# Presentation: 312232

## The Higgs Mechanism

**The Higgs Mechanism**

**In the Standard Model **
**Electroweak symmetry breaking ****occurs through introduction of a ****scalar field ******** ******** masses of W and Z**
**Higgs field permeates space with ****a finite vacuum expectation value = 246 GeV**
**If ******** also couples to fermions ******** generates fermion masses**
**An appealing picture: is it correct?**
**One clear and testable prediction: there exists a ****neutral scalar particle ****which is an excitation of the Higgs field**
**All its properties (production and decay rates, couplings) are fixed except its own mass**
**Highest priority of worldwide high energy physics program: find it!**

## God particle disappears down £6billion drain

**God particle disappears down ****£6billion drain**

**This field need not result from a single, elementary, scalar boson**
**There can be more than one particle**
**e.g. SUSY**
**Composite particles can play the role of the Higgs**
**e.g. technicolor, topcolor**
**We do know that**
**EW symmetry breaking occurs, so something is coupling to ****the W and Z**
**Precision EW measurements imply that this thing looks very much like a Standard Model Higgs **
**though its fermion couplings are less constrained**
**WW cross sections violate unitarity at ~ 1 TeV without H**
**A real LHC experiment:**

## Searching for the Higgs

**Searching for the Higgs**

**Over the last decade, the focus has been on ****experiments at the LEP e****+****e****–**** ****collider at CERN **
**precision measurements of parameters ****of the W and Z bosons, combined with ****Fermilab’s top quark mass measurements, ****set an upper limit of m****H**** ~ 200 GeV **
**direct searches for Higgs production exclude ****m****H**** < 114 GeV**
**Summer and Autumn 2000: Hints of a Higgs?**
**the LEP data may be giving some indication of a Higgs with mass 115 GeV (right at the limit of sensitivity)**
**despite these hints, CERN management decided to shut off LEP operations in order to expedite construction of the LHC**
*	**“**The resolution of this puzzle is now left to Fermilab's Tevatron and the LHC.”*
*– *Luciano Maiani

## Higgs at the Tevatron

**The search for the mechanism of EWSB motivated the construction of supercolliders (SSC and LHC)**
**After the demise of the SSC, there was a resurgence of ****interest in what was possible with a “mere” 2 TeV**
**Ideas from within accelerator community (“TeV33”)**
**Stange, Marciano and Willenbrock paper 1994**
**TeV2000 Workshop November 1994**
**Snowmass 1996**
**TeV33 committee report to Fermilab director**
**Run II Higgs and Supersymmetry Workshop, November 1998**
**A convergence of**
**technical ideas about possible accelerator improvements**
**clear physics motivation **
**Plan for integrated luminosities, before LHC turn-on, ****much larger than the (then) approved 2fb****-1**** **

## Higgs decay modes

**The only unknown parameter of the SM Higgs sector is the mass**
**For any given Higgs mass, the production cross section and decays are all calculable within the Standard Model**

**One Higgs**

**H ********bb**

**H ******** WW**

## Higgs Production at the Tevatron

**Higgs Production at the Tevatron**

**Inclusive Higgs cross section is ****quite high: ~ 1pb**
**for masses below ~ 140 GeV,****the dominant decay mode H ******** bb ****is swamped by background**
**at higher masses, can use inclusive****production plus WW decays**
**The best bet below ~ 140 GeV appears ****to be associated production of H plus ****a W or Z**
**leptonic decays of W/Z help give ****the needed background rejection**
**cross section ~ 0.2 pb**

**H ********bb**

**H ******** WW**

**Dominant decay mode**

## mH < 140 GeV: H bb 

**m****H**** < 140 GeV: H ********bb **

**WH ******** qq’********bb is the dominant decay mode but is overwhelmed by QCD background**** **
**WH ******** ****l****±******** bb ****	****	****backgrounds W********bb, WZ,********tt, single top**
**ZH ******** ****l****+****l****-******** bb****	**** ****	****backgrounds Z********bb, ZZ,********tt**
**ZH ******** ******** bb****	**** ****	****backgrounds QCD, Z********bb, ZZ,********tt **
**powerful but requires relatively soft missing E****T**** trigger (~ 35 GeV)**

