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0 baryon at LHCb The UNIVERSITY OF BIRMINGHAM SCHOOL OF PHYSICS AND ASTRONOMY SEMINAR 21/10/15 Peter Griffith University of Birmingham, UK 1 Contents B-physics at the LHC Heavy baryons in B-physics The LHCb detector 0

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SLIDE 1

The Λ𝑐

0 baryon at LHCb

Peter Griffith University of Birmingham, UK

1

UNIVERSITY OF BIRMINGHAM SCHOOL OF PHYSICS AND ASTRONOMY SEMINAR 21/10/15

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SLIDE 2

Contents

  • B-physics at the LHC
  • Heavy baryons in B-physics
  • The LHCb detector
  • Understanding the Λ𝑐

0 baryon at the LHC

  • Key measurements
  • FCNC decays with Λ𝑐
  • Λ𝑐

0 β†’ π‘žπΏβˆ’πœˆ+πœˆβˆ’ in detail

  • Summary

University of Birmingham 21/10/15 Lb baryon at LHCb Peter Griffith 2

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SLIDE 3

Flavour physics, SM and BSM

University of Birmingham 21/10/15 Lb baryon at LHCb Peter Griffith 3

The very successful Standard Model Dark Matter Dark Energy Gravity Hierarchy Problem Matter/antimatter asymmetry

? ? ? ? ?

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SLIDE 4

B-physics at LHCb:

  • B-physics presents many ways to test and

constrain the SM

  • Excellent probes for New Physics

& precise measurements of SM

  • CP measurements
  • FCNC observables (bs->ll etc.)
  • New intermediate states/particles

Lb baryon at LHCb Peter Griffith 4 University of Birmingham Seminar

reconstructed decay 𝐢 β†’ π‘Œ 3872 𝐿 LHCb |π‘Š

𝑣𝑐| measurement

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SLIDE 5

B-physics at LHCb:

  • Abundant b-quark production at the LHC
  • 𝜏 π‘ž

π‘ž β†’ 𝑐 𝑐X ~ 80πœˆπ‘

  • ~ 100,000 𝑐

𝑐 pairs per second

  • 40% of heavy quark production within the acceptance of LHCb
  • Production fraction,

𝑔Λ𝑐 𝑔𝑒 ~0.4 – plenty of Λ𝑐 0′𝑑 at the LHC! (20% of b hadrons)

  • Λ𝑐

0 has half integer spin – opens the door for unique measurements

University of Birmingham 21/10/15 Lb baryon at LHCb Peter Griffith 5

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SLIDE 6

The LHCb detector

University of Birmingham 21/10/15 Lb baryon at LHCb Peter Griffith 6

VELO - high precision tracking and tagging RICH – large background rejection from PID Extensive muon detection system with clean muon triggering Trackers

  • ~4𝑛𝑛 from beam
  • able to reconstruct secondary

vertices (B meson flight distance ~10𝑛𝑛)

Magnet Calorimeters

𝑃(1𝑛𝑛)

  • SPD
  • PD
  • ECAL
  • HCAL
  • 4Tm
  • Polarity regularly

switched to cancel systematic effects

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SLIDE 7

Data taking at LHCb

  • Total amount of data after Run1: 3π‘”π‘βˆ’1
  • ~1π‘”π‘βˆ’1 in 2011 < ΞΊ > ~2.7𝑓32 π‘‘π‘›βˆ’2π‘‘βˆ’1
  • ~2π‘”π‘βˆ’1 in 2012 < ΞΊ > ~4.0𝑓32 π‘‘π‘›βˆ’2π‘‘βˆ’1
  • Comparatively low
  • LHCb employs β€˜lumi levelling’ – constant

rather than high instantaneous luminosity preferred.

