workshop on Statistical Issues for LHC

Physics, CERN-2008-001, p. 205:

A pedestrians guide . . . to help the confused physicist tounderstand the jargon and methods used by HEP

Phystatisticians.

A Phystatistician is a Physicist who knows his way inStatistics and knows how Kendalls advanced theory of

statistics book looks like....

Every collaboration has phystatistician experts and they allhave quite different ideas how to analyse data...


Last 2 PHYSTAT-LHC Workshops


Statistics Committees


Likelihood

Poisson distribution (ni events in bin i):

P(ni|µi) =µ

nii e−µi

ni!

Poisson likelihood: L = ΠiP(ni|µi)

Expected < ni >: µi =∑

j Lσjǫji

L: luminosity (∼ collision rate),σj : cross section of source j,

ǫji: efficiency (Monte Carlo) of source j in bin i.


Luminosity: collision rate

Luminosity: L = fnN1N2

A

[L] = s−1cm−2 (∼ flux)

f : circulation frequency; n: nr. of bunches in ring;N1, N2 particles/bunch; A: spatial overlap

Rate of reaction with cross section σ at ǫ efficiencyR = ǫσL

Integrated luminosity:∫ t2t1

Ldt

measured in units of inverse cross-section:[pb−1, fb−1]


Exclusion and Discovery

General convention inaccelerator

experiments:

Exclusion of a givenphenomenon at

≥ 95% confidencelevel.

Observation ofsomething new:> 5σ abovebackground.

(x−x )/0 σ

ε/2ε/2

One-sided exclusion:X > X0 at 95% CL ifXobs − X0 > 1.64σ


And what is σ?The total uncertainty of the physics parameters P

according to the best honest guess of the experimentalist.

It has a statistical component(from the number of observed events)

and systematic ones from various sources:

Monte Carlo statistics and inputs, calibration factors,efficiencies, etc. (nuisance parameters Θ)

could be added up with correlations accounted for with a

final uncertainty roughly: σ =√

σ2stat + σ2

syst

However, we derive the final uncertainty via marginalizing(integrating out) the nuisance parameters in likelihood L

using the related probability distributions W:

L(P ;x) = W(x|P ) =∫

W(x|P,Θ)W(Θ|P )dΘ


Blind Analysis

„A blind analysis is a measurement which is performedwithout looking at the answer. Blind analyses are the

optimal way to reduce or eliminate experimenter’s bias, theunintended biasing of a result in a particular direction.”

A. Roodman: Blind Analysis in Particle Physics,http://arxiv.org/abs/physics/0312102, SLAC, 2003

Originally coming from medicine

Basic analysis method of Higgs search at LHC:

Optimize, prove and publish your analysis technique usingsimulations and earlier data only before touching new data

in the critical regionCMS, 2012: 110 < MH < 140 GeV blinded

because of 3σ excess observed in 2011

Simultaneous unblinding for all analysis channelsHorváth Dezso: Higgs-keresés StatFiz Szem., ELTE, 2014.11.19. – p. 18

The Large Electron Positron collider


Accelerators at CERN, LEP era


The LEP Collider

Year E(e+e−), GeV∫

Ldt/4, pb−1 main goal

1989–94 ∼ 91 140 Z0

1995 130–136 5

1996 161–172 20 W+W−

1997 184 60 WW, ZZ

1998 189 190 WW, ZZ

1999 192–202 220 Higgs

2000 204–209 220 Higgs


Search for the SM Higgs boson at LEP

Dominant formation:

Higgs-strahlung

e−e+→ZH

Dominant decay:

H → bb

Various analyses for different Z decaysHorváth Dezso: Higgs-keresés StatFiz Szem., ELTE, 2014.11.19. – p. 22

What is observed: resonance

τ = Γ−1 lifetime ⇒ exp. decay: N(t) = N0e−Γt

Probability distribution:

|χ(E)|2 = 1(E−M)2+Γ2/4

Breit-Wigner equation

M

Γ

resonance

centre

width

(~ = 1, c = 1)Lorentz curve

New particle discovery: resonance at decay energycorresponding to the particle mass


Hunting the Higgs boson

Compose a complete SM background using Monte Carlo simulationtaking all types of possible events normalized to their cross-sections.