**CDF Z ********bb in Run I**

**DØ simulation for 2fb****-1**

**2 ******** 15fb****-1 ****(2 experiments)**

**m****H**** = 120 GeV**

**Higgs**

**Z**

****_**bb mass resolution**_
**Directly influences signal significance**
**Z ********bb will be a calibration**

**~**

## pp  WH 

**Two b-jets from**
**Higgs decay**

**Missing E****T**

**Electron Track**

**EM cluster**

**Calorimeter**
**Towers**

**p ******

******p**

******pp ******** WH **
**	****    ********bb**
**             ******** ****e******

**Hits in Silicon Tracker**
**(for b-tagging)**

## Example: mH = 115 GeV

**Example: m****H**** = 115 GeV**

**~ 2 fb****-1****/expt (2003): exclude at 95% CL**
**~ 5 fb****-1****/expt (2004-5): evidence at 3******** level **
**~ 15 fb****-1****/expt (2007): expect a 5******** signal**
**Events in one experiment with 15 fb****-1****:**
**If we do see something, we will want to test whether it is really a Higgs by measuring:**
**production cross section**
**Can we see H ******** WW? (Branching Ratio ~ 9% and rising w/ mass)**
**Can we see H ******** ********? (Branching Ratio ~ 8% and falling w/ mass)**
**Can we see H******** ********? (not detectable for SM Higgs at the Tevatron)**

**Every factor of **
**two in luminosity**
**yields a lot **
**more physics**

## Associated productiontt + Higgs

**Cross section very low (few fb) ****but signal:background good**
**Major background is********tt + jets**
**Signal at the few event level:**

**H ********bb**

**H ******** WW**

**Tests top quark Yukawa coupling **

**15fb****-1 ****(one experiment)**

## mH > 140 GeV : H  WW(*)

**gg ******** H ******** WW****(*********) ******** ****l****+****l****-**** ********	****    ****	**
**	****Backgrounds ****	****Drell-Yan, WW, WZ, ZZ, tt, tW, ********	****	****Initial signal:background ratio ~ 10****-2 **
**Angular cuts to separate signal from “irreducible” WW background**

**Before tight cuts:**
**verify WW modelling**

**After tight cuts**

**~**

**2 ******** 15fb****-1 **
**(2 experiments)**

**Higgs signal**

**Background **
**(mainly WW)**

## 
No guarantee of success, but certainly a most enticing possibility

**No guarantee of success, but certainly a most enticing possibility**

**15 fb****-1**

**110-190 GeV**

**m****H**** probability ****density, J. Erler****(hep-ph/0010153)**

**Tevatron Higgs mass reach**

## Indirect Constraints on Higgs Mass

**Indirect Constraints on Higgs Mass**

**Future Tevatron W and top mass measurements, per experiment**
**	****	****	********m****W**
**	****2 fb****-1****	****	****±27 MeV**
**	****15 fb****-1**** **** ****	****±15 MeV**
**	****	****	********m****t**
**	****2 fb****-1****	****	****±2.7 GeV**
**	****15 fb****-1**** **** ****	****±1.3 MeV**

**Impact on Higgs mass fit using**
******m****W ****= 20 MeV, ********m****W ****= 1 GeV,**
****** ****= 10****-4****, current central values**
- M. Grünewald et al., hep-ph/0111217

## Supersymmetric Higgs sector

**Expanded Higgs sector: h, H, A, H****±**
**Properties depend on**
**At tree level, two free parameters (usually taken to be m****A****, tan ********)**
**Plus radiative corrections depending on sparticle masses and m****t**** **

**Multiple Higgses**

**One of us looks much like the Standard Higgs...**

**~**

## Supersymmetric Higgs Masses

**Over much of the remaining allowed parameter space, **
**m****h**** ~ 130 GeV,**
**m****A**** ~ m****H**** ~ m****H****±**** = “large”**

_**From LEP:**_** **
**m****h**** > 91 GeV, m****A**** > 92 GeV, m****H****±**** > 79 GeV, ****tan******** > 2.4**

