1. Heavy-quark and Quarkonia production in high-energy heavy-ion collisions
André Mischke
1st International Workshop on Multiple Partonic Interactions at the LHC
Universita’ degli Studi di Perugia, Perugia, Italy
27-31 October 2008

2. Outline In-medium production of heavy flavor at RHIC
Open heavy flavour
- charm cross section
nuclear modification factor
two particle correlations
Quarkonia (J/ and )
Perspectives
Andre Mischke (UU)
– Perugia – 5/7/2019

3. Matter in extremes: The QGP
Study strongly interacting matter under extreme conditions
high temperature
high density
Lattice QCD predicts a phase transition from hadronic matter to a deconfined state, the Quark-Gluon Plasma
Experimental access via high energy heavy-ion collisions
Temperature
Quark-Gluon Plasma
RHIC
Hadronic matter
Baryon density
Andre Mischke (UU)
– Perugia – 5/7/2019

4. Probing the hot, dense QCD matter with jets
Au+Au collision
p+p collision
Hard processes occur in the early stage of the collision (pQCD)
Hard scattered partons traverse through the medium & interact strongly
General picture: Energy loss via medium induced gluon radiation (Bremsstrahlung)
Energy density at RHIC (Bjørken estimate)
more than 30 times normal nuclear matter density
Andre Mischke (UU)
– Perugia – 5/7/2019

5. Results from light quarks
photons
light hadrons
What have we learnt so far ?
Central Au+Au collisions produce dense, rapidly thermalizing matter
Jet quenching in opaque medium  strongly interacting plasma (sQGP)
Produced matter shows collective behavior; well described by ideal hydrodynamics (no viscosity)  “Perfect Liquid”
Relevant degrees of freedom seem to be partonic (constituent quark scaling)
Andre Mischke (UU)
– Perugia – 5/7/2019

6. Limitations of RAA
K.J. Eskola et al., Nucl. Phys. A747 (2005) 511
light hadrons
central RAA data
increasing density ?
Jet quenching well described by energy loss models
Surface bias effectively leads to saturation of RAA with density
Limited sensitivity to the region of highest energy density
Needed: - insensitive trigger particles: Prompt photons probes with higher penetrating power: Heavy quarks
Andre Mischke (UU)
– Perugia – 5/7/2019

7. Energy loss of heavy quarks in QCD matter
Large mass
primarily gg  QQ;
production rates from pQCD
- sensitivity to initial state gluon distribution
 To be verified for heavy-ion collisions
Heavy quarks
- ”grey probes”
energy loss due to suppression of small angle gluon radiation (dead-cone effect) Dokshitzer & Kharzeev, PLB 519, 199 (2001)
Which questions can be addressed ?
- Energy loss mechanism, degree of thermalization: Open heavy flavor
- Deconfinement (dissociation in QGP), degree of thermalization: Hidden heavy flavor
parton
hot and dense medium
Wicks et al, NPA784, 426 (2007)
Andre Mischke (UU)
– Perugia – 5/7/2019

8. Detection of heavy-flavor particles
called non-photonic electron
Full reconstruction of open charmed mesons
D0  K- + p (BR = 3.89%)
direct clean probe: signal in invariant mass distribution
difficulty: large combinatorial background; especially in a high multiplicity environment
event-mixing and/or vertex tracker needed
Semi-leptonic decay of charm and bottom mesons*
c  lepton + X (BR = 9.6%)
D0  e+ + X (BR = 6.87%)
D0  m+ + X (BR = 6.5%)
b  lepton + X (BR = 10.9%)
robust electron trigger
needs handle on photonic background
* F.W. Buesser et al. (CCRS), NPB 113, 189 (1976)
Andre Mischke (UU)
– Perugia – 5/7/2019

9. Detectors at RHIC Au+Au at sNN = 200 GeV
Designed for leptonic measurements
DC, PC, TEC, RICH, EMC and Muon tracking  low radiation length
Open heavy flavors
muons (muon arms at forward rapidities)
electrons
Quarkonia states
Large acceptance magnetic spectrometer
High resolution TPC, ToF, CTB and EMC
Open heavy flavors
hadronic reconstruction of D mesons using TPC + ToF
muon identification with TPC + ToF
electrons
Quarkonia states using special triggers
Andre Mischke (UU)
– Perugia – 5/7/2019

10. Electron identification
Ke3 decays (MC)
p0 Dalitz and
g conversion (MC)
MC (p0+Ke3)
Data
Phenix
Electromagnetic calorimeter and RICH at mid rapidity
pT < 5 GeV/c
STAR
ToF + TPC
pT < 4 GeV/c
EMCal + TPC
pT > 1.5 GeV/c
E/p
Andre Mischke (UU)
– Perugia – 5/7/2019

