Study of charm physics in neutrino scattering

Di Capua FrancescoUniversity of Napoli, Italy

Heavy Quarks and Leptons 2004San Juan, Puerto Rico

Outline

The CHORUS experiment

• The CHORUS detector

• Automatic acquisition of nuclear emulsions

Physics motivation• What do we measure and why it is interesting

Results on charm analysis• Measurement of c, D0 and quasi-elastic charm production

• Semi-leptonic branching ratio B

• Associated charm production (CC and NC)• Anti-neutrino charm production

Conclusions and perspectives

A short theoretical introduction

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-

Physics motivationMeasure strange content of the nucleon

• Possible strange/anti-strange asymmetry non-p QCD effects

• Crucial role in relating charged-lepton and neutrino F2 structure

function • Knowledge of the strange sea is important to search for stop

at hadron colliders (largest background: g+sW+c )

Constrain/study charm production models • in NLO pQCD is a challenging theoretical problem

R.Demina et al., Phys. ReV. D 62 (2000) 035011S.J.Brodsky and B.Ma, Phys. Lett. B 381 (1996) 317

2 scales, QCD and charm mass

(J.Conrad et al. Rev.Mod.Phys. 70 (1998) 1341-1392)Measure charm mass and Vcd

Dimuon available statistics

CDHS (CERN WBB)CDHS (CERN WBB)

CCFR (NuTeV)CCFR (NuTeV)

CHARMII (CERN WANF)CHARMII (CERN WANF)

Zeitschr. Phys. C (1982) 19-31

Zeitschr. Phys. C (1995) 189-198

Eur. Phys. J., C11 (1999) 19-34

NOMAD (CERN WANF)NOMAD (CERN WANF) Phys.Lett.B486:35-48,2000

9922 -+ , 2123 +- events

5044 -+ , 1062 +- events

4111 -+ , 871 +- events

2714 -+ , 115 +- events

Background due to , K, Kos

Cross section measurement depends on knowledge of BR (C ) ~ 10%

and on the uncertainty on it

High statistics, but:

Emulsion experiments These experiments study charm production

by looking “directly” at the decay topology of the charmed hadron with micrometric resolutionContra: till few years ago the charm

statistics was limited by the scanning power (but this is not the case anymore); the anti- statistics is very poor Pro: low background; sensitivity to low Emc thr. effect;

reconstruction of the charmed hadron kinematics (direction and momentum) fragmentation studies are possible

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

p/p = 10 – 15%

(p < 70 GeV/c)

(with lead and scintillating fibers, 112 ton )

E/E = 32 %/ E (hadrons)= 14 %/ E (electrons)

h = 60 mrad @ 10 GeV

E ~ 27 GeV

Air-core magnetActive target

Muonspectrometer

CalorimeterWB Neutrino beam

:: : : e : : e

1.00 :: 0.06 :: 0.017 :: 0.007

•nuclear emulsion target (770kg)•scintillating fiber trackers

CHORUS experimentCHORUS experiment(CERN Hybrid Oscillation Research ApparatUS)

CalorimeterAir-core magnet

beamMuon spectrometer

Emulsion target

Interaction vertex

Electronic detector

prediction

All track segments infiducial volume

After a low momentumtracks rejection(P > 100 MeV) and numberof segments 2

After rejection ofpassing-through tracks

Tracks confirmedby electronic detectors

Nuclear emulsion analysis

~ 100 m

Visual inspection to confirm the event

Charm production by interactions in emulsions

Phys. Lett. B 206 (1988) 375-379

E531 (Fermilab, E531 (Fermilab,

Nagoya)Nagoya)

122 charm events in emulsion

only measurement of D0 : D+ : Ds+ :

c+

(no anti-neutrino charm events)

B(c) crucial for other experiments

CHORUS (CERN CHORUS (CERN

WANF)WANF)Just got the final statistics :

2059 charm events!

The analysis is in progress!

