# Presentation: 902090

## DØ results on Higgs Search

- Yuji Enari
- Brown University
- On behalf of DØ Collaboration
- Lake Louise Winter Institute 2007

**Notes:**
Today I report Dzero result on Higgs search. I’m Yuji Enari, on behalf of Dzero collaboration

## SM Higgs boson

- Gauge invariance: No mass term
- Mass of fundamental particles are given by Higgs boson
- From theory
- Missing part of SM
- SM higgs mass is light

- From experiment:
-  - MH > 114.4 GeV @95% CL
-    search by LEP2
-  - MH < 166 (199) GeV @95%
-    CL global EW fitting

- Center value
- = 85 + 39 – 28 GeV

**Allowed**

- Higgs self-coupling diverges

- unstable vacuum

**Tevatron can explore the mass range of 115 < M****H**** < 185 GeV**

- Dzero results on Higgs Search       Lake Louise     Y.Enari

- 19th Feb 2007

**Notes:**
Why we need Higgs?
Because nature needs gauge invariance, there is no mass term in the SM lagrangian.
Mass of fundamental particles are given by Higgs boson.
Interesting point is no one have found higgs boson.
So Higgs is missing part of SM.

There is constrain on higgs mass from Higgs self coupling diverges and vacuum.
This region is only allowed by theory.

From experiment, LEP excluded this mass region by direct search and 
Global EW fitting tell us higgs mass is less than 175 GeV at 95% CL.

So both experiment and theory tell us higgs is light, and this mass range can be explore by Tevatron.

## SM Higgs search at Tevatron

**Analysis Strategy**
**m****H**** < 135 GeV**
**          ****WH/ZH ****   +    ****H******** bb**
**m****H**** > 135 GeV**                                                **Gluon fusion****   +    ****H********WW**

**Production**
**1. Gluon fusion **(0.8 ~ 0.2 pb)
**2. WH associated production **(0.2~0.03pb)
**3. ZH associated production **(0.1~0.01pb)
**Decay**
**m****H**** < 135 GeV**
**	****H ******** bb is dominant**
**m****H**** > 135 GeV**
**	****H******** WW **

**top, Wbb, Zbb**
**WW, DY, WZ**

**Background**

- Dzero results on Higgs Search       Lake Louise     Y.Enari

- 19th Feb 2007

**Notes:**
How to search higgs at Tevatron.
Upper figure show production cross section as function of higgs mass as Tevatron energy 1.96TeV.
Gluon fusion has highest cross section, then Vector boson associated production. 
Lower figure shows branching ration of Higgs decay.
Under mass rage 135GeV, higgs to bb bar is main decay, and mass greater than 135GeV, H to WW decay is dominant decay. 

Here is analysis strategy, Because of we need at least one lepton, to trigger signal and suppress QCD,
At low mass region, we use WH or ZH associated production with H to bb bar decay.
At high mass region, we use Gluon fusion and H to WW decay. 

## Current Status of Higgs search at DØ

|   | mode | fLdt (pb) |
| --- | --- | --- |
| ZH | eebb
bb
bb | 840
920
260 |
| WH | ebb
bb | 370
380 |
| WH
WWW | ee + qq
e+ qq 
+ qq | 380
370
360 |
| H WW | ee

e | 950
930
950 |

|   | mode | fLdt (pb) |
| --- | --- | --- |
|  bh |  bbb
b | 880
340 |
| h |  h | 1000 |

**Others**
**  ****h++ ******** tt,  Htb, **
**   ****tt(t******** H****+****b, H+********cs)  **
**   ****H++ ******** ********ee**

**SM**

**MSSM**

|  | mode | fLdt (pb) |
| --- | --- | --- |
| VhfH | X | 1000 |
| VhfV |   | 190 |

**Fermiophobic**

- Dzero results on Higgs Search       Lake Louise     Y.Enari

- 19th Feb 2007

**Notes:**
This table lists current status of Higgs search at D0. 
In the SM, low mass and middle range, and higmass, and this column shows how much data we are using.
Today I would like to show you latest results which hatched in yellow, ZH and H to WW modes. 

We also search Higgs beyond standard model, and we have results. Also I’ll show you these two modes, MSSM h to tautau and Fermiophobic Higgs search.

