# Presentation: 717515

## Search For New Physics with the D0 Detector

**Eric Kajfasz**
**CPPM, Marseille**
**on behalf of the D0 collaboration**
**ICHEP 2006, Moscow**

- [Only the most recent results not shown elsewhere at this conference]

## Standard Model

**Based on**:
- - 4-D space-time
- - Poincaré group
- - SU(3)c x SU(2)L x U(1)Y
-  3 generations of quarks and leptons
- - Higgs mechanism

- Phenomenologically **successful** so far,
**but **many questions unanswered...

- Higgs field filling our Universe and slowing down elementary particles.
- Is it elementary?

**If so, some drawbacks**:
-  no dynamical explanation to EWSB
-  unnatural, requires fine tuning   -> MH unstable against rad. corr.
-  in GUTs, leads to hierarchy problem  -> 2 very different scales
-  no insight to flavor physics

**Standard Model**

- E. Kajfasz

- ICHEP Moscow 29/07/06

## Some Ways to go Beyond ...

- - Relate quarks and leptons -> **Leptoquarks ****                                 ****- jets+MET**
**                                 ****- b-jets+MET**
- - Extend Poincaré -> Supersymmetry
- 	and include gravitation (Supergravity)
-  Increase the number of dimensions- Enlarge the gauge group
- - Repeat History (compositeness)

**Some Ways to go Beyond ...**

- Numerous D0 results given
- in other talks at this
- conference

- Notes and results on New Physics can be found at:
**http://www-d0.fnal.gov/Run2Physics/WWW/results/np.htm**
**http://www-d0.fnal.gov/Run2Physics/WWW/results/higgs.htm**

- To answer some of the questions ... new theories and models

- E. Kajfasz

- ICHEP Moscow 29/07/06

## The Tevatron @ Fermilab

- Luminosity:
-  Peak:  > 1.7 1032 cm-2s-1
-  Delivered: > 1.5 fb-1
-  On tape: > 1.2 fb-1
-  Design goal 8 fb-1 (end of 09)
- In this talk: 0.3 to 0.4 fb-1

**The Tevatron @ Fermilab**

- E. Kajfasz

- ICHEP Moscow 29/07/06

## Technicolor

**Technicolor ****(****TC**** - first introduced by Weinberg and Susskind):**
**New strong dynamics**** ****‘a la QCD’**** ****SU(N****TC****) -> ****TC condensates of ****technifermions**
**Coupling of condensates with unbroken electroweak gauge fields -> mass to W&Z**
**Extended TC (ETC) [****mass and mixing to quarks and leptons****]**
**Walking Technicolor (WTC****) ****[****flavor changing neutral current in ETC****]**
**Topcolor-assisted Technicolor (TC2) [****high value of m****top****]**

**Technicolor Straw Man Model (TCSM2):**** **
**Framework to search for light technihadrons (relevant for Tevatron searches).**
**lightest technifermions expected to be an isodoublet of color singlets**
**-> color-singlet vector mesons: ********T**** and ********T**
**-> color-singlet pseudo-scalar mesons:**** ****************and **************
**produced with substantial cross-section at the Tevatron**
**cross-sections and branching fractions depend on:**
**masses of ********T**** and ********T**
**technicolor charges of the technifermions**
**mass difference between vector mesons and technipions**
**2 mass parameters: ****M****A**** for axial-vector and M****V**** for vector couplings**
**Implemented in PYTHIA [S. Mrenna]**** **

- K. Lane, S. Mrenna  *Phys. Rev.* **D 67** (2003)

**Analysis focuses on**
************** ********W********* ***************
******************b****b**
**         ****and**
**************  ********W********* ***************
**************b****c,b****c**

- MA = MV = 500 GeV

- E. Kajfasz

- ICHEP Moscow 29/07/06

## W(e)T(bb/c) event selection

**One isolated electron ****(EM TRIGGER)****p****T**** > 20 GeV, |********| < 1.1**
- select  W(e) events
- veto on other electrons to  suppress Z
**Missing E****T**** > 20 GeV, M****T ****> 30 GeV**
- select  W(e) events
- eliminates multi-jets events
**Two jets p****T**** > 15 GeV, |********| < 2.5**
- At least one jet has to be associated with a Secondary Vertex (b-tagging)
- Veto on a third jet, suppresses tt background

-  multijet production (mis-IDed electron)
-  W + light flavored jets (mistag)

