BPER,BPWT,BSIZ,SIBE : chunk-by-chunk beam position for MCarlo

The ALPHA variables XGETBP, QVTXBP(I), QVTEBP(I), and QVTSBP(I) (see chapter 6.2) provide chunk-by-chunk beam position information for real data. They also provide effective beam positions for correctly simulating the size of the luminous region in Monte Carlo. For Monte Carlo, the default behavior is to use the luminous region size parameters (database bank ALRP) for the geometry year of the Monte Carlo file.

The BPER card allows the user to override the default. The parameters from the year(s) specified on this card are then used; each event is assigned at random to a particular year. The years (in the LEP 1 era) are weighted according to the numbers of qqbar events in the MAYB/PERF runs in the VD run selection.

Different weights may be specified by means of the BPWT card . This card is mandatory for specifying the relative weights of LEP 2 periods, if two or more periods are selected with BPER .

Arbitrary beam sizes may be simulated by means of the BSIZ card.

The x,y beam position uncertainties for Monte Carlo datasets may be smeared using the SIBE data card.

The BPER, BPWT, BSIZ and SIBE cards have no effect when real data is analyzed.

BPER [per1 [per2...]

]

per1,per2... are run periods as specified in the first column of ADBR. Years may be given as ``1992'' or ``92'' or ``9200''. Other run periods have the form ``yymm'', such as ``9510''. A list of valid run periods is printed (and execution terminates) if the BPER card is given with invalid or no run periods.

BPWT [iwt1 [iwt2...]

]

iwt1,iwt2,... are *integer* weights for the periods listed on the BPER card. An error results if there is no accompanying BPER or if it has a different number of tokens. The weights may have an arbitrary normalization.

BSIZ $\sigma_{x}^{}$ $\sigma_{y}^{}$ [$\sigma_{z}^{}$]

$\sigma_{x}^{}$ and $\sigma_{y}^{}$ are floating point numbers giving the desired sizes of the luminous region in cm, transmitted to QVTXBP(1) and (2). The BSIZ card overrides all values in ALRP. The value of $\sigma_{z}^{}$ , if given, is returned in QVTXBP(3) but has no other effect. If $\sigma_{z}^{}$ is not given, the value 1 is returned in QVTXBP(3).

Notes: the beam position uncertainty is set to zero if BSIZ is given. BPER/BPWT cards are ignored if BSIZ is given.

SIBE meanx $\sigma_{x}^{}$ meany $\sigma_{y}^{}$

Allows to perform a smearing of the x and y beam position uncertainties for Monte Carlo datasets. meanx (resp. meany) is the central value of the error, $\sigma_{x}^{}$ (resp $\sigma_{y}^{}$) is the gaussian dispersion around this mean value. Units are in 10^-3 cm. The results are returned in QVTEBP(i).

Examples :

1. To simulate 1993 and 1994 beam size conditions with natural relative weights:

BPER 1993 1994

2. To simulate 1993 and 1994 with equal weights:

BPER 1993 1994

BPWT 50 50

3. To simulate a luminous region size of 120 x 7 microns:

BSIZ 0.0120 0.0007

4. To smear the beam position uncertainties as follows:

error in x 27.4 microns with 2 microns dispersion,

error in y 23.3 microns, 4.7 microns dispersion:

SIBE 2.74 0.2 2.33 0.47