  • Some precision measurements require very

well known luminosity

  • PID system becomes β€˜saturated’ at higher

luminosities

University of Birmingham 21/10/15 Lb baryon at LHCb Peter Griffith 7

LHCb Atlas/CMS

~5 𝑙𝐼𝑨 read out rate to disk (1 𝑙𝐼𝑨 originally planned )

High operational efficiency (~2% deadtime)

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SLIDE 8

Λ𝑐

0 at LHCb

Interesting measurements and discoveries

University of Birmingham 21/10/15 Lb baryon at LHCb Peter Griffith 8

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SLIDE 9

Measuring |π‘Š

𝑣𝑐| with Λ𝑐 0 β†’ π‘žπœ‰πœˆ

  • Previous inclusive measurements by Babar and Belle
  • Large disagreement between inclusive and exclusive

measurements – new particle with right-handed coupling?

University of Birmingham 21/10/15 Lb baryon at LHCb Peter Griffith 9

πœ—π‘†~ βˆ’ 0.2 β†’ new particle would have ~20% coupling strength of the W boson π‘Š

𝑣𝑐 2

π‘Š

𝑑𝑐 2 =

𝐢 Λ𝑐

0 β†’ π‘žπœˆβˆ’ πœ‰πœˆ

𝐢 Λ𝑐

0 β†’ Λ𝑑 +πœˆβˆ’ πœ‰πœˆ

𝑆𝐺𝐺 Where 𝑆𝐺𝐺 is the ratio of relevant form factors

Λ𝑐

0 β†’ π‘žπœˆβˆ’ πœ‰πœˆ candidates are

reconstructed using m𝑑𝑝𝑠𝑠 = π‘›β„Žπœˆ

2 + π‘žβŠ₯ 2 + π‘žβŠ₯

Visible mass Transverse momentum of β„Žπœˆ pair

Candidates with 100π‘π‘“π‘Š/𝑑2 uncertainty are selected

New LHCb measurement removes the need for a new particle. But why the initial disagreement?

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SLIDE 10

Resonances in Λ𝑐

0 β†’ 𝐾/πœ”π‘žπΏβˆ’

University of Birmingham 21/10/15 Lb baryon at LHCb Peter Griffith 10

  • Two resonances observed in Λ𝑐

0 β†’ 𝐾/πœ”π‘žπΏβˆ’

  • Consistent with pentaquark state with

content quark cuud

Six dimensional amplitude fit. Using just Ξ›βˆ— states is not adequate. Two additional states required

𝑸𝒅(πŸ“πŸ“πŸ”πŸ) 𝑸𝒅(πŸ“πŸ’πŸ—πŸ) Mass (Meπ‘Š/𝑑2) 4449.8 Β± 4.2 4380Β±37 𝐾𝑄 5 2

+

3 2

βˆ’

Significance, 𝜏 12 9

arXiv:1507.03414

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SLIDE 11

Measurement of the Λ𝑐

0 polarisation

  • First of its kind at a hadron collider
  • Uses Λ𝑐

0 β†’ J/πœ”Ξ› decays

  • Decay of a spin

1 2 particle into spin 1 and 1 2

particles

University of Birmingham 21/10/15 Lb baryon at LHCb Peter Griffith 11

Decay amplitudes

Transverse production polarisation: 0.06Β±0.07Β±0.02

Appears to be small (O(10%) or less)

  • Not so favourable for studying photon helicity in

Λ𝑐

0 β†’ Λ𝛿 and Λ𝑐 0 β†’ Ξ›βˆ—π›Ώ decays if small ☹

Angular analysis performed on all three angles to Transverse polarisation parameter Angular distributions

downstream long

arXiv:1302.5578

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SLIDE 12

𝛭𝑐

0 lifetime measurement

  • Lifetime measured with 𝛭𝑐

0 β†’ 𝐾/πœ”π‘žπΏβˆ’

