CMS Observation of a new boson at the LHC and its implications for the origin of mass

KIT – University of the State of Baden-Wuerttemberg and National Research Center of the Helmholtz Association

Institut für Experimentelle Kernphysik

www.kit.edu

CMS Observation of a new boson at the LHC and its implications for the origin of mass.

Wim de Boer (for the CMS Collaboration)

2Wim de Boer Time and Matter, Venice, March 2013

Outline

Evidence for a Higgs particle in CMS Is it Peter´s Higgs or just a Higgs? What it has to do with the “origin of mass” in

the universe? What is the Higgs boson good for? What is so special about observed Higgs

particle?


The LHC

Two rings with 1232superconducting dipolesand 858 quadrupoles,26,7 km circumference

max. 2808 proton bunches, 40 MHZ collision rate,~1011 Protons / bunch

~500 million pp collisions / s at 7 & 8 TeV centre of mass energy

Bending magnets

Cavities for acceleration


Design Criteria for the CMS Experiment

Very good muon identification and momentum measurement.

H® ZZ, with Z®mm

Most precise photon detector. H®gg

Powerful inner tracking for electron identification.

H®ZZ, Z®ee

Hermetic calorimetry for missing ET signatures: H®WW, W® mn

First conceptual design of a “Compact Muon Solenoid” (CMS) was presented in Aachen (1990) based on a 4 Tesla solenoid.

4

From M. Della Negra, Wess-prize recipient (with P. Jenny), 2013, Karlsruhe


Compact Muon Solenoid (CMS) Experiment

Silicon Detectors

Measure tracks left by charged particles

CalorimetersAbsorb particles and

measure their energy

Muon DetectorsIdentify and

measure muons that penetrate

3.8 T MagnetBend tracks of

charged particles

z

0 (center)


CMS Collaboration

1400 Physicists600 Graduate students175 Institutes38 Countries


Assembly in the surface hallWaiting for the cavern to be ready


Descent of the central wheel (2000 tons)


Heart of CMS: all silicon tracker (200 m2!)

66 million silicon pixels: 100 150 µm2 9.3 million silicon microstrips: 80µm - 180µm. ~200 m2 of active silicon area (cf ~ 2m2 in LEP detectors)~13 precise position measurements (15 µm ) per track.

9

Pile-up: many collisions pro bunch crossing


78 reconstructed vertices in high pile-up run


Dimuon mass resolution

24 years of e+e- machines 24 hours of LHC


LHC Luminosity

New records: – centre-of-mass energy 8 TeV – peak luminosity 0.77∙ 1034 / cm² /sec – best week ∫L=1.35 fb-1 ( 75% design luminosity @ half energy & half # of bunches)

summer conferences

2012

HCP 2012

(delivered)

TAM 2013


Status of Higgs Hunt in July 2012


pp processes in Standard Model

7 14 TeV

9 orders of magnitude: 1 in a billion

Higgs events are rare !Need 5x more lumi at 14 TeVto discover 500 GeV Higgs


SM background

well understood


Higgs Production at the LHC

„gluon fusion“

„vector boson fusion“

„vector boson radiation“

„tt associated produktion“

Rate @ 8 TeV 25-50% higher than7 TeV


Higgs branching ratios

below ZZ “threshold” there is a lZl mode with an “off shell Z”, conventionally called ZZ*. The decay width, Z ~ 2.5 GeV and the Breit-Wigner resonant mass distribution,

2 2 2/ ~ ( / 2) /[( ) ( / 2) ]od dM M M means that the ZZ* decay rate is suppressed by a factor of 2~ [( / 2) /( )]Z ZM M with respect to ZZ decays

Note that q,l width ~ M while W,Z width ~ M3. Hence bb dominates below WW “threshold”. is down by ~ 9 due to coupling to mass, and 1/3 color factor.


Higgs branching ratios bb dominates below WW

threshold. is down by ~ 9 due to

coupling to mass, and 1/3 color factor.

WW higher than ZZ because distinguisable particles:

In addition phase space.

We are lucky with Mh=126 GeV: bb down to 60 % and „golden“ channelsZZ->4l and gg already appreciable! (golden, since they show narrow invariant mass peak with width limited by experimental resolution)


Searching for the Higgs in the four leptons final state

For a low mass Higgs the fourth lepton is soft.Selection cuts:Electrons pT > 7 GeVMuons pT > 5 GeV40 GeV < m12 < 120 GeV m34 > 12 GeV


Higgs candidate ZZ event (8TeV) with 2 µ and 2 e


H ® ZZ ® 4 leptons

Expected: BG:9.4, SIGNAL: 18.6 Total: 28Observed: 25 Signal strength: m0.9 0.3Significance 6.7 (7.2 exp) Mass: 125.8 ± 0.5 (stat) ± 0.2 (syst) GeV

6

7


December 2012 data

Significance 4.5 Mass 126.2 ± 0.6 (stat) ± 0.2 (syst) GeV


Search for the SM Higgs boson in the gg channel

m/m = 0.5 [E1/E1 E2/E2 cot(q/2)Dq]

H ® gg Simulation (100 fb-1)

E3%

E 0.39%129MeV

E

PbWO4 crystalsTest Beam October 2003

Target for the intercalibration < 0.5%

Mass resolution is the key for Higgs discovery in this channel


Mass resolution of gg system: Find the right vertex

• Algorithm to find the right vertex based on SpT2 of tracks and pT

gg balance.