## DØ detector

- Toroid & solenoid polarity flipped regularly
- ~equal exposure to 4 possible field configurations

|  | || | || |
| --- | --- | --- |
| Muon ID | ~2 | ~15o |
| Tracking | ~2.5 | ~5o |
| EM / Had CAL | ~4 | ~2o |

_**Multi purpose detector**_

- New silicon detector for
- improvement of b-jet ID
- Installed last spring

**Layer 0**

- Dzero results on Higgs Search       Lake Louise     Y.Enari

- 19th Feb 2007

**Notes:**
Here is Dzero detector. I’ll skip detail explanation. Because you already heard about this today.
Just I would like to emphasize Dzero is multi purpose detector with large coverage. 
Also we have new slicon layer scince last spring which improves b-jet ID.

##  Improvement on b-tagging

-  Characteristic of b-quark
- Lepton from semileptonic B decay (Br~10%)
- Longer lifetime, ~1.6ps
- 	 Travel distance from PV ~ 1mm
- Tagging Algorithms
- Secondary vertex reconstruction
- Impact Parameter based
- NN tagger
- Use these information as input of NN
- 	 33% gain with same fake rate of 0.5%

- Dzero results on Higgs Search       Lake Louise     Y.Enari

- 19th Feb 2007

**Notes:**
I would like to show you about status of b-tagging.

There are two characteristic of b-quark, one is it has semileptonic decay,
Other is longer life time, so B meson travel about 1 mm, so b decay has secondary vertex as illustrated here. 

So far, we used these two tagging algorithms, Secondary vertex reconstruction and impact parameter based.
Recent improvement is use these information as input of Neural net.

This figure shows it’s result, blue line shows NN tagger efficiency as function of fake rate, and green line shows impact parameter based tagger.
We get 33 % gain with same fake rate of 0.5%.

## Low mass SM Higgs:  ZH  llbb 

- Low mass SM Higgs:  ZH  llbb

-  e : pt>15GeV, 2 loose electron
-   : pt>15GeV, 2 loose  muon

**New result!**

|  | data | BG exp. | mH=115  |
| --- | --- | --- | --- |
|  e | 7 | 10.7 ± 3.7 | 0.20 |
|   | 11 |  9.8 ± 3.4 | 0.17 |

- _ __f__Ldt = 920 / 840pb__-1_

**After double NN b-tag **

**Combine e and ********, 1 tag + 2 tag**
- Modified frequentist approach (CLs)
- from dijet mass distribution

- _Mass window_
-  e
- 

**q**

**q**

**Z**

**Z**

**H**

**b**

**b**

**e, ******

**e, ******

- Main BG:
- Z+jj, Z+bb** **

- Dzero results on Higgs Search       Lake Louise     Y.Enari

- 19th Feb 2007

**Notes:**
Let’s move on results on SM higgs search.
First result is ZH, dilepton mode, ee or mumu with data of about 900 fb-1.

For Z reconstruction 2 loose electron or muon is required with pt greater then 15 GeV.
Right upper plot shows invariant mass of di-electron in log scale, you can see Z peak here.
We select this region. Then, we apply NN b-tagging, and reconstruct di-jet mass which is shown left lower plot.
In this figure, dot is data, open histogram is sum of all BG, and red histogram shows ZH signal with higgs mass of 115GeV.

This table shows number of event after double b-tag in this dijet mass window.
We observed 7 event in electron and 11 event in muon mode. These are consistent with BG expectation.
So we set limit. For limit setting, we conbine e and mu and 1 tag and 2 tag  using modified frequentist approach from diget mass distribution.

Expected limit is blue dot, and observed limit is this line. You can see slightly better CDF result, because they apply NN analysis.

## High mass SM Higgs: HWW

- High mass SM Higgs: HWW

- Two isolated high pT  leptons + missing ET
-  ee,  e channel are considered.

**W****+**

**e****+**

**W**-

**e**-

****

****

****** ****Use Angular correlation**

**WW is daughter of scalar H.**
**Leptons from W tend to have same direction**

**No excess from BG exp in ********  dist.**

- _ __f__Ldt = 930-950 pb__-1_

**g**

**g**

- t

**W**

**W**

**H**

****

****

**e, ******

**e, ******

****** ****Missing**

- Main BG:
-   ggWW

- Can’t reconstruct H invariant mass

|  | Data | BG exp. | mH=160  |
| --- | --- | --- | --- |
|  ee | 10 | 10.3 ± 1.5  | 0.42 |
|   | 9 |  9.8 ± 1.6 | 0.35 |
|  e | 18 |  24.4 ± 3.7 | 0.97 |

- Dzero results on Higgs Search       Lake Louise     Y.Enari

- 19th Feb 2007

**Notes:**
Next is H to WW.
Higgs produce via gluon fusion and decay in to WW and both decay in to lepton.

To search this mode, we require two isolated high pt leoton and missing Et.

