# Presentation: 409770

## Probing the Physics Frontier with

**LBNL RPM **
**    ****15 February 2007**

**Probing the Physics Frontier with**
**Rare B Decays at CDF**

**Cheng-Ju S. Lin**
**(Fermilab)**

## Interesting time in particle physics with

- many exciting questions:
- 	-  Origin of EW symmetry breaking
- 	-  Nature of cosmological dark matter
- 	-  Nature of dark energy
-        -  + ...
- To get a consistent picture would require
- physics beyond the Standard Model
- Tevatron could potentially uncover those
- mysteries.  We can:
- 	-  Look for things directly (e.g. production
-            of new particles)
- 	-  Look for deviations from the Standard
-            Model predictions !!!

## Gold Mine for Heavy Flavor Physics

- Mixing:
- Bs, Bd, D0

- Lifetimes:
- b, Bs, Bc,
- B+, Bd ...

-  New particles:
- X(3872), Xb,
- Cascade(b) ...

- Mass measurements:
- Bc, b, Bs, ...

- Rare decays:
- Bs, BK* 
- D0 , ...

- Production properties:
- (*b*), (J/), (D0), ...

- CP Violation:
- Acp(Bhh),
- Acp(D0K), ...

- B and D
- Branching ratios

**SURPRISES!?**

- Focus of today’s talk

## Indirect Search of New Physics : Bs 

-   Solid prediction from the Standard Model (SM)
-   In the SM, the decay of Bs +- is heavily suppressed

-   Bd is further suppressed by another factor of ~20
-   SM prediction is well below the sensitivity of current generation of
-    experiments  no observation yet
-   New physics could significantly enhance the branching ratio
-           **Any signal would be a clear indication of NP**

- SM prediction 

- ~ a few decays per 1 billion Bs produced

- Bs =

## Some Scenarios of NP

-  - MSSM:  Br(B) is proportional
-    to tan6. BR could be as large as
-    ~100 times the SM prediction
- - Tree level diagram is allowed in
-    R-parity violating (RPV) SUSY
-    models.  Possible to observe decay
-    even for low value of tan.

**Some Scenarios of NP**

- Either discovery or null result could shed light on the
- the structure of new physics !!!

## TEVATRON Collider 

**TEVATRON Collider **

**Lots of B****s**** produced**
**in the collision debris !**

- Record luminosity:
-  ~270E30 cm-2s-1
- (design 300E30)

## Integrated Luminosity 

**Integrated Luminosity **

- Close to 2fb-1 of data
- collected by CDF

**Analyses presenting today use from **
**780pb****-1**** to ~1fb****-1**** of data**

## Heavy Flavor Physics in Hadron Environment

-  *b*’s produced via strong interaction
-  decay via weak interaction

**Tevatron is great for heavy flavor:**
-   Enormous *b* production cross-section,
-     x1000 times larger than e+e- B factories
-   All B species are produced (B0, B+, Bs,
- b, b, etc...)
**However,**
-   Inelastic (QCD) background is about
-    x1000 larger than b cross-section
-   Online triggering and reconstruction is
-     a challenge:  collision rate ~1MHz 
-     tape writing limit ~100Hz

**Heavy Flavor Physics in Hadron Environment**

## CDF II Detector 

**CDF II Detector **

- Significant detector, trigger, and DAQ upgrades in Run II

**Looking for B****s************ with CDF Detector**

- Look for Bs production
- and decay vertices

- Measure muon
- track momentum
- and charge

- CMU: ||<0.6

- CMX
- 0.6<||<1.0

**Notes:**
Silicon microstrip detector 5+1+2 layers double-sided
Driftchamber 8 SL Argone Ethane, dpt/pt2=210E-3
Muon drift chambers
Em shower detector lead sheets plus scintillator, tower 50x50 cm

## CDF Trigger: Lifeline of B Physics Program

-   CDF has implemented a 3-tier trigger
-   Level-1 is a synchronous hardware trigger
-    - Can process one event every 132ns
-    - Input rate = 1.7MHz (396ns 36x36 bunches)
-      L1A rate ~ 30KHz  (limited by L2)
-   Level-2 is a combination of hardware and
-    software trigger (asynchronous)
-    - Average Level-2 processing time is ~30s
-    - L2A rate ~1KHz  (limited by event-builder)
-   Level-3 is purely a software trigger
-    - Massive PC farm
-    - L3A rate ~ 100Hz  (limited by tape writing)
-   Data reduction rate (L1+L2+L3)  1 : 17000

**CDF Trigger: Lifeline of B Physics Program**

## Three Classes of B Physics Triggers at CDF

******+ ****(e****+****)**

******-**** (e****-****)**

- IP

- (1) Dimuon trigger:
-          For triggering on J/ and rare B decays
-          (e.g. Bs and BX)

- (3)  Lepton+Displaced Track(SVT):
-           For triggering on semileptonic B decays.

