Jonathan Link Columbia University Fermilab Wine & Cheese November 18 th 2005 Meson Production Results from E910 and Their Relevance to MiniBooNE E910 MiniBooNE

Talk Outline 1.Motivation: What MiniBooNE needsWhat MiniBooNE needs What’s been done in the pastWhat’s been done in the past 2.Brookhaven E910 About the experimentAbout the experiment Pion production analysisPion production analysis K 0 production analysisK 0 production analysis 3.Pulling things together for MiniBooNE Now add HARPNow add HARP

What MiniBooNE Needs MiniBooNE’s primary objective is to observe a small excess of ν e interactions in a beam composed mostly of ν μ. What do I mean by “composed mostly of ν μ ?

  e ? The MiniBooNE Neutrino Beam Start with an intense 8 GeV proton beam from the Booster incident on a beryllium target. In the Be target mostly pions are produced, but also some kaons. Charged pions decay almost exclusively as  +  + . K +   e + e, K L  ± e  e and  +  e + e ν μ contribute e ’s. This directly related to the observed ν μ ’s These must be understood using a combination of external production data and evidence in our own data.

What MiniBooNE Needs At a minimum we need to understand the relative ν e to ν μ flux, as a function of energy, at the detector, prior to any oscillations. This requires accurate Primary production models for π ±, K + and K L by protons in the target Be at 8.9 GeV/c. Primary production models for π ±, K + and K L by protons in the target Be at 8.9 GeV/c. MiniBooNE’s primary objective is to observe a small excess of ν e interactions in a beam composed mostly of ν μ.

ExperimentP beam (GeV/c)Year Allaby Cho Marmer Vorontsov ExperimentP beam (GeV/c)Year Abbott Aleshin Allaby Dekkers18.8, Eichten Lundy Marmer Piroue Vorontsov Pre-existing Production Data π Production K + Production ExperimentP beam (GeV/c)Year Abe K 0 Production E910 and HARP HARP only Initially E910 only New Preliminary Results in this talk

What MiniBooNE Needs At a minimum we need to understand the relative ν e to ν μ flux, as a function of energy, at the detector, prior to any oscillations. This requires accurate Primary production models for π ±, K + and K L by protons in the target Be at 8.9 GeV/c. Primary production models for π ±, K + and K L by protons in the target Be at 8.9 GeV/c. Secondary interaction models (absorption, secondary production, etc.) in the target and surrounding materials. Secondary interaction models (absorption, secondary production, etc.) in the target and surrounding materials. Descriptions of the beam line, target, horn field, and decay volume. Descriptions of the beam line, target, horn field, and decay volume. MiniBooNE’s primary objective is to observe a small excess of ν e interactions in a beam composed mostly of ν μ.

Initial Look at Monte Carlo Tools Let’s take a look at some neutrino flux determinations from the past… Running with a sample of common monte carlo tools results in a wide range of neutrino fluxes. Both normalization and energy distribution vary. Maybe they did better at predicting ν flux back when 8 GeV was closer to the high energy frontier? Only the primary production (p+Be→X) is different! Study by Dave Schmitz

They didn’t even try to determine their ν flux from pion production and beam dynamics. In subsequent cross section analyses the theoretical (“known”) quas-ielastic cross section and observed quasi- elastic events were used to determine the flux. Brookhaven AGS 7ft D 2 Bubble Chamber

Fermilab 15ft D 2 Bubble Chamber Again, they use QE events and theoretical cross section to calculate the ν. When they try to get the flux from meson (π and K) production and decay kinematics they fail miserably for E ν <30 GeV.

The Procedure Pion production cross sections in some low momentum bins are scaled up by 18 to 79%. The K + to π + ratio is increased by 25%. Overall neutrino (anti-neutrino) flux is increased by 10% (30%). All driven by the neutrino events observed in the detector! Brookhaven AGS Liquid Scintillator

Argonne ZGS 12ft D 2 Bubble Chamber Flux derived from pion production data. Were able to test assumptions about the form of the cross section using absolute rate and shape information. Pion production measured in ZGS beams were used in this analysis A very careful job was done to normalize the beam. Yet they have a 25% inconsistency between the axial mass they measure considering only rate information verses considering only spectral information. Yet they have a 25% inconsistency between the axial mass they measure considering only rate information verses considering only spectral information. Interpretation: Their normalization is wrong.

So What Have We Learned… 1.Predicting a neutrino flux from meson production data and decay kinematics is difficult. Most groups didn’t even try, and those that did often failed. 2.If all of the low energy neutrino cross sections are measured with respect to the quasi-elastic cross section, how is the quasi-elastic cross section measured?

