LHCb

1

Status and physics at LHCb
Vienna Central European Seminar Particle Physics
and the LHC Jeroen van Tilburg Physikalisches
Institut Heidelberg On behalf of the LHCb
collaboration

• Outline
• LHCb experiment and detector performance
• Selected physics results
• Outlook and summary

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New physics effects in B and D decays
Strength of indirect approach

• New particles can appear as virtual particles in
  loop and penguin diagrams.
• Indirect searches have a high sensitivity to
  effects from new particles.
• Can see NP effects before the direct searches.
• Indirect measurements can access higher scales.
• Possible to measure the phases of the new
  couplings
• New physics at TeV scale must have a flavour
  structure to provide suppression of FCNC.

? Complementary to direct searches.
3
CKM picture

• Incredible success of CKM paradigm in last
  decades.
• All measurements coherent with CKM of SM.
• Accuracy of angles determined by experiment
• Accuracy of sides determined by theoretical
  uncertainties
• But, SM fails to explain matter-antimatter
  asymmetry in the Universe
• New physics must hold additional sources of CP
  violation
• Effects are small but there is still room for NP
  effects.
• Precision measurement of CKM elements.
• Comparison between tree and penguin decays.
• Not all CKM angles well constrained (e.g. ? and
  ßs).

From CKMFitter
? CP violation and rare decays of B hadronsand
charm are the main focus of LHCb ? Large amounts
of clean data available ? Precision tests allow
to look for small effects beyond SM
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LHCb detector
LHCb made for Heavy Flavour physics

• Good vertex resolution
• Time-dependent measurements.
• Suppress background from prompt decays.
• Good particle identification
• Important for trigger, flavour tagging
• Suppress background.
• Good momentum resolution
• Mass resolution of heavy flavours.
• Suppress background.

Muon
RICH12
Calo
Tracking stations
Velo
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LHCb detector

• High B hadron production at LHC
• ?bb 284 53 ?b (vs 7 TeV) PLB 694 209
• Forward spectrometer
• Most B hadrons produced along beam axis.
• Acceptance 2 lt ? lt 5. Complementary to GPDs.
• Vertex detector close to beam.
• Easy access to planar subdetectors.

Angular coverage optimised for B-physics.
L1 cm
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Collaboration
760 members 15 countries 54 institutes
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Detector performance Luminosity

• LHCb recorded 1.1 fb-1 in 2011
• Data taking ended on 30 Oct.
• Only 340 pb-1 used for most results shown here.
• Data taken with high efficiency 90
• Offline data quality rejects lt 1
• Sub-detectors all with gt 98 active channels.

• Luminosity leveling
• LHCb already running above design lumi
• Average L31032 cm-2s-1 (nominal 21032)
• Need to cope with higher occupancies
• More pile-up average ?1.5 (nominal 0.5)
• Continuous, automatic adjustment of offset of
  colliding beams.
• Allows optimal conditions throughout a fill.

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Detector performance vertex resolution
VELO tomography with hadronic vertices
Sensors

• VELO sensors only 8 mm from beam.
• Impact parameter resolution 12 ?mfor high pT
  tracks.
• Good primary and secondary vertex resolution.
• Suppress background from prompt decays.
• Good proper-time resolution
• Important for time-dependent measurements.

RF foil
8 mm
Beamaxis
in good agreement with simulation
Primary vertex resolution
Decay time in Bs ? J/? ?
Prompt J/y
Bs ? J/y f
LHCb-CONF-2011-049
Resolution from prompt J/? ?t 50 fs
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Detector performance PID

• Particle ID with RICH detectors
• Kaon ID efficiency 96,
• misID p?K 7
• Particle ID with Muon detector
• Muon ID efficiency 97.31.2 (pgt4 GeV/c)
• misID p?µ 2.4, p?µ 0.18

• Flavour tagging
• Tagging of production flavour (B or B)
• Important for mixing CP analyses.
• Performance calibrated using control channels
  such as B ? J/? K
• Tagging power e(1-2?)2
• (3.2 0.8) (opposite side)
• (1.3 0.4) (same side)from Bs?Ds? mixing
  analysispreliminary LHCb-CONF-2011-049

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Detector performance mass resolution
Dimuon mass spectrum

• Integrated Bdl 4 Tm
• Accurate field map and alignment
• Momentum resolution 0.40.6
• Mass resolution J/? 13 MeV
• MC 10 MeV
• ? Accurate mass measurements.

