1

On the Trail of the Higgs Boson

Meenakshi Narain

2

Outline• Higgs Primer

– Why do we think there is a Higgs Boson ?

• How and where have we looked for the Higgs– Discussion of Higgs Search Results at LEP

• How and where will we look in the future– LHC and the Tevatron

• Search Strategies at the Tevatron:– Standard Model Higgs

• Low and High Mass regions

– Top/Higgs associated production– SUSY Higgs

• Conclusions

3

The Standard ModelQuarks Leptons

Interactions described by local gauge theories:

strong electroweak

SU(3)color £ SU(2)L £ U(1)Y

8 gluons W§ Z0 Adding mass terms for W§, Z bosons, fermions breaks local

gauge invariance

R

L

R

L

R

L

e

e

R

R

L

R

R

L

R

R

L

b

tb

t

s

cs

c

d

ud

u

R

R

L

R

R

L

R

R

L

b

tb

t

s

cs

c

d

ud

u

R

R

L

R

R

L

R

R

L

b

tb

t

s

cs

c

d

ud

u

4

The Higgs MechanismBreaks symmetry while maintaining local gauge invariance (renormalizability)

Add complex weak isospin doublet with “mexican hat” potential

3 components of form longitudinal components of W§, Z (massive)

1 component real scalar particle

Higgs boson

04

03

21

i

i

Couple fermion fields to fermion mass terms

B (Hfermions) / fermion mass

5

Theoretical Limits on Higgs Mass

If SM is valid up to ¼ Planck Scale

130 . MH . 180 GeV

updated EW precision

updated direct limit

M

Planck,gravity

MH too large: Higgs self coupling blows up at some

scale

MH too small: for scalar field

values O() the Higgs potential

becomes unstable

e.g. Riseelmann, hep-ph/9711456

6

Experimental Limits on Higgs MassIndirect

Higher order corrections link SM parameters

e.g. MW = Mtree+ +

Measure MW, mt (or others) constrain MH

LEP,TeV,NuTeV,SLC global fit: MH < 193 GeV @ 95% CL

(LEPEWWG Summer 2002)

DirectLEP: e+e-ZH

MH > 114.4 GeV @ 95% CL (LHWG Note/2002-01)

WW t

b2

2

W

t

M

m

W WW

Higgs

W

H

M

Mln

FEMZ GM ,,

7

Experimental Limits on Higgs Mass

(LEPEWW Summer 2002

8

Is there anything beyond the SM?

Problems of the SMMany free parameters

Hierarchy: Planck scale vs ewk scalelarge corrections to scalar masses (MH)

fine tuning required to keep MH light

Triviality:self couplings of scalars blow up at high energies

Gravity not included

SM can only be the low energy limit of a more comprehensive theory

9

SupersymmetrySymmetry between fermions and bosons

Natural solution to hierarchy problemAdditional corrections to MH precisely cancel

divergences

More complicated Higgs sector¸ 2 Higgs doublets 5 physical scalar particles:

CP-even: h0, H0, CP-odd: A0, charged: H§

MSSM: Mh . 135 GeV

SUSY with gauge coupling unification: Mh . 205 GeV (Quiros&Espinosa hep-ph/9809269)

10

Can the Higgs be heavy?Global fit to electroweak data MH<193 GeV

Assumes no physics beyond SM

If Higgs heavier, there must be new physics at some scale

Peskin, Wells PRD 64, 093003 (2001)

e.g. topcolor-seesaw modelpositive contributions to T

allows MH. 450 GeV Chivukula, Hölbling, hep/ph-0110214

11

Higgs Searches

• Very low mass

•LEP: e+e- collider,•Two different Eras

–LEP1: ps = Mz–LEP2: ps above Mz upto 209 GeV

12

The LEP Detectors

Being dismantled (1989-2000)

13

Higgs Production at LEP•Dominant Production Process:

Bjorken Process

``Higgsstrahlung’’

LEP1LEP1

s s m mHH+m+mZZ

s = ms = mZZ

LEP2LEP2

Higgs Production Cross Section

Center of mass energy (GeV)

(pb)

14

Very little background expected

Events expected

at LEP

among 2x107 Z

Higgs Search at LEP1

For mH<2mW :

H bb (~80%)

0.0 mH 65 GeV/c2

Excluded at 95% C.L.

