Charm%20production%20with%20neutrinos

1
Charm production with neutrinos
Giovanni De Lellis University of Naples
on behalf of the CHORUS Collaboration

• Physics motivation
• Results
• Outlook

2
n DIS charm production
Quark density functions, strange sea (?)
Production from d(anti-d) quarks Cabibbo
suppressed ? large s contribution ?50 in n and
?90 in anti-n
3
Physics motivation

• measure charm mass and Vcd
• e.g. G. De Lellis, P. Migliozzi, P. Santorelli ,
  Charm Physics with neutrinos Phys. Rept. 399
  (2004) 227.
• measure strange content of the nucleon
• Possible s/anti-s asymmetry ? non-p QCD effects
• crucial role in relating F2 structure function
  for charged- and neutral-lepton
• strange sea is important for stop searches at
  hadron colliders largest background gs?Wc
• R.Demina et al., Phys. ReV. D 62 (2000) 035011
• S.J.Brodsky and B.Ma, Phys. Lett. B 381 (1996)
  317
• constrain/study charm production models
• in NLO pQCD is a challenging theoretical problem
• 2 scales, LQCD and charm mass
• J.Conrad et al. Rev.Mod.Phys. 70 (1998) 1341-1392

4
Experimental techniques
Experiment ?-? events ??- events Reference paper
CDHS 9922 2123 Z. Phys. C (1982) 19
CCFR 5044 1062 Z. Phys. C (1995) 189
CHARMII 4111 871 Eur.Phys. J. C11 (1999) 19
NOMAD 2714 115 PLB486 (2000) 35
CHORUS 8919 430 In preparation

• massive high density detectors (CDHS, CCFR,
  CHARMII, NuTeV, NOMAD, CHORUS)
• Pro large statistics
• Contra background from p, K decays not
  sensitive to low-neutrino energies (Enlt15GeV)
  not possible to study separately the different
  charmed types Bm is needed
• bubble chamber filled with dense liquid (BEBC,
  Fermilab 15-ft)
• nuclear emulsions (E531, CHORUS)

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Emulsion experiments

• Look directly at the decay topology of the
  charmed hadron with sub-micron resolution
• Contra the anti-n statistics is still poor
• Pro
• low background sensitivity to low En
• ? mc threshold effect
• not depending on muonic branching ratio
• which in turn depends on fragmentation
• fractions (energy)
• hadron species identification
• reconstruction of charmed hadron
• kinematics ? fragmentation studies

100 mm
6
Inclusive charm production cross-section induced
by n
CHORUS final statistics 2000 charms! Analysis
finalized for most of the searches!
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CHORUS detector
Active target
?p/p 0.035 p (GeV/c) ? 0.22
Air-core magnet
-nuclear emulsion target (770kg) -scintillating
fiber tracker
?p/p 10 ?15 (p lt 70 GeV/c)
?
muon spectrometer
En 27 GeV
Calorimeter
Neutrino beam
?E/E 32 /? E (hadrons) 14 / ? E
(electrons) ?? h 60 mrad _at_ 10 GeV
nm nm ne ne 1.00
0.05 0.017 0.007
8
CHORUS emulsions and their visual inspection
100 µm
9
Automatic emulsion data acquisition (phase-II)
1
1
Location of n interaction vertex guided by
electronic detectors
2
2
Full data taking around n interaction vertex
Volume 1.5 x 1.5 x 6.3 mm3
Angular acceptance 400 mrad
11 minutes / event
3
Offline tracking and vertex reconstruction
Reconstruct full vertex topology
At least 2-segment connected tracks
Track segments from 8 plates overlapped
Eliminate passing through tracks
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Lc production rate
Phys. Lett. B 555 (2003) 156
Statistical approach using flight length
distribution

• Short flight decay 40 µm lt FL lt 400 µm
• ? c enriched sample
• 128 candidates out of 50,414 CC
• Long flight decay 400 µm lt FL lt 2400 µm
• D, Ds dominated sample
• 210 candidates out of 56,761 CC
• Using both selections
• 1 and 3 prong decays

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Quasi-elastic charm production
a) ?? n ? ?- ?c b) ?? n ? ?- ?c
(?c) c) ?? p ? ?- ?c(?c)
Phys. Lett. B 575 (2003) 198 (based on 46105 ??
CC)
Topological and kinematical selection criteria

