# Presentation: 215694

## Qizhong Li
Fermilab
for the CDF and D0 collaborations

Februaty 13, 2006

2006 Aspen Winter Conference “Particle Physics at the Verge of Discovery”

- Fermilab
- for the CDF and D0 collaborations
- Februaty 13, 2006
- 2006 Aspen Winter Conference “Particle Physics at the Verge of Discovery”

_**Searches for Higgs and **_
_**New Physics at the Tevatron**_

## Outline

- Tevatron Performance
- SM Higgs search
- MSSM Higgs Search
- New Physics
- Summary

- 2006 Aspen Conference

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## Tevatron Run II

**Run IIa**
**    ****2001 - 2006**
**    ****E****CM**** = 1.96 TeV**
**    ****~ 1.4 fb****-1**
**Run IIb **
**     ****2006 - 2009**
**     ****E****CM**** = 1.96 TeV**
**     ****~ 7 fb****-1**

- Run I
-     1992 - 1996
-     ECM = 1.8 TeV
-     ~120 pb-1

_**The World’s Highest Energy Accelerator**_

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## Tevatron Performance

- Record high:
- Peak luminosity:      1721030  cm-2 s-1
- Weekly intergrated luminosity:  27 pb-1/week
- Total delivered intergrated luminosity:   1.4 fb-1

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## Experimental Limits on Higgs Mass

- _Experimental Limits on Higgs Mass_

- Direct searches by LEP on SM Higgs Boson:
***m******H***** > 114.4 GeV (95% CL)**
- Indirect limit from fits to precision EW measurements from LEP-SLC-Tevatron
***m******H***** ****< 219 GeV (95% CL) **
**using “latest” *****m******t*****=172.7 ******** 2.9 GeV (CDF+D0, Run I+II)**
- preferred value:** *****m******H***** = 91 ****+45****−32**** GeV**

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## SM Higgs Production and Decay

- Search strategy:
-     MH <135 GeV associated production WH and ZH with Hbb decay
- 	Backgrounds: Wbb, Zbb, top...
-     MH >135 GeV gg H (or WH) production with HWW* decay
- 	Backgrounds: WW/WZ production...

- Production

- Decay

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## Higgs sensitivity

- The integrated luminosity required per experiment, to either exclude a SM Higgs at 95% C.L. or discover it at the 3 or 5 level; no systematics

-  No single channel guarantees success.
-  Combine two experiment’s results.
-  Improved understanding of detectors is necessary.
-  Need advanced analysis techniques to maximize sensitivity.

- Tevatron enters sensitive region with 2 fb-1 by the end of 2006.

**LEP**

**Tevatron**

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## WH  bb   

- Best channel for       low mass higgs.
- Event signature:
- A high pT lepton (e or )
- Large missing ET
- Two b-jets (_>_ 1 b-tag)
- Backgrounds:
- Wbb, Wcc,
- W+jets (mistags)
- Diboson
- Top
- QCD

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## WH  bb

- _WH ____ __****____bb_

- D0:  WH ebb   ( 382 pb-1 )

- After 2 b-tags, observe 13 events,
- expect:  Wbb:          4.29_+_1.03
-        Other bkg:  5.73_+_1.45
-       WH:            0.14_+_0.03

- CDF:  WH ****bb   (319 pb-1)
-            (ebb, bb combined)

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## ZH  bb

- Missing ET > 25 GeV,
- 2 acoplanar b-jets, ET > 20 GeV
- Background: W+jets, Z+jets, top, WZ, ZZ
- No isolated track, HT < 200 GeV
- Instrumental bkg: multijets w/mistag
- Jet acopalarnarity, various asymmetries

- no b-tag

- single b-tag

- double b-tag

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## ZH  bb

- _ZH ____ ____bb_

- Jets: 84.7GeV,  71.9GeV (b-tagged)
- missing ET: 98 GeV,
- dijet mass: 128.6 GeV

| Dijet mass cut  | ZH 120 | mistag | QCD | Top | EWK | Total bkg | observed |
| --- | --- | --- | --- | --- | --- | --- | --- |
| Before  | 0.16 | 7.04 | 2.58 | 2.09 | 7.0 | 19.7 |     19 |
| Mass cut for 120 GeV higgs | 0.13 | 2.2 | 0.9 | 0.8 | 0.5 | 4.36 |      6 |

- . 2 jets
-   ET >25GeV
- . veto 3nd jet
- . ET >70GeV
- . _>_ 1 b-tag

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## H  W+W-  +- 

- Leptonic decay channels are promising: ee,  or e
- Backgrounds include WW, tt, W/Z+jets, Z/*, QCD.
-        WW is dominant background.

- Heavy Higgs:
-        Br(HWW*)>0.9, when mH>160 GeV
- Search strategy:
-  Two high **p****T** leptons with large missing **E****T**
-  Opening angle between leptons (******ll**) is useful discriminant
-  Two leptons from Higgs tend to move in parallel (small ll ) , due to spin correlations in  H  WW decay products.

