# Presentation: 452596

## Context

- Tuesday Morning, Congress A, 8am (ouch)
- 20 minutes + 4 minutes questions
- First Talk of the Section
- Other DZERO Talks in section:
- Search for Higgs in WW*
- Higgs Searches at DZERO (bbar stuff)
- Search for associated ZH
- Prospects for a Higgs search at D0 in the WH(e)
- Prospects for Higgs search in nnbb at D0
- Search for associated production of WH

## Absract

- Expectations for the Higgs particle searches at the upgraded Tevatron and DO in Run II are discussed in view of recent detailed analyses. Higgs searches are very demanding to many aspects of detector performance, particularly important being the b-tagging capabilities, di-jet mass resolution, excellent lepton identification and efficiencies including taus. Current results on these issues obtained with data and envisaged in the near future performance figures will be discussed. Finally, the discovery potential for the Standard Model and Supersymmetric Higgses will be assessed.

## Prospects for Higgs Searches at

- Gordon Watts
- University of Washington
- For the DØ Collaboration

- 2003 April Meeting

- DPF

## Previous Searches

- MH > 114.4 GeV/c2 @ 95% CL

- LEPEWWG

- LEP Direct Searches:

- The LEP & Tevatron Run I Era

- 15 Years of Precision Measurements

- Global Fit of SM Measurements

- Light SM Higgs Favored

## Run II at the Tevatron

- Center Of Mass Energy Increase

- TeV

- 20-30% Increase in the SM Higgs Cross Section

- Main Injector, Recycler, etc.

- DØ Has Written ~110 pb-1 to tape

- This talk < 60 pb-1

- 1.96 TeV

- Accelerator Improvements

- D0

- MI

- TeV

**Notes:**
Where does that 20-30% come from?? Hard to find out!

## The DØ Detector

- Tracking

- Calorimeter

- Muon

- Shielding

- Roman Pots
- (far forward)

- Forward Muon

## The DØ Detector

- Tracking Volume
- Silicon Track Detector
- Central Fiber Tracker
- High Precision LAr Calorimeter
- 4 Muon System with Absorber

- Forward Muon Chambers

- Muon Scintilator

## The DØ Upgrade

- Added a 2T Magnetic Field

- Track pT, Lepton ID, Jet Calibrations

- New Silicon Detector & Central Tracking Detector

- Displaced Vertex ID, Tracking

- Preshower Detector

- Improved electron ID

- Trigger/DAQ Upgrade

- Better Efficiency for difficult signals

- Regularly collect > 85% of data delivered by the Tevatron

- Finding the Higgs will require all components of the detector

## The Higgs in Run II

- Mt < 2.5 GeV/c2

- MW < 40 MeV/c2

- 1

- Further Constrain the SM

- Currently 59 MeV/c2 *

- Currently 5.1 GeV/c2*

- 2

- The rest of this talk...

- Indirect Measurements

- Direct Searches

- *these are combined, Run II predictions are per experiment

**Notes:**
Are these combined numbers, or total for the TeV? The 5.1 and 59 are combined. The 2.5 and the 40 are per experiment.

## Higgs Decays

*High Mass Higgs Searches*

*Low Mass Higgs Searches*

- Nominal Mass Reach Spans Two Decay Modes

- Search strategies are a function of Decay Channel and Production Channel

- HDECAY

- MH[GeV/c2]

- Excluded

**Notes:**
What are the uncertainties in the HDECAY calculation here? Turns out this really depends upon the inputs to the HDECAY program. If you look at how you are supposed to run it, you would not expect anything there.

