Charm Quarks at the PANDA Experiment

Transcription

1 Charm Quarks at the PANDA Experiment Thomas Mannel Theoretische Physik I, Universität Siegen PANDA Collaboration meeting, Bochum,

2 Contents Introduction 1 Introduction General Relevance of Charm 2 Generalities The Situation at PANDA Cross Section Calcuations 3 Spectroscopy of Charmonium (like) states Open Charm

3 General Relevance of Charm General Relevance of Charm Strong interactions QCD laboratory Intermediate case between heavy and light quarks Interesting Spectroscopy Strong decay modes Weak interactions Complementary to measurements for b quarks Mixing and CP violation Possible Window to Physics beyond the Standard Model

4 General Relevance of Charm Looking up: Investigate the up-type quarks Flavour Physics of charm: Compared to B and K : The roles of up and down quarks are interchanged Complementarity to top quark (flavour) physics Up-type Flavour tests are mandatory for a full test of our understanding of Flavour Physics

5 Charm is unique... General Relevance of Charm FCNC s are suppressed in the SM by GIM For bottom and strange: GIM CKM Factor 1 16π 2 m 2 t m 2 u M 2 W GIM is weakened by the large Top mass For charm (and top): GIM CKM Factor 1 16π 2 m 2 b m2 d M 2 W GIM is MUCH more efficient

6 General Relevance of Charm Up-type FCNC s have a very small SM pollution Relative Strength of New Physics (NP) in Up vs. Down-Type FCNC s might be different Cleaner (but not neccessary larger) signals of new physics: ( ) NP Signal ( ) NP Signal SM noise up-type > SM noise down-type Top plays a special role No Top Hadrons Flavour Phenomenology less rich Strong interactions perturbative Charm: Novel access to flavour dynamics

7 General Relevance of Charm Charm and Strong Dynamics Spectroscopy of ordinary Charmonia Radiative and Strong transitions of excited Charmonia A lot of new states : Interpretation in terms of QCD Fock States? Decays of these new states

8 The Charm of the world General Relevance of Charm Many Experiments have done / can do charm physics: CLEO-c (finished) BaBar (finished) LHC, in particular LHCb BESS III in Beijing BELLE and BELLE II COMPASS (to some extend)... and of course : PANDA Very Different rates and very different accessible states

9 Ingredients Introduction General Relevance of Charm 1 High Production Rate for charm quarks 2 Appropriate trigger windows and detector sensitivities 3 Clean environment At PANDA: (Probably) a sizable cross section: 100 nbarn Problem: Signal/Background PANDA will not be easy!

10 Generalities The Situation at PANDA Cross Section Calcuations

11 General Remarks Generalities The Situation at PANDA Cross Section Calcuations Hadronic at high energies: Perturbative QCD, known up to NLO Tevatron and LHC Energies (Figure from Kniehl et al., 2005) Hadronic Charm production at low energies: Perturbative QCD fails! We do not have a reliable method to calculate!

12 Generalities The Situation at PANDA Cross Section Calcuations at PANDA The PANDA Energy is close to Charm Theshold: Final state in pp Thresh. s [GeV] Thresh. p lab [GeV] η c (res.) 3.68 J/ψ (res.) 4.07 χ c0 (1P) 3.415(res.) 5.19 D 0 D D s Ds D 0 D Ds D s Λ c Λc Σ c (2455) Σ c (2455) p pj/ψ Λ c p D

13 Perturbative Approaches Generalities The Situation at PANDA Cross Section Calcuations Perturbative calculation of p p c c at NLO Nonperturbative input: proton pdf s Large Charm mass dependence close to threshold σ(p p Λ c Λc, p lab = 15 GeV) = nbarn Braaten et al.

14 Generalities The Situation at PANDA Cross Section Calcuations Alternatively: Perturbative calculation, Input: generalized parton distributions Hints at σ(p p Λ c Λ c, p lab = 15 GeV) 1 nbarn (Goritschnig, Kroll, Schweiger)

15 Generalities The Situation at PANDA Cross Section Calcuations however, Pertrubative QCD only at high energies, far above threshold at PANDA is hard to compute: Perturbative QCD is questionable... Only model dependent methods available Specific class of approaches: Regge Model: Exchanges of the leading Regge trajectories However, this is also limited to s t

16 Regge Model X-Sections Generalities The Situation at PANDA Cross Section Calcuations Regge Theory Calculation Universal coupling constant (Kaidalov, Volkovitsky) (determined from ρ ππ) Absorption factors for rescatterings of the inital and the final state

17 Generalities The Situation at PANDA Cross Section Calcuations σ(p p Λ c Λc, p lab = 15 GeV) 200 nbarn

18 Generalities The Situation at PANDA Cross Section Calcuations Alternatively: Regge Theory Calculation Coupling constants from Flavour SU(4) (Titov, Kämpfer) Absorption factors as in Kaidalov Volkovitsky σ(p p Λ c Λc, p lab = 15 GeV) 100 nbarn

19 Generalities The Situation at PANDA Cross Section Calcuations Alternatively: Regge Theory Calculation Couplings from QCD Sum rules Khodjamirian, C. Klein et al.) Absorption factors as in Kaidalov Volkovitsky σ(p p Λ c Λc, p lab = 15 GeV) = nbarn

20 Generalities The Situation at PANDA Cross Section Calcuations Other calculations (e.g. Haidenbauer, Krein) Coupled Channel Approach One Boson Exchange Potentials, with modfications Hints at σ(p p Λ c Λc, p lab = 15 GeV) O(µbarn)

21 Generalities The Situation at PANDA Cross Section Calcuations Summary on the Cross Section Perturbative Estimates turn out to be typically small... this is known also from other observables... must fail close to threshold Regge models are consistent with a cross section σ(p p Λ c Λc ) 100 nbarn Potentials are even larger... It is virtually imposible to compute this beyond an order-of-magnitude estimate Measurement!

