Review on parton fragmentation studies in BABAR Fabio Anulli INFN – Sezione di Roma On behalf of the B A B AR Collaboration On behalf of the B A B AR Collaboration Workshop on parton fragmentation processes in the vacuum and in the medium ECT* - Trento February 25-29, 2008 Trento

Trento, February 27, 2008Fabio Anulli2 Outline:  Physics motivation  BABAR and PEPII  Inclusive production of light particles at ~10 GeV  Inclusive studies on charmed baryons at ~10 GeV Inclusive  c and  c spectra Inclusive  c and  c spectra  c   c  correlated production and popcorn mesons  c   c  correlated production and popcorn mesons  Studies of exclusive state at ~10 GeV e  e   pppp e  e   pppp e  e    e  e     e  e  interactions at low energy via Initial State Radiation  Conclusions

Trento, February 27, 2008Fabio Anulli3  (e  e   hadrons) BABAR (ISR)  High E cm : perturbative QCD holds ==> e  e   qq(g)  jets  QCD predicts energy dependence of “rare” few-body processes  Low E cm : resonances, quasi 2-,3-body processes,…  lots of physics: spectroscopy, form factors, QCD tests,…  the same also at cc and bb threshold (and at Z 0 )  difficult predictions (and models poorly tested) in the “transition” region  total  had is the experimental input for evaluation of hadronic contribution to (g  2)  and  QED (M Z ) KLOE (ISR) BESVEPP-II LEP B-factories PEP/PETRA

Trento, February 27, 2008Fabio Anulli4 The asymmetric B-factory PEP-II E e– = 9.0 GeV; E e+ = 3.1 GeV √s  M  (4S) = GeV/c 2 E e– = 9.0 GeV; E e+ = 3.1 GeV √s  M  (4S) = GeV/c 2 Both machine and detector optimized for study the CP violation in B mesons decays very well suited also for any type of physics at this energy  PEP-II largely outperformed the design parameters:  L peak = 1.2  10  cm  s   Best 24h : L = 910 pb    logging efficiency >96% delivered 523 fb  503 fb  recorded ~0.6 billion of e  e   bb ~0.7 billion of e  e   cc ~1.1 billion of e  e   qq (q=u,d,s) >15 million of e  e    ISR J/ 

Trento, February 27, 2008Fabio Anulli5 The BABAR detector  SVT:  97%, ~15  m z hit resolution  Tracking (SVT+DCH):  (p T )/p T  ( 0.13 p T (GeV/c)  0.45 ) %  K-  separation >3  ( p ~ 4 GeV/c)  EMC energy resolution:  E)/E  (2.3 E   1.8 ) %  Polar angle coverage in c.m. frame (w.r.t. e  beam): 0.9 < cos  < 0.85 Excellent detector performances: PID efficiencies and mis-ID rates  Analysis presented here make use of very good PID performances PID eff > 90% for most of interesting range mis-ID < 3% almost everywhere

Trento, February 27, 2008Fabio Anulli6 Inclusive Hadronic Particle Spectra  The total fragmentation function for a hadron h in e  e  annihilation at an energy E cm is:  precise measurements of IPS at different energies needed to: better comprehension of fragmentation processes better comprehension of fragmentation processes check consistency with a number of fragmentation models check consistency with a number of fragmentation models test scaling violation test scaling violation test QCD predictions test QCD predictions  many recent high-energy results  limited precision measurements at low-energy before B-factories  So far, BABAR have measured IS of:  3 light mesons (    K   )  1 light baryon ( p/p )  3 Heavy baryons (  c,  c,  c )  measurements performed both at  s=10.54 GeV and at  (4S) mass peak

Trento, February 27, 2008Fabio Anulli7 IHPS:      p/p  BABAR measurement based on: 0.9 fb -1 off-resonance 0.9 fb -1 off-resonance 3.6 fb -1 on-resonance 3.6 fb -1 on-resonance  plot scaled momentum distribution x p = 2p  /E cm  data available at E cm = GeV (some example shown here)  good consistency between BABAR and ARGUS data ARGUS extends to lower values ARGUS extends to lower values BABAR covers the high side of the spectrum BABAR covers the high side of the spectrum precision of data already limited by systematics effects. precision of data already limited by systematics effects.  reviewed analysis of BABAR data ongoing

Trento, February 27, 2008Fabio Anulli8 IHPS:      p/p  comparison of BABAR data with some models on the market : good consistency for pions good consistency for pions reasonable agreement with other scalar mesons, for most of the energy range reasonable agreement with other scalar mesons, for most of the energy range no model really works with protons (and baryons in general) no model really works with protons (and baryons in general)

