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 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)
• measure charm mass and Vcd

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 (Enlt15GeV)
  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)

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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
• hadron species identification
• reconstruction of charmed hadron kinematics
• ? fragmentation studies

100 mm
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Inclusive charm production cross-section induced
by n
CHORUS is currently analysing about 1000
events Final statistics (1year from now) about
3000-4000 events!
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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
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CHORUS emulsion
MIP 30 ? 40 grains/100?m Resolution 0.3
?m Focal depth 1 to 3 ?m
S. Aoki et., Nucl. Instr. Meth. A 447 (2000) 361
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CHORUS Phase II
scanning speed
1.5 mm
1.5 mm
8 plates
All tracks (?lt400mrad) in the scanning volume
(1.5X1.5X6.3mm3) are recorded at 11 min./event
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Emulsion data acquisition

• All track segments (q lt 0.4 rad)
• Fiducial volume 1.5 x 1.5 mm2 x 8 plates
• Offline analysis of emulsion data

Reconstruct full vertex topology
At least 2-segment connected tracks
Track segments from 8 plates overlapped
Eliminate passing-through tracks
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Selection criteria
At least one among daughter particle and muon
tracks formed by at least 2 segments and
reconstructed by the fiber tracker systems Tracks
with big impact parameter with respect to vertex
point ? visual inspection for decay confirmation

impact parameter vs. vertex depth
?0.4 rad
Selected events
?0. rad
dz vertex depth parameterize the angular
error
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Diffractive Ds production Phys. Lett. B 435
(1998) 458, CHORUS Coll.
?? N ? Ds ?- N Ds ? ? ??
? ????
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D0 production rate
Phys. Lett. B 527 (2002) 173, CHORUS Coll.

• 25,693 nm CC analyzed (15 of the full
  statistics)
• 851 (3.3) selected events for visual inspection
• Confirmed D0 sample 226 V2, 57 V4

s(D0)/s(CC)
E531
D0 ? V4 / D0 ? V2 0.231 ? 0.04
s (D0 )/s (CC)x Br(D0?V2V4 ) 1.99 ? 0.13
(stat.) ? 0.17 (syst.)
CHORUS
J.Phys.G28 (2002) 713 (all channels) all
existing data are combined s(D0)/s(CC)
2.58?0.26(stat.)?0.13(syst.)
En (GeV)
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?c production rate
Statistical approach using flight length
distribution

• Short flight decay selection A
• (40 mm lt FL lt400 mm)
• ? c enriched sample
• 128 candidates out of 50,414 CC
• Long flight decay selection B
• (400 mm lt FL lt 2400 mm)
• D, Ds dominated sample
• 210 candidates out of 56,761 CC

parent particle track
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Evidence for Lc production 3-prong decays
(background free)
Data
Data
MC D and Ds
Background check Pt distribution for 1-prong
decays
Data
Data
b.g. excess
Monte Carlo
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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.)
• Phys. Lett. B 555 (2003) 156
• s(DDs)/s (CC) 2.00?0.21(stat) by product
• s (Lc) / s (CC) 1.54 ? 0.35(stat) ? 0.18 (syst)

-54
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Quasi-elastic charm production
a) ?? n ? ?- ?c b) ?? n ? ?- ?c
(?c) c) ?? p ? ?- ?c(?c)

• QE charm production has a peculiar topology
• pure Lc sample with a small (lt10)
  contamination
• i.e. normalization error ? absolute BR
  determination

P. Migliozzi et al. Phys. Lett. B 462 (1999)
217-224
Many candidates have been found in CHORUS and
the cross-section measurement is in progress
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Associated charm production
CC
NC
?
?
?
?
Z
W
c
c
DDX
c
DDX
c
Gluon Bremsstrahlung
Z-Gluon Fusion
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Associated charm production in CC

• In the past this search was based on the
  observation of tri-muon events m-(mm-) and
  same-sign di-muons
• 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 a larger statistics is in
  progress. The discrepancy between data and
  theoretical predictions will be clarified soon.

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First observation in CC Phys. Lett B 539 (2002)
188, CHORUS Coll.
30
29
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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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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
• Several candidates have been found and the
  cross-section measurement will be finalised by
  the end of this year.

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Event 81332312
V2V2 in 0mu
1ry_at_pl23 Ns1, Nh3 V2(1) _at_pl 23 Dq 96.3
mrad fl 62.8mm V2(2) _at_pl 22 fl 976.6mm Dq
203.4 mrad
TT 5
TT 8
TT 3
TT 6
pl23
pl22
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Event 77393952
Ns 6 Nh 1 (gray)
4Vee _at_ pl 17 FL 884 µm
C3 _at_ pl 17 FL 426 µm
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Conclusions and Outlooks

• 200K events in CHORUS for Charm analysis
• From a sub-sample of data 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)

• Analyses in progress
• Associated charm production in CC and NC
• D production
• D0 decay? all neutrals
• Charm topological branching ratio
• Anti-neutrino charm production
• QE Lc production