Charm production with neutrinos

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					Charm production with neutrinos
             Giovanni De Lellis
            University of Naples




      (on behalf of the CHORUS Collaboration)

• Physics motivation
• Results
• Outlook
              DIS charm production
       Beam
        knowledge                  -             
                                                         
|Vcd|2,|Vcs|2        Charm fragmentation
                     fD0 ; fD+ ; fDs ; fc
                                                         ,h
     d,s             z = pD/pc, pT2
                       c                                h
  Quark density functions,                             Ehad
  strange sea ()
Production from d(anti-d) quarks Cabibbo suppressed
 large s contribution: 50% in  and 90% in anti-
                    Physics motivation
• 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+sW+c
            R.Demina et al., Phys. ReV. D 62 (2000) 035011
            S.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
       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 (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
          Inclusive charm production
           cross-section induced by 
Inclusive charm-production cross-section measurement
possible only with nuclear emulsions
 So far only E531: 122 events
 (  N  c X )
              

                   4.90..6 %
                       
                         07

 (  N   X )
             


   CHORUS has just got the
 final statistics: ~ 2000 charms!
    Analysis finalized by the
          end of the year!
                               CHORUS detector
         Active target                  Air-core magnet
                                   p/p = 0.035 p (GeV/c)  0.22
-nuclear emulsion target (770kg)
-scintillating fiber tracker




                                                          muon spectrometer
  E ~ 27 GeV                                                   p/p = 10 15%
                                                                 (p < 70 GeV/c)
      Neutrino beam                        Calorimeter
   :       :   e   : e           E/E = 32 %/ E (hadrons)
                                          = 14 %/  E (electrons)
1.00 : 0.05 : 0.017 : 0.007              h = 60 mrad @ 10 GeV
                CHORUS emulsions
                                                      350  m

                                                       90  m




 -54 m

             -36 m

MIP: 30  40 grains/100m
Resolution ~ 0.3 m       -21 m
Focal depth: 1 to 3 m                       0 m

            S. Aoki et., Nucl. Instr. Meth. A 447 (2000) 361
Automatic emulsion data acquisition (phase-II)
                                                                         1
1     Location of  interaction vertex guided by
                                                          2
      electronic detector.
2    Full data taking around  interaction vertex
     called Netscan
                                  2
           Volume : 1.5 x 1.5 mm x 6.3 mm
           Angular acceptance : 400 mrad
           ~ 11 minutes / event

3    Offline tracking and vertex reconstruction
                        At least 2-segment                        Reconstruct full
                         connected tracks                         vertex topology




    Track segments                            Eliminate passing
     from 8 plates                             through tracks
      overlapped
                       Selection criteria
 Emulsions 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

  IP  3.02  (2dz) 2 m              impact parameter vs. vertex depth




       dz = vertex depth


parameterize the angular error

   (0.0305) 2  (0.0194 ) 2
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
•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
                                       f2 f6 
                      f 0  1  f 4 1   
                                    
                                       f4 f4 
                                              
                f 4  13 .38  0.58 from 4 / tot        PDG
                f4
Ingredients:         f 2  57 .2  5.2%
                f2                       CHORUS new results
                   f6
                       1 . 1  0 .7 %
                   f4
                  New measurements! preliminary
f 6  (1.5  0.9) 10   3
                             f 0  28 .7  5.2%      assumed to be 5%!!!
                                           0
          Measurement of D production
  D0
       BR( D0  V2  V4 )  1.99  0.13 (stat) 0.17 (syst)%
  CC
         Phys. Lett. B 527 (2002) 173, based on ~25% of statistics



             NOW: full sample: 95450 CC events
         and D0  fully neutral taken into account
Observed D0 events
    2 prong (V2)   841 (background: 37)
    4 prong (V4)   230 (no background)
                                                    (D0)=0.1450.010
                                               1ry location and 2ry detection
    6 prong (V4)   3 (no background)

        D
              2.97  0.09(stat) 0.22(syst)
            0
                                           %
         CC
                  Measurement of D0 momentum
                                                  Use correlation between opening
                                                 angle of decay daughters and charm
 Inverse of
                                                  momentum to obtain momentum
 geometrical                                                 distribution
  mean of
opening angle
 of daughters




                    D Momentum



   Momentum distribution of D0 can be measured
       by unfolding opening angle distribution
      (curve is the model in the CHORUS MC)
           Z-distribution
                                          N
Peterson formula DP ( z ) 
                            z (1  1 / z   P /(1  z )) 2
                            dotted curve is MC model
    Also an E531 measurement
    Indirect measurements from dimuon data:
        CDHS, CCFR, CHARMII, NuTeV,
         CHORUS




        Feynman
      x distribution
                  Charm fragmentation results




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

 Remark: z  1 in collider experiments
D 0  cu u from sea          c  cud u,d from sea and valence            z 1
     incorrect to put all charms together, but difficult to tag separately
                 c production rate           Phys. Lett. B 555 (2003) 156

        Statistical approach using flight length distribution
  •Short flight decay: selection A
     (40 mm < FL <400 mm):
       Λ c enriched sample                   Λ   c
128 candidates out of 50,414 CC
  •Long flight decay: selection B                D+
          (400 mm < FL < 2400 mm):
           D+, Ds dominated sample                    Ds
210 candidates out of 56,761 CC
      (A)             (B)
                                                     Flight length in μm

