Progress Report Keith Drake, Tera Dunn, Jack Gill, The BeamCal Simulation Project Progress Report Keith Drake, Tera Dunn, Jack Gill, Gleb Oleinik, Uriel Nauenberg University of Colorado at Boulder

Pointed out by our group around 1998 Beam Calorimeter Studies Two photon process cross section about 105 larger than SUSY cross section. Serious source of background for SUSY if not tagged . Pointed out by our group around 1998

2 Photon Process e+ e+ Very forward into BEAMCAL - - γ q , l - - γ q , l Very forward into BEAMCAL in the detector γ q , l e- e-

Lumi Cal -7 mrad ent. 7 mrad exit Beam Cal

Solenoid field keeps the low energy charged particle in the forward direction. Beam hole is at 7 mrad. Need to add an x field component to move low energy charged particles in the 7 mrad direction. Anti-DiD dipole field proposed by Andrei Seryi.

Beamstrahlung e+e- pairs. Energy deposited in 0.25 x0.25 cm2 cells.

Energy into the Beam Pipe is ~TeV Integrated Outside Beam Pipe Energy into the Beam Pipe is ~TeV

Shower in Beamcal from 2 γ process alone head-on view side view core of shower Radius of 25 mm Radius of 25 mm

electron from 2γ process head on view side view beamstrahlung electron from 2γ process

Beamstrahlung Energy Deposition in a Tile Tile at start of BeamCal Tile 3.0 cm in

Beamstrahlung Energy Deposition in a Tile Tile 4.7 cm in Tile 6.0 cm in

Consequences of Beamstrahlung Energy Deposition Energy Deposition is not Gaussian until one reaches a depth > 3 cms. Distribution is very wide and hence affects energy resolution if we subtract an average value. This problem is seen in the study how to measure the electron/positron energies. Resolution.

with average subtracted Electron from 2 photon overlayed Beamstrahlung Beamstrahlung with average subtracted

Clustering Cuts in Depth and Energy, Example 1 Beamstrahlung + Electron from 2-photon Beamstrahlung Alone Cut 30 mm Work in Progress Cut 10 MeV

Clustering Cuts in Depth and Energy, Example 2 Beamstrahlung + Electron from 2-photon Beamstrahlung Alone

Clustering Cuts in Depth and Energy, Example 3 Beamstrahlung + Electron from 2-photon Beamstrahlung Alone

Energy observed as a function of distance from center of BeamCal φ r Exit Beam Pipe Entrance Beam Pipe Δφ = 5 deg Δr = 1 mm

Energy Deposition versus r and φ Φ=0.0 Φ=30.0 30.0 Effect of Exit Beam Pipe Effect of Exit Beam Pipe Distance from center of beamcal (mm) Distance from center of beamcal (mm)

Energy Deposition versus r and φ Φ=150.0 Φ=180.0 150.0 180.0 Effect of Entrance Beam Pipe Effect of Entrance Beam Pipe Distance from center of beamcal (mm) Distance from center of beamcal (mm)

Full detector Full Detector with clustering Within a radius of 25mm sensors Within a radius of 25mm no clustering Full detector Full Detector with clustering

Fraction of Energy Observed within a Radius of 0.5 cm of Electron Path No clustering cuts With clustering cuts

Fraction of Energy Observed within a Radius of 1.0 cm of Electron Path No clustering cuts With clustering cuts

Fraction of Energy Observed within a Radius of 2.0 cm of Electron Path With clustering cuts No clustering cuts

Fraction of Energy Observed within a Radius of 3.0 cm of Electron Path

Energy Resolution of High Energy Electrons {E(measured)- E(expected)} /E(expected) Best Possible Resolution No Beamstrahlung effects included

Energy Resolution of High Energy Electrons {E(measured)- E(expected)} /E(expected) Energy Resolution with Beamstrahlung Included. Average Substracted. Only energy deposited in a 25 mm radius from maximum. Sum energy over full Beamcal thickness. Effect of Beamstrhalung fluctuation in resolution clearly has an effect

Energy Resolution of High Energy Electrons {E(measured)- E(expected)} /E(expected) Energy Resolution. Beamstrahlung Included and Average Substracted. Measurements from 3.0 cm in and Including only cells with more than 10 MeV energy deposited.

Energy resolution of the reconstruction of the electrons from 2-photon Energy resolution of the reconstruction of the electrons from 2-photon events including the effects of beamstrahlung Preliminary results Preliminary results Using Bayesian Statistical Analysis

Case of no Beamstrahlung Included in analysis Case of Best Analysis with Beamstrahlung Included. Exit Beam Pipe Region Exit Beam Pipe Region

Measured Energy loss due to cuts Reason for Resolution Tail Measured Energy loss due to cuts

Understand the low energy tails of the energy resolution Work to be Done Understand the low energy tails of the energy resolution distribution. Develop a better scan. What is the missing Pt distribution of 2 photon events given the resolution. Study the resolution of new geometries.

Work to be Done Optimize signal to Background. Check all our Calculations. Find other analysis techniques that reduce the beamstrahlung fluctuations and hence improve the signal resolution. Study the effect of this analysis on SUSY signal. Missing Pt limits.

Study of a Scintillator Calorimeter We are simulating a scintillator based calorimeter where the tiles are offset in alternate layers. We are making now a great deal of progress.