11. Electron background sources
Phenix
Photonic electron background
- g  e+ + e- (small for Phenix)
- p0  g + e+ + e-
- h, w, f, etc.
Phenix is almost material free  their background is highly reduced compared to STAR
Background is subtracted by two independent techniques - very good consistency between them
- converter method (1.68% X0)
- cocktail method
STAR determines photonic background using invariant mass
mass (GeV/c2) e-  e+
dca
STAR
Andre Mischke (UU)
– Perugia – 5/7/2019

12. Non-photonic electron spectra
Phys. Rev. Lett. 98, (2007)
Phys. Rev. Lett. 98 (2007)
Au+Au
Au+Au
0-5%
10-40%
40-80%
d+Au
p+p
p+p
Spectra measured up to 10 GeV/c
Integrated yield follows binary collision scaling
Yield strongly suppressed at high pT for central Au+Au
Andre Mischke (UU)
– Perugia – 5/7/2019

13. Charm cross section in Phenix
after subtraction of cocktail
c dominant
b dominant
Channels:
Electrons
Di-electrons
Start looking at open charm: D0 K+p-p0, where p0  gg
Comparison to charm, bottom and Drell-Yan from PYTHIA
In good agreement with single electrons
scc= 518 ± 47 (stat) ± 135 (sys) ± 190 (model) mb
sbb= 3.9 ± 2.4 (stat) +3/-2 (sys) mb
Andre Mischke (UU)
– Perugia – 5/7/2019

14. Open charm reconstruction in STAR
d+Au 200 GeV
PRL 94 (2005)
Au+Au 200 GeV
arXiv: [nucl-ex]
Cu+Cu 200 GeV
A. Shabetai, QM 2008
First identified D mesons in heavy-ion collisions
Current method has its kinematical limits
Andre Mischke (UU)
– Perugia – 5/7/2019

15. Charm cross section in STAR
Use all possible signals
- D0 mesons
- electrons
- muons
Charm cross section is well constrained
- 90% of total cross section
- direct measurement
- D0 mesons and muons constrain the low-pT region m p
Andre Mischke (UU)
– Perugia – 5/7/2019

16. Total charm cross section
centrality
Both STAR and Phenix are self-consistent
STAR data factor of ~2 larger than Phenix data  work in progress…
Cross section follows binary collision scaling
 charm exclusively produced in initial state
Andre Mischke (UU)
– Perugia – 5/7/2019

17. RAA for non-photonic electrons  a surprise !+
+ STAR, prel.: Cu+Cu 200 GeV, 0-54%
STAR
Phenix
RAA(e) ≈ RAA (h) at pT > 6 GeV/c  not in line with expectations from dead-cone effect
Models implying D and B energy loss are inconclusive yet
collisional energy loss
dissociation in the medium may play a role
Smoothly decrease from peripheral to central Au+Au
Cu+Cu data fits into systematics
Andre Mischke (UU)
– Perugia – 5/7/2019

18. Heavy-flavour correlations
M. Cacciari et al., PRL 95, (2005)
e–D0 azimuthal angular correlations
- D/B discrimination
- sensitive to NLO processes for charm
Significant bottom contribution to non-photonic electrons
Charm content in jets ~5%
A. M., arXiv: (hep-ph)
essentially from B decays only
75% from charm
25% from beauty
pQCD: Large uncertainty in D/B crossing point: pT = 3-10 GeV/c
Andre Mischke (UU)
– Perugia – 5/7/2019

19. “Melting” of Quarkonia states in QGP
Charmonia: J/, ’, c Bottomonia: (1S), (2S), (3S)‏
Color screening of static potential between heavy quarks (λD)
- J/suppression Matsui and Satz, Phys. Lett. B 178 (1986) 416
Suppression of states is determined by TC and their binding energy
 QCD thermometer
Lattice QCD: Evaluation of spectral fcts
Sequential disappearance of states
H. Satz, HP2006
Andre Mischke (UU)
– Perugia – 5/7/2019

20. RAA for J/ in Phenix  a surprise !
Comprehensive J/ measurements in p+p, d+Au, Cu+Cu and Au+Au
RAA(RHIC, y=0) ≈ RAA(SPS)
RAA(y=0) > RAA (y>1.7)
Possible mechanisms
- final state: recombination?
- initial state: cold nuclear effects?  Run8 d+Au data
centrality
Andre Mischke (UU)
– Perugia – 5/7/2019

21. J/ spectra and RAA in STAR
J/ p+p cross sections: consistent within ~1 up to 10 GeV/c
J/ production in Cu+Cu at pT>5 GeV/c (fit): RAA = 0.9 ± 0.2(stat.)
Contrast to AdS/CFT prediction
Due to Cronin? – Run8 d+Au data
Andre Mischke (UU)
– Perugia – 5/7/2019

22. Disentangle contributions to J/ via correlations
preliminary
5.4 signal
(S+B)/B: 54/14
J/-h azimuthal correlations sensitive to source of J/ UA1, PLB 200, 380 (1988) and 256, 112 (1991)
B  J/ feed-down <15%
Phenix: J/y from y’ = 8.6 ± 2.5%
Andre Mischke (UU)
– Perugia – 5/7/2019

