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LHCb precision measurements
7th of October 2013

Alexey Dzyuba / PNPI, Russia
on behalf of the LHCb collaboration

Workshop on Precision Physics and Fundamental Physical Constants (FFK-2013) Central Astronomical Observatory of the Russian Academy of Sciences at Pulkovo Saint-Petersburg, Russia / October 7-11, 2013


Outline
Main goal of this talk: Show how precise LHCb measurements in b- and c-sectors make constraints on fundamental prameters of Standard Model (SM) and provide a New Physics (NP) searches.


Standard Model (SM) and its difficulties
­ ­ ­

Cabibbo-Kobayashi-Maskawa (CKM) matrix, CP violation (CPV) Why and where to find New Physics (NP)? MFV or not? Power of indirect measurements apparatus, physical program etc.



LHCb setup (
­ ­ ­

)



Selected results
Mixing, CP violation, CKM in B systems Mixing and CP violation in charm sector Rare decays (B2, BK*2)
what can be achieved after upgrade?



Summary and Outlook (

)
2


Introduction

3


Standard Model
No doubt that SM is great achievement! (no conflict with HEP)

Reasons for NP:
1) Neutrino sector
Flavour sector of SM

- mass - oscillations 2) Radiative correction to M(Higgs) - fine tuning - desert between M 3) Astrophysics - dark matter - baryon asymmetry of Universe
(CPV is needed) 4
EW

and M

GUT

SUSY good candidate to solve 2) & 3)


Cabibbo-Kobayashi-Maskawa


Flavour eigenstates do not coincide with week eigenstates Mixing matrix VCKM CP violating phase appears than there are 3 generations of fermions Elements of the CKM matrix appear at the decay vertexes Wolfenstein parametrization







5


Unitarity of CKM matrix
Unitarity is a very important property of VCKM

Neutral Currents can be written in the first order of EW theory as:

As a result Flavour Changing Neutral Currents (FCNC) is forbidden at tree level but can appear at the loop level! For example :
6


Unitarity triangles



Two of six relation have all three contribution of same size Can be drawn as triangle at the complex plane Almost all SM CPV is sitting here Parameters of the triangle can be measured at the decays







7


Unitarity triangles



Many different experimental constraints There are another fitting groups In this talk I will show LHCb results on , m





8


Unitarity triangles



Other triangles are also very important In this talk I will show LHCb results on s Note: Another consequence of VCKM unitarity is that squares of elements in raws and columns must be equal to one. [see for example RPP 73, 046301]
9






NP and flavour symmetry; Wilson's coefficients


Progress of theory calculations allows to take into account QCD corrections needed for SM FCNC implementation to decays. (Calculation of Ci in SM as well as quite precise predictions for certain processes) Heff is an effective way to test different classes of possible NPs, because Ci depend on their flavour structures. Minimal Flavour Violation (MFV) paradigm: NP has same source of FV as SM => real numbers, same CPV effects, relations like:


Example





If NP contains additional FV sources of Ci become complex as well as new CPV effects might appear!
10


Indirect measurements at LHC


How NP related to flavour physics? Is NP weakly coupled to flavour sector (MFV) or at very high scale? Important to have a probes beyond LHC energies (direct observation)!





Better to use processes which are either forbidden either highly suppressed in SM Flavour Changing Neutral Currents (FCNC) can be such a probe



Other possibilities Lepton Flavour Violation (LFV) mLQ>100TeV [not discussed here, but see LHCb result on Be in PRL 111, 141801] CPV in charm sector
11




Power of indirect measurements
Example #1: CP violation in kaon system
Has been done when only 3 quark were known 1972 Kabayashi-Maskawa 6-quark model ~ 13 years before Upsilon discovery

Example #2: Weak neutral current (Gargamelle bubble chamber)
~ 10 years before Z discovery at UA1/2

Example #3: ARGUS collaboration report large B-mixing
Suggest large mass of top quark ~8 years t has been discovered at Tevatron

12


LHCb features

13


Beauty and charm production


LHCb: forward spectrometer 2 < < 5 (ATLAS & CMS: ||<2.5)

s

pp

= 14 TeV



In LHCb acceptance (pp-collisions s = 7TeV)

14


Experimental setup

15


Operation in 2010/12
pp-collisions at s = 7 & 8 TeV (2011-12) pPb-collisions at sNN = 5 TeV in 2013

We also have set of pp data at s =2.76 TeV (collected in 2011)

16


LHCb data analysis
Tagging
Efficient trigger (L0/HLT1/HLT2): 40MHz 5kHz Tagging if needed Event selection Kinematical and topological info (pT, p, IP, vertex and track quality) PID information Cut based or multivariate selection BDT, Neurobayes, etc. Optimization of selection Using MC Using small sample of real data Angular analysis++ Check for systematics And a lot of other checks!