Trento, February 27, 2008Fabio Anulli9 IHPS:      p/p  same data shown in previous slide, in log scale

Trento, February 27, 2008Fabio Anulli10 IHPS: cross section scaling IHPS: cross section scaling Hadronization should be scale invariant except for “small” effects of hadron masses, running of  S,… Hadronization should be scale invariant except for “small” effects of hadron masses, running of  S,… scaling violations at low x p, due to masses are well known and modeled adequately (here JETSET is shown for comparison) scaling violations at low x p, due to masses are well known and modeled adequately (here JETSET is shown for comparison) expect substantial scaling violations at high x p expect substantial scaling violations at high x p seen clearly in  and  data; reproduced by models seen clearly in  and  data; reproduced by models NOT seen in p/p data! Wrong model predictions NOT seen in p/p data! Wrong model predictions pions protons etas kaons

Trento, February 27, 2008Fabio Anulli11    K , , p/p : test QCD predictions Gaussian fit to cross section distributions p/p     In the Modified Leading Logarithmic Approximation (MLLA ), distributions versus ξ = -ln(x p ) should be Gaussian near the peak. π+π+π+π ± 0.01 K+K+K+K ± 0.01 p 1.61 ± 0.01  1.44 ± 0.02 peak position  from symmetric gaussian fits  QCD prediction is that  falls monotonically with increasing particle mass. while it is observed  * p   * K

Trento, February 27, 2008Fabio Anulli12    K , p/p : test QCD predictions  All data are consistent with the expected logarithm dependence with the center-of-mass energy  but, different slopes, protons data above kaons…  peak position         p/p s (GeV 2 )

Trento, February 27, 2008Fabio Anulli13    K , p/p : production rate  total number of particles produced per event extrapolated using fit to dσ/dξ distributions BABARARGUSCLEOJETSETUCLAHerwig π+π+π+π ± ± ± K+K+K+K ± ± ± p/p ± ± ± 0.276± ±0.04 ±

Trento, February 27, 2008Fabio Anulli14 Charm production at BABAR  Heavy hadrons produced in e  e  annihilations provide a laboratory for the study of heavy-quark jet fragmentation  Relevant quantities are Relative production rates for different spin, parity, etc Relative production rates for different spin, parity, etc Associated momentum spectra Associated momentum spectra Differences among mesons and baryons Differences among mesons and baryons  Measurements at GeV, below BB production threshold, are the ideal place to study e  e   cc reactions, and test charm fragmentation functions, the charmed hadrons being made of one of the leading quarks  Large amount of data to study b  c decays from inclusive measurements at the Y(4S): B-mesons  charmed mesons/baryons B-mesons  charmed mesons/baryons  Great potential for charm spectroscopy (search for new states, precise measurements of fundamental quantities, e.g. masses, spin, I-spin,…) ! last results on this topic shown yesterday by S. Pacetti last results on this topic shown yesterday by S. Pacetti

Trento, February 27, 2008Fabio Anulli15 Inclusive  c studies  The  c + (cud) is the lightest c-baryon  We precisely measured its mass reconstructing two low-Q decays, to minimize systematic uncertainties  We find (PRD 72, (2005) ) m(  c + ) =  0.14 MeV/c 2 m(  c + ) =  0.14 MeV/c 2  More precise and  higher than the previous PDG value: m PDG (  c + ) =  0.6 MeV/c 2 m PDG (  c + ) =  0.6 MeV/c  C  mass measurement

Trento, February 27, 2008Fabio Anulli16 Inclusive  c spectrum measurement  reconstruct  c +  p     from tracks consistent from originating from interaction point  evaluate track efficiencies from data in two-dimensional (p,  ) bins  weight events according to inverse efficiency matrix  fit mass peak in each x p bin differential cross-section vs x p  Determine e  e   cc events from off-resonance data (E cm =10.54 GeV)  Determine e  e   BB events from on-resonance data subtracting the off-resonance cross section scaled by the different c.m. energy PRD 75, (2007) 9.5 fb  off-resonance 81 fb  on-resonance

Trento, February 27, 2008Fabio Anulli17 Inclusive  c spectrum measurement  We measure (at E cm =10.54 GeV):  =   Total rate per event:  assuming  C + from e  e   cc, we get a production rate per c-jet of:  Result consistent with previous CLEO and Belle measurements  Compare to other baryons or mesons   C peak slightly lower w.r.t.  c  D mesons (both PS and V state), show broad peaks and differ significantly for x p ~ 1

