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Measurement of the CP parameters in Bs DsK and first observations of B(s)

0DsKSteven Blusk

Syracuse University

Time dependent BsDsK analysisFirst observations of BsDsK and B0DsK

CKM Workshop, University of Cincinnati, Cincinnati, Ohio, Sept 28 – Oct 2, 2012

on behalf of the LHCb Collaboration

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Introduction

Amplitudes of CC weak interactions depend on 4 parameters in the CKM matrix.

Do these 4 parameters fully describe both the magnitudes and phases associated with many B, D, K decay processes?

PhaseArg(Vub) is least well measured of the CKM angles, and among the most challenging experimentally

Small BFs ( Vub small ) Purely hadronic modes

Wolfenstein parameterizationA~1, = sinc, are real and imaginary parts in Vub (also in Vtd)

CKM Matrix

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Measuring using Tree Decays• Motivation

– Expected to be insensitive to new physics– Theoretically clean, experimental precision will dominate

• Time independent measurements– Self-tagging modes, no time-dependence– B-D0K- (ADS, GLW, GGSZ, multi-body) [see talk by Sneha Malde]– Many other modes being explored as well:

B0D0K*0, B- D0K-+-, BsD0(KK), bD0pK [see talk by M. Williams]

• Time-dependent measurements– BsDsK– Other modes under investigation: BsDsKBsDsK*, B0D

• In loops:– Bhh and hhh: See talks by Stefano Perrazini and Jussara de Miranda

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BsDsK Phenomenology CPV requires at least two paths to the same final state

Here: direct bc decay and (Bs mixing + bu decay).

s

Advantage: Both decay amplitudes are O(3) LARGE INTERFERENCE

Ds-K+Bs

sB

Ds-K+

Bs

sB Two rateequations

Also, CP conjugate final state: 0s sB D K

( )

Ds+K-Bs

sB

Ds+K-

Bs

sB Two more rateequations

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BsDsK Decay rates

The 5 observables are related to the 3 physics parameters (fs):

0.4 is expectedff

f

Aq

p A

2

2

1

1

f

f

f

C

2

2

2 sin ( 2

2 cos ( 2 )

1

1

)f s

f

f

f s

f

f

S

D

where

0

0

2 2

22 2

( ) 1 1 cosh sinh cos sin

2 2 2

( ) 11 cosh sinh cos sin

2 2 2

s s

s s

B f t s sf f s s

B f t s sf f s s

f

f

ff

f f

d t t te A m t m t

dt

d t t tpe A m t m t

dt q

D

S

C

CD

S

0

0

2 2

22 2

( ) 1 1 cosh sinh cos sin

2 2 2

( ) 11 cosh sinh cos sin

2 2 2

s s

s s

B f t s sf f s s

B f t s sf f s sf

f f

f

f

f

d t t te A m t m t

dt

d t t tqe A m t m t

dt p

S

S

C

C

D

D

2

2

2 sin ( 2

2 cos ( 2 )

1

1

)f s

f

f

f s

f

f

S

D

Terms containing have large|f | (analogous to rB, in BD0K)

BsDsK• Challenges

– (fBs / fb) * BR ~ 10-6.

– Fast Bs oscillations

– Flavor tagging

– Good background rejection needed.

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Also, see: LHCb Collab, JHEP 1206, 115 (2012)

t ~ 50 fs « 175 fs timefor BsBs oscillation

~1010 Bs per fb-1

in LHCb acceptance(at s = 7 TeV) +high eff. trigger

Excellent vertex & mass resolution.

Excellent muon, electron and hadron ID (RICH)

LHCb-CONF-2012-029

Measuring the CP parameters

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Two strategies being pursued

“sFit”1) Fit DsK invariant mass spectrum extract sWeights2) Apply sWeights to measured Bs candidate decay times to statistically subtract the background.3) 1D fit to the (pure signal) time distribution (no need to model time structure of backgrounds)

5 free parameters in fit

“cFit”1) Simultaneous fit to: mass time2) Need to additionally model time distribution of backgrounds.

