Sergey Burdin FNAL DØ Collaboration 8/12/2005 Chicago Flavor New Bs Mixing Result from DØ.

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Sergey Burdin FNAL DØ Collaboration 8/12/2005 Chicago Flavor New Bs Mixing Result from DØ

Transcript of Sergey Burdin FNAL DØ Collaboration 8/12/2005 Chicago Flavor New Bs Mixing Result from DØ.

Page 1: Sergey Burdin FNAL DØ Collaboration 8/12/2005 Chicago Flavor New Bs Mixing Result from DØ.

Sergey BurdinFNAL

DØ Collaboration8/12/2005

Chicago Flavor

New Bs Mixing Result from DØ

Page 2: Sergey Burdin FNAL DØ Collaboration 8/12/2005 Chicago Flavor New Bs Mixing Result from DØ.

8/12/2005 S.Burdin /FNAL/ @ CF 2

DØ conference notes 4878 & 4881 ∫Ldt=610pb-1 (All available statistics up to

June 2005) Many people contributed to this work

Bs mixing with Bs Ds μX, Ds π, K*K and

opposite-side flavor tagging

Page 3: Sergey Burdin FNAL DØ Collaboration 8/12/2005 Chicago Flavor New Bs Mixing Result from DØ.

8/12/2005 S.Burdin /FNAL/ @ CF 3

History: from Simple to Complex

2003 Reconstruction of semileptonic B decays:

μD0, μD*±, μD±, μDs

Understanding of sample composition, resolution, K-factor (momentum of non-reconstructed particles) Precise measurement: B+/B0 lifetime ratio (PRL 94, 182001 (2005))

2004 Bd mixing measurements

Opposite-side muon tagging Same-side tagging

2005 Bs mixing measurements

First result for Moriond 2005Update for EPS 2005

Considerable improvement

Page 4: Sergey Burdin FNAL DØ Collaboration 8/12/2005 Chicago Flavor New Bs Mixing Result from DØ.

8/12/2005 S.Burdin /FNAL/ @ CF 4

B Mixing Analyses

Signal Selection Initial and final state flavor tagging Study of time evolution of tagged B

signal Use Visible Proper Decay Length for semileptonic

decays Use special variable “Asymmetry”

Fit Comparison with expected asymmetry gives Δm

AsymmetryNnon osc Nosc

Nnon osc Nosc

Page 5: Sergey Burdin FNAL DØ Collaboration 8/12/2005 Chicago Flavor New Bs Mixing Result from DØ.

8/12/2005 S.Burdin /FNAL/ @ CF 5

Bs data sample @ DØ World largest

sample Data up to end of May 2005

(~610pb-1)

Ds Ï †Ï €, φ K K

15640±190 Dsπ

4349±152 D±π

18780±782

3233±208

14112±910

Bs0 Ds μΠ½X

Ds K 0K

Charge of muon gives the final state tagging

Page 6: Sergey Burdin FNAL DØ Collaboration 8/12/2005 Chicago Flavor New Bs Mixing Result from DØ.

8/12/2005 S.Burdin /FNAL/ @ CF 6

Signal Selection

A set of discriminating variables is constructed for a given event

Cut on combined variable

fs(xi) and fb(xi) --- pdf for signal and background

Page 7: Sergey Burdin FNAL DØ Collaboration 8/12/2005 Chicago Flavor New Bs Mixing Result from DØ.

8/12/2005 S.Burdin /FNAL/ @ CF 7

Improvement wrt Moriond

Page 8: Sergey Burdin FNAL DØ Collaboration 8/12/2005 Chicago Flavor New Bs Mixing Result from DØ.

8/12/2005 S.Burdin /FNAL/ @ CF 8

Analyses road map Binned asymmetry Asymmetry fitting procedure

Essentially the same as for the lifetime ratio and Bd mixing analyses

Inputs to the fitting procedure MC

sample composition K-factor taking into account non-reconstructed particles Efficiencies Visible Proper Decay Length (VPDL) resolution

Scale factor for VPDL resolution from tuning procedure Tagging algorithm tested and its dilution determined from Bd

and Bu semileptonic samples

Page 9: Sergey Burdin FNAL DØ Collaboration 8/12/2005 Chicago Flavor New Bs Mixing Result from DØ.

