# Presentation: 132807

## B0(s)  h+h’- decays at CDF

- HEP2005 International Europhysics Conference on High Energy Physics
- July 21st  –  27th, 2005 – Lisboa, Portugal
_*Diego Tonelli*_
***tonel@fnal.gov***
-  Istituto Nazionale di Fisica Nucleare, Pisa
- for the CDF Collaboration

## Motivation

- Joint study of *B*0 and *B*0s 2-body decays into charged kaons and pions (*KK*,  and* **K*): a privileged insight into flavor physics and a useful tool in searching for New Physics.
- CDF has simultaneous access to both *B*0 /*B*0s  *h**+**h**'**-* decays:  _flavor__* *__physics program complementary to __*Y(4S).*_
- R. Fleischer PLB459:306-320, 1999 - constrain hadronic unknowns with SU(3) symmetry. Use approximated *s*  *d**  *quark symmetry (i.e. measure jointly *B*0 and *B*0s) to extract phase  .

- WEAK
- amplitude  theoretically clean

- HADRONIC/ EW
- theoretically uncertain

## Motivation (cont’d)

- Fleischer’s method needs: time-dependent asymmetries in *b-*flavor tagged samples, size of SU(3) breaking, sin(2) and ms                _CDF ultimate long term goal_.

- Currently accessible BR can constrain theory too:  compare CDF measurements with  allowed regions in spaces of *B*0 +- and *B*0s *K*+*K*-  observables   (*Y(4S)* and theory): a _probe for __both ____ and NP_
- Fleischer and Matias PRD66: 054009,2002  - London and Matias PRD70:031502, 2004.

- ...many other interesting measurement, e.g. s/s in *B*0s *K*+*K*-  see talk by M. Donega’ - Friday 17.08 Room 5.

## Experimental challenge #1:    write signal events to tape

-  S/N at production ~10-9;
-  high track multiplicity per event;
-  generic final states (2 tracks, *K*
-     and/or ) in  huge QCD BCKG.
- Crucial role of trigger:
- Reconstruct silicon tracks online. Trigger on displaced secondary vertices with ~30 m impact parameter (IP) resolution.

-  large (*B*)  large *B* decay length and IP of tracks;
* **pp * *bb + *X  *B* from primary vertex, small IP of *B*.

## Analysis overview

- SIGNAL RECONSTRUCTION unbiased optimization of the selection requirements (use MC and data)

- FIT OF COMPOSITION Unbinned ML fit: kinematics and dE/dx to distinguish each *B*0(s)  h+h'-    mode

- BR RATIOS and ASYMMETRIES                Correct raw fit results for   trigger / selection efficiencies (use MC and data)

- dE/dx CALIBRATIONS Accurate calibrations of dE/dx with *D**+ decays

-   CONTROL SAMPLES   *B*0s and *B*0 exclusive decays in J/X and* D*

- SIGNAL SIMULATIONRealistic MC sample

## Experimental challenge #2: signal extraction

- Unbiased optimization of selection cuts: maximize S/(S + B) with signal from MC and background from data sidebands.

- _isolation_: fraction of *p*T carried by the *B* candidate after fragmentation. Rejects 15% of signal and 400% of background.

## Experimental challenge #3:    peak composition 

- Excellent CDF mass resolution:
- 5 silicon layers + drift chamber measure *p*T  in 1.4 T solenoidal  field with 132 cm lever arm
-       resolution ~ (0.7  0.1 pT)%
- Still, the four (expected) major modes overlap into an unresolved mass peak.
- Extract composition statistically with an unbinned 5-dimensional ML fit. Combine information from:
-  kinematics   (mass and *p);*
-  particle ID    (dE/dx).

*B*0s modes

*B*0 modes

- simulated signals

## Peak composition handle 1: kinematics 

- -mass *vs* signed momentum imbalance: (1- *p*min/*p*max)qmin discriminates among modes (and flavors in *K* modes).

## Peak composition  handle 2:          specific ionization in the drift chamber 

- Tracks have  hits in drift chamber:
-  96 layers,  |η| ≤ 1.0;
-  44 cm < r < 132 cm, 30k channels;
-  σ(hit) ~ 180 μm;
-  dE/dx encoded in  hit pulse-width.