Measurement of c production

Strategy:Analysis is based on statistical approach using flight length distribution

Short flight decay:

c enriched sample

Long flight decay:

D+, Ds dominated sample

Analysis has been performed applying two different

selections

Phys. Lett. B. 555 (2003) 156-166 based on 50414 CC

D : Λc : Ds = 6 : 3 : 1(E531 result)

Λc

D

Ds

Measurement of c production

Short flight decay (A):

Daughter track: Distance to the muon 5 m to 30 m1614 events were selected for visual inspection

Long flight decay (B):

Parent track: distance to the muon < 5 mDistance between daughter and parent 5 m to 30 m586 events were selected for visual inspection

After flight length cut:

A: 40 m < FL < 400 mB: 400 m < FL < 2400 m

1 prong62133

3 prong66195

Combining short (A) and long (B) decay search and taking into account efficiencies and background:

c = 861 ± 198 (stat) ± 98 (syst) (QE)+140-54

BR(c 3 prong) = ( 24 ± 7 (stat) ± 4 (syst) ) x 10-2

(c) / (CC) x BR (c 3 prong) = ( 0.37 ± 0.10 (stat) ± 0.02 (syst) ) x 10-2

(c) / (CC) = ( 1.54 ± 0.35 (stat) ± 0.18 (syst) ) x 10-2

Measurement of c production

Quasi-elastic charm productionPhys. Lett. B. 575 (2003) 198 based on 46105 CC

Topological and kinematical selection criteria:Require 2 or 3 tracks at primary vertex

Flight length < 200 m (enriched c sample)

Calorimeter energy < 10 GeV and electromagnetic energy < 2

GeV

165º (angle between muon and charm in transverse plane)

13 events with a background of 1.7±0.6 (mainly from DIS c)

QE production is about 15% of c

production

Quasi-elastic charm production

Azimuthal angle

Measurement of D0 productionPhys. Lett. B. 527 (2002) 173 based on ~25% of statistics

NOW full sample: 95450 CC eventsCandidate selection

Primary track matched to detector muonDaughter track matched to detector track3~13 m < I.P. wrt. 1ry vtx < 400 m

Selection efficienciesV2 : (56.3 ± 0.5) x 10-2

V4 : (74.2 ± 0.9) x 10-2

V2 : 841V4 : 230

Confirmed D0 sample

V2 : 1428 ± 49V4 : 310 ± 20

BG subtracted, efficiency correctedD0 V4D0 V2

= (22.7 ± 1.8) x 10-2

Measurement of D0 production

Fully neutral D0 decay mode:

BR4/BR2 measuredBR4 = 0.1338 ± 0.0058 (PDG)BR(D0 neutrals) = 1 – BR4 x ( 1 + BR2/BR4 ) = (27.3 ± 4.5) %

Total production cross section:

All D0 ’s Relative detection efficiency D0/CC = 0.87

(D0) / (CC) = ND0 / 95450 / 0.87 = (2.97 ± 0.24) x

10-2

Preliminar

y

Number of selected events 1055

90.6% selection purity 956 35

Dimuon sample 88 10 (stat) 8 (syst)B = 9.3 0.9 (stat) 0.9 (syst) %

only ‘direct’ measurement available

B as measured in CHORUS

2ry Muon identification(Average efficiency ~ 55 %)

Revised result (D0 neutrals effect)

B = 8.1 0.8 (stat) 0.8 (syst) %

Phys. Lett. B. 549 (2002) 48 based on ~50% of statistics

Analysis with full statistics is in

progress!

Associated charm production in CC

Charged-current

Gluon bremsstrahlungCurrently a search is in progress in CHORUS:

1 event observed and confirmed by kinematical analysis (Phys. Lett. B. 539 (2002) 188)A new analysis with full statistics is in

progress (5 events on 95450 CC); The discrepancy between data and prediction should be clarified soon.

