Sandro De Cecco

1
Charm production cross section and charm physics
at the Tevatron

• Sandro De Cecco
• INFN Roma 1
• Rencontres de physique du Vietnam, Hanoi 07
  aout 2004

2
Outline

• The Tevatron collider
• CDF detector and triggers.
• Highlights on hadronic heavy flavours production.
• Measurement of prompt charm production cross
  section.
• Search for direct ACP in D0 Cabibbo suppressed
  decays.
• Search for FCNC decay D0?mm.
• Conclusions and perspectives

! Disclaimer results come from CDF only D0 is
going to publish charm physics results soon
3
The Tevatron pp collider
Superconducting proton-synchrotron 36p?36p
bunches, crossing each 396 ns at vs 1.96
TeV Luminosity.. record peak L 1
? 1032 cm-2s-1 (as of July 04) interactions /
bunch-crossing... lt N gt 1.5 (_at_ 5 x 1031
cm-2s-1) Luminous region size... 30 cm
(beam axis) x 30 mm (transverse)
4
Tevatron plans

• RECYCLER had a first successful test
• Plans beyond FY 05 depends on Recycler ring and
  electron cooling performances
• Will see after aug./nov.04 shutdown

Year Base plan luminosity/yr (fb-1) Design plan Luminosity/yr (fb-1)
FY02 0.08 0.08
FY03 0.20 0.22
FY04 0.31 0.38
FY05 0.39 0.67
FY06 0.50 0.89
FY07 0.63 1.53
FY08 1.14 2.37
FY09 1.16 2.42
Total 4.41 8.56
5
Tevatron FY04 performance
L (pb -1)
FY04 Design
FY04 Base
1st May 2004
2003
1st Jan. 2004
2002

• Tevatron is working very well this year (Design
  plan)
• Initial luminosity (may 04) 7.2 X 1031 sec-1
  cm-2 (now 1.x1032)
• Weekly Integrated luminosity 10 pb-1/w
• 350 pb-1 on tape, 100-200 pb-1 used for
  analysis so far

6
The upgraded detectors

• New tracking silicon and
• fibers in magnetic field
• Upgraded muon system
• Upgraded DAQ/trigger
• (displaced track soon)

• New silicon detector
• new drift chamber
• Upgraded calorimeter, m
• Upgraded DAQ/trigger,
• displaced-track trigger
• New TOF PID system

7
HF Physics at pp collider
bb/cc production mechanics in hadron collider
LO
NLO

• Huge cross-section 50-100 ?b
• All B/D species produced
• Bu,Bd,Bs,Bc,B,?b, ?b
• D0,D?,D,Ds,D,?c, ?c

• BUT ?(bb,cc) ltlt ?(pp) (65 mb) ? HF events have
  to be selected with specific triggers
• Trigger requirements large bandwidth, background
  suppression, small dead-time

8
B production x-section, Run I
B cross section measured from Run I at Tevatron
is consistently higher than NLO QCD
Theoretical development still ongoing. Ex
fragmentation effect .
Experimental Approaches
More cross section measurement -- energy at
1.96TeV -- lower pT(B)
? Measure CHARM production cross section
9
Heavy Flavours triggers at CDF II
With the New Silicon Vertex Trigger
Conventional at colliders (Run I)
Di-Muon (J/?) Pt(?) gt 1.5 GeV J/? modes down to
low Pt(J/?)0 (Run II) Rare decays
Displaced track lepton (e, ?) I.P.(trk) gt
120?m Pt(lepton) gt 4 GeV Semileptonic modes
2-Displaced tracks PT(trk) gt 2 GeV pT gt 5.5
GeV I.P.(trk) gt 120(100) ?m fully hadronic modes


10
SiliconVertexTracker the hadronic B trigger

• Online Impact parameter
• Available at Level 2 trigger (20µs latency)
• ?Trigger decision
• ?convolution of transverse size of the beam spot
  with the impact parameter resolution of the SVT

s 47 um 35 um 30 um
SVT resolution
Beam spot size
( Compare to offline 46 mm )
Impact parameter distribution
Collect large amount of fully reconstructed B,D
hadrons
11
Prompt Charm Meson X-Section
With early CDF data 5.8?0.3pb-1