8/12/2005 S.Burdin /FNAL/ @ CF 9

Initial State Tagging

Initially bb pair is produced – use decays of b to tag flavor of b

Flavor at production moment determined by sign of opposite side muon (electron), tracks from Secondary Vertex and Jet Charge For example

+ - no oscillation+ + or - - oscillation

Beware: Additional dilution from oscillations on the opposite side

Page 10: Sergey Burdin FNAL DØ Collaboration 8/12/2005 Chicago Flavor New Bs Mixing Result from DØ.

8/12/2005 S.Burdin /FNAL/ @ CF 10

Initial state flavour taggingFor this analysis, we use opposite-side flavour tagging to determine the flavour of a given B meson at production. b quarks are produced in pairs (b-b); we use the decay products of the “other b” to infer the initial flavour of the B.

A method based on likelihood ratios is used to combine different discriminating variables into one continuous tagging variable d (b-like: d>0 ; b-like: d<0). We distinguish different categories of events, and use the following discriminating variables:

If an opposite muon [cos (p,pB) < 0.8] is found:

Muon jet charge: constructed from pT and charge of muon and tracks within R < 0.5 of muon. Muon pT

rel: transverse momentum of muon w.r.t. nearest track-jet. If secondary vertex is found (e.g. from B decay): Secondary vertex jet charge constructed from charge and momenta of tracks from vertex.

If an opposite electron [cos (pe, pB) < 0.5] is found:

Charge of the electron

Otherwise:

Secondary vertex jet charge pT of secondary vertex Event jet charge: constructed from charge and momenta of all tracks at R > 1.5 from B.

Distribution of combined variablein data samples enriched in B0 and in B0:

B0-enrichedB0-enriched

Page 11: Sergey Burdin FNAL DØ Collaboration 8/12/2005 Chicago Flavor New Bs Mixing Result from DØ.

8/12/2005 S.Burdin /FNAL/ @ CF 11

Dilution from Δmd measurement

Bd oscillation measurement with the same opposite-side tagger as for Bs

md= 0.5010.030±0.016ps-1

Dilutions D(Bd)=0.4140.023±0.017

D(Bu)=0.3680.016±0.008 Used for systematic error

MC shows that dilutions for Bs and Bd are in agreement

Dilution for Bd agrees in data and MC

Better use of tag variables εD2=2.17±0.13±0.09 %

Combined dilution: D=0.384±0.013±0.008εD2=1.94±0.14±0.09 %

Page 12: Sergey Burdin FNAL DØ Collaboration 8/12/2005 Chicago Flavor New Bs Mixing Result from DØ.

8/12/2005 S.Burdin /FNAL/ @ CF 12

Tagged Bs→DsμX events

Tagging efficiency --- 12.3% In agreement with Bd and Bu

1917± 66 Dsπ candidates

566±55 D±π candidates

Page 13: Sergey Burdin FNAL DØ Collaboration 8/12/2005 Chicago Flavor New Bs Mixing Result from DØ.

8/12/2005 S.Burdin /FNAL/ @ CF 13

Measurement of Bs Oscillation Frequency

Asymmetry cos Î ”mS tAmplitude fit = Fourier analysis + Maximum likelihood fit can be used for the Δms measurements

If A=1, the Δm’s is a measurement of Bs oscillation frequency, otherwise A=0

A Dcos Δms' t

Need to know dilution (from Δmd analysis)

Amplitude fit for Bd mixing• Is not the best method to determine the oscillation frequency• Good to establish the oscillation frequency range

Page 14: Sergey Burdin FNAL DØ Collaboration 8/12/2005 Chicago Flavor New Bs Mixing Result from DØ.

8/12/2005 S.Burdin /FNAL/ @ CF 14

Asymmetry in μDs sample (π mode)

Expected curve is affected by bin width, resolution and K-factor

Page 15: Sergey Burdin FNAL DØ Collaboration 8/12/2005 Chicago Flavor New Bs Mixing Result from DØ.

8/12/2005 S.Burdin /FNAL/ @ CF 15

Asymmetry for K*K decay mode

Page 16: Sergey Burdin FNAL DØ Collaboration 8/12/2005 Chicago Flavor New Bs Mixing Result from DØ.

