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Search for Higgs. Amitabh Lath Rutgers The State University of NJ. What is the Higgs?. Short answer : Field/Particle responsible for mass. Longer answer : Completes the Standard Model of Particles and Fields. So what is this Standard Model of P & F?. Our Periodic Table.

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Search for higgs

Search for Higgs

Amitabh Lath

Rutgers

The State University of NJ

Rutgers University

September 7 2005


What is the higgs
What is the Higgs?

  • Short answer: Field/Particle responsible for mass.

  • Longer answer: Completes the Standard Model of Particles and Fields.

  • So what is this

    Standard Model of P & F?

Rutgers University

September 7,2005


Our periodic table
Our Periodic Table

Rutgers University

September 7,2005


Our periodic table1
Our Periodic Table

Quark stuff: hadrons.

3q  baryon

q-anti(q)  meson

Q=2/3

-1/3

0

1

+ Higgs!

(not yet found)

Rutgers University

September 7,2005


Experimentalist view prologue
Experimentalist View: Prologue

Einstein,

photoelectric

effect

J.J. Thomson, 1897

Street and Stevenson, 1937

cloud chamber

Rutgers University

September 7,2005


Experimentalist view weak effects
Experimentalist View: Weak Effects

Reines and Cowan

Reactor (beta decay)

Lederman, Schwartz and Steinberger

group using AGS pion beam

Rutgers University

September 7,2005


Experimentalist view quarks
Experimentalist View: Quarks

Kendall,

Friedman,

Taylor group

at SLAC.

Gell-Mann’s quarks

Feynman’s “partons”

Rutgers University

September 7,2005


Experimentalist view quarks1
Experimentalist View: Quarks

Gell-Mann predicts

Omega- particle.

Found by bubble

chamber group at

BNL (Samios et al)

Rutgers University

September 7,2005


Experimentalist view quarks2
Experimentalist View: Quarks

The strange particle

decay, KLmm not

as prolific as predicted

  • Glashow, Iliopoulos, and

  • Maiani posit a “new”

  • particle. (GIM Mechanism)

  • Diagrams with “charm”

    destructively interfere.

Found by Ting, Richter groups (almost

simultaneously) at BNL, SLAC.

Rutgers University

September 7,2005


Experimentalist view 3 rd generation
Experimentalist View: 3rd Generation

Note: Sq for each

generation = 0

Fermilab collider program

(cast of hundreds)

Fermilab fixed-target

experiment (Lederman)

Beautiful analysis by Martin Perl

at SLAC’s SPEAR

Rutgers University

September 7,2005


Experimentalist view weak bosons
Experimentalist View: Weak Bosons

  • Glashow, Weinberg and

  • Salaam introduce two

  • primordial fields:

  • Weak Isospin

  • Weak Hypercharge

  • that mix (weak mixing angle)

  • to give W,Z and g

+ Higgs!

They also introduce a

scalar field (Higgs).

W, Z discovered by UA2

Rutgers University

September 7,2005


Electro weak unification
Electro-Weak Unification

  • Weak Isospin (3-component)

    • W1 + iW2 = W+

    • W1 – iW2 = W-

  • Weak Hypercharge (1-component)

    g cosqw -sinqw W3

    Z sinqw cosqw B0

Left

Handed

Int. only!

=

Weak Mixing Angle

Rutgers University

September 7,2005


Higgs and electroweak unification
Higgs and ElectroWeak Unification

  • Adding scalar field to Lagrangian gives mass-like terms, leading to

  • Masses of bosons determined by couplings, and parameters of the scalar field potential (v,l).

  • Mhiggs is a free parameter.

All three things

in this equation

can be measured

by experiments.

MW/MZ = cosqW

Rutgers University

September 7,2005


What is higgs
What is Higgs?

  • Scalar Field. Introduced in: A MODEL OF LEPTONS Steven Weinberg, Phys.Rev.Lett.19:12641266,1967 .

  • Gives mass to everything,

    but Higgs boson not seen.

  • Fermion masses? Need (arbitrary) couplings. Called Gi in Halzen & Martin.

MH < 246 GeV/c2

(fit of all EW data and top mass)

Rutgers University

September 7,2005


Different types of higgs
Different Types of Higgs

  • SM Higgs

    • One (complex) doublet.

    • Cross section for direct production at Tevatron depressingly low.

    • Theoretical problems.

  • Beyond SM Higgs

    • Different models fix (some) SM problems.

    • Tevatron can compete in some parts of parameter space.