Higgs signal: simulation of all possible production and decayprocesses with all possible Higgs-boson masses

Put all these through the detector simulation to get eventsanalogous to the measured ones.

Optimize the event selection: reduce B background, enhance S

signal via maximizing e.g.NS/

√NB or NS/

√NS + NB or 2 · (

√NS + NB −

√NB)†

Calculate at experimental luminosity expected nr. of events forsignal and background at various conditions.

SM background ∼ experiment? (YES ⇓ / NO ⇑).

†Bityukov and Krasnikov, 1999


Hypothesis Testing: Test Statistic

Likelihood ratio: signal+background/background Q = Ls+b/Lb

Usually analysed and plotted:−2 lnQ(mH) =

2∑Nch

k=1

[

sk(mH) −∑nk

j=1 ln(

1 +sk(mH)Sk(xjk;mH)

bkBk(xjk)

)]

nk: events observed in channel k, k = 1 . . . Nch

sk(mH) and bk: signal and background events in channel k forHiggs mass mH

Sk(xjk;mH) and Bk(xjk): probability distributions for events forHiggs mass mH at test point xjk

xjk: position of event j of channel k on the plane of itsreconstructed Higgs mass and cumulative testing variableconstructed of various features of the event like b-tagging, signallikelihood, neural network output, etc.


No Higgs at LEP: MH > 114.4 GeV

10-5

10-4

10-3

10-2

10-1

1

100 102 104 106 108 110 112 114 116 118 120

mH(GeV/c2)

1-C

Lb

3σ

2σ

4σ

ALEPH

ObservedExpected signal+backgroundExpected background

10-5

10-4

10-3

10-2

10-1

1

100 102 104 106 108 110 112 114 116 118 120

mH(GeV/c2)

1-C

Lb

3σ

2σ

4σ

DLO

ObservedExpected signal+backgroundExpected background

Expected and observed signal confidence level

assuming background only

(ALEPH, DELPHI, L3 and OPAL: Phys. Lett. B 565 (2003) 61-75.)

Excess in ALEPH’s 4-jet events at 115 GeV:

ELEP2000 = 206 GeV mH(115) + mZ(91) = 206 GeV !!


LEP: exclusion by experiment


LEP: exclusion by channel


ALEPH event (e+e−→bbqq)

b quark: long lifetime ⇒ secondary vertexHorváth Dezso: Higgs-keresés StatFiz Szem., ELTE, 2014.11.19. – p. 29

LEP: spaghetti diagrams

Event weightsvs. Higgs mass

for 17 selected LEPevents

The LEPCollaborations,Search for the

Standard Model HiggsBoson at LEPPhys. Lett. B

565 (2003) 61.


Accelerators of CERN now

LHC: Large Hadron Collider

SPS: Super Proton

Synchrotron

AD: Antiproton Decelerator

ISOLDE: Isotope Separator

On Line DEvice

PSB: Proton Synchrotron

Booster

PS: Proton Synchrotron

LINAC: LINear ACcelerator

LEIR: Low Energy Ion Ring

CNGS: Cern Neutrinos

to Gran Sasso


LHC and its main experiments


Steering magnets of LHC

1232 superconducting magnets (before installation)(L = 15 m, M = 35 t, T = 1.9 K, B = 8.3 T)


Dipole magnets of LHC in the tunnel


CMS: Compact Muon Solenoid

14000 ton digital camera:100 M pixel, 20 M pictures/sec, 1000 GB/sec data

Processes max 400 pictures/sec ⇒ intelligent filter!!Horváth Dezso: Higgs-keresés StatFiz Szem., ELTE, 2014.11.19. – p. 35

The (Compact Muon) Solenoid itself


The CMS Collaboration (2013)

181 institutions of 42 countries

3275 physicists (incl. 1535 students)

790 engineers and technicians

Participants by countries of institutes:USA: 1426, Italy: 545, Germany: 349, Russia: 270

Participants by nationality:USA: 861, Italy: 697, Germany: 375, Russia: 353

390 publications since 2010, the start of LHC data taking

Huge joint effort:3000 people worked on it for 20 years!