## Higgs Production

- No Good at Low Mass

- Overwhelmed by QCD background

- Good at High Mass

- Good at Low Mass

- Gluon Fusion

- Associated Production

- M. Spira; NLO

## SM Higgs Searches At DØ

- SUSY Higgs Searches at End of talk

- Gluon Fusion

- Associated Production

- Select W,Z Boson

- Understand Jets (W+2j, Z+2j)

- b-Tagging

- Lepton Identification

- Select W Bosons

- Lepton Identification

- Apply cuts to remove backgrounds

- Apply Mass Window Cut

- Low Mass

- High Mass

- 1

- 2

- Similar to WH,ZH Topology

## Electron ID

- 35 pb-1 of data

- Calorimeter EM Object

- pT>20 GeV/c
- Quality Cuts

- Matching Track

- M (ee)

**Z ********ee**

- QCD

**   ****: Data**
**   ****: MC**

- M (ee)[GeV/c2]

- Trigger on EM Object

- Pythia MC

- See U14.02 for more!

**Notes:**
This does not seem to be shown on the W/Z workgroup web site, unfortunately. What do we want to convince people of here – see the W/Z talks. 
Check Calibrations
What are the backgrounds and why the shoulder in Z mumu?
What about various efficiencies?
What MC went into this?
QCD background isn’t “fake” background – it is jets in QCD that trick us into thinking it is an electron.

## Lepton ID (muon)

- MT ()

- Pythia MC

- DØ Run II Preliminary

- W,Z to 

- QCD

## W Boson

- PT(W)[GeV/c]

- MT(W)[GeV/c]

- Good modeling of Missing Energy in Monte Carlo

- W Transverse Mass

- W PT

- Data

- SM Expected

- SM Expected includes W(e), W(t), Z(), Z(ee), QCD

- See Talk by D. Meder

**Notes:**
Check – why about mu nu? Can we put both on this page? No – leave it as is, I think is the right idea for now.
Standard JES is used. No good for ET < 20 GeV.
In this same note the tracking eff in Z->ee events is measured to be 73% +- 7.3%. New tracking is coming, however.
Fake rate is determined to be about 2.8% in the central region, 3.8% overall. This bit is determined with data, by looking at the ETmiss < 20 GeV signal region.
What is that peak in SM backgrouns vs Data??

## Understanding W+Jets

- Important for both Top and Higgs

**1****st**** leading jet**

**W(e/********)+jets**

- Pythia Used for Signal and Background

**2****nd**** leading jet**

- Isolated electron:

- Missing Energy:

- Jets:

- JES uncertainty shown

**Notes:**
Make sure we understand what all the various bits of MC are here!
And how they are normalized. 
The ratios determined by Pythia? Yes, Pythia is used, indeed. QCD is the background (only) used at the moment. Is there any other background? Could be top – single top would be expected to contribute even more.
The uncertainty is due to the JES.
Normalization is not absolute as it was in previous set of plots – Pythia doesn’t get the jet descriptions right. One reason we are trying to move to ALPGEN. Normalized by area here. Indeed – if you look at njets, will get it wrong (??).

## Jet Properties in  W+jets

- Dijet Mass

- Di-jet Separation

- Pythia, Alpgen used to model all signal and background processes

**Notes:**
Get more on the calibrations, etc.

In the muon case, ALPGEN is used. Otherwise it is pythia all the way for the muons.
 - match to centrla track, pt > 8 Gev, eta < 1.5, 1 A layer wire hit, 1 BC layer wire hit, 0 A layer scintillator hits, 0 BC layer scintilator hits. Scintilator timing info. Isolation.

## Z+Jets

**1****st**** leading jet**

**2****nd**** leading jet**

- Pythia MC, normalized by area. Error includes statistical and systematic error from JES

- 2 Electrons

- or

- 2 Muons

- Jets

**Notes:**
Did we require at least 2 jets? No – that explains the stat differences between these two plots, bozo.

## Jets in Z+Jets

**Di-jet Mass**

******R between di-jets**

**#jets in Z+jets**

- Pythia used to generate both signal and background processes

- See talk by M. Buehler

## Tagging a B

**B**

**Impact Parameter (d)**

**Impact Parameter Resolution**

**d/********(d)**

**Vertex Tagging a B**

**Decay Lengh (L****xy****)**

**Decay Length Resolution**

**L****xy****/********(L****xy****)**

**Hard Scatter**

**Top, Higgs contain b-quark jets**
**Most backgrounds do not**
**Jets look like any light quark jet**
**Other than contain a B meson**
**Has finite life time**
**Travels some distance from the vertex before decaying**
**~ 1mm**
**With charm cascade decay, about 4.2 charged tracks**

- Several algorithms under development

**Notes:**
This slide might need some reworking. Perhaps find a better picture of how the tracking works (or draw a schmatic). Split the inner vs outter discussions up into two slides – this is something anyone can deal with, I think.