- (2)  Two-track trigger (SVT):
-           For triggering on hadronic B and
-           charm decays.  Both tracks are required to
-           have an impact parameter  d0> 120m.
-           (D0, Be, etc...)

**Three Classes of B Physics Triggers at CDF**

## Silicon Vertex Tracker (SVT)

**to be able to trigger on fully hadronic B events**

**Level-2 SVT Trigger**

-   SVT links drift chamber tracks from
-    Level-1 with silicon hits to compute the
-    impact parameter of the track.

**SVT impact parameter (********m)**

**-600  -300    0      300    600**

-  SVT d0 resolution is ~ **47********m**
-   (35m beamline  33m resol).
-  SVT revolutionized B and Charm
-    physics at CDF.

- Track impact
- parameter

**Silicon Vertex Tracker (SVT)**

## SVT Performance

**SVT Performance**

-   **Our physics program**
**    ****is dictated by what**
**    ****triggers we have**
-   In Run I, Bhh
-     physics was a fantasy
-   In Run II with SVT,
-     we are making world
-     class measurements
-   First observations of:
-  BsK+K-
-  BsK+-
-  bp-
-  bpK+

-   Did I mention Bs mixing too?

## RARE B TRIGGERS AT TEVATRON

**Main issue:  trigger rate blows **
**    ****up rapidly vs. luminosity **
**For illustration, the following**
**    ****rare B dimuon triggers alone:**
**        ****-  CMU-CMU pT>1.5GeV**
**        ****-  CMU-CMX pT>1.5GeV**
**    ****would take up the entire level-2**
**    ****trigger bandwidth at L=200E30 cm****-2**** s****-1**
**In the latest trigger table, there are more than ****150**** level-2 triggers that need to co-exist**

**RARE B TRIGGERS AT TEVATRON**

- CDF L2 Dimuon Trigger Cross Section

## KEEPING RARE B TRIGGERS ALIVE

-   Handles to control rates:
-       -  Tighter selection cuts           (e.g. pT of muon)
-       -  Apply prescales
-          (DPS, FPS, UPS, etc.)
-       -  Improving trigger algorithm
-       -  Upgrading trigger hardware
-   We’ve been using a combination of all four handles to    control the trigger rate  trading efficiency for purity
-   It’s been a great challenge keeping B and high pT triggers
-    alive at Tevatron
-   It’ll be an even greater challenge at the LHC !!

- Non-optimal for rare searches

## B   Data Sample

-    trigger data:
-         CMU-CMU trigger
-           CMU-CMX trigger
-  Use this inclusive sample
-    to search for:
-       Bs+-  (Mass Bs=5.37GeV)
-       Bd+-
-   Even if BR is x10 the
-    SM value, only expect
-    a hand full of signal events in
-    the signal region
-   Signal region is swamped with various
-    kinds of background: both from SM processes
-    and detector effect (fake muons)

**B ******** ******** Data Sample**

- Effective background
- rejection is the key
- to this analysis!!

- Search region

## Analysis Overview

- Motto:  reduce background and keep signal eff high

- Step 1:  pre-selection cuts to reject obvious background
- Step 2:  optimization (need to know signal efficiency
-              and expected background)
- Step 3:  reconstruct B+ J/ K+
-              normalization mode
-              (take into account Br of BJ/K
-                  and J/: >> 100million B+)
- Step 4: open the box  compute
-              branching ratio or set limit

## CDF Pre-selection

**Pre-Selection cuts:**
- 4.669 < m< 5.969 GeV/c2
- pT()>2.0 (2.2) GeV/c   CMU (CMX)
- pT(Bs cand.)>4.0 GeV/c
- Track, muon and vertex quality cuts
- 3D displacement L3D between primary and secondary vertex

**CDF Pre-selection**

**Bkg substantially reduced but still**
**sizeable at this stage**

##  Background Rejection:Bs Decay Characteristics

- Bs-mass:
- MBs=5.37 GeV

- Bs-flight distance

- 2 muons point to a
- “common vertex”

- Background rejection cuts:
- muons add up to Bs mass
- muons are isolated and have common vertex
- vertex is well separated from beam-spot

- No other tracks
- from this vertex

**p**

**p**

******+**

******-**

**Notes:**
Mass resolution thru momentum reolution

## B  Signal vs Background Discrimination

-                (Eenergy,  P  momentum)
- B vertex displacement:
- Isolation (Iso):
- (fraction of pT from B within R=(2+2)1/2 cone of 1)
- “pointing ()”:
- (angle between Bs momentum and decay axis)

**B******** ******************** Signal vs Background Discrimination**

- For each di-muon
- candidate, we compute
- the 4 variables:
-    M
-    
-    *Iso*
-    