Formation of the SM Higgs bosonin p-p collisions at LHC

q H

g

g

gluon fusion

q_

q_

HW,Z

q q

vector bosonfusion


Decay of the SM Higgs boson

March 2012

Not excluded by 2011

CMS data:

114 < MH < 127 GeV

(at 95% CL)

(where many decay

processes contest)

Best identified:

H → γγ;

H → ZZ∗ → ℓ+ℓ−ℓ+ℓ−

(ℓ± = e±, µ±)

Excess observed

2 − 3σ at ∼125 GeV! ⇑Horváth Dezso: Higgs-keresés StatFiz Szem., ELTE, 2014.11.19. – p. 39

CMS: elektromagnetic calorimeter

optimized for studying H →γγ

75,848 PbWO4 single crystal scintillators


Eseményregisztrálás, triggerEsemény (event)

Valamilyen érdekes észlelés (trigger) indítja

Minden jellemzo adatot tartalmaz,de csak a megszólalt detektorelemekét

Egyidejuleg többfélét figyelünk (és regisztrálunk)

Fizikai, kalibrációs, ellenorzo

Triggertol függ, milyen adatokat olvasunk/tárolunk

TriggerAmi az érdekes

Elektronikus és számítógép-generált

CMS: 2 trigger-szint0: 20 MHz (2009-12); 1: ∼ 20 kHz; 2: ∼ 400 Hzeseményhozam


A CMS event: H → γγ candidate


CMS: 78 identified vertices!

Many p-p collisions can be in the same event (same bunchcollision). Record: 78 identified vertices. This increases

data taking speed and makes life hard.


MINOS-bizonytalanságNem-lineáris becslésnél

rengeteg elhanyagolás ⇒ eredmény torzítása

szimmetrikus szórás nem életszeru

MINUIT MINOS-hibája

Paramétert változtatni,amíg χ2 →χ2 + 1

többi paraméteroptimalizálásával

χ2n−m−1

χ2min+1

χ2min

p~ σ1− p~ p~ σ2+

2+ σ1− σp = p

exp∼

p


Szisztematikus bizonytalanságMinden bizonytalanság, amely nem az észlelteseményszámból eredBecslése: Valamennyi bevitt információ ésszeruváltoztatásának hatása az eredményreÖsszegzés korrelációk figyelembevételévelEredeti illesztési munka sokszorosa

Késobb korrigálható Nem korrigálhatókorábbi mérések eredménye szimuláció eredménye

elméleti számítás adott méréstechnika elemeglobális kalibráció (ELEP) aldetektor kalibrációja

Ésszeru változtatás:

(Mért – szimulált) érték

Bemeno paraméter ± szórás

Különbözo algoritmusok(fragmentáció, jet-keresés)

to eliminate fro theHorváth Dezso: Higgs-keresés StatFiz Szem., ELTE, 2014.11.19. – p. 45

Teljes bizonytalanság

Felfedezés: +5σtot. σtot = ?

A P fizikai paraméterek teljes bizonytalansága akísérletezo legjobb becsületes becslésével meghatározva.

Durva becslés: összeadni, σ =√

σ2stat + σ2

syst

Korrelációkat figyelembe kell venni. Szimulációból?

LHC-nál: sziszt. bizonytalanság eltüntetése a likelihoodbóla zavaró (nem fizikai) Θ paraméterek marginalizációjával

(kiintegrálás) a megfelelo W eloszlásokkal:

L(P ;x) = W(x|P ) =∫

W(x|P,Θ)W(Θ|P )dΘ


Fizikatörténet I: mérés vs. év

Review of Particle Physics, K. Nakamura et al, J. Phys. G 37, 075021 (2010)


Fizikatörténet II: mérés vs. év

Review of Particle Physics, K. Nakamura et al, J. Phys. G 37, 075021 (2010)


4 July 2012: we have something!

ATLAS and CMS, at LHC collision energies 7 and 8 TeV, intwo decay channels H → γγ and H → ZZ → ℓ+ℓ−ℓ+ℓ−,at invariant mass of m ≈ 126 GeV see a new boson at aconvincing statistical significance of 5σ conf. level each withproperties corresponding to those of the SM Higgs boson.

H → γγ ⇒ JH = 0 or 2

Data analysis was optimized for SM Higgs search...

Nevertheless, it has to be shown to be the SM Higgs, e.g.