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## H  W+W-  +-

- CDF:  ~ 360 pb-1

| Expected signal |       0.68+0.01 |
| --- | --- |
| diboson |       12.3+0.3 |
| Other bkg |         7.5+1.1 |
| Total bkg |       19.8+1.2 |
| data |          19 |

| Expected signal |      0.58+0.04 |
| --- | --- |
| diboson |      10.2+1.0 |
| Other bkg |        3.6+0.7 |
| Total bkg |      13.8+1.2 |
| data |         16 |

- mH=160GeV

- mH=160GeV

- D0: ~ 320 pb-1

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## WHWWW* qq

- Associated Higgs production, WH, where Higgs decays to WW
- Very clean signature: 2 like sign e or  + 2 jets + Missing ET

- _D0 (ee/e__****____****__  384-363 pb__-1__):_
-  2 like-sign isolated e or ****,   pT>15 GeV, veto 3rd lepton
-  Track quality cuts
-    (reduce charge flip)
-  Missing ET > 20 GeV
- Background:
-   physics:  WZ  ************
-   instrumental:
-   - charge flips ( Z/* ****** **)
-   - QCD or W+jets

| D0 Analysis |    ee |    e |  |
| --- | --- | --- | --- |
| Observed |      1 |     3  |     2 |
| Total bkg | 0.70 | 4.32 | 3.72 |

- CDF:
- 193.5pb-1

- D0:
- ~370pb-1

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## SM Higgs: where we stand today

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## Supersymmetry

- Main motivation – protect Higgs boson mass from large radiative corrections (Hierarchy problem).
- Phenomenology – every SM particle gets a SUSY partner with S=1/2.
- SUSY partners have same quantum numbers, but opposite R-parity.
- R=(–1)3B+L+2S = +1 (SM) or –1 (SUSY).
- If R-parity is conserved (RPC) –
- SUSY particles are produced in pairs.
- Lightest SUSY particle (LSP) is stable.
- Missing ET from LSP is a typical SUSY signature.
- Higgs sector required to have two Higgs doublets.
- Large number of  SUSY searches in CDF and D0.
- too many to describe here, can only present some of them today.

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## MSSM Search: (b)bh bbb(b)

- Search for neutral Higgs in a two-Higgs-doublet MSSM SUSY model.
- Cross-section rises as tan2
- 260 pb-1 sample of triple b-tagged
-       multi-jet events.
- No distinction between h or H and A

**Sample Selection:**
**- **Trigger >3 jets with ET>15 GeV,
- - Offline cut on ET of leading jets
-             optimised for each Higgs mass.
-          - 3 b-tagged jets or more** ****Backgrounds:**
**  **bbjj, ccjj, cccc, bbcc, bbbb
-   Z(bb,cc), tt
- “QCD fakes” : jjjj

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## b(b)h  bbb(b)

- _b(b)h ____ bbb(b)_

- Expected and measured 95% C.L. upper limits on the signal cross section

- The 95% C.L. upper limits on tan as a function of mA and for two scenarios of MSSM

- With 5 fb-1 of data, assuming the current performance, can probe tan values down to 20-30 depending on the mass, model

- No mixing in stop sector: Xt = 0
- 		Xt = At – cot, At – tri-linear coupling,  = – 0.2 TeV
- Maximal mixing: Xt = √6×MSUSY, MSUSY= 1 TeV

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## h  

- In MSSM at high tanhiggs production can be much larger than SM.
- Event signature:
- a lepton, e or , (from  decay)
- a –jet  (pencil-like)
- missing ET
- Backgrounds:
- Z  +-
- W+jets, QCD  (fakes)
- Top, diboson, Zee/
- tau efficiency: ~ 46%
- Fake rate: ~ 1.5% for 20 GeV jet;
-                       ~ 0.1% for 100 GeV jet
- mvis: invariant mass of (******, ******had, ET)

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## h   

- Data: 310 pb-1
- Expected total background: 496±5±28±25
- Observe:  487 events
- Binned likelihood fit of mvis(****, ******had**, ET) for set limit.

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## MSSM Higgs Prospects

- Projections are made for the *combined *reach of CDF and D0.

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## MSSM Charged Higgs: t  H+b

- BR(tH+b) can be large,
-      competing with the tW+b.
- Search based on the tt cross section
-      (top disappearance in lepton channels).