## MSSM Higgs Decays

**	****Very rich structure!**
**	**
**	****For most of allowed mass range h behaves very much like H****SM**
**H ******** WW and ZZ modes suppressed compared to SM**
**bb and ******** modes enhanced**
**	****A ********bb and ********      **
** **
**	****H******** ******** ******** and********tb**

## SUSY Higgs Production at the Tevatron

**SUSY Higgs Production at the Tevatron**

**bb(h/H/A) enhanced at large tan ********:**
****** ****~ 1 pb for tan******** = 30 and****m****h**** = 130 GeV**

**bb(h/A) ******** 4b**

**CDF Run 1 analysis (4 jets, 3 b tags) **
**sensitive to tan ******** > 60**

**10 fb****-1**
**m****A**** =150 GeV,**
**tan ******** = 30**

- one
- expt

**Preliminary**

**increasing**
**luminosity**

## Charged Higgs

**Tevatron search in top decays**
**Standard tt analysis, rule out competing decay mode *****t ************ H************b***
**Assumes 2 fb****-1****, n****obs**** = 600, background = 50 ******** 5**
**LEP not really sensitive to MSSM region (expect m****H**** > m****W****)**

**LEP summer 99**
**77 GeV**

## SUSY Higgs reach at the Tevatron

**Enhances h ******** ********  ?**

**95% exclusion**

**5******** discovery**

**Exclusion and discovery**
**for maximal stop mixing,**
**sparticle masses = 1 TeV**

**Most challenging scenario:**
**suppressed couplings to bb **

**95% exclusion**

**5******** discovery**

**5 fb****-1**

**5 fb****-1**

**15 fb****-1**

**20 fb****-1**

**15 fb****-1**

**20 fb****-1**

**Luminosity per experiment, CDF + DØ combined**

## What if we see nothing?

**As long as we have adequate sensitivity, exclusion of a Higgs is still a very ****important discovery for the Tevatron**
**In the SM, we can exclude most of the ****allowed mass range**
**In the MSSM, we can potentially exclude **_**all**_** the remaining mass range**
**A light Higgs is a very basic prediction of ****the supersymmetric SM**
**e.g. Strumia, hep-ph/9904247**

** ****LEP limit**

**Still allowed**

**It’s a good thing**

## What if we see something else?

**Alternatives to SUSY: dynamical models like technicolor and topcolor **
**the Higgs is a composite particle: no elementary scalars**
**many other new particles in the mass range 100 GeV - 1 TeV **
**with strong couplings and large cross sections**
**decaying to vector bosons and (third generation?) fermions**

**SM**

******T ********bb**

******T ******** ****l******** ********T **

**At the Tevatron,**
**you have to be lucky,**
**but if you are, you can****win big:**

## Run 2B

**Planning has started on the additional detector enhancements that will be needed to meet the goal of accumulating 15 fb****-1 ****by end 2007 **
**major components are two new silicon detectors to replace the present CDF and D****Ø ****devices which can not survive the radiation dose**
**Technical design reports submitted to the laboratory Oct 2001**
**goal: installed and running by early 2005**

**Proposed D****Ø Run 2B **
**silicon detector**

**Run 2B silicon installed**

## Tevatron plan for 2002

**Only ~ 20pb****-1**** delivered so far, which CDF and D****Ø have used**** to commission their detectors **
**2002 will be the year that serious physics running starts**

**2002 PLAN**

## By 200x at the Tevatron, if all goes well
We will observe a light Higgs
Test its properties at the gross level
but not able to differentiate SM from MSSM 
Or we will exclude a light Higgs
Interesting impact on SUSY
We will tighten exclusion regions for MSSM charged Higgs and  multi-b jet signals at high tan 
We may even be lucky enough to find something else 
e.g. low scale technicolor

**We will observe a light Higgs**
**Test its properties at the gross level**
**but not able to differentiate SM from MSSM **
_**Or**_** we will exclude a light Higgs**
**Interesting impact on SUSY**
**We will tighten exclusion regions for MSSM charged Higgs and  ****multi-b jet signals at high tan ******
**We may even be lucky enough to find something else **
**e.g. low scale technicolor**