• Require 2 or 3 tracks at primary vertex
• ? ? 165 (angle between muon and charm in the
  transverse plane)
• Flight length lt 200 ?m (enriched ?c sample)
• Calorimeter energy lt 10 GeV and electromagnetic
  energy lt 2 GeV

13 events with a background of 1.7 (mainly from
DIS ?c)
QE production is about 15 of ?c production
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Neutrino-induced charm sample final statistics
Decay topology (prong) Sample
Kink 452
Vee 819
Trident 491
4Vee 226
C5 22
6Vee 3
Total sample 2013
final sample of 93807 located interactions with a
m-
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Measurement of the fully neutral D0 decay mode
PLB613 (2005) 105

• No measurement so far, 5 value by comparison
  with charged modes
• Essential to extract the D0 production
  cross-section
• Essential to get the correct muonic branching
  ratio and hence the
• inclusive charm production cross-section from
  dimuon data

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Measurement of D0 production rate PLB613 (2005)
105
Topology Observed events Main background source Background event yield
V2 819 K0 and ? decays 37.03.5
V4 226 D0 ?V2?0??ee- 7.31.5
V6 3 D0 ?V4?0??ee- 0.840.1
Full sample of 93807 CC events and D0 ? fully
neutral
Gluk, Reya and Vogt, Z. Phys. C (1995) 433
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Measurement of charm fragmentation into D0
Phys. Lett. B604 (2004) 145
Use correlation between opening angle of decay
daughters and charm momentum unfolding
curve is the model in the CHORUS MC
Inverse of geometrical mean of opening angle
of daughters
D0 momentum
CollinsSpiller
ltxf gt 0.38 0.04 0.03
Peterson
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Charm fragmentation results
Experiment    z     eP and eCS    xF     and A
CDHS 0.680.08                                                          
E531 0.590.04 ?P 0.0760.014 A0.6200.092
CCFR 0.560.03 ?P 0.220.05
?CS 0.880.12
BEBC 0.590.030.08
CHARM II 0.660.03                                                                   
NOMAD 0.670.020.02                                                                                                   xF 0.470.05
?CS 0.130.080.11
NuTeV ?CS 2.070.31
CHORUS 0.630.030.01 ?P 0.1080.0170.013  xF 0.380.040.03
                                                                             A0.790.140.05

• Different final states
• E531 all charm decays
• Nomad D
• CHORUS D0
• Dimuon experiments weighted by µ decay mode

incorrect to put all charms together, but
difficult to tag separately
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Bµ muonic branching ratio (preliminary)
Direct observation of the charm parent and its
muon decay
Taking into account the new CHORUS measurement
of Br (D0 ? V0)
B? 7.3 ? 0.8
B? (8.3 ? 1.6)
Dimuon events have larger visible energy Evis gt
30 GeV
Bµ Vcd2LO(0.474 ? 0.027)x10-2 CDHS, CHARM II
CCFR averaged
VcdLO 0.239?0.046
VcdNLO 0.254?0.066
Bµ Vcd2NLO(0.534 ? 0.046)x10-2 CCFR
0.221lt Vcdlt0.227 at 90 CL using CKM unitarity
and 3 generations
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Anti-neutrino studies Phys. Lett. B604 (2004) 11

• Charm production mainly from anti-s sea quark ?
  combined analysis with neutrino data can separate
  valence and sea quark contributions
• Different production and hadronization mechanisms
  ? no quasi-elastic process and suppressed
  due to baryon number conservation
• About 5 contamination in the neutrino beam ?
  limiting factor is still the low statistics

Final data sample 2704 interactions with a m
19.72.1 contamination from
measured interaction ratio
consistent with a measurement done using
interactions in the calorimeter (2.20.1),
consistent with beam contamination and the
different energy spectrum and cross-section
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Anti-neutrino induced charm production
Decay topology Candidate events background
Vee 16 1.40.2
V4 6 0.130.05
Kink 4 1.30.2
Trident 4 0.30.1
C5 2 0.020.01
Total 32 2.70.4
background is practically only from charm in ?
6.0 in neutrinos (higher energy and presence of
QE process)
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Measurement of D production
Phys. Lett. B614 (2005) 155
Search for D in the decay channel D ? D0 ?
m-
n
D0 flgt100mm
p
qlt60 mrad
D signal in the D0 h sample
No signal in the D0h- sample
K-
m-
n
p
D
D0
0.4 ltp(?)lt4 GeV/c 10lt pTlt50 MeV/c
p
No signal in the Ch- sample
No signal in the Ch sample
Background prediction

