1. Discovering CP Violation and Mixing in the Charm Sector
NEW
D+ production asymmetry
ΔACP
yCP, AΓ
CPV search in four-body pion
On behalf of the LHCb(c?) collaboration

2. Muon System RICH Detectors Vertex Locator Tracking System Calorimeters
Interaction
Point
Muon System
Calorimeters
Tracking System
Vertex Locator
RICH Detectors
Chris Parkes

3. LHCb was designed for b-quark studies But also ideal for charm
LHCb LHCc c
LHCb was designed for b-quark studies
But also ideal for charm
shorter lived and lower p
20 times more events
Chris Parkes

4. Charm – Prompt and Secondary
Two types of charm production:
Prompt:
charm produced directly
in the primary reaction
Secondary:
charm produced in
B decays [>50% of B->DX]
Prompt charm more abundant
Secondary can have higher purity
Must discriminate between them
Use D impact parameter
Chris Parkes

5. D± production asymmetry
Time-integrated direct CPV searches are sensitive to production effects
Initial pp – no net charm !
Direct production QCD/EW – cc
But hadronisation with valence quarks can break
D+/D- symmetry
Previously measured
Measure:
using
NEW
Chris Parkes
LHCb-PAPER to be submitted to PLB

6. LHCb-PAPER-2012-026 to be submitted to PLB
CPV in decay ?
CPV in D+ ? Cabbibo allowed, tree
Expected Measured by Belle
CPV in Ks considered
Grossman, Nir arXiv:
Ks decaying inside VELO used
Short lifetime
(mean 7ps, c.f. 90 ps)
Fold with indirect CPV in Ks, ε
Effect is small
2.8 x 10-4
Preliminary
Chris Parkes
LHCb-PAPER to be submitted to PLB

7. LHCb-PAPER-2012-026 to be submitted to PLB
Result (prelim.)
Measurement performed in bins (pT,η)
Preliminary
Preliminary
In kinematic region probed:
3 σ evidence for a production asymmetry
No significant dependence on pT,η seen at this statistics
Primary systematic
from trigger asymmetry
Chris Parkes
LHCb-PAPER to be submitted to PLB

8. Direct CP violation in two-body charm
Search for CP asymmetry
Use decays
where slow pion charge determines the D flavour at production
(used in all analyses that follow in this presentation)
What we
measure
What we
want
What we
don’t want (1)
What we
don’t want (2)
Phys. Rev. Lett. 108, (2012)

9. Production Asymmetry of D*+
Technical Scale Drawing of LHC Collision
Proton (Matter)
Proton (Matter)
+ve charge
-ve charge
Cancel by measuring difference of KK and ππ final states
Detection Asymmetry of D and of π+s
Symmetric final states
no D detection asymmetry
Difference of final states
cancel π+s detection asym.
Periodic reversal of magnetic field
Chris Parkes
Phys. Rev. Lett. 108, (2012)

10. Subtle Reconstruction Effects
Regions of phase space where only a D*+ or D*- can be reconstructed, due to LHCb detector geometry
While in principle they cancel in magnet reversal they are removed using
fiducial cuts
π+s reconstructed
π-s not reconstructed
Chris Parkes
Phys. Rev. Lett. 108, (2012)

11. Direct CP Violation in Charm
High Statistics
1.4M K+K-, 0.4M π+π-
0.6 fb-1 analysed,
now have 2.5 fb-1 recorded
Many cross-checks have been performed
Independent analysis using secondary charm in preparation
Chris Parkes
Phys. Rev. Lett. 108, (2012)

12. Results First evidence of CPV in charm decays
Supported by recent CDF and Belle results
ΔACP = [-0.62 ± 0.21 (stat) ± 0.10 (syst)]%
ΔACP = [-0.87 ± 0.41 (stat) ± 0.06 (syst)]%
Chris Parkes
Phys. Rev. Lett. 108, (2012)

13. Theorists
Until recently most calculations suggested CPV in charm < 10-3
There are honourable exceptions e.g. “…There is no theorem, though, ruling out SM effects of 1%”
S. Bianco, F. L. Fabbri, D. Benson, and I. Bigi, A Cicerone for the physics of charm, Riv. Nuovo Cim. 26N7 (2003)
89 citations for LHCb paper
Consensus?
Compatible with NP models,
Large for SM but NOT excluded
Phys. Rev. Lett. 108, (2012)
Chris Parkes

14. Time-dependent two-body measurements
Lifetime ratio measurements:
Pure mixing measurement
In absence of CPV
Measured for first time at a hadron collider
2010 (0.03 fb-1) data only
CPV indirect (and direct)
Chris Parkes
JHEP04 (2012) 129

15. Measuring propertime acceptance
Determined from data
“swimming” – move the D vertex and reapply the selection
LHCb trigger – all lifetime biasing selections in software
Chris Parkes
JHEP04 (2012) 129

16. Measuring propertime acceptance
Chris Parkes
JHEP04 (2012) 129

17. Measuring propertime acceptance
Chris Parkes
JHEP04 (2012) 129

18. Measuring propertime acceptance
Chris Parkes
JHEP04 (2012) 129

19. Measuring propertime acceptance
Chris Parkes
JHEP04 (2012) 129

20. Prompt/Secondary Separation
Separate prompt /secondary charm on statistical basis through ln(χ2 IP of D)
Primary systematic, improve with better secondary modelling
Chris Parkes
JHEP04 (2012) 129

21. Results
Based on 2010 data, 0.03 fb-1
Chris Parkes
JHEP04 (2012) 129

22. Four-body CPV search Model independent search
Four-body “Dalitz” plot, 5 dimensions
Compare bins across phase space
Sensitive to local variations
SCP normal (μ=0,σ=1) in absence of CPV
α – normalisation – insensitive to global asymmetries
global CP and global detector/production effects
Adaptive binning >100 entries/bin
Chris Parkes
LHCb-CONF

23. Detector/production asymmetries
Equal amounts of two magnet polarities
Apply fiducial cuts (as earlier)
Accept/reject in (η,ϕ) space for equal D,D
2011 1fb-1 data, 180k events, 96% purity
Chris Parkes
LHCb-CONF

24. CPV Search Results Method cross-checked No evidence of CPV in CF decay
Simulated phase differences
No evidence of CPV in
P-value 99.8%
Chris Parkes
LHCb-CONF

25. Summary D± production asymmetry
LHCb’s huge charm samples fulfilling potential
D± production asymmetry
3σ evidence
ΔACP with CDF+Belle, 4.6σ evidence of CPV
No lose theorem:
New Physics OR the FBI arrest a theorist
yCP and AΓ
First hadron collider measurement – precision results to come
Acceptance effect from data
3 and 4-body CPV searches
Binned (generalised) Dalitz plot searches
NEW
(KKπ Phys. Rev. D 84 (2011) )
Chris Parkes

26. 6th International Workshop on Charm Physics
Manchester, UK, 31 August – 4 September 2013
Topics:
New Charmonium-like Hadrons (XYZ Hadrons)
Hidden Charm Spectroscopy and Transitions
Production of Charm and Charmonia
Hidden and Open Charm in Media
Charm Meson and Baryon Spectroscopy
Light Hadronic Spectroscopy from Decays of Charm and Charmonia
Leptonic, Semileptonic and Rare Charm Decays
Advances in Theoretical Tools
D -Dbar Mixing and CP Violation
New Physics Scenarios for Charm Decays
Experimental Charm Facilities - Status and Future