Future Perspectives for Charm Physics at Hadron Machines

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Future Perspectives for Charm Physicsat Hadron
Machines
Sandro De Cecco FNAL-PPD/CDF and INFN Roma 1
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Outline

• Introduction on Heavy Flavour physics at hadron
  colliders

• Charm production, charm as a probe for QCD
• Heavy quarks hadro-production in pp and NN
  interactions
• DD correlations
• Charmonium
• Excited states, c-barions

• Charm input to CP violation picture
• D0 mixing
• Direct CPV in Charm decays
• FCNC decays

• The Experimental Charm of Hadron Colliders

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Heavy-Quark production in hadron collisions
Leading Order and Next to Leading Order
Q
g
Q
g
g
g
Flavor excitation
radiative corrections
Gluon splitting
Flavor creation
B/D-Hadrons and/or b/c-jets are the observables
rather than b/c-quark
Observed
Proton structure
Fragmentation
NLO QCD
Factorize physical observable into a calculable
part and a non-calculable but universal piece
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Fragmentation functions Db/c ?B/D
Perturbative part probability to find a hadron
with fraction x of original parton momentum
Hadronization non perturbative QCD, need models
Charm will have softer P-spectrum than b.
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Charm and beauty at collider

• Total inelastic x-sec 100 mb
• 103-104 x s(cc/bb)
• x-sec is 105-106 larger than at ee-
• Open spectrum of mesons and barions
• Bu , Bd , Bs , Bc , ?b , ?b
• D, D0, Ds , ?c , cc , ?c

• Large cross section ?
• Select triggering on
• Semileptonic decays
• Trigger m, e
• Hadronic decays (CDF-SVT)
• One or more displaced tracks i.e. large impact
  parameter

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Selecting heavy flavour decays
CLEO

• To select charm and beauty
• In hadronic environment
• ? High resolution tracking
• detector is mandatory
• Only way to access hadronic
• decays is to trigger on tracks

CDF
Example
the CDF Secondary Vertex Trigger SVT

• Online (L2) selection of displaced tracks
• based on Silicon detector hits.

D0 ?K?
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Charm program at hadronic machines
Tevatron

• First experiment doing high precision charm
  physics at collider, collecting huge yields in
  hadronic D modes
• Many results already (in this talk) and more to
  come

• Nice charm physics program mainly on rare FCNC
  and LFV rare decays ( see Frank Lenher talk )
• Relies on the presence of a muons to trigger
  charm

• Expect to be able to select clean charm signals
  thanks to fine tracking and PID
• Will measure cc x-sections in pp, pN and NN
  collisions

LHC

• Thinking about having a dedicated D charm
  trigger selecting huge and clean samples of
  hadronic D modes
• Will definitely take over what CDF started in
  the search for CPV and mixing in charm

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Open cc Production
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Prompt Charm Meson X-Section
With very 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 is not statistics limited
• Large and clean signals

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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
D impact parameter
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 mesons are prompt ?
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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
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Differential Charm Meson X-Section
Ds
D
D
D0
PT dependent x-sections
(as reference)
Data/Theory
PRL89122003,2002
Theory prediction
Calculation from M. Cacciari and
P.Nason Resummed perturbative QCD (FONLL) JHEP
0309,006 (2003)
? Measured x-section is 1.5 factor higher
similar to B
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Open cc production future studies

• Studying cc correlations through angular
  difference Df .
• Can separate contributions from different
  production mechanisms
• Flavour creation
• Flavour Excitation
• Gluon splitting
• Issues are
• Low efficiency to have opposite charm in the
  acceptance
• Backgrounds at low Df from B?DDX decays.
• CDF already has clean samples of D-D0, D-D
  and DDs consisting of few 100s / few 1000s
  events depending on the modes.
• Expect to have correlation results based on 1
  fb-1 of Luminosity

Df
B?DD
BBbar
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Charm as a probe in Pb-Pb collisions
( from C. Fabjan )

• Heavy quarks with momenta lt 2030 GeV/c ? v ltlt
  c
• Gluon radiation is suppressed at
  angles lt mQ/E
• dead-cone effect
• Due to destructive interference (inside cone
  gluon with vc would violate causality)
• Contributes to the harder fragmentation of heavy
  quarks and implies lower energy loss for heavy
  quarks relative to light quarks

A.Dainese nucl-ex/0311004
D mesons quenching reduced Ratio D/hadrons (or
D/p0) enhanced and sensitive to medium properties
Yu.L.Dokshitzer and D.E.Kharzeev, Phys. Lett.
B519 (2001) 199 arXivhep-ph/0106202.
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Hadronic charm selection
Combine ALICE tracking secondary vertex finding
capabilities (sd060mm_at_1GeV/c pT) large
acceptance PID to detect processes as D0?K-?
1 in acceptance
/ central event 0.001/central
event accepted after rec. and all cuts
Results for 107 PbPb ev. ( 1/2 a run)
significance vs pT
S/?BS 37
S/?BS 8 for 1ltpTlt2 GeV/c (12 if K ID required)
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D0 Cross section measurement
Pb-Pb
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Charmonium Production
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Inclusive J/y production
CDF Lower pT trigger threshold for ? pT(?)
1.5 GeV J/y acceptance down to pT0
0ltpTlt0.25 GeV
D0 Larger acceptance for ?
total J/y production cross section at Tevatron is
D0 4.8 pb-1
CDF 39.7 pb-1
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Inclusive b cross section