## Distribution of the Discriminating Variables

**Distribution of the Discriminating Variables**

-  Blue = Bs signal
-    events from simulation
-    (Monte Carlo)
-  Black = expected bkg
-    distributions
-   Using  and Iso
-     to construct a new
-     variable, likelihood
-     ratio:

- Ps(b)i is the probability distribution function for signal (background)
-        for variable i, with i loops over , , iso

## Likelihood Ratio (LR) Distribution

- Di-muon events with
- large LR (near 1) are
- more likely to be signal
- Events with LR near 0
- are more likely to
- be background

- Signal distribution is based on simulation

## Background Estimate

-   Use control samples to cross-check bkg estimate

-   Assume linear background shape
-    extrapolate # of background events in sidebands to signal
-    region (± 60 MeV signal window)

- 	1.)  OS- :  opposite-charge dimuon, < 0
- 	2.)  SS+ :  same-charge dimuon, > 0
- 	3.)  SS-  :  same-charge dimuon,  < 0
-           4.)  FM  : fake muon sample  (at least one leg failed
-                                                              muon stub chi2 cut)

## Cross Check BKG Estimate in Control Samples

-             cut           pred     obsv     prob         pred       obsv     prob
-         >0.50      489±12    483     41%      351±10    338         27%        28%
- OS-   >0.90        62±4        73     12%         56±4       63         22%          7%
-          >0.99       4.8±1.2       9       8%        3.9±1.1      8           7%          2%
-          >0.50       5.4±1.3       4      40%        3.3±1.0      2          39%        27%
- SS+  >0.90        <0.10         0        -            0.9±0.5      0          43%        43%
-          >0.99        <0.10         0        -             <0.10        0           -              -
-          >0.50       6.6±1.4       7      49%        4.2±1.1      5          41%        40%
- SS-   >0.90       0.6±0.4       1      45%        0.3±0.3     0           70%        57%
-          >0.99        <0.10         0        -            <0.10        0            -               -
-                       >0.50      188±8       159      3%         33±3        37         29%        7%
- FM    >0.90         34±3       24       7%           6±1         5           46%       6%
-          >0.99       4.5±1.0        9        6%        0.6±0.4     0          55%      12%

-   Using  a wider ± 150 MeV signal window for cross-check

- (Probability factor in uncertainty on Poisson mean)

- Combined
-    prob

**Cross Check BKG Estimate in Control Samples**

## Bhh Background

-   CDF signal region is also contaminated
-    by Bh+h- (e.g. BK+K-, K+, )
-   K muon fake rates measured from data using D* sample
-   Convolute fake rates with expected Bh+h- distributions to
-     to obtain Bhh bkg
-   Total bkg = Bhh + combinatorial

| Decay | Bhh Background | Combinatoric Background | Total Background |
| --- | --- | --- | --- |
| Bs | 0.19±0.06 | 1.08±0.36 | 1.27±0.36 |
| Bd | 1.37±0.16 | 1.08±0.36 | 2.45±0.39 |

- LR > 0.99

##  MC modeling checked by comparing LH(B+)

** **determined from Bs MC
-  MC modeling checked by comparing LH(B+)
-   between MC and sideband subtracted Data

- (stat uncertainties only)

**Likelihood Ratio Efficiency for Bs Signal**

**  ****Optimize analysis based on a-priori expected upper  **
**    ****limit ******** L****R****>0.99 !!!**

## Now Look in the Bs and Bd Signal Windows

- Bs Branching Ratio Limit:
-   Br(Bs)<1.0×10-7 @ 95%CL
-   Br(Bs)<0.8×10-7 @ 90%CL

- Bd Branching Ratio Limit:
-   Br(Bd)<3.0×10-8 @ 95%CL

- Number of observed events
- in the signal box is consistent
- with bkg expectation
-      set branching ratio limit

- Bs:
-   Observed 1 candidate
-   Expect ~1.3 background events
- Bd:
-   Observed 2 candidates
-   Expect ~2.5 background events

- Best limits in the
- world, but still no
- hints of new physics

## Branching Ratio Limits

| CDF Bs-> | 176 pb-1 | 7.5×10-7 | Published |
| --- | --- | --- | --- |
| DØ Bs-> | 240 pb-1 | 5.1×10-7 | Published |
| DØ Bs-> | 300 pb-1 | 4.0×10-7 | Prelim. |
| DØ <Bs-> | 700 pb-1 | <2.3×10-7> | Prelim.
Sensitivity |
| CDF Bs-> | 364 pb-1 | 2.0×10-7 | Published |
| CDF Bs-> | 780 pb-1 | 1.0×10-7 | Prelim. |

**Branching Ratio Limits**

-  Evolution of limits (in 95%CL):

