1 Recent LHCb results on rare decays ICNFP 2014 Kolymbari, Greece Sajan Easo On behalf of the LHCb collaboration

2 Outline  Introduction to LHCb : Talk on Friday by D. M. Santos Saturday by M.Kreps  Indirect searches for New Physics  Beauty rare decays  Charm rare decays  Summary Leptonic decays Electroweak penguin decays

3 LHCb Experiment  Forward spectrometer : 2 <  < 5 Phys.Lett. B 694 (2010) Nucl. Phys. B 871 (2013)1-20 Vertex resolution:  x ~ 16  m,  y ~16  m  z ~76  m for 25 tracks Tracking :  p/p = % RICH : PID in GeV/c Muon system : ECAL : (E in GeV) HCAL : (E in GeV) B s Mass resolution = 6 MeV/c 2 in JINST 3 (2008) S08005

4 LHCb: Trigger and Offline selections 2011 : 1 fb -1 of data at 7 TeV 2012 : 2 fb -1 of data at 8 TeV  Level 0 : Hardware Trigger  HLT : Software Trigger  Offline Selection:  One of the Multivariate classifiers: Largest P T (E T ) of hadron/e/  /  Muon P T > 1.76 GeV, Hadron E T > 3.7 GeV e/  E T > 3.5 GeV Stage 1 : Selection based on IP, P T Stage 2 : Full event reconstruction mass cuts, Multivariate selection (MVA) Cuts based on Event topology P,P T of tracks, vertex quality, IP etc. Use PID information Multivariate selections (MVA) Boosted Decision Tree (BDT) JINST 8 (2013) P04022

5  Measure FCNC transitions, where NP is likely to emerge Example: OPE expansion for b  s transitions  NP may modify,add new operators Misiak: Nucl. Phys B393 (1993) Buras : arXiv: hep-ph: (1998) Indirect searches for New Physics (NP)  Precision measurements: Discover “virtual” new particles in loop processes i = 1,2 Tree = 3-6,8 Gluon penguin = 7 Photon penguin = 9,10 Electroweak penguin = S Higgs (scalar)penguin = P Pseudoscalar penguin

 Suppressed by FCNC and helicity  SM prediction Decay SM Bobeth et.al PRL (2014)  MSSM (with R-Parity conservation)  Ratio is a test of the minimal flavour violation hypothesis Eur. Phys. J C72 (2012)  is suppressed by a factor compared to that of B s Relative uncertainties in SM for B s   +  -

7 B0B0 Bs0Bs0 BDT trained on MC and calibrated using real data Control channels: Branching fraction normalized with respect to the control channels. Simultaneous unbinned maximum-likelihood fit to determine the branching fractions for the two channels. Mass plot here with BDT > 0.7, for illustration. Red: B s 0 Green : B 0

8  In 3 fb -1, LHCb sees evidence at 4  level for and at 2  level for the B 0 channels. PRL 111 (2013)  Preliminary combination of CMS+LHCb yields Observation at more than 5   All consistent with SM expectations. In CMSSM regions with large tan  excluded (in m 0, m 1/2 plane: 0-2TeV range)  Work in progress to combine CMS+LHCb results in a more sophisticated way. PRL 112 (2014) F.N.Mahmoudi, arXiv:

9 Photon polarization in b  s  decays  First penguin decay ever observed : CLEO in 1992 PRL 71 (1993) 674  B-factories: Inclusive and exclusive branching fractions are compatible with SM expectations.  Yet untested: photon polarization in b  s  In SM : photons are predominantly left-handed due to charged current interaction  One of the ways of testing Gronau & Pirjol PRD 66 (2002)

10  Conceptually similar to the Wu experiment in 1956 which observed parity violation.  In LHCb, we reconstruct the decay  Infer photon polarization from the up-down asymmetry of the photon direction in the K +  +  - rest-frame. Unpolarized photons would have no asymmetry. Photon polarization in b  s  decays