So What Have We Learned… 1.Predicting a neutrino flux from meson production data and decay kinematics is difficult. Most groups didn’t even try, and those that did often failed. 2.If all of the low energy neutrino cross sections are measured with respect to the quasi-elastic cross section, how is the quasi-elastic cross section measured? MiniBooNE has access to two modern production data sets. One of these data sets (HARP) includes thick target data which will help us construct the secondary interaction model. The other data set comes from the E910 Experiment…

Brookhaven Experiment 910 E910 used a spectrometer with good acceptance and particle ID over the momentum and angular range of interest to MiniBooNE. Particle ID from dE/dx in the TPC, threshold Čerenkov, and Time of Flight.

The E910 Collaboration

Used a tagged proton beam which was operated at momenta of 17.5, 12.3 and 6.4 GeV/c on targets of Au, Cu, Pb, U and Be. Their main objective was to study nuclear processes relevant to the relativistic heavy ion collisions. At the end of their run they took a short set of runs with a low bias trigger that is well suited for cross section measurements. Brookhaven Experiment 910 Antiproton production in p+A collisions at 12.3 and 17.5 GeV/c (Phys.Rev.C64:064908) Semi-inclusive Λ 0 and K S production in p-Au collisions at 17.5 GeV/c (Phys.Rev.Lett.85:4868 ) Measuring centrality with slow protons in proton-nucleus collisions at 18 GeV/c (Phys. Rev. C 60, ) Strange particle production and an H-dibaryon search in p+A collisions at the AGS (Nucl.Phys.A639: )

Pion Production in E910 This paper focused on pions with momentum less that 1.2 GeV/c. The preliminary analysis in this talk extends the pion momentum range beyond 1.2 GeV/c and includes a small data set with beam momentum at 6.4 GeV/c. cosθ Inclusive soft pion production from 12.3 and 17.5 GeV/c protons on Be, Cu, and Au (Phys.Rev.C65:024904)

Expression for a Cross Section The π + cross section is given by: Where A is the mass (9.01 GeV/c 2 for Be) N A is Avagadro’s number ρ is the target area density (3.4 g/cm 2 ) a is the acceptance and cut efficiency ε is the trigger efficiency and w is the reciprocal of the bin area in GeV/c and steradians

Acceptance and Cut Efficiency Monte Carlo events are used to calculate the acceptance of the spectrometer and the efficiency of the analysis cuts. The efficiency or acceptance is given by: The Error on a is binomial: TPC TOF p θ Efficiency

E910 ran for a brief period of time with a low bias trigger. This trigger required that there be a beam particle upstream of the target, but not downstream. The Trigger DatasetBeam ProtonsTrigger Efficiency (ε) 6.4 GeV/c93, ± GeV/c745, ± GeV/c2,576, ±0.006 This trigger should fire on all interacting protons and will have a small inefficiency that grows with the secondary multiplicity. Trigger efficiency (ε) is measured on a totally unbiased, highly pre-scaled, beam proton trigger.

Bullseye Trigger (Low Bias) Non-interacting beam particles will pass through the bullseye veto region, but most other tracks will not.

E910 ran for a brief period of time with a low bias trigger. This trigger required that there be a beam particle upstream of the target, but not downstream. The Trigger DatasetBeam ProtonsTrigger Efficiency (ε) 6.4 GeV/c93, ± GeV/c745, ± GeV/c2,576, ±0.006 This trigger should fire on all interacting protons and will have a small inefficiency that grows with the secondary multiplicity. Trigger efficiency (ε) is measured on a totally unbiased, highly pre-scaled, beam proton trigger.

π + Track Selection Tracks must be in the geometrical acceptance of the relevant particle ID system (TPC for p 1.2) Tracks must be in the geometrical acceptance of the relevant particle ID system (TPC for p 1.2) Tracks must point back to the interaction vertex. Tracks must point back to the interaction vertex. The vertex must be consistent with originating from the target. The vertex must be consistent with originating from the target. Tracks above π Čerenkov threshold (~2.8 GeV/c) must have a consistent pion hypothesis. Tracks above π Čerenkov threshold (~2.8 GeV/c) must have a consistent pion hypothesis cm

Track Binning θ is divided into 6 bins from 0º to 20.6º (or 0 to 360 mr) And p is divided into 13 bins from 0.4 to 5.6 GeV/c Each bin is weighted by the inverse of the bin area in GeV/c and steradians Selected tracks are binned in zenith angle (θ) and total momentum (p)

Particle Identification Used below 1.2 GeV/c p K π p K π Log dE/dx vs. Momentum Good below 5.4 GeV/c 1/β vs. Momentum TPC dE/dx Time of Flight π Čerenkov threshold

Particle Identification and Yield Residuals are formed in each PID system between each different particle hypothesis and the observed system response. The residuals are constructed such that the correct hypothesis forms a unit Gaussian distribution centered on zero. The pion hypothesis residual in the dE/dx (p 1.2 GeV/c) is plotted for each candidate track. The pion yield in each bin is determined by fitting the residual distribution, or by counting the entries between ±2σ.

