# Presentation: 868362

## 34th International Conference on High Energy Physics

**University of California, Riverside**
**for the CDF, DØ and H1 Collaborations**

**Single Top Quark Studies**

**34th International Conference on High Energy Physics**

## Single Top Quark Production at Tevatron

**Single Top Quark Production at Tevatron**

**Single Top: Electroweak Interaction**
**Study Wtb coupling**
**Direct measurement of the |Vtb| CKM matrix element**
**Test of CKM unitarity**
**Anomalous *****Wtb *****couplings**
**New physics, example:**
**s-channel is sensitive to  W’, H****+**
**t(s)-channel is sensitive to FCNC**
**4****th**** quark generation? **
**Study top properties:**
**Polarization, decay width, lifetime, CP violation ... **
**Background study helps other physics searches, e.g. SM Higgs**

**Tev : ******** ~1 pb**

****** ****~ 2pb**

****** **** ****~ 0.25 pb**

** ****s-channel**
**(“*****tb*****”)**

** ****t-channel**
**(“*****tqb*****”)**

** ****tW production**
**(not yet seen)**

## CKM Matrix Element |Vtb|

**Direct measurement of |V****tb****| from cross section measurement:**
**Calculate posterior in |V****tb****|****2**** : ********|V****tb****|****2**
**Assuming standard model production:**
**Pure V-A and CP conserving Wtb interaction**
**|V****td****|****2**** + |V****ts****|****2**** << |V****tb****|****2**
**Additional theoretical errors needed (top mass, scale, PDF etc...)**
**No need to assume three quark generations or CKM unitarity**

**|V****tb****| = 0.88 ± 0.14 (exp.) ± 0.07 (theory)**

**|V****tb****| = 1.00 ****+ 0.00 ****(exp.+ theory)**

**- 0.12**

## Anomalous Wtb Couplings

**Top couplings to the W boson is a good place to look for deviations from SM**
**Effective single top production cross section: ******** = A (f****1****L****)****2 ****+ B (f****1****R****)****2 ****+ C (f****1****L ****+ f****2****R****)****2 ****+ D (f****2****L ****+ f****1****R****)****2 **
**f1: “Vector”-like, f2: “Tensor”-like**
**SM (left-handed vector coupling, ****LV**** ): f****1****L****=1, rest=0**
**Contributions also from left-handed left-handed tensor (****LT****), right-handed vector (****RV****), right-handed tensor (****RT****) couplings**
**Single top production directly sensitive to the Wtb interaction: rate, kinematics and angular distributions **

**Standard Model:   ******** ~ 2.9 pb **
**f****2****L(R)****=1, rest=0 :     ******** ~ 10.4 pb**

**Notes:**
put Larangian here, explain LT/RV/RT

## Anomalous Wtb Couplings

**Anomalous Wtb Couplings**

**Use same multivariate analysis technique and event selection as for DØ “single top evidence” analysis ****(Phys. Rev. Lett. 98,181802(2007))**
**Simultaneous limit setting for two signals by calculating 2 dimensional posterior probability density**

**arXiv:0807.1692 [hep-ex]**

**|V****tb****f****1****L****| = 1.31 ****+ 0.25**

**- 0.21**

**First direct constraints on *****Wtb***** tensor couplings**
**Data favor the standard model left-handed vector hypothesis over the alternative hypotheses**
**Compare with SM value**

**Notes:**
put standard model value

## Heavy W’ Resonance

**Heavy W’ Resonance**

**Single top quark decay channel is a promising searching background for heavy W’ with SM-like couplings**
**W’ decays leptonically into a single top quark**** **
**Same final states as single top production**
**Concentrate on s-channel production**
**Enhancement from W’ resonance**** **
**Consider purely left- and right-handed states**
**Left-handed couplings W’**
**W-W’ interference**
**DØ includes this term in signal model**
**Right-handed W’****R**** with M(W’****R****) > M(********R****)**
**Decays to (l, ********) and (q,q)**
**Right-handed W’****R**** with M(W’****R****) < M(********R****)**
**Decays to (q,q) only**

## Heavy W’ Resonance

**Four-vectors of all final state objects are added to obtain the invariant mass of the W’ boson**
**Use the mass distribution to separate W’ from background and set limit**

**Notes:**
get original CDF plot, D0 already published

## Charged Higgs Resonance

**Charged Higgs Resonance**

**Discovery of charged Higgs boson is an unambiguous evidence for new physics:  no “charged” Higgs boson in SM**
**Identical final state as s-channel single top quark electroweak production**
**Three Two-Higgs Doublet Model (2HDM) studied:**
**Type-I, II and III have different strategies to give mass to fermions**
**tb decay channel dominates for large region of parameter space**
**First direct search for heavy (****m****H+**** > m****top**** )**** ****H****+**** decaying to top**
**Reconstructed invariant mass M(jet1, jet2, W) showed to be the single most sensitive variable, used to construct binned likelihood function**
**Upper limits set close to predicted cross sections**
**Excluded parameter region for 2HDM Type-I: 180< m****H+****<184 GeV with 23 < tan********< 70**

**95%CL upper limit on 2HDM type-I,III H****+**

## Flavor-Changing Neutral Currents

**Any evidence for FCNC will be a signal of new physics beyond the SM **
**FCNC cross sections scale with (********gtu****/********)****2**** and (********gtc****/********)****2**** **
**Use same event selection as in CDF standard model single top production measurement ****(CDF note 9251) ****except:**
**Require exactly one hadronic jet (instead of two jets)**

**Assume no anomalous coupling**

## Anomalous Single Top Production at HERA

**Looking for new physics at HERA: anomalous single top production via FCNC**
**Highest sensitivity to ********tu******
**Coupling to V****tuz**** suppressed due to high Mz**
******tc******** suppressed due to low c-density**
**Events with e + P****T****miss**** in HERA I+II e****+****p data**
**Form top/W discriminator (MVA method)**

**@ 95% CL**

**478 pb****-1**

## Summary

**Single top quark production provides a rich testing ground for SM ******** new physics**
**Five studies from three collaborations so far**
**|v****tb****|, Anomalous Wtb coupling, W’/H****+ ******** tb resonances, FCNC production**
**Many improved limits**
**More studies and data to come, stay tuned!**