8/12/2005 S.Burdin /FNAL/ @ CF 16

Asymmetries in μDs and μD± samples (large bin)

See oscillations in μD± (D±π) sample

Page 17: Sergey Burdin FNAL DØ Collaboration 8/12/2005 Chicago Flavor New Bs Mixing Result from DØ.

8/12/2005 S.Burdin /FNAL/ @ CF 17

Asymmetry Fitting Procedure

Use amplitude method to set a limit on the Bs oscillation frequency

Page 18: Sergey Burdin FNAL DØ Collaboration 8/12/2005 Chicago Flavor New Bs Mixing Result from DØ.

8/12/2005 S.Burdin /FNAL/ @ CF 18

Asymmetry Fitting Procedure

For given decay mode j:

For given VPDL interval i:

Minimize χ2 for given Δms in range from 1 to 20 ps-1 with step 1 ps-1

Page 19: Sergey Burdin FNAL DØ Collaboration 8/12/2005 Chicago Flavor New Bs Mixing Result from DØ.

8/12/2005 S.Burdin /FNAL/ @ CF 19

Sample Composition

Inputs from MC Sample composition

for signal peak

+ 3.5±2.5% contribution of from gluon splitting

1.3%Bs→Dsτν

0.9%Bs→DsDX

4.1%B-→DsDX

4.0%B0→DsDX

2.9%Bs→DsDsX

3.1%Bs→D*1sμν

1.4%Bs→D*0sμν

60.7%Bs→D*sμν

21.7%Bs→Dsμν

Sample composition

Decay

Useful signal — 88.3%

cc

Page 20: Sergey Burdin FNAL DØ Collaboration 8/12/2005 Chicago Flavor New Bs Mixing Result from DØ.

8/12/2005 S.Burdin /FNAL/ @ CF 20

contamination

From MC: tagging suppresses the

ccbar by factor of ~3

From lifetime ratio analysis: 10±7% contamination

Result: 3.5±2.5% contribution

VPDL distribution from MC

cc

Page 21: Sergey Burdin FNAL DØ Collaboration 8/12/2005 Chicago Flavor New Bs Mixing Result from DØ.

8/12/2005 S.Burdin /FNAL/ @ CF 21

K-factors

0.687B-→DsDX

0.681B0→DsDX

0.762Bs→DsDs

X

0.830Bs→D*1sμ

ν

0.815Bs→D*0sμ

ν

0.861Bs→D*sμν

0.881Bs→Dsμν

<k>Decay

kPt Î ¼Ds

Pt Bs

cÏ „BskxM

Page 22: Sergey Burdin FNAL DØ Collaboration 8/12/2005 Chicago Flavor New Bs Mixing Result from DØ.

8/12/2005 S.Burdin /FNAL/ @ CF 22

Efficiency vs VPDL Use MC Have lifetime cuts in the

analysis → efficiency (VPDL) In the Bs oscillation analysis the

asymmetry in the range [-0.01, 0.06] cm is the most important → efficiency shape is a large effect over all sensitivity region

Would cancel out if not the sample composition

Good news : same turn-on shape for different processes

Signal

Background

Page 23: Sergey Burdin FNAL DØ Collaboration 8/12/2005 Chicago Flavor New Bs Mixing Result from DØ.

8/12/2005 S.Burdin /FNAL/ @ CF 23

VPDL Resolution

Understanding of resolution is crucial for Δms measurement

Measured and tuned tracking errors in data and MC

Tracking errors depend on Track momentum and angles Silicon detector hit configuration and cluster width

~150 configurations are being considered

Page 24: Sergey Burdin FNAL DØ Collaboration 8/12/2005 Chicago Flavor New Bs Mixing Result from DØ.

8/12/2005 S.Burdin /FNAL/ @ CF 24

Tuning VPDL resolution

Data before tuning MC before tuning

Data after tuning MC after tuningln

(σ2 IP

)

-ln(p2sin3θ)

Track IP errors

IP resolution

ln(σ

2 IP)

ln(σ

2 IP)

ln(σ

2 IP)

Page 25: Sergey Burdin FNAL DØ Collaboration 8/12/2005 Chicago Flavor New Bs Mixing Result from DØ.