Trento, February 27, 2008Fabio Anulli18 Inclusive  c spectrum measurement  Several fragmentation functions implemented in JETSET generator distributions affected by JETSET simulation of gluon radiation distributions affected by JETSET simulation of gluon radiation test each models against our data using a binned  2 test each models against our data using a binned  2  No model seems to correctly reproduce the data, but  The fitted values of the free parameters are quite different from those used for light hadrons and charmed mesons  These results indicate the needs of different functions for baryons and mesons (like in DIS, where there is a dependency on the number of spectator quarks)

Trento, February 27, 2008Fabio Anulli19 Inclusive  c spectrum at the Y(4s)  Spectrum for Y(4S) decays obtained subtracting the much harder e  e   cc spectrum  Kinematic limit x p = 0.47  Shape consistent with previous results  We measure  i.e. (4.5  1.2)% of B u,d decays include a  c Y(4S)  c  X  Data suggest a dominance of quasi-two-body decays like: B  (  c  p,  c  n,  c  ,  c p ) + m  B  (  c  p,  c  n,  c  ,  c p ) + m  comparing with MC simulations the favorite range for the number of pions is 3 < m < 5 + comparing with MC simulations the favorite range for the number of pions is 3 < m < 5 + also B decays into 2 charmed baryons seem to contribute significantly also B decays into 2 charmed baryons seem to contribute significantly

Trento, February 27, 2008Fabio Anulli20 More c-baryons inclusive spectra:  c   c first observed by CLEO in 1999   m = m(  c ) - m(  c ) = 107 MeV/c 2 electromagnetic decay  c   c  electromagnetic decay  c   c  State Mass (MeV/c 2 ) JPJPJPJP cccc2470 1/2 + c’c’c’c’2575 c*c*c*c*2645 3/2 + c+  c+  c+  c+  c+  c+  c+  c+   c 0   c 0   c 0   c 0  hep-ex/  first evidence of B   c decays fit fragmentation function for p*>2. Gev/c

Trento, February 27, 2008Fabio Anulli21  What about baryon number conservation? Measurements at high energies shows small rapidity differences between Baryon- antiBaryon couples ==> “local baryon correlation” Measurements at high energies shows small rapidity differences between Baryon- antiBaryon couples ==> “local baryon correlation” if “local” correlation and two charmed baryons produced from leading c-quarks, we expect to see two more baryons ==> kinematically E cm ~10 Gev if “local” correlation and two charmed baryons produced from leading c-quarks, we expect to see two more baryons ==> kinematically E cm ~10 Gev CLEO measured CLEO measured Correlated  c   c  production PRD 63, (2001)  BABAR looks for e  e    c   c  X events  Observe 649  31 events vs ~150 expected ==> ratio of ~4.2 consistent with CLEO result  very few additional baryons observed  most of additional tracks are pions produced at the e  e  vertex ==> we measure 2.6  0.3   /event  there is room for additional ~1.3 popcorn   /event  2.2 units of rapidity differences observed on average cccc cccc all indicate these are “jetty” events with long-range baryon number conservation ! For details see the talk by S. Pacetti

Trento, February 27, 2008Fabio Anulli22 Exclusive reactions at 10.6 GeV  Very rare final states can be studied with the full BABAR statistics  Select events with a specific set of identified tracks, reconstructed photons and   ’s,  ’s  Look at mass combinations, momentum and angular distributions, etc  clear signals in each channel ==> interesting features of hadronic interactions can be studied      this talk PRL 97, (2006) PRD 74, (2006) 225 fb 

Trento, February 27, 2008Fabio Anulli23 e  e         we observe clear     signal in         events and    in          Both channels have C = +1: ==> forbidden in single   annihilation ==> allowed (and expected ~at this level) in  -   annihilation (TVPA) ==> check angular distributions…. PRL 97, (2006)

Trento, February 27, 2008Fabio Anulli24 e  e        - angular distribution     production angle   : TVPA predicts TVPA predicts other process may give sin 2  , flat, 1+cos    other process may give sin 2  , flat, 1+cos     Decay helicity angles : TVPA predicts transverse  polarization, i.e. sin 2  H distribution for decay helicity angles TVPA predicts transverse  polarization, i.e. sin 2  H distribution for decay helicity angles  First observation of TVPA!  (Fiducial) cross sections: (20.7  0.7  2.7) fb for     (20.7  0.7  2.7) fb for     ( 5.7  0.5  0.8) fb for   ( 5.7  0.5  0.8) fb for   consistent with vector-dominance two-photon exchange (hep/ph ) consistent with vector-dominance two-photon exchange (hep/ph )

