Charm Physics at LHCb
Surapat Ek-In
EPFL, Lausanne, Switzerland
On behalf of the LHCb collaboration
20th Lomonosov Conference on Elementary Particle Physics

Charm Physics Programme @LHCb● Mixing and CP violation-First observation of a diﬀerence between D0 mass eigenstates [arXiv:2106.03744]-Time-dependent CPV search in D0 → K+K- , π+π- [arXiv:2105.09889]-Time-integrated CPV search in D0 → K0SK0S [arXiv:2105.01565]● Production and spectroscopy-Lifetime of Ω0c [LHCb-PAPER-2021-021(Preliminary)]● Rare decays-Flavour-changing neutral current (FCNC)
etc.

Surapat Ek-In

Charm Physics @LHCb

Aug. 25th, 2021

2LHCb experimentPID
εPID (K) ≈ 95%
εPID (μ) ≈ 97%
εPID (e) ≈ 90%Vertex
εVELO ≈ 98%

JINST 3 (2008) S08005

Calorimeter

Tracking
εTrack ≈ 95%

Muon

Run 1
3/fb at 7/8 TeV

Run 2
6/fb at 13TeV

Aug. 25th, 2021

3σ(IP) = 20 μm
Surapat Ek-In

Charm Physics @LHCb

Charm Productions at the LHCb experiment● Unique- Up-type quark decay- New physics coupling can be probed● Indirect CPV in charm decays

Prompt [π-tagged]- Small mixing, sensitive to CPV- Probe high BSM scales (suppressed in SM)● Large cross section- Billions of charm hadron decays to bestudied at LHCb!

Semileptonic [μ-tagged]
Surapat Ek-In

Charm Physics @LHCb

Aug. 25th, 2021

4

Mixing and CPV
Mixing parameters●Flavour mixing is the transition between a neutral ﬂavoured meson andits antiparticle. The time evolution is described by-Eigenstates of this Hamiltonian are-with eigenvalues●Mixing parameters in charm have yet to be measured with highprecision. [Mixing occurs when x and y ≠ 0]

●Measurements of these parameters are sensitive to probe physics(0, 0)

beyond the Standard Model (SM).
SM:Surapat Ek-In

Int.J.Mod.Phys.A21:5686-5693,2006

Charm Physics @LHCb

Aug. 25th, 2021

5

Mixing and CPVDirect CPV

CPV in mixing

CPV in decay-mixing interference

Surapat Ek-In

Charm Physics @LHCb

Aug. 25th, 2021

6

arXiv:2106.03744

First non-zeromeasurement of x

Surapat Ek-In

Charm Physics @LHCb

Aug. 25th, 2021

7

Phys. Rev. D 99, 012007●Self-conjugate decay-Reconstruction eﬃciency is equivalent between D0 ﬂavours.

-Decay path: Cabibbo-favored (CF),Doubly-Cabibbo-suppressed (DCS)●●Mixing and indirect CPV-Sensitive to x, y-Indirect CPV measurement of q/p and 𝜙fAnalysis approaches: Model independent with Binﬂip method-

Measure the time-dependent ratio between positive and negative
Dalitz bins of constant strong phase diﬀerence, which gives
access to mixing parameters-

Suppress biases due to nonuniform event reconstruction
eﬃciencies.

●Analysis on Run 2 dataset π-tagged sample
Surapat Ek-In

Charm Physics @LHCb

Aug. 25th, 2021

8

Binﬂip method

Phys. Rev. D 99, 012007

WSRS● Measure the ratio of signal yields between Dalitz bins -b and +b,
in bins of the decay time j.
● z = y - ix and rb is the ratio at t = 0.
● Strong phase diﬀerences: Xb = cb - isb [constrained from CLEO

~31M

and BESIII, arXiv:2003.00091]● With CP conservation (q/p = 1):- Sensitive to both x and y parameters!
Surapat Ek-In

Charm Physics @LHCb

Aug. 25th, 2021

9

Binﬂip Results

Surapat Ek-In

Charm Physics @LHCb

arXiv:2106.03744

Aug. 25th, 2021

10

Binﬂip Results

arXiv:2106.03744

First observation of a diﬀerence between“D0 mass eigenstates ( > 7σ signiﬁcance)’’However, no signiﬁcant CPV is observed.
Surapat Ek-In

Charm Physics @LHCb

Aug. 25th, 2021

11

Binﬂip Upcoming Results
Semileptonic [μ-tagged]● Model independent Binﬂip Method- Cover wider decay time distribution because events are selected with muoncandidate- Combination with prompt sample● Model dependent amplitude model- Perform amplitude ﬁt with parameterized Dalitz and decay time eﬃciencies