## B-Quark ID

** ****IP resolution as the function of P****T**

** ****IP resolution**

**Mean = 0.9 ******** 2.2 ********m**
**Sigma = 36.3 ******** 1.8 ********m**
**Beam ~ 30 ********m**
****** ****IP resolution ~ 20 ********m**

## Vertex Tagging

- High pTrel 

- Negative Tag

- Resolution Effects, Tracking Errors, etc.

- Positive Tag

**B**

**B**

- Evidence of displaced vertex

- Fold over

## SM Higgs Searches At DØ

- Gluon Fusion

- Associated Production

- Select W,Z Boson

- Understand Jets (W+2j, Z+2j)

- b-Tagging

- Lepton Identification

- Select W Bosons

- Lepton Identification

- Apply cuts to remove backgrounds

- Apply Mass Window Cut

- Low Mass

- High Mass

- 1

- 2

## mee

- Lepton cuts similar to previous analysis

- Results from *ee,e****, *and **channels

- New for DPF

- Mass Window Cut

- 2 neutrinos

- Can’t Determine mH

- Cut on mll and

- mee

- mee

- (other backgrounds not shown)

- [GeV/c2]

- [GeV/c2]

- More details in talk P. Tamburello.

- Higgs: spin correlations in WW* decay keep leptons in parallel

- Z/y* and QCD: leptons tend to be back to back

- mH = 160 GeV/c2

**Notes:**
We should write down what the lepton cuts are for mu and e Make sure they are both hard
Spin correlations – see Tamburello’s talk.

## Opening Angle Cut

- After Selection

- Use additional opening angle between the leptons as cut

- Higgs: spin correlations in WW* decay keep leptons in parallel

- Z/y* and QCD: leptons tend to be back to back

- Selection

- Cuts

## Production Limits

**ee**

**e******

- 0.7 ± 1.4 ± 0.1

- 0

- 0.9 ± 1.5 ± 0.1

- 1

- ~12%

- ~8%

- For MH=120

- The ee and e Channels

- Expected:

- Observed:

- :

- Expected:

- Observed:

- :

- For MH=120

**Notes:**
How is the sensitivity flat at low mass?

## New for DPF

- Selection
- Cuts

- MC Info (mass, etc.)

**Notes:**
What Mass???

## New for DPF

- More details in talk P. Tamburello.

- Beam-pipe View

- Expected: 0.32 ± 0.01 (stat)
- Observed: 1
- sig: 14.6 ± 0.6% (stat)
- 	mH=160GeV/c2

- Run 163305
- Event 3024474

-  #1 pT = 23.7 GeV/c

-  #2 pT = 33.7 GeV/c

- = 45.7 GeV

- = 1.84

- m = 52.5 GeV/c2

- 48.4 pb-1

**Notes:**
Luminosity was 48 pb-1.

Muon: Medium Quality muon:
Two wire hits in the A layer
A Matching scintillator hit
At least two wire hits in the BC layers
At least one matching scintillator hit
A central track is required to be matched.
A cut to remove cosmic ray muons is done (timing in the scintilator)
Isolation cut around the muons is further applied (the standard definition)
Muon resolution in MC is smeared to make the Z width match – in data it is 11.5 Gev, and in MC it is 6.

MC Normalization is not done by an absolute dude yet. We do it by fitting to the data at the moment. Fitting the Z. There are a number of MC effiecencies that are left to be determined. Scale the cross section we measured in Run I to sqrt(s) we have now.

Muon energy loss in cal is about 2 GeV – use global track pt to correct it – and fix up the Missing ET.

Backgrounds are QCD and W+Jets MC.