Sample Residual Distributions Last dE/dx bin First TOF bin Just before Čerenkov Just after Čerenkov Last momentum bin 2 nd to last momentum bin

Error Studies Several possible sources of systematic error were studied including: Bin to bin event migration Bin to bin event migration Bin specific trigger inefficiency Bin specific trigger inefficiency Particle ID systematics (by lifting PID cuts on π - ) Particle ID systematics (by lifting PID cuts on π - ) Comparison of yield extraction methods. Comparison of yield extraction methods. There is an overall normalization uncertainty from the target thickness (2%) and from the trigger efficiency error. The preliminary differential cross sections results with full errors follow…

π+π+π+π+ π-π-π-π- 6.4 GeV/c Beam Momentum The Pion Production Cross Section Preliminary

π+π+π+π+ π-π-π-π GeV/c Beam Momentum The Pion Production Cross Section Preliminary

π+π+π+π+ π-π-π-π GeV/c Beam Momentum The Pion Production Cross Section Preliminary

Translating Pion Production to MinBooNE Energies The parameterization of Sanford and Wang describes meson production as a function of beam momentum (p B ), secondary momentum (p), angle (θ), and 8 parameters (C 1 …C 8 ) This function is fit to all the data by minimizing the following χ 2 The Sanford-Wang fit to E910 data was performed by Jocelyn Monroe.

The K 0 Analysis The K S analysis follows the same basic prescription as the pion analysis: The main difference is that the K S yield, N(K S ), is extracted from the reconstructed mass distribution. We are concerned about K L for backgrounds, but the K L cross section can’t be easily be directly measured. Neutral kaon are actually produced as K 0 and K 0, but they decay as K S and K L. Therefore, measuring the K S cross section is equivalent to measuring the K L cross section.

The K s Analysis Begin with a vertex between a positive and negative track. Both tracks are required to be consistent with the pion hypothesis in all relevant PID systems. Candidates where one of the tracks is also consistent with the proton hypothesis and the pπ mass is in the Λ 0 mass peak are rejected. The K S → π + π - branching fraction (68.6%) is accounted for in the acceptance.

The K s Sample 12.3 GeV/c 17.6 GeV/c The 6.4 GeV/c data set has no visible K s mass peak.

Yield Determined by Side Band Subtraction Subtract the appropriately weighted number of events in the blue regions from the red region. What’s left in the red region is the K s yield. This assumes that the background is linear across the signal and side band regions.

The K s Production Cross Section Data Preliminary Here again the data are fit with the Sanford-Wang function.

Pulling Things Together for MiniBooNE While, the E910 data are at 6.4, 12.3 and 17.6 GeV/c, MiniBooNE’s beam is at 8.9 GeV/c. Momentum scaling from the Sanford-Wang fit gives us the production cross sections at MiniBooNE energies. Beyond E910, HARP has a large dedicated production data set at 8.9 GeV/c. The HARP will provide cross sections for π ± and K +. HARP also took data on thick beryllium targets including replica MiniBooNE target slugs. We need to make a production model that reproduces what comes out of the HARP replica target, but HARP needs independent verification…

Comparison of HARP Pion Production to E910 π+π+π+π+ π-π-π-π- Use the Sanford-Wang Parameters from E910 to compare to HARP. Preliminary

If You’re Not Impressed by That Comparison… Let’s take another look at that study comparing Monte Let’s take another look at that study comparing Monte Carlos. The differences are dramatic in the π spectra as well! But the E910 and HARP cross sections determine the correct model, which is very close to MARS. D. Schmitz

Conclusions Determining the neutrino flux is an essential component of the MiniBooNE oscillation analysis, and this starts with obtaining reliable meson production cross sections. Determining the neutrino flux is an essential component of the MiniBooNE oscillation analysis, and this starts with obtaining reliable meson production cross sections. The data set of E910 has been used to measure some of these cross sections. The data set of E910 has been used to measure some of these cross sections. I’ve shown you a new differential cross section measurement for π + and π - production in p Be interactions at 6.4, 12.3 and 17.6 GeV/c beam momentum. I’ve shown you a new differential cross section measurement for π + and π - production in p Be interactions at 6.4, 12.3 and 17.6 GeV/c beam momentum. I’ve also shown you preliminary cross section measurement for K S production at 12.3 and 17.6 GeV/c. I’ve also shown you preliminary cross section measurement for K S production at 12.3 and 17.6 GeV/c. These data are fit to the Sanford-Wang parameterization and scaled to the MiniBooNE beam momentum. These data are fit to the Sanford-Wang parameterization and scaled to the MiniBooNE beam momentum. These data will be combined with HARP data for the final flux calculations. These data will be combined with HARP data for the final flux calculations.