Recent results obtained by the HARP collaboration on the measurements of the
double-differential production cross-section of positive and negative pions in
proton interactions with nuclear targets from Beryllium to Lead are presented.
They cover production at small angles (30-210 mrad) and relatively large
momenta up to 8 GeV/c as well as large angles (0.35 - 2.15 rad) and small
momenta (0.1 - 0.8 GeV/c). These results are relevant for a detailed
understanding of neutrino fluxes in accelerator neutrino experiments, better
prediction of atmospheric neutrino fluxes, optimization of a future neutrino
factory design and for improvement of hadronic generators widely used by the
HEP community in the simulation of hadronic interactions.Comment: Talk presented at the XLIII Recontres de Moriond on Electroweak
  Interactions and Unified Theories, La Thuile, 1-8 March 200

Tsenov, Roumen

English

arXiv

Recent results obtained by the HARP collaboration on the measurements of the double-differential production cross-section of positive and negative pions in proton interactions with nuclear targets from Beryllium to Lead are presented. They cover production at small angles (30-210 mrad) and relatively large momenta up to 8 GeV/c as well as large angles (0.35 - 2.15 rad) and small momenta (0.1 - 0.8 GeV/c). These results are relevant for a detailed understanding of neutrino fluxes in accelerator neutrino experiments, better prediction of atmospheric neutrino fluxes, optimization of a future neutrino factory design and for improvement of hadronic generators widely used by the HEP community in the simulation of hadronic interactions.Recent results obtained by the HARP collaboration on the measurements of the double-differential production cross-section of positive and negative pions in proton interactions with nuclear targets from Beryllium to Lead are presented. They cover production at small angles (30-210 mrad) and relatively large momenta up to 8 GeV/c as well as large angles (0.35 - 2.15 rad) and small momenta (0.1 - 0.8 GeV/c). These results are relevant for a detailed understanding of neutrino fluxes in accelerator neutrino experiments, better prediction of atmospheric neutrino fluxes, optimization of a future neutrino factory design and for improvement of hadronic generators widely used by the HEP community in the simulation of hadronic interactions