                                     parent particle track
                        
Evidence for c production: 3-prong decays (background free)

       Data
                                          Data
               MC: D and Ds




    Background check: Pt distribution for 1-prong decays
                                   Data
        Data
                                                 b.g. excess
                     Monte Carlo
                     c production rate
   Combining short (A) and long (B: only 3-prong) decay
   searches and correcting for efficiencies and background:
                     3 equations and 3 unknowns
•D+Ds = 1118 116(stat)
                                      -54
• c = 861  198 (stat.)  98 (syst.)+140 (QE)

•Br(c 3prong) = 24  7 (stat.)  4 (syst.)%

          c
               1.54  0.35(stat)  0.18(syst)%
          CC
           charm
                   6.03  0.13 (stat)  0.13 (sys)%   Preliminary
            CC
               Quasi-elastic charm production



       a)   n   -  c+   b)   n   -  c+ ( c*+)   c)   p   -  c++( c*++)

          Phys.Lett.B 575 (2003) 198 (based on 46105  CC)
       Topological and kinematical selection criteria:
  •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
      13 events with a background of 1.7 (mainly from DIS c)
 QEcharm        0.12       0.02
           0.230.06 (stat)0.03 (syst)%                     QE production is about
   CC                                                        15% of c production
                          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  c suppressed due to baryon number conservation
       • About 5% contamination in the neutrino beam  limiting factor is still the
         low statistics

  Final data sample: 2704 interactions with a +
                                                 with   identified as  
   19.7±2.1% contamination from                  charm with c    and   not seen
                                               p , k punch thro or decays
                                                              ugh
                             
 measured interaction ratio:     2.1  0.1%
                             
 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
                            E  18 GeV  E  27 GeV
              Anti-neutrino induced charm production
  Decay           Candidate background
  topology         events
  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

background is essentially from charm in neutrinos

 (  N    c X )      1.4
                                                    6.0% in neutrinos (higher energy
                      5.11.0 (stat)  0.1 (syst)%
 (  N   X )
                                                     and presence of QE process)
  fC 0
          2.4 1..0
               
                15
                            0.97±0.15 in neutrinos (suppression of  c )
  fC 
             Associated charm production

             CC                       NC
                                             


         W                            Z
                                           c
                                           c
                                                    D+D+X
                  c
                          D+D+X
                  c

Gluon Bremsstrahlung                  Z-Gluon Fusion
     Associated charm production in CC

• In the past, observation of tri-muon events -(+-)
  and same-sign di-muons (controversial interpretation)
     • 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)
• Currently a search is in progress in CHORUS
     • 1 event observed and confirmed by kinematical analysis
                 (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
             First observation in CC
Phys. Lett B 539 (2002) 188, CHORUS Coll.
        30    29                                    21

                                                                         Ns = 2
                                                                          Nh = 6



        1010 m                   6735 m
                                                             B.G. = 0.04±0.01
    D0 f.l. = 340 m
       1st vertex                2ry vertex
                                               kink parent
kink= 420 mrad              2 = 310 mrad                            D0
f.l. = 1010 m               f.l. = 7560 m

     pb  500   +180
                        MeV/c      P = 0.78 GeV/c                    -
                - 110


     dE/dx              proton     P > 330   MeV/c          transverse plane
                        Newly found CC event



Evis= 53.8 GeV     E=36.9 GeV    P=-16.9 GeV/c


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

                                       Pd1>4.70 GeV/c @ 90 CL.(TT #2)

                                        Pd2>0.67 GeV/c @ 90 CL.


                                       Pd2>1.92 GeV/c @90 CL.(TT #5)
                                       Pd3>2.32 GeV/c @90 CL.(TT #7)
                 Pl31           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 (2.61.6)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
   Ns = 6
   Nh = 1 (gray)

   4Vee @ pl 17
   FL = 884 µm

     C3 @ pl 17
    FL = 426 µm

PLATE 18      PLATE 17
                                 TT

                                           TT


                                      TT
      210µm        140µm 120µm
    Associated charm production cross-section
                 Process                 Observed         Estimated
                                          events         background
                    CC                      4             0.79±0.10
                    NC                      3             0.12 ±0.02
      Background in CC comes from single charm + hadronic “white” interaction
Background in NC comes from single charm + hadronic “white” interaction + missed muon

 (cc  )
           (3.9  1.9  0.6) 10 4        first direct measurement!
   CC
 (cc   )                                     preliminary
             (3.5  2.1  0.6) 10 4
   NC

     •agreement with the theory for the CC process
     •agreement with NuTeV for NC (different energy spectrum)
               Conclusions and Outlooks
•150K events in CHORUS emulsions for Charm analysis
•CHORUS has measured:
   –Diffractive Ds* production (Phys. Lett. B 435 (1998) 458)
   –σ (D0)/σ(CC) (Phys. Lett B 527 (2002) 173)
   –CC associated charm production (Phys.Lett. B 539 (2002) 188)
   –B (Phys. Lett B 548 (2002) 48): first direct measurement
   –σ( c)/σ(CC) (Phys.Lett.B 555 (2003)156)
   –QE c production (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

				
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