Measurement of charm production and decay properties

by CHORUS

Francesco Di CapuaUniversity of Napoli and INFN

Italy

GRAVITY, ASTROPHYSICS AND STRINGS AT THE BLACK SEAkiten – Bulgaria June 2005

Outline

The CHORUS experiment• The CHORUS detector

• Automatic analysis of nuclear emulsions

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

Results on charm analysis• D0 production in neutrino charged current interaction• D*+ production in neutrino charged current interaction • Fragmentation properties of charmed particles• Anti-neutrino charm production

• Muonic branching ratio B of charmed particles (preliminary results)

• Associated charm production (CC and NC)• Dimuon analysis in the calorimeterConclusions and perspectives

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

“Charm Physics with neutrinos”, G.De Lellis, P.Migliozzi, P.Santorelli , Phys. Rept.399:227-320,2004

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:

CHORUS (CERN WANF)CHORUS (CERN WANF) 8919 -+ , 430 +- events To be published

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

The CHORUS charged current data sample and charm

subsampleLocated CC events 93807Selected for visual

inspection2752

C1 452

C3 491

C5 22

V2 819

V4 226

V6 3

Total charm candidates

2013

Measurement of D0 production and of decay branching fractions in -N scattering

Phys. Lett. B. 613 (2005) 105

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

After BG subtraction and efficiency correction:

= 0.207 ± 0.016 ± 0.004B(D0 V4)B(D0 V2)

The relative rate is:

(D0)/(CC)=0.0269 ± 0.0018 ± 0.0013

Assuming B(D0 V4)=0.1339±0.0061 (PDG);

D0 topological branching fractions

INCLUSIVE measurement in CHORUS:

B(D0 V2) = 0.647 ± 0.049 ± 0.031

B(D0 V6) = (1.2 ± 0.2)x10-3+1.3- 0.9

B(D0 V2)B(D0 V4)

B(D0V0)=1- B(D0V4)[1+ + ]B(D0 V6)B(D0 V4)

B(D0V0) = 0.218±0.049±0.036 very important for B measurement!!!

B(D0 V0) 5% (PDG) Sum over all exclusive channel for which measurement exist

B(D0 V2) = 0.485 ± 0.020 (PDG) Sum over all exclusive channel for which measurement exist

B(D0 V6) = (0.59 ± 0.12)x10 -3 (FOCUS coll.) sum of all exclusive measured channel

To be compared with:

Energy dependence of the cross section ratio and charm mass

CHORUS data

E531 data

Fit to a theoretical model

mc=(1.42 0.08(stat) 0.04(syst)) GeV/c2

Fit parameters for the model curve(M.Gluk,E.Reya and A.Vogt, Z.Phys.C (1955) 433)

(sp as measured in CHORUS, see next

slides)

Accepted by Phys. Lett. B. - CERN-PH-EP-2005-010.

Looking for events in the channel: D*+ D0 +

D0 fl>100m

<60 mrad

0.4 <p(+)<4 GeV/c10.< pT<50. MeV/c

Number of candidates

Background prediction(1) Expected shape of the candidates normalized

to the observed events;(2-3-4) shape normalized to the total number of D0

and C+ respectively;

D*+ signal in the D0 h+

sample

No signal in the D0h-

sample as expected

No signal in the C+h-

sample as expected

No signal in the C+h+

sample as expected

D0

D*+

Measurement of D*+ production in CC -N scattering

Measurement of D*+ production in CC -N scattering

Assuming B(D*+ D0 +)=0.677±0.005 (PDG) the relative rate is:

(D*+)/(D0)=0.38 ± 0.09(stat) ± 0.05(syst)

assuming that the D*+ and D*0 production rate are equal and recalling that D*0 always decays into D0:

(D* D0)/(D0)=0.63 ± 0.17By using the measure of (D0)/(CC) made in CHORUS:

(D*+)/(CC)=(1.02 ± 0.25(stat) ± 0.15 (syst))%To be compared

with:At similar neutrino energy beam:

•NOMAD (D*+)/(CC)=(0.79 ± 0.17(stat) ± 0.10 (syst))%•BEBC (D*+)/(CC)=(1.22 ± 0.25)%

At the higher energy of the Tevatron beam: • (D*+)/(CC)=(5.6 ± 1.8)%

Defining fV=V/(P+V) , V= vector production and P pseudoscalar production of D meson

fV=0.51 ± 0.18Consistent within the error: with V:P=3:1, as expected from simple spin arguments; with measurements in e+e-, N, N experiments.

