# Presentation: 797450

## Flux and Alignment Issues for a BNL Long Baseline Neutrino Beam

- Steve Kahn
- Brookhaven National Laboratory

- 1 March 2004

## Neutrino System Parameters

- The table shows parameters that were used to describe the BNL Very Long Baseline neutrino beam system.
- Some of the parameters differ from those in the study reports.
- These parameters are not to be considered official at this point.

- 1 March 2004

## Pbeam: The Tool for Calculating Neutrino Fluxes

- The Pbeam program was borrowed from Fermilab where it was used to calculate fluxes for the *NuMi* beamline.
- The Pbeam program was written by Noel Stanton at Kansas State University and modified by Wesley Smart at Fermilab and Richard Milburn of Tufts University.
- Provide capabilities for alignment studies.
- Provide weighting techniques for fast simulations.
- The program tracks ±, K± and K0 from the target through the horn focusing system and decay tunnel.
- A weight is assigned for the particles produced from the meson decays corresponding to the probability for that particle to reach the detector.

- 1 March 2004

## Limitations of Pbeam

- The target production spectrum is not the same as that which comes from *Geant*.
*Pbeam* does not produce as many high energy mesons.
- This may not be critical since we look at ratios of perturbed to unperturbed distributions in this analysis.
*Pbeam *does not handle *cascade decays* such as e.
- This is an important source of e background for the BNL spectrum.

- 1 March 2004

## Criteria for Determining Allowable Tolerances

- Criteria used for the NuMI beamline:
- Documented in NuMI Note L-221 by W. Smart (1996)
- The worst acceptable flux variation in a 1 GeV energy bin from 1-80 GeV was 2%.
- This yields an error for positioning the beam, target and horn of 0.5 mm.
- Criteria that we are proposing for the BNL-HS beamline:
- The worst acceptable flux variation should be 5%.
- We have ~20 parameters which we can align.
- Position and angle of *beam, target-horn system, horn 1, horn2.*
- If these are randomly misaligned any single variable would be allowed to have 11⁄4% variation.
- We could allow some of the parameters to exceed the the 11⁄4% variation since other parameters would be able to come under this tolerance.
- Thus we have chosen a tolerance of 2.5% variation for each of the variables

- 1 March 2004

## Will these Tolerances be good enough?

- We have seen that NuMI gets 0.5 mm positioning tolerances with a 2% allowable variation.  Since we are allowing 5% positioning tolerance we might expect (to be shown) that we will mostly expect ~1 mm tolerances.
- Are these tolerances good enough?
- We can position the neutrino beam elements to 0.5-1.0 mm initially.
- Experience at the AGS (Al Pendzick) has shown that large spectrometer magnets weighing 100 tons can move 3 mm in year by settling.
- This is a large tolerance to work with.
- Can we have a realignment scheme to reposition elements after a specified period?
- Targeting enclosures are quite hot and we would want to avoid unnecessary entries.

- 1 March 2004

## Flux at the Detectors

- The upper figure shows the flux at the far detector
- We will concentrate on the 70-80 cm target.
- The interesting part of the spectrum is below 5 GeV since we need statistics.
- The lower figure shows how the flux at the close detector position as a function of horizontal position for various energy bands.
- The lower energy component tends to spread out more.

- 1 March 2004

## The Variables that will be Varied

- We examine the flux at the near and far detector position for variations in the following parameters:
- Positioning the beam on target:
- Vary *x, x’, y, y’     *(*x’, y’ *are the angle variables)
- Positioning the target relative to horn1:
- Vary *x, x’, y, y’*
- Positioning horn1 and target ensemble:
- Vary *x, x’, y, y’*
- Positioning horn2
- Vary *x, x’, y, y’*
- Variations in the horn current
- Vary Ihorn

- 1 March 2004

## Effect of Beam Deviations on the FAR Detector --Ratio of Perturbed Distribution to Unperturbed Distribution

- 1 March 2004

## Effect of Beam Deviations on the Close DetectorRatio of Perturbed Distribution to Unperturbed Distribution

- 1 March 2004

## Displacing the Beam on the Target

- The table below summarizes from the previous plots the effect of perturbing  the beam.
- A tolerance is given for these displacements based on the allowable 2.5% flux change from the individual variations.

- 1 March 2004

## Effect of Varying the Position of the Target Relative to Horn1 on the Flux at the Far Detector

- y’=-2.5mrad
- R(5 GeV)=0.997

- y=1 mm
- R(5 GeV) = 0.985

- x=1 mm
- R(5 GeV) = 0.981

- x’ = -2.5 mrad
- R(5 GeV) = 0.994

- 1 March 2004

## Effect of Varying the Position of the Target Relative to Horn1 on the Flux at the Close Detector

- x = 1 mm
- R(5 GeV) = 0.968

- x’= -2.5 mrad
- R(5 GeV) = 0.993

- y = 1 mm
- R(5 GeV) = 0.980

- y’= - 2.5 mrad
- R(5 GeV) = 0.998

- 1 March 2004

## Displacing the Target Relative to Horn1 

- The table below shows the flux lost by displacing the target relative to the horn1 with respect to the true beamline.
- Tolerances are shown for ~ 2.5 % lost in flux

- 1 March 2004

## Effect of Varying the Target plus Horn1 Ensemble on the far Flux

- x = 1 mm
- R(5 GeV) = 0.989

- x’ = -2.5 mrad
- R(5 GeV) =  1.0

- y = 1 mm
- R(5 GeV) = 0.994

- y’ = -2.5 mrad
- R(5 GeV) = 1.0

- 1 March 2004

## Effect of Varying the Target plus Horn1 Ensemble on Close Flux

- x = 1 mm
- R(5 GeV)=0.981

- y = 1 mm
- R(5 GeV) = 0.998

- x’ = -2.5 mrad
- R(5 GeV) = 0.999

- y’ = -2.5 mrad
- R(5 GeV) = 0.998

- 1 March 2004

## Displacing the Horn1 plus Target Ensemble

- The table below shows the flux lost by displacing the target plus horn1 ensemble with respect to the true beamline.
- Tolerances are shown for ~ 2.5 % lost in flux

- 1 March 2004

## Effect of Varying the Position of Horn2 on the Flux at the far Detector

- x = 1 mm
- R(5 GeV) = 1.0

- x’ = -1 mrad
- R(5 GeV) = 1.0

- y = 1 mm
- R(5 GeV) = 0.994

- y’ = -1 mrad
- R(5 GeV) = 1.0

- 1 March 2004

## Effect of Varying the Position of Horn2 on the Flux at the Close Detector

- x = 1 mm
- R(5 GeV) = 1.0

- y = 1 mm
- R(5 GeV) = 1.0

- x’ = -1 mrad
- R(5 GeV) = 1.0

- y’ = - 1 mrad
- R(5 GeV) = 0.998

- 1 March 2004

## Displacing Horn2

- The flux is less dependent on the precise positioning of horn2.  However it is still reasonable to use the same tolerances for horn2 as is used for horn1.

- 1 March 2004

## Effect of Varying the Current on the Flux

- I/I = -1%
- R(5 GeV) = 1.0

- I/I = -2%
- R(5 GeV) = 0.999

- I/I = -5%
- R(5 GeV) = 0.984

- 1 March 2004

## Tolerances

- Below are tolerances summarized from the previous tables.
- These number should be considered preliminary at this point.
- I am very skeptical that we want to allow the current to vary as much as the table shows!

- 1 March 2004