In the past this search was based on the observation of trimuon events -( + -) and same-sign dimuons; Large background from and K decays Observed rate 60 times larger than

expected from theoretical calculations! (K.Hagiwara Nucl.Phys.B 173 (1980) 487

Event Event 7789107177891071

E=35.4 GeVE=35.4 GeV P=-13.5 P=-13.5 GeV/cGeV/c

Pl 7Pl 7 Pl 6 Pl 6 pl 4pl 4

Evis=48.9 Evis=48.9 GeVGeV

Associated charm production in CC

11ry@pl7ry@pl7

NNs=6, Nh=1s=6, Nh=1

V2 @V2 @pl 6pl 6

fl= 257.0fl= 257.0mm

kink @pl 4kink @pl 4

fl= 2271.6 fl= 2271.6 mm

= 67.4mra= 67.4mradd

Associated charm production in NC

Neutral-current

Z-gluon fusion

In the past only one event observed in the E531 emulsion:

Currently a search is in progress in CHORUS:3 candidates on 26568 NC have been

found and the cross-section measurement will be finalised by the end of this year

Production rate 1.3 x 10-3 normalised to CC

+3.1-1.1

Indirect search performed by NuTeV:

Production rate (2.6±1.6)x10-3 normalised to CC at 154 GeV

mc = (1.40 ±0.26) GeV, in agreement with other measurements

+0.83-0.36

(A. Alton et al., Phys. Rev. D64 (2001) 539)

Gluon bremsstrahlung

+

Associated charm production in NC

N+ = 2704

N- = 93768= 1 spectrometer events

After reconstruction cut:

Strategy:observed events with 1+ from spectrometer

induced charm = 32

All ‘s = 4975 ± 187

(N +cX)(N +X)

= 5.1 %+ 1.4- 1.0

fC-

fCo= 2.4 + 1.5

- 1.0(stat)

Estimated background = 2.7mainly due to the muon wrong sign identification

Preliminar

y

Charm production in antineutrino interactions

Charm production in antineutrino interactions

Charm production rate as a function of energy

Theoretical prediction

Analyses in progress

),( 2)(2

2

4 )(T

hch hdyd

cXNd pzDfTdydzdpd

CXNd

- From charm quark to charmed hadrons

Charmed fractions fh (present results based on the 122 E531 events and a reanalysis discussed in T. Bolton hep-ex/9708014)

Fragmentation functions (z and PT2

distribution)- Total charm production cross-

section- Charm mass mc, Muonic branching ratio B, Vcd

- x distribution charm (anti-charm) events

- D* production, D* D0 +

ConclusionCharm physics in interactions very interesting

So far, from a subsample of charm data in CHORUS we have measured:

Λc production

QE charm production

D0 production

CC associate charm production

BR

Diffractive Ds* production

Phys. Lett. B. 555 (2003) 156Phys. Lett. B. 575 (2003) 198Phys. Lett. B. 527 (2002) 173Phys. Lett. B. 539 (2002) 188Phys. Lett. B. 549 (2002) 48Phys. Lett. B. 435 (1998) 458

Many analyses are still in progressNew results will be available within 2004

Backup slides

Charmed fractions fh can only be measured in emulsions! Present results based on the 122 E531 events

and a reanalysis discussed in T. Bolton hep-ex/9708014

Analysis in progress of the CHORUS data: 2000 eventsResults should be available in a couple of months

Fragmentation functionsThe z distribution can be parametrized as follows

2

2 1

11

1

121

)( z

zz

zz

zz

NzDc

c

c

Collins-SpillerJ.Phys. G 11 (1985) 1289

2

11

1

)(

zzz

NzD

p

p Peterson et al.