Trento, February 27, 2008Fabio Anulli25 e  e   pppp fb  Sorry, cannot show wait for Moriond QCD…

Trento, February 27, 2008Fabio Anulli26 Initial State Radiation essential ISR studies at the  (4S) yield the same observables as the low energy e  e   experiments with enough statistics can probe the transition region from form factors to jets  The radiator function W is known at ~ 1% level  Features : access to wide s range access to wide s range very small point-to-point systematic errors very small point-to-point systematic errors c.m. boost ==>  0 at threshold c.m. boost ==>  0 at threshold  ISR detected ==> hadronic system contained  ISR detected ==> hadronic system contained  disadvantages: mass resolution > beam-energy spread mass resolution > beam-energy spread required very high luminosity required very high luminosity Hadronic system e+e+ e-e- X

Trento, February 27, 2008Fabio Anulli27 The BABAR ISR physics program  Measure cross section for all significant e  e   f processes, threshold up to 4-5 GeV  Purpose: improve understanding of spectroscopy of J PC =1  states, and of resonant sub- structures observable in their decays improve understanding of spectroscopy of J PC =1  states, and of resonant sub- structures observable in their decays time-like form factors measurements (e.g. proton,  ) time-like form factors measurements (e.g. proton,  ) improve precision on determination of R(s) =  hadron (s)/    s  in the energy region 1<E cm < 3 GeV, by summing the measured exclusive cross sections improve precision on determination of R(s) =  hadron (s)/    s  in the energy region 1<E cm < 3 GeV, by summing the measured exclusive cross sections  Published (or accepted or submitted):    , pp,                                                                                 S 0                 J/      S      Analysis on progress :                            J/  DD  ISR inclusive,…                            J/  DD  ISR inclusive,…      shown here as an example, for a general discussion see talk by S. Pacetti contribution to R from various process at low energies

Trento, February 27, 2008Fabio Anulli28 Analysis strategy  Events selection:  require exact topology: “hard”  + all particles inside a fiducial volume   /K/p discrimination using dE/dx and Cherenkov angle  kinematic fit requiring :  p and E conservation  add mass constraint for each    fit result used to select signal events and reject background  Monte Carlo simulations used for detector acceptances, selection efficiencies and estimates of different background sources:  ISR generators based on: H.Czyz et al, Eur. Phys. J. C 35(2004)527  multiple ISR soft photons: M.Caffo et al, N. C. 110A(1997)515  final state radiation: (PHOTOS) E. Barberio et al, Comp. Phys Comm. 66(1991)115 event selection for       final state event selection for       final state

Trento, February 27, 2008Fabio Anulli29 e  e  →             e  e  →             ISR photon + 6 charged hadrons 1C fit in 6  hypothesis. Cut at    topology ISR photon + 4 h   5C fit (constrain   masses). Cut at     Agreement with existing data only at low masses  Total systematic error ~10%  Good agreement with existing data  Total systematic error ~8%  A structure observed around 1.9 GeV, already seen by DM2 and FOCUS experiments  … but resonance fit gives inconsistent parameters (?)  is this the “same dip” visible in         channel or is it something else?  is it connected to the observed enhancement of the proton FF at threshold ?

Trento, February 27, 2008Fabio Anulli30 e  e  →              Very rich resonance structure:             f 0     f 0     f 2 (1270)/f 0 (1370)     ? f 2 (1270)/f 0 (1370)     ? J/  2(  +  - )  0  0 J/  2(  +  - )  0  0   ±±  Data MC f      J /   (e + e -   ) (nb)  (1680) →    (1680) →    Observed submode e  e                 J/  peak clearly visible (measure the decay rate)  Fit the large peak to a resonant shape, we find: m = 1645  8 MeV/c 2 m = 1645  8 MeV/c 2  = 114  14 MeV  = 114  14 MeV  is the  ) (  ), or the  ) (  ) ?  ….. or something new…? substructures in          final state

Trento, February 27, 2008Fabio Anulli31 e  e  →              The only structure observed in 2/3  combinations is the  (780)  data consistent with e  e           J  DataMC  substructures in      final state (    (  production ratio  The              production ratio is flat and ~4 except where the  submode contribute except where the  submode contribute  difficult to explain, also because the former has a much richer substructure  inclusive distribution of      somewhat consistent with “jetty” behavior, but… hard to make any guess at this energy