JH = 0: H → ZZ and H →WW angular distribution ofdecay products

H → XY... cross sections follow the SM predictions

There is one Higgs boson only(no charged or more neutral ones)


2012 július 4: valami van!

ATLAS és CMS, 7 és 8 TeV ütközési energián, H → γγ ésH → ZZ → ℓ+ℓ−ℓ+ℓ− csatornában, m ≈ 126 GeV

tömegnél statisztikusan jelentosen (kísérletenként 5σszignifikanciával) lát egy új H részecskét a SMHiggs-bozonjának megfelelo tulajdonságokkal.

François Englert és Peter Higgs elso találkozása


CMS: H → γγ (VBF)

Vertex for measuring the γγ invariant mass:two hadron jets from vector boson fusion.


CMS and ATLAS: A new boson

ATLAS: 2931 authors

CMS: 2899 authors


CMS: H → γγ mass distribution

2012 (2011 + 25% of 2012 data) 2014 (2011 + all 2012 data)

σexpt/σSM = 1.14 ± 0.21(stat)

+0.09

−0.05

(syst)

+0.13

−0.09

(theo)

CMS Collaboration, Eur. Phys. J. C (2014) 74:3076Horváth Dezso: Higgs-keresés StatFiz Szem., ELTE, 2014.11.19. – p. 53

ATLAS: H → γγ mass distribution

2012 (2011 + 25% of 2012 data)2014 (2011 + all 2012 data)

ATLAS Collaboration,arXiv.org:1408.7084, 2014


CMS: H → ZZ∗ → ℓ+ℓ−ℓ+ℓ−

2012 (2011 + 25% of 2012 data) 2014 (2011 + all 2012 data)

σ/σSM = 0.93

+0.26

−0.23

(stat)

+0.13

−0.09

(syst)

CMS Collaboration, Physical Review D 89, 092007 (2014)Horváth Dezso: Higgs-keresés StatFiz Szem., ELTE, 2014.11.19. – p. 55

CMS: H → ZZ∗ → ℓ+ℓ−ℓ+ℓ−

CMS : H→ ZZ∗→ ℓ+ℓ−ℓ+ℓ− animated


CMS_HZZ4l_animated.gif

p-value

The probability of obtaining a test statistic at least asextreme as the one that was actually observed, assuming

that the null hypothesis is true.

Higgs search: The probability that random fluctuation of themeasured background could give the observed excess.

Discovery:excess above 5σ

p-value:how much above


The Look Elsewhere effect

Looking for something with threshold p value p < α?If you did not find it you will look elsewhere(e.g. at different simulated Higgs-masses).

ndf (degrees of freedom) independent tests should giveprobability p = 1/ndf possibly leading to false discovery.

CMS recommendation: quote 2 p-values

local (discovery place) and

global (whole region)

No such effect in exclusion


CMS: p−distributions (4 July 2012)

The probability that random fluctuation of the measured background couldgive the observed excess.

γγ and ZZ: 5.0σ γγ, ZZ and WW: 5.1σ All together: 4.9σ

ATLAS got the same: γγ and ZZ: 5.0σAdding WW increased the ATLAS excess to 6.0σ


CMS, Dec. 2012: significance

Doubling 8 TeV statistics increased CMS excess to 6.9 σSharp peak, close to SM exp. at 126 GeV, far less elsewhere


CMS 2014: mass vs. x-sec

mH = 125.03+0.26

−0.27(stat)

+0.13

−0.15(syst) GeV

(CMS Physics Analysis Summary HIG-14-009, 2014)


CMS, March 2013: spin, parity

CMS data favor + parity for SX = 0CMS Physics Analysis Summary HIG-13-005


CMS: is it the SM Higgs boson?

