Past Neutrino Mass & Oscillations Present Atmospheric neutrinos Solar neutrinos Future
Charm production with neutrinos Physics motivation Results Outlook Giovanni De Lellis University of...
-
date post
22-Dec-2015 -
Category
Documents
-
view
212 -
download
0
Transcript of Charm production with neutrinos Physics motivation Results Outlook Giovanni De Lellis University of...
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