Typical flight distance of B meson ~ 1 cm

Selection using IP:
PV = Primary Vertex DV = Daughter Vertex (secondary vertex) 17


Physics program of LHCb
GOAL: Search for evidence of NP in CP violation and rare decays of beauty and charm hadrons . (Probing large mass scales via study of virtual quantum loops of new particles) LHCb results are available in more that 160 papers submitted to journals and 110 conference contributions

Main direction of searches: 1) Rare decays
RD with di-muons

2) Properties of the B systems
Mixing observ., A(CP)

CPV, ms; s, , s ; CKM determination

3) Mixing and CPV in the D systems

talk this d in e ver y co l tial Par ( d= e ve r o ot c N
18

4) Spectroscopy and production of heavy quarks 5) Electroweak physics 6) Soft QCD physics, pA and Ap results


Properties of the B (B , B , Bs) systems
1) Direct CP asymmetry in B(s)0 decays 2) Bs0 oscillation frequency measurement 3) Mixing induced CPV in Bs0, e.g: Bs0J/ and Bs0 J/f (980) 4) CKM angle
19

+

0


Direct CP asymmetry in B
Direct CP asymmetry hard but to calculate, "easy" to measure 1 fb-1 dataset, PRL 110, 221601 ~41k B0K+

0 (s)

decays
Detection asymmetry Production asymmetry

CP asymmetry:

Oscillation considered in the analysis! ACP(B0K+) = = -0.080 ± 0.007stat± 0.003syst World best precision

~1k Bs0K+
ACP(Bs0K+) =
Raw asymmetry

= 0.27 ± 0.04stat± 0.01syst 1st observation (6.5) of direct CP asymmetry in Bs0 system
20


Oscillation frequency for B
Corresponding SM box-diagrams
Bs: Fast oscillations Excellent time resolution required! = (L+H) / 2;

s

Data

ms = MH ML x = (MH ML) / ; y = (L H) / 2

Most precise measurement up to date Agreement with world average & SM Also measured in semileptonic decays [arXiv:1308.1302] !
21


Mixing induced CP violation in B


Decay of particle and antiparticle to same state CP violating phase predicted to be very small in SM CKMfitter group [PRD 84, 033005]

s





Observable very sensitive to NP ! LHCb measured it in two modes (1 fb-1 dataset) [PRD 87,112010] Measurement of time-dependent CP asymmetry







Tagging and high decay time resolution required!
22


Mixing induced CP violation in B
B0s J/


s

~ 27600 events tagD2 = 2.29%

Narrow (1020): experimentally clean VV final state: mixture of CP even/odd components Time-dependent angular analysis Fit of more than 10 physics parameters ms from BsDs decay
Proper time resolution ~ 45 fs









[PRD 87, 112010]

23


Mixing induced CP violation in B
B0s J/+­


s

Dominated by f0+­ BF~35% of B0s J/ CP-odd final state No angular analysis is required Constrain s and s to B0s J/ result









[PLB 713, 378]
Combined fit of B0s J/ and J/ +­

Consistent with SM prediction!

[PRD 87, 112010]

24


Constrain on NP parameters
Consistent with SM prediction and data from other experiments!
HFAG preliminary

25


Parameters of CKM triangle
CKM angle measured with high uncertainty! (but very precise SM prediction for these observable)
Leading diag. Diagram with other CKM structure highly suppressed!

Very high potential for NP searches!

26

EPJ C 73 (2012) 2373


GLW / ADS / GGLZ methods

27


Result on CKM

28


Mixing and CPV in charm sector

29


D mixing

0

30


D mixing

0

LHCb already reported about first observation of D0 mixing (by single experiment, 9) PRL 110, 101802

31


Newest results on D mixing (and CPV)
Wrong-sign-to-Right-sign ratio: R+ = R(t) WS-to-RS ratio for D0K+­ decay

0

RS: 230 в WS ev.

WS: 2.3 в 105 ev.

Result of the fit with no-CPV assumption: In case of no-CPV and no-Mixing assumption should be constant!

World-best result!

[arXiv:1309.6534]

32


Newest results on D mixing (and CPV)
Wrong-sign-to-Right-sign ratio: Fit with CPV assumptions has been also done
Direct CPV: MixingInduced CPV:

0

RS: 230 в WS ev.

WS: 2.3 в 105 ev.

No CP V
[arXiv:1309.6534]
33

Result of the fit with no-CPV assumption:

World-best result!

ef f ec ts fo un d!


Newest results on D mixing (and CPV)
Wrong-sign-to-Right-sign ratio: Fit with CPV assumptions has been also done
Direct CPV: MixingInduced CPV:

0

RS: 230 в WS ev.

WS: 2.3 в 105 ev.

Result of the fit with no-CPV assumption:

World-strongest constraints!

No CP V

World-best result!