Branching ratios of different decay channelsas compared to SM predictions for a 125.03 GeV Higgs

boson

CMS Physics Analysis Summary HIG-14-009, 3 July 2014


Signal strengths vs. SM expectations

CMS preliminaryresults

Relative signalstrengths for variousproduction and decay

channels

68% confidence levelcontours

All agree with the SM

CMS Physics AnalysisSummary HIG-14-009,

3 July 2014


CMS vs. ATLAS: masses


CMS vs. ATLAS: mass(determined consistently, in various ways)

Mass averaged for both channels and all decay modes

CMS, 2013: 125.7 ± 0.3(stat) ± 0.3(syst) GeV/c2

CMS, 2014: 125.03 ±

+0.26

−0.27

(stat) ±

+0.13

−0.15

(syst) GeV/c2

ATLAS, 2013: 125.5 ± 0.2(stat) ±

+0.5

−0.6

(syst) GeV/c2

ATLAS, 2014: 125.36 ± 0.37(stat) ± 0.18(syst)

= 125.36 ± 0.41 GeV/c2

High gain in systematics with some loss of statistics.


CMS vs. ATLAS: signal strength

Total cross section for all production and decay channels as compared tothe SM prediction for MH = 125 GeV (µ = σobs/σSM):

CMS, 2013: 0.80 ± 0.14

CMS, 2014: 1.00 ± 0.09(stat) ± 0.07(syst) ±

+0.08

−0.07

(theo)

ATLAS, 2013: 1.43 ± 0.16(stat) ± 0.14(syst)

All agree with the Standard Model (unfortunately)


Fizikai Nobel-díj, 2013The Nobel prize was awarded to François Englert and PeterW. Higgs "for the theoretical discovery of a mechanism that

contributes to our understanding of the origin of mass ofsubatomic particles, and which recently was confirmed

through the discovery of the predicted fundamental particle,by the ATLAS and CMS experiments at CERN’s Large

Hadron Collider."

Rolf-Dieter Heuer, a CERN foigazgatója, bejelenti aNobel-díjat az ATLAS és CMS közös irodaépületében.


CMS, H→γγ: mass and cross section

All results (ATLAS & CMS, properties of various production and decaychannels) agree within uncertainties.

Mass:mγγ = 124.70 ± 0.31(stat) ± 0.15(syst)GeV

= 124.70 ± 0.34 GeV

Signal strength as compared with SM prediction:

σexpt/σSM = 1.14 ± 0.21(stat)

+0.09

−0.05

(syst)

+0.13

−0.09

(theo)

= 1.14

+0.26

−0.23

CMS Collaboration, Eur. Phys. J. C (2014) 74:3076


CMS, H→ZZ: mass and cross section

H→ZZ→ℓ+ℓ−ℓ+ℓ− (ℓ = e, µ)

m4e = 126.2

+1.5

−1.8

m2e2µ = 126.3

+0.9

−0.7

m4µ = 125.1

+0.6

−0.9

.

Mass average: mZZ = 125.6 ± 0.4(stat) ± 0.2(syst) GeV

Signal strength as compared with SM prediction:

σ/σSM = 0.93

+0.26

−0.23

(stat)

+0.13

−0.09

(syst)

CMS Collaboration, Physical Review D 89, 092007 (2014)


CMS, 2014: mass and cross section

Combination of all channels:H→γγ, H→ZZ→ℓ+ℓ−ℓ+ℓ−, H→WW→ℓνℓν, H→ττ ,

WH, ZH;H→bb, ttH, H→hadrons, leptons.

(CMS Physics Analysis Summary HIG-14-009, 2014)

Measured mass:

mH = 125.03

+0.26

−0.27

(stat)

+0.13

−0.15

(syst) GeV

Signal strength as compared to SM prediction at themeasured mass:

σ/σSM = 1.00 ± 0.09(stat) ± 0.07(syst)

+0.08

−0.07

(theo)


What does MH = 126 GeV mean?Conference Why MH = 126 GeV?, Madrid, 25-27 Sep. 2013

MH vs. Mtop is critical,at vacuum stability border

Need very preciseMH, Mtop and αs.

SM may be valid untilPlanck energy (1018 GeV)!

New physics anywhere??

OR:

Somebody is pulling ourleg???

Anthropic principle???

S. Alekhin et al.,arXiv:1207.0980, 2012


Conclusion

We very probably observed the Standard Model Higgsboson or (unfortunately, less probably) a Higgs bosonof a more general model.

The LHC will restart in 2015 with much higher energyand luminosity.

Let us hope for some deviation from the StandardModel (although none seen yet).

Thanks for your attention!


A Higgs-bozon keresése: a kizárás és felfedezés statisztikus...

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