Rutgers University

September 7,2005


Problems with higgs
Problems with Higgs

  • Fundamental Scalar Field

    has problems.

    • What are the corrections to its mass?

  • Two basic types of solutions:

    • Higgs is a composite (Technicolor)

    • Other diagrams cancel problems. (SUSY)

Rutgers University

September 7,2005


Beyond sm higgs technicolor
Beyond SM Higgs (Technicolor)

  • “pion” like composite Higgs.

    • Techniquarks make technipions

  • QCD-like strong force (ergo “technicolor”).

  • Ruled out!

    • The electron-positron asymmetries at the Z pole were not kind to this theory.

    • However, a lot of physicists have a soft spot for compositeness.

T = isospin breaking terms

Rutgers University

September 7,2005

S = Isospin cons. terms


Beyond sm higgs supersymmetry
Beyond SM Higgs (Supersymmetry)

  • The “GIM Mechanism” solution to the Higgs problem.

    • Got a problem diagram? Add another to cancel it out.

    • Fermion sFermion

    • Boson  Bosino

  • A very expensive theory.

    • Doubles the particle spectrum.

    • Consolation prizes: LSPDark Matter? Unification of couplings?

Rutgers University

September 7,2005


The mssm higgs
The MSSM Higgs

  • Minimal SuperSymmetric Standard Model.

    • Simplest realistic SUSY theory.

    • 3 neutral(h,A,H), 2 charged Higgs Bosons (masses related).

    • tanb ratio of up/down type couplings.

  • The LEP experiment (e+e- collider) covered a large swath of parameter space by ruling out higgs up to 90 GeV.

Rutgers University

September 7,2005


Mssm higgs production
MSSM Higgs Production

  • At large tanb, both gg and bb production contribute.

    • s rises like tanb2.

  • A, and h/H are produced simultaneously.

  • ~100 pb!

  • For inclusive mode, ttdecay is very interesting.

Double this!

~SM Higgs

Rutgers University

September 7,2005


Higgs decays
Higgs Decays

  • Higgs decays to bb 90% and tt 10%

    (Higgs couples to mass)

    • higgs bb? No hope

      for inclusive.

    • higgs tt ? Yes!

  • Decays to WW, ZZ take over if Higgs is heavy enough.

Rutgers University

September 7,2005


Higgs decays1
Higgs Decays

  • Most Higgs searches look for b-quarks.

    • SM, SUSY higgses (ask SVS).

  • Problem: “real” b-quarks from hadronic interaction swamp those from Higgs.

    • About 6 orders of magnitude!

  • Usual solution: Look at “associated” stuff:(Higgs+W/Z, Higgs+extra b-quarks)

  • Our solution: Forget b. Look for tt.

    • Give up (some) sensitivity to SM Higgs.

    • Gain a clean channel for MSSM Higgs.

Rutgers University

September 7,2005


The tevatron accelerator

CDF

Tevatron

Main Injector

The Tevatron Accelerator

p-pbar collisions at 1.96 TeV C.M. Energy

Rutgers University

September 7,2005


CDF Collaboration

Missing Conway…

Rutgers University

September 7,2005


The cdf detector
The CDF Detector

beampipe

Collision point

Superconducting Magnet

Rutgers University

September 7,2005


Particle detection
Particle Detection

  • Electron track, contained cluster, E/P~1 g, no track

  • Quark matter (p) - track, extended (hadron) cluster

  • Muon penetrating track

  • Weak, no charge (n) Missing momenta

Rutgers University

September 7,2005


Particle detection1
Particle Detection

s

  • Electron track, contained cluster, E/P~1 g, no track

  • Quark matter (p) - track, extended (hadron) cluster

  • Muon penetrating track

  • Weak, no charge (n) Missing momenta

~nb

~mb

~nb

HIGGS? ~pb

Rutgers University

September 7,2005


The tau lepton
The tau lepton.

  • 3rd generation lepton.

  • Heavy. Mass = 1.77 GeV/c2

  • Lots of decays

    • Leptonic: t enn, t  mnn(17% each)

    • Hadronic: t  pn, pp0n, pppn, pp0p0n(64%)

  • Shorthand: te, tm, th

Rutgers University

September 7,2005


Looking for higgs
Looking for Higgs

t

t

n

H

n

n

p, quark

matter

e or m

Signal:

  • One t goes to electron or muon.

    • We know how to detect e, m

  • Second t goes to pions

Backgrounds?

  • Ztt (irreducible)

  • We, m + “jets” (quark stuff including p)

Rutgers University

September 7,2005


Detecting taus
Detecting taus?

