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Search for CP violation in multi-body charm decays

Search for CP violation in multi-body charm decays SM predicts the magnitude of CPV in charm 10 -3 -10 -2 The size of CPV can be significantly enhanced in new physics models Many LHCb searches for CPV in many different final states

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Search for CP violation in multi-body charm decays

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  1. Search for CP violation in multi-body charm decays • SM predicts the magnitude of CPV in charm 10-3-10-2 • The size of CPV can be significantly enhanced in new physics models • Many LHCb searches for CPV in many different final states • Singly-Cabibbo-suppressed charm hadron decays are promising channels with which to search for CPV • So far, no evidence for CPV in charm sector is observed • Today • three-body D+ → p-p+p+ • four-body D0 → K-K+p-p+ , D0 → p-p+p-p+

  2. u 1 p+ W+ d c d λ p- d d Search for CPV in D+ → p-p+p+ • D+ → p-p+p+ is singly-Cabibbo Suppressed (SCS) and gets contribution from penguin diagram • If tree and penguin amplitudes interfere with different phases then CP symmetry is broken • Penguin diagram opens possibilities for finding New Physics effects tree penguin +NP W+ λ,1,λ2 1, λ, λ3 u d,s,b p+ c d g d D+ p- u D+ u u u p- p- d d weak phases strong phases

  3. Search for CPV in D+ → p-p+p+ Warsaw contributes to the analysis • Decay products form many resonance • states visible in Dalitz plot • The charge asymmetry can be • measured locally in the regions • of Dalitz plots • No clear indications where CPV would • appear • To find asymmetries we compare locally • Dalitz plots for D+ and D-(we perform • here searches based on techniques • that are model-independent): • binned method – used few times at LHCb • unbinned method – used for the first time f2(1270)/f0(1370) arXiv:1310.7953 f0(980) f0(980) r

  4. Search for CPV in D+ → p-p+p+ • Binned method • For each bin in the Dalitz plot we measure • local charge asymmetry • Instead of: we calculate • SCP value • SCPis a significance of a difference between D+ and D- • To cancel global asymmetries (production asymmetry, etc.) we normalizeDalitz plots for D+ and D- • If no CPV (only statistical fluctuations) • then SCP is Gauss distributed (m=0, s=1) • We calculate c2 = SSiCP2to obtain p-value • for the null hypothesis to test if D+ and D- • distributions are statistically compatible • p-value ≪ 1 in case of CPV if asymmetry Monte Carlo Bediaga et al. Phys.Rev.D80(2009)096006

  5. Search for CPV in D+ → p-p+p+ Results for binned method To increase the sensitivity of the method we use uniform and adaptive binning schemes with different bin numbers 49 adaptive bins arXiv:1310.7953 100 adaptive bins All p-values for null CPV hypothesis are above 50% SCPdistributions agree with the standard normal Gaussian function Binned results are consistent with no CPV

  6. Search for CPV in D+ → p-p+p+ • Unbinned method – k-nearest neighbor technique • To compare probability distribution function of phase • space for D+ and D-we define a test statistic T which • is calculated for a pooled sample of D+ and D-: • I(i,k) = 1 if ith event and its kth nearest neighbor • have the same charge (D+—D+ , D-—D-) • I(i,k) = 0 if pair has opposite charge (D+—D-) • T is the mean fraction of like pairs in the pooled sample of the two data sets • We calculate p-value for case of no CPV by comparing T with expected mean D+ D- y nk=10 x query event

  7. Search for CPV in D+ → p-p+p+ Results for unbinned method arXiv:1310.7953 To increase the sensitivity of the method we divide the Dalitz plot into few regions: 7 and 3 defined around resonances Recent LHCb results for B± → hhh show large CPV in the regions not associated to resonances R0 – full Dalitz plot All p-values for null CPV hypothesis are above 30% Binned and unbinned results are consistent with no CPV

  8. Four-body charm decays • Singly-Cabibbo suppressed: D0 → K-K+p-p+ , D0 → p-p+p-p+ (signal channels) • The Cabibbo-favouredD0 → K-p+p-p+decay, where no significant CPV is expected within the SM, is used as a control channel • The analysis is based on D0 mesons produced in D*+ → D0p+decays. • The charge of the soft p+ identifies the flavor of the meson at production • So far, only the binned method is used: • The phase space is partitioned into Nbins bins, and the significance of the difference in population between CP conjugate decays for each bin is calculated • Here the Dalitz plot has 5 dimensions

  9. 1/fb 2011 Plots for magnet up polarity PLB726(2013)623-633 Dm is the difference in the reconstructed D*+ mass and m(hhhh) Signal yields are extracted from the two-dimensional fits SCS: 57k D0 → K-K+p-p+ SCS: 330k D0 → p-p+p-p+ CF: 2.9MD0 → K-p+p-p+

  10. D0 → K-K+p-p+ PLB726(2013)623-633 s(K-,K+) s(K+,p-) s(K+,p-,p+) s(K-,K+,p-) s(p-,p+)

  11. D0 → p-p+p-p+ PLB726(2013)623-633 s(p+,p+) s(p-,p+) s(p-,p+,p+)

  12. Results for control mode 5D Dalitz plot is partitioned with a different number of bins with similar statistics in each. Control mode, partitioned with 128 bins PLB726(2013)623-633 No evidence for a significant asymmetry in any bin is found

  13. Results for signal modes Signal mode, partitioned with 32 bins, ~1800 events in each PLB726(2013)623-633 Signal mode, partitioned with 128 bins, ~2500 events in each All results are consistent with CP conservation at the current sensitivity

  14. Warsaw wants to participate to the four-body analysis • Use the kNN technique to four-body charm decays • the binned analysis has just published for 1/fb, LHCb-PAPER-2013-041 • The details are in LHCb-ANA-2013-004 • twiki: https://twiki.cern.ch/twiki/bin/view/LHCbPhysics/D2hhhhCPV • Proponents: University of Bristol: Matt Coombes, Jonas Rademacker • extend to 3/fb(make one publication with binned and unbinned techniques) • expectation: 250k D0 → K-K+p-p+ , 1.4M D0→ p-p+p-p+ • How to divide the Dalitz plot into regions (5D)? • To increase the sensitivity of the kNN method we divide the Dalitz plot into regions defined around resonances • How to do 5D plot to chose regions?

  15. Ho to divide 5D Dalitz plot into regions? • Region division proposition • Global region R0 with 5D • In binned method 5D Dalitzplot is partitioned with a given number of bins with similar statistics (probably using adaptive binning algorithm). So, divide the full Dalitz plot into small number of binsto have as much statistics as possible using the same algorithm (example 16 bins as used). Then each bin still has 5D and in each bin (“pseudoregion”) use the kNN. • Make the new Dalitz subplots 2D and 3D corresponding to the combinations: s(1,2), s(2,3), s(3,4), s(1,2,3), s(2,3,4): • use global regions for 2D and 3D Dalitz subplots • divide these Dalitz subplots into regions defined around resonances • eventually divide each 2D and 3D projection into subregions where the differences between particles and antiparticles are the highest • Other propositions?

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