Héctor Moreno

Advisor : Dr. Héctor Méndez

UPRM

HEP Group

May 9, 2014

Study of a decay

Outline

• Intoduction

• Event Selection

• Ψ(2s) ―› μ+μ- Data analysis

• Λb0 Reconstruction

• Branching ratio measurement

• Λb0 Reconstruction with

Ψ(2s) ―› Ψ(1s)π+π- Data analysis (Confirmation)

• Conclusions

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Objective

• Study of the exclusive hadronic decay

• Measurement of the relative branching fraction (B)

‘’Normalizing mode’’

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Introduction

The Standard Model

Is a theory that

describes the

interactions between

elementary particles

consistent with the

quantum mechanics and

the special relativity.

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& Higgs boson

Hadrons

•Baryons •Mesons

Introduction

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-

•Mesons ( quark - antiquark )

Ψ(1s) / Ψ(2s) (cc) states

(3 quarks) (3 anti-quarks) •Baryons :

Introduction

Large Hadron Collider

The largest and most powerful particle collider,

built by (CERN) to allow physicists test the

predictions of different theories of particle

physics and high-energy physics.

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•27 km circunference •Collides pp at center-of-mass energy √s = (7 TeV) (8 TeV) (14TeV). •Proton bunches collide every 25 ns. •11000 turns/sec. •L = 1034 cm-2 s-1

Introduction

The Compact Muon Solenoid (CMS)

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•CMS is an experiment to investigate a wide range of physics, including the search for the Higgs boson, extra dimensions, and particles that could make up dark matter.

CMS Collaboration

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More than 4300 scientists, engineers and students. 182 institutes in 42 countries.

Introduction

CMS experiment • Transversal view

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• Pseudorapidity η

• Transverse momentum PT

• Longitudinal view

Data

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• CMSSW_4_2_8_patch7 release

/MuOnia/Run2011A-PromptReco-v4/AOD

/MuOnia/Run2011A-05Aug2011-v1/AOD

/MuOnia/Run2011A-PromptReco-v6/AOD

/MuOnia/Run2011B-PromptReco-v1/AOD

MuOnia, recorded in 2011 Integrated Luminosity : 5.05 fb-1

Center-of-mass energy : √s = 7 TeV

L = 2.16 fb-1

L = 2.89 fb-1

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Topology decay

CMS Volume

(2 )S 0

Pr( , )xy p im VtxL I

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Topology decay

CMS Volume

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Topology decay

CMS Volume

α―›0

α´―›0

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Opp. Charged dimuon pair 2 Global or 1 G or 1 T muon pair μ+μ- Vertexing

Vtx Conf. Level >1 % Track muons be inside

|ημ|<2.2 region Dist. Closest App.

dcaμ+μ-<0.5 cm

μ+μ- Candidates

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Matching High Level Trigger (HLT):

Displaced Low Mass Trigger (LMT)

•Chooses and sort the best muon candidates from the regional muon triggers and pass them to the Trigger together with their parameters.

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Λ0 ―› p π- Candidates

Displacement from prim. Vtx. (Signif.)

( L / σL ) xy > 5 Imp. Parameter ( IP / σ ) > 0.5 › 1 GeV/c

| Mpπ – MPDG | < 8 MeV/c2

Pointing angle cos( α’ ) > 0.95 Suppresion of

( π- as a p ) | Mπ π – M

PDG | |< 20 MeV/c2

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Candidates

Displacement from prim. Vtx

( L / σL ) > 3 Primary Vtx according to its closest and Pointing angle primary Vtx. -

cos( α ) > 0.95

> 10 GeV/c

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Λb0 ―› Λ0Ψ(2s) with Ψ(2s) ―›μ+μ-

- We look μ+μ- distribution under Λb0 resonance (5.620±0.05 GeV/c2)

Ψ(2s)

Ψ(1s)

Λ0b―›Λ0Ψ(2s)

Λ0b―›Λ0Ψ(1s)

-Fit dimuon at the 3-body Vtx by constraining Mμ+μ- to the nominal mass Ψ(2s) (Ψ(1s) ) if Mμ+μ- falls around 150 MeV around Ψ(2s) (Ψ(1s) ) resonances. -ClmassC > 1% - Λb

0 Rapidity |y(Λb0)| < 2

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Λ0b―›Λ0Ψ(2s) and Λ0

b―›Λ0Ψ(1s) signal

Data

MC

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K0s ―› π+π- Contamination

Λ0―›p π-

K0s ―› π+π- Ψ(2s) mode

Ψ(1s) mode

K0s ―› π+π-

Λ0―›p π-

Rejected

K0s mesons come from B0 ―› K0

sΨ(2s)(Ψ(1s)) decays and need to be removed From the sample, (p π) invariant mass is changed by (π π).