• Shape of signal background normalized to the
  observed events
• (2-3-4) shape normalized to the total number of
  D0 and C respectively

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Measurement of D production (2)
Br(D ? D0 ?)0.6770.005 (PDG)
NOMAD 0.79 0.17 0.10 BEBC 1.22
0.25 Tevatron 5.6 1.8 (higher energy)
assuming that prompt D and D0 production rates
are equal we get
fVV/(PV) , V vector and P pseudoscalar
production of D meson

• Consistent within the error with
• VP 31 as expected from simple spin arguments
• measurements in ee-,?N, ?N experiments.

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Associated charm production
cross-section in CC
Z-gluon fusion
Gluon Bremsstrahlung
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Associated charm production in CC

• In the past, observation of tri-muon events
  m-(mm-) and same-sign di-muons (controversial
  interpretation)
• Large background from p and K decays
• Observed rate 60 times larger than expected from
  theoretical calculations! (K.Hagiwara Nucl.Phys.B
  173 (1980) 487)
• Currently a search is in progress in CHORUS
• 1 event observed and confirmed by kinematical
  analysis
• (Phys. Lett B 539 (2002) 188,
  CHORUS coll.)
• A new analysis with larger statistics is in
  progress. Four candidates found and the first
  cross-section estimation reported

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First observation in CC Phys. Lett B 539 (2002)
188, CHORUS Coll.
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Ns 2 Nh 6
n
B.G. 0.040.01
6735 mm
1010 mm
D0 f.l. 340 mm
1st vertex
2ry vertex
kink parent
qkink
q2
420 mrad
310 mrad
D0
f.l. 7560 mm
f.l. 1010 mm
m-
P 0.78 GeV/c
pb 500 MeV/c
180 - 110
P
transverse plane
dE/dx proton
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A newly found event in CC
E36.9 GeV
P -16.9 GeV/c
Evis 53.8 GeV
Both neutral decays inconsistent with two-body
decay (acoplanarity)
Pd1 gt 4.70 GeV/c _at_ 90 C.L. (TT 2)
Pd2 gt 0.67 GeV/c _at_ 90 C.L.
Pd2 gt 1.92 GeV/c _at_90 C.L. (TT 5)
Pd3 gt 2.32 GeV/c _at_90 C.L. (TT 7)
Pl31 pl30
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Associated charm production in NC

• Neutral-current interactions (g-brem. Z-g
  fusion)
• In the past only one event observed by E531
• Production rate 1.33.1-1.1 x10-3 normalised to
  CC
• Indirect search performed by NuTeV
• A.Alton et al., Phys. Rev. D64 (2001) 539
• Production rate (2.6?1.6)x10-3 normalised to CC
  at 154 GeV
• mc(1.400.83-0.36 ?0.26) GeV, in agreement with
  other measurements
• The search for this process is in progress in
  CHORUS
• 3 candidates have been found and the preliminary
  measurement of the cross-section is reported

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An event in NC
Ns 6 Nh 1 (gray)
4Vee _at_ pl 17 FL 884 µm
C3 _at_ pl 17 FL 426 µm
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Associated charm production cross-section
preliminary
Process Observed events Estimated background
CC 4 0.790.10
NC 3 0.12 0.02
Background in CC comes from single charm
hadronic white interaction
Background in NC comes from single charm
hadronic white interaction missed muon

• agreement with the theory for the CC process
• agreement with NuTeV for NC (different energy
  spectrum)

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Conclusions and Outlooks

• CHORUS has measured
• Diffractive Ds production Phys. Lett. B 435
  (1998) 458
• D0 production Phys. Lett B 527 (2002) 173
• CC associated charm production Phys. Lett. B539
  (2002) 188
• Bm Phys. Lett B548 (2002) 48 first direct
  measurement
• L c production Phys. Lett. B555 (2003)156
• QE Lc production Phys. Lett. B575 (2003) 198
• Anti-neutrino charm production Phys. Lett B604
  (2004) 11
• Charm fragmentation into D0 Phys. Lett B604
  (2004) 145
• D0 studies Phys. Lett B613 (2005) 105
• D production Phys. Lett. B614 (2005) 155

• Analyses in progress with preliminary results
• Associated charm production cross-section in CC
  and NC
• Muonic branching ratio
• Charm topological branching ratios