# Presentation: 273306

## B physics results from DØ

- Jan Stark
- (LPSC Grenoble)
- for the DØ Collaboration

**Moriond EW, March 21-28, 2004**

## DØ detector

- Moriond EW, March 21-28, 2004

- Jan Stark for DØ

## Tracker

**Trigger: muon+track covers |********|<2.2**

**SMT+ CFT**
******max**** = 1.65**

***8******×2 CFT layers***

**SMT region**
******max**** = 2.5**

***4****** SMT layers***

****** ****= - ln (tan(********/2))**

***SMT***

- Moriond EW, March 21-28, 2004

- Jan Stark for DØ

## Tracking performance

- Impact Parameter Resolution

- (DCA)  53 m @ PT = 1 GeV
- and 15 m @ higher PT

- Can provide
-    K/ separation for Ptot< 400 MeV
-    p/ separation for Ptot<700 MeV
- NOT yet used for PID

- SMT dE/dx

**MC ******** Data**

- Moriond EW, March 21-28, 2004

- Jan Stark for DØ

## Tracking performance

- || for kaons from D*D0

- pT spectrum of soft pion from D*D0

**Efficient muon and tracking system give us a**
**large sample of semileptonic B decays**

**Tracks are reconstructed**
** ****over a wide ******** range  **
** ****starting from p****T ****= 180 MeV**

**Data from semileptonic decays (B **  D X)

- Moriond EW, March 21-28, 2004

- Jan Stark for DØ

## X(3872)  J/ + - 

- Last summer, Belle announced a
- new particle at  3872 MeV/c2,
- observed in B+ decays:
- B+  K+ X(3872),
-    X(3872)  J/ + -.
- Belle’s discovery has been
- confirmed by CDF and DØ.
- DØ preliminary:
-   300  61 events
-   4.4 effect
-   M = 0.768  0.004 (stat)  0.004 (syst) GeV/c2

- Moriond EW, March 21-28, 2004

- Jan Stark for DØ

## X(3872) production properties 

**What kind of particle is the X ?**
-   - charmonium ?
-   - an exotic meson molecule ?
-   - something else ?
**Compare our sample of X particles**
**to our sample of ********(2S), e.g.**
-   - split into two || regions (plot),
-   - two bins in decay length dl:
-       dl < 0.02 cm:   230  59 events
-       dl > 0.02 cm:     77  25 events

- Moriond EW, March 21-28, 2004

- Jan Stark for DØ

## X(3872)  (2S) comparison 

- No significant differences between
- (2S) and X have been observed
- yet.
- This comparison will be even more
- useful once we have models of
- the production and decay of, e.g.,
- meson molecules that predict
- the observables used in the
- comparison.

- Observation of the charged analog X+  J/ + 0 would rule out cc hypothesis.
- Observation of radiative decays X   c would favour cc hypothesis (Belle set limit).
- Use Dzero’s calorimeter to identify low energy 0 and  : work in progress.

- Moriond EW, March 21-28, 2004

- Jan Stark for DØ

## (B+)/(B0) from semileptonic decays 

- Have record statistics of reconstructed
- semileptonic B+ and B0 decays in hand.
- First application:
-    measure lifetime ratio (B+)/(B0)
-    will show some other applications later
**Sample compositions:**
-     “D0 sample”:  + K+ - + (anything except
-                                                slow )
-          B+   82 %
-          B0   16 %
-          Bs     2 %
-     “D* sample”:  + D0 - + anything
-          B+   12 %
-          B0   86 %
-          Bs     2 %
-     Estimates based on measured
-     branching fractions and isospin relations.

