# Presentation: 923380

## Measurement of b-Baryons with the CDF II Detector

- Joachim Heuser (University of Karlsruhe)
-  for the CDF Collaboration

- HEP 2007, Manchester

## Short Reminder: b-Baryons

- b-baryon is system of one heavy b-quark and two light quarks
- Naming scheme as for light baryons, b replaces s-quark
- Status as of 2006: only b0 directly observed
- This talk: b, b

- b lifetime result from CDF covered by M.Milnik on Friday
- B meson results from CDF covered by A.Gessler on Thursday

- HEP 2007, Manchester

- 2007/07/21

## b-baryon interesting laboratory for understanding non-perturbative QCD and potential models
heavy b-quark  sizeable simplification in theoretical description
basic model: light diquark system qq surrounding the heavy b-quark „nucleus“ Q
coupling similar as in hydrogen/helium atom
never bad to observe new states 

- b-baryon interesting laboratory for understanding non-perturbative QCD and potential models
- heavy b-quark  sizeable simplification in theoretical description
- basic model: light diquark system qq surrounding the heavy b-quark „nucleus“ Q
- coupling similar as in hydrogen/helium atom
- never bad to observe new states 

- Why Look for b-Baryons ?

- HEP 2007, Manchester

- 2007/07/21

## Expectations on b(*)

- light diquark system has isospin I=1, spin j=1
- isospin-triplet: +b , 0b , -b 	(0b singlet)
- diquark spin j=1 can couple with b spin to J=1/2 (b) or J=3/2 (b*)
- Theory Predictions:

| Prediction on | Value |
| --- | --- |
| m(b)-m(b)-m() | 40-70 MeV |
| m(b*)-m(b) | 10-40 MeV |
| m(-b)-m(+b) | 5-7 MeV |
| b), (b*) | ~8 MeV, ~15 MeV |

- Expectations on b(*)

- HEP 2007, Manchester

- 2007/07/21

## b Search

- b Search

- Channel: +/-b → b +/-     with b → +c -   and   +c → p K- +
- Search for resonances in Q=m(b ) – m(b) – m()

- # 0b:~2800

- HEP 2007, Manchester

- 2007/07/21

## b Event Selection

- b Event Selection

-  exclude 0.03 < Q < 0.10 GeV region from signal selection procedure (blinding)
-  optimize selection based on
-  MC simulation for  signal sample
-  sidebands from data, containing only background events
-  fix background contributions

-  unblind

- HEP 2007, Manchester

- 2007/07/21

## b Results

- b Results

- Observation of four signal peaks, associated with +/-b(*)
- Significance of the signals:
- >5.2(4 peaks vs. only BG)
- each peak >3 (except +b)
- Submitted to PRL
- arXiv:0706.3868

- HEP 2007, Manchester

- 2007/07/21

## b Masses

- b Masses

| Prediction on | Value |
| --- | --- |
| m(b)-m(b)-m() | 40-70 MeV |
| m(b*)-m(b) | 10-40 MeV |
| m(-b)-m(+b) | 5-7 MeV |

- Good agreement with predictions !

- HEP 2007, Manchester

- 2007/07/21

## What Do We Know About the b ?

- What Do We Know About the b ?

-  quark content (usb / dsb)
-  mass from extrapolation of charm baryons:
- 	m(b) - m(b) ~ m(c) - m(c)
- 		m(b) ~ m(b) + 180 MeV ~ 5.8 GeV
-  decay properties dominated by b-quark (with light 	quarks as “spectators”)
-   expect similarities to other weakly decaying b-hadrons

- HEP 2007, Manchester

- 2007/07/21

## Search in channel: 

-b → J/ -,

with - →0 -, 0 → p - 

- -b → J/ -,
- with - →0 -, 0 → p -

- Decay of the -b

- - is charged, long-lived, particle
-  can be measured in silicon detector
-  significantly improves resolution
-  improves background suppression

- HEP 2007, Manchester

- 2007/07/21

## Lifetime and energy released in decay similar between

		-b → J/ -	  and	B+ → J/ K+

 unbiased selection optimization on B+ → J/ K+ sample

- 		-b → J/ -	  and	B+ → J/ K+
-  unbiased selection optimization on B+ → J/ K+ sample

- Selection Strategy

- Keep 50% signal, reject factor 500 of background

- HEP 2007, Manchester

- 2007/07/21

## Apply obtained selection on sample ....

- Observation of the -b

- m = 5792.9 ± 2.5 ± 1.7 MeV
- 7.7  significance

- Submitted to PRL
- arXiv:0707.0589

- HEP 2007, Manchester

- 2007/07/21

## Comparison

- In agreement with simultaneous observation by D0 and theory predictions

- HEP 2007, Manchester

- 2007/07/21

## Summary & Outlook

-  CDF observed the -b baryon
-  m(-b) = 5792.9 ± 2.5 ± 1.7 MeV
-  arXiv:0707.0589
-  CDF observed the charged b(*) baryons
-  arXiv:0706.3868
-  results in good agreement with theory predictions
-  CDF working great, let’s see what we can still do in the future (e.g. b lifetime) !

- HEP 2007, Manchester

- 2007/07/21

## Backup

- HEP 2007, Manchester

- 2007/07/21

## 
Excellent tracking due to silicon layers near interaction point and large tracking volume

Very important: dedicated triggers for data selection

- Excellent tracking due to silicon layers near interaction point and large tracking volume
- Very important: dedicated triggers for data selection

- CDF II Detector

- HEP 2007, Manchester

- 2007/07/21

## b Significance Determination

- b Significance Determination

- Form likelihood ratios between different hypotheses (e.g. compare “see 4 peaks” to “see only two”)
- Ratios relative to “4-peak-hypothesis”

| Hypothesis | (-ln(L)) | 1/LR |
| --- | --- | --- |
| Null | 44.7 | 2.6x1019 |
| Two b states | 14.3 | 1.6x106 |
| No b- signal | 10.4 | 3.3x104 |
| No b+ signal | 1.1 | 3 |
| No b*- signal | 10.1 | 2.4x104 |
| No b*+ signal | 9.8 | 1.8x104 |

- HEP 2007, Manchester

- 2007/07/21

## b: Cuts

- b: Cuts

- Selection cuts for b

- Selection cuts for b

- HEP 2007, Manchester

- 2007/07/21

## b : Backgrounds

- b : Backgrounds

- 3 main sources of background:
- Hadronization and underlying events:
- Tracks from hadronization of the b-quark, modelled by b PYTHIA MC
- Physics background:
- Misidentified B, studied by B PYTHIA MC sample
- Combinatorial background:
- Studied from upper data sideband

- HEP 2007, Manchester

- 2007/07/21

## b Significance Determination 

- b Significance Determination

- Assume uniform distribution of background in mass
- Search window of 800 MeV
- “Width” of observed signal 75 MeV
- Binomial Probability of
- observing >= 18 events within 75 MeV bin
- from total of 23 events within 800 MeV

- HEP 2007, Manchester

- 2007/07/21