**What will we know and when will we know it?**

## Top ten reasons to pursue the Higgs search at Fermilab

**10.****	**** Window of opportunity before LHC startup is not getting shorter  **
**9.****	****The origin of EWSB has been unclear for way too long, and theorists   can’t figure the question out by themselves**
**8.****	****Find it while Mr. Higgs is still alive and can win the Nobel Prize**
**7.****	****Learn if there really are fundamental scalars (SUSY?)**
**6.****	****Learn why the standard model seems to work so well**
**5.****	****We might find something other than a Higgs**
**4.****	****Excluding a light Higgs is almost as interesting as finding it**
**3.****	****Huge potential payback for a (relatively) small investment**
**2.****	****Excitement and discovery move the field forward**
**1.****	****Because we can!**

## A three-stage relay race

**Tevatron**
**Discovery if we’re lucky**
**Fermilab’s role is obvious**
**LHC**
**Guaranteed discovery of one or more Higgs or some other signal of EWSB**
**Measure properties at the 20% level**
**Learn a lot more about physics at the TeV scale ****(SUSY? Extra dimensions?)**
**Fermilab’s role is significant but needs to be consolidated for the physics analysis phase**
**Linear Collider**
**Measure, measure, measure:****Higgs couplings to W, Z, individual fermions, HHH coupling**
**What is Fermilab’s role? **

## What the Higgs search will teach us

**What is the source of mass of the W and Z? **
**Why is the weak force weak?**
**What is the source of mass of the fundamental fermions?**
**Are there fundamental scalars?**
**Is there SUSY?**
**if no light Higgs, no weak scale SUSY...**
**Is there other new physics at the weak scale?**
**New forces like technicolor**
**Are m****W****, m****t**** and m****H**** consistent with precision EW fits?**
**What is the mass scale of new physics?**
**What is the next machine we’ll want to build after the linear collider?**

## What the Higgs search won’t explain

**Why fermion masses have the values they do**
**Why is the top quark so heavy?**
**The origin of all mass in the universe**
**The universe is roughly **
**70% dark energy (???)**
**20% cold dark matter **
- e.g. neutralinos with mass ~100 GeV
**5% neutrinos?**
**5% baryons **
- whose mass is almost all due to QCD
**Flavor**
**What distinguishes a top quark from an up quark?**

## Supersymmetry searches

**Supersymmetry predicts multiple Higgs bosons, strongly interacting squarks and gluinos, and electroweakly interacting sleptons, charginos and neutralinos**
**masses depend on unknown parameters, ****but expected to be 100 GeV - 1 TeV**
_**Direct searches all negative so far**_
**LEP**
**squarks (stop, sbottom) > 80-90 GeV**
**sleptons (selectron, smuon, stau) > 70-90 GeV**
**charginos > 70-90 GeV**
**lightest neutralino > 36 GeV**
**Tevatron Run I**
**squarks and gluinos**
**stop, sbottom**
**charginos and neutralinos**

## Supersymmetry signatures

**Squarks and gluinos are the most copiously produced SUSY particles**
**As long as R-parity is conserved, cannot decay to normal particles **
**missing transverse energy from escaping neutralinos (lightest supersymmetric particle or LSP)**

**Missing E****T**
**SUSY ****	****        backgrounds**

**Possible decay chains always end in**
**the LSP:**

**Search region typically > 75 GeV**

## Two complementary searches 
jets plus missing ET and no electrons/muons
2 electrons, 2 jets + Missing ET

**jets plus missing E****T**** and no electrons/muons**
**2 electrons, 2 jets + Missing E****T**

**Run 1 search for squarks and gluinos**

**Reach with 2 fb****-1****:**
**gluino mass ~ 400 GeV**

**Run I excluded**

**Run I reach**
**gluino ~ 200 GeV**
**squark ~ 250 GeV**

## Chargino/neutralino production

**Chargino/neutralino production**

**“****Golden” signature: three leptons**
**very low standard model ****backgrounds**
**This channel was searched in Run 1, ****but limits not competitive with LEP**
**however, becomes increasingly ****important as squark/gluino ****production reaches its kinematic ****limits (masses 400-500 GeV)**
**Run II reach on ************ mass ~ 180 GeV (tan ******** = 2, μ< 0)****	****	****	****  ~ 150 GeV (large tan ********) **
**Challenges**
**triggering on low momentum leptons**
**how to include tau leptons?**
**	****It is quite conceivable that we discover ****SUSY in this mode before we find the Higgs!**

