# Presentation: 719394

## Meson Production Results from E910 and Their Relevance to MiniBooNE

- Jonathan Link
- Columbia University
- Fermilab Wine & Cheese
- November 18th 2005

**E910**

**MiniBooNE**

## Talk Outline

- Motivation:
- What MiniBooNE needs
- What’s been done in the past
- Brookhaven E910
- About the experiment
- Pion production analysis
- K0 production analysis
- Pulling things together for MiniBooNE
- Now add HARP

## What MiniBooNE Needs

- MiniBooNE’s primary objective is to observe a small excess of νe interactions in a beam composed mostly of νμ.

- What do I mean by “composed mostly of νμ?

## The MiniBooNE Neutrino Beam

## What MiniBooNE Needs

- At a minimum we need to understand the relative νe to νμ flux, as a function of energy, at the detector, prior to any oscillations.  This requires accurate
-  Primary production models for π±, K+ and KL by protons in the target Be at 8.9 GeV/c.

- MiniBooNE’s primary objective is to observe a small excess of νe interactions in a beam composed mostly of νμ.

## Pre-existing Production Data

| Experiment | Pbeam (GeV/c) | Year |
| --- | --- | --- |
| Allaby | 19.1 | 1970 |
| Cho | 12.4 | 1971 |
| Marmer | 12.3 | 1969 |
| Vorontsov | 10.1 | 1983 |

| Experiment | Pbeam (GeV/c) | Year |
| --- | --- | --- |
| Abbott | 14.6 | 1992 |
| Aleshin | 9.5 | 1977 |
| Allaby | 19.1 | 1970 |
| Dekkers | 18.8, 23.1 | 1964 |
| Eichten | 24.0 | 1972 |
| Lundy | 13.4 | 1965 |
| Marmer | 12.3 | 1968 |
| Piroue | 2.74 | 1966 |
| Vorontsov | 10.1 | 1983 |

- π Production

- K+ Production

| Experiment | Pbeam (GeV/c) | Year |
| --- | --- | --- |
| Abe | 12 | 1987 |

- K0 Production

- E910 and HARP

- HARP only

- Initially E910 only

## What MiniBooNE Needs

- At a minimum we need to understand the relative νe to νμ flux, as a function of energy, at the detector, prior to any oscillations.  This requires accurate
-  Primary production models for π±, K+ and KL by protons in the target Be at 8.9 GeV/c.
-  Secondary interaction models (absorption, secondary production, etc.) in the target and surrounding materials.
-  Descriptions of the beam line, target, horn field, and decay volume.

- MiniBooNE’s primary objective is to observe a small excess of νe interactions in a beam composed mostly of νμ.

## 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.

- 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 D2 Bubble Chamber

## Fermilab

- 15ft D2 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 Eν<30 GeV.

##  The Procedure

-  _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 D2 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.
-  Interpretation: Their normalization is wrong.

## So What Have We Learned...

- 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.
- 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?

## Slide 14

## So What Have We Learned...

- 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.
- 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

## Brookhaven Experiment 910

- 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.

- Antiproton production in *p*+*A* collisions at 12.3 and 17.5 GeV/*c* (Phys.Rev.C64:064908)
- Semi-inclusive Λ0 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, 024902)
- Strange particle production and an H-dibaryon search in *p+A* collisions at the AGS  (Nucl.Phys.A639:407-416)

## 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/c2 for Be)
- NA is Avagadro’s number
- ρ  is the target area density (3.4 g/cm2)
*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:

- p

- θ

- Efficiency

## The Trigger

| Dataset | Beam Protons | Trigger Efficiency (ε) |
| --- | --- | --- |
| 6.4 GeV/c | 93,632   | 1.000±0.01 |
| 12.3 GeV/c | 745,216 | 0.968±0.006 |
| 17.6 GeV/c | 2,576,352 | 0.896±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.

## The Trigger

| Dataset | Beam Protons | Trigger Efficiency (ε) |
| --- | --- | --- |
| 6.4 GeV/c | 93,632   | 1.000±0.01 |
| 12.3 GeV/c | 745,216 | 0.968±0.006 |
| 17.6 GeV/c | 2,576,352 | 0.896±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 and TOF for *p*>1.2)
-  Tracks must point back to the interaction vertex.
-  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.

- 1.83 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) or TOF (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

- 2nd to last momentum bin

## Error Studies

- Several possible sources of systematic error were studied including:
-  Bin to bin event migration
-  Bin specific trigger inefficiency
-  Particle ID systematics (by lifting PID cuts on π-)
-  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...

## The Pion Production Cross Section Preliminary

- π+

- π-

- 6.4 GeV/c Beam Momentum

- The Pion Production Cross Section Preliminary

## The Pion Production Cross Section Preliminary

- π-

- 12.3 GeV/c Beam Momentum

- The Pion Production Cross Section Preliminary

## The Pion Production Cross Section Preliminary

- π-

- 17.6 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 χ2

- The Sanford-Wang fit to E910 data was performed by Jocelyn Monroe.

## The K0 Analysis

- The KS analysis follows the same basic prescription as the pion analysis:
- The main difference is that the KS yield, N(KS), is extracted from the  reconstructed mass distribution.

- We are concerned about KL for backgrounds, but the KL cross section can’t be easily be directly measured.
- Neutral kaon are actually produced as K0 and K0, but they decay as KS and KL.
- Therefore, measuring the KS cross section is equivalent to measuring the KL cross section.

## The Ks Analysis

- The Ks 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 *p*π mass is in the Λ0 mass peak are rejected.
- The KS → π+π- branching fraction (68.6%) is accounted for in the acceptance.

## The Ks Sample

- 12.3 GeV/c

- 17.6 GeV/c

- The 6.4 GeV/c data set has no visible Ks mass peak.

## Yield Determined by Side Band Subtraction 

- 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 Ks yield.
- This assumes that the background is linear across the signal and side band regions.

## The Ks Production Cross Section Data Preliminary

- The Ks 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-

- 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 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.
-  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 also shown you preliminary cross section measurement for KS 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 will be combined with HARP data for the final flux calculations.