Direct CP violation in two-body decays experiment Towards the Ultimate Precision in Flavour Physics INFN and University of Bologna TUPIFP University of Warwick, UK 16 18 April 2018
The direct CPV Grossman, Kagan, Nir Phys.Rev.D75 036008 Guadagnoli@8thMeetingOnBPhysics CPV in decay occurs when the absolute value of the decay rate! # differs from the decay rate involving the CP-conjugate states +! % # + 7! % # CPV can happens if the final state can be reached at least with two different path The amplitude of a CP eingenstate, i.e. $ % # with # = ' ( ' ) or # = * ( * ), it can be written with a leading term and a sub-leading as follows Sub-leading amplitude: with relative strong (9, ) and weak (:, ) phases +, = +, - 1 + 0, 1 2 3 4)5 4 Leading amplitude: its phase is taken to be zero TUPIFP, Warwick, UK, 16-18 April 2
The direct CPV Grossman, Kagan, Nir Phys.Rev.D75 036008 Grossman, Kagan, Nir Phys.Rev.D75 Guadagnoli@8thMeetingOnBPhysics Guadagnoli@8thMeetingOnBPhysics CP violation in the decay can be observed if the asymmetry! $%& "# ' ( * =!, -!,!, - +!, - - is different from zero In the limit where 2, 1 (which is a good approximation)! $%& "# ' ( * = 22, sin3, sin4, TUPIFP, Warwick, UK, 16-18 April 3
The direct CPV Grossman, Kagan, Nir Phys.Rev.D75 Bucella F. et al. Phys.Lett. B302 (1993) 319-325 Petrov, A. J.Phys.Conf.Ser. 556 (2014) Santorelli, P. See talk@charm2016 Giudice, Isidori, Paradisi JHEP 1204 (2012) 060 Khodjamirian, Petrov Phys.Lett. B774 (2017) 235-242 In the Standard Model direct CP violation is naively estimated to be! $%& "# ' ( hh ~10./ 10.1 Non-perturbative QCD as well as New Physics effects can contribute to enhance CPV à but we already know that these effects can not be large In the U-spin symmetric limit (5 7), the same calculations holds for the 44 final state, with! $%& "# ' ( 22 =! $%& "# ' ( 44 Other promising decays are also interesting... ' ( 4 ( 4 (, D ; : 2 ( : h ;, ' ; (:) >4 ;, ' ( 2 ( : 2 ( :, ' ; h ; 4 (, ' ; :? @ 4 ;, etc.. TUPIFP, Warwick, UK, 16-18 April 5
The direct CPV Grossman, Kagan, Nir Phys.Rev.D75 Bucella F. et al. Phys.Lett. B302 (1993) 319-325 Petrov, A. J.Phys.Conf.Ser. 556 (2014) Santorelli, P. See talk@charm2016 Giudice, Isidori, Paradisi JHEP 1204 (2012) 060 In the Standard Model direct CP violation is naively estimated to be! $%& "# ' ( hh ~10./ 10.1 Non-perturbative QCD as well as New Physics effects can contribute to enhance CPV à but we already know that these effects can not be large Experimentally direct CP violation in (two-body) charm decays is not yet observed In the U-spin symmetric limit (5 7), the same calculations holds for the 44 final state, with $%& ' ( 22 =! $%& "# ' ( 44! "# Other promising decays are also interesting... ' ( 4 ( 4 (, D ; : 2 ( : h ;, ' ; (:) >4 ;, ' ( 2 ( : 2 ( :, ' ; h ; 4 (, ' ; :? @ 4 ;, etc.. TUPIFP, Warwick, UK, 16-18 April 6