## Stop and Sbottom

**Stop and Sbottom**

**Often the SUSY partners of b and t are the lightest squarks**
**Stop**
**stop ******** b + chargino or W ****(top like signatures)**
**stop ******** c + neutralino**
**top ******** stop and gluino ******** stop**
**Sbottom**
**2 acollinear b-jets + E****T****miss**** **

**CDF Run I stop and sbottom limits**

**Sbottom sensitivity **
**~ 200 GeV in Run II **

**115 GeV**

**145 GeV**

## Has SUSY been discovered?

**Has SUSY been discovered?**

**Is this selectron pair production?**
**All we can say is that searches for ****related signatures have all been negative**
**CDF and DØ ******** + missing E****T **
**DØ ******** + jets + missing E****T**
**LEP**

**2 events observed**
**2.3 ± 0.9 expected**

**LEP**

## Gauge mediated SUSY

**Standard benchmark is so-called “minimal supergravity inspired” (mSUGRA) models — but other scenarios for SUSY breaking give other signatures**
**e.g. Gauge mediated SUSY:**
**lightest neutralino decays to a photon plus a gravitino, maybe with a finite path length**
**Run 2 DØ direct reconstruction with ********z**** = 2.2 cm, ********r**** = 1.4 cm**

## TeV-scale gravity

**TeV-scale gravity**

**Observable effects can be direct and spectacular . . .**
**Or indirect . . . **
**DØ Run 1 limits from virtual graviton effects on e****+****e****-**** and ******** production (1.0 - 1.3 TeV for 2-7 extra dimensions, ADD)**
**Prospects for Run 2:  1.5 - 2.5 TeV (2fb****-1****) 2.1 - 3.5 TeV (20fb****-1****)**

**Production of Black Holes may even occur**
**Decay extremely rapidly (Hawking radiation)**
**with spectacular signatures**

## Sleuth

**A new approach from DØ: attempt at a model-independent analysis framework to search for new physics**
**will never be as sensitive to a particular model as a targeted search, but open to anything**
**searches for deviations from standard model predictions **
**Systematic study of 32 final states involving electrons, muons, photons, W’s, Z’s, jets and missing E****T**** in the DØ Run 1 data **
**Only two channels with some hint of disagreement**
**2 electrons + 4 jets****	**
**observe 3, expect 0.6± 0.2, CL = 0.04**
**2 electrons + 4 jets + Missing E****T **
**observe 1, expect 0.06±0.03, CL = 0.06**
**While interesting, these events are not an indication of new physics, given the large number of channels searched**
**89% probability of agreement with the Standard Model (alas!)**
**This approach will be extremely powerful in Run 2**

## Quaero

**DØ has now largely completed the analysis of Run 1 data**
**We have therefore decided to make a number of well-understood ****Run 1 data sets **_**publicly available**_** through a web interface**
**http://quaero.fnal.gov**
**This is a new direction for high energy physics**
**Please try it!  **
**For details see hep-ex/0106039**

## The scientific record to date

**CDF (1988-2002)**
**Publications from Run I and earlier **
**158 articles in Physical Review Letters**
**82 in Physical Review**
**61 in Nuclear Instruments and Methods**
**24 of these publications have over 100 citations in the SPIRES database**
**6 papers on the top quark, including the two papers on the discovery which each have over 500 citations.**
**7 on QCD, 5 on W and Z bosons, 2 on Supersymmetry searches, 1 on other exotic searches, 1 on CP violation and 2 on instrumentation **
**This is more highly cited results than any other HEP experiment.**
**188 Ph.D. theses completed**