To remove Z -> mu mu we also apply a Z window cut.

##  Candidate Event

- Beam-pipe View

- 

- 

- Run 163305
- Event 3024474

-  #1 pT = 23.7 GeV/c

-  #2 pT = 33.7 GeV/c

- = 45.7 GeV

- = 1.84

- m = 52.5 GeV/c2

- m = 60.3 GeV/c2

## Non Standard Model Higgs Searches

- Ongoing
- H++
- hbb at high tan 
- Talk by A. Haas on Monday
- Two Photon -
- SM Decay Process
- Decay mode in SM extensions that suppress Higgs Fermi coupling
- Fermiphobic Higgs
- Top Color Higgs

## L=51.8 pb-1

- L=51.8 pb-1

- Require 2 Isolated EM

- No Track (photon)

- SM Backgrounds

- Drell-Yan, Z/g(ee), QCD

- [GeV/c2]

- Data

- SM Backgrounds

- QCD Background (data)
- DY Background (data)

**Notes:**
Backgrounds – there are two, both are done from data – the di-EM sample.
QCD gg – take photon fake rate in loose di-em sample (with DY removed)
DY gg – use the diphoton and dielectron from di-em loose sample and understanding the efficiency between them.

## Results

- See talk by A. Melnitchouk

- Top Color

- MH = 120 GeV/c2

- BR(h)=1

- DØ Run II Preliminary

- Central Photons

- With more data will be sensitive to other exotic Higgs Models

- Cross over at

- Pythia used for Signal

- Look Specifically at the Top Color Higgs

- Mass Window Cut

**Notes:**
What is the top color model? Why would you use it here?

Top color is a typical dynamical EWSB model. There are some versions of it that have the Higgs coupling to only very heavy fermions (like the quark). Apparnetly, in those, the gg is enhanced. Do not know the specific model parameters.

## Prospects

- A Combined Detector

- Parameterized b-tagging

- Many initial Higgs Analysis are attempting to repeat WG Results

- Luminosity

- Joint CDF/DØ/Theorist Study

- What is the Run II Reach For the Tevatron

- _SM Channels_

- ZH, WH (low mass Higgs)

- H (high mass Higgs)

- pHp (low mass Higgs)

- _SUSY Channels_

- _Assumptions_

- H+, hbb, etc.

- 10% di-jet mass resolution

**Notes:**
Make sure you understand exclusive production. Why does this work only for light higgs? Does the final plot contain the exclusive higgs mass limits?

## Luminosity

- The right direction

- SUSY WG hoped for 15 fb-1

- Currently Average 6pb-1 per week

- Need a factor of 8 in luminosity to make 10fb-1 by LHC

**Notes:**
Algorithm improvements and adding new channels will only get us so far. The big issue is the luminosity.

## Displaced Vertex

- Fake Rate of 0.5%

- B-tag Eff used in WG Report

- Parameterized Function used in WG

- Algorithm’s Performance depends vitally on Tracking in jets

- DØ’s tracking algorithm has been undergoing improvements

- Silicon Detector Has Been Well Behaved

- Current Algorithm is within striking distance

- We are also exploring other tagging algorithms and proper methods of combining them

**Notes:**
Can the background rate be shown!!???

## Di-jet Mass

- WG Report

- Small Variations lead to large differences in reach

- Current Estimates (MC)

- New Preshower

- No bbar jet energy scale

- Still Understanding Calibrations

- WG

- A lot of work to do here

- Just getting started...

## Conclusions

- Analysis Efforts for the Higgs search are well under way
- Results for the first 50 pb-1 reported here
- We can clearly see the pre-cursors for the Higgs search
- Next Steps at DØ
- Improved object ID efficiencies
- b-quark tagging algorithm maturity
- Steady progress on di-jet mass resolutions
- What to watch for at Fermilab
- More Luminosity!
- Prospects for Discovery
- DØ has work to do in btagging, di-jet resolutions and tau to achieve the working groups levels.
- Dijet mass distribution will require the most work.
- Joint CDF/DØ group put together to study all of this now.