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Rencontres de Moriond 2008377HARP COLLABORATION RESULTS ON THE PROTON-NUCLEIINTERACTIONS AT FEW GEV ENERGIESRoumen TsenovDepartment of Atomic Physics, Faculty of Physics,St. Kliment Ohridski University of Soﬁa, Soﬁa, Bulgaria(on behalf of the HARP Collaboration)Recent results obtained by the HARP collaboration on the measurements of the double-diﬀerential production cross-section of positive and negative pions in proton interactions withnuclear targets from Beryllium to Lead are presented. They cover production at small angles(30-210 mrad) and relatively large momenta up to 8 GeV/c as well as large angles (0.35 -2.15 rad) and small momenta (0.1 - 0.8 GeV/c). These results are relevant for a detailedunderstanding of neutrino ﬂuxes in accelerator neutrino experiments, better prediction ofatmospheric neutrino ﬂuxes, optimization of a future neutrino factory design and for improve-ment of hadronic generators widely used by the HEP community in the simulation of hadronicinteractions.1 The HARP experimentThe HARP experiment 1,2 at the CERN PS was designed to make measurements of hadronyields from a large range of nuclear targets and for incident particle momenta from 1.5 GeV/c to15 GeV/c. The main motivations are the measurement of pion yields for a quantitative designof the proton driver of a future neutrino factory, a substantial improvement in the calculationof the atmospheric neutrino ﬂux and the measurement of particle yields as input for the ﬂuxcalculation of accelerator neutrino experiments, such as K2K 3,4, MiniBooNE 5 and SciBooNE 6.The experiment makes use of a large-acceptance spectrometer consisting of a forward andlarge-angle detection systems. A detailed description of the experimental apparatus can be foundin Ref. 2. The forward spectrometer – based on large area drift chambers and a dipole magnetcomplemented by a set of detectors for particle identiﬁcation 8: a time-of-ﬂight wall, a largeCherenkov detector and an electromagnetic calorimeter – covers polar angles up to 250 mradwhich is well matched to the angular range of interest for the conventional neutrino beams. Thelarge-angle spectrometer – based on a Time Projection Chamber (TPC) and Resistive PlateChambers (RPCs), located inside a solenoidal magnet – has a large acceptance in the momentumand angular range for the pions relevant to the production of the muons in a neutrino factory.It covers the large majority (∼ 70%) of the pions accepted in the focusing system of a typicaldesign.Rencontres de Moriond 2008378Figure 1: Overall mechanical lay-out of the HARP detector. Thediﬀerent sub-detectors are shown.The target is inserted inside theTPC.Figure 2: Double-diﬀerential production cross-section of π+ and π− in p–C reactions at 12 GeV/c (points witherror bars) and comparison with model predictions.Rencontres de Moriond 2008379Figure 3: p–N2 to p–C production ratio for π+ and π− at 12 GeV/c, compared with GEANT4 simulationpredictions using diﬀerent models. Only statistical errors are displayed, since most systematic ones cancel.2 Results obtained with the HARP forward spectrometerThe ﬁrst HARP physics publication 7 reported measurements of the π+ production cross-section from an aluminum target at 12.9 GeV/c proton momentum for the K2K experimentat KEK PS. The results were subsequently applied to the ﬁnal neutrino oscillation analysisof K2K 4, allowing a signiﬁcant reduction of the dominant systematic error associated withthe calculation of the so-called far-to-near ratio. Our next result 9 was the measurement ofthe π+ cross-sections from a thin 5% λI beryllium target at 8.9 GeV/c proton momentum. Itcontributed to the understanding of the MiniBooNE and SciBooNE neutrino ﬂuxes 10. Theyare both produced by the Booster Neutrino Beam at Fermilab which originates from protonsaccelerated to 8.9 GeV/c by the booster before being collided against a beryllium target.Further, measurements of the double-diﬀerential production cross-section of π± in the colli-sion of 12 GeV/c protons and π± with thin 5% λI carbon target and liquid N2 and O2 targetswere performed . These measurements are important for a precise calculation of the atmosphericneutrino ﬂux and for a prediction of the development of extended air showers. The results forthe pion production on the carbon target, the ratio N2/Carbon, and comparison with modelstypically used in air shower simulations 11 are shown in Figs. 2 and 3 12. The conclusion ofcomparing the predictions of the models to the measured data is that they do predict the ratioof cross-sections and often fail in predicting the absolute rates, especially in certain regions ofthe phase space.In practice production targets are not thin and cascade calculations or dedicated measure-ments with ’replica targets’ are needed. HARP has taken, albeit with somewhat lower statistics,and analyzed p+A data at diﬀerent beam momenta with 100% λI targets. They can be usedfor parametrizations or tuning of models. Preliminary spectra are available for p + Be, C, Al,Cu, Sn, Ta, Pb interactions at 3 – 12 GeV/c. The measurements are on the tapes and can beanalyzed on demand.Rencontres de Moriond 2008380Figure 4: Double-diﬀerential π+ production cross sections for p–Ta at 5 GeV/c and comparison with GEANT4and MARS MC predictions, using several generator models.3 Results obtained with the HARP large-angle spectrometerThe HARP TPC is the key detector for the analysis of tracks emerging from the targetat large angles with respect to the incoming beam direction. It suﬀered from a number ofshortcomings that were discovered during and after the data taking 2. A description of themeasures taken to correct for the eﬀects of them is given in 2,15,16. Wide range of experimentalcross-checks has been employed to assess the momentum scale and momentum resolution in theHARP TPC, summarized in our recent paper 16.A group of people formerly belonging to the HARP collaboration and subsequently detachedthemselves from it have been criticizing our methods of TPC and RPCs calibration 13. Ourarguments against this criticism and for the correctness of our results are presented in 14,16.A ﬁrst set of results on the production of pions at large angles