# Presentation: 183518

## ATLAS  B-Physics Reach

**ATLAS  B-Physics Reach**

**M.Smizanska, Lancaster University, UK**
**     ****maria.smizanska@cern.ch**

## ATLAS: b-events from central pp LHC collisions

**230********b**

**100********b**

- 25/6/02

## B-physics strategy with tight funding constraints

**Recent work has addressed the issue of maximizing B-physics capabilities in context of reduced initial Trigger/DAQ system (funding limitations)**
- Extend Region-of-Interest mechanism of level-2 trigger to reconstruction of B decays:
- Level-1 muon was always used to provide region of interest
- Now, level-1 jet to guide reconstruction of hadronic modes, e.g. Bs **** Ds , and electrons, e.g. J  **** e+e-
- Use result of level-2 trigger to seed reconstruction in the Event Filter
- Only reconstruct limited region of Inner Detector containing B candidate
- Strong reduction in processing requirements compared to previous strategy that involved full scan of Inner Detector at level-2
**Nevertheless, with presently assured funding, the initial Trigger/DAQ system will be almost saturated by the priority “discovery physics” programme when the luminosity is at the target of L = 2 ******** 10****33**** cm****-2****s****-1**
- At this luminosity, B-physics would be based on dimuon trigger only which has very low rate but nevertheless covers many interesting channels
- At lower luminosities, e.g. towards end of LHC coast, spare Trigger/DAQ capacity can be used to extend the B physics potential

- 25/6/02

##  B – physics trigger strategies, cont.                          

**Level-1:  single-muon or  di-muon**
**Efficient down to p****T**** 5GeV ( lower still in endcap). Different scenarios according to luminosity conditions & rates  **

**1. Di-muon trigger:**
**L1 2******** +   L2 precision ******** tracking in muon spectrometer and Inner detector.**
**B****d******** J/********K****s****0 ****, B****s******** J/********,********etc**
** ********b ******** J/******** ********, rare decays B ******** ********  ****B****d**** ******** K****0***** ********B****d**** ******** ******** ********etc**
**2. Muon-electron(********) trigger:  **
**L1 ******** + L1 e/********cluster (E****T****>2GeV)+ L2 tracking in region**
**B****d******** J/******** (ee) + K****s****0****  + B******** ******
******b******** J/******** (ee) ********+  B ******** ******
**B****d**** ******** K****0***** ********+  B ********etc**
**3. Muon-hadron trigger:**
**L1 ******** + L1 Jet (E****T****>5GeV) + L2 tracking in region**
**B******** ******** + B********B****s******** D****s********B********etc**

- 25/6/02

##                  Low pT electron identification

_**ATLAS performance parameters principal for B-physics**_
**                 ****Low p****T**** electron identification**

**Combined EM calorimeter-TRT **
**electron identification **

**Rejection of bb ******** ********6X events without electron vs efficiency of  events  bb ************6e5X.  Eff=70%,R=570, level-2 rate of signal is 40Hz, fake rate 10Hz due to hadrons misidentified as electrons.**

**TRT electron identification**

**Invariant mass for all track pairs in bb ********J/******** (ee)K****0**** events before and after TRT selection cuts. Electrons have p****T****>1GeV.**

- 25/6/02

##    Low and medium-pT muon performance

_**  **__**ATLAS performance parameters principal for B-physics, cont.**_
**   ****Low and medium-p****T**** muon performance**

**Lowest p****T**** muon  identification & reconstruction efficiency**

**Inner detector + **
**Muon spectrometer**

**Inner detector + **
**Muon spectrometer**
**+ Hadron calorimeter**

**J/********) reconstruction in the environment of b-jet with p****T****~(50-80) GeV (for QCD b-production studies)**

**the same**
** ****in log scale**

**Even in high p****T**** jet, a mass reconstruction is negligibly affected by fake pairs when a muon identified in Muon spectrometer match to the wrong track in the Inner Detector.**

- muons

- pions

- 25/6/02

## Precise measurements of Bd  J/Ks0 decay

**Method: maximum likelihood fit, using experimental   inputs:  proper time resolution, tag  probability, wrong tag fraction, background composition.**
**Direct CP violation term neglected here.                      **

- 25/6/02

##         sensitivity in

** ****The current theoretical uncertainty |P/T|~30% dominates  other systematical  and statistical errors of full LHC potential.**