LHCb-CONF-2011-027 Preliminary
Measured B masses MeV/c2
PDG
5279.17 0.29
5279.50 0.30
5279.50 0.30
5366.30 0.60
5620.2 1.6
6277 6
World-best mass measurements! (2010 data only)
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Selected physics results
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Measurement of ?ms
LHCb-CONF-2011-50

• ?ms Bs-Bs mixing frequency using Bs?Ds?
• Flavour specific final state
• High branching ratio (0.3)
• Important to resolve the fast Bs oscillations.
• Average decay time resolution 45 fs
• Event selection based on kaon ID, track IP and
  vertex ?2
• ?ms extracted from unbinned ML fit to Bs?Ds?
  candidates
• Uses mass, decay time and flavour tagging
• Method includes now same side tagging (cf 2010
  fit)

Event yield in 340 pb-1
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Measurement of ?ms
LHCb-CONF-2011-50
Bs oscillations
Dilution of mixing amplitude from tagging and
proper time
Most precise measurement of ?ms
Preliminary
?ms17.725 0.041(stat) 0.025 (sys) ps-1
Dominant systematics uncertainty z-scale and
momentum scale
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Measurement of ?s from Bs? J/? ?/f0

• ?s interference phase between Bs mixing and
  b?ccs decay.
• Small penguin pollution.
• Bs counterpart of Bd? J/? K0.
• Small in SM ?s -0.0360.002
• Prediction from CKMfitter 2011
• New particles in box diagrams can modify measured
  phase ?s ?sSM ?sNP

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Measurement of ?s
Two decay modes
Bs? J/? ?
Bs? J/? f0(980)
LHCb-CONF-049
LHCb-CONF-051
? First seen by LHCb last winter
? Narrow ? resonance (clean) ? Vector-vector
final state (requires angular analysis)
? CP odd final state (no angular analysis) ? BR
about 20 of Bs? J/? ?
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Measurement of ?s
Angular analysis of Bs? J/? ?

• Bs? J/? ? has vector-vector final state
• Mixture of CP-odd and CP-even decay amplitudes
• Even and odd amplitudes can be disentangled
  using decay angles.

Transversity angles
Decay amplitudes used in fit
P wave
? S wave(non resonant KK-)
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Measurement of ?s
Angular analysis of Bs? J/? ?
PDF of unbinned ML fit described as
Complicated PDF 3 independent implementations in
LHCb
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Measurement of ?s
Angular analysis of Bs? J/? ?
Time and angular distributions
Main systematic errors from uncertainties in the
description of angular and decay time acceptance
and background angular distribution.
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Measurement of ?s
Result of the two fits
Bs? J/? ?
Bs? J/? f0(980)
CL contours obtained using Gs from J/?f.
Two solutions PDF insensitive to
CP-odd final state, cannot determine Gs and ?Gs
simultaneously. When using both Gs and ?Gs from
Bs?J/?f ?s -0.440.44(stat)0.02(syst)
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Measurement of ?s
Comparison with Tevatron
Combined fit
?s-0.03 0.16(stat) 0.07 (sys)
Preliminary
LHCb-CONF-2011-056

• Next steps
• Resolve ambiguity by fitting S-wave phase in
  bins of M(KK)
• Y. Xie et al., JHEP 0909074 (2009)
• Included more data (2.5 times more data
  recorded)
• Include same-side tagging (1.5x more tagging
  power)
• ? Expect 2x smaller statistical error.

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Direct CP in Bd,s?K?
Charmless charged two-body B decays
Tree
Penguin
Tree-penguin interference in Bd,s?K ? decays
allows to look for direct CP violation.

• LHCb has a very good particle identification
  capability.
• Isolate decays contributing to B-gthh (K,?,p)

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Direct CP in Bd,s?K?
Bd,s ? Kp- Clear asymmetry in raw distributions
B0 ? K p-
B0 ? K- p
LHCb-CONF-2011-042
Bs ? p K-
Bs ? p- K
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Direct CP in Bd,s?K?
Raw asymmetry has to be corrected for detector
and production asymmetry.
Detector asymmetry ? measured using charm control
samples D?D0(K?)?, D?D0(KK)? and D0?K?.