have been published by theHARP collaboration in the papers 15,18, based on the analysis of the data in the beginning ofeach accelerator spill. Track recognition, momentum determination and particle identiﬁcationwere all performed based on the measurements made with the TPC. The reduction of the dataset was necessary to avoid problems in the chamber responsible for dynamic distortions to theimage of the particle trajectories as the ion charge was building up during each spill. Correctionsfor such distortions that allow the use of the full statistics have been developed 16 and appliedin the analysis. The results exploiting the full spill data have been obtained recently 17. Theyare fully compatible with the previous ones and cover pion production by proton beams in amomentum range from 3 GeV/c to 12 GeV/c hitting Be, C, Al, Cu, Sn, Ta and Pb targets witha thickness of 5% λI in the angular and momentum phase space 100 MeV/c ≤ p < 800 MeV/cand 0.35 rad ≤ θ < 2.15 rad in the laboratory frame.As an example we show in Fig. 4 the results for the double-diﬀerential cross-sections d2σ/dpdθat 5 GeV/c incident proton beam momentum and Ta target compared to the respective predic-tions of several diﬀerent generator models used in GEANT4 and MARS simulation packages.The comparison between data and models is reasonable, but some discrepancies are evident forRencontres de Moriond 2008381Figure 5: The dependence on the beam momentum and on the atomic number A of the π− (right) and π+ (left)production yields in p–Be, p–C, p–Al, p–Cu, p–Sn, p–Ta, p–Pb interactions averaged over the forward angularregion (0.350 rad ≤ θ < 1.550 rad) and momentum region 100 MeV/c ≤ p < 700 MeV/c. The results are givenin arbitrary units, with a consistent scale for all panels.Figure 6: Predictions of the π+ (closed symbols) and π− (open symbols) yields for diﬀerent designs of the neutrinofactory focusing stage. Integrated yields and the integrated yields normalized to the kinetic energy of the protonfor p–Ta and p–Pb interactions. The circles indicate the integral over the full HARP acceptance (100 MeV/c <p < 700 MeV/c and 0.35 rad < θ < 1.55 rad), the squares are integrated over 0.35 rad < θ < 0.95 rad, while thediamonds are calculated for the smaller angular range and 250 MeV/c < p < 500 MeV/c. Although the unitsare indicated as “arbitrary”, for the largest region the yield is expressed as d2σ/dpdΩ in mb/(GeV/c sr). Forthe other regions the same normalization is chosen, but now scaled with the relative bin size to show visually thecorrect ratio of number of pions produced in these kinematic regions.Rencontres de Moriond 2008382some models. Discrepancies up to a factor of three are seen. For details see the full paper 17.The dependence on the beam momentum and on the atomic number A of integrated yields arepresented in Fig. 5. Predictions of the π+ and π− integrated yields relevant for the design ofthe neutrino factory focusing stage are given in Fig. 6.4 ConclusionsThe full set of HARP data is in process of publishing now, It covers the pion production byprotons and pions on nuclear targets spanning the full periodic table of elements and large solidangle and momentum range in the diﬃcult energy region between 3 and 15 GeV/c of incidentmomentum. HARP results ﬁll in an essential gap in the available experimental information forsoft hadron production and help in the understanding of neutrino ﬂuxes in accelerator neutrinoexperiments, prediction of atmospheric neutrino ﬂuxes, optimization of a future neutrino factorydesign and may be used for improvements of the event generators for simulation of hadronicinteractions.AcknowledgmentsIt is a pleasure to thank the organizers and INFN – Section Bari for the ﬁnancial supportwhich allowed me to participate in the conference and to present these results on behalf of theHARP Collaboration.References1. M.G. Catanesi et al. [HARP Collaboration], “Proposal to study hadron production forthe neutrino factory and for the atmospheric neutrino ﬂux”, CERN-SPSC/99-35 (1999).2. M.G. Catanesi et al. [HARP Collaboration], Nucl. Instrum. Methods A 571 (2007) 527.3. M.H. Ahn et al. [K2K Collaboration], Phys. Rev. Lett. 90 (2003) 041801.4. M. H. Ahn et al. [K2K Collaboration], Phys. Rev. D 74 (2006) 072003.5. A. A. Aguilar-Arevalo et al. [The MiniBooNE Collaboration], arXiv:0704.1500. E. Churchet al. [BooNE Collaboration], FERMILAB-PROPOSAL-0898, (1997).6. A. A. Aguilar-Arevalo et al. [SciBooNE Collaboration], “Bringing the SciBar detector tothe Booster neutrino beam”, FERMILAB-PROPOSAL-0954, (2006), [hep-ex/0601022].7. M. G. Catanesi et al. [HARP Collaboration], Nucl. Phys. B 732 (2006) 1.8. M. G. Catanesi et al. [HARP Collaboration], Nucl. Instrum. Methods A 572 (2007) 899.9. M. G. Catanesi et al. [HARP Collaboration], EPJC 52 (2007) 29.10. A.A.Aguilar-Arevalo et al., Phys. Rev. Lett. 98 (2007) 231801.11. H. Fesefeldt, report PITHA-85/02, RWTH Aachen, 1985. M. Bleicher et al., J. Phys. G:Nucl. Part. Phys. 25 (1999) 1859. S. Roesler, R. Engel, and J. Ranft, in Proc. of Int.Conf. on Advanced Monte Carlo for Radiation Physics, Particle Transport Simulationand Applications (MC 2000), Lisbon, Portugal, 23-26 Oct 2000, A. Kling, F. Barao, M.Nakagawa, L. Tavora, P. Vaz eds., Springer-Verlag Berlin, p. 1033-1038 (2001).12. M. G. Catanesi et al. [HARP Collaboration], DOI: 10.1016/j.astropartphys.2008.02.002.13. V. Ammosov et al., Nucl. Instrum. Methods A 571 (2007) 562.V. Ammosov et al. , J. Inst. 3 (2008) P01002.14. M.G. Catanesi et al., [HARP Collaboration]. Nucl. Instrum. Methods A 571 (2007) 564.A. Artamonov et al., J. Inst. 2 (2007) P10004,15. M.G. Catanesi et al., [HARP Collaboration], Eur. Phys. J. C 51 (2007) 787.16. M. G. Catanesi et al., [HARP Collaboration]. J. Inst. 3 (2008) P04007.17. M.G. Catanesi et al., [HARP Collaboration], “Large-angle production of charged pions inthe HARP experiment with incident protons on nuclear targets”, to be publ. in Phys.Rev.C.18. M.G. Catanesi et al., [HARP Collaboration]. Eur. Phys. J. C 53 (2008) 177.M.G. Catanesi et al., [HARP Collaboration]. Eur. Phys. J. C 54 (2008) 37.

HARP Collaboration results on the proton-nuclei interactions at few GeV energies

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