8/12/2005 S.Burdin /FNAL/ @ CF 25

VPDL Resolution

Resolution described by 3 gaussians One scale factor for all 3 gaussians: 1.142±0.020 Tuning is crucial for event by event fit

Dependence of resolution from VPDLMC

MC

Before tuning

After tuning

Page 26: Sergey Burdin FNAL DØ Collaboration 8/12/2005 Chicago Flavor New Bs Mixing Result from DØ.

8/12/2005 S.Burdin /FNAL/ @ CF 26

Result on Bs oscillations in π mode

1.7 times better than our Moriond result

Page 27: Sergey Burdin FNAL DØ Collaboration 8/12/2005 Chicago Flavor New Bs Mixing Result from DØ.

8/12/2005 S.Burdin /FNAL/ @ CF 27

Result on Bs oscillations in K*K mode

New Result

Page 28: Sergey Burdin FNAL DØ Collaboration 8/12/2005 Chicago Flavor New Bs Mixing Result from DØ.

8/12/2005 S.Burdin /FNAL/ @ CF 28

Systematic Errors

Tagging Puritycc

Resolution

Br(BsDsμX)

Page 29: Sergey Burdin FNAL DØ Collaboration 8/12/2005 Chicago Flavor New Bs Mixing Result from DØ.

8/12/2005 S.Burdin /FNAL/ @ CF 29

Combined DØ result in π and K*K modes

Page 30: Sergey Burdin FNAL DØ Collaboration 8/12/2005 Chicago Flavor New Bs Mixing Result from DØ.

8/12/2005 S.Burdin /FNAL/ @ CF 30

Sensitivity in Comparison

(this analysis, 610 pb-1)(prior to this conference, 355 pb-1)

Jan Stark, EPS 2005

Page 31: Sergey Burdin FNAL DØ Collaboration 8/12/2005 Chicago Flavor New Bs Mixing Result from DØ.

8/12/2005 S.Burdin /FNAL/ @ CF 31

Bs Mixing Projections

Planned hardware improvement L3 bandwidth increase from 50 to 100 Hz

Expect considerable increase in signal yield Tests are successful !

Layer0 Improvement in decay length resolution

Layer0 + L3 BW upgrades No upgrades

We are here

Analysis improvement

event by event fit better tagging

Improved OST Same-Side Tagging

Page 32: Sergey Burdin FNAL DØ Collaboration 8/12/2005 Chicago Flavor New Bs Mixing Result from DØ.

8/12/2005 S.Burdin /FNAL/ @ CF 32

New Tevatron Combination

Combined Tevatron average comparable to the best single measurement

Page 33: Sergey Burdin FNAL DØ Collaboration 8/12/2005 Chicago Flavor New Bs Mixing Result from DØ.

8/12/2005 S.Burdin /FNAL/ @ CF 33

New World Combination

Page 34: Sergey Burdin FNAL DØ Collaboration 8/12/2005 Chicago Flavor New Bs Mixing Result from DØ.

8/12/2005 S.Burdin /FNAL/ @ CF 34

Δms

Experimental Status of Unitarity Triangle

Present and future experiments to improve our knowledge of the Unitarity Triangle B-factories

Access to Bd mesons

Δmd = (0.510 ± 0.005) ps–1

Tevatron and LHCAccess to all B hadrons (Bd,

Bs, Bc, b etc)

Measurement of ms/md

Strong constraint on one of the triangle's sides

CKM fit predicts : Δms = 18.3 ps–1 + 6.5– 2.3

[ CKM constraint dominated by theory error ]

CKM fit predicts : Δmd = 0.47 ps–1 + 0.23– 0.12

HFAG – Winter 2005

Δms measured

Page 35: Sergey Burdin FNAL DØ Collaboration 8/12/2005 Chicago Flavor New Bs Mixing Result from DØ.

8/12/2005 S.Burdin /FNAL/ @ CF 35

Conclusion We are entering era when Bs mixing

will be defined by the Tevatron results Our result has the second best

sensitivity (after ALEPH inclusive lepton analysis)

Impressive team work of many people Good prospects

10-fold increase statistics during next 3 years (more lumi + increased bandwidth)

Layer 0 Now it is clear that we will push the

sensitivity well beyond 20 ps-1 measure Δms if it is close to 20 ps-1