- -sensitivity as
-  a function of  and
-  **theoretical uncertainty**
** ****of ****|P/T| using full **
**LHC potential**

- 25/6/02

## Physics of Bs meson

** ********m****s**** from B****s**** ******** D****s********and B****s******** D****s**** a****1**** ****already after 1 year  sensitivity up ********m****s**** - 36 ps****-1**** fully explore  SM allowed range ********m****s**** (14.3 - 26) ps****-1**

**Program for  precise measurements of B****s****-anti-B****s**** system parameters : ********s,  ********m****s**** and probing B****s**** mixing phase ********s***************** *****allowing to investigate new physics.**

******s**** and ********s****= -**************** from B****s**** ******** J/******** **
**or B****s**** ********J/******** both sensitive, but precision **
**sufficient only in B****s**** ******** J/******
**Angular analyses of cascade decay B****s ******** ****J/********determine ********s****, ********s**** and ********s ****simultaneously with parameters of helicity amplitudes A||(t=0), A****T****(t=0), A****0****(t=0), ********1****, ********2****. Parameter  ********m****s**** will be measured by decays to flavor specific final states ****B****s**** ******** D****s********and B****s******** D****s**** a****1 .**

- 25/6/02

## CP - violation weak phase in Bs  J/ 

** **
**Standard Model region-updated 2003**
**New physics Left-right symmetric model (NP-LR) - version used here last updated in 2000.**
**ATLAS (3years): 1st level trigger 1******** only. Extension by 2******** trigger under investiga- tion, not included. TDR Detector.**
**ATLAS  - same – as above with Final Detector Layout– Preliminary**
**LHCb(5years): full 1st Level trigger, performance parameters  as given in 2000**
**Experimental potential of both experiments not yet fully exploited: more studies on additional  triggers, tagging.**

- 25/6/02

## Potential for Rare decays

**     ****Before LHC **
**     ****B********K*********will be measured however mass and angular distributions detailed enough to show New Physics only at LHC.**
**     ****B************ can be seen before LHC only if drastically enhanced.**
**     **

**A study proved good performance at nominal LHC luminosity. After 1 year 10****34****cm****-2**** s****-1**

**3 years at  luminosity 10****33****cm****-2**** s****-1**

**B**********

**Will measure branching ration of B****s**** ******** ******** which is in SM of order Br<(10****-9****)**
** ****Perform high sensitivity search on B****d**** ******** ******

- 25/6/02

##    Exclusive Rare decays of B mesons

-    Exclusive Rare decays of B mesons

- ATLAS statistics will allow angular analyses that can carry evidence for new physics.  E.g. forward-backward asymmetry:

**SM**

**MSSM C7******** >0**

**MSSM C7******** <0**

- Lowest mass region: sufficient accuracy  to separate SM and MSSM if Wilson coefficient C7 <0

**Three points: mean values of A****FB**** in three q****2****/M****B****2**** experimental regions with error bars**

- 25/6/02

## other studies of ATLAS b-physics group 

**Studies not mentioned here:**
**Double heavy flavor mesons. **
**QCD tests of beauty production at LHC central region. Correlations bb.**
**Physics of Beauty baryons, production polarizations, decays.**

- other studies of ATLAS b-physics group

- 25/6/02

## B-physics prospects with ATLAS - conclusions

**ATLAS is preparing a multi thematic B-physics program - including B-decays and B-production.**
**ATLAS B-physics trigger strategy revised to maximize physics potential within tight funding constraints - rely on dimuon trigger for initial luminosity ****2 ******** 10****33**** cm****-2****s****-1**** ****- extend selection at lower luminosities when there is spare processing capacity.**
**In CP violation the main emphasis will be on underlying mechanisms and evidence of New physics. ATLAS is especially precise in measurement of ********In B****s**** ******** ****J/******** large CP violation would indicate new physics.**
** ****Bs mixing studies make clear that there is sensitivity to ********m****s**** beyond SM expectations. The width difference ********s**** can be measured best in B****s**** ******** ****J/********with relative precision******
** ****Rare decays B ******** ******** have favorable  experimental signature allowing to measure also at nominal LHC  luminosity 10****34****cm****-2**** s****-1***.*** Will measure branching ration of Bs ******** ********  which is in SM of order Br<(10****-9****) Precision measurements will be done for B ******** ****K*********.**
**Beauty production and bb correlations in central LHC collisions will be measured for QCD tests.**

- 25/6/02