16 free parameters in fit

cFit used

as x-check

Currently, default method

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BsDs(,K) Selection• Trigger (LHCb-PUB-2011-016)

– L0: Any L0 trigger (high pT hadron, , , etc)

– HLT: 2, 3 or 4-body displaced vertex, w/ large pT and 1 track w/ pT>1.7 GeV/c.

• Offline– Reconstruct: Ds

+K+K-+ (B=5.5%), -+ (B=1.1%) and K+-+ (B =0.7%)

– Cross-feed suppression from other bc: E.g. BDh, bch

– Combinatorial background suppression: Data-driven BDT

– BsDs x-feed into BsDsK: Stringent PID requirements on “bachelor” kaon.

– Charmless: Require Ds to be significantly displaced from Bs decay point.

• Ds mass sidebands show remaining charmless background negligible.

Remaining backgrounds

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Backgrounds Shape,based on

Yields

Partially reconstructed Bs

BsDs(*)BsDs

* Simulation Floated

Partially reconstructed B0

(with or w/o misID)B0D-B0D*-B0Ds

(*)Simulation

Fixed fromknown BFs, sel

Fully reconstructed B0:(with misID)B0D-+

DataFixed from BD data

and meas PID

Fully reconstructed b:(with misID)bc+

Simulation Floated

CombinatorialBs and Ds Data

sidebandsFloated

BsDs

BsDs mass fit

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Signal yield = 27965 ± 395Includes: DsKK, , K

Signal yield = 27965 ± 395Includes: DsKK, , K

Remaining backgrounds

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Decaysconsidered

Shape,based on

Yields

BsDs*KBsDs

(*)K

B0DsKSimulation Floated

BsDs*

BsDs(*)BsDs

*Data

SimulationFixed from known BFs,

sel and meas PID

B0D-K+

(D- Ds- misID)Simulation +

meas. PID

Fixed to 1/15 of B0D-reflection into BsDs

bcKcDs misID)

Simulation +meas. PID

Fixed to 1/15 of bc reflection into BsDs

CombinatorialBs and Ds data

sidebandsFloated

b Ds(*)p,

(with pK misID)Simulation

Fixed, based onobserved bDsp

signal in data

BsDsK

Analogous/similar to BsDs

BsDsK mass fit

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Signal yield = 1390 ± 98Includes: DsKK, , K

Signal yield = 1390 ± 98Includes: DsKK, , K

B0DsK

Time fits - Ingredients• Flavor tagging: Determine flavor of B at production

– With a tag comes an efficiency (tag), and a mistag prob (tag).

– Recall

– We fit for the coefficients of the cos(mst) and sin(mst) terms Need to have good understanding of tag!

• Good decay time resolution

• Knowledge of decay time acceptance

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0 ( )

...... cos sins sB f ts sf f

d te m t m t

dtSC

( + imperfect tagging algorithms)

tag tag)tag)

Flavor Tagging

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Bs Ds-

K-

K+

K+

e-, -

D0K- Vertex

charge

“Signal (same)” side

“Opposite” sid

e

Flavor of signal b-hadron can be determined using either Opposite (OS) side tag: Same side kaon tag Currently, only OS tag used in this analysis: optimized on flavor-specific decays

(J/K+, BD*+l ..)

More details in talk by Julian Wishahi

K+

Signalb-hadron

B-

Details in:LHCb-CONF-2012-026

Time resolution• Shape obtained from

simulated BsDsK– Resolution function described

by the sum of 3 Gaussians.

• Each Gaussian width scaled up by a factor of 1.15(Data/MC correction)Determined by comparing width of “fake Bs” == prompt Ds + random track between data and simulation.

– Prompt ‹ t › = 0 , and width is measure of time resolution

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<t> ~ 50 fs

Time acceptance

• Fit BsDs data with fixed s, s, (HFAG averagevalues) to get a, b, n, .

• In BsDsK time fit, a correction is applied to accountfor small difference in acceptance between DsK andDs (~1% difference per 1.5 ps)

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1( ) 1 1 0.2

(1 ( ) )na t t t ps

at b

Reconstruction effects on flavor-tagged BsDstoy

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Assuming 80,000reconstructed

BsDs.