• Run I b cross-section 3x old NLO QCD
• Theoretical approaches new physics,
  Next-to-Leading-log resummations, non
  perturbative fragmentation function from LEP, new
  factorization schemes
• Experimentally unbinned maximum likelihood fit
  to the flight path of the J/y in the R-? plane to
  extract the b fraction

Run II Bottom Quark Production
cross-section
PRD 71, 032001 (2005)
Good agreement ?
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g b/c x-section

• Probes heavy flavor content of the proton and
  its PDF (also with Z0)
• Experimental approach
• One isolated and High Et g (gt 25 GeV)
• One jet with a secondary vertex (b/c like jet)
• Fit on the secondary vertex mass distribution of
  the tagged jets to separate b, c and light quarks

g c
g b
s(b g) 40.6 /- 19.5 (stat.) 7.4 -7.8
(sys.) pb s(c g) 486.2 /- 152.9 (stat.)
86.5 -90.9 (sys.) pb
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Other charm states
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excited D states

• Plenty of D Dj narrow, wide, radial, orbital,
  resonant, nonresonant
• Narrow states are the only widely observed
  objects so far
• HQET predicts splitting of states vs mQ
• The large statistics of charm at CDF gives access
  to D

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D Properties
D1,2? D?- D?D0?
D0?K-?
D2? D?- D?K?-?-
Prompt D1,2

• Huge sample of narrow D resonances
• Competitive in measuring prompt D properties!
• and secondary from Bs

Secondary D
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D results
High precision masses and widths from prompt D1,2
M(D1)2421.7 ?0.7 ?0.6 MeV ?(D1)20.0 ?1.7 ?1.3
MeV M(D2)2463.3 ?0.6 ?0.8 MeV ?(D2) 49.2 2.3
1.3 MeV
Non-leptonic mass in B?l?Xc where Xc is D ?
mass moments analysis
mean
r.m.s
Probe HQET and contraints for CKM element Vcb
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charm et al.
c-Barions decaying in fully hadronic
modes accessibles with SVT trigger
and X(3872) ? J/y pp
M(pp) spectrum
fraction from B (16.0 4.9 1.0)
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Charm Rare Decays
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Search for FCNC D0?mm

• SM expectation BR 310-13
• Best limit lt4.110-6 90 CL, Beatrice/WA92,E771
• Enhanced in N.P. (R-Parity Violation Susy
  3.510-6)

• Experimental strategy CDF
• Events from two-track trigger using first 69pb-1
  of data
• To cancel acceptance effects normalize to D0?pp

Result
BR(D0?mm)lt2.4x10-6 at 90 CL
Comment muon fake rate will set limit
(10-6) Next use full muon coverage, add
statistics, explore electron modes (less coverage
but lower fake rate) ? also look at D?pmm,
D?Kmm, D0?me and Ds see Frank Lenher talk in
this workshop for details
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CP Violation and Mixing in neutral D
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D0?hh- direct CP Asymmetries and BRs

• Search for direct CP asymmetries where f is CP
  eigenstate (ex. KK-,pp-)
• in single Cabibbo suppressed modes (KK)
• Almost null in Cabibbo allowed (Kp)
• ? Use D0?Kp as normalization mode
• Data collected by the SVT trigger with 123 pb-1
  of int. Luminosity
• Relative branching ratios
• G(D0?KK-) / G(D0?Kp)
• G(D0?pp-) / G(D0?Kp)
• G(D0?KK) / G(D0?pp)2.8 (SM)
• Candidates selected as D/- ?D0 p
• (unbiased tag of the D0 flavor)

Normalization mode D0?Kp 180k from D/-? D0 p
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Direct ACP in Cabibbo suppressed D0 decays
D0?KK 16220 ?200
D0?pp 7334 ?97

• Systematic dominated by tracking charge
  asymmetry, scales with statistics of control
  sample
• KK channel suffers from partially reconstructed
  D background , would benefit from PID.
• CDF yields prospects 2M D tagged D0?Kp per 1
  fb-1
• sACP 10-3 is achievable with full Tevatron
  run (4-9 fb-1) - at SM limit
• issue will be if SVT trigger can cope
  with Lumi increase.