• Production asymmetry
• ? dilution of Aprod due to B mixing, lifetime
  and acceptance ?(B0)0.3, ?(Bs)-0.03
• Aprod measured using B0?J/? K(K?)

LHCb-CONF-2011-042
Interaction asymmetry
L/R detector asymmetry
Final correction factors
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Direct CP in Bd,s?K?
Preliminary LHCb-CONF-2011-042
ACP for K? modes
WA
? Most precise, and first 5? observation of CP
violation in hadronic machine.
? first 3? evidence of CP violation in Bs0?pK
Also measured BRs for CP eigenmodes
? First observation of Bs???

• Eventual goal to measure time-dependent
  asymmetries in e.g. B(s) ???-, KK-? determine
  CKM angle ? from loop decays
• Compare to ? measurements from tree decays, e.g.
• B/0?D0K/ ADSGLW and Dalitz method.
• Bs?DsK Time-dependent, tagged analysis.
• ? determine any contribution from new physics

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Search for Bd,s ? ??-
The decay Bd,s ? ??- provides sensitive probe
for New Physics.

• Very rare decay (FCNC and helicity suppressed)
  BR(Bs ? ??-)SM (3.2 0.2)x10-9
• BR(Bd ? ??-)SM (1.1 0.1)x10-10
• Sensitive to New Physics
• E.g. branching ratio in MSSM enhanced by sixth
  power of tan?

A.J.Buras, arXiv1012.1447
Exclusion regions in MSSM (NUHM)
EPJ C64 391
Blue Allowed regions for given BR measurement
Recent excitement from CDF measurement BR(Bs ?
??-) (1.8 )x10-8 (7 fb-1)
arXiv1107.2304
1.1-0.9
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Search for Bd,s ? ??-
Selection analysis strategy

• Loose selection to reduce data set
• Evaluate signal/background in a 2D-space of
• Invariant mass m??
• MVA classifier BDT combining kinematic and
  geometrical variables
• Data driven calibration through control channels
  and mass sidebands
• Normalize to channels with known BR

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Search for Bd,s ? ??-
Expected mass resolution obtained from
interpolation of dimuon resonances (from J/? to
?s) ? Verified with B ? hh events
LHCb-CONF-2011-037
Mmm for signal region in 4 bins of BDT

• Mass distribution studied in 4 bins of BDT
• Expect 1 event in each bin from SM.
• Main background from bb???X and misidentified
  B?hh-

Small excess (2 events) in most sensitive bin,
compatible with SM.
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Search for Bd,s ? ??-
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Search for Bd,s ? ??-
Normalization
The final branching ratio can be calculated as
Three complementary normalization channels with
very different systematics
Production ratio fs/fd taken from LHCbs
measurements using semileptonic and hadronic
decays. ? Smaller error than HFAG average. ?
Dominant systematic error.
LHCb-CONF-034
Values for a very compatible
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Search for Bd,s ? ??-

• No significant excess observed in 0.3 fb-1
• Upper limits (preliminary)
• BR(Bs ? ??-) lt 1.5 x 10-8 (95 CL)
• BR(Bd ? ??-) lt 5.2 x 10-9 (95 CL)
• CMS also set a limit this Summer with 1.1 fb-1
• BR(Bs ? ??-) lt 1.9 x 10-8 (95 CL)
  arXiv1107.5834
• LHCb CMS analyses combined (preliminary)
• BR(Bs ? ??-) lt 1.1 x 10-8 (95 CL)
• This is 3.4 SM value
• Most probable value 4 10-9
• Excess over SM not confirmed.

LHCb-CONF-2011-037
LHCb-CONF-2011-047
Future prospects
arXiv1108.3018
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Angular distributions in Bd ? ??-K
Flipping the b?s diagram

• Bd ? ??-K rare decay in the SM.
• BR (Bd ? ll-K) 1.0 x 10-6
• SM diagrams can be easily modified in presence of
  NP
• Angular distributions contain a lot of
  information.
• Many observables probe helicity structure of NP
• Zero crossing point of AFB(q2) well predictedin
  SM
• Hadronic uncertainties are minimized
• Measures ratio Wilson coefficients C9/C7.
• Sensitive to SUSY, graviton exchanges, extra
  dimensions