**Instrumental Background**
- estimated from data

**Select W(e********)+Heavy Flavor events**

**SM Background**

**Signal**

- E. Kajfasz

- ICHEP Moscow 29/07/06

## (W+Heavy Flavor)-like events

| Data | 117 |
| --- | --- |

| tt | 22.0 |
| --- | --- |
| Single top | 7.8 |
| W + Heavy Flavor | 56.4 |
| WZ | 1.2 |
| Zee | 1.1 |
| SM total | 88.5 |

| Tot Background | 115.1 |
| --- | --- |

- backgrounds

| multijet | 16.3 |
| --- | --- |
| W + light quarks | 10.3 |

**Instrumental**

**(W+Heavy Flavor)-like events**

**SM**

**2 strategies to extract the signal:**
**	****- Cut based (CB)**
**	****- Neural Net based (NN)**

- E. Kajfasz

- ICHEP Moscow 29/07/06

## Cut based analysis

**Define kinematic and topological**
**quantities to extract the W********T**** signal**
**H****T****e**** ****(electron p****T ****+ ∑ jet p****T****)****discriminates against t****t**
**p****T****(jj)**** ****(p****T ****of the dijet system)****discriminates against t****t**
******(jj) and ********(e,MET)****against multijet and W + light quarks**
**M(jj)**** ****(inv. mass of the dijet system)****-> ****indication of ********T ****narrow resonance**
**M(Wjj)**** ****(W + dijet system)****-> ****indication of ********T ****narrow resonance**
**Mass dependant optimization of cuts on S/√B**

**D0 Run II Preliminary 388 pb****-1**

**M(********T****) = 105 GeV  M(********T****) = 200 GeV M****V ****= 500 GeV **

**M(********T****) = 110 GeV  **
**M(********T****) = 210 GeV**

**M(********T****) = 105 GeV  M(********T****) = 200 GeV M****V ****= 500 GeV **

**Data:   12**
**Bkg:    12.7 ± 0.9**
**Signal: 10.3 ± 1.0**

**no excess**
**seen ...**

**M(jj)**

**M(Wjj)**

- E. Kajfasz

- ICHEP Moscow 29/07/06

## Neural Net analysis

**M(********T****) = 105 GeV  M(********T****) = 200 GeV M****V ****= 500 GeV **

**D0 Run II Preliminary 388 pb****-1**

**no excess**
**seen ...**

**2 stage NN using 8 kinematic ****and topological variables**** ****H****T****e****, ****p****T****(jj)****, ********(jj), ********(e,MET), **** p****T****(j1), p****T****(j2), p****T****(e), MET**
**Mass dependent optimization ****on S/√B **

- E. Kajfasz

- ICHEP Moscow 29/07/06

##  Result of the WT analyses

** ****First measurement done ****  with TCSM2 model ****  ****(cannot be compared with the   ****   now obsolete TCSM)**
** ****No evidence was found for ****  ********T****, ********T**** production for the****  parameters used with 388 pb****-1**
** ****> 1 fb****-1**** is now available**
** ****Add ******** channels soon**
** ****Possibility of exploring larger****  TC parameter space**

**D0 Run II Preliminary 388 pb****-1**

**Observed Excluded (NN)**
**Expected  Excluded (NN)**
**Observed Excluded (CB)**
**Expected  Excluded (CB)**
**Forbidden Region**

- 95% CL

- Limits computed using:
-  Bayesian statistics (CB)
-  2D maximum likelihood using  (M(Wjj),M(jj)) correlations (NN)

- E. Kajfasz

- ICHEP Moscow 29/07/06

## Leptoquarks

**Predicted by many extensions of the SM**
**Carry both lepton and quark quantum numbers****=> connection of lepton and quark sectors**
**Description with effective couplings**
**invariant under SU(3)****C****xSU(2)****L****xU(1)****Y**
**conserve lepton and baryon number separately (proton lifetime)**
**couple to lepton and quark in the same family (FCNC)**** **
**scalar and vector leptoquarks are possible****but only limits for scalar leptoquarks will be shown ****(lower cross-sections and less model dependant)**

