Charm production with neutrinos

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
• 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

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

5
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 has just got the final statistics 2000
charms! Analysis finalized by the end of the
year!
7
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 ?
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
9
Automatic emulsion data acquisition (phase-II)
1
1
Location of n interaction vertex guided by
electronic detector.
2
2
Full data taking around n interaction vertex
called Netscan
Volume 1.5 x 1.5 mm2 x 6.3 mm
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
10
Selection criteria
Emulsions have no time information at least one
among charm daughter particles must be
reconstructed by the tracker systems (necessary
for D0 search) Emulsion-electronic tracker
matching for the m track as well Tracks with
large impact parameter with respect to vertex
point ? visual inspection for decay confirmation

impact parameter vs. vertex depth
?0.4 rad
Selected events
dz vertex depth parameterize the angular
error
?0. rad
11
Neutrino-induced charm sample
final sample of 95450 located interactions with a
m-
12
Fully neutral D0 decay mode

• 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

New measurements! preliminary
13
Measurement of D0 production
14
Measurement of D0 momentum
Use correlation between opening angle of decay
daughters and charm momentum to obtain momentum
distribution
Inverse of geometrical mean of opening angle
of daughters
Preliminary
D Momentum
Momentum distribution of D0 can be measured by
unfolding opening angle distribution (curve is
the model in the CHORUS MC)
15
Z-distribution
16
Charm fragmentation results

• Large spread in values due to different mixtures
  of charm final states
• E531 all charm decays
• Nomad D
• CHORUS D0
• Dimuon experiments weighted by muonic decay mode

incorrect to put all charms together, but
difficult to tag separately
17
Lc production rate
Phys. Lett. B 555 (2003) 156
Statistical approach using flight length
distribution

• Short flight decay selection A
• (40 mm
• ? c enriched sample
• 128 candidates out of 50,414 CC
• Long flight decay selection B
• (400 mm
• D, Ds dominated sample
• 210 candidates out of 56,761 CC

parent particle track
18
Evidence for Lc production 3-prong decays
(background free)
Background check Pt distribution for 1-prong
decays
19
Lc production rate

• Combining short (A) and long (B only 3-prong)
  decay searches and correcting for efficiencies
  and background
• 3 equations and 3 unknowns
• DDs 1118 ?116(stat)
• Lc 861 ? 198 (stat.)?? 98 (syst.)140 (QE)
• Br(Lc? 3prong) 24 ? 7 (stat.) ? 4 (syst.)

-54
Preliminary
20
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
• Calorimeter energy energy

13 events with a background of 1.7 (mainly from
DIS ?c)
QE production is about 15 of ?c production
21
Anti-neutrino studies

• 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
22
Anti-neutrino induced charm production
background is essentially from charm in neutrinos
6.0 in neutrinos (higher energy and presence of
QE process)
23
Associated charm production
CC
NC
?
?
?
?
Z
W
c
c
DDX
c
DDX
c
Z-Gluon Fusion
Gluon Bremsstrahlung
24
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

25
First observation in CC Phys. Lett B 539 (2002)
188, CHORUS Coll.
30
29
21
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
26
Newly found CC event
E36.9 GeV
P-16.9 GeV/c
Evis 53.8 GeV
Both neutral decays inconsistent with two-body
decay (acoplanarity)
Pd14.70 GeV/c _at_ 90 CL.(TT 2)
Pd20.67 GeV/c _at_ 90 CL.
Pd21.92 GeV/c _at_90 CL.(TT 5)
Pd32.32 GeV/c _at_90 CL.(TT 7)
Pl31 pl30
27
Associated charm production in NC

• Neutral-current interactions (g-brem. Z-g
  fusion)
• In the past only one event observed in the E531
  emulsion
• 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
• Currently a search for this process is in
  progress in CHORUS
• 3 candidates have been found and the preliminary
  measurement of the cross-section is reported

28
An event in NC
Ns 6 Nh 1 (gray)
4Vee _at_ pl 17 FL 884 µm
C3 _at_ pl 17 FL 426 µm
29
Associated charm production cross-section
Background in CC comes from single charm
hadronic white interaction
Background in NC comes from single charm
hadronic white interaction missed muon
first direct measurement!

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

30
Conclusions and Outlooks

• 150K events in CHORUS emulsions for Charm analysis

• CHORUS has measured
• Diffractive Ds production (Phys. Lett. B 435
  (1998) 458)
• s (D0)/s(CC) (Phys. Lett B 527 (2002) 173)
• CC associated charm production (Phys.Lett. B 539
  (2002) 188)
• Bm (Phys. Lett B 548 (2002) 48) first direct
  measurement
• s(L c)/s(CC) (Phys.Lett.B 555 (2003)156)
• QE Lc production (Phys.Lett.B 575 (2003) 198)
• Anti-neutrino charm production (being submitted
  to the journal)
• D0 decay? all neutrals (being submitted to the
  journal)

• Analyses in progress with preliminary results
• Associated charm production cross-section in CC
  and NC
• Z and x-Feynman distributions
• Charm topological branching ratios