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Mixing in the D0 system

• D0 mixing receives x and y contributions
• SM model expectations
• x and y 10-4 - 10-2
• (depending on the model)
• Enhancements in x could be hint of New Physics
• RSM O(10-6)

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Search for D0 mixing through DG
Can search for DG comparing lifetime of
CP eigenstate (D0?KK) and CP mixed state
(D0??K) yCP ? t(K?)/t(KK) - 1
Best measurement at present from BaBar syCP0.006
yCP0.034? 0.014?0.007

• CDF is currently performing D0 ? KK, pp, Kp
  lifetime analysis
• expect s(ct) lt 2 mm (statistical only)
• most of systematics cancel in the ratio, but
• Deconvolve SVT trigger bias at 1 mm level is a
  challenge
• Nasty effect from secondary D0 from Bs

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Direct Search for Mixing

• Most sensitive method comes from looking for
  Wrong Sign ?K pairs in D0 decays.
• These occur directly through DCS decays.
• Time dependent analysis can decouple
  contributions from

DCS

• Direct DCS
• Interference
• Mixing

D0 K? - D0
Mix
(x and y because of possible strong phase
difference between diagrams)
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D0 Wrong Sign decays (time integrated analysis)

• Almost 0.5 M Right Sign D?D0p reconstructed in
  350 pb-1 selected by SVT trigger
• No PID so use of kinematics to reduce background
  from misreconstructed D0

Get the WS D yield binning in D mass difference
? fit the signal
NWS 2005 104
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D0 Wrong Sign rate results
Time integrated WS/RS ratio
Which in the limit of no mixing is RWSRS RD
BR(D0?Kp-)/BR(D0?K-p)

• Results competitive with B-factories (CDF has x2
  data on tape)
• Next step time dependent analysis and limit in
  the x y plane

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LHC-b prospects for charm CPV and mixing
( from Guy Wilkinson and Frederic Teubert )

• Will implement a dedicated D trigger stream
• Hadron trigger displaced vertex high PT tracks
  (4kHz). Expected composition bc
  5020
• High level D?(D0?hh)p selection offline
  quality (250Hz). Expect bc
  3624
• In one year of running (107 s) at nominal
  luminosity (21032 cm-2s-1)
• Expect 250 - 500 M D ? D0p decays with D0?Kp
  channel, 102 x CDF !

• Raw estimates (based on signals statistics only)
  for sensitivity to charm CPV and mixing are
• s(ACP) D0?KK 10-4 normalizing to Kp mode
• s(yCP) 10-4 in the lifetime difference
  analysis
• s(x) 10-5 in mixing search through Wrong
  Sign' Kp signals

LHC-b will possibly be sensitive in SM range,
detailed studies on-going
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Summary

• Charm production (cc and charmonium) is usefull
  test of QCD calculations to be tuned for precise
  background estimates in NP searches.
• Already high precision results from Tevatron, to
  be explored at LHC.
• A wide range of charmed hadrons are accessible at
  collider experiments, complementarity to ee-
• CDF demonstrates that is possible to perform high
  precision searches for charm CPV and mixing in
  hadronic modes D0?hh
• LHC-b will have 2 orders of magnitude more D0?hh
  yields and will be very competitive in this
  field.
• Huge CDF and D0 legacy of knowledge in doing
  Charm Physics at hadronic machines is left to
  next generation experiments.

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Backup slides
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Tevatron performances

• CDF II has collected so far 1.26 fb-1 out of
  1.57 fb-1 delivered by Tevatron.
• Record peak luminosity is 1.81032 cm-2s-1
• Around 900 pb-1 are available for Charm/Beauty
  physics (good tracking detector conditions)
• Current analyses use 180 - 350 pb-1 of integrated
  luminosity

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The CDF II detector
CDF Tracking System
Particle ID
Lepton ID
Muons CMU, CMP, CMX (?lt1.1)

• dE/dX in COT

Electrons CEM (EM calorimeter) CPR
(pre-shower detector)

• Time Of Flight detector

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SVT the CDF hadronic h.f. trigger

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

s 47 mm 35 mm 30 mm
SVT resolution
Beam spot size
Impact Parameter distribution
Offline s 45 mm
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B physics triggers at CDF II
Conventional at colliders (Run I)
With SVT trigger
2-Displaced tracks PT(trk) gt 2 GeV 120 ?m lt
I.P.(trk) lt 1mm SpT gt 5.5 GeV fully hadronic
modes
1-Displaced track lepton (e, ?) 120 ?m lt
I.P.(trk) lt 1mm PT(lepton) gt 4 GeV Semileptonic
modes
Di-Muon (J/?) Pt(?) gt 1.5 GeV J/? modes down to
low Pt(J/?)0 (Run II)

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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
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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)
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Charmonium as probe for diffractive Higgs

• Calibration signature
• exclusive D.P.E. production of cc
• search for cc ? J/y g
• ? Esclusive channel p p ? p H (?bb) p
• ?Hexcl 3 fb , signal / background 3 _at_ LHC
• then MH Mmiss

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Welcome back to Bc

• Mode that gave the first evidence of the Bc (CDF
  Run I)
• Large yield, no clean resonance though!

106 events
46.0?7.3 events

• First signal of fully reconstructed Bc
• Mass measurement on 0.8 fb-1

39 signal candidates
Hep-ex/0505076