Current experimental status on SCS (not only hh) Observable Current knowledge 10 $ Experiments (ordered by precision) Δ& )*+ '( = & '( -- & '( (00) 13 ± 7 LHCb, CDF, BaBar, Belle & '( 5 6-8 - 9 0 ± 15 LHCb, CDF, Cleo, Focus, BaBar, Belle & '( 5 6 0 8 0 9 16 ± 12 LHCb, CDF, Cleo, Focus, BaBar, Belle & '( 5 6 0 6 0 6 3 ± 64 Cleo, Belle & '( 5 6 - > 6 - > 6 36 ± 147 Belle [arxiv:1705.05966], LHCb, Cleo (*my avg) & '( 5 9 0 9 0 6 240 ± 115 Belle[arXiv:1712.00619], Cleo (*my avg) & '( 5 9 - > 6-9 11 ± 17 LHCb, Belle, BaBar & '( 5 > 9 - > 6 0 9 38 ± 48 LHCb, BaBar & '( 5 > 9-9 0 6 2660 ± 2380 Cleo & '( 5 9 @0 9 11 ± 16 & '( 5 9 A B 0 9 16 ± 70 source HFLAV LHCb [JHEP 06 (2013) 112], Belle [arxiv:1110.0694], BaBar [arxiv:1212.1856](*my avg) LHCb [PLB 771 (2017) 21-30], Cleo, Belle (*my avg) TUPIFP, Warwick, UK, 16-18 April 7
The most recent (and precise) measurements with! " hh with Run-1 data TUPIFP, Warwick, UK, 16-18 April 8
A closer look at! " hh @ LHCb (the most recent measurement) Run-1: L = 3/fb LHCb-PAPER-2015-055, PRL 116 (2016) 191601 This is the most precise measurement of a time-integrated CP asymmetry in the charm sector from a single experiment. Non-systematic-limiting factors (so far) TUPIFP, Warwick, UK, 16-18 April 9
A closer look at! " hh @ LHCb (the most recent measurement) Run-1: L = 3/fb LHCb-PAPER-2015-035, PLB 767 (2017) 177 Individual asymmetries rely on ability to determine the production and detection asymmetry with Cabibbo-favored! " K & ' (,! ( K & ' ( ' ( and! ( ) * " ' ( decays! " ) & ) ( statistics reduced by reweighting procedure by about factor 5 Precision driven by! ( ) * " ' ( statistics TUPIFP, Warwick, UK, 16-18 April 10
A closer look at! " hh @ LHCb (the most recent measurement) Combining %-tagged result with the &-tagged ones LHCb-PAPER-2015-035, PLB 767 (2017) 177 From the previous Δ, -. mesurement, is possible to measure, -. %% with a correlation between the two mesurements /, -. 00,, -. %% = 0.24 An additional independent sample of ' (! " & ) * decays is available at LHCb, where the muon tags the f! " flavour Run-1: L = 3/fb TUPIFP, Warwick, UK, 16-18 April 11
Future prospects Two players on the scene: LHCb-Upgrade (U1, Run-3,4) and assuming a future LHCb- Upgrade-II (U2, Run-5+ ) Belle-II @LHCb the hadronic charm decays during U1 and U2 phase will benefit by: the increase of the signal yields by 10% due to cross-section rise (from! = 7 TeV to! = 8 TeV ) a factor 2 of signal yields improvement expected on the trigger (based on preliminary studies) @Belle-II where the expected final integrated luminosity is 50 ab -1 TUPIFP, Warwick, UK, 16-18 April 12
Future prospects (my personal extrapolation) Belle projections (stat only) à measurement rescaled with the integrated luminosity LHCb projections (stat only) à Run-1 results rescaled with luminosity, considering the increase of bbar crosssection with energy trigger improvements already achieved Run-1 à Run-2 expected with U1 and U2 TUPIFP, Warwick, UK, 16-18 April 13
Future prospects (my personal extrapolation) Observable Current WA (stat + syst) Belle-II 50 ab -1 (stat) precision 10 $ LHCbRun [1-2] 9 fb -1 (stat) LHCbRun [1-*] 300 fb -1 (stat) )*+ Δ& '( ±7 ±6 ±3 ±0.5 & '( 1 2 4 5 4 6 ±15 ±3 ±5 ±1 & '( 1 2 7 5 7 6 ±12 ±5 ±6 ±1 & '( 1 2 7 2 7 2 ±64 ±9 -- -- & '( 1 2 4 < 2 4 < 2 ±147 ±22 ±100 ±12 & '( 1 < 6 4 < 2 7 6 ±48 ±29 ±23 ±3 & '( 1 6 4 < 2 4 6 ±17 ±4 ±4 ±0.5 & '( 1 6 7 6 7 2 ±115 ±18 -- -- & '( 1 6 >7 6 ±16 ±4 ±3 ±0.5 & '( 1 6? @ 7 6 ±70 ±14 ±15 ±2 Belle-II will give important contributions for search of direct CPV in particular with neutrals but LHCb is (and will remain) the main player TUPIFP, Warwick, UK, 16-18 April 14