Phys.Rev. D 27 (1983) 105

NOMAD

Fit to z distribution Direct measurements

E531, NOMAD, CHORUS-Emul in progress

z distribution is extracted for charmed hadrons and fitted

Indirect measurements CDHS, CCFR, CHARMII, NuTeV, CHORUS-Calo in progress

p or c (depends on the choice) is one of the free parameters of the fit to the dimuon data, see later

Determination of p and c

p c

E531 0.0760.014 ---

NOMAD 0.0750.028 0.036 0.130.08 0.11

CDHS 0.02-0.14 ---

CCFR 0.220.05 0.880.12

CHARMII 0.0720.017 ---

NuTeV --- 2.070.31

All the above numbers have been obtained with a LO analysis

At e+e- exps s1/210 GeV P0.16(D+)0.27(c)O.Biebel, P.Nason, B.R.Webber hep-ph/0109282

pT2 distribution of

charmed particles

The transverse momentum of charmed particles wrt thedirection of the hadronic system is usually parametrized as

2

2Tbp

T

edp

dN

Available statistics in exp• E531 122 eventsPhys. Lett. B 206 (1988) 380-384• NOMAD 47 eventsPhys. Lett. B 526 (2002) 278-286

E531Phys.Lett.B 206 (1988)

380

NOMADPhys.Lett.B 526 (2002)

278

b 3.250.37 (GeV/c)-2 3.38 0.40 (GeV/c)-2

• Analysis in progress of the CHORUS data: •Results should be available in a couple of months• New analysis of the NOMAD data in progress

One measurement available with 360 GeV pp interactions

b = 1.10.3 (GeV/c)-2

M.Aguilar-Benitez et al., Phys. Lett B 123 (1983) 103

pT2 distribution of

charmed particles

The strange sea distribution

No new results Both at LO and NLO ~0.5 At LO is not zero =2.50.7, while it is at

NLO =’=-0.460.420.360.650.17

The momentum distributions of s and anti-s are consistent and the difference in the two distributions is limited to –1.9< <1.0 at 90% C.L.

In the near future: NuTeV NLO analysis will be available; CHORUS-Calo and NOMAD-FCAL LO analyses will be available, too

Relevant parameters of the fit to dimuon data

Input parameters Charmed fractions and decay model constrained by other

experiments Vcs (In the following we use 0.996±0.024 Riv.NuovoCim.

23(2000)1) BR(C ) (In the following 9.31±0.95% for E>30 GeV)

Output parameters Charm mass: mc

Element of the CKM matrix: Vcd Fragmentation parameter: Two parameters for each mode ( and anti-) that describe the

magnitude and the shape of the s and anti-s PDFs =2S/(U+D) is the proportion of s-quarks to non strange quarks

in the nucleon sea x(1-x) is the shape of the s-quark PDF

Vcd determinationAt LO order severalexperiments extracted

)006.0224.0( cdV

At NLO only CCFR analysis

)015.0239.0( cdV

As expected LO and NLO give consistent results!

)225.0(

)014.0224.0(013.0011.0

cd

cd

V

VPrevious estimates

mc determination

At LO order severalexperiments extractedthe charm-quark mass

GeV )13.040.1( cm

At NLO only CCFR analysis

GeV )19.070.1( cmincludes also kinematic effects associatedwith heavy quark productions

GeV )74.1( 13.018.0

cmg fusion

E691 Phys. ReV. Lett. 65 (1990) 2503

determinationAt LO order several experiments extracted

)031.0405.0(

At NLO only CCFR analysis

)036.0484.0( LO and NLO give consistent results at 1.2

A fit to all available data (N,eN,N) gives

)045.0714.0(

)044.0667.0(

Barone,Pascaud,Zomer E.Phys.J.C 12, 243

Chorus dimuon analysis result (calo)

(preliminary)

mc = 1.46 0.15 (stat) 0.10 (syst)

= 0.56 0.05 (stat) 0.045 (syst)

= 0.040 0.003 (stat) 0.015 (syst)

B = 0.098 0.005(stat) 0.014 (syst)

VVudud

0.1 %0.1 % nuclear beta decay

The CKM matrix

VVcbcb 5 %5 %

Be3 decay

VVcscs 15 %15 %

De3 decay

VVubub 25 %25 %

b u l

VVusus 1 %1 %

Ke3 decay

VVcdcd 7 %7 %

charm production

VVtdtd VVtsts

VVtbtb 30 %30 %

t b l

Review of particle physics, 98 edition

d’d’

s’s’

b’b’

dd

ss

bb

==