One difficulty of this mode is we can not reconstruct H mass peak due to two neutrino.
In this channel, we use angular correlation. Because WW is dauter of scalar paticle and it decay in to neutrino.
So it has very strong spin correlation. In this case charged lepton tend to have same direction.

We extract signal from this Delta phi between two charged lepton.
Dod shows data and over all BG expectation shows this histogram. Higgs signal shows this black histogram.
Table show observed event. There is no excess from BG exp. We set limit as blue hutched region.
We start to exclude 4 the generation model. 

## Limits on SM Higgs production

- Latest ZHllbb is not included in these limits.
- New result of  WHlbb and ZHbb will be coming soon.

**Data/SM ~ 10**
**@ 115GeV**

**Data/SM ~ 5**
**@ 160GeV**

- Dzero results on Higgs Search       Lake Louise     Y.Enari

- 19th Feb 2007

**Notes:**
This figure shows combined limits for all D0 runII analysis.
Even though these latest results are not included, The ratio of observed limit and SM cross section is about 10 at 115 GeV and 5 at 160GeV.
But Latest ZH  llbb is not included. And These mode will coming soon.

## MSSM
Two Higgs doublets to avoid anomaly
8 degrees of freedom – 3 (longitudinal pol. of W±,Z )
	 5 physical scalars (h, H, A, H±)

Search for  
Br(bb) ~ 90%,   Br()~10%
	   High QCD BG     l+had (17%x62%) 

   Tau ID (hadronic  decay)
 NN: 8 variables related to jet shape
 Train NN each topology separately

         Performance: @ ’s pt=15GeV 
	   hwithfake
hwithfake
hwithfake

- MSSM
- Two Higgs doublets to avoid anomaly
- 8 degrees of freedom – 3 (longitudinal pol. of W±,Z )
- 	 5 physical scalars (_h, H, A_, H±)
- Search for ********** ******
- Br(bb) ~ 90%,   Br()~10%
- 	   High QCD BG     l+had (17%x62%)
-    **Tau ID** (hadronic **** decay)
-  NN: 8 variables related to jet shape
-  Train NN each topology separately
-          Performance: @ ’s pt=15GeV
- 	   hwithfake
- hwithfake
- hwithfake

- MSSM Higgs

- 

- _At high tan____=H__u__/H__d____, ____(h or H, A)_
- _ __is enhanced_

**t**

- 

**b**

- 

-   ~ 1/tan

-   ~ tan

**b**

- 

** ********+**

** **********

******+**
****
********

** ******
****
** ****hadron**

- MW < 20 GeV

- Dzero results on Higgs Search       Lake Louise     Y.Enari

- 19th Feb 2007

**Notes:**
Next is MSSM higgs,
In the MSSM, there is two higgs doublet to avoid anomaly. 
There is 8 degree of freedom but 3 is used by longitudinal polalization of W and Z.
Therefore, 5 physical scalars, Three of them are neutral, and charged higgs.
We call these three neutral higgs as phi.

Interesting point of this scheme is these cross section is enhanced at high tan beta.
Especially This mode, phi to tautau or bb is both couple down type, so it highly enhanced at large tan beta.

In this analysis forcus in tautau channel because bbbar has high QCD. And two tau decay in to lepton had hadron  is not small braching ration.
So requirement is one isolated high pt lepton and missing ET pulse hadron tau ID.

To suppress BG from W, we use this W mass variable which calculated using missing and muon. We require Mw less than 20 GeV.
For TauID, we use NN with 8 variable related to jet shape. Tau ID efficiency and fake rate is listed here.

## MSSM Higgs  

- MSSM Higgs  

-  h
-  NN>0.9
-  R > 0.5
-  MW < 20 GeV
- Main BG
- Z 
- QCD is well suppressed

**New result!**

**DATA:  1141 evt.**
**MC    :  1287 ± 130 evt.**
**Eff(****************) : 1.4%**

- _ __f__Ldt = 1000 pb__-1_

**Observed events are fully consistent with expectation**
**No excess ~ 140 GeV**

- Dzero results on Higgs Search       Lake Louise     Y.Enari

- 19th Feb 2007

**Notes:**
Selection are NN > 0.9, and deta R between mu and tau are greater than 0.5. 
Then we get eleven hundred event which is within back ground exectation.
This figure show visble mass, dot is data, and red histogram is all BG. And this light blue shows signal with 160 higgs.
Recently CDF claims 2 sigma excess around 160 GeV, unfortunately we don’t see any excess.