• Measure prompt charm meson
• production cross section

• Data collected by SVT trigger
• from 2/2002-3/2002

• Measurement not statistics limited
• Large and clean signals

12
Separating prompt from secondary Charm
Separate prompt and secondary charm based on
their transverse impact parameter distribution.
Prompt D
Secondary D from B

• Need to separate direct D and B?D decay
• Prompt D point back to collision point
• I.P. 0
• Secondary D does not point back to PV
• I.P.? 0

Prompt peak
Detector I.P. resolution shape measured from data
in K0s sample.
B?D tail
Direct Charm Meson Fractions D0
fD86.40.43.5 D fD88.11.13.9 D
fD89.10.42.8 Ds fD77.33.82.1
Most of reconstructed charm mesons are direct ?
13
Prompt Charm Meson X-Sections
? Determine trigger and reconstruction efficiency
from data and MC ? Measure charm meson pT spectrum
Integrated cross sections
As a comparison the beauty meson x-sec (CDF Run
I)
CDF prompt charm cross section result published
in PRL hep-ex/0307080
14
Differential Charm Meson X-Section
PT dependent x-sections
Theory prediction
CTEQ6M PDF Mc1.5GeV, Fragmentation ALEPH
measurement Renorm. and fact. Scale
mT(mc2pT2)1/2 Theory uncertainty scale factor
0.5-2.0
Calculation from M. Cacciari and P.
Nason Resummed perturbative QCD (FONLL) JHEP
0309,006 (2003)
15
Comparison with Theory
Ratio of measured to predicted cross sections
PRL89122003,2002

• NLO calculations compatible within errors
• pT shape is consistent for D mesons

• Measured cross section is
• 1.5 factor higher similar to B

16
D0?hh- direct CP Asymmetries and Decay Rate
ratios

• The huge amount data collected by the Two Track
  Trigger have been used for this analysis
• Relative branching ratios
• G(D0?KK-) / G(D0?Kp)
• G(D0?pp-) / G(D0?Kp)
• G(D0?KK) / G(D0?pp)2.8 (SM)
• Direct CP asymmetries where
• f is CP eigenstate (ex. KK-,pp-)
• Candidates selected as D/- ?D0 p (unbiased
  tag of the D0 flavor)

Normalization mode D0?Kp 180000 D/-? D0 p!!!
17
D0 Cabibbo suppressed 2 body decays
D0
pp
KK
D0
18
CP Asymmetries and Decay Rate ratios
Very important to understand the asymmetry of the
CDF detector at per mille level !!!

• Results are computed after correction for
• intrinsic charge asymmetry
• relative acceptance between the D0 modes

Submitted to PRL august 04
Relative BRs CDF FOCUS
G(D0?KK) / G(D0?Kp) (9.92 ? 0.11 ? 0.12) (9.93 ? 0.14 ? 0.14)
G(D0?pp) / G(D0?Kp) (3.594 ? 0.054 ? 0.040) (3.53 ? 0.12 ? 0.06)
G(D0?KK) / G(D0?pp) (2.760 ? 0.040 ? 0.034) (2.81 ? 0.10 ? 0.06)
Direct CP asymmetries CDF CLEO II
ACP (D0?KK) (2.0 ? 1.2 (stat.) ? 0.6 (syst.)) (0.0 ? 2.2 (stat.) ? 0.8 (syst.))
ACP(D0?pp) (1.0 ? 1.3 (stat.) ? 0.6 (syst.)) (1.9 ? 3.2 (stat.) ? 0.8 (syst.))
19
Search for FCNC D0?mm

• SM expectation BR 310-13
• Best limit lt4.110-6 (90 CL) (Beatrice/WA92,
  E771)
• BR significantly enhanced with New Physics (e.g.
  R-Parity Violation Susy 3.510-6)
• Experimental strategy
• Events from two-track trigger using first 69pb-1
  of data
• To cancel acceptance effects normalize to D0?pp
• Only relative efficiency needed