decays

  • Relative to 𝐢0 β†’ 𝐾/πœ”πœŒ+πΏβˆ’ lifetime
  • 1π‘”π‘βˆ’1 of data

University of Birmingham 21/10/15 Lb baryon at LHCb Peter Griffith 12

πœΞ›π‘

𝑀𝐼𝐷𝑐 =

1.482 Β± 0.018 Β± 0.012 ps

Acceptance ratio of Λ𝑐

0 and 𝐢0

Decay time distributions for Λ𝑐

0 and 𝐢0

Unprecedented precision dominates world average

arXiv:1509.00292

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SLIDE 13

Rare Decays at LHCb

Lb baryon at LHCb Peter Griffith 13

  • LHCb ideal for studying rare FCNC decays
  • f mesons and baryons, e.g. 𝑐 β†’ 𝑑
  • High resolution tracking
  • High performance PID
  • Muon signals β€˜clean’ at LHCb
  • FCNC’s can occur through

loops

  • Highly suppressed
  • Sensitive to new physics e.g.

additional diagrams from new BSM particles in loops

  • Numerous observables – many

very sensitive to NP

𝜈+ πœˆβˆ’ 𝑐 𝑑 𝜈+ πœˆβˆ’ 𝑐 𝑑

University of Birmingham 21/10/15

An effective field theory is employed

𝜈+ πœˆβˆ’ 𝑐 𝑑 𝜈+ πœˆβˆ’ 𝑐 𝑑

Operators (local interaction terms) Wilson coefficients

All Wilson coefficients calculable β†’ predictive NP can be seen in deviations of Wilson coefficients

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SLIDE 14

Λ𝑐

0 β†’ Ξ› 𝜈+πœˆβˆ’ Branching ratio measurement

Lb baryon at LHCb Peter Griffith 14

  • Previously measured at CDF
  • No signal observed at low π‘Ÿ2 at either CDF or LHCb but results consistent with SM
  • Now updated to 3π‘”π‘βˆ’1, with angular analysis

LHCb-PAPER-2013-025

University of Birmingham 21/10/15

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SLIDE 15

𝛭𝑐

0 β†’ 𝛭 𝜈+πœˆβˆ’ 3π‘”π‘βˆ’1 update

  • First evidence of the signal at low π‘Ÿ2! (3𝜏)
  • Slight deviation from SM predictions – similar

to other 𝑐 β†’ π‘‘π‘šπ‘š measurements

  • Forward backward asymmetries measured

University of Birmingham 21/10/15 Lb baryon at LHCb Peter Griffith 15

arXiv:1503.07138

BR as a function of π‘Ÿ2 Leptonic 𝐡𝐺𝐢 Hadronic 𝐡𝐺𝐢

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SLIDE 16

Λ𝑐

0 β†’ π‘žπΏβˆ’πœˆ+πœˆβˆ’

Branching fraction measurement

University of Birmingham 21/10/15 Lb baryon at LHCb Peter Griffith 16

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SLIDE 17

Λ𝑐

0 β†’ π‘žπΏβˆ’πœˆ+πœˆβˆ’

  • Rare FCNC decay through excited states
  • Likely dominated by Λ𝑐

0 β†’ Ξ›βˆ—(1520)𝜈+πœˆβˆ’

  • 𝑛(π‘žπΏβˆ’) structure known
  • β€˜Unobserved’

University of Birmingham 21/10/15 Lb baryon at LHCb Peter Griffith 17

Non-resonant Λ𝑐

0 β†’ π‘žπΏβˆ’πœˆ+πœˆβˆ’

𝑛(π‘žπΏβˆ’) in Λ𝑐

0 β†’

𝐾/πœ” β†’ 𝜈+πœˆβˆ’ π‘žπΏβˆ’

  • Very limited theoretical

knowledge

SUSY Wilson coefficients from M. J. Aslam, Y.-M. Wang and C.-D. Lu,

  • Phys. Rev. D 78, 114032 (2008)

Branching fraction predictions (in units of 10e6) for SCA (SM1) and MCN (SM2) models. (a and b without and with LD charmonium contributions respectively) arXiv:1108.6129

All variables blinded in mass region of the 𝚳𝐜

𝟏

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SLIDE 18

𝛭𝑐

0 β†’ π‘žπΏβˆ’πœˆ+πœˆβˆ’ branching fraction measurement

  • Measured relative to Λ𝑐

0 β†’ 𝐾/πœ”π‘žπΏβˆ’

