Charm production with neutrinos

• Physics motivation

• Results

• Outlook

Giovanni De LellisUniversity of Naples

(on behalf of the CHORUS Collaboration)

cc

|Vcd|2,|Vcs|2

d,sd,s

-- Beam

knowledge

Quark density functions,strange sea ()

,h,h

EEhadhad

hh

Charm fragmentationfD0

; fD+ ; fDs

; fc

z = pD/pc, pT2

DIS charm production

Production from d(anti-d) quarks Cabibbo suppressed large s contribution: 50% in and 90% in anti-

• 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: g+sW+cR.Demina et al., Phys. ReV. D 62 (2000) 035011S.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, QCD and charm mass (J.Conrad et al. Rev.Mod.Phys. 70 (1998) 1341-1392)

• measure charm mass and Vcd

Physics motivation

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<15GeV); not possible to study separately the different charmed types; B is needed

– bubble chamber filled with heavy liquid (BEBC, Fermilab 15-ft)

– nuclear emulsions (E531, CHORUS)

Emulsion experiments

• Look “directly” at the decay topology of the charmed hadron with sub-micron resolution

• Contra: the anti- statistics is still poor

• Pro: – low background; sensitivity to low E

mc threshold effect

– hadron species identification

– reconstruction of charmed hadron kinematics fragmentation studies

100 m

%9.4)(

)( 7.06.0

XN

XcN

Inclusive charm production cross-section induced by

Inclusive charm-production cross-section measurement possible only with nuclear emulsions So far only E531: 122 events

CHORUS is currently analysingabout 1000 events

Final statistics (~1year from now)about 3000-4000 events!

p/p = 0.035 p (GeV/c) 0.22

p/p = 10 15%

(p < 70 GeV/c)

-nuclear emulsion target (770kg)

-scintillating fiber tracker

CHORUS detector

E/E = 32 %/ E (hadrons)

= 14 %/ E (electrons) h = 60 mrad @ 10 GeV

E ~ 27 GeV

Air-core magnetAir-core magnetActive targetActive target

muon spectrometermuon spectrometer

CalorimeterCalorimeterNeutrino beamNeutrino beam:: : : e : : e

1.00 : : 0.05 : : 0.017 :: 0.007

0 m0 m

-21 m-21 m

-36 m-36 m

-54 m-54 m

MIP: 30 40 grains/100m

Resolution ~ 0.3 m

Focal depth: 1 to 3 m

S. Aoki et., Nucl. Instr. Meth. A 447 (2000) 361

CHORUS emulsion

350 m

90 m

8 plates

1.5 mm

1.5 mm

All tracks (θ<400mrad) in the scanning volume (1.5X1.5X6.3mm3) are recorded at 11 min./event

0,001

0,010

0,100

1,000

10,000

100,000

1994 1996 1999 2000

#frames/s

scanning speed

CHORUS Phase II

•All track segments (All track segments ( < 0.4 rad) < 0.4 rad) •Fiducial volume: 1.5 x 1.5 mmFiducial volume: 1.5 x 1.5 mm2 2 x 8 plates x 8 plates •Offline analysis of emulsion dataOffline analysis of emulsion data

Track segments from 8 plates overlapped

At least 2-segment

connected tracks

Eliminate passing-through

tracks

Reconstruct full vertex topology

Emulsion data acquisition

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

dz = vertex depth

parameterize the angular error

θ=0.4 rad

θ=0. rad

Selected events

Selected events

mdzIP 22 )2(0.3

22 )0194.0()0305.0(

N Ds* - N’

Ds+

+

+

Diffractive Ds production Phys. Lett. B 435 (1998) 458, CHORUS Coll.

D0 production rate

DD00 V4 / D V4 / D00 V2 = 0.231 V2 = 0.231 0.04 0.04

• 25,693 25,693 CC analyzed (~15% of the full statistics) CC analyzed (~15% of the full statistics)

•851 (3.3%) selected events for visual inspection851 (3.3%) selected events for visual inspection

•Confirmed DConfirmed D00 sample: sample: 226226 V2, V2, 5757 V4 V4

σ(D

0)/

σ(C

C)

E (GeV)

Phys. Lett. B 527 (2002) 173, CHORUS Coll.