[arXiv:1309.6534]

e ff ec ts fo un d!
34


CP violation in D decays
In SM direct CP violation predicted to be small ~ 10-3 - 10 Access via asymmetry measurement
-4

LHCb: Time integrated difference of asymmetries

With 0.6fb-1 data sample LHCb found 3.5 evidence of direct CP violation

PRL108, 111602 Later some indication came from other experiments Led to discussion: "Is it sign from NP?"
35


CP violation in D decays
In SM direct CP violation predicted to be small ~ 10-3 - 10 Access via asymmetry measurement
-4

LHCb measured time integrated difference of asymmetries

Two complementary analysis with 1 fb-1 data sample

[PLB 723,33]
36


CP violation in D decays
LHCb results:
[LHCb-CONF-2013-004] [PLB 723,33]

Consistent with no CPV hypothesis!

HFAG averages:

Note:
37


Rare decays

38


Rare decays B(s)
0

+­

Helicity suppressed in SM [arXiv 1303.3820]

s correction [PRD 86, 014027]

5% precision SM calculations! Sensitive to new scalar, pseudoscalar, axial-vector particles in loops In MSSM:

39


Some words about analysis strategy


Blind analysis of 3fb-1of data (full 2011-12 sample) Robust selection cuts for reduction of combinatorics Boosting Decision Tree (BDT) method using 9 topological variables (to avoid correlation with Minv)



PRL 110, 021801





BDT trained on signal and bkg MC BDT calibrated on data using B->h+h- as signal and mass sidebands for bkg. 8 BDT bins. In each bin, the compatibility of the observed events with bkg only and SM+bkg hypotheses is calculated.
40






Result: first evidence of B
0 s
Background sources:

PRL 111, 101805 +­

Statistical significance 4 for B0s signal! Consistent with SM prediction!

Upper limit for B0 +­

41


Combination of CMS and LHCb results

First evidence of the decay!

42


Result vs NP

Any model that violates flavour via (pseudo)scalar is constrained. High tan SUSY too

43


B-hadron Hadron + , D
+­
FCNC processes with a lot of observables Clear experimental signatures with low background Well developed SM calculations NP can be found in ­ Rates ­ Angular distributions ­ Asymmetries As an example zero-crossing point at forward-backward asymmetry for B0 K*+ is well predicted within SM and has potential for NP searches.

+­

44


b xl l and c xl l menu @ LHCb
A lot of channels = a lot of new (Apr-Sep 2013) results

+­

+­

b sl+l
­ ­ ­ ­ ­ ­



B0 K*+ B0 K+ B+ K++ B0 *+


JHEP8(2013)131 / 1308.1340

1st multiD angular analysis CP asymmetry (4160) / CP asymmetry 1st angular analysis 1st evidence in low q2 baryons, 1st @ LHC

PRL 110, 031801
1308.1707 / 1308.1340

arXiv:1305.2168 JHEP 05,(2013)159 PLB725, 25

B0 K*e+e b +


c ul+l
­

D(s)+ ++ arXiv:1304.6365 D(s)+ ++

factor ~50 improvement in limit
45


Analysis of B K*
(2S) J /
Excluded

+­
[arXiv:1304.6325]

B


Loose preselection cuts Using BDT trained on proxy BK*J/ Background from upper B sideband Choice of variables to avoid biases on angles and q2=m2() Final selection from BDT decay time, flight direction, trk/vtx quality, p T, PID BR measured relative to BK*J/
46












Analysis of B K*

+­

First multi-dimensional angular analysis

47


Analysis of B K*

+­
JHEP 08 (2013) 131

zero-crossing point SM predictions:
(Ref. at next slide)

48


Analysis of B K*

+­
JHEP 08 (2013) 131

49


Further analysis of B K*

+­

50


Further analysis of B K*

+­

P'6,8 predicted to be small!

[arXiv:1308.1707]

51


Further analysis of B K*

+­

P'6,8 predicted to be small!

[arXiv:1308.1707]

m fro on iati ev r td d/o es an rg La t C7 in ne NP Geno sote sc De

! HC at L SM ed ? est 83 gg u 56 as s 1307. C9 iv: rX a a l.
52


Summary
LHCb, the forward spectrometer for precision studies in flavour physics domain Excellent performance of the LHC and LHCb has led to a lot of physics results ­ Test of SM ­ Search for NP ­ Make CP violation measurements in b- and c-sectors World best quality of the results in charm and beauty physics! Remember, that presented here measurements use mainly the 1 fb -1 dataset (70% of the 2010-12 data still in progress)

OUTLOOK:
1) Plan to have more than ~ 5 fb 2) Upgrade (next slide)
53
-1

at s = 13 TeV during next LHC run (2015-18)
(in comparison with presented results)

=> ~ 8 times higher statistics in 2019


Outlook. Theory vs. 50 fb

-1

54

EPJ C 73 (2012) 2373