For mH<2m :

H ee,

For mH<2mb: H gg, cc,

15

Higgs Searches at LEP2• Extending the reach

to s-MZ.

L ~200 pb-1

5533 ~ 0.04 pb

Higgs Decay modes (mH=115 GeV)

tau

b quarks

gluons

WW

other73.6%

7.2%

6.6%8.1%

Cross Sections

Decay Branching Ratios

16

Event SignaturesDefined by the Z decay mode:

taus

quarks

neutrinos

electrons

muons

Higgs Z Fraction

bb qq 51.5% bb 14.7% Any ll 6.7%

bb 2.5% qq 5.0% Total 80.9%

“4-jets”“missing E” “leptons”

17

SM background processesAt LEP SM processes

well understood and measured.

18

SM Four Jet Channel• Topologies:

• Backgrounds:– ZZ: Dominant for mH ~ 90 GeV/c2 when Z bb

• Most important for 4b channel at all masses

– WW:A priori reducible (no b-quark jets, apart from Vub ).• Tedious if jets are mistagged.

– Quark pair production (QCD processes):• Important near threshold production for mH>mZ

• b’s and gluons back-to-back,

reconstructed mass = maximum possible

4b: Hbb/Zbb and 2b: Hbb/Zqq (where q= [u,d,s,c])

Different backgrounds and hence performance

19

Event Selection• Discrimination from event shape & kinematics

• Correlated quantities Likelihood or Neural Network Analyses

• B-tagging critical in enhancing signal contribution

ThrustThrust

EEminminmin (di-jet) massmin (di-jet) mass

Log YLog Y3434

20

Identifying b-jets1) Semileptonic decays of the b-quark B(b + X) 20% detect in jets

2) life time 1.5 ps c 0.5 mm

Flight Length ~ few mm

Collision

Impact Parameter

Decay

Vertex

B Decay Products

precise tracking silicon microstrip detectorse+e-bbqq

21

After full alignement, hit precisions are :

~10 m in R ~15 m in Rzin the central part of the detector.

Ex: DELPHI

~3 double-sided layers

~0.5 X0

Silicon Vertex Detector

More on this later in the week

22

• Simulated IP distributions and resolutions tuned on data. data/simulation agree within 5%

R significances

before tuning after tuning

Tuning b-tagging performance

23

B-taggingPerformance checked on control samples:

Data and predictions agree within 5%

Excellent WW rejection reached, but control of tail is critical!

24

Mass ReconstructionNeed to understand all significant distributions

The mass reconstruction depends heavily on good calibration of the detectors (tracking, calorimetry..) and on software techniques…

ALEPH

Pre-selection level

25

pairing & mass reconstruction

•For each pairing: make a 5C fit with Mij =MZ & build a likelihood including the probability that the two other jets are b-tagged coming from the Higgs decay.• A unique mass value is selected from the most likely combination

six possible pairings:

(1,2)(1,3)(1,4)

M=MZ

B=2.0

(2,3)(2,4)(3,4)

M=MZ

B=-0.5

Z dijet

(3,4)(2,4)(2,3)

M=113

B=3.4

(1,4)(1,3)(1,2)

M=97

B=5.7

H dijet

from Jesus Marco, Budapest

2 4

1

3

26

Reconstructing mass• Typical resolution: 3 GeV Preselection sample

ALEPH – 4C fit and

DELPHI & OPAL: 5C fit

L3: 6C fit with mH

Incorrect Pairing

Correct pairing mREC~2mW-mZ

Fully Hadronic WW control sample

WW events selected with the WW events selected with the Aleph (Cut) analysis where Aleph (Cut) analysis where none of the jets are none of the jets are b-taggedb-tagged

mH=mpair1+mpair2-mZ

27

Fishing out the signal:The baits:

Ingredients for the first likelihood variable L1

28

Fishing Cont’dVariables used

for the second likelihood L2

The discriminant D = L1 x L2

29

One of the 3 Aleph events4 b cand.

