1. Reconstruction Charm and Bottom with the ALICE EMCAL
Mark Heinz for the ALICE collaboration
Yale University
Winter Workshop of Nuclear Dynamics
Big Sky, Montana, Feb 2007

2. Outline Physics Motivation
Method for reconstructing Bottom via displaced vertices
ALICE Electromagnetic Calorimeter
EMCAL simulation status
Conclusion
Winter Workshop, Feb 2007

3. Physics Motivation
Current theoretical estimates for bottom and charm production still have large uncertainties.
NLO pQCD, pp, s = 14 TeV
MNR code: Mangano, Nason, Ridolfi, NPB373 (1992) 295.
CERN/LHCC ,
hep-ph/
Winter Workshop, Feb 2007

4. Physics Motivation Heavy ion collisions:
STAR, submitted to PRL (nucl-ex/ )
non phot. el.
Heavy ion collisions:
Interactions of heavy quarks with the medium
RHIC has recently shown the that the suppression of non-photonic electrons is not consistent with current energy loss predictions
Using the current best estimates for medium density (q-hat) the suppression pattern is consistent with charm quarks only up to 8 GeV/c in pT
Similar uncertainties are present for LHC energies
Winter Workshop, Feb 2007

5. Charm and Bottom via semi-leptonic decays
Semileptonic Channels:
c  e+ + anything (B.R.: 9.6%)
D0  e+ + anything (B.R.: 6.87%)
D  e + anything (B.R.: 17.2%)
b  e+ + anything (B.R.: 10.9%)
B  e + anything (B.R.: 10.2%)
 single “non-photonic” electron continuum
“Photonic” Single Electron Background:
g conversions (p0  gg)
p0, h, h’ Dalitz decays
r, f, … decays (negligible)
Ke3 decays (neglible)
Winter Workshop, Feb 2007

6. Displaced Vertex Method
Search for semi-leptonic B-decay
B  e + D0  e + K- + +/e
Idea of Displaced vertex finding using muons was first tested at CDF
Create pairs of leptons and charged tracks which match the criteria for a secondary vertex:
pT> 2 GeV/c, R=2+2 K
/e
Pe+K
Signed DCA: Lxy= r .pe+k / |pe+k|
Lxy
CDF Phys.Rev.D66 (2002)) e- D0
SecVtx r B-
Reminder:
B ct: ~500 mm
D ct: ~100 mm
PrimVtx
Winter Workshop, Feb 2007

7. Displaced Vertex Simulations (signal)
1st Step: pure signal  efficiency
PYTHIA: 14 TeV, p+p, 40k events, pt(hard)>2.75
Yields 6000 electrons within detector acceptance from beauty
Reconstruction efficiency per selected electron trigger ~70%
Signal
Efficiency of method improves significantly with #ITS hits
Lxy (cm)
Winter Workshop, Feb 2007

8. Displaced Vertex (charm backgrounds)
Dominant backgrounds are semi-leptonic charm decays
Simulation: PYTHIA, 14 TeV p+p, c-cbar, pt(hard)>2.1 GeV
Effective way of eliminating is by cut on invariant mass
Charm PYTHIA events
Winter Workshop, Feb 2007

9. Displaced vertex (backgrounds)
80k Minbias PYTHIA events (MSEL1)
Combinatoric, pi0 and photon backgrounds can be investigated
Background is consistent with zero, but more simulation statistics are needed to obtain an exact estimate of significance
Minbias PYTHIA, 14 TeV
Minbias PYTHIA, 14 TeV
Winter Workshop, Feb 2007

10. Track impact parameter resolution
Primary vertex finding proceeds in 2 passes
Select primary tracks on the basis of their d0
Cut |d0| < nsd0(pt)
sd0(pt) = svtx  strack(pt)
parametrized resolution
track
vertex x y
Winter Workshop, Feb 2007

11. Secondary vertex resolution (simulation)
Determine position resolution for semi-leptonic heavy flavor vertices from PYTHIA
Position resolution in x,y,z is ~180mm, no strong dependency on coordinate
/e K
SecVtx
reconstruced- MC (cm)
reconstruced- MC (cm)
reconstruced- MC (cm)
Winter Workshop, Feb 2007

12. Secondary vertex resolution (simulation)
Study of vertex resolution as a function of hits in the inner tracker ITS-hits, maximum of 6 hits.
Winter Workshop, Feb 2007

13. ALICE Set-up TRD ITS TPC Size: 16 x 26 meters Weight: 10,000 tons
Winter Workshop, Feb 2007

14. ALICE Electromagnetic Calorimeter
Lead-scintillator sampling calorimeter
Shashlik fiber geometry
Avalanche photodiode readout
Coverage:
|h|<0.7, Df=110o
Winter Workshop, Feb 2007

15. ALICE EMCAL (2) 12 supermodules 24 strips in η 12 (or 6) modules in φ
12672 elementary sensors (towers)
77 alternating layers of
1.44 mm Pb (1% Sb)
1.76 mm polystirene scintillator
Dh x Df = 0.014x0.014
Module (2x2 towers)
Winter Workshop, Feb 2007

16. EMCAL energy resolution
Energy resolution has been measured and is within specifications ~12%/E +2%
Production Module Spec
Prototype Module Spec
Winter Workshop, Feb 2007

17. EMCAL Project milestones
18 institutions worldwide of which 13 are from ALICE-USA collaboration
Assembly of supermodules will be shared between Yale (US) and Grenoble (F)
US-portion of project dependant on funding from DOE: CD-2 (critical decision) this summer.
Assembly and testing of supermodules (SM) at Yale to start in 2008
Installation of first SM in ~2009 (low luminosity PbPb)
Winter Workshop, Feb 2007

18. EMCAL software development
Cluster shape analysis for PID
Electron/Hadron discrimination
Track-Cluster Matching
Electron trigger simulations
High-Pt simulations (jet-finder)
Institutes involved in HF simulations:
Yale, LBL, LLNL, WSU, Nantes (Subatech), Strassbourg, Catania
Winter Workshop, Feb 2007

19. EMCAL PID e/p discrimination p/E distribution g/p0 discrimination
Cluster shape analysis
Effective mass
Cluster in EMCAL  °
hadrons
Study by Guenole Bourdaud
Winter Workshop, Feb 2007

20. Hadron/p0 discrimination
Granularity study of EMCAL
Granularity 2x2
Granularity 3x3
For a 30 GeV photon the 0 suppression factor improve from 10 to 100 when increasing the granularity from 2x2 to 3x3
Study by A.Pavlinov (WSU)
Winter Workshop, Feb 2007

21. TPC track to EMCAL cluster matching
Code is now in Alice CVS
Good matching effiency for low multiplicity
Still some parameter tuning needed for Hijing simulations
Cluster Matching Prob for electrons
dN/dη = 4000 %
Mult = 10 %
Study by A.Pulvirenti (Catania)
Winter Workshop, Feb 2007

22. Conclusion
Displaced vertex method will be promising in measuring direct B-meson contribution to non-photonic electrons
The method combines the EMCAL PID and triggering capabilities
The ALICE EMCAL project is a collaboration between ALICE USA and European institutions
The simulations for the EMCAL are on track, however more detailed physics simulations are required for the DOE CD-2 decision this summer
Winter Workshop, Feb 2007