  • Simpler calculation
  • Cancellation of systematic effects
  • Lack of theoretical and experimental knowledge
  • β†’Lots of β€˜correcting’ to be done

University of Birmingham 21/10/15 Lb baryon at LHCb Peter Griffith 18

MC DATA 𝑛(π‘žπΏβˆ’) in Λ𝑐

0 β†’ 𝐾/πœ”π‘žπΏβˆ’

No clean separation

  • f Ξ›βˆ—(1520)

MC is produced with only phase- space kinematics Experimentally motivated model for decay structure would need full amplitude analysis

Dimuon mass squared Λ𝑐

0 β†’ π‘žπΏβˆ’πœˆ+πœˆβˆ’ MC

β€˜Typical’ differential decay rate (𝐢0 β†’ πΏβˆ—0𝜈+πœˆβˆ’) as function of dimuon mass squared

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SLIDE 19

𝛭𝑐

0 β†’ π‘žπΏβˆ’πœˆ+πœˆβˆ’ branching fraction measurement

  • Measured relative to Λ𝑐

0 β†’ 𝐾/πœ”π‘žπΏβˆ’

  • Simpler calculation
  • Cancellation of systematic effects
  • Lack of theoretical and experimental knowledge
  • β†’Lots of β€˜correcting’ to be done

University of Birmingham 21/10/15 Lb baryon at LHCb Peter Griffith 19

MC DATA 𝑛(π‘žπΏβˆ’) in Λ𝑐

0 β†’ 𝐾/πœ”π‘žπΏβˆ’

No clean separation

  • f Ξ›βˆ—(1520)

MC is produced with only phase- space kinematics Experimentally motivated model for decay structure would need full amplitude analysis

Dimuon mass squared Λ𝑐

0 β†’ π‘žπΏβˆ’πœˆ+πœˆβˆ’ MC

β€˜Typical’ differential decay rate (𝐢0 β†’ πΏβˆ—0𝜈+πœˆβˆ’) as function of dimuon mass squared Could see large signal where MC statistics are relatively low

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SLIDE 20

Analysis strategy:

University of Birmingham 21/10/15 Lb baryon at LHCb Peter Griffith 20

Trigger Stripping Selection The LHCb dataflow

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SLIDE 21

Analysis strategy:

University of Birmingham 21/10/15 Lb baryon at LHCb Peter Griffith 21

Trigger Stripping Selection

Offline Loose cuts to minimise kinematic biases Large mass windows accept full kinematic phase space

The LHCb dataflow

  • DecayTreeFitter
  • Cuts
  • Particle

identification

  • Neural Network

Muon triggers only at L0

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SLIDE 22

Analysis strategy:

University of Birmingham 21/10/15 Lb baryon at LHCb Peter Griffith 22

Trigger Stripping Selection

Offline Loose cuts to minimise kinematic biases Large mass windows accept full kinematic phase space

The LHCb dataflow

  • DecayTreeFitter
  • Cuts
  • Particle

identification

  • Neural Network

Muon triggers only at L0

Imposes kinematic constraints based

  • ff decay chain to

final state Proton π‘žπ‘ˆ > 500π‘π‘“π‘Š Λ𝑐

0 𝑀𝑒𝑦 πœ“2/𝐸𝑝𝐺 < 5.0

π‘Ÿ2 < 17.6 π»π‘“π‘Š2

Proton π‘žπ‘ˆ background vs signal from neural net output

500 MeV

Cuts on the `probNN` variables Kaon:

  • Probability of being kaon > 0.2
  • Probability of being proton < 0.8

Proton:

  • Probability of being proton > 0.2
  • Probability of being kaon< 0.8
  • Probability of being pion < 0.7

Training Samples:

  • Background: Λ𝑐

0 β†’ 𝐾/πœ”π‘žπΏβˆ’ sideband (> 6 𝐻𝑓V)