• Tested on Z®mm events by treating muons as gammas.• Overall efficiency to find the right vertex for Higgs (m = 120 GeV)

integrated over pT spectrum: ~ 80%

g1

g2m/m = 0.5 [E1/E1 E2/E2 cot(q/2)Dq]

Need vertex to better than 10 mm, bunch 50 mm


Diphoton Candidate


gg Mass Distribution

Background is estimated from the data by a polynomial fit.

An excess is observed consistent with a narrow resonance around

125 GeV mass at 4.1


Outline



particle?


Other Channels

• Search for the Higgs in other decay modes : WW, bb and • Combined significance at MH=125.8 GeV: 6.9 • Overall satisfactory level of compatibility with the SM cross section. • Combined /SM = 0.88 ± 0.21 (so signal consistent with Peter’s Higgs)

MH=125.8 GeV

Expected ()

Observed ()

ZZ 5.0 4.5gg 2.8 4.1

WW 4.3 3.0bb 2.2 1.8 2.5 1.5

Combination 7.8 6.9


A first glimpse at SpinParity

in favour of 0+ ! p(0–) = 0.072 p(0+) = 0.72

So spin and parity consistent with Peter’s Higgs

Spin 0 2 S=1 particles angular correlations.

Positive parity 12 allowed decay planes aligned.

Negative parity 12 allowed decay planes orthogonal


Couplings for various channels


Fit of generalized couplings

So couplings consistent with Peter’s Higgs


Outline



particle?


Is Higgs Field the „Origin of Mass“?Answer: Yes and No. Energy or mass in Universe has little to do with Higgs field. Higgs field gives only elementary particles mass.

Mass in universe:

1) Atoms: most of mass from binding energy of quarks in nuclei, provided by energy in colour field, not Higgs field. (binding energy

potential energy of quarks kinetic energie of quarks, ca. 1 GeV, mass of u,d quarks below 1 MeV!)

2) Mass of dark matter: unknown, but in Supersymmetry by breaking of this symmetry, not by breaking of electroweak symmetry.

3) Dark energy: Higgs energy density seems too large. Why? Gigantic problem!

matter = 0.3

dark

ene

rgy =

0.7


The gigantic dark energy problemAccelerated expansion of universe implies a constant energy density in space time, either a cosmological constant or some kind of vacuum energy. The Higgs field is thought of as permeating space time with a constant energy density, which can be easily estimated from the effective potential to be 55 orders of magnitude above the dark energy density of about 10-29 g/cm3

If zero-point fluctuations of field considered and integrated to Planck scale, problem even more severe: (1018)4 GeV4 = 120 orders of magnitude larger than the dark energy density

In Supersymmetry problem somewhat less, since above breaking scale fermions and bosons cancel in zero-point fluctuations,problem „only“ 60 orders of magnitude.

V(=0) = -mH2mW

2/2g2

= O(108 GeV4) = 1026 g/cm3

1 GeV4=(GeV/c2 )(GeV3/(ħc)3)= 10-24 g 1042 cm-3 = 1018 g/cm3

Average density in universe:

crit = 2.10-29 g/cm3

WHY IS THE UNIVERSESO EMPTY???


Outline

Evidence for a Higgs particle in CMSIs it Peter´s Higgs or just a Higgs?What it has to do with the “origin of mass” in the universe?What is the Higgs boson good for? What is so special about observed Higgs particle? Does the observation point to physics beyond the Standard Model?


What is the Higgs boson good for?

Answer: without Higgs field we would not exist!

E.g.

It gives mass to the electron: without electron mass no atoms (r1/me)

It gives mass to the W,Z bosons, which make weak interactions weak at low energy, so the sun shines for 8 billion years


Outline

Evidence for a Higgs particle in CMSIs it Peter´s Higgs or just a Higgs?What it has to do with the “origin of mass” in the universe?What is the Higgs boson good for? What is so special about the observed Higgs particle?


What is so special about the Higgs boson?

Higgs mass below 130 GeV, as PREDICTED by SUSY!

W. Hollik: for me the observed Higgs boson with a mass consistent with Supersymmetry is the strongest hint for Supersymmetry!