  • Taus are leptons that can decay to “jets” of pions.

  • jets from q,g are fatter.

  • Signal cone.

  • Isolation cone (annulus).

    • Up to 30o.

    • Veto tracks, p0…

  • Should get:

    • Characteristic 1,3 track enhancement.

    • |Q| = 1

    • m < 1.8

te ,tm

Rutgers University

September 7,2005

Standard cuts


Problem with taus
Problem with taus.

  • Fakes from jets(as with almost everything at hadron machines).

  • th IS a jet; albeit a narrow one (pencil jet).

  • Jet production 100’s mb. Compare to 100’s of pb for t production.

  • Don’t know enough about JETS  need fake rate from data. This is where the problems start.

    • Different sources of jets give very different fake estimates.

Rutgers University

September 7,2005


Fake rates prologue
Fake Rates. Prologue.

  • CDF Run 1(U.C. Berkeley)

    • Jet triggered samples give lower fake rates than lepton triggered ones.

    • Fake rates rising with jet ET.

  • What is going on?

Huge difference!

Rutgers University

September 7,2005


Solution multi parameter
Solution: Multi-Parameter.

  • Instead of parameterizing fake rate in one variable, we now use several.

  • Big discrepancy in rates disappears.

  • Is this the right thing to do?

  • Why bother?

“Relative” fake rates

Rutgers University

September 7,2005


Check of fake rate predictor
Check of Fake Rate Predictor

  • Newfangled multi-parameter fake rate function is scary.

    • Jet variables (energy, direction, etc)  BLACKBOX  probability of a fake t.

  • Let’s test it on different samples of jets.

    • Jet triggered sample (assume one jet is “lepton”)

    • Photon+jet (use photon as lepton)

    • W+jet.

    • MC Jets.

  • Let’s look at different distributions, not just absolute numbers.

Rutgers University

September 7,2005


Checking jet t fake rates

Pure

sample of

jets

Predictor

Fake rate prediction

Checking Jett Fake Rates

Pure

sample of

jets

t reconst

Fake rate measured

Rutgers University

September 7,2005


Checking fake rates qcd
Checking Fake Rates (QCD)

This is a sanity check at best, since we built our “black box” -- fake predictor-- using Jet Triggered data.

Rutgers University

September 7,2005


Checking fake rates g jet
Checking Fake Rates (g +jet)

This is the

most heartening

set of plots.

Rutgers University

September 7,2005


Checking fake rate w jet
Checking Fake Rate (W+jet)

Rutgers University

September 7,2005


Tt signature
tt signature

Classic

Hadronic tau

signature

  • Bothte th andtmth are included in these plots

  • Ntracks = 1,3 and |Qt| = 1 not applied to the

  • left plot to demonstrate tau signature

Rutgers University

September 7,2005


Expected vs observed events
Expected vs. Observed Events

source thtethtµall

Z → τ τ 215.8±3.9 186.5±3.4 402.4±5.3

Z → ll 6.5±0.5 8.3±0.8 14.8±1.0

tt, VV 1.0±0.1 0.9±0.1 1.9±0.1

jet → τ 44.6±0.2 30.0±0.4 73.2±0.5

total bg 268.9±3.9 225.7±3.7 492.3±5.4

Observed 260 229 489

Errors are stat. only

No big whopping discrepancy…

Rutgers University

September 7,2005


Higgs-Z Separation.

Define p(ET) as (EX,EY, 0 ,ET)

Define mvis = m(p(t1) + p(t2) + p(ET))

Use these shapes to fit the data,

 Is there a “Higgs bump”?

Total acceptance ~1.5%

(from simulations).

Rutgers University

September 7,2005


Mvis Plot

  • We use this “mass-like” variable to get Higgs/Z separation.

  • Nice fit!

  • Note: Z does not peak at MZ!

Rutgers University

September 7,2005


More on higgs fit
More on Higgs Fit

  • Fix Z, other bg

  • by known s and

  • luminosity.

  • Fit Att shapes

  • from simulation

  • We don’t see a

  • higgs signal.

?

Rutgers University

September 7,2005


Events in high mass tail

Tau (3-prong)

These look like good

Z/g* tt events

(Or higgs signal?)

More data coming soon!