HZ hyp.mH=114.4

GeV/c2

NN = 0.997

jet b-tag: Z1 0.9942 0.78 H3 0.9934 0.999

A 22 GeV shower in SICAL that was giving Evis = 252 GeV is rejected by a better algorithm : mH= 112.8 mH=114.4

ELEP=206.7

ZZ hyp.mZ=97 GeVmZ=94 GeV

30

Missing Energy Channel

Cross-section ~ few fb at 115: Not accessible with ½ fb-1 per experiment

Any quark

WW

s=192GeV

MH (GeV)

Cross Section

Fusion

fb

31

The “Missing Energy Channel”• Preselect events, use Likehood or Neural Nets

– Btags Emiss, Cosmiss, Acollinearity• double ISR, and bb events (when the neutrinos take most

of the energy), give collinear topologies; for an event at rest, the mass recoiling to a Z is pushed to s-MZ. While, due to the Z width, even in the Higgstrahlung close to the kinematical limit, the H is not usually produced at rest.

To improve on signal mass reconstruction: kinematic fits with E,p conservation and the Z mass constraint.

Mass resolution: 7 GeV

32

L3 H characteristics

Mass and neural network output both

at signal peak

Used for discriminato

r

33

The signal is not collinear !

for acollinearity < 5o 5% of Higgs ~ 0.015 pb 30% of qq(g) ~ 80 pb

The collinear events are: -Z double radiative events to the Z with (visible mass ~M(Z))

-qq where the energy is lost in or for detector problems, (high visible mass)

at 206 GeV 6x10-4 ee qq 5x10-4 ee bb loose 60 GeV in neutrinos:

In 2000 for L= 220 pb-1, every exp.

has ~10 events ee bb that loose more than 60 GeV in

neutrinos

Of these 10 evts , 80% have pT10 GeV

WP

HA

CT

Montecarlo for Higgs 115 GeV/c2, Ecm=206 GeV

H: irreducible background, eebb

34

The L3 event

35

The lepton channel

Background

llqq

L3 eeqq, Ecm=206 GeVM(ee)= 89 GeV/c2

M(qq)= 108 GeV/c2

If the is included in the jet:a very high di-jet mass

good high mass Higgs candidate !

If the is associated to the muon a perfect ZZ

but…radiated photonsthe golden candidates!but BR = 3 % for each flavor...

36

SM Higgs combined results3 selections with increasing purity for a 115 GeV/c2 signal

•All channels contribute Hqq,H,Hll,qq•event selection based on a discriminant variable and mass

Data 5Bkg 3.9Sig 3.8

Data 17Bkg 15.8Sig 7.1

Data 4Bkg 1.2Sig 2.2

S/N for m(H) > 109 GeV/c2

> 0.5 >1 >2

37

Interpreting the Results• Combine all channels in a 2-D space:

– reconstructed Higgs mass MHrec – discriminant variable G (b-tag, kinematical info..)

• In each bin of MHrec and G:– Background (MC) bi – Signal (MC) si

– Num. of candidates Ni

• For each “test mass” mH

Construct a parameter Q to order experimental outcomes:Does the experiment look signal like or background like?

LEP HIGGS WG

38

Combined LEP Test Statistic Likelihood: The Final LEP Result

1, 2 bandsfrom background only

Data consistent with a Higgs signal of MH=115.6 GeV/c2

39

The results of each experiment

40

The results per channel

41

Confidence Level Estimation

Prob of seeing the candidates (or more) if they were background: 1 -CLb = P(Q>Qobs|background)

MH=116

MH=110 MH=120

1 -CLb 0.32 2.7 x 10-3 5.7x10-7

1 3 5

1-CLbCLs+b

s+b

bobs

42

Compatibility with the background

1-CLb @ MH=116

GeV/c2

ALEPH 2.4 x 10-

3

DELPHI 0.874L3 0.348OPAL 0.543

4-jets 5.7 x 10-3

l++0.368

Neutrinos 0.474Leptons 0.275Taus 0.255

LEP 0.099

43

Confidence Levels…

Probability of missing the signal if it is there: CLs+b = P(QQobs|signal+background)

CLs = CL s+b / CLb gives the lower bound on Higgs mass

MH=116

1-CLbCLs+b

s+b

bobs

44

The combined limit

Exp ObsALEPH 113.5 111.5DELPHI 113.3 114.1L3 112.4 112.0OPAL 112.7 112.7

4-jets 114.5 113.3l++114.2 114.2

LEP 115.3 114.4

45

The events

The first 4 events maintain the highest weight in the final analyses

46

Higgs discovery?