**D0 (1994-2002)**
**Publications from Run I **
**69 articles in Physical Review Letters**
**14 in Physics Letters**
**31 in Physical Review**
**38 in Nuclear Instruments and Methods**
**5 of these publications have over 100 citations in the SPIRES database**
**2 top quark papers, including the discovery paper with over 500 citations**
**1 on a Supersymmetry search, 1 on QCD, and 1 on instrumentation**
**128 Ph.D. theses completed**

## Physics prospects for Run 2100 pb-1

**measure first W, Z, jet, top, b, cross sections at 1.96 TeV**
**start B-physics program**
**300 pb****-1**** **
**pin down high-E****T**** jet behavior (fix gluon PDF at large x) **
**measure top mass with half current statistical error **
**extra dimensions scale 1.6 TeV **
**Measurement of B****s ****mixing**
**500 pb****-1**** **
**signals for WW, WZ production **
**observe radiation zero in W******** process **
**signals for technicolor? **

## 1 fb-1 

**~1000 top events per experiment  **
**~100 dilepton, ~800 lelpton + jets with b-tag **
**start to see single top signal **
**signals for SUSY in trileptons or jets+Missing E****T****? **
**signals for gauge mediated SUSY (photons +Missing E****T****)? **
**SUSY Higgs (4b jet) signal for m(A) ~ 100 GeV, tan ******** = 35 **
**2 fb****-1**** **
**SUSY in chargino/neutralino (trileptons) up to m(********)=180 GeV ****(tan ******** =2) **
**SUSY in squarks/gluinos (jets+Mmssing E****T****) up to m(gluino)=400 GeV**
**measure top mass to 2.7 GeV/expt **
**observe spin correlation between top pair (exclude spin=0 stop) **
**extra dimensions with a scale of 2.0 TeV **
**measure W mass at level needed to improve on LEP (30 MeV per experiment) **
**95% exclusion of SM Higgs for mass =115 GeV **

## 5fb-1 

**95% exclusion on SM Higgs up to 125 GeV. **
**95% exclusion of all MSSM Higgs parameter space (maximal mixing)**
**SUSY Higgs (4b jet) signal for m(A) ~ 150 GeV, tan ******** = 35 **** **
**8 fb****-1**** **
**3 sigma evidence for SM Higgs mass = 115 GeV **
**3 sigma evidence for H -> WW around 160 GeV **
**95% exclusion for SM Higgs up to 130 GeV and 150-180 GeV **** **
**15 fb****-1**** **
**4-5 sigma signal for SM Higgs mass=115 GeV **
**95% exclusion for SM Higgs over all range up to 185 GeV **
**SUSY Higgs (4b jet) signal for m(A) ~ 200 GeV, tan ******** = 35 **
**SUSY trilepton signal extended to large tan ******** and gluino masses 600-700 GeV **
**measure top mass to 1.3 GeV/expt **
**measure W mass at the level of 15 MeV/expt **** **

## Complementarity with LHC

**Complementarity with LHC**

**The Physics goals of the Tevatron and the LHC are not very different, but the discovery reach of the LHC is hugely greater**
**SM Higgs:**
**Tevatron < 180 GeV  ****	****	****LHC < 1 TeV**
**SUSY (squark/gluon masses)**
**Tevatron < 600 GeV****	****	****LHC < 2 TeV**
**	****Despite the limited reach, the Tevatron is interesting because ****both Higgs and SUSY “ought to be” light and within reach**
**For Standard Model physics systematics may dominate:**
**Top mass precision**
**Tevatron ~ 1-2 GeV****	****	****LHC ~ 1 GeV? **
**m****W**** precision**
**Tevatron ~ 20 MeV?****	****	****LHC ~ 20 MeV?**

## Conclusions

**For as long as I have done high energy physics, the highest priority of the field has been to explore experimentally the question of EW symmetry breaking and TeV-scale physics**
**That is about to change dramatically: the next few years will see the Higgs and/or SUSY become a discovery or set of discoveries to be understood and measured**
**and, we hope, the first window on to a new domain of ****physics at the TeV scale**
**Personally, I can’t wait to see what’s behind the curtain**

**?**