11  Reconstruction of  Selection using BDT  ~ signal candidates in 3 fb -1  Several overlapping resonances in m (K +  +  - )  Data divided in to 4 bins in m (K +  +  - )  Up-down asymmetry : K 1 (1270), K 1 (1400), K 2 *(1430), K 2 (1580), K 2 (1770),K 3 *(1780) Photon polarization in b  s  decays PRL 112 (2014) red solid:signal comb.background: green dotted missing pion background: black dotted other partially reconstructed background: purple dash-dotted Bin boundaries: GeV/c PRL 112 (2014)

12 Best Fit in Blue, Fit with no photon polarization in red (C’ C 2 7 )/(C’ C 2 7 )=0 Photon polarization in b  s  decays PRL 112 (2014)

13  Combining the 4 bins the photon is observed to be polarized at 5.2  level .  This is the first observation of photon polarization in b  s  decays  In order to determine if the polarization is as expected in SM, further input from theory is needed. PRL 112 (2014) Photon polarization in b  s  decays 4  2.5  3.1  2.4 

14 Electroweak penguins : b → ll s  Standard Model (SM)  New physics (NP) : Loop order and tree level  Sensitivity to the different SM and NP contributions from decay rates, angular observables and CP asymmetries  Long Distance effects :, can be removed with mass cuts S.Jäger

15 Angular distribution: A FB : Dimuon forward-backward asymmetry F L : Fraction of longitudinal K *0 polarisation S 3 : Transverse asymmetry (sensitive to virtual photon polarization) A 9 : A CP Asymmetry (A CP ) 11 terms reduced to 7 terms using angular folding :    if  <0 LHCb measured these parameters and the branching fraction as a function of q 2 

16 b → ll s  Differential branching fraction  LHCb reconstructed  Modes with are experimentally challenging due to its long lifetime.  Signals reconstructed for all these modes with 3 fb -1 of data. For the, results from 1 fb -1 of data quoted, for now.  Branching fractions normalized to those of the corresponding

17  Differential branching fraction b → ll s JHEP 06 (2014) 133 JHEP 1308 (2013) 131 with 1 fb -1 of data, all others with 3 fb -1 of data

18 JHEP 1308 (2013) 131 using 1 fb -1 of data  LHCb measurements:  All in agreement with SM

19 A CP using 3 fb -1 of data LHCb-Paper prelim.  In agreement with SM.  Most precise measurement to date.

20  LHCb also measured which are largely free from form-factor uncertainties Descotes-Genon et.al. JHEP,1305:137,2013  In the 1 fb -1 of data, LHCb observes a local discrepancy of 3.7  in P 5 ’ (Probability that one bin varies by this this much (look-elsewhere effect) is 0.5 % ). PRL 111 (2013)

21  Interpreting the anomaly in P 5 ’ : At least 28 theory papers so far.  Descotes-Genon, Matia, Vitro: Fit this and other measurements to get a 4.5  discrepancy with SM. They favour a modified C 9 NP = -1.5 (Non-SM vector current )  Altmannshofer & Straub : [ EPJC 73 (2013) 2646 ] Perform a global analysis and find discrepancies at the level of 3 . Data best described by a modified C 9 and C 9 ’ and introducing a flavour changing Z’ boson at O (1 TeV)  Gauld, Goertz & Haish : [ JHEP 01 (2014) 069 ] Also prefer Z’ but with mass O( 7 TeV)  Beaujean, Bobeth &van Dyk : [ arXIV: ] Float form factor uncertainties as nuisance parameters and find the discrepancy can be reduced to 2 . [ PRD 88 (2013) ]

22  Further verification needed with more data and channels -Some of the models expect suppression of B ( )  Jaeger & Camalich : JHEP 05 (2013) 043 Also explore the size of the form factor uncertainties in the low q 2 region and gets a reduced discrepancy  J.Lyon & R.Zwicky : arXiv: Explore the QCD effects related to the interference pattern of various charm resonances in the. They perform a combined fit to the BESII data on and the LHCb data. They claim that these charm resonance effects can accomodate the discrepancy.

