# Presentation: 677782

## Higgs Sensitivity Prospects @ DØ

** ****	****	**
**	****WH,ZH, WW and advanced techniques**

**Higgs Sensitivity Prospects @ D****Ø**

**	****               ****Gregorio Bernardi **
**	**

## SM Higgs Search: Outlook

**Prospects updated in 2003 in the low Higgs mass region**
** **
**W(Z) H******** l********(********,ll) bb****  **
****** ****better detector understanding**
****** ****optimization of analysis**

**Sensitivity in the mass region above LEP limit (114 GeV ) starts at ~2 fb****-1**
**With 8 fb****-1****:  exclusion 115-135 GeV & 145-180 GeV, **
**                    ****5 - 3  sigma discovery/evidence @ 115 – 130 GeV**
**  ****Meanwhile**
****** ****understanding detectors better, optimizing analysis techniques               ******** measuring SM backgrounds  (Zb, WW, Wbb)**
****** ****Placing first Higgs limits which can be compared to the prospects**

**Tevatron8 fb****-1**

**Ldt (fb****-1)**

**LEP Excluded**

## ZHbb searches

**Missing E****T ****from Z************ and 2 b jets from H********bb**
**Large missing E****T**** > 25 GeV**
**2 acoplanar b-jets with E****T ********20 GeV, |********| < 2.5**** **
**Backgrounds**
**“****physics”**
**W+jets, Z+jets, top, ZZ and WZ**
**“****instrumental”**
**QCD multijet events and mismeasured jets**
**Huge x-section/small acceptance**
**Strategy**
**Trigger on events with large missing H****T**
**Estimate “instrumental” bckgd from data**
**Search for an excess in di-b-jet mass distribution**

## ZHbb Comparison with Prospective Study 

| All numbers @261pb-1 | D0 analysis
261pb-1
ZHnnbb | SHWG
(no NN)  |  | Ratio
SHWG/
D0 anal | Ratio
HSS-nn/
D0 anal |
| --- | --- | --- | --- | --- | --- |
| #data | 3 | - |  | - | - |
| #signal (ZH+WH) | 0.065+0.017 | 0.57+0.43 |  | 8.8(12) | 8.5(12) |
| #physics bkg | 1.8 | 12 |  | 6.6 | 2.3 |
| #instrumental bkg | 0.37 | 12 |  | 32 | 7.3 |
| #total bkg | 2.2 | 24 |  | 11 | 3.1 |
| S/B | 0.037 | 0.041 |  | 4 | 4 |
| S/B | 0.055 | 0.20 |  | 3.6 | 7  (NN) |

| Mass window (GeV) | 80-130 | 85-130 |  | 0.9 | 0.72 |
| --- | --- | --- | --- | --- | --- |
| Mass resolution | 16% | 10% |  | 0.6 | 0.6 |
| Taggability (2 jets) | 60% | 100% |  | 1.7 | 1.7 |
| B-tagging (2 b jets) | 16% | 40% |  | 2.5 | 1.6 |
| Trigger | 70% | 100% |  | 1.4 | 1.1 |
| Effi. W/o trig, b-tag | 20% | 30% |  | 1.5 | 2.5 |
|  |  |  |  | 8.9 | 7.5 |

- Need to improve signal acceptance!!

**Need progress on**
**- B-tagging**
** ****Trigger**
** ****Selection **
**  ****optimization**
**- mass reconstruction**

## The gg  H  W+W-  Channel

**The gg ******** H ******** W****+****W****-****  ****Channel**

**Signal Process:**

** ****Interesting Angular **
**   ****Correlation due to**
**   ****Scalar nature of Higgs Boson**
** ****Different from SM W****+****W****-**** bg**
**decay angular correlation!**

## Comparison of H WW  with Sensitivity Report

**S/B ratio is worse **
**compared to HWG report **
**We are missing**
** ****factor of 2 in**
** ****sensitivity for 1 (fb-1)**

**Using same cuts (no likelihood) as in Tevatron Higgs Working group study now: **
**1. Smaller selection efficiency to H******** WW ******** ll**
**(HWG report assumes higher em-id efficiency and improved muon resolution);**
**2. Larger WW background and tt background contribution;**
**3. Only W +jet background was considered in HWG (no W+******** background)**

**Comparison of H******** WW  with Sensitivity Report**

## DØ  SM Higgs Summary

**       **

## Ratio between Limit and SM expectation

**For WW* this “x-section factor”  is  about 13 at 160 GeV**
**For WH+ZH combined: x-section factor is about 20-25 ****	****	******** and “helped” by WW above 120 GeV**
**     ****The “kink” at around 140 GeV  goes away **** **

**Work in progress**

##  Combination: Comparison with CDF

**We are similar everywhere !**
****** ****Progressing together, needed for final combination !**

- .

