# Presentation: 936556

## Associated Production for the Standard Model Higgs at CDF

**D. Bortoletto**
**Purdue University**

**Outline:**
**Higgs at the Tevatron**
**WH******** ************ bb**
**ZH ******** ******** bb**
**WH and ZH ******** met bb**
**Outlook**

## SM Higgs

**SM Higgs**

**The Higgs remains the ****Holy Grail of Particle Physics**
**Direct LEP searches: M****H****>114 GeV at 95 %CL**
**Indirect searches improving. Smaller error on top and W mass: M****top****=170.9 ****±1.8 GeV and M****W****=80.398 ****±0.25 GeV**

**M****H****<144 GeV (ignoring direct limit)**
**M****H****<182 GeV (including 114 GeV limit)**

## Higgs at the Tevatron

**m****H****<135 GeV  use                                            W/Z H and H********bb**
**Trigger on                                                      leptons or met **
**m****H****>135 GeV  direct production and H********WW **

**ZH **** llbb**

**ZH ****bb**

**WH **** l ** **bb**

**H ** **WW****l ** **l **

**Total**

## ZHbb

- Strategy:
- Optimize lepton selection to  improve Z acceptance by 70%
- Improve S/B :
- Two loose b-tag: 50% efficient, 1.5% fake rate
- One tight b-tag: 40% efficient, 0.5% fake rate
- Improve mass resolution
- Use MET to improve mass resolution using NN since no real MET expected

- CDF secondary vertex

## ZHbb

**ZH************bb**

- Reduce the background with 2D NN:
- Training on ZZ, Z+bb, tt and ZH MC
- Fakes and mistags from data

- (1,1)

- (1,0)

- (0,0)

- 40

- fakes

- mistags

- Z+jets

- ZZ

- tt

- ZH

**Z+jets versus ZH**

**tt versus ZH**

## Signal region

**Single tag**

**Signal region**

**Expected: 101.6 ****±17.8**
**Data: 100 events**

**Expected: 12.8 ****±3.5**
**Data: 11 events**

**S/B =1/4                      (before selections 5/10****15****)**

## Limits

- 95% CL σ over SM expectation

| 1fb-1  | 1 tag | 2 tag | Comb. |
| --- | --- | --- | --- |
| ×BR (pb)
Observed
(expected) | 2.3
(2.2) | 1.9   (1.8) | 1.2               (1.3) |
| Limit/SM
Observed
Expected | 
28    (27) | 
23    (22) | 
16    (16) |

- Major systematic uncertainties:
- Z+ jet Background shape
- Z+ heavy flavor
- Jet Energy scale
- Total systematic shift in  0.19 pb

- mH=115 GeV

## WHbb

**Observable**

**Lepton(e/μ): P****T****>20 GeV, |****η****|<1**

** ****Missing *****E******T ******>20 GeV***

**Backgrounds:**
**Non-*****W***** QCD (lepton fakes)****: Data based estimation **
**Mistag****         :  Data based estimation**
***W*****+Heavy Flavor (Wbb, Wcc, Wc): ****Data and MC based estimation**
**Other standard model background (tt, single top, di-boson, Z********tau tau):**
** ****MC based estimation**

## NN Tagging 

- Apply neural net b-tagger on the information of SECVTX to improve the separation between b-jets and c-jets or light-jets
- NN input: Lxy significance, vertex mass, pseudo-ct...

**Keeping 90% of true b-jets, 65% of l-jets and 50% of c-jets are removed!**

## Results WHbb

**At least 2 b-tagging (double tag)                          ****NN b-tagging is NOT applied**

- Higgs

**≥****2 SECVTX without NN**

- Expected 44.2 ± 8.5    Observed 39

## Limits

- About 10  × SM

## W/ZMET and Hbb

**Signal has a  distinctive                 topology**
**Two jets**
**|****η****|<2.0** **and one |********|<0.9**
**ET,jet1 > 35 GeV**
**ET,jet2 > 25 GeV**
**Δ****R(j1,j2)>1.0**
**No other jets with ET> 20 GeV, |****η****|<2.0**
**Large MET (>50 GeV)**
** ****b-jets (use b-tagging)**