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Angular distributions in Bd ? ??-K
Results from CDF B-factories show intriguing
behaviour at low q2 ? however, precision is
limited.
arXiv1101.0470
SM C7-C7SM
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Angular distributions in Bd ? ??-K
Event selection
302 signal events

• 309 pb-1 in 2011
• 302 signal candidates
• B/S 0.3

LHCb-CONF-2011-038
Bd mass window

• Selection using BDT
• BDT variables chosen to minimize acceptance
  effects
• Angular acceptance from MC
• Trained on Bd ? J/? K for signal and mass
  sidebands for background

?(2S) veto
J/? veto
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Angular distributions in Bd ? ??-K
Angular fit

• Not enough data yet to perform full angular
  analysis.
• ? Measure in 6 q2 bins
• AFB
• Longitudinal polarisation, FL
• Differential branching fraction d?/dq2
• ? Fit AFB and FL using the 1D projections of ?l
  and ?K

Used Bd ? J/? K to validate fitting procedure
and angular acceptance
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Angular distributions in Bd ? ??-K
LHCb-CONF-2011-038
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Angular distributions in Bd ? ??-K
Data consistent with SM predictions at present
sensitivity and indicate that AFB is changing
sign as predicted by the SM (most recent CDF
result also has negative first bin
arXiv1108.0695)
Already effective in constraining NP
arXiv1111.1257

• Next steps
• Determine zero-crossing point in AFB(q2)
• Add phi angle and AT(2)
• Include full 2011 data set.
• With gt 2 fb-1 do full angular analysis

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Charm physics
Mixing established in the charm sector. Next
step look for CP violation

• No mixing excluded at 10.2?
• Presence of mixing allows to search for indirect
  CPV
• CP violation expected to be very small in SM
• Good place to look for new physics effects.

HFAG averages x(0.630.19) y(0.750.12)
Many opportunities for charm physics at LHCb
LHCb-CONF-2011-023

• Dedicated trigger lines for charm decays
• Yield of O(108) events per fb-1
• Flavour tag from charge of slow pion.
• Large statistics available
• gt 106 D0 ? KK- from D ? D0 p

D0 ? KK-
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Charm physics
LHCb-CONF-2011-054
yCP in D0?KK- (CPV in mixing)
Combined with measurement of y gives access to
CPV. Measurement (2010 only 28 pb-1)
LHCb-CONF-2011-046
A? in D0?KK- (CPV in mixing)
Measurement (2010 only 28 pb-1)
LHCb is currently updating with more statistics
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Charm physics
?ACP in D0?hh- (CPV in decay)
Preliminary
New result! Only presented last week at HCP
LHCb-CONF-2011-061
Production and detector asymmetry
cancel. Measurement (2011 only 580 pb-1)
Signifance 3.5?
First evidence of CP violation in charm sector!
Preliminary
0.4 M events
1.4 M events
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LHCb Upgrade

• Main limitation that prevents exploiting higher
  luminosity is the Level-0 (hardware) trigger
• To keep output rate lt 1 MHz requires raising
  thresholds ? hadronic yields reach plateau
• Proposed upgrade is to remove hardware trigger
  read out detector at 40 MHz (bunch crossing
  rate)Trigger fully in software in CPU farm.
• Will allow to increase luminosity by factor 5
  to 12 1033 cm-2 s-1
• Requires replacing front-end electronicsand part
  of tracking system. Planned for the long shutdown
  in 2018. Running for 10 years will then give 50
  fb-1
• Letter of Intent recently submitted to the
  LHCCPhysics case endorsed, detector RD underway
  (e.g. scintillating-fibre tracking, TOF, )

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LHCb Upgrade
LHCb Upgrade LoI CERN-LHCC-2011-001
Integrated luminosity of order 50 fb-1 allows to
measure NP effects below the level.
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Conclusion

• LHCb will have huge contribution to flavour
  physics in the years to come.
• LHCb will perform the precision measurements
  needed to see effects from new physics.
• The future will bring an even better
  understanding of our detector and much more
  statistics!
• Hope to see first hints from new physics soon.
• Expect more interesting results this Winter.

• No time to mention
• Bs ? ? ? and other radiative B decays.
• Semileptonic B decays
• Electroweak physics.
• Higgs and exotica.
• LFV tau decays
• And much, much more