H(SM,

1 doublet)

h,H,A,H+,H-

(MSSM, 2 doublets)

h1,h2,h3,a1,a2,H+,H-

(NMSSM, 2 doublets, 1 singlet)


Other beautiful SUSY features

SUSY provides UNIFICATION of gauge couplings

SUSY provides UNIFICATION of Yukawa couplings

SUSY has no quadratic divergencies Higgs mass can be calculated up to unification scale SUSY predicts EWSB with lightest Higgs below 130 GeV LHC: Mh = 126 GeV

SUSY provides „dark matter miracles“: Neutralino annihilation x-section a few pb correct relic density Neutralino-nucleon scattering cross section < 10-8 pb consistent with experimental limits


Unification for TeV SUSY massesU

. Am

aldi

, WdB

, H. F

ürst

enau

, PLB

, 199

1,

wdb

. C, S

ande

r, PL

B 2

004,

hep

-ph/

0307

049

i are gauge couplings of SU(3)SU(2)LU(1) (in first order i 1/log (energy Q)


Common masses at GUT scale:m0 for scalarsm1/2 for S=1/2 gauginosm1,m2 for Higgs bosons

m2 driven negative by top loops ,electroweak symmetry breaking at MZ for 140<Mt<200 GeV!

BINGO, Mtop predicted in this rangeby SUSY and it was found at171 ± 1.3 GeV!

Higgs mechanismus predicted in SUSY

EWSB only works if starting point at GUT scale not too large:need m EW scale, but it is termof supersymm. potential, could beGUT scale (m-problem)


<S> is m term of MSSM. If m is vev from singlet S, no problem to be small. Now 3 scalar Higgs bosons! (and 2 pseudoscalar)

NMSSM solves m-problem

MSSM NMSSM


Higgs mass in MSSM and NMSSM

MSSM

Higgs mass in MSSM 125 GeV for mstop 3 TeV

NMSSM: mixing with singlet

increases Higgs mass at BORN level for small tan and large NO MULTI-TEV stops needed


Branching ratios in NMSSM may differ from SM

Total width of 126 GeV Higgs tot may be reduced somewhat by mixing with singlet (singlet component does not couple to SM particles).

Then branching ratios enhanced, e.g. BR(H gg(ggtot enhanced (enhancement may be

reduced by light stops at gluon fusion loop by neg. interference with top loops)

Main decay mode BR(H bbar(bbartot hardly effected, as long as (bbar tot

Higgs with largest singlet component usually lightest one. Since it has small couplings to SM particles, it is NOT excluded by LEP limit.


Many papers on NMSSM after Mh=126 GeV and hint of too high Br into gg, see arXiv:1301.6437, arXiv:1301.1325, arXiv:1301.0453, arXiv:1212.5243, arXiv:1211.5074, arXiv:1211.1693, arXiv:1211.0875, arXiv:1209.5984, arXiv:1209.2115, arXiv:1208.2555, arXiv:1207.1545, arXiv:1206.6806, arXiv:1206.1470, arXiv:1205.2486, arXiv:1205.1683, arXiv:1203.5048, arXiv:1203.3446, arXiv:1202.5821, arXiv:1201.2671, arXiv:1201.0982, arXiv:1112.3548, arXiv:1111.4952, arXiv:1109.1735, arXiv:1108.0595, arXiv:1106.1599, arXiv:1105.4191, arXiv:1104.1754, arXiv:1101.1137, arXiv:1012.4490, ………..

Status of NMSSM

NMSSM consistent with h1=95 GeV, h2=126 GeV, motivated by 2 excess observed at LEP at 95 GeV with signal strength 2 well below SM.

Hard to discover at LHC, may be in decay mode h3h2+h1


Determining allowed SUSY parameter range

Variables calculated withNMSSMTools 3.2.4 usingUlrich Ellwanger*, John F. Gunion**, Cyril Hugonie*** http://www.th.u-psud.fr/NMHDECAY/nmssmtools.html

MicrOMEGAs 2.4.1G. Bélanger, F. Boudjema, P. Brun, A. Pukhov, S. Rosier-Lees, P. Salati, A. Semenov http://lapth.in2p3.fr/micromegas/

Minuit for minimization

LHC limits on squarks and gluinos. Mh=126 GeV

These dominate parameter space


Allowed parameter space

LHCXenon

+MA

B smm

LEP


LHC exclusion at 7 and 14 TeV


Expected Higgs masses in NMSSM


Expected Higgs decays in NMSSM


Expected Higgs x-sections in NMSSM


Expected coupling precision (SM)


Summary

Higgs boson at 126 GeV well established

All properties (Br and Spin) consistent with SM Higgs boson

Higgs hunt not over, since mass in range expected from Supersymmetry, which predicts more Higgs bosons

Hopefully a Higgs comes seldom alone

Need Br at level of a few % to check possible deviations expected in NMSSM


From Concept to Data Taking: 18 years

CMS cut in mid-plane

Letter of Intent (1992)Technical Proposal (1995)10 Technical Design Reports (1997-2006)3000 scientists from 40 countries

Silicon Tracker

Hermetic electromagnetic calorimeterScintillating Crystals

Hermetic Hadron Calori-meter: Brass scintillatorMuon

Chambers








Documents

CMS Observation of a new boson at the LHC and its implications for the origin of mass