**W/Z********MET and H********bb**

## Z/WMeT and Hbb

**Control Region 1 – QCD**
-  **Veto events with identified leptons**
** **ΔΦ(j2, MET)<0.4

**Extended Signal Region**
**Veto events with leptons**
**ΔΦ****(j2, MET)>0.4**

**Control Region 2** **– EWK**
**1 identified lepton**
**ΔΦ****(j2, MET)>0.4**

- Unbiased analysis

## Results

**Double b- tag CR2 :**** Dominated by top**

- Tight SECVTX applied to this analysis both for single and double tagging

- Double tag

**Expect 14.8 ± 2.65            Observe 16**

**Sensitivity Optimization performed in extended signal region:**
**E****T,1**** > 60 GeV and ********(E****T,1****, MET) > 0.8**
**MET ****> 70 GeV**
**H****T**** =scalar sum of the jet Et-s**
**Missing H****T**** (vectorial sum of jet Et-s)**
**Missing H****T**** / H****T**** > 0.45**

## Exclusion limits

| Mass (GeV) | Rexpected/×BR
ZH | Rexpected /×BR
WH | Rexpected /×BR
VH | Robserved /×BR
VH |
| --- | --- | --- | --- | --- |
| 110 | 22.5 / 2.2 pb | 27.9 / 4.6 pb | 12.4 (+5.1 / –4.0) / 3.3 pb | 18.9 / 5.0 pb |
| 115 | 28.0 / 2.2 pb | 33.0 / 4.5 pb | 14.4 (+7.0 / –4.7) / 3.1 pb | 22.0 / 4.7 pb |
| 120 | 28.3 / 1.8 pb | 37.8 / 4.1 pb | 16.4 (+7.1 / -4.7) / 2.8 pb | 25.1 / 4.3 pb |
| 125 | 33.1 / 1.6 pb | 46.5 / 3.9 pb | 20.7 (+8.2 / -6.1) / 2.8 pb | 32.4 / 4.3 pb |
| 130 | 42.0 / 1.6 pb | 58.3 / 3.7 pb | 24.8 (+8.6 / -7.1) / 2.5 pb | 40.4 / 4.1 pb |
| 135 | 55.1 / 1.5 pb | 76 / 3.4 pb | 32.6 (+15.2 / -10.3) / 2.4 pb | 51.9 / 3.8 pb |
| 140 | 75.3 / 1.4 pb | 104.7 / 3.2 pb | 44.9 (+18.2 / -13.5) / 2.2 pb | 67.3 / 3.4 pb |

- Systematic uncertainties:
- B-tagging:  8.6 % for double tags
- Jet energy scale: 7%-26%
- Luminosity: 6%
- Z/W + heavy flavor normalization: 40%

## Candidate event

**Double-tagged event**

**Di-jet invariant mass = 82 GeV**

**Leading Jet E****T**** = 100.3 GeV**** **

**Second Jet E****T**** = 54.7 GeV **** **

**Missing E****T**
**144.8 GeV**

## Combination

- Combination of all CDF channels and with D0 in ongoing

-  ICHEP 06

- CDF Combination does not include the improved llbb analysis

## Outlook

**Outlook**

- Current limits with 1 fb-1
-  2.5 fb-1 have been collected

- Tevatron operating well  6 fb-1 by 09

- Improved analysis methods

- Improved triggers implemented
- Ex. New Calorimeter trigger
- We keep working and searching

**2007**

- Backup slides

## Validation

- Pre-tagged sample

## Results WHbb

- Expected 394.4 ± 66.6    Observed 421

**=1 SECVTX with NN tagging**

## Backgrounds

**Single tag CR1: ****Dominated by QCD and mistags**

**Double b- tag CR2 :**** Dominated by top**

- A few examples!

- Tight SECVTX applied to this analysis both for single and double tagging

## Signal Region

**Signal Region**

**S/B Optimization is performed in extended signal region**
**Jet energy**
**Missing ET**
**HT =scalar sum of the jet Et-s**
**Missing HT (vectorial sum of jet Et-s)**

- Double tag

- Single tag

**Expect 14.8 ± 2.65            Observe 16**

**Expect 251.0 ± 43.2 Observe 268**

******(1****st**** Jet, Missing E****T****) > 0.8**
** ****Missing E****T**** > 70 GeV**
** ****Missing H****T**** / H****T**** > 0.45**
** ****1****st**** Jet E****T**** > 60 GeV**