Changes: +10% L @ 206 final Ebeam final detector calibrations Aleph 2D correlation in Hqq Delphi Hee optimized New MC for sig and bkg L3 more MC OPAL better bgk estim. New analyses, new mass rec.

Nov 2000

4.2 x 10-3 mH>113.5(115.3 expected)

~ 0.09 mH>114.4(115.3 expected)

~0.03 mH>114.1(115.4 expected)

Jul 2001 final

Background Probabilities 1-CLb (mH=115)

Nov 2000 July 2001 finalALEPH: 0.00065 0.0015 0.0024DELPHI: 0.68 0.77 0.73L3: 0.068 0.32 0.32 OPAL: 0.19 0.20 0.50

from end of 2000 to the final results 2002…

Earlier analyses suggested hints of signal which generated much excitement. Even now, the result is consistent with background only at 9% level.

47

The “final” results• All 4 experiments implemented various modifications in order to

improve the sensitivity and/or better control the background

• Full data processing: final detector calibration, alignment, b-tagging… New MC generators (DELPHI) , more MC statistics (all) Precise knowledge of the LEP cm energy (all) Upgrades for some analyses: - New analyses with better sensitivity (OPAL): new jet pairing (4- jet), and L NN(miss.ener)

- Better rejection of beam-related background (ALEPH) - Extension of analyses down to bb threshold (DELPHI)

• L3: final result already last year : Few candidate events compatible with the Higgs hypothesis

• ALEPH: Excess of events compared to what is expected from SM background, suggesting a Higgs boson with mass mH~114 GeV/c2

• DELPHI: No evidence for any Higgs signal, limit set to mH> 114.1 GeV/c2

• OPAL: No evidence for any Higgs signal, limit set to mH> 112.7 GeV/c2

48

The Far Future: LHC• Large Hadron collider (p-p, ps » 14TeV)

– Reach for Higgs upto 1TeV

49

Meanwhile in the PrairieThe Fermilab Tevatron Collider

(p anti-p):

Main Injector(new)

Tevatron

DØCDF

Chicago

p source

Booster 1992-96 Run 1: 100pb-1, 1.8TeV2001-2007(?) Run 2: ~15fb-1, 1.96TeV

CDF DØ

50

The D experiment

5000 tons500+ physicistsRun I: 1992-1996100 pb-1

80 publications100 Ph.D.s

muon detector

calorimeter

tracker

beam pipe

51

H-disks (4)

Barrels (6)F-disks (12)

20cm

50cm

1.3m

D Tracker

et=1.7

Solenoid (2 T)

Fiber Tracker

Silicon Tracker

800,000 channels1400 silicon elements area : 4.7 m2

10 m single hit resolution

52

The CDF experimentmuon detector

calorimeter

tracker

53

SM Higgs Production at Tevatron

[pb] (mH=120 GeV)

typical production cross-sections

gg HWHZH

0.70.170.1

WZWbb

3.211

tttb+tq+tbq

7.53.4

QCD O(106)

Gluon fusion Associated Production

WZ/ZH production is cleanestM. Spira, hep-ph/9810289

54

SM Higgs Decays and BRs•Divide into two regions•Low Mass

–H!bb domintaes–gg!H precluded by QCD background

•High Mass–Gauge Boson decays dominate–H!WW becomes promising

•Less sensitivity in cross over region

_

M. Spira, hep-ph/9810289

55

Low Mass Higgs Search•Higgs couples most strongly to massive particles:

•Focus on associated production (WH/ZH)– Best Prospects: leptonic W/Z decays – QCD background large for hadronic channels

•SM Background processes:

•Sensitivity will depend on – b-jet tagging– dijet mass resolution

1

32

56

SM Higgs: Leptonic Channel (1)

• Typical Selection:

•Main backgrounds:•Event selection optimized to maximize S/B

57

Expected Events and Sensitivity

Sensitivity crucially depends on dijet mass resolutions

58

Sensitivity crucially depends on dijet mass resolutions

CDF RunI “Calibration” for Higgs Search

Problem is not intrinsic jet resolutionIn 2 jet WH events, mass resolution ~ 10%

(but, costs 30-70% in efficiency)With 2 jet requirement relaxed,

mass resolution is about 15%

59

Multivariate Analysis Techniques•Further Improvements from use of Neural Networks, Grid Search, Likelihood methods.