Time fit results: BsDsK

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Fixed parameters:ms = 17.719 ps-1

s = 0.105 ps-1

s = 0.661 ps-1

Includes both tagged (40%) + untagged (60%) events

proper time [ps]

(From HFAG)

Results for CP parameters

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First measurement of the CP parameters in BsDsK.

Several possible improvements to sFit analysis being explored lower stat.

Also lower uncertainties expected withcFit (mass time ) 2D fit.

All uncertainties reduciblewith either larger signal/control samples, and withforthcoming analysisimprovements.

Uncertainties, given as a fraction of the statistical error.Total systematic error is absolute.

Extraction of sensitive to correlations : Requires a bit more work on syst. error covariance matrix. (Stat. error correlation matrix in backup)

Time Dep Time Indep

First observations of BsDs

+K-and B0Ds+K-

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LHCb-PAPER-2012-033

Motivation

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Bs Decay Diagramsbc tree bu tree bc W-exchange

K-, K*-, K1-, etc

bc W-exchangebc tree, w/ ss bc tree, w/ ss

B0 Decay Diagrams

BsDsK can also be used to measure (ala BsDsK)B0DsK presents a significant background.Neither of these decays have been observed to date.

First goals• Observe these decay modes, and measure ratios of BFs:

• Selections very similar to BsDsK analysis

– Only use Ds, K*K: Non-resonant KK shows significant charmless background contribution to B0 signal (~none for Bs)

– BDT to suppress combinatorial background.

• Main differences:– or K mass: 0 < M(3h) < 3 GeV

– Backgrounds challenging, due to lower <pT> of daughters.

• Types of backgrounds similar.

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0 0

00

( )

((

)

)

(

)s

s

ss

s ss

B

B

B B

B D

D K B K

B D K

D

B

Signals in Data

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N(Bs) = 568383

BsDsN(B0) = 40233N(Bs) = 21621

BsDsK

Preliminary Preliminary

Results (Preliminary)

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• B(BsDsK) consistent with Cabibbo suppression

• B(B0DsK) and daughter invariant masses suggest dominantcontribution from ss popping

• K* and K dominate K final state, with perhaps small contributions from excited strange states (K1(1270), K1(1400), etc)[ next slide ]

Systematicuncertainties

Two and Three-Body Masses

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Bs DsK

K Mass (MeV) K Mass (MeV) Mass (MeV)

K Mass (MeV) K Mass (MeV) Mass (MeV)

Prominent contribution from “narrow” excited strange states

Small contribution from narrow excited strange statesB0 DsK

PreliminaryPreliminary

Preliminary

PreliminaryPreliminary

Preliminary

First Observation of BsDs(2536)+-

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BsDs1(2536), Ds1

+ Ds

031 1

0

( (2536) ) ( (2536) )(4.0 1.0 0.4) 10

( )s s s s

s s

B B D B D D

B B D

Ds1(2460)would be

here

(No Ds0*(2317)+ peak seen)

LHCbPreliminary

> 6 significant

Summary

• First time-dependent CP analysis of BsDsK presented– Room for improvement in uncertainties,

with addn’l refinements in analysis.– Include SS Kaon tags– extraction in progress– Incl. 2012 data will increase sample

size ~3-4x current yield.

• Other decays also being explored– BsDsK (first observation): Expect signal yield of ~40% of BsDsK

yield.

– Other possibilities: BsDsK*+, addn’l Ds decays:DsKsK, KK0..B0 decays: B0D-, D- …

• Other first observations– B0DsK, BsDs(2536).

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Matter

Anti-matter

Summary• First time-dependent CP analysis of BsDsK

presented– Room for improvement in uncertainties, with addn’l

refinements in analysis.– Include SS Kaon tags– extraction in progress– Incl. 2012 data will increase sample size ~ 3x current yield.

• Other decays also being explored– BsDsK (first observation): Expect signal yield of ~40% of

BsDsK yield.

– Other possibilities: BsDsK*+, addn’l Ds decays:DsKsK, KK0..B0 decays: B0D-, D- …

• First observations:– B0DsK, BsDs(2536). 28

Many thanks to the organizers

and session chairs

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Backup

BsDsK, by Ds final state

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Correlation matrixfor CP parameters in BsDsK

(Statistical errors only)

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BsDs Masses

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Masses