( π- as a p ) | Mπ π – MPDG | < 20 MeV/c2

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B0 ―› K0sΨ(2s)(Ψ(1s)) Contamination

B0 ―› K0sΨ(2s)(Ψ(1s)) inv. Mass rec. B0 signal under Λb

0 candidate

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Relative Branching Fraction Measurement

For

and for

Λb0 ―› Λ0Ψ(2s)

Λb0 ―› Λ0Ψ(1s)

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Relative Branching Fraction Measurement

For Ψ(1s) ―> μ+μ-:

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/LambdaBToPsiMuMu 2MuPEtaFilter Tight 7TeV-pythia6-evtgen /Fall11-HLTBPh2011 START42 V14B-v2/GEN-SIM-RECO.

MC Sample (2011)

LambdaB To Psi MuMu, Signal MC, GEN-SIM-RECO .

• Generated MC

branching fraction.

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Relative Branching Fraction Measurement

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Statistical uncertainty

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Systematic uncertainty

σsyst = 0.669*0.064 = 0.043

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Λb0 ―› Λ0Ψ(2s) with Ψ(2s) ―› J/Ψπ+π-

Ψ(2s) ―› J/Ψπ+π- is the largest decay of Ψ(2s)

B(Ψ(2s) ―› J/Ψπ+π-) ~ 2% assuming 100% π+π- efficiency

• Two extra pions (π+π-) attached to the secondary Vtx. • Λ0 and μ+μ- sel. Criteria similar to prev. analysis .

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Ψ(2s) ―› Ψ(1s) π+π- reconstruction

- We work in a wide dimuon region ( 2.8 < Mμ+μ- < 4.0 GeV/c2 )

π+π- Candidates: Distinct from μ+μ- and p π- reconstructed tracks

> 0.25 GeV/c

> 0.75 GeV/c

> 1%

|MPDG

Ψ(1s) – Mμ+μ-|<150 MeV/c2

dca < 0.5 cm

Pion and muon tracks required to be close kinematically:

R =

R < 0.75

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Λb0 ―› Λ0Ψ(2s) reconstruction

For Λb0 Candidates:

Prim. Vtx as Ψ(2s)-›μ+μ- And re-fitting CMS prim. Vtx With good quality:

CL primary > 5% Min. Λb

0 detachment

(L/σ) > 3 Λb

0 pointing trajectory to its prod. Point by: cos(α prim - ) > 0.95

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Conclusions

The preliminary relative branching fraction is.

Superposition of B0 ―› K0sΨ(2s)(Ψ(1s)), K0

s are negligible.

We confirmed our observation of Λb0 ―› Λ0Ψ(2s) using Ψ(2s) ―›J/Ψπ+π-,

the data analysis for this decay shows a preliminary signal of 165 events.

However, this analysis is still in progress. MC analysis and extra cuts

have to be taken for appropiate calculations for the relative fraction

of Λb0 ―› Λ0Ψ(2s) to Λb

0 ―› Λ0Ψ(1s).

Thank you !

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Backup

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Λb0 ―› Λ0Ψ(2s)(Ψ(1s)) in B0 MC Sample

To see if B0 cont. is negligible, we search for Λb0 decays in MC B0 dataset

After Λb0,

Λ0, K0s rej

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Mass fit

Signal : Two gaussian funcions with same mean value

B = c1x3 – c2x

Background: 3rd Chebychev polinomial function

Background

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Data adquisition

Raw Data : From detector Reco : Objects created from reconstructed process Ex: Hits tracks, etc. Full event (FEVT) : RAW + RECO. AOD : Subset of RECO, enough for most of physical standard analysis . -Particle identification. There are subsets smaller and specific. ( n-tuplesm minitrees, etc ) Data coming from simulation have the Same format as RAW data GEN + SIM + DIGI = RAW in MC