Studiesof Semileptonic(B Decays(at( LHCb(

Studies of Semileptonic B Decays at LHCb Marco Fiore

Università di Ferrara -‐ XXVIII Ciclo Tutor: DoD. Concezio Bozzi

26/11/13 Marco Fiore 1

Outline •  Semileptonic B0 Decays:

1.  Theory & MoPvaPon; 2.  B0-‐>D*-‐µ+ν sample; 3.  Monte Carlo Studies; 4.  Conclusions

•  Summary


Neutral B mixing and CP ViolaPon •  Neutral B mesons: mass eigenstates are not flavour

eigenstates ; 〉±〉=〉 qqHL BqBpB ||| ,

3

Prob(B0; B0(t))=

Prob(B0; B0(t))=

!U (t) = e"!t (1+ cos#mt) / 2

!M (t) = e"!t pq

2

(1" cos#mt) / 2

Current WA Δmd= (0.510 ± 0.004) ps-‐1

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Flavour specific asymmetries B0 à D*-‐ µ+ ν is a flavour specific decay, we can compute

afs =!(B0 " B0 " D*#µ+!µ )#!(B

0 " B0 " D*+µ#!µ )!(B0 " B0 " D*#µ+!µ )+!(B

0 " B0 " D*+µ#!µ )

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Current WA afsd= (-‐0.03 ± 0.20) %

afsd (!10"2 )

afss (!10"2 )

B0àD*-‐µ+ν; D*-‐àD0πsl-‐; D0-‐>K+π-‐

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We have 500k signal events with 2011 data, including also 2012 data (2M events in total) we get a staPsPcal error on Δmd of 0.002 (half the error from the world average) and of 0.18% on afs (from the WA it is 0.20%).

Decay Pme •  For oscillaPon and CPV studies it is required to compute the decay Pme:

where k is a correcPon due to the missing neutrino and is parameterized as a funcPon of momentum and invariant mass of detectable parPcles •  k-‐factor can be computed from Monte Carlo but there are limitaPons due to:

•  StaPsPcs; •  ProducPon mechanisms; •  Decay dynamics; •  Limited knowledge of processes that are indisPguishable from signal (e. g. B-‐>D*µνX);

What is the impact of all this? How can we put remedy to these limitaPons?


t = mB

pBd = d *mB

pD*µk k =

pD*µpB

MC Studies •  The idea is to generate several sets of MC samples (~50M

events each) with different parameterizaPons of poorly known quanPPes, in order to assess their impact on systemaPc uncertainPes;

•  Performing these studies on the Full SimulaPon would require excessive compuPng Pme. Therefore, we generate the decay of interest and simulate the detector response parametrically;

•  We compare the parameterized Monte Carlo with the Full Monte Carlo SimulaPon. We must check the observables to be in good agreement with the Full SimulaPon.

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Smearing •  We apply smearing, detecPon efficiencies and other

correcPons only to the signal parPcles. Given the kinemaPcal range of the signal parPcles, we do not apply any momentum resoluPon;

•  B0 decay length; •  z(B0) – z(PV); •  z(D0) – z(B0); •  Cuts on IPPV, p, pT; •  µ & K simulated PID; •  MagnePc Field Effect; •  Trigger

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Bd

νµ

µ+

D*-‐

πs-‐

_ D0

K+

π-‐

PV

Marco Fiore

ResoluPons from Full SimulaPon


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dReco-dTrue hdEntries 229318Mean 0.002176RMS 0.04804

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dReco hdREntries 229318Mean 1.237RMS 1.052

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z(B0)-z(PV) histozPVEntries 229318Mean 0.01068RMS 0.4989Underflow 4921

/ ndf 2χ 388.1 / 141Prob 5.98e-25p0 13.3± 5921 p1 0.0099± 0.3331 p2 0.00117± 0.00439 p3 0.0024± 0.1683 p4 0.00690± 0.04729 p5 0.021± 1.029 p6 0.0070± 0.2161 p7 0.002117± 0.003795 p8 0.0071± 0.3987