– Significant gains, compare S/B with and without neural nets

60

SM Higgs: Leptonic Channel (2)

• Main backgrounds:•Event selection optimized to maximize S/B •Typical Selection:

61

•Some distributions:

62

•Use Neural Networks to optimize analysis:– use different networks

• one for signal

• 4 different ones for bkg

63

SM Higgs: Leptonic Channel (3)

•Small rate but good S/B•Main backgrounds:•Typical Selection:

64

•Neural Network Analysis:•signal

•Backgrounds

(4 different networks)

•Kinematic fit may enhance sensitivity•Add Taus?

65

Low Mass Higgs Search•It’s going to be challenging…

A 120 GeV Higgs signal

Total Background

66

High Mass Higgs Search•Around MH=130 GeV, H0! bb takes a plunge

•For MH>130 GeV, H0! WW* rises–Exploit the large gg! H0 cross section–Identify topologies with small SM cross sections–Focus on leptonic Gauge Boson Decays

Stange, Marciano, Willenbrock (PRD49, 1994); Gunion & Han (PRD51, 1995); Mrenna & Kane (hep-ph/9406337)

67

High Mass Higgs Search (1)

•Dileptons, Missing Energy signature•Leading contribution from gluon fusion

•SM backgrounds:

–Bkg¼ 25pb–S/B ¼ 4x10-4

68

• Typical Selection:

Exploits difference in kinematics for WW prod• Continuum vs. at threshold production via spin 0

resonance – Utilize angular correlations between leptons & ET

69

• Angular correlations between leptons:Due to spin correlation of Higgs Boson decay

products, the two charged leptons tend to move in parallel

70

•Add likelihood analysis based on variables

•Define “Cluster Mass” MC to sharpen mass

•Likelihood analysis give a factor of 40 reduction for dominant WW background. (MH=170 GeV)• S/pB for 30fb-1 » 3.8

Likelihood analysis

Kinematic cuts

Bkg: WW

71

High Mass Higgs Search (2)

•Distinct Signature:–Same sign dileptons + jets

•Contributions from process:

•Backgrounds to consider:–Di-boson (WZ, ZZ), Tri-Boson, top pair production…

72

•Selection criterion:

•Dominant bkg: WZ, ZZ– (WZ)=0.15fb–W/Zjjj = 0.15fb (fake j! e)– (top, di/tri-boson) = 0.18fb

•Good S/B, but low rates–Limits significance–Control of systematics challenging–Fine tuning of cuts

73

High Mass Higgs Search•Results for MH > 130 GeV:

•Require large luminosity » 30fb-1

74

Combined Significance •Combine all SM channels

•Use Neural Network Analyses for low mass •Assume 10% resolution for mass reconstruction•Systematic error: Min of 10% or 1/p(sLdt £ B)

•Band) 30% effect from mbb, b, bkgs

75

• Striking topologies:

• Small £ B– key: Multijet reconstruction – Critical: b-jet tagging

• New NLO corrections k=0.8

• Backgrounds:

Goldstein et. al., hep-ph/0006311

76

•Low Mass– Lepton+6 jets

•require least 3 or 4 b-tagged jets

– Reconstruct top•“Know” jet assignments

–For 3 or more jets:•For 1fb-1:

– S=0.4, B=0.3 and S/pB=0.7

•For 15 fb-1 data–Expect 5 or 6 signal events–2.8(4.1) for 1(2) experiment(s)

–Assumes 70% b-tagging efficiency.