  • Signal: Λ𝑐

0 β†’ π‘žπΏβˆ’πœˆ+πœˆβˆ’ MC

Most powerful variables:

  • DecayTreeFitter πœ“2
  • Proton π‘žπ‘ˆ
  • πΏπ‘π‘π‘œ 𝐽𝑄 πœ“2

Optimised with β€˜punzi figure of merit’

𝑑 𝐢+𝜏

2

𝜏 chosen to be 5

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SLIDE 23

Analysis strategy:

University of Birmingham 21/10/15 Lb baryon at LHCb Peter Griffith 23

Trigger Stripping Selection

Offline Loose cuts to minimise kinematic biases Large mass windows accept full kinematic phase space

The LHCb dataflow

  • DecayTreeFitter
  • Cuts
  • Particle

identification

  • Neural Network

Muon triggers only at L0

Imposes kinematic constraints based

  • ff decay chain to

final state Proton π‘žπ‘ˆ > 500π‘π‘“π‘Š Λ𝑐

0 𝑀𝑒𝑦 πœ“2/𝐸𝑝𝐺 < 5.0

π‘Ÿ2 < 17.6 π»π‘“π‘Š2

Proton π‘žπ‘ˆ background vs signal from neural net output

500 MeV

Cuts on the `probNN` variables Kaon:

  • Probability of being kaon > 0.2
  • Probability of being proton < 0.8

Proton:

  • Probability of being proton > 0.2
  • Probability of being kaon< 0.8
  • Probability of being pion < 0.7

Training Samples:

  • Background: Λ𝑐

0 β†’ 𝐾/πœ”π‘žπΏβˆ’ sideband (> 6 𝐻𝑓V)

  • Signal: Λ𝑐

0 β†’ π‘žπΏβˆ’πœˆ+πœˆβˆ’ MC

Most powerful variables:

  • DecayTreeFitter πœ“2
  • Proton π‘žπ‘ˆ
  • πΏπ‘π‘π‘œ 𝐽𝑄 πœ“2

Optimised with β€˜punzi figure of merit’

𝑑 𝐢+𝜏

2

𝜏 chosen to be 5

slide-24
SLIDE 24

University of Birmingham 21/10/15 Lb baryon at LHCb Peter Griffith 24

Analysis strategy: acceptance and efficiency

Geometric acceptance Stripping/ selection Trigger PID Neural Net

Between 10 and 400 mrad

PID behaviour difficult to replicate in MC. Highly dependent on kinematics Evaluated using β€˜calibration samples’

  • Data containing high rate, well understood decays.
  • Calibration samples binned in kinematic variables
  • Essentially a β€˜look up table’ for MC event efficiency

PID efficiency is not stable

  • ver time and changes

with magnet polarity β†’ needs to be treated separately Strong dependence on kinematics for most selections and acceptances β†’ issue with data/MC mismatch

πœ— = π‘‚π‘žπ‘π‘‘π‘‘ 𝑂

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SLIDE 25

Dealing with MC discrepancies

Correcting 𝚳𝐜

𝟏 production kinematics

  • Use another Ξ›b

0 mode?

  • Only 𝚳𝐜

𝟏 β†’ 𝑲/πŽπ’’π‘³βˆ’ has similar phase-

space coverage

  • Need strong cuts to achieve pure sample

𝚳𝐜

𝟏 β†’ π’’π‘³βˆ’π‚ + π‚βˆ’ decay structure

  • Correlation between all angles and

the two masses

  • Need model of at least 5D to account

for all correlations* πœ— π‘‘π‘π‘‘Ξ˜π‘, π‘‘π‘π‘‘Ξ˜π‘š, Ξ”πœš, 𝑛 π‘žπΏβˆ’ , π‘Ÿ2

  • Needs to perform well with high no.
  • f dimensions and finite MC stats

University of Birmingham 21/10/15 Lb baryon at LHCb Peter Griffith 25

𝚳𝐜

𝟏 * 7D if we do not assume negligible production polarisation

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SLIDE 26

Dealing with MC discrepancies

Correcting 𝚳𝐜

𝟏 production kinematics

  • Use LHCb’s fΞ›/𝑔

𝑒 measurement

  • Measured as function of π‘„π‘ˆ and πœƒ
  • Can use well known 𝐢𝑒 decay to extract