- Moriond EW, March 21-28, 2004

- Jan Stark for DØ

## (B+)/(B0): fitting strategy 

- Group events into 8 bins of
*Visible Proper Decay Length* (VPDL):
- Measure ri = N(+ D*-)/N(+ D0) in each bin i.
- Combinatorial background with true D0 in D* sample is
- subtracted using wrong-sign distribution
- (normalisation from full sample, previous slide).
-      no need for parameterisation of
-          background VPDL distribution
**Additional inputs to the fit:**
-    - sample compositions (previous slide)
-    - K-factors (from simulation)
-          K = pT(D0) / pT(B)     [separately for different (groups of) decay modes]
-    - Relative reconstruction efficiencies CY for different decay modes B  Y (from simulation)
-    - Slow pion reconstruction efficiency  [flat for pT(D0) > 5 GeV  (one of our cuts)]
-    - Decay length resolution (from simulation)
-    - (B+) = 1.674  0.018 ps  [PDG]

- one example VPDL bin

- VPDL = LT / pT( D0)  MB

- LT = transverse decay length

- Moriond EW, March 21-28, 2004

- Jan Stark for DØ

## (B+)/(B0): results 

**Preliminary result:**
- (B+)/(B0) = 1.093  0.021 (stat)  0.022 (syst)

**Syst. dominated by:**
-   - time dependence of slow  reconstruction efficiency
-   - relative reconstruction efficiencies CY
-   - Br(B+  +  D*- + X)
-   - K-factors
-   - decay length resolution differences D0  D*
- The preliminary DØ measurement is one of the most
- precise results, and it is consistent with previous
- measurements.

- Moriond EW, March 21-28, 2004

- Jan Stark for DØ

## Exclusive B decays 

- Can also reconstruct
- hadronic B decays
- exclusively
- ( improved proper
-       time resolution).
- Some examples
- on the right.

- Preliminary lifetime measurement
- using B0  J/(+-) KS(+-):
- (B0)
-   = 1.56        (stat)  0.13 (syst) ps
- Consistent with world average:
- (B0) = 1.542  0.016 ps  [PDG]

- B0  J/(+-) KS(+-)

- b  J/(+-) (p -)

**lxy/********(lxy)>4.5**

- 114 pb-1
- N = 39  12

- 250 pb-1

- Moriond EW, March 21-28, 2004

- Jan Stark for DØ

## B0/B0 mixing 

- B0/B0 mixing

- The B0/B0 mixing frequency md has been measured with high precision, most recently
- at the B factories.
- Measurements of md constrain |Vtd|, but current limitations are due to theoretical inputs.
**We use our large sample of semileptonic B****0****/B****0**** decays to **
**measure ********m****d****:**
-    - benchmark the initial state flavour tagging
-          results in this talk are based on
-          opposite side muon tags
-                                                       - can also constrain more exotic models
-                                                         of b production at hadron colliders
-                                                              e.g. Berger *et al*., Phys. Rev. Lett. 86, 4231 (2001)

- 

- B0

- Moriond EW, March 21-28, 2004

- Jan Stark for DØ

## B0/B0 mixing: results 

- B0/B0 mixing: results

**Preliminary results:**
-    md = 0.506  0.055 (stat)  0.049 (syst) ps-1
-    Syst. dominated by uncertainty on +D*- yield
-    per VPDL bin.
-    Consistent with world average:
-           0.502  0.007 ps-1
-    Tagging efficiency:
-    Tagging purity:

**Work in progress:**
-     - also use electron tags
-     - other tagging methods:
-           jet charge,
-           same side tagging.

- 250 pb-1

- Moriond EW, March 21-28, 2004

- Jan Stark for DØ

## Bs decays

- Bs decays

**Semileptonic decays:**
-    - Very good statistics
-    - If ms  15 ps-1 expect
-      a measurement with 500 pb-1.

**Fully reconstructed hadronic decays:**
-    - Poor statistics
-    - Excellent proper time resolution
-    - Need a few fb-1 of data
-      to reach ms  18 ps-1.

- Moriond EW, March 21-28, 2004

- Jan Stark for DØ

## Observation of B    D** X 

- Figure from *CLEO Collaboration*, hep-ex/9908009

- Plot on the right summarises D meson spectroscopy.
- Qualitative understanding from HQET (heavy quark limit)
-     Spin of heavy quark becomes conserved quantity
-        (good quantum number).
-        Angular momentum of light degrees of freedom
-        also becomes good quantum number.
-     Expect sets of doublets, e.g. (D1, D2*).
-        Sates of this particular doublet decay
-        via D-wave  narrow.