γ s are well separated 5 cm 100 GeV 100 GeV π0 mostly low p

· · · · ····· φ ALCPG θ Geometrical Arrangement Scintillator Panels 5 cm Scintillator Panels Worst separation 1.25 cm · · · · φ ····· 0 0.5 1.0 0.25 0.75 θ Best separation

Track Following into the Calorimeter Low momentum curlers

Cluster Correlation with Charged Tracks Success Probability Energy cluster in the calorimeter associated with a charged track interaction Success Conclude that it is a neutral cluster Failure

ALCPG 9 i,j =1 The Chi-Square Structure μi = average photon energy deposited in ith tile σi = standard deviation in the energy deposition Hij = σi σj χ2 = Σ (xi – μi )Hij (xj – μj ) where xi is the energy deposited by the shower being tested in the ith tile. 9 -1 i,j =1

We are now in the middle of trying to separate photon clusters by means of the chi-square method. Hard problem. Crucial aspect of pattern recognition and calorimeter resolution.

Fitted γ direction from shower energy distribution Z vs R 20 GeV 50 GeV

Study of the Characteristics of Silicon Photomultipliers

New Silicon Photo-Detectors Bias Voltage ~40 volts Photonique, SA Pulsar, Russia + Moscow Eng. Physics Inst. 2mm Scintillator performance

Need to Improve Resolution 2mm scint., cosmic rays 20 < t < 70 nsec 0 < t < 200 nsec 1 photo elec. Similar resolution 5 photo elec. Need to Improve Resolution 8 photo elec.

Sipm attached to the center of surface of the scintillator tile

New Nat. Inst. PHA

Special Budgetary Issue ILC R&D in DOE (Paul Grannis) awarded us a $20 K late award that could not be sent to CU but could only be deposited at SLAC because of the timing. I request that I use these funds for BaBar work and be allowed to used BaBar funds deposited in Colorado for ILC R&D work.

Because ILC R&D funds become available in ~ July the funds cover 2 years of BaBar work 1 year of differential housing costs for Nagel $5 K 1 year travel costs from Colorado to SLAC The total award from ILC R&D is $53 K

The University has contributed to my research a total of $38 K towards support of a Research Associate since I have become Chair of the Boulder Faculty Assembly and my research time is now limited. I propose to use these and the ILC R&D funds towards the Research Associate if DOE accepts the ILC-BaBar fund exchange.

The Calorimeter Modules Each module = ~12 tons

Extrapolation of charged tracks Removal of Charged Track Hits Extrapolation of charged tracks Charged hits removed Track Interact Jason Gray, Jiaxin Yu

Pattern Recognition of Showers Chris Geraci

Chi Square Separation, 1st order 100 GeV π0 Odd layers Sarah Moll Joseph Proulx 100 GeV π0 Even layers

2 Photon Process Very forward into BEAMCAL e+ e+ - - γ q , l - - γ q , l in the detector γ q , l Very forward into BEAMCAL e- e- Discussion in Beam Cal section at end

Study the efficiency to observe the electron and positron of the two photon process above the beamstrahlung background Essential to remove this background in the study of Supersymmetry in the dynamic region of low Pt. Needed to measure the masses.

Testing GEANT 4.0 Evidence for multiple scattering air in beam pipe No field, 50 GeV muons No field, 50 MeVmuons

50 MeV, solenoid on, forward 50 MeV, no field, forward 50 MeV, solenoid on, forward Solenoid field shrinks mult. Scat.

Beamstrahlung Distribution with Solenoid + Anti-DiD Beam pipes Entrance Exit No beam pipes Difficult region to detect 2 photon process

GEANT 4.0 seems to be working properly We have fixed various bugs in collaboration with SLAC team. All Simulation is work in progress.

Hardware Studies Keith Drake, Elliot Smith

Long Term Tests of Scint. Fiber Stability

Latest Pulse Distribution from Photonique/Russia 6 photoelectrons 10 photoelectrons

Pulse National Inst. . . . . . . . 3 pe 1 pe 8 pe Scan every 2.5 nsec

Our Measurements 6 photo-elec. Blue LED, 10nsec, 2.5 volts drive 50 nsec gate noiseless SiPD

1st 10 nsec 2nd 10 nsec 3rd 10 nsec 4th 10 nsec

Cosmic Rays in a 1 cm Thick Scintillator 20 < t < 70 nsec 0 < t < 200 nsec poorer resolution 1 pe 2pe 4pe

1cm scint 10 < t < 20 30 < t < 40 40 < t < 50 60 < t < 70

Pulse Height versus Temperature Gain of SiPD Increases ~x4 Noisy SiPD Could not detect peaks Room temp -300 C Needs to be repeated with New SiPDs; noiseless

2 mm scint 10 < t < 20 30 < t < 40 40 < t < 50 nsec 60 < t < 70 nsec

By time tagging we are observing the photons arriving in time sequence. Possibility to use this to improve resolution. Need beam tests to check this hypothesis.

Work still in progress. Comparison with Russian plots indicate 100 Mhz x 4 (measuring pulse height every 2.5 nsec) not enough resolution. National Instruments has just released a 2 Gigahertz unit. Using our trick of x4 will allow us to scan every 0.125 nsec. A demo is on its way here to check whether 8 bits resolution is good enough.

Conclusions A new revolution in photo-detection. A lot of improvements still possible. A lot of work to be done in this area. If one is bold and reckless one may say that “It may revolutionize calorimetry resolution.”

Conclusions Our simulation work with the undergraduates is moving ahead. A lot of work needs to be done still. Need manpower help. Most of the pieces are in place to study Z and W mass resolution.

We helped with the organization of the Linear Collider Workshop and the various ALCPG meetings up to but not including Vancouver