**TIME OF FLIGHT**

- Accurate, time dependent dE/dx calibration using ~95% pure *K */  samples from ~70k decays:
*D**+  *D*0 +  [*K*-+] +  + c.c.
- Strong *D**+  decay tags the *D*0  flavor.

## Peak composition handle 2: dE/dx (cont’d) 

- Angle, gas pressure, time and hit-multiplicity dependences corrected.

- 1.4 *K*/ separation at *p *> 2  GeV/c
- ( 60% of “perfect” separation)
- Residual gain fluctuations cause correlated dE/dx shifts: measured and included in the fit of composition.

## Raw fit results 

- ~900 evts/180 pb-1 in initial CDF data, taken with still non optimized detector/trigger.      _Now much better_: ~2700 / 360 pb-1

- What we measure:

## Efficiency/acceptance corrections

- Correct for relative acceptance, trigger and selection effic.: 5 -10%

- Kinematics and nuclear interaction efficiencies                     (Monte Carlo)

- Trigger-bias: correct for dE/dx-dependent trigger efficiency         (*D*+ data)

- Isolation efficiency, measured from exclusive decays      (*B*0 and *B*0s data)

## Dominant systematic uncertainties 

-  dE/dx track-to-track correlations (_partially reduces with statistics_);
-  *B*-meson masses input to the fit (_reduces with statistics_);
-  Relative isolation efficiency between *B*0s and *B*0 (_reduces with statistics_);

-  Effect of final state radiation;
-  Trigger bias on efficiency;
-  Charge-dependence of dE/dx;

-  Background shape;
-  Charge asymmetries in background;
-  Others.

- (stat. ~ 7.8%) syst. ~ 1.2%

- (stat. ~ 17%) syst. ~ 15%

- (stat. ~ 24%) syst. ~ 14%

- (stat. ~ 29%) syst. ~ 13%

## Final results: B0s sector 

_*B*__0_s_ ____ __*K*__+__*K*__-__ decay established_.  BR ratio may favor large SU(3) breaking as predicted from sum rules (Khodjamirian et al. PRD68:114007, 2003).

- Allows first comparisons with *Y(4S)* and theory expectations, test of NP.

- No evidence for *B*0s  *K*-+, set a  limit a_ factor ~40 better than PDG04._

- Great improvement on annihilation mode *B*0s   -+. _A factor >100 below PDG04 _ (time-evolutions of *B*0s  -+ and *B*0s  *K**-**K*+ assumed the same).

## Final results: B0 sector 

- ACP compatible with *B*-factories, _systematic uncertainty comparable_ as well, Babar statistic uncertainty just ~30% better with same sample size.                                 With currently available data (3x statistics), we expect < 4.5% statistical uncertainty to be compared with current world best:  2.2% (Belle).

- Limit on pure annihilation/exchange mode *B*0  *K*+*K*-. A factor ~2 above *B*-factories, expect much better performance on current sample.

- Consistent with *B*-factories. Valuable cross-check for other measurements.

## Concluding remarks

- CDF has unique joint access to  *B*0  / *B*0s  h+h'-  modes: rich physics program complementary to *B*-factories. Results shown ready for PRL submission in  first *B*0(s)  h+h'-  paper from an hadronic collider:
-  *B*0s* K*+*K*-  decay established and BR measured (first *B*0s  *PP* observed);
-  x100 improvement with respect to PDG04 on the upper limit on
-      BR(*B*0s  +-) and x40 improvement on the limit on BR(*B*0s  *K**-***+);
-  measurement of ACP (*B*0  *K*+-) with small systematics.
- Just the beginning: now 900 pb-1 on tape, of which 360 ready for analysis with ~2x increase in yield/pb-1 (optimized efficiencies), improved mass resolution (better tracking alignment and reconstruction). By end of 2005 we expect:
-  Observe *B*0s * K*-+ and reduce to ~10% statistical error on BR(*B*0s  *K*+*K*- );
-  ACP (*B*0  *K*+-) much closer to *Y(4S)* with  ~4%  statistical uncertainty;
-  World  best limits on BR(*B*0s  +-)  and  on BR(*B*0  *K*+*K*-).