•High Mass–Both lepton+jets and dilepton channels

•Like sign dileptons: 3-6 signal events, less than 1 bkg•Trilepton: 2 signal events, less than 1 bkg

77

SUSY Higgs Search•Neutral Higgs

–Translate SM results into SUSY (tan, MA) parameter space according to SUSY couplings–Vh, VH can be Standard Model-like

•reinterpret the SM analysis

–In addition: enhanced at large tan

)( Vhqq )(sin2 )( SMVhqq )( VHqq )(cos2 )( SMVHqq mixing angle

between CP even h and H

,tan1

2

v

v

78

MSSM Higgs Search •Exploit enhanced Yukawa coupling due to large bb cross section at the Tevtraon:

•Event selection: –Trigger on 4 jets–At least 3 jets b-tagged

–Mass dependent jet ET cuts

•e.g. leading jet pT> M/2 -5 GeV

–Reconstruct mass with b-tagged jets pairs

•Backgrounds: •Limited by trigger efficiency, hard to trigger on jets

–Impact parameter triggers will help

•Require excellent b-tagging efficiency•Adding ! will help

79

•Sensitivity: tan vs MA plane

•With 2 fb-1 data, sensitivity for MA » 125 GeV

(for interesting region for tan» mt/mb» 35)

Relatively modest integrated luminosity required !

Exclusion Discovery

80

MSSM Higgs: V Channel•Model Independent interpretation:

•Apply to any “New Physics” model–Compare the above R (for experiments) to theoretical expectations R for “SUSY”, assuming some typical values of SUSY parameters (tan, mixing angle , etc.)

Exclusion

Discovery

81

Sensitivity for MSSM Higgs •V and bb:

Consider different scenarios•Minimal Mixing

–At each point Left-Right Stop mixing= 0

•Maximal Left-Right Stop Mixing •Large A and ) Suppression of H(bbbb)

10fb-1 20fb-1

30fb-1

5 discoveryLEP

V, 5fb-1

Exclusion

10fb-1 15fb-1With 15 to 20 fb-1, can cover most of the MSSM parameter space.

Maximal Mixing Minimal Mixing

82

References• The Tevatron studies described were performed by the

RunII SUSY/Higgs working group at the Tevatron. The details of the study can be found in hep-ph/0010338.– A comprehensive note – with multitude of theoretical and

experimental references.

• ttH production at the Tevatron: hep-ph/0006311• Latest LEP results:

– For Higgs from LHWG Note/2002-01– For Electroweak Global Fits: LEP EWWG/2001-02

• LHC:– ATLAS and CMS TDR

83

Conclusion

Tractricious, designed by Wilson and constructed by members of the Technical Support Section, sits in front of the Industrial Complex. The structure is comprised of 16 stainless steel outer tubes, made from scrap cryostat tubes from Tevatron magnets, and 16 inner pipes from old well casings. Each tube is free standing and designed to withstand winds up to 80 mph.

•Does the Higgs Boson Exist?…lots of theoretical motivation and

…mounting indirect evidence

•LEP… a “scent” of the Higgs?•Tevatron Run II:

– no single discovery channel, combine all modes• If NO SM Higgs: exclude upto 190 GeV with 10fb-1 data

• If SM Higgs exists: a 3 to 5 discovery upto 190 GeV with 30fb-1 data

•Can rule out 115 GeV Higgs with 2fb-1 data per experiment

•Verification at 3 will require 5-6 fb-1.

– Other models – beyond the SM, .eg. MSSM, can cover a large parameter space with 15 to 20 fb-1 data

•LHC: In the far future, potential to cover the entire range

84

Onward to uncharted Territories….

85

86

Cross Sections

87

Mass Resolutions: cont’d•Signal significance depends on bb mass resolution

–For RunII aim for 10% mass resolution–30% better than in the previous Run

WHlbb

CDF RunI “Calibration” for Higgs Search

88

Mass Resolutions: cont’d• Compare Run I Jet ET

resolution to Fast MC• Optimize b-jet reconstruction

and corrections• corrections (partly for b’s):

– b/light-q jet calibration• Improvement due to increased

+jets statistics• Significant sample of Z bb

– Correct for in bl– Correct for in jets

• Can get 12% at M=120 GeV

– If only 12% mass resolution • Required luminosity increases

by 20%

WHlbb

89

Mass Resolution Issues•Problem is not intrinsic jet resolution

–In 2 jet WH events, Mjj is close to gaussian•Mass resolution is about 10% (but, costs 30-70% in efficiency)

–With 2 jet requirement relaxed, •Mass resolution is about 15%

3rd jet must be judiciously used!

90

More Improvements – b-tagging•b-jet tagging: Will it be good enough?

–Displaced Vertices

•3-D vs 2D vertexing possible•Improved impact parameter resolution•(Extrapolation from CDF Run I eff.)