22 Spectroscopy of Charmonium (like) states Open Charm

23 Spectroscopy of Charmonium (like) states Open Charm Spectroscopy: Ordinary Charmonia Difficult! Potential / NRQCD: Instantaneous Potentials, v/c Expansion Sum Rules: Ψ Ψγ need more Theoretical Engineering

24 Spectroscopy: Exotic States Spectroscopy of Charmonium (like) states Open Charm A whole set of unexpected states has been found in the charmonium region, e.g. the 3940 family

25 Spectroscopy of Charmonium (like) states Open Charm

26 Spectroscopy of Charmonium (like) states Open Charm Theory model dependent, connection to QCD?

27 Open Charm Introduction Spectroscopy of Charmonium (like) states Open Charm Bread-and-Butter Topics Spectroscopy of excited Charm states Strong decays if excited charm states Standard Weak interactions of ground states: D K π, Λ c Λπ, and alike Rare weak decays of charm: FCNC s Mixing and CP

28 Rare FCNC Decays Spectroscopy of Charmonium (like) states Open Charm c u + γ transitions D (s) γ + K /ρ/ω/φ... SM short distance contributon: BR few dominated by long distance contributions: BR(D 0 K γ) BR(D 0 ργ) NP appears as local Penguin operators Can a convincing NP case be constructed in these decays?

29 Spectroscopy of Charmonium (like) states Open Charm c u + l + l transitions D (s) l + l + K /ρ/ω/φ... also dominated by long distance contributions: BR(D 0 π/ρ + l + l ) 10 6 Analysis of the lepton spectra can help Likewise: Can a convincing NP case be constructed in these decays? D 0 µ + µ : A channel for LHCb! In the SM: BR(D 0 µ + µ ) D 0 γγ: Not a channel for LHCb! LD Contributions, interplay with D 0 µ + µ Forbidden Modes: D 0 e + µ etc...

30 Charm Mixing Introduction Spectroscopy of Charmonium (like) states Open Charm Transitions between D 0 and D 0 : Two Mass Eigenstates in the neutral D System D 1,2 = p D 0 ± q D 0 p 2 + q 2 = 1 Mixing Parameters x = m 1 m 2 Γ y = Γ 1 Γ 2 2Γ Opens a window to new physics with Γ = 1 2 (Γ 1 + Γ 2 ) Opens the road to time-dependent CP violation

31 Spectroscopy of Charmonium (like) states Open Charm Standard Model: At the quark level: Pollution by long distance effects In the SM: x O( ), y O( )

32 Spectroscopy of Charmonium (like) states Open Charm (Petrov) Exclusive calculations D [K π/ππ/πρ/...] D (Falk, Grossman, Ligeti, Nir, Petrov) Inclusive calculation: OPE in terms of inverse Powers of the charm mass (Bigi, Uraltsev, Georgi, Simmons. Ricciati, Ohl)

33 Spectroscopy of Charmonium (like) states Open Charm There are data!! y (%) HFAG-charm 1.5 no CPV April 2013 y (%) HFAG-charm 1.5 CPV allowed April σ 2 σ 3 σ 4 σ σ x (%) 0 1 σ 2 σ 3 σ 4 σ σ x (%)

34 Spectroscopy of Charmonium (like) states Open Charm Interpretation of Charm Mixing Difficult, due to long distance contributions A scenario x > 1% and x y could be interpreted as a manifestation of NP... but seems to be ruled our already Observations can be due to SM dynamics... yet may still contain a large NP contribution A precise SM prediction requires a theoretical breakthrough Knowing x and y is also of practical importance with respect to CP violation

35 CP Violation in Charm Spectroscopy of Charmonium (like) states Open Charm LHCb Measurement: Difference of time-integrated CP asymmetries for D K + K and D π + π : a CP = A CP (D 0 K + K ) A CP (D 0 π + π ) = (0.82 ± 0.21 ± 0.11)% (2012) World Average for this quantity (May 2013) a CP = (0.329 ± 0.121)% The SM tends to have a smaller value: a CP = m (2) f m (1) f

36 Spectroscopy of Charmonium (like) states Open Charm dir a CP HFAG-charm March 2013 A CP BaBar A CP Belle prel. A CP CDF A CP LHCb prompt prel. A CP LHCb semil. A Γ LHCb A Γ BaBar A Γ Belle prel ind a CP

37 Outlook: Charm at PANDA Spectroscopy of Charmonium (like) states Open Charm Projected HESR Luminosity: L cm 2 s 1 Optimists Cross Section: σ(p p Charm) 100 nbarn Charm events per snowmass year However: Signal to background is a problem: σ tot =( ) mbarn Signal Background 10 (5...6) Detailed Studies under way concerning open charm and weak processes. (Achim Denig, TM)

38 Outlook: Charm Physics Spectroscopy of Charmonium (like) states Open Charm Charm is becoming increasingly interesting: Evidence for D D Mixing (Still weak) Evidence for CPV in charm Extensive Spectroscopy of charmonia-like states Room for O(1) surprises in the up-quark sector PANDA may have have a shot at this...