Surapat Ek-In

Charm Physics @LHCb

Aug. 25th, 2021

12

Time-dependent CPV in●arXiv:2105.09889

Search for CPV in two-body decay-Measure the time-dependent decay rate asymmetry●

The raw asymmetry can be factored to●Analysis on Run2 dataset π-tagged sample~58M

Final state dependent CPV~ 10-5~519M~18M

Control sample
No signiﬁcant CPV
Surapat Ek-In

Charm Physics @LHCb

Aug. 25th, 2021

13

Time-dependent CPV in

Surapat Ek-In

Charm Physics @LHCb

arXiv:2105.09889

Aug. 25th, 2021

14

Measurement of CPV in●Time-integrated CPV search-●

arXiv:2105.01565

Measure decay width diﬀerence between D0 ﬂavours

This quantity can be large up to around 1%●

Consistent with no CPV at 2.4σ●

Most precise measurement up to date!

Phys. Rev. D 92, 054036●Analysis on Run 2 dataset π-tagged sample

Surapat Ek-In

Charm Physics @LHCb

Aug. 25th, 2021

15

Lifetime ofbaryon

LHCb-PAPER-2021-021

Charm hadron hierarchy●On PDG 2018

PRD 98, 030001 (2018)●In 2018, LHCb measured longer

lifetime insemileptonic b-baryon decays

PRL 121, 092003(2018)●Cross-check the result with an independent sample-Run 2 dataset on promptly produced
Ω0c/Ξ0c → pK−K−π+ ﬁnal state●

Use prompt D0 → K−K+π−π+ decays as control mode

Estimate lifetime with least squares ﬁts to decay time

Surapat Ek-In

Charm Physics @LHCb

Aug. 25th, 2021

16

Lifetime ofbaryon

LHCb-PAPER-2021-021● Measure the lifetimes to be[ Preliminary ]Preliminary

Preliminary

Surapat Ek-In

Charm Physics @LHCb

Aug. 25th, 2021

17

Conclusions● LHCb has produced the largest dataset of charm hadrons.
- This leads to new interesting results and provides often world-bestmeasurements- More results are coming soon!
● However, the measurements are limited by statistics- This is expected to be improved in Run 3 which is starting next year withluminosity up to 50/fb by 2030
- Working on preparing upgraded detector as well as upgraded online trigger

Surapat Ek-In

Charm Physics @LHCb

Aug. 25th, 2021

18

Thank you!
Any questions?

BACKUPMixing and CPV● Mass eigenstates of neutral meson mixing● There are diﬀerent scenarios of CPV
Direct CPV● Usually described by mixing parameters x, y,,CPV in mixing● and interference parameter● Mixing occurs when x and y ≠ 0
CPV in decay-mixing interference

Surapat Ek-In

Charm Physics @LHCb

Aug. 25th, 2021

21

Binﬂip Results

More than 7σ deviation from zero!

Consistent with no CPVSurapat Ek-In

Charm Physics @LHCb

Aug. 25th, 2021

22

Binﬂip Results

First observation of a diﬀerence between D0 mass“eigenstates with signiﬁcance of more than 7σ.

’’However, no signiﬁcant of CPV is observed.
Surapat Ek-In

Charm Physics @LHCb

Aug. 25th, 2021

23

Binﬂip Results

Surapat Ek-In

Charm Physics @LHCb

Aug. 25th, 2021

24

Binﬂip Results

Surapat Ek-In

Charm Physics @LHCb

Aug. 25th, 2021

25

Time-dependent CPV in

Surapat Ek-In

Charm Physics @LHCb

Aug. 25th, 2021

26

Time-dependent CPV inarXiv:2105.09889● The analysis procedure is controlled on Kπchannel where CPV is not expected.
● We found no signiﬁcant CPV in thechannel, and the analysis is not aﬀectedsigniﬁcantly by the systematics.

Surapat Ek-In

Charm Physics @LHCb

Aug. 25th, 2021

27

Measurement of CPV in

Surapat Ek-In

Charm Physics @LHCb

arXiv:2105.01565

Aug. 25th, 2021

28

Lifetime ofSurapat Ek-In

baryonCharm Physics @LHCb

Aug. 25th, 2021

29

Lifetime ofSurapat Ek-In

baryonCharm Physics @LHCb

Aug. 25th, 2021

30