–Semileptonic tags

do

primaryvtx

secondaryvtx

Lxy

e or in jet

b

•secondary vtx 2 tracks•tagged if Lxy/ Lxy

91

can we improve?

b-tagging

LEP2, S.Jin PHENO2000•For bb backgrounds:

•Relative Luminosity goes as

• Eff increase from 60% 65% would result in the same signal significance for 20% less integrated luminosity.

92

Low Mass Higgs Searches•Channels:

93

WH: Leptonic ChannelsDistributions

94

bb mass reconstruction

the extracted signal significance depends on input dijet mass resolution

WHlbb

improvement from use of tracking and preshowerin jet reconstruction? (also, different algorithms?)corrections (partly specific to b’s): - corrections for into jets (bl) - corrections for into jets - b/light-q jet calibration - b/light-q parton corrections

and...-effect of extra interactions on jet reconstruction

optimized b-jet reconstruction+corrections

E. Barberis

95

b-tagging

•displaced vertices: RunI SVX algorithms on RunII detector (3D Si, large )

+ soft lepton tagging (~10%)

~55-60%

fakes:

doprimaryvtx

secondaryvtx

Lxy

•secondary vtx 2 tracks•tagged if Lxy/ Lxy

e or in jet

b DØ used only ‘s in top analyses

M.RocoM.Roco

96

Collisions and particle identification

Hadron collisions: a proton (anti-proton) beam is a broad- band beam of partons

hard scattering

p

p_

- total energy: unknown- total longitudinal momentum: unknown- total transverse momentum: zero

• heavy quarks and leptons decay via weak interactions to lighter counterparts:

(stable) m 650~c W(delayed) m 90~c W(delayed) m 470~c cWb(prompt) fm 1~c bWt

*

*

*

97

Particle identification• an energetic quark or gluon appears in a detector as a jet of colorless hadrons:

• the total transverse energy of invisible particles (e.g. ) can be inferred from the energy of the visible particles:

E E

E E E

T T

T T T

inv vis

inv vis

0

98

A generic detector

neutrinos

detector cross section around the collision point

99

Beyond the Standard Model

• in the window mH~130-180 GeV: SM valid up to mPlank

but: 222222 ooo gmmmm

quadratic divergencies in scalar masses

22

2

2

22

oo

o gmm

10-38 !

needs adjustment to the 38 decimal place: violates concept of naturalness

SM valid to EW scale EWSB Fundamental th. to higher scales

• SM, further problems, ad hoc couplings, mixings..• Extended, MSSM?• Composite, TC?

Higgs sector:

100

Higgs in MSSM the simplest minimal supersymmetric standard model (MSSM) supersymmetric 1) SM recipe 2) an extra Higgs doublet 3) supersymmetric partners

5 physical Higgs bosons ),,,( HAHh ooo

geduAHhZHW ,,,,,,,

gedu

edu

RRRR

LLLLoooo ~~,~,

~,~

~,~,~

,~~~~~~,~

1234

SM

SUSY

fermion boson symmetryfor every SM spin degree of freedom there is

a supersymmetric spin degree of freedom

CP even

CP odd

mh<130 GeV theory limit on lightest

Higgs

101

LHC Higgs Search•SM discovery modes:

Higgs Mass Reach

102

LHC: Higgs Coupling•Measure production rate and couplings•Large top-Higgs coupling cross section for ttH associated production is sizeable

•Also an additional discovery mode and test of SM couplings

•With 300fb-1:

g

g

yt

H

t

t

1v

m2y t t

103

invisibleinvisible

NeutrinosNeutrinos do not interact with the detector.

Momentum conservation tells us:

But don’t measure pz. Therefore

0213

pppn

ii

T

n

i

iTT ppp

5, 21

104

Identifying Muons

105

b-tagging•Exploit long lifetime of the b-jet: b» 1.6ps

Mrec=1103 GeV/c2

Three well b-tagged jets with two reconstructed displaced vertices

HZ Candidate, ALEPH Experiment

e+e-bbbb

s = 206.7s = 206.7

106

Four fermion backgrounds

acollinear

Two fermion collinear

Total well modelled

Collinearity of H

We cannot add criteria in the light

of the data.

Otherwise classical statistical

analysis is impossible.

L3 candidate

107

Identifying particlesDijet event

W! e