Recent results from LHCb on searches for new physics M. Witek (IFJ PAN Cracow, Poland)

On behalf of the LHCb Collaboration Theory Meeting Experiment 2013 Warsaw, Poland

CERN

850 physicists 17 countries 63 institutes

LHC – Large Hadron Collider

LHCb

Atlas CMS

Alice

Outline •

Introduction

•

LHCb experiment

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Searches for New Physics

•

–

Rare decays

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CPV for beauty

–

CPV for charm

As of today 122 papers in the list at http://lhcb.web.cern.ch/lhcb/

Precision measurement of

„Standard” measurement –

•

Selected results.

X(3872) quantum numbers

Summary

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CPV and Baryogenesis

Planck satellite

 n baryon n



n baryon  n baryon n

~ O  10  10 

The source of current matter domination over antimatter is unknown. CPV is one of the three necessary conditions (Sacharow 1967)  d'   Vud Vus Vub  d The unique source of CPV in Standard Model is a single phase in the CKM matrix

    s'    Vcd  b'   V    td

Vcs Vts

 d   ˆ   Vcb  s   VCKM s  b  Vtb  b   

CPV predicted in SM gives Δnbaryon/nγ ~O(10-20). It is 1010 too small. There must be other CPV beyond SM 10-06-2013

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Two ways of search for New Physics Direct observations Probe up to ~4 TeV Direct production of new objects at √s =14 TeV LHC operates now at √s =8 TeV only

Probe up to ~100 TeV Indirect searches Precision measurements of well predicted observables in SM , in particular these with small values, search for suppressed processes.

Examples of indirect discoveries: • Prediction of third generation of quarks (b,t) to introduce CPV in SM • c and t quarks first „seen” in FCNC processes in K and B mesons • (ν+N→ν+N) seen in 1973; direct Z observation 10 years later

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LHCb experiment LHCb physics programme Search for New Physics (NP) which may appear in CP violation or in rare decays mediated by new particles at high mass scale

• Atlas/CMS and LHCb are complementary – CMS/ATLAS: direct search for New Physics – LHCb: indirect search for New Physics 10-06-2013

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LHCb detector

• Forward spectrometer with 15 < θ < 300 mrad and ∫Bdl = 4Tm  VELO: silicon strip detector for precise secondary vertex reconstruction  TT,T1,T2,T2: tracking stations, silicon strip and straws for charged particles  RICH1, RICH2: ring imaging Cherenkov detectors (π/K/p separation)  ECAL, HCAL: electromagnetic & hadronic calorimeters (trigger and neutrals)  M1-M5: tracking stations for muon identification 10-06-2013

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Trigger system Challenge is  to efficiently select most interesting beauty and charm decays.  while maintaining manageable data rates

Main backgrounds  „minimum bias” inelastic pp scattering

 other beauty and charm decays

„On-line charm and strange signals” Signal/background ratio used to inspect data quality

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LHCb „performance summary” plot Fast oscillations of Bs neutal mesons

Monte Carlo

Δms = 17.768 ± 0.023 (stat) ± 0.006 (syst) ps−1

Demanding measurement which includes all: • momentum resolution • tracking resolution & efficiency

• particle identification, • flavour tagging,

Data

• trigger New J. Phys.15 (2013) 053021

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Rare decays Bs,d → μ+μD0→ μ+μK0s→ μ+μBd → K*μ+μ-

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B0(s)→μμ

GIM and helicity suppressed in SM

Very high sensitivity to New Physics, eg. CMSSM and NUHM1: [O. Buchmuller et al, arXiv:1112.3564v2, May 2012]

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Analysis strategy B0(s)→μμ

2011

2012

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Phys. Rev. Lett.110 (2013) 021801

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BDT discriminant - B0(s)→μμ

BDT discrimination is performed using 9 input variables.

The topological variables are chosen to avoid correlation with invariant mass i.e. kinematical variables of B and μ related to impact parameter, vertex isolation, transverse momenta, …

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B0(s)→μμ Phys. Rev. Lett. 110 (2013) 021801

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B0(s)→μμ

Phys. Rev. Lett. 110 (2013) 021801

First evidence

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B0(s)→μμ Unoffficial compilation based on arXiv:1107.0266 (D. M. Straub)

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D0→μμ • FCNC has been extensively studied in the strange and beauty sectors • In the charm sector most effectively suppressed by the GIM mechanism –

Absence of a high mass down type quark

• Small D mixing and small BR of rare D decays • D0→μμ dominated by the long distance contribution to the two-photon intermediate state Best exp limit from Belle Phys. Rev. D81 (2010) 091102

SM

Long distance SM limit > 6 x 10-11

3 orders of magnitude to gain before reaching the SM long distance contributions

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D0→μμ

arXiv:1305.5059

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D0→μμ

[arXiv:1305.5059]

arXiv:1304.6365 ] 10-06-2013

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K0s→μμ

SM BR(K0L→μμ) ~ ρ

( 6.85 ± 0.32 ) × 10−9

BR(K0S→μμ) ~ η

( 5.0 ± 1.5 ) × 10−12

Exp ( 6.84 ± 0.11 ) × 10−9

Long (a) and short (b) contributions comparable

< 3.1 × 10−7

NP contribution to BR(K0S→μμ) at the level of 10-11 is still allowed.