23.  cross-section in p+p STAR run 6 p+p at sNN = 200 GeV 3σ signaly
d/dy (nb)
Counts
preliminary
preliminary
STAR run 6 p+p at sNN = 200 GeV
3σ signal
(1s+2s+3s)  e+e-:
BReed/dy = 91 ± 28(stat.) ± 22(sys.) pb
Cross section consistent with NLO pQCD calculations and world data trend
Upsilon RAA; signal already seen in Au+Au !
Andre Mischke (UU)
– Perugia – 5/7/2019

24. Summary Charm production cross-section Non-photonic electron spectra
important baseline measurements for Quarkonia studies
follows binary collision scaling and agrees with FONLL within errors
Non-photonic electron spectra
energy loss in heavy-ion collision is much larger than expected
Electron-D0 azimuthal correlations
- B and D contributions comparable at pT>5 GeV/c & consistent with FONLL
J/
- p+p: cross section up to 14 GeV/c
- Cu+Cu: RAA~1 at high pT – more accurate measurements
Quarkonia
 cross-section in pp consistent with pQCD and world data
first  signal in Au+Au
Next: absolute cross-section in p+p, d+Au (run 8) and Au+Au and RAA
Run 7 Au+Au data
Andre Mischke (UU)
– Perugia – 5/7/2019

25. Perspectives: RHIC II
STAR and Phenix upgrades visioning heavy-flavor measurements
STAR heavy-flavour tracker and full ToF: Open charm spectra at higher pT and flow measurements
Phenix silicon vertex tracker
RHIC II upgrade will provide more luminosity (~2012)
Andre Mischke (UU)
– Perugia – 5/7/2019

26. ALICE Inner Tracker System
Perspectives: ALICE at LHC
D0  K
D+  K-++
D,B  e + X
S/B ≈ 10 %
S/(S+B) ≈ 40
(1 month Pb-Pb running)
statistical.
systematic.
TI2 injection test: muons from beam dump
ALICE Inner Tracker System
Andre Mischke (UU)
– Perugia – 5/7/2019

27. Backup
Andre Mischke (UU)
– Perugia – 5/7/2019

28. Silicon Strip Detector
The ALICE detector
A Large Ion Collider Experiment
Size: 16 x 26 meters
Weight: tons
lead beam lead beam
large acceptance / excellent tracking capabilities / very good PID
Silicon Strip Detector
Especially designed for measurements in heavy-ion collisions
Utrecht/NIKHEF group built a part of the inner particle tracker
Full azimuthal coverage
Andre Mischke (UU)
– Perugia – 5/7/2019

29. Total bottom cross section from Phenix
Several extrapolations used (pT, rapidity and mass)
Different methods agree
Reasonably good agreement with NLO pQCD
Andre Mischke (UU)
– Perugia – 5/7/2019

30. D* - jet measurement D* - Jet azimuthal correlation:
- visible near side peak.
Raw fragmentation function:
- D(z), where z = pL(K)/E jet
- Ejet found and corrected using cone algorithm.
- Match of data and LO Monte Carlo at high z
- Excess at low z: NLO contribution.
Andre Mischke (UU)
– Perugia – 5/7/2019

31.  trigger in STAR Sample -triggered event e+e- candidate Offline:
mee = 9.5 GeV/c2
cosθ = -0.67
E1 = 5.6 GeV
E2 = 3.4 GeV
Offline:
charged tracks +
EMC tower
Fast L0 Trigger (Hardware)
Select events with at least one  high energy tower (E~4 GeV)
L2 trigger (Software)
Clustering, calculate mee, cos q.
Very clean to trigger up to central Au+Au
Offline: Match TPC tracks to triggered towers
Andre Mischke (UU)
– Perugia – 5/7/2019

32.  mass resolution and expected
STAR detector does not resolve individual states of the 
- finite p resolution (B=0.5 T)
- e-bremsstrahlung
Yield is extracted from combined ++ states
FWHM ≈ 700 MeV/c2
  e+ e-
NLO calculations
R. Vogt et al., RHIC-II Heavy Flavor White Paper
State
Mass [GeV/c2]
Bee [%]
(dσ/dy)y=0
Bee×(dσ/dy)y=0 
2.38
2.6 nb
62 pb 
1.91
0.87 nb
17 pb 
2.18
0.53 nb
12 pb
++
91 pb
Andre Mischke (UU)
– Perugia – 5/7/2019

33.  cross section and uncertainties
N = 48±15(stat.)
Ldt = (5.6±0.8) pb-1
 = geo×L0×L2×2(e)×mass
geometrical acceptance geo
0.263±0.019
efficiency L0 trigger L0
0.928±0.049
efficiency L2 trigger L2
0.855±0.048
efficiency of e reconstr. 2(e)
0.47±0.07
efficiency of mass cut mass
0.96±0.04 
0.094±0.018
Andre Mischke (UU)
– Perugia – 5/7/2019