Λ𝑐

0 kinematic correction factor

  • 𝐢0 β†’ 𝐾/πœ”πΏπ‘‘

←obtain clean sample with loose cuts

University of Birmingham 21/10/15 Lb baryon at LHCb Peter Griffith 26

Fit 𝐢0 π‘„π‘ˆ and πœƒ In data* and MC Small corrections on 𝐢0 MC Fit 𝐢0 π‘„π‘ˆ and πœƒ at β€˜generator level’ Fit Λ𝑐

0 π‘„π‘ˆ and πœƒ

at β€˜generator level’

π‘₯ = 𝑔Λ𝑐 𝑔

𝑒

Pπ‘ˆ, πœƒ Γ— π‘žπ‘’π‘”πΆ0 π‘„π‘ˆ, πœƒ π‘žπ‘’π‘”Ξ›π‘

0 π‘„π‘ˆ, πœƒ Γ—

1 π‘₯𝐢0 π‘„π‘ˆ, πœƒ

doi:10.1007/JHEP08(2014)143

LHCb LHCb *background subtracted using fit model to 𝑛(𝐢0) (s-weighting)

Corrected MC MC Background subtracted data

Perfect agreement not expected. Corrects for production kinematics

  • nly
  • Physics motivated
  • Independent of Λ𝑐

0 decay

  • Works!
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SLIDE 27

Dealing with MC discrepancies

Finding a β€˜goldilocks’ model

(or an adventure in failed techniques!)

  • Always a trade off between accuracy

and speed

  • Speed important when it comes to

systematics (e.g Toy MC’s)

  • Need to find a trade-off that’s β€˜just

right’ 𝚳𝐜

𝟏 β†’ π’’π‘³βˆ’π‚ + π‚βˆ’ decay structure

  • Correlation between all angles and

the two masses

  • Need model of at least 5D to account

for all correlations* πœ— π‘‘π‘π‘‘Ξ˜π‘, π‘‘π‘π‘‘Ξ˜π‘š, Ξ”πœš, 𝑛 π‘žπΏβˆ’ , π‘Ÿ2

  • Needs to perform well with high no.
  • f dimensions and finite MC stats

University of Birmingham 21/10/15 Lb baryon at LHCb Peter Griffith 27

* 7D if we do not assume negligible production polarisation

slide-28
SLIDE 28

Dealing with MC discrepancies

Kernel density estimation?

University of Birmingham 21/10/15 Lb baryon at LHCb Peter Griffith 28

  • Phase space populated with kernels

to estimate the pdf.

  • A form of β€˜data-smoothing’
  • Good for low statistics/many dimensions
  • Estimate density in 1D projections
  • Then perform correlated multi-

dimensional KDE on full phase-space

  • Perform boundary correction

Good: Incredibly accurate!

Slices through each plain of the multi-dimensional phase- space, unfolded into 1 dimension, showing ratio between MC after full reconstruction/selection and generator level MC weighted with the KDE pdf.

Bad: Incredibly CPU intensive!

slide-29
SLIDE 29

Dealing with MC discrepancies

University of Birmingham 21/10/15 Lb baryon at LHCb Peter Griffith 29

Good: Very fast!

