Objectives Determine Detector offsets in hall B reference frame and thus absolute beam position at Hycal Examine Flux calculation and see if beam trips can be eliminated more effectively by changing parameters within existing software.

Beam Position Mathew Reece & Dustin Woolford

Beam Position Ideally to find the absolute beam position two BPMs can be used and then offsets determined from the projection of that line to other detectors. However there is a magnetic field present between the two BPMs in hall B. Is it negligible? There is a single run (4943) where the beam position is known to change abruptly midway through the run at BPM1 and at Hycal but very little at BPM2.

Whats known BPM data suggests that readouts are in the hall B frame HYCAL, x = 0.02 mm beam right, y = 0.09 mm high relative to CLAS center line. Gamma Profiler needs to be determined

Linearity By using only data from (4349), the unknown detector offsets do not affect the calculations. We assume that the beam is linear between the BPMs and compare every other event in the run with the first event. The angles are determined by the arctangent of the difference between the measured points on a detector for the first event and a later event divided by the distance between that detector and BPM 2. As shown on the previous slide, α1 is for BPM 1 and α2 is for the γ profiler. By our conventions, the ratio α2/α1 will be -1 if the beam is linear [since arctan x = -arctan (- x)]

Important note It is important to verify that the beam position on BPM 2 does not vary significantly in order for this method to be valid. As the graph shows, the location where the beam passes through BPM 2 does not move more than 0.2 mm during the run.

Now that the constancy of BPM 2 has been verified, let us look at the α2/α1 ratio:

Determining offsets A Java program that will use BPM2 and Hycal to determine (x,y) at the gamma profiler is written. Average offsets for each run must be determined and then entered into the MySQL database The same program must be re run for BPM2 and Gamma Profiler to determine (x,y, cos(x), cos(y) Yet to be completed

Luminosity Dustin Woolford

General Idea Tagged Yield = Cross Section x target thickness x solid angle x Nγ tagged (exp) Nγ tagged (exp) = Ne (exp) x Tagging ratio Tagging ratio = Nγ tagged (cal) / Ne (cal) Given a Tagged yield, target thickness, solid angle, and the flux the Pi0 cross section can be extracted

Flux Nγ tagged (exp)  (Flux) Tagged photons per run per T channel  N γί = N eί x R ί where N and R are the number of electrons per T channel and the tagging ratio respectively.  R ί is determined during the TAC runs  N eί = ( η eί / w x η trigs ) x live 1 - η eί = # e- in a T channel in a given window - w = size of the TDC window - η trigs = # of trigger events  Basically average e- rate for a T channel x live time

Live Time of DAQ Dead time = Live 1 / Live 2 Both Live 1 and Live 2 are driven by a / kHz internal clock. Live 1 is gated, Live 2 is free TDC start is attached to the tagger and the stop is initiated by a Pi0 event Trigger is also activated by a Pi0 event in hycal There is a 25 ns internal dead time for the TDC separate from the trigger dead time. Don’t need to correct for dead time because only tagged Pi0 event go to elastic scattering.

Considerations  Two types of tagging ratios 1) Absolute – uses lead glass solid block and is assumed to have 100% efficiency at low photon intensities (TAC) - given by R abs = N γTAC · e- / N e- 2) Relative – uses the pair spectrometer to monitor the tagging ratio during runs but has 0.06% efficiency. -given by R rel = N ps e+e- - e- / N e-  Method 1 must be used to calibrate 2.

Considerations cont’d  Effects that may reduce the Absolute tagging ratio from 1, three primary factors 1) photon is produced but absorbed before reaching the TAC ( effect is reduced by helium bag…but not corrected for ) 2) electron decelerates in the target without producing a photon 3) extra electrons in the tagger (effect gets large at high beam intensities so R rel must be corrected for )

Corrections ( brief list, non-exhaustive )  Relative tagging ratio has back ground that must be accounted for (background = Integral of events / w)  R rel is intensity independent at the at low beam intensity ( 0.1 – 100 nA

Corrections cont’d To correct for dependence at high beam intensity the relative tagging ratio per T counter was averaged for all runs. Then for each affected run, R rel was normalized to its corresponding average per T counter. Collimators 8.6 mm and 12.7 mm were found to cut 4 % and 1% of the beam respectively Run to run stability ( good up to run 5100) Live time problem ( implemented algorithm to solve )

Tagger Detector Rate  3 ways ( Integral, exponential, and Poisson method)  Integral is primary means  The time distribution is integrated over a range which excludes the triggering events and depletion from LIFO limits. The integral is divided by the product of integration interval and # of events over which the distribution was accumulated. (Aram’s luminosity monitoring, Primex notes)  Independent of TDC dead time due to using Live 1  Can be used for high and low rate detectors  Tosses a lot of data and abstract coincidence detectors are affected subtly by the LIFO limit and dead time

Pflux package Prim_ana has Pflux package that links data analysis with the luminosity Attempts to identify and eliminate beam trips. Run is pre-segmented into 5 second intervals. Pflux Uses the integral method to calculate tagging rate and live time for each segment. Averages live time for all segments and fits Gaussian to the “avg. histogram” Identifies everything outside 3 σ as a beam trip. cuts 2 five second intervals following identified beam trip. Configurations - beam_trip : activates beam trip cuts - num_bad : # of 5 second intervals cut after beam trip - livetime_sigma : number of standard deviations that contain “good” data

Live Time Study ( courtesy of Eric Clinton and Aram Teymurazyan)  Uses Pflux package to output flux per run per T channel, per E channel, live time and average flux and live time for each run  Standalone from prim_ana  Use Root and excel to graph flux as a function of sigma and # of cut intervals.