Electron

Rutgers University

September 7,2005


Expected and observed limits
Expected and Observed Limits

Rutgers University

September 7,2005


Expected and observed limits1
Expected and Observed Limits

fluctuated high

around m=130 GeV

fluctuated low

near MZ

Rutgers University

September 7,2005


Compare to run 1 limits
Compare to Run 1 Limits

m=120

(914 exp, 700 obs)* (BR to tt) = 82.3 exp, 63 obs

(836 exp, 643 obs)* (BR to tt ) = 75.2 exp, 57.9 obs

m=140

We’re a factor of 8

better, with approx

three times the

luminosity.

  • Get the low pT leptons (trig)

  • Reconstruct p0.

  • Understand bg (esp W+jet)

  • Fit, don’t count.

Rutgers University

September 7,2005


Extracting mssm parameters
Extracting MSSM Parameters

  • We need production cross-section for inclusive A/H/h production.

    • We only require two taus, no extra jets, b-quarks, leptons, neutrinos…nothing.

    • Most of the recent work has concentrated on Higgs production associated with “spectator” b-quarks.

    • Why? Nobody thought tt could compete.

  • We need bb  A and ggA.

Rutgers University

September 7,2005


Getting the cross section
Getting the Cross Section

  • Not trivial! Consensus emerging slowly among theorists.

    • These results have spurred some activity.

  • The method (as of June 2005):

    • Get bbhiggs and gghiggs for SM.

    • Multiply by a MSSM/SM factor.

  • This ensures corrections apply properly.

This is for tanb=30

Rutgers University

September 7,2005


The exclusion plot
The Exclusion Plot

  • We did not see a higgs signal, but we can put limits on mass/coupling (tanb).

  • The exclusion depends in “scenarios” chosen by theorists  points in the SUSY parameter space that are considered good benchmarks.

Rutgers University

September 7,2005


Exclusion
Exclusion

benchmark

parameters

Rutgers University

September 7,2005


Exclusion vs the m parameter
Exclusion vs. the m Parameter.

  • The higgs  bb search (D0) is sensitive to the SUSY parameter m.

  • This parameter controls the higgs/bb coupling.

  • As higgs/bb coupling goes up (down), higgs/tt coupling goes down (up).

Rutgers University

September 7,2005


The near future
The near future

tanb=40 is an

interesting

benchmark.

Rutgers University

September 7,2005


Conclusions
Conclusions

  • Taus are the new b.

    • Lower BR offset by (much) lower bg.

    • Not thought possible at start of Run2.

    • Bonus: insensitive to higgs radiative corrections.

  • More sensitivity soon.

    • 3x data.

    • Add th-th and tm-te channels.

    • Smarter fitting.

    • May find ways to be sensitive to SM Higgs.

  • Taus may be only way to see light higgs at LHC (SM or SUSY).

Rutgers University

September 7,2005


Afterword the sm higgs
Afterword: The SM Higgs

  • Current results from

    DØ and CDF:

    • WH->lnbb

    • ZH->nnbb

    • WW->llnn

    • WWW->l±l± + X

  • Standard Model predictions much lower than current analyses

Can we close the gap?

Maybe.

Rutgers University

September 7,2005


Backup slides
Backup slides

Rutgers University

September 7,2005


Big problem w quark jet
Big Problem: W+quark “jet”

  • W gives electron +…

  • …Jet fakes hadronic t.

  • OLD (Run 1):

    • require n to “go along” t

  • Now (Run 2)

    • Geometrical cut

z = bisector of 2 tau directions

Pzvis= sum of the projections of visibleproducts(onto z axis)

Pz = sum of the projections of visible products andmissing transverse energy

Rutgers University

September 7,2005


Removing w jet
Removing W+jet

Pz > 1.6 Pzvis – 10

Suppresses W+jet background without hurting signal

Rutgers University

September 7,2005


Checking fake rate mc w jet
Checking Fake Rate (MC W+jet)

Maybe Pythia

jets aren’t as

wrong as we

all supposed…

Rutgers University

September 7,2005


Systematic errors for higgs search
Systematic Errors for Higgs Search

Source Uncertainty(%)

  • Event cuts 0.9

  • Electron ID / Trigger 1.9

  • Muon ID / Trigger 4.6

  • Tau ID / Trigger /

    Hadronic scale 3.6

  • QCD estimate

    (on predicted fakes) 20

  • Z cross section 2.1

  • PDF (Z,W) 3.0

  • PDF (Higgs) 5.7

  • Luminosity 6.0

Comes from Wtn

Price you have

to pay at hadron

machines.

Large error on small bg

Huge, b,g come from sea

This hurts everybody

Rutgers University

September 7,2005


Compare to run 1
Compare to Run 1

Run 1, ~100 pb-1

Rutgers University

September 7,2005


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