20
FCNC D0?mm Results
Combinatorial1.5-0.7 events Fakes 0.22-0.02
events
?1.7 expected events 0 events
observed
Mmm with D tag and 2 muons
BR(D0?mm)lt2.4x10-6 (_at_90 CL)
Factor 2 improvement over best limit
Next use full muon coverage and 2-3 times more
data (1year) ? also look at
D?pmm, D?Kmm, D0?me, Ds
21
Conclusions

• Prompt charm cross-section has been measured for
  the first time at collider ? useful input to QCD
  calculations for HF production and hadronization
  models.
• Hadronic D0 decays relative BRs measured with
  high accuracy
• Search for direct CP asymmetries in Cabibbo
  suppressed D0 decays is world best single
  measurement.
• CDF will soon be sensitive to beyond SM theories
  with rare D decays
• Charm yields are competitive to B-factories and
  physics program complementary to CLEO-C.

The charming side of the Tevatron
22
BACKUP slides
23
CDF II tracking system
TOF 100ps resolution, 2 sigma K/? separation for
tracks below 1.6 GeV/c (significant improvement
of Bs flavor tag effectiveness)
- charge)
TIME OF FLIGHT
CDF Roma

• COT large radius (1.4 m) Drift chamber
• 96 layers, 100ns drift time
• Precise PT above 400 MeV/c
• Precise 3D tracking in ?lt1
• ?(1/PT) 0.1GeV 1 ?(hit)150?m
• dE/dx info provides gt1 sigma K/? separation
  above 2 GeV

• SVX-II ISL 6 (7) layers of double-side
  silicon (3cm lt R lt 30cm)
• Standalone 3D tracking up to ? 2
• Very good I.P. resolution 30?m (20 ?m with
  Layer00)

LAYER 00 1 layer of radiation-hard silicon at
very small radius (1.5 cm)
(achievable 45 fs proper time resolution in Bs ?
Dsp )
24
CDF II particle ID handles
s
TOF PID

• Specific Ionization of charged particles (dE/dx)
  measurement in the COT gas chamber.
• Time of flight measurement with the new
  scintillator bars detector (TOF) at R1.4m with a
  sTOF 100 ps

dE/dx PID
p
Total K/p separation power of at least 2s for
momentum up to 1.6 GeV/c with TOF And at least
1s for momentum up to 4-5 GeV/c with TOF dE/dx
25
CDF Trigger System Overview

• Crossing 396 ns 2.5 MHz
• Level 1 hardware
• Calorimeter, Muon, Track
• 15kHz (reduction x200)
• Level 2 hardware CPU
• Cal cluster, Silicon track
• 300 Hz (reduction x5)
• Level 3 Linux PC farm
• Offline quantities
• 50 Hz (reduction x6)

26
CDF data tacking performance
Data-Taking Efficiency
Integrated Luminosity
Detector efficiency 85-90
27
Charge Asymmetry in the CDF Detector
Study asymmetry using unbiased tracks and correct
Residual asymmetry syst.error
(same track quality cuts generic track sample)
(Expect no CP asymmetry)
28
Normalization Mode D0?pp
Search window 1.84ltmlt1.884 GeV
Selection intersect D0 with soft
p 0.144ltm(D)-m(D0)lt0.147 Optimized cuts
Lxylt0.45 cm, dxylt0.015cm, Angle cut
between track and muon stub, Track quality
cuts N(pp) 1371-53
Kp
Relative efficiency from Monte Carlo ( muon
reconstruction and p decay in flight efficiency)
29
D0?mm Background
Fakes from p misidentification N(D0?pp) in mass
window times (misid probability)2
Estimate combinatorics from high mass
sideband where both tracks are muons
p misid probability
From D tagged D0?Kp
Fakes 0.22-0.02 events
Combinatorics1.5-0.7 events
30
X(3872) physics the B fraction