23 Test of Lepton Universality  In the SM, dominant processes couple with equal strengths to all leptons. Test this using  Reconstruction of is experimentally challenging due to bremsstrahlung emission from. The effect from this is corrected using photons detected in the calorimeter, with E T > 75 MeV. in SM JHEP 12 (2007) 040

24 Candidates Triggered by  Measurement in the 1<q 2 <6 GeV 2 /c 4 region: Away from the resonant decays Avoid region above the  (2S) where broad charmonium resonances decay to l + l - Migration of events into and out of this region corrected using simulations  Ratio of the relative branching fractions with respect to cancels potential sources of systematic uncertainties. Test of Lepton Universality Dark shaded:combinatorial background Light shaded: partially reconstructed b-hadron decays

25  This differs from SM at 2.6  level This is using the 3 fb -1 of data This is the most precise measurement of R K to date. LHCb: arXIv: Belle: PRL 103 (2009) BaBar : PRD 86 (2012)  At least one of the models with Z’ predicts a suppression of the BF for  LHCb plans make the same measurement in other similar channels and also plans to use more data in the coming years. Test of Lepton Universality

26 Charm Decays  In SM, in D-decays, FCNC at loop level is suppressed by GIM mechanism more effectively than in B-decays. ( no top quark in the loop) Typical branching fractions of c  u  +  - in the range (1 -3 ) X  This allows for search for BSM physics in D-decays. Example:

27 Backgrounds from Green: best fit to Charm Decays LHCb Search for Using 1 fb -1 of data PLB 724 (2013)

28 Charm Decays  Use the CLs method to find the upper limits:  Each of these limits is an improvement over the existing limits, by a factor of 50 Existing limits from D0 and FOCUS : Phys. Rev. Lett. 100 (2008) , Phys. Lett B572 (2003) 21 For lepton number violating decays: existing limits from BaBar, LHCb: Phys.Rev D84 (2011) , arXiv PLB 724 (2013) % (95%) CL limits

29 Charm Decays  LHCb used 1 fb -1 of data from 2011 to search for  D 0 selected in  Data divided into 4 ranges of m(  +  - ) Low m(  +  - )  High m(  +  - ) Signal region PLB 728 (2014) 

30 Charm Decays PLB 728 (2014)  SM predictions of order (10 -9 )  LHCb improves the limits by a factor of 50, over the previous limits Previous limits from E791: Phys. Rev.Lett. 86 (2001) 3969

31 Summary  LHCb has published several results on the search for New Physics from the data collected in  The discrepancy with SM observed in the B  K*  has generated lots of interest in from theory colleagues.  The test of lepton universality produces a deviation from SM at 2.6  level, which is starting to be interesting.  In the coming 3 years we expect to collect 5 fb -1 of data. From 2018 onwards with LHCb upgrade we would get 5 fb -1 of data per year. These would enable LHCb to increase its sensitivity to New Physics.

32 Backup Slides

33 b → ll s

 Event Selection :  Branching Fraction: Normalized after similar event selection in B +  J/  K +, B  K  Search for B (s)   +  - BDT, trained on MC and calibrated using real data Signal : B  h + h - (h= K or  Background : B s mass sidebands PRL 107(2011) LHCb: A control channel

35 Charm Decays  Similar search in 4-body decays  Lepton number violating decay:

36 P 5 ’ Discrepancy J.Lyon, R.Zwicky : arXiv:

37 Charm Decays  Upper limits estimated using the CLs method, for the  SM predictions of order Hence these results are compatible with SM.  Current limits improves the previous limits by a factor of 50. Previous limits from E791: arXiv:hep-ex: PLB 728 (2014)

38 Constraints on CMSSM Black line: Direct search limits from ATALS SUSY searches with 20.3 fb -1 White line: Where the Higgs mass can reach a value of 122GeV F.N.Mahmoudi, arXiv:

39 Search for Majorana neutrinos in  Lepton Number Violating channel : search for majorana neutrino masses in the range between 250 and 5000 MeV and lifetimes ps. Phys. Rev. Lett. 112 (2014) B At 95 % C.L.

40 Search for Phys. Lett. B724 (2013)  About 70%  from Expected limits at 90 %(95% ) CL Observed limits at 90% (95%) CL