Control of systematic uncertainties à focus on LHCb prospects TUPIFP, Warwick, UK, 16-18 April 15
Instrumental asymmetries Detector layout causes asymmetries in the reconstruction of positive and negative tracks The main mechanisms are: Asymmetric material distribution, detector misalignment, beam spot position (fixed offset), beam crossing angle (added horizontal boost), different positive/negative interaction cross-sections, etc. LHCB-PAPER-2013-033 LHCB-PAPER-2012-009 Asymmetries are largely reduced when averaging data collected with opposite magnet polarities Reverse of magnet polarity is fundamental to keep under control these effects, as well using a data driven approach to measure them with high precision TUPIFP, Warwick, UK, 16-18 April 16
Asymmetries due to material interaction " # and " $ have different interaction cross section with matter causing an asymmetry of " ± & ± final state the level of ~1% This a key feature for several measurements in LHCb, in particular for the single ' () * + hh Owing on a data driven approach LHCb measured this effect with high precision at the level of 0.1% with * # " $ & # & # and * # ". + & # decays à Very different final states means effective statistical power is much reduced by the need of weighting the kinematics This is already a dominant systematic for the Run-2 measurements Need to keep our ability to reconstruct ". + with good efficiency and/or find different ways to measure these asymmetries in data Chin. Phys. C 38 (2014) 090001 LHCB-PAPER-2014-013 TUPIFP, Warwick, UK, 16-18 April 17
Neutral kaons detection asymmetry Neutral kaons interact with the material, but in addition violate CP and their mixing can be affected by material interaction à regeneration of! " # in! $ # beams Both effects lead to a tiny detection asymmetry when using! " # that decay in the VELO The uncertainty is limited by the knowledge of the detector material If you apply the above results to a measurements, e.g. % &' ( #! *! + due to! # " momentum reweighing the correction is [arxiv:1405.2797] This is a limiting factor for the ultimate precision measurements DD à! " # decays after the VELO LL à! " # decays in the VELO TUPIFP, Warwick, UK, 16-18 April 18
Conclusions Direct search for CP violation in charm charged two-body decays is approaching to a precision close to SM predictions SM prediction! $%& "# ' ( hh ~10./ 10.1 With RUN-1 data, LHCb excluded large values of direct CP violation (> 10.3 ) Δ! $%& "# precision expected to be 3 10.1 with the full LHCb Run-2 data without systematic limiting factors expected Run-2 LHCb precision will achieve the same precision of Belle-II with full data set (50 ab -1 ) in most of the two-body decays Belle-II will give an important contribution, mainly with neutrals For ultimate precisions LHCb will play the main role, but with several challenges ahead know with high precision 9(10.1 ) 9(10.; ) the asymmetries induced by the detector on <, > and < B ( (maybe it will be not enough to reverse the magnet polarity) keep high the reconstruction efficiency of neutrals Improve ECAL calorimeter resolution and granularity TUPIFP, Warwick, UK, 16-18 April 19