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 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: 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

Physics motivation

Experimental techniques

– massive high density detectors (CDHS, CCFR, CHARMII, NuTeV, NOMAD, CHORUS Calo):

• Pro: large statistics

• Contra: background from , K decays; not sensitive to low-neutrino energies (E<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 – 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 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 has just got the final statistics: ~ 2000 charms!

Analysis finalized by the end of the year!

CHORUS detector

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

p/p = 10 15%

(p < 70 GeV/c)

-nuclear emulsion target (770kg)

-scintillating fiber tracker

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 emulsions

350 m

90 m

Automatic emulsion data acquisition (phase-II)

1

2

3

Angular acceptance : 400

mrad

Track segments from 8 plates overlapped

At least 2-segment connected tracks

Eliminate passing through tracks

Reconstruct full vertex topology

Volume : 1.5 x 1.5 mm2 x 6.3 mm

1

2Location of interaction vertex guided by

electronic detector.

Full data taking around interaction vertex

called Netscan

Offline tracking and vertex reconstruction

~ 11 minutes / event

Selection criteriaEmulsions 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 track as well

Tracks with large impact parameter with respect to vertex point visual inspection for decay confirmation

impact parameter vs. vertex depth

θ=0.4 rad

θ=0. rad

Selected events

Selected events

mdzIP 22 )2(0.3

22 )0194.0()0305.0(

dz = vertex depth

parameterize the angular error

Neutrino-induced charm sample

Decay topology (prong) Sample

Kink 461

Vee 841

Trident 501

4Vee 230

C5 23

6Vee 3

Total sample 2059

final sample of 95450 located interactions with a -

Fully neutral D0 decay mode

4

6

4

240 11

f

f

f

fff

•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

totf / from58.038.13 44 PDG

Ingredients: CHORUS new results

%2.52.5722

4 ff

f

%7.01.14

6 f

f

36 10)9.05.1( f

New measurements! preliminary

%2.57.280 f assumed to be 5%!!!

Measurement of D0 production

Phys. Lett. B 527 (2002) 173, based on ~25% of statistics

)%syst( 17.0(stat) 13.099.1)( 4200

VVDBRCC

D

2 prong (V2) 841 (background: 37)

4 prong (V4) 230 (no background)

Observed D0 events

NOW: full sample: 95450 CC events

and D0 fully neutral taken into account

6 prong (V4) 3 (no background)

(D0)=0.1450.0101ry location and 2ry detection

%0.22(syst) 0.09(stat) 2.970

CC

D

Preliminary

Measurement of D0 momentumUse correlation between opening

angle of decay daughters and charm

momentum to obtain momentum

distribution

D Momentum

Inverse of

geometrical

mean of

opening angle

of daughters

Momentum distribution of D0 can be measured

by unfolding opening angle distribution

(curve is the model in the CHORUS MC)

Prelim

inary

Z-distribution

Prelim

inary

Also an E531 measurement Indirect measurements from dimuon

data: CDHS, CCFR, CHARMII, NuTeV,

CHORUS

Feynman x distribution

2))1/(/11()(

zzz

NzD

PP

Peterson formula

Prelim

inary

dotted curve is MC model

Charm fragmentation results

sexperimentcollider in 1zRemark:

c0 cuducD u,d from sea and valenceu from sea 1z

incorrect to put all charms together, but difficult to tag separately

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

Statistical approach using flight length distribution

Λ c

Ds

D+

Flight length in μm

c 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

Phys. Lett. B 555 (2003) 156

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

MC: D and DsData

Data

b.g. excessData

Monte Carlo

DataBackground check: Pt distribution for 1-prong decays

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:

33 equations and 3 unknownsequations 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.)%

-54-54

%0.18(syst)(stat)35.054.1

CC

c

(sys)% 13.0 (stat) 13.003.6 CC

charm

Preliminary

a) n - c+ b) n - c

+ (c*+) c) p - c

++(c*++)

Quasi-elastic charm production

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

Topological and kinematical selection criteria:

13 events with a background of 1.7 (mainly from DIS c)

(syst)%(stat)23.0 02.003.0

12.006.0

CC

QEcharm

QE production is about

15% of c production

Phys.Lett.B 575 (2003) 198 Phys.Lett.B 575 (2003) 198 (based on 46105 (based on 46105 CC) CC)

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

c

Final data sample: 2704 interactions with a +

19.7±2.1% contamination from decaysor ugh punch thro ,

seennot and with charm

as identified with

k

c

measured interaction ratio: %1.01.2

consistent with a measurement done using interactions in the calorimeter (2.2±0.1%), consistent with beam contamination and the different energy spectrum and cross-section

GeV 27 GeV 18 EE

Anti-neutrino induced charm productionDecay topology

Candidate events

background

Vee 16 1.4±0.3

V4 6 0.13±0.06

Kink 4 0.8±0.2

Trident 4 0.3±0.2

C5 2 0.02±0.01

Total 32 2.7±0.4

(syst)% 1.0(stat) 1.5)(

)( 4.10.1

XN

XcN

5.10.14.2

0

C

C

f

f

background is essentially from charm in neutrinos

0.97±0.15 in neutrinos (suppression of )c

6.0% in neutrinos (higher energyand presence of QE process)

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, observation of tri-muon events -(+-) and same-sign di-muons (controversial interpretation)

• 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 larger statistics is in progress. Four candidates found and the first cross-section estimation reported

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

Newly found CC eventNewly found CC event

E=36.9 GeVE=36.9 GeV P=-16.9 P=-16.9 GeV/cGeV/c

Evis= 53.8 GeVEvis= 53.8 GeV

Both neutral decays Both neutral decays inconsistent with two-body inconsistent with two-body decay (acoplanarity)decay (acoplanarity)

PPd1d1>4.70 GeV/c @ 90 CL.(>4.70 GeV/c @ 90 CL.(TTT #2)T #2)

PPd2d2>0.67 GeV/c @ 90 CL.>0.67 GeV/c @ 90 CL.

PPd3d3>2.32 GeV/c @90 CL.(>2.32 GeV/c @90 CL.(TTT T #7)#7)

PPd2d2>1.92 GeV/c @90 CL.(>1.92 GeV/c @90 CL.(TTT #5)T #5)

Pl31Pl31 pl30 pl30

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• 3 candidates have been found and the preliminary measurement of the

cross-section is reported

An event in NC

120µm210µm

PLATE 18 PLATE 17

140µmTT

TT

TT

Ns = 6Nh = 1 (gray)

4Vee @ pl 17FL = 884 µm

C3 @ pl 17FL = 426 µm

Associated charm production cross-section

Process Observed events

Estimated background

CC 4 0.79±0.10

NC 3 0.12 ±0.02

4

4

10)6.01.25.3()(

10)6.09.19.3()(

NC

CC

cc

cc

preliminary

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

first direct measurement!

Background in CC comes from single charm + hadronic “white” interaction

Background in NC comes from single charm + hadronic “white” interaction + missed muon

Conclusions and OutlooksConclusions and Outlooks•150K events in CHORUS emulsions for Charm analysis•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)–QE c production (Phys.Lett.B 575 (2003) 198)(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