Comparison

  • f

weighted generator level MC and full selection MC

Bad: Not so accurate… Neural Network?

slide-30
SLIDE 30

Dealing with MC discrepancies - efficiency

Legendre polynomials

University of Birmingham 21/10/15 Lb baryon at LHCb Peter Griffith 30

  • Reweighting function generated for each event.
  • Models acceptance effects assuming flat at generator level
  • True for angles (spherically isotropic in phase-space MC)
  • Not true for mass
  • β†’ Model both MC samples and perform ratio of efficiency functions

πœ—π‘“π‘€π‘“π‘œπ‘’ π‘‘π‘π‘‘Ξ˜π‘, π‘‘π‘π‘‘Ξ˜π‘š, Ξ”πœšβ€², 𝑛 π‘žπΏβˆ’ 2β€², π‘Ÿ2β€² =

𝑗,π‘˜,𝑙,π‘š,𝑛

π‘‘π‘—π‘˜π‘™π‘šπ‘›π‘„π‘— cosπœ„π‘š 𝑄

π‘˜ cosπœ„π‘ 𝑄𝑙 Ξ”πœšβ€² π‘„π‘š 𝑛 π‘žπΏβˆ’ 2β€² 𝑄 𝑛(π‘Ÿ2β€²)

π‘‘π‘—π‘˜π‘™π‘šπ‘› = 𝑑0π‘π‘—π‘˜π‘™π‘šπ‘›(2𝑗 + 1)(2π‘˜ + 1)(2𝑙 + 1)(2π‘š + 1)(2𝑛 + 1) π‘π‘—π‘˜π‘™π‘šπ‘› = 1 π‘‚π‘“π‘€π‘“π‘œπ‘’π‘‘

π‘‚π‘“π‘€π‘“π‘œπ‘’π‘‘

𝑄𝑗 cosπœ„π‘š 𝑄

π‘˜ cosπœ„π‘ 𝑄𝑙 Ξ”πœšβ€² π‘„π‘š 𝑛 π‘žπΏβˆ’ 2β€² 𝑄 𝑛(π‘Ÿ2β€²)

𝑑0 is chosen to be Β½ and controls

  • verall integral. Mostly arbitrary as

whole model is normalised to the integrated phase-space efficiency

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SLIDE 31

University of Birmingham 21/10/15 Lb baryon at LHCb Peter Griffith 31

Dealing with MC discrepancies - efficiency

Fast enough and accurate enough! π‘‘π‘π‘‘πœ„π‘š π‘‘π‘π‘‘πœ„π‘ Ξ”πœš π‘Ÿ2 𝑛 π‘žπΏβˆ’ 2 5𝐸 scan Efficiency correction now largely independent

  • f MC model

Systematic uncertainty evaluated with `bootstrapping`

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SLIDE 32

Calculating

𝐢 Λ𝑐

0β†’π‘žπΏβˆ’πœˆ+πœˆβˆ’

𝐢(Λ𝑐

0→𝐾/πœ”π‘žπΏβˆ’)

𝑂 = 𝑗

π‘₯𝑗 πœ—π‘—

β†’

𝐢 Λ𝑐

0β†’π‘žπΏβˆ’πœˆ+πœˆβˆ’

𝐢(Λ𝑐

0→𝐾/πœ”π‘žπΏβˆ’) =

𝑂 Λ𝑐

0β†’π‘žπΏβˆ’πœˆ+πœˆβˆ’

𝑂(Λ𝑐

0→𝐾/πœ”π‘žπΏβˆ’) =

𝑗 π‘₯𝑗

𝜈𝜈/πœ—π‘— 𝜈𝜈

π‘˜ π‘₯π‘˜

𝐾/πœ”/πœ—π‘˜ 𝐾/πœ”

University of Birmingham 21/10/15 Lb baryon at LHCb Peter Griffith 32

Corrected yield Event efficiency correction Event weight from background subtraction

Systematics propagation:

𝜏 𝑂 =

𝑗

π‘₯𝑗 πœ—π‘—

2

β†’ πœπ‘’π‘π‘’ 𝑂 = 𝜏 𝑂 2 +

𝑂 𝑂𝑝𝑐𝑑 πœπ‘‘β„Žπ‘π‘žπ‘“(𝑂) + …

Includes sources of systematic uncertainty on acceptance/efficiency Other sources, e.g yield extraction model uncertainties

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SLIDE 33

Sources of systematic uncertainty

University of Birmingham 21/10/15 Lb baryon at LHCb Peter Griffith 33

Λ𝑐

0 lifetime

Λ𝑐

0 kinematics

correction Efficiency model + MC statistics Particle Identification Yield extraction fit

