b º π + π - : status of analysis

BBººππ++ππ--: status of : status of analysisanalysis

Vitaliano CiulliRiccardo Ranieri

Nicolò Magini

TISB-Pisa,12 Ottobre 2001

BBººππ++ππ--: status of analysis Riccardo Ranieri 2

Generated BGenerated Bººππ++ππ--

ACPsin(2α)

b -_ _

b

At least 1 μ

•ptμ>4 GeV/c

•lημl<2.6

At least 1 BBººππ++ππ--

•ptB>8 GeV/c

•lηπl<2.4

Hard interaction pt>10 GeV/c^



MC SignalMC Signal9196 events simulated (4384 digitized)

PYTHIA 6.152 CMSIM 122 ORCA 5.1.2 (oohit) [ORCA 5.1.2 (digi)]

Cross section σ=4622 fb

32.7% Gluon Splitting

20.6% Flavour Excitation

46.7% Pair Production



Decay reconstructionDecay reconstruction

ForwardKalmanFilter + ConnectionMachinept>0.8 GeV/c

lηl<2.4Well identified muonCombinatorial on other

opposite-charge tracks

lMBrec(GeV/c2)-5.2794l<1

? 50 MeV/c2 Resolution ?



BackgroundBackground

Br(BºK+π-) = (1.72±0.27)x10-5 4xBr(Bºπ+π-)

5.24 GeV/c2 mass peak 50 MeV/c2 resolution½ bkg

over signal S/B=1/2

Other Two-body decaysS/B=1/1

Estimation of Two-body BackgroundS/B1/3

CMS-TN 1994/328 CP Violation Study of the BBdd

ººππ++ππ-- decay for the Technical Proposal



More on BackgroundMore on BackgroundOfficial muon MC production http://cmssun4.pd.infn.it/~ugs/cms/hlt/prod2001_new.html

PYTHIA 6.152 CMSIM 121 ORCA 5.1.1 (oohit) ORCA 5.1.2 (digi)

dataset mu_MB1mu_pt4 (at least a true muon pt>4 GeV/c no pt cut)

Events: 106562 Lumi: 0.4071 nb-1

σ=262 μb

High lumi (=10 nb-1s-1) Rate =

10 nb-1s-1x262 μb= 2.62 MHz

^

Rate = 400 KHz

CMS-IN 2000/053 CMS-NOTE 2001/011

http://cmssun4.pd.infn.it/~ugs/cms/hlt/prod2001_new.html



List of cutsList of cuts

Kinematic cuts: ptB>10 GeV/c

ptπ>5 GeV/c

I=ΣΔR<1(pt/ptB)<0.1

Vertex cuts: SIP=tIP/σIP>3

cos(Δα)>0.995χ2

vtx<10

Mass cut: lMBrec(GeV/c2)-5.29l<1x0.05



Some plotsSome plots

SIP=tIP/σIP>3ptB>10 GeV/c



Some numbers on Some numbers on signal…signal…

Cuts Nsim Eff. N(60 fb-1)

MC signal 4384 1 277320

Reco BBºº 3729 .851±.005 235900±1400

Kinematic 513 .117±.005 32500±1400

Vertex 322 .073±.003 20200±800

Mass 167 .038±.003 10500±800



……and backgroundand background

Cuts Nsim Eff. N(60 fb-1)

MC background

11993

1 16x1012

Fake BBºº 3767 .314±.005 (5.02±0.08)x1010

only

Kinematic12 (3.2±0.9)x10-3

only Vertex 1 (2.7-1.7+4.6)x10-

4

only Mass 178 .473±.035

K+V+M 0 (1.2-0.8+2.0)x10-

8

1.9-1.3+3.2 x105



L1+L2 TriggerL1+L2 TriggerL1+L2 Trigger cuts pt

μ>10 GeV/c Events used: 11993 After trigger: 306

Efficiency ε=2.55%

High lumi Rate= 70 KHz

CMS-NOTE 2001/011

Results on L2 trigger reconstruction in single and di-muon topologies

Rate=30 KHz



Single muon TriggerSingle muon Triggeronly L1+L2 Trigger cuts pt

μ>10 GeV/c

Signal Efficiency (9.1±0.4)%Background Efficiency (2.55±0.14)%

Total selection EfficiencySignal (3.4±0.9)x10-3

Background (3.2-2.1+5.6)x10-10

3 Years Low Luminosity (3x20 fb-1=60 fb-1)

Nsig=940±250 Nbkg=4800-3300+9000

N2body=2800±800



Sensitivity to sin(2α)Sensitivity to sin(2α)

Time integrated analysis sensitivity:

CMS-TN 1994/328 CP Violation Study of the BBddººππ++ππ--

decay for the Technical Proposal

1 Year Low Luminosity 10 fb-1

NNNS

BS

D

+1=))α2(sin(δ D~0.416



Concl…Concl…

4 aspects to be investigated further:1. Two-body decay backgroundestimated 2800±800 @ 60 fb-1

(events BBººKπ needed)2. Bug-fix on BBºº lifetime

this MC: =13.85 ps instead of 1.56 ps(decay length normalized to expected

one)new MC signal =1.56 ps

(some changes on Vertex cuts efficiencies…)



……usionusion

3. New strategies to reject combinatorial background in udsc events(more statistics needed)

4. New ideas to enlarge Trigger Rate of signal events

b º π + π - : status of analysis

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