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K0s→μμ J. High Energy Phys.01 (2013) 090

L=1.0 fb-1

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B0  K*m+m Sensitive to NP in loops which modify angular distributions (SUSY, graviton exchange , extra dimension). Forward-backward asymmetry AFB sensitive to modification of the helicity structure. AFB(q2) – asymmetry in the m+m rest frame, q2 = m2m+m Phys. Rev. Lett.110 (2013) 031801

q2 at zero of AFB is a good probe of NP

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CPV for beauty decays

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ϕs - the phase of CPV for Bs How to measure the phase ϕs?

Interference of two amplitudes

Bs  J/y f - golden mode Bs  J/y f0 - independent measurement 10-06-2013

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ϕs - the phase of CPV for Bs

Mixture of CP-odd and CP-even Need angular analysis

Phys. Lett. B713 (2012) 378-386

arXiv:1304.2600

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>97.7% CP-odd No angular analysis

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ϕs - the phase of CPV for Bs Unoffficial compilation based on arXiv:1107.0266 (D. M. Straub)

The world most precise measurements

arXiv:1304.2600

BR(B0s→μμ)

Comparison with other experiments

Impact of ϕs measurement (together with BR(B0s→μμ) 10-06-2013

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CPV for charm decays

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Direct CP violation in D0 decays D0 mixing now established but CPV not yet seen experimentally In SM, indirect CP violation in charm is expected to be very small asymmetries ACP~ O(10-5)

Direct CP violation can be a bit larger in SM: ACP ~ O(10-3) - O(10-4) Both direct and indirect CPV can be affected by New Physics: ACP up to O(10-2)

Measure difference between two asymmetries ΔACP between D*+→D0(K+K-)π+ and D*+→D0(π+π-)π+ AD and AP cancel. Nearly all systematic effects cancel in the double difference

ΔACP measures direct CPV for charm

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Direct CP violation in D0 decays •

At the end of 2011 LHCb presented 3.5σ evidence for direct CPV in 0.6/fb sample – ΔACP = [ -0.82 ± 0.21(stat) ± 0.11(syst) ]%

•

Phys. Rev. Lett. 108 (2012) 111602

Two new analyses were presented in Moriond QCD2013. Independent samples, totally different systematics: – D* prompt sample, updated with full 2011 reprocessed data (1/fb) – D0 from a sample of B→D μ± X (1/fb) , with D0 flavor tagged by the sign of the μ

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Direct CP violation in D0 decay ΔACP with prompt D* The result is closer to zero that the result in 2011, but the shift is consistent with originating from the larger statistics (LHCb-CONF-2013-003)

ΔACP with semileptonic tag (Phys. Lett. B 723 (2013) 33-43)

•

The results are statistically compatible (2.2 σ) – LHCb results combined •

ΔACP = (-0.15 ± 0.16)%

– New preliminary world average •

ΔACP = (-0.33 ± 0.12)%

Previous evidence for CPV in charm not confirmed

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X(3872)

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X(3872) quantum numbers arXiv:1302.6269

X(3872) found 10 years ago by Belle. JPC narrowed to 1++ or 2-+ by CDF

The angular correlations in the B+ decay carry information about X(3872) quantum numbers. Details in arXiv:1302.6269 and refs therein.

5D fit to angular variables to test against JPC hypotheses

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X(3872) quantum numbers Projection of 5D fit

2*106 toy experiments

arXiv:1302.6269

JPC = 2-+ rejected at 8σ •

y 10-06-2013

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Summary • Indirect measurements probes New Physics at mass scales orders of magnitude above 100 GeV • The LHCb performed many precise measurements searching for the phenomena beyond the Standard Model – World’s most sensitive measurements of mixing and CPV in b- and c-hadron decays. – World’s most sensitive measurements of very rare b- and c-hadron decays

• No sign of New Physics seen yet – 200% of additional data is being analysed currently

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Backup slides

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Mixing of B(s)0 mesons Flavour eigenstates are not mass eigenstates, both are not CP eigenstates.

Eigenstates differ by Δm i ΔΓ

Large mixing, large CPV test SM CPV

Fast mixing, small CPV test non SM CPV

LHCb specialty

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B0  K*m+m angular observables

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B0(s)→μμ

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