## ADDITIONAL MATERIAL                     

- ADDITIONAL MATERIAL

## The Tevatron pp collider

- The Tevatron *pp* collider

- Superconducting proton-synchrotron: 36 *p*  36 *p* bunches
-                                                              collision every 396 ns at √s = 1.96 TeV
- Luminosity..................................: record peak is  1.3  1032 cm-2 s-1
-                                                               ~ 10 pb-1 / week recorded on tape
- # interactions / bunch-crossing........: < N >poisson  = 6  (at 2** ** 1032 cm-2s-1)
- Luminous region size....................: 30 cm (beam axis)   30 m (transverse)
-                                                                           **need long Si-vertex****     ****small wrt c********(B) ~ 450 ********m **

**2005, regularly exceeds 10****32 ****cm****-2****s****-1**

## Delivered Luminosity 

- Delivered Luminosity

- Stable data taking efficiency:  ~85%
- The results shown here from an analysis that uses ~180 pb-1

**April 2001**

**Feb 2002**

**first data for analyses**

** ****data for physics**

**detector commiss.**

**Jul 2002**

- ~ 900 pb-1 on tape

** ****1 fb****-1**** milestone!**

## Heavy Flavor physics at the Tevatron

*bb* production x-section  O(105) larger than e+e-  at (4S) /Z0. Incoherent strong production of all *b*-hadrons:  B, B0, Bs, Bc, b, b .
- The Bad
- Total inelastic x-section ~ 103    (*bb*).                    BRs’ for interesting processes O(10-6).
-                      ...and The Ugly
- Messy environments with large combinatorics.

- Need highly selective trigger

## CDF Detector Upgrades

## Triggering bs’ (and cs’)

- Triggering* b*s’ (and *c*s’)

- _Di-lepton_
- B  charmonium  Rare  B  
- Two  muons with:
- pT> 1.5 GeV        ||< 1
- pT> 2.5-4.5 GeV  ||<2

- _electron or  ____  and displaced track_
- Semileptonic decays
- Electron  ()  with:
- pT> 4 (1.5) GeV     ||< 1
- and one track  with:
- pT > 2.0 GeV     IP > 120 m

- _Two displaced tracks_
- n-body hadronic B
- Two tracks with:
-  pT > 2.0 GeV
-  pT > 5.5 GeV
- IP > 120 (100) m

- Displaced track trigger at Level 2:  a revolution in hadronic environment ! Makes it accessible rare hadronic decays with high S/B.

***conventional***

***new approach***

## Systematics - detailed

## Raw physics results

## Raw physics results

## Corrected results

## Correlation matrix

**Legenda**

## p.d.f. projection: momentum imbalance

## p.d.f. projection: |p(1)| + |p(2)|

## p.d.f. projection: dE/dx

## p.d.f. projection: dE/dx

## Momentum p.d.f.

- p

- 

- 

- p

- Monte Carlo

- Binned ML fit

- signal

- background

## dE/dx model 

## Silicon Vertex Trigger 

## Silicon Vertex Trigger (cont’d)

- (35      33) m SVT   beam
-   = 48m

## B0s K+K- lifetime

- B0 lifetime from PDG04. B0s K+K- lifetime depends on:
- - s/s : width difference between “long” and “short”
-               eigenstates
- -the relative composition in short and long-lived components
- Assume Standard  Model s = d and s / s = -0.12  0.06    B0sK+K- is expected almost 100% “short-eigenstate”                                              Fleischer and Matias:PRD66-054009,2002)
- Therefore the lifetime of B0s K+K-  is determined as:

## Physics Motivations (backup)

- The combination of Bd and Bs decays provides a promising way to extract CP-related physical parameters avoiding the “penguin pollution”. *(R. Fleischer PLB45**9** (1999) 306)*
- Assume U-spin symmetry (d  s), the  ACP  are function of the CKM angles  and  and of the amplitude ratio P/T (~ dei)   4 equation with 4 unknowns (, , d, ).                                        A combined fit of the 4 CP asymmetries measures ,   and P/T ratio.
- Above strategy need time-dependent analysis with tagged samples: long term goal