La Imposibilidad de Eludir La Mentira, Profesor Héctor Sevilla
Héctor Moreno Advisor : Dr. Héctor Méndez UPRM HEP...
Transcript of Héctor Moreno Advisor : Dr. Héctor Méndez UPRM HEP...
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