J.Phys.G28 (2002) 713 (all channels):

all existing data are combined

σ(D0)/σ(CC) = 2.580.26(stat.)0.13(syst.) %

E531

CHORUS

σ (Dσ (D0 0 )/σ (CC)x Br(D)/σ (CC)x Br(D00V2+V4 ) =V2+V4 ) =1.99 1.99 0.13 (stat.) 0.13 (stat.) 0.17 (syst.)% 0.17 (syst.)%

Statistical approach using flight length distribution

Λ c

Ds

D+

Flight length in μm

Λc production rate

(A)

•Short flight decay: selection A(40 mm < FL <400 mm):

Λ c enriched sample

128 candidates out of 50,414 CC•Long flight decay: selection B

(400 mm < FL < 2400 mm):

D+, Ds dominated sample

210 candidates out of 56,761 CC

(B)

parent particle track

Evidence for c production: 3-prong decays (background free)

MC: D and DsData

Data

Background check: Pt distribution for 1-prong decays

b.g. excessData

Monte Carlo

Data

cc production rate production rate

Combining short (A) and long (B: only 3-prong) decay Combining short (A) and long (B: only 3-prong) decay searches and correcting for efficiencies and background:searches and correcting for efficiencies and background:

3 equations and 3 unknowns3 equations and 3 unknowns •D+Ds = 1118 D+Ds = 1118 116(stat)116(stat)• c c = 861 = 861 198 (stat.) 198 (stat.) 98 (syst.) 98 (syst.)+140 +140 (QE)(QE)•Br(Br(cc 3prong) = 24 3prong) = 24 7 (stat.) 7 (stat.) 4 (syst.)% 4 (syst.)%

Phys. Lett. B 555 (2003) 156Phys. Lett. B 555 (2003) 156σ(D+Ds)/σ (CC) = 2.00σ(D+Ds)/σ (CC) = 2.000.21(stat)% by product 0.21(stat)% by product

σ (σ (c) / σ (CC)= 1.54 c) / σ (CC)= 1.54 0.35(stat) 0.35(stat) 0.18 (syst)% 0.18 (syst)%

-54-54

a) n - c+ b) n - c

+ (c*+) c) p - c

++(c*++)

Quasi-elastic charm production

QE charm production has a peculiar topology “pure” c sample with a small (<10%) contaminationi.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 thecross-section measurement is in progress

Associated charm production

D+D+D+D+XXcc

cc

WW cc

ccD+D+D+D+XX

ZZ

CC

Gluon Bremsstrahlung Z-Gluon Fusion

NC

Associated charm production in CC

• In the past this search was based on the observation of tri-muon events -(+-) and same-sign di-muons:

• Large background from 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.)(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.

30 29

21

1010 m 6735 m

transverse plane

-

D0kink parent

Ns = 2Nh = 6

kink= 420 mrad

D0 f.l. = 340 m

f.l. = 1010 m2 = 310 mradf.l. = 7560 m

2ry vertex

pMeV/c

dE/dx proton

P = 0.78 GeV/cP > 330 MeV/c

+180- 110

1st vertex

First observation in CC Phys. Lett B 539 (2002) 188, CHORUS Coll.Phys. Lett B 539 (2002) 188, CHORUS Coll.

B.G. = 0.04±0.01

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 1.3+3.1

-1.1 x10-3 normalised to CC

– Indirect search performed by NuTeV A.Alton et al., Phys. Rev. D64 (2001) 539

• Production rate (2.61.6)x10-3 normalised to CC at 154 GeV

• mc=(1.40+0.83-0.36 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.

11ry@pl23ry@pl23

NNs=1, Nh=3s=1, Nh=3

V2(1) @V2(1) @pl 23pl 23

=96.3 mrad=96.3 mrad

fl= 62.8fl= 62.8mm

V2(2) @pl 22 V2(2) @pl 22

fl= 976.6fl= 976.6mm

=203.4 mra=203.4 mraddTTT #6T #6

TTT #3T #3

TTT #8T #8

TTT #5T #5

ppl23l23 ppl22l22

EEvent 81332312vent 81332312 V2&V2&V2 in 0muV2 in 0mu

120µm210µm

PLATE 18 PLATE 17

140µmTT

TT

TT

Event 77393952

Ns = 6Nh = 1 (gray)

4Vee @ pl 17FL = 884 µm

C3 @ pl 17FL = 426 µm

• 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)

– σ (Dσ (D00)/σ(CC) )/σ(CC) (Phys. Lett B 527 (2002) 173)(Phys. Lett B 527 (2002) 173)

– CC associated charm production CC associated charm production (Phys.Lett. B 539 (2002) 188)(Phys.Lett. B 539 (2002) 188)

– B (Phys. Lett B 548 (2002) 48): first direct measurement

– σ(σ( cc)/σ(CC) )/σ(CC) (Phys.Lett.B 555 (2003)156)(Phys.Lett.B 555 (2003)156)

Conclusions and OutlooksConclusions and Outlooks

• 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 c production