## New limit on MA vs tan

- To maximize sensitivity NN output is used in the limit calculation
- 	 NN input:  Visible Mass, pT, pT (cal), pT (trk), 

**New result with 1fb****-1**** **

****

****

****

- Dzero results on Higgs Search       Lake Louise     Y.Enari

- 19th Feb 2007

## Fermiophobic Higgs search with         SM VVhf  coupling:
LEP: e+e-  Zhf        mhf  > 105 GeV
		    e+e-  Ahf        mhf +mA > 160 GeV
TeV: qq  V  V+hf    mhf  > 82 GeV

There is still possibility in 2HDM
   tan>1, mhf < 90 GeV, mH < 200GeV

Signature
	pp  hfH±  hfhfW±  X
    pt1 >30 GeV, pt2 >20 GeV, pt3 >15 GeV

- Fermiophobic Higgs search with         **SM** VV*h**f*  coupling:
- LEP: e+e-  Z*h**f        *m*hf * > 105 GeV
- 		    e+e-  A*h**f        *m*hf *+mA > 160 GeV
- TeV: qq  V  V+*h**f    *m*hf * > 82 GeV
- There is still possibility in **2HDM**
-    tan>1, m*hf *< 90 GeV, mH < 200GeV
- Signature
- 	pp  *h**f*H±  *h**f**h**f*W±  X
-     pt1 >30 GeV, pt2 >20 GeV, pt3 >15 GeV

- New search: Fermiophobic Higgs *h**f **h**f *W  () X

**u**

**d**

**W**

**h****f**

**H**

**h****f**

**W**

*h**f*

- 

- 

**m****H**** = 150 GeV**
- m*hf***  = 50GeV**

****

****

****

****

**q**

**q**

**W/Z**

**VV*****h******f***** ****coupling **

** ****pt ********        (GeV/c) **

- Dzero results on Higgs Search       Lake Louise     Y.Enari

- 19th Feb 2007

**Notes:**
One more other new result is about Fermiophobic higgs.
Related search has been done at LEP and TeVatron, but it was focused on only SM VVh coupling.

We aware there is still possiblility in this couple within 2HDM under this parameter range.
In this range, This WHh coupling enhanced while VVh coupling suppressed. 

We search this mode by requiring high pt 3 gammas. This figure shows MC expectation of the signal.
These points show First leading and second and third photon.

## hf hf W  () X 

- Additional selection
-     HT > 25 GeV

- Before applying HT cut

**Observed Event  :         0      ev**
**Expected # of BG:  1.1 ± 0.2 ev**
**Acceptance         :     0.16 ****± 0.03**

**Limit:  ******** = 25.3 fb  @95%CL**

- Mhf = 66GeV for mH < 100 GeV  @ tan =3
- Mhf = 44GeV for mH < 150 GeV  @ tan =3
- Mhf = 80GeV for mH < 100 GeV  @ tan =30
- Mhf = 50GeV for mH < 150 GeV  @ tan =30

- preliminary result

**New result**

** ****Invariant mass of ********  (GeV/c****2****)**

- _ __f__Ldt = 1000 pb__-1_

- MC: 3.5±0.6

- Dzero results on Higgs Search       Lake Louise     Y.Enari

- 19th Feb 2007

**Notes:**
This search has been done with 1 fb-1. This histogram shows invariant mass of gamma gamma with BG exectation.
Then Additinally we apply Ht cut, we observe 0 event with signal acceptance with 0.16.  
Therefore we set upperlimit from this result.  

Limit on cross setion times branching ratio is show this black dot line as function fremiophobic higgs mass.

## Summary and Prospect

- No excess yet observed in data from BG expectation.
- Observed limit is getting close to SM expectation.
- We are currently improving our analysis
-  bID performance much improved by using Neural Net
-  Optimization of selection
-  Use Event shape:  NN, Matrix Element, etc...
-  Increased acceptance
-  Jet energy resolution
-  Reduce systematic uncertainty
-  Adding new channels
-  Combine with CDF
- Increase statistics: 2fb-1 of data on tape,
- 				 expect 4-8fb-1 by 2009.

**NOW is time for Higgs search at Tevatron!  Stay tuned!**

- Dzero results on Higgs Search       Lake Louise     Y.Enari

- 19th Feb 2007

- Dzero results on Higgs Search       Lake Louise     Y.Enari

- 19th Feb 2007

## Prospect

- 4~8fb-1 will be available by 2009

- Dzero results on Higgs Search       Lake Louise     Y.Enari

- 19th Feb 2007

- Dzero results on Higgs Search       Lake Louise     Y.Enari

- 19th Feb 2007

## MSSM parameter for   

- Dzero results on Higgs Search       Lake Louise     Y.Enari

- 19th Feb 2007