- The D10, D2*0 have been observed and studied
- in several experiments, most recently by
- BaBar and Belle in B-  D**0 - [hep-ex/0308026, hep-ex/0307021].

- We study D10, D2*0 produced in semileptonic B decays.
- Constrain D spectroscopy; also improve understanding of the sample of semileptonic B decays
- we use for lifetime, mixing, ... measurements.

- Moriond EW, March 21-28, 2004

- Jan Stark for DØ

## Observation of B    D** X 

- Start from our “B    D*- + anything” sample, and “reconstruct another +”.
- Look at mass of D*- + system.

**Work in progress:**
- extract separate
- amplitude, phase
- for each state.

- wrong-sign combinations

- Excess in right-sign combinations
- can be interpreted as
- combined effect of D10 and D2*0.

- From topological analyses at LEP we know:
-    Br(B  D*+ -   X) = 0.48  0.10 %
- DØ’s preliminary result constrains the resonant contribution
-    Br(B  {D10,D2*0}   X)  Br({D10,D2*0}  D*+ -) = 0.280  0.021 (stat)  0.088 (syst) % .

- Moriond EW, March 21-28, 2004

- Jan Stark for DØ

## Bs  + - sensitivity study

- Bs  + - is a promising window on possible physics beyond the SM.
- In the SM, the expected branching ratio is small:
- 	Br(Bs  + -) = (3.4  0.5)  10-9
- 	[Buras, Phys. Lett. **B**566 115 (2003)]
- 	Bd  + - is suppressed by additional factor |Vtd/Vts|  410-2.
- MSSM: 	Br(Bs  + -)  tan6 
- 	 at large tan , enhancement of up to 2-3 orders of magnitude
- 	     [Dedes *et al*., FERMILAB-PUB-02-129-T]

- Background rejection via
-   - isolation of muon pair
-   - decay length
-   - opening angle
-       between    and

- Data  (L dt  100 pb-1)
- loose selection

- Moriond EW, March 21-28, 2004

- Jan Stark for DØ

## Bs  + - sensitivity study

- Optimised cuts using Random Grid Search [Prosper, CHEP’95; Punzi, CSPP’03]
- based on the mass sidebands.
**After optimisation:**
-     expect 7.3  1.8 background events in signal region

**Expected limit**** (Feldman/Cousins):**
-     Br(Bs  + -) < 9.1  10-7  @ 95 % CL    (stat only)
-     Br(Bs  + -) < 1.0  10-6  @ 95 % CL    (stat + syst)
-     (expected signal has been normalised to B  J/ K )

******180 pb****-1**

- The analysis has not been
*unblinded* yet
- (signal region still hidden).

- Published CDF Run I
- result (98 pb-1):
-   Br(Bs  + -)
-      < 2.6  10-6  @ 95 % CL

- Moriond EW, March 21-28, 2004

- Jan Stark for DØ

## Summary

- Observation of the X(3872) at DØ;
- study of production properties
- Precise measurement of (B+)/(B0)
- Measurement of md, benchmark flavour tagging
- Observation of B    D** X at DØ
- DØ’s sensitivity to Bs   
- The exciting times have started; stay tuned for more.

- Reminder: all results are preliminary.

- Moriond EW, March 21-28, 2004

- Jan Stark for DØ

## Backup slides

- Moriond EW, March 21-28, 2004

- Jan Stark for DØ

## Flavour tagging: figure of merit

**Opposite side muon tags:**
-     Dilution:    	D = 2  -1 = 0.460  0.045
-     Figure of merit:	 D2 = 1.01  0.20 %
**Summary:**

|  D2 [%] | CDF | DØ |
| --- | --- | --- |
| Opp. muons | 0.66  0.09 | 1.01  0.20 |
| Opp. electrons | in progress | in progress |
| Jet charge | in progress | 3.3  1.7 |
| Same side | 1.9  0.9 | 5.5  2.0 |
| Opp. kaons | in progress | N/A |
| Same side kaons | in progress | N/A |

- older results

- Moriond EW, March 21-28, 2004

- Jan Stark for DØ