Absolute uncertainty on Λ𝑐

0 β†’ π‘žπΏβˆ’πœˆ+πœˆβˆ’

Relative uncertainty near negligible thanks to LHCb and CMS lifetime measurements LHCb unofficial

Corrected MC MC Background subtracted data

PID systematic is combination

  • f two uncertainties:
  • Statistical uncertainty from

bin populations of correction table

  • Uncertainty from bin

widths ( can hide fine structure in PID efficiency space)

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SLIDE 34

Yield extraction

University of Birmingham 21/10/15 Lb baryon at LHCb Peter Griffith 34

Λ𝑐

0 β†’ 𝐾/πœ”π‘žπΏβˆ’

LHCb unofficial

Signal: Double crystal ball π‘ͺ𝒕

𝟏 and π‘ͺ𝟏 backgrounds: DCB (opposite sign tails)

Combinatorial: exponential 𝐢𝑑

0 β†’ 𝐿+πΏβˆ’πœˆ+πœˆβˆ’ yield

constrained by fitting mass reflection in upper sideband Swap proton β†’ kaon 𝐢𝑑

0 pdf parameters constrained from MC.

Yield constrained from data using: 𝐽 =

𝑛𝑏 𝑛𝑑

𝑔 𝑦 𝐢𝑑𝑒𝑦 ≑

𝑛𝑏 𝑛𝑐

𝑔 𝑦 𝐢𝑑𝑒𝑦 +

𝑛𝑑 𝑛𝑐

𝑔 𝑦 𝐢𝑑𝑒𝑦

𝑛𝑏 𝑛𝑐 𝑛𝑑

Take side band – clean of Λ𝑐 Λ𝑐

0 β†’ π‘žπΏβˆ’πœˆ+πœˆβˆ’ to be

unblinded in the coming weeks followed by publication

  • stay tuned!
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SLIDE 35

Summary - Ξ›b

0 β†’ π‘žπΏβˆ’πœˆ+πœˆβˆ’

  • First official observation and branching fraction measurement
  • Blind analysis
  • Blind in another sense!
  • No experimental knowledge
  • Almost no theoretical knowledge
  • 𝑐 β†’ π‘‘π‘šπ‘š studies currently a β€˜hot topic’
  • Opens the door for further measurements with Run2 data
  • CP-asymmetry
  • Forward-backward asymmetry
  • Amplitude analysis
  • Still in progress but almost there
  • Scheduled for review this winter

University of Birmingham 21/10/15 Lb baryon at LHCb Peter Griffith 35

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SLIDE 36

Summary - Ξ›b

0 physics at LHCb

  • Some of the most precise Λ𝑐

0 measurements yet

  • Still a lot less well known than the mesonic b-sector
  • Anomalies seen in 𝑐 β†’ π‘‘π‘šπ‘š decays at LHCb prompt further study of these hadronic counterparts
  • Recent LHCb results from Λ𝑐

0 rare decays hint at similar pattern of SM discrepancy!

  • To take full advantage of the Λ𝑐

0 sector requires a lot of groundwork

  • Experimentally: πœΞ›π‘

0,

𝑔Λ𝑐 𝑔𝑒 , polarisation, branching fraction measurements of ideal control channels , e.g

Λ𝑐

0 β†’ 𝐾/πœ”π‘žπΏβˆ’, Λ𝑐 0 β†’ 𝐾/πœ”π‘žπœŒβˆ’

  • Theoretically: Form factors, predictions (BR, 𝐡𝐺𝐢) etc.
  • Some surprises, e.g discovery of states consistent with pentaquark in Λ𝑐

0 β†’ 𝐾/πœ”π‘žπΏβˆ’!

University of Birmingham 21/10/15 Lb baryon at LHCb Peter Griffith 36

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SLIDE 37

Thanks for listening!

Lb baryon at LHCb Peter Griffith 37 University of Birmingham 21/10/15 Fig1: penguin decay