- E. Kajfasz

- ICHEP Moscow 29/07/06

##       Leptoquarks

**Pair production modes**:
- - quark anti-quark annihilation
- - gluon fusion

**Decay**: parameterized by 
- the LQ branching fraction
- to charged lepton + quark

**Topology**:
- 2 (light/b)-jets + missing energy

**‘****QCD’ or instrumental:**
-  - multijet production  determined from data

**Standard Model (SM) :** (ALPGEN interfaced with PYTHIA)
-    - Vector boson production associated with jets
- - Z + 2 jets   + 2 jets (irreducible)
- - W + 2 jets l  + 2 jets (l = e, ,)    (lepton not reconstructed)
- - W + 1 jet   l  + 1 jet (l = e, )
-    (lepton identified as a jet)
-    - diboson production : WW, WZ, ZZ
-    - top production (single and pair)

**SIGNAL**

**BACKGROUNDS**

- reported on in this talk

- E. Kajfasz

- ICHEP Moscow 29/07/06

## Leptoquarks in acoplanar jet topology

- Start with ~ 14 million events collected with the Jets+MET trigger
- Initial cuts:
- - MHT =                    > 40 GeV		- (2 leading jets) < 165o
- - MET > 40 GeV			- |zPV| < 60 cm
- - at least 2 jets			- data quality cuts

- mLQ = 140 GeV

**Selection**

- E. Kajfasz

- ICHEP Moscow 29/07/06

## Angles between jets and MET

- (**Δφ****max**** – ****Δφ****min**) cut at 120° removes almost all of QCD
-    with minor induced signal inefficiency

- (**Δφ****min**** + ****Δφ****max**) cut at 280° removes a good fraction
- of the SM bkg with moderate
- added signal inefficiency

- mLQ = 140 GeV

- E. Kajfasz

- ICHEP Moscow 29/07/06

## QCD background estimation

- mLQ = 140 GeV

- E. Kajfasz

- ICHEP Moscow 29/07/06

## leptoquarks in acoplanar jet topology

**no excess**
**seen ...**

- After all cuts

- E. Kajfasz

- ICHEP Moscow 29/07/06

## leptoquarks in acoplanar jet topology

****** ****= 0**

- what about the 3rd generation?

- Most stringent limit for 1st and 2nd generation scalar leptoquarks decaying exclusively in a quark and a neutrino (=0)

- mLQ > 136 GeV @ 95% CL

- E. Kajfasz

- ICHEP Moscow 29/07/06

## 3rd gen. LQ

- Decay:
- BR(LQ3->b) = 1
- as long as M(LQ3) < M(t)+M()
- Phase space suppression factor Fs
- for higher masses
- BR(LQ3->b) = 1 – 0.5*Fs

**Selection**

**Signal**

- charge 1/3

- Use b-tagging to increase sensitivity to signal

- E. Kajfasz

- ICHEP Moscow 29/07/06

## Before b-tagging

- SM background (W/Z + jets and top)  normalized to the integrated luminosity (310 pb-1) reproduces the data well => contribution of QCD multijet processes is small

- mLQ = 200 GeV

- E. Kajfasz

- ICHEP Moscow 29/07/06

## Two taggers used:
Jet LIfetime Probability (JLIP): based on impact parameter of tracks in jet
-tag: if muon within a cone R = 0.5 around the jet axis
2 b-tags are required:
at least 1 -tag and at least 1 JLIP-tag
2 JLIP-tags and Xij > 0.8  (                                                    )

**Two taggers used**:
- Jet LIfetime Probability (JLIP): based on impact parameter of tracks in jet
- -tag: if muon within a cone R = 0.5 around the jet axis
**2 b-tags are required**:
- at least 1 -tag and at least 1 JLIP-tag
- 2 JLIP-tags and Xij > 0.8  (                                                    )

**Using b-tagging**

**no excess**
**seen ...**

- E. Kajfasz

- ICHEP Moscow 29/07/06

## 3rd generation leptoquarks

**if LQ decays in t******
**m****LQ**** > 213 GeV @ 95% CL**
**if not:**
**m****LQ**** > 219 GeV @ 95% CL**
**[B(LQ -> b********) = 1]**

- E. Kajfasz

- ICHEP Moscow 29/07/06

## Conclusions and Outlook

**So far, no convincing hint of physics BSM at D0**
**But, substantially improved limits ...****... and we are still hopeful for discoveries!**
**Results presented were obtained with < 0.4 fb****-1**
**~1.2 fb****-1**** already available and being analyzed**
**More integrated luminosity is on its way ... ****design goal of 8 fb****-1**** likely to be achieved**

**... Stay tuned ...**

**СПАСИБO!**

**D0 is open to new physics ideas that can be tested **
**with our data, so do not hesitate to get in touch with us!**

- E. Kajfasz

- ICHEP Moscow 29/07/06