- World’s best
- limits

| Babar Bd-> | 111 fb-1 | 8.3×10-8 | Published |
| --- | --- | --- | --- |
| CDF Bd-> | 364 pb-1 | 4.9×10-8 | Published |
| CDF Bd-> | 780 pb-1 | 3.0×10-8 | Prelim. |

- 90% CL

## SO(10) Grand Unification Model

**JHEP 0304 (2003) 037**

**SO(10) Grand Unification Model**

-   tan()~50 constrained by unification of Yukawa couplings

- Pink regions are excluded by either theory or experiments
- Green region is the WMAP preferred region
- Blue dashed line is the Br(Bs) contour
- Light blue region excluded by old Bs analysis

**R. Dermisek *****et al*****.,  **
**hep-ph/0507233 (2005)**

**Red arrows indicate exclusion**
**from this result!!!**

-   Remaining white region is
-   still not excluded by experiment

## Implications on SUSY Flavor Violation

- J. Foster et al.
- Hep-ph/0604121

- xy parameters
- quantify variations
- from Minimal
- Flavor violating
- assumption

- Bs, Bs, and
- Bs mixing severely
- constrain non-MFV

**Implications on SUSY Flavor Violation**

## non-MFV SUSY phase space is severely constrained

- J. Foster et al.
- Hep-ph/0604121

- 2-D scan over xy space

**non-MFV SUSY phase space is severely constrained**

**Implications on SUSY Flavor Violation**

- tan=40

## Sneak Preview of Bs

-   1fb-1 update is near completion
-   Implemented NN selection to enhance signal
-     efficiency and bkg rejection:

- NN contains additional
- variables:
-   pT(Bs), pT(muon), etc.
- For a given bkg level,
- NN signal eff is 15-20%
- higher than LR!!

## Sneak Preview of Bs

**Sneak Preview of B****s**********

-   Apply improved muon selection and particle ID
-     to suppress fake muons and Bhh backgrounds
-   Instead of single-bin counting experiment, use
-     multi-bin parameterizations:
-   780pb-1  1fb-1, only
-     about 30% increase in stat
-     Expect the sensitivity to
-     increase by a factor
-     of 2!!!

**Neural Net Output**

- Bs Signal Eff

## CDF Projection

- Conservative projection
- based on our current (780pb-1) performance

- Improvement expected
- from 1fb-1 analysis

- Achievable in RunII

## Bu,d,s  K+/K*/

- B Rare Decays B  h :
- B+   K+
- B0  K*
- Bs   
- b  
- Penguin or box processes in the Standard Model:
- Rare processes:  predicted BR(Bs   )=16.1x10-7

- observed at Babar, Belle

- 

- 

- not seen

- 

- 

**B****u,d,s**** ******** ************************K****+****/K*/******

- PRD 73, 092001 (2006)
- PRL 96, 251801 (2006)

- C. Geng and C. Liu, J. Phys. G 29, 1103 (2003)

## Probe of New Physics

- Probe various Wilson coefficients (bs)
- -  Predicted in several new physics scenarios (e.g. SUSY)
- -  Large forward backward asymmetry in B0   K* decay expected
**	****	**

-   Need better statistics
-    In low q2 region
-   CDF may be able to
-     contribute to resolving this

- Flipped signs

**Probe of New Physics**

## Discriminating Variables For BK

-        significance
- Pointing () | B –  vtx|
- Isolation (Iso)

**Discriminating Variables For B************K**

-   Using similar discriminating variables and analysis
-     strategy as Bs search

- SIGNAL
- SIDEBAND

- SIGNAL
- SIDEBAND

- SIGNAL
- SIDEBAND

## Bu,d,s  K+/K*/Results with 1fb-1

-   Using similar discriminating variables and strategy
-     as Bs analysis

**Signal**
**Sideband**
**Extrapolated fit**

**Note:  bins are counted. Gaussian is for **
**       ****illustration of expected width only**

**       ****B****u**** ******** ************************K****+********B****d**** ******** ************************K*********B****s**** ******** **********************

## Bu,d,s  K+/K*/Summary

- We see evidence for the B+   K+ B0   K* rare modes
- We are homing in on the Bs rare mode

**B****u,d,s**** ******** ************************K****+****/K*/********Summary**

- With 1fb-1 of data:

## Summary

-   Tevatron heavy flavor physics program is in
-     full swing.   What I’ve showed today is only the
-     “tip of the iceberg”
-   CDF could observe any modest enhancement of
-     Bsin Run II.  CDF is also on the verge of
-     observing Bs decay
-   For the next few years, Tevatron will continue
-     to search for new physics with direct and
-     indirect searches
-   The ultimate frontier machine will be the LHC.
-     We may finally have a first clean glimpse of the
-     physics beyond the Standard Model
-   Look forward to seeing what that new physics really is