CHORUS data Prediction

simulation

The momentum of D0 can be inferred by the geometrical average () of the angle of the decay daughters with respect to the direction of the D0

(as described in S.Petrera, G.Romano, Nucl.Instrum. And Meth.174 (1980) 61 )

Measurement of fragmentation properties of charmed particle production in CC neutrino interaction

Phys. Lett. B 604 (2004) 145

Momentum distribution of D0’s produced inclusively in CHORUS

),( 2)(2

2

4 )(T

hch hdyd

cXNd pzDfTdydzdpd

CXNd

From charm quark to charmed hadrons

Defined z as the ratio of the energy of the charmed particle E D and the energy transfer to the hadronic system zE D / we measure <z> = 0.63 ± 0.03(stat) ± 0.01(syst)

2

2 1

11

1

121

)( z

zz

zz

zz

NzDc

c

c

Collins-Spiller

J.Phys. G 11 (1985) 1289

2

11

1

)(

zzz

NzD

p

p Peterson et al.Phys.Rev. D 27 (1983) 105

Z distributionCHORUS dataPetersonCollins-Spiller

Fit to Collins-Spiller distribution:

cs = 0.21 ± 0.04 +0.05 -0.04

Fit to Peterson distribution:

P = 0.108 ± 0.017 ± 0.013

To be compared with:

To compare results:If zs = E D / string energyS

P = 0.083 ± 0.013 ± 0.010If zQ = P charmed particle / P charm quark

QP = 0.059 ± 0.010 ± 0.008

Fragmentation properties

XF is defined as: XF= 2 pLD – ED

W

pLD longitudinal momentum of D0

ED energy of D0

W invariant mass

From the distribution we mesure <XF>:

<XF >=0.38 ± 0.04(stat) ± 0.03(syst)

To be compared with NOMAD: <XF >= 0.47 ± 0.05

forward-backward asymmetry:

<A>=0.79 ± 0.14(stat) ± 0.05(syst)

To be compared with E531: <A> = 0.620 ± 0.092

From the distribution production angle out of the lepton plane we mesure:

<tanout>=0.030 ± 0.002

Analysis based on the full statistics

B muonic branching ratio of charmed particlesPrelim

inar

yB = (7.3 0.8(stat))

%The results takes into account the new

CHORUS measurement of B(D0 V0)22%

B = (8.3 1.6(stat))%

Considering only events with visible energy above 30 GeV

B x |Vcd|2LO=(0.474

0.027)x10-2

(CDHS,CHARM II, CCFR average value)

|Vcd|

LO=(0.2390.046)

B x |Vcd|2NLO=(0.534

0.046)x10-2

(CCFR)

|Vcd|

NLO=(0.2540.066)To be compared with:

0.221< |Vcd|<0.227 at 90% CL Obtained imposing CKM unitarity and only 3 generations

Phys. Lett. B. 604 (2004) 11-21

Measurement of charm production in antineutrino charged-current

interactions

Strategy: look for the + generated in the antienutrino CC interaction

After reconstruction cut and charm topology selection

TOT 32

(N +cX)(N +X)

= 5.0 ±0.7%

+ 1.4- 0.9

Theoretical prediction obtained from leading order calculation with mc=1.31 GeV/c2

Derived from di-lepton data

(G.de Lellis et al., J.Phys.G28 (2002), 713)

CHORUS DATA

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 93807 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 p 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

Chorus dimuon analysis result (calo)

mc = 1.26 0.16 (stat) 0.09 (syst)

= 0.33 0.05 (stat) 0.05 (syst)

P = 0.065 0.005 (stat) 0.009 (syst)

B = 0.096 0.004(stat) 0.008 (syst)

Nleading -

=8910180 Nleading + = 43060

Chorus dimuon analysis result (calo)

MC prediction obtained using fitted values of parameters mc, k, P, B

dimuon cross-section relative to CC events

data

Conclusion

Interesting charm physics results from CHORUS thanks to: high beam flux; Nuclear emulsion target (0.8t); Automatic emulsion analysis

D*+ production

D0 production

Antineutrino charm production

Fragmentation properties

QE charm production

Λc production

BR CC associate charm production

D0 production

Diffractive Ds* production

Accepted by Phys. Lett. B. Phys. Lett. B. 613 (2005) 105Phys. Lett. B. 604 (2004) 11Phys. Lett. B. 604 (2004) 145 Phys. Lett. B. 575 (2003) 198Phys. Lett. B. 555 (2003) 156Phys. Lett. B. 549 (2002) 48Phys. Lett. B. 539 (2002) 188 Phys. Lett. B. 527 (2002) 173 Phys. Lett. B. 435 (1998) 458

Other analyses in progress

Measured so far:

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

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

BR(C ) 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

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

==