Trento, February 27, 2008Fabio Anulli32Summary  PEP-II is not only a B-factory, but also a qq-factory (q=u,d,s,c)  The large amount of data make possible stringent test on hadronic reactions at low energies, with unprecedented accuracy  IS measured for light mesons (      ), for proton, and for some charmed baryons (  c +,  () c ) covering most of the scaled momentum range  Jets in the “extreme” region studied:  e  e   c   c  X ==> long range baryon number conservation  e  e   pppp ==> first observation, consistent with “jetty” behavior  exclusive reactions studied both at 10 GeV and at lower energies via ISR  Many new charmed states discovered and studied with inclusive measurements at Y(4S) energy PEP-II shutdown on April 6 th, 2008 after an exciting journey lasted 9 years This would not be the end of the story: expect many more results from analysis of BABAR data for the years to come!

Trento, February 27, 2008Fabio Anulli33 BACKUP SLIDES

Trento, February 27, 2008Fabio Anulli34 PID performances PID efficiencies and mis-ID rates K-  separation Cherenkov angle for different particle types

Trento, February 27, 2008Fabio Anulli35 IHPS:      p/p from Y(4S) decays

Trento, February 27, 2008Fabio Anulli36 Inclusive  c spectrum

Trento, February 27, 2008Fabio Anulli37  What about baryon number conservation? Measurements at high energies shows small rapidity differences between Baryon- antiBaryon couples ==> “local baryon correlation” Measurements at high energies shows small rapidity differences between Baryon- antiBaryon couples ==> “local baryon correlation” if “local” correlation and two charmed baryons produced from leading c-quarks, we expect to see two more baryons if “local” correlation and two charmed baryons produced from leading c-quarks, we expect to see two more E cm ~10 GeV, m(B c +B + B c +B) > 6.5 E cm ~10 GeV, m(B c +B + B c +B) > 6.5 GeV/c2 kinematically suppressedkinematically suppressed CLEO measured CLEO measured primary c-quarks do not fragment independently !primary c-quarks do not fragment independently ! Correlated  c   c  production BcBc BcBc B B X Y PRD 63, (2001)

Trento, February 27, 2008Fabio Anulli38  BABAR looks for e  e    c   c  X events  Analysis strategy: reconstruct  c in pK-KS reconstruct  c in pK-KS reject Y(4S) decays by p   >2.3 GeV/c reject Y(4S) decays by p   >2.3 GeV/c  Observe 649  31 events ~150 expected (based on single  c rate) ~150 expected (based on single  c rate) ratio of ~4.2 consistent with CLEO result ratio of ~4.2 consistent with CLEO result Correlated  c   c  production cccc cccc  very few additional baryons (13  8 events compatible with 4 baryons)  very few additional K , K S,  K  mesons observed  most of additional tracks are pions produced at the e  e  vertex

Trento, February 27, 2008Fabio Anulli39  Very few two-body or quasi-two-body events observed no evidence for e  e    c   c  no evidence for e  e    c   c  small fraction of additional mesons coming from heavier baryons decays small fraction of additional mesons coming from heavier baryons decays no evidence for unknown baryons no evidence for unknown baryons  we measure 2.6  0.3   /event  there is room for additional ~1.3 popcorn   /event  2.2 units of rapidity differences observed on average Correlated  c   c   measurements indicate these are jetty events with long-range baryon number conservation ==> new type of events  among the various models, only UCLA is able to qualitatively produce these type of events: production rate too high production rate too high suppression of kaons and vector mesons production suppression of kaons and vector mesons production  multiplicity distribution broad, with peak at 1 and average of 1.8  multiplicity distribution broad, with peak at 1 and average of 1.8

Trento, February 27, 2008Fabio Anulli40 Fit of e  e   6  cross sections FOCUS: PL B514, 240 (2001) M = 1910  10 MeV  = 37  13 MeV  = 37  13 MeV e  e   3(  +  - ) e  e   2(  +  - )     Dip of cross section near 1.9 GeV is confirmed, but wider than in DM2 (e  e  ) and in FOCUS (diffractive photoproduction) M(GeV/c  )  (GeV) phase BABAR      1.88 ± ± ± 40 BABAR 2(         1.86 ± ± 0.02  3 ± 15 FOCUS      1.91 ± ± ± 30 B A B AR preliminary