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## Chargino/Neutralinos

- _Chargino/Neutralinos_

- Higgsinos and gauginos mixcharginos/neutralinos
-    LEP:
-    20 1±  ****±************±1010X
**   ****** = e, , 

-  Small x-section, but
-  Trileptons with missing ET are very clean, low background.
-  Major backgrounds:
-  Dibosons.
-  QCD (fakes).
-  Top

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## Chargino/Neutralinos

- D0: 6 analyses (325 pb-1)

| Channel | SM bkg | Data |
| --- | --- | --- |
| ee + track | 0.210.12 | 0 |
| e + track | 0.310.13 | 0 |
|  + track | 1.750.57 | 2 |
| e + track | 0.580.14 | 0 |
|  + track | 0.360.13 | 1 |
|  like sign | 0.660.37 | 1 |

- CDF: e, final states
-      346 pb-1

| Channel | SM bkg | Data |
| --- | --- | --- |
| ee | 0.170.05 | 0 |
|  | 0.090.03 | 0 |

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## Squark/Gluino

- Squarks and gluinos are pair-produced by strong interaction and decay into quarks and LSP.
- Signature: jets + missing ET (2, 3, or 4 jets).
- Backgrounds: W, Z, top, QCD.

| Channel | SM bkg | Data |
| --- | --- | --- |
| D0 2 jets (310 pb-1) | 12.85.4 | 12 |
| D0 3 jets (310 pb-1) | 6.13.1 | 5 |
| D0 4 jets (310 pb-1) | 7.10.9 | 10 |
| CDF 3 jets (254 pb-1) | 4.11.5 | 3 |

- 3 jets

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## Scalar bottom

- Sbottom pair production: qqbbbb.
- Event signature: 2 acoplanar b jets + missing ET.
- Backgrounds: W, Z, diboson, top, QCD.

- ~

- ~

- _

- _

- ET > 60 GeV
- Jet ET > 40, 15 GeV
-  < 1650
- _>_ 1b-tag (impact par.)

| 318 pb-1 | SM background | Data |
| --- | --- | --- |
| Before b-tag | 133548 | 1433 |
| After b-tag | 38.62.8 | 36 |

- Before b-tag

- After b-tag

- _

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## GMSB SUSY +ET

*PRL 94, 041801 (2005)*
*PRD 71, 031104(R) (2005);*

|  | SM bkg | Data | m+(GeV) |
| --- | --- | --- | --- |
| D0 (263 pb-1) | 3.7±0.6 | 2 | 195 |
| CDF (202 pb-1) | 0.3±0.1 | 0 | 167 |
| Comb. |  |  | 209 |

- CDF & D0 Combined result
- (first of many to come)

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## 2nd Generation Leptoquarks

- Pair production: qq  LQLQ  qq ,   = Br(LQq)
- Search channels: 2+2j (CDF and D0);  +2j+ET (CDF); ET+2j (CDF).
- Backgrounds: Z/, QCD (fake)
- No evidence found.

- Submitted to *PRL*

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## R-parity Violation

- R-parity violating (RPV) interactions violate B or L, but are not ruled out.
- LSP decays to SM particles (+–).
- SUSY particles can be produced singly.

| SM bkg | Data |
| --- | --- |
| 7.660.63 | 5 |

- Backgrounds:
-   . Diboson
-   . Top
-   . Z

- Signal region:
- 100 < Me< 180Gev

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## Signature-based searches for dileptons + X 

- _Signature-based searches for dileptons + X__ _

- Look for excess above SM prediction in dilepton + X (X = photon, lepton, b-jet, HT, Missing ET; dileptons can be same-sign or opposite-sign)
- Set cuts on first 1/3rd of dataset (now, 305pb-1), apply to next part of data (coming soon)
- can be further applied to many models; e.g. heavy quarks as first example

- High pT Z’s (inclusive) in dimuons

- HT == scalar sum of electron and jet ET, muon pT, missing ET

- No excess seen in these channels!

- Good agreement in HT<200 control region.
- No events in HT>400 signal region.

- Dilepton (ee, , e) + high HT

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## Summary

- CDF and D0 have searched for Higgs and new physics in many different channels.
- No Higgs has been found yet.
- No evidence for new physics.
- Tevatron is performing well. Delivered ~1.4 fb-1 luminosity for each experiment so far.
- New analyses with 1 fb-1 coming soon.
- Expect ~8 fb-1 total in Run II.
- Will be able to reach 3**** evidence or  95% CL exclusion for Higgs up to 180 GeV in mass.
- Many additional searches not covered in this talk
- LED, new gauge bosons, stop, technicolor,...
- Experiments will be upgraded 2006.
- Prospects are excellent for exciting new physics results!

- if nature is kind

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## Backup slides

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## Bs 

- In SM, small BR ~ 3.510-9
- But in SUSY, enhancement  ~ tan6factor

| at 90% C.L. | Luminosity | BR(Bs) |
| --- | --- | --- |
| CDF | 364 pb-1 | <1.510-7 |
| D0 | 300 pb-1 | <3.010-7 |

- B+J/K+

- Bs:  m vs limelihood

- mSUGRA  M0 vs M1/2

- excluded

- excluded

- Excluded by CDF

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