**Work in progress**

**D****Ø**

**we should be around 6, not around 20 with the current lumi (0.3 fb****-1****)****	****     ****	****	****	****Where can we gain  ?**

**CDF**

##      b-tagging Optimization: 	     signal vs. bkg (MH=115GeV)

**     ****b-tagging Optimization: ****	****     signal vs. bkg (M****H****=115GeV)**

- S/B=0.01

- S/B =0.02

- S/B =0.03

- S/B =0.04

- S/B =0.05

- S/B =0.06

- S/B =0.07

- S/B =0.08

- S/B =0.09

- S/B =0.1

- #bkg (Physics + QCD)

- #sig (ZH+WH)

- ExtraLoose

- SuperLoose

- Loose

- Midium

- Tight

- UltraTight

- MH=115GeV,  ExtraLoose jlip for 2nd leading jet,   Mass window is 1.5 sigma

## ZHbb : How limits are improved?

|  | MET+bb
(105GeV) | MET+bb
(115GeV) | MET+bb
(125GeV) | MET+bb
(135GeV) |
| --- | --- | --- | --- | --- |
| #ZH(nnbb)
Acceptance
(preliminary) | 0.23
0.80  0.21%
(0.28%) | 0.19
0.96  0.25%
(0.33%) | 0.14
1.1  0.29%
(0.35%) | 0.078
1.1  0.29%
(0.34%) |
| #WH(lnbb)
#ZH+WH
Acceptance | 0.14 
0.37
1.28  0.33% | 0.11
0.30
1.51  0.39 % | 0.09
0.23
1.84  0.48% | 0.057
0.14
1.99  0.52 % |
| Total Backgd | 9.8  3.2 | 10.3  3.4 | 10.8  3.6 | 10.8  3.6 |
|  |  |  |  |  |
| ZH Estimate 
 |       (6.6) pb
      (8.8) pb |       (5.9) pb
      (7.5) pb |       (5.2) pb
      (6.0) pb |       (5.2) pb
      (6.5) pb |
|  ZH Est.+WH |       (4.0) pb |        (3.7) pb |       (3.0) pb |       (2.8) pb |

**Factor ****2****  since preliminary! (equiv to 4 times more lumi) using looser selection, tagging and misidentified WH**

**(expected)**

**Prel ****(260pb****-1****)**

**Work in progress**

##  How to Reach “Expected” Sensitivity

**Use Neural Net**
** ****b-tagging                 in all Higgs analyses**
** ****the NN tagger combines the 3 b-tagging algorithms used in D****Ø**
** **

**Several points,**
**2 Examples:**

## Use Neural Net Event Selection 

**Use Neural Net Event Selection **

**No Neural Net selection yet.    Working group being formed,      using single top expertise**
**In D0 we have gained factor 2 in (S/√B) in single top NN analysis**
**Example of CDF Run II Neural Net:**
**NN analysis done for ZH********llbb**
****** ****Improves S/√B by factor 1.5**
**Factor 1.8  used  for 2003-HSWG is in reach, assumed that we will have it by summer.**

##  How to Reach “Expected” Sensitivity: Step 2

**          ****WH/ZH ******** ****include WH********WWW and Z******** l****+****l****- **** channel !  (*1.3)**
**	****	****WH/ZH: ****use Neural Net Tagger                           ****(*1.34*1.34)**
**	****	****WH/ZH: ****use Neural Net Selection    (*1.8)**
**	****	****WH/ZH: ****use TrackCalJets******** mass resolution     ****(*1.3)**
**	****	****WH(e): ****include End-Cap calorimeter                  **
**	****	****WH(********): ****improve QCD rejection ******** loosen b-tag**
**	****	****WH     :  ****include W******** ******** ********  (*1.4)**
**	****	**
**     ****Total for WH/ZH:  ****1.34 ****2**** ********* ****1.3 * 1.2 =2.8****  ********another gain of sqrt(2.8)=1.7 in sensitivity****   ****(compare to the missing 1.5)**
** ****	********we can reach  the expected sensitivity by summer 06**

** ****How to Reach “Expected” Sensitivity: Step 2**

**(*1.2)**

## Summary and Remarks

**After the first round of analyses, both experiments are devoting more efforts to sensitivity optimization:**
**       ****Combination (channels, but also 1-2 tags)**
**       ****Include all channels (taus, WWW)**
**       ****Neural Net selections**
**       ****b-tagging (neural-net, combination etc..)**
**       ****Mass reconstruction (track cal jet)**
**Our studies show, that, barring surprise  D0 (and CDF?) could reach the expected sensitivity by summer 2006**** ****(1fb****-1****)**
**If we are lucky, we could already say something on 115 GeV Higgs at the end of next year, else wait for 2007... but we do need to work coherently/critically.**
**In the mean time, we will probably be able to progress beyond the expected sensitivity. **