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/ ndf 2χ 468.8 / 141Prob 8.086e-37p0 60.5± 6046 p1 0.0166± 0.2249 p2 0.002732± 0.004991 p3 0.0077± 0.2494 p4 0.00338± -0.01079 p5 0.0227± 0.5629 p6 0.0127± 0.5073 p7 0.01495± -0.03441 p8 0.2± 1.5

z(D0)-z(B0)

mm

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PID efficiency from real data

is expected, since tracks with higher transverse momentum traverse the detector at higher215

polar angles, in the lower occupancy regions. The proton misidentification probability is216

smaller than 0.5% for all pT ranges and momentum above 30GeV/c. It drops quickly with217

momentum for the lowest pT ranges, reaching a plateau at about 30-40 GeV/c. The pion218

and kaon misidentification probabilities have a similar behavior, increasing with decreas-219

ing pT . Above 40 GeV/c, the pion misidentification probability is almost at the level of the220

proton misidentification probability. At low momentum, decays in flight are the dominant221

source of incorrect identification, as can be seen from the difference between the pion/kaon222

and proton curves. While the proton misidentification probability, within the pT intervals223

chosen, lies within 0.1-1.3%, the pion and kaon misidentification probabilities are within224

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Figure 5: IsMuon efficiency and misidentification probabilities, as a function of momen-tum, in ranges of transverse momentum: εIM (a), ℘IM(p → µ) (b), ℘IM(π → µ) (c) and℘IM(K → µ) (d).

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MagnePc field effect

•  The LHCb magnet has a bending power of 4Tm. Since p(GeV) = 0.3B(T)R(m) we correct for the Lorentz force due to the magnet field (along the y axis) by giving a “kick” to px of ±1.2 GeV;

•  (x,y)µ,π,K,πsl required to be in the acPve regions of tracking detectors;

•  Same for (x,y)µ with respect to muon staPons 11 26/11/13 Marco Fiore

Trigger

•  A parametric descripPon of trigger lines is not straighworward. The reason is that informaPon available in the Full SimulaPon are not accessible in parameterized Monte Carlo;

•  Therefore, we limit our studies to trigger lines which can be reproduced by simple cuts on signal parPcles;

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k-‐factor matching


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Conclusions

•  Semileptonic B decays offer the highest staPsPcal power; •  The fast simulaPon is very useful to study systemaPc

uncertainPes, however it needs more tuning (work in progress);

•  In principle this could also be a very important tool for the whole collaboraPon, provided it is generalized;

26/11/13 17

Summary •  In my first year I worked on the development of a fast and simplified Monte Carlo;

•  Status of my work was presented regularly at the Ferrara LHCb group, to the LHCb SimulaPon Working Group and to the Semileptonic Asymmetry Working Group;

•  I also worked on the data acquisiPon system of a prototype for the LHCb Muon Detector to be installed axer the second LHC long shutdown;

•  In October I performed tests on the Front End electronics of the LHCb Muon Detector, to be concluded in December;


Other AcPviPes •  I parPcipated to the Hadron Collider Summer School in Goeyngen, Germany where I gave a seminar talk about “Bayesian Inference”; to the Cabeo School in Ferrara about Physics beyond Standard Model and to a detector school in Legnaro (PD);

•  I parPcipated to the InternaPonal Conference on B-‐Physics at Hadron Machines (Beauty) in Bologna;

•  I aDended three ParPcle Physics seminars at the Physics Department in Ferrara;

•  I aDended the LHCb Analysis&Soxware Week at CERN and will aDend the next LHCb week in December



Backup Slides

Muon Detector Front-‐End Board CalibraPon


LHCb (muon) detector


A MulP Wire ProporPonal Chamber

•  Gas detector (Ar, CO2, CF4); •  The signal can be read on: – Wire: anode à negaPve charge collecPon – Pad: cathode à posiPve charge collecPon

•  LHCb MWPCs have both readings mode – FEBs for anodic (negaPve) reading [AN] – FEBs for cathodic (posiPve) reading [CP]

•  For the short LHC upgrade it’s needed to test the spare FEBs (≈ 800)

26/11/13 23 Marco Fiore

A Front-‐End Board of the Muon Detector

•  Each Region(R1,R2,R3,R4) of MD has a different number of FEBs per MWPC;

•  Each FEB has 16 channels; •  One FEB can be used in anodic or cathodic readings; •  One FEB is a PCB with three chips:

2 CARIOCAs: analog part (amplificaPon and discriminaPon 8+8) 1 DIALOG: digital part (logical combinaPon of discriminated signal, internal

counter for measuring the rate)

T O P

B O T T O M


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FEBs TEST: goal

1.  Check if they are workable; 2.  Measurement of the electronic noise –  Dark Rate Threshold scan -  EvaluaPon of the RMS

3.  FEB Ranking; 4.  SubsPtuPon of broken or noisy FEBs

currently on the detector with the tested ones


FEBs test: setup

•  a tester MWPC [M2R2] because it has the most complicated reading approach;

•  6AN + 8CP = 14FEBs connected to the tester; •  The tests were done only in the CP posiPons, because we just need the FEB to see a MWPC;

•  Readout electronics; •  Power supply (HV àM2R2 and LV à FEB)


1) Tester MWPC

2) 4 FEBs (right side) connected to tester MWPC

3a) Readout electronics 4) PC for data acquisiPon

3b) LV Power supply

27 Marco Fiore

Data AcquisiPon

DIALOG 0 AN 9 Ch Thres Rate(KHz) Mean RMS 01 071 004111.34 71.01 4.06 02 071 002935.45 70.58 4.03 03 065 003117.48 65.31 3.75 04 075 001079.69 74.70 2.88 05 063 000944.92 62.92 2.90 06 066 000825.69 66.17 2.59 07 067 001108.34 66.76 2.59 08 066 000777.94 66.27 2.02 09 069 001859.37 68.77 3.75 10 070 001388.11 69.76 2.88 11 061 001543.64 60.63 3.45 12 068 002721.11 67.87 3.16 13 074 001082.28 74.17 2.95 14 068 000457.75 68.20 2.01 15 068 001995.69 68.13 3.17 16 067 000485.21 66.39 2.04

1) Threshold scan: for each threshold the dark rate is measured; 2) The mean and RMS of the Rate DistribuPon as a funcPon of the threshold are evaluated;

3) As a reference we took the <RMS> of all Channels of all FEBs; 4) Then we evaluated the pull defined as:

!

pulli =RMSi " RMS

#tot26/11/13 28 Marco Fiore

Data Analysis AN (315 FEBs)

•  STRATEGY: in each FEB we evaluate the pulli (i=1,…,16) mean value and rank the FEBs in four categories: – A: very good (pull <= -‐0.30) à 30 FEBs = 10% – B: good (-‐0.30 > pull >= 0.15) à 241 FEBs = 76% – C: noisy (0.15 > pull >= 2.00) à 33 FEBs = 10% – D: very noisy (pull >= 2.00) à 11 FEBs = 4%


Data Analysis CP (301 FEBs)

•  STRATEGY: in each FEB we evaluate the pulli (i=1,…,16) mean value and rank the FEBs in four categories: – A: very good (pull <= -‐0.30) à 59 FEBs = 20% – B: good (-‐0.30 > pull >= 0.15) à 141 FEBs = 47% – C: noisy (0.15 > pull >= 2.00) à 97 FEBs = 32% – D: very noisy (pull >= 2.00) à 4 FEBs = 1%


Conclusion

•  616 FEBs were tested; •  We studied the electronic noise and classified them;

•  More than 70% of them can be considered good;

•  We are aware that CP FEBs are more noisy; •  Residual